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Preview: Advanced Materials for Optics and Electronics

Advanced Functional Materials



Wiley Online Library : Advanced Functional Materials



Published: 2017-09-01T00:00:00-05:00

 



A Textile Dressing for Temporal and Dosage Controlled Drug Delivery

2017-09-19T01:05:02.547951-05:00

Chronic wounds do not heal in an orderly fashion in part due to the lack of timely release of biological factors essential for healing. Topical administration of various therapeutic factors at different stages is shown to enhance the healing rate of chronic wounds. Developing a wound dressing that can deliver biomolecules with a predetermined spatial and temporal pattern would be beneficial for effective treatment of chronic wounds. Here, an actively controlled wound dressing is fabricated using composite fibers with a core electrical heater covered by a layer of hydrogel containing thermoresponsive drug carriers. The fibers are loaded with different drugs and biological factors and are then assembled using textile processes to create a flexible and wearable wound dressing. These fibers can be individually addressed to enable on-demand release of different drugs with a controlled temporal profile. Here, the effectiveness of the engineered dressing for on-demand release of antibiotics and vascular endothelial growth factor (VEGF) is demonstrated for eliminating bacterial infection and inducing angiogenesis in vitro. The effectiveness of the VEGF release on improving healing rate is also demonstrated in a murine model of diabetic wounds. A smart textile dressing is fabricated using composite fibers with a core electrical heater covered by a layer of hydrogel containing thermoresponsive drug carriers. The fibers are assembled into fabrics using textile processes in which each thread operates as an independent functional unit that can be individually triggered to allow the on-demand release of a specific drug.



Synthesis and Applications of Stimuli-Responsive DNA-Based Nano- and Micro-Sized Capsules

2017-09-18T07:42:54.392657-05:00

Stimuli-responsive, drug-loaded, DNA-based nano- and micro-capsules attract scientific interest as signal-triggered carriers for controlled drug release. The methods to construct the nano-/micro-capsules involve i) the layer-by-layer deposition of signal-reconfigurable DNA shells on drug-loaded microparticles acting as templates, followed by dissolution of the core templates; ii) the assembly of three-dimensional capsules composed of reconfigurable DNA origami units; and iii) the synthesis of stimuli-responsive drug-loaded capsules stabilized by DNA−polymer hydrogels. Triggers to unlock the nano-/micro-capsules include enzymes, pH, light, aptamer−ligand complexes, and redox agents. The capsules are loaded with fluorescent polymers, metal nanoparticles, proteins or semiconductor quantum dots as drug models, with anti-cancer drugs, e.g., doxorubicin, or with antibodies inhibiting cellular networks or enzymes over-expressed in cancer cells. The mechanisms for unlocking the nano-/micro-capsules and releasing the drugs are discussed, and the applications of the stimuli-responsive nano-/micro-capsules as sense-and-treat systems are addressed. The scientific challenges and future perspectives of nano-capsules and micro-capsules in nanomedicine are highlighted. Stimuli-responsive, drug-loaded, nano- and micro-capsules consisting of DNA shells, DNA origami units, and DNA hydrogel shells provide versatile carriers for controlled drug release. DNA-based capsules are prepared by layer-by-layer deposition processes, assembly of DNA-origami units, and the stabilization of the capsules by DNA-polymer hybrids. Unlocking of the capsules and release of the drugs are triggered by enzymes, pH, aptamer−ligand complexes, and redox agents.



In-Plane Micro-Supercapacitors for an Integrated Device on One Piece of Paper

2017-09-14T07:25:56.378169-05:00

Portable and wearable sensors have attracted considerable attention in the healthcare field because they can be worn or implanted into a human body to monitor environmental information. However, sensors cannot work independently and require power. Flexible in-plane micro-supercapacitor (MSC) is a suitable power device that can be integrated with sensors on a single chip. Meanwhile, paper is an ideal flexible substrate because it is cheap and disposable and has a porous and rough surface that enhances interface adhesion with electronic devices. In this study, a new strategy to integrate MSCs, which have excellent electrochemical and mechanical performances, with sensors on a single piece of paper is proposed. The integration is achieved by printing Ni circuit on paper without using a precoating underlay. Ink diffusion is also addressed to some degree. Meanwhile, a UV sensor is integrated on a single paper, and the as-integrated device shows good sensing and self-powering capabilities. MSCs can also be integrated with a gas sensor on one-piece paper and can be charged by connecting it to a solar cell. Thus, it is potentially feasible that a flexible paper can be used for integrating MSCs with solar cell and various sensors to generate, store, and use energy. An integrated device that is composed of in-plane micro-supercapacitors (MSCs) and sensor on one piece of paper is fabricated based on screen-printed Ni circuit for flexible and wearable electronics. The fabricated MSC shows excellent static and dynamic bending performances. The as-integrated devices present good sensing responsibility and self-powering capability.



3D Foam Strutted Graphene Carbon Nitride with Highly Stable Optoelectronic Properties

2017-09-14T07:23:26.988483-05:00

Controlled morphology modulation of graphene carbon nitride (g-C3N4) is successfully realized from bulk to 3D loose foam architecture via the blowing effect of a bubble, which can be controlled by heating rate. The loose foam network is comprised by spatially scaffolded few-atom-layer interconnected flakes with the large specific surface area, as supporters to prevent agglomeration and provide a pathway for electron/phonon transports. The photocatalytic performance of 3D foam strutted g-C3N4 toward RhB decomposition and hydrogen evolution is significantly enhanced with the morphology optimization while its excellent optoelectronic properties are maintained simultaneously. Herein, the ultrathin, mono-, and high-quality foam g-C3N4 interconnected flakes with controlled layer are facilely obtained through ultrasonic, thus overcoming the drawbacks of a traditional top–down approach, opening a wide horizon for diverse practical usages. Additionally, the layer control mechanism of 3D hierarchical structure has been explored by means of bubble growth kinetics analysis and the density functional theory calculations. 3D foam strutted g-C3N4 synthesized upon bubble template shows effective photocatalytic activity as well as highly stable optoelectronic properties, overcoming the problem of its photoluminescence degradation when applied as photocatalyst. Kinetic characterization and theoretical calculations reveal ultrathin foam growth and a layer control mechanism, which is crucial for the application of this promising class of materials.



3D-Printed All-Fiber Li-Ion Battery toward Wearable Energy Storage

2017-09-14T07:22:44.80012-05:00

Conventional bulky and rigid power systems are incapable of meeting flexibility and breathability requirements for wearable applications. Despite the tremendous efforts dedicated to developing various 1D energy storage devices with sufficient flexibility, challenges remain pertaining to fabrication scalability, cost, and efficiency. Here, a scalable, low-cost, and high-efficiency 3D printing technology is applied to fabricate a flexible all-fiber lithium-ion battery (LIB). Highly viscous polymer inks containing carbon nanotubes and either lithium iron phosphate (LFP) or lithium titanium oxide (LTO) are used to print LFP fiber cathodes and LTO fiber anodes, respectively. Both fiber electrodes demonstrate good flexibility and high electrochemical performance in half-cell configurations. All-fiber LIB can be successfully assembled by twisting the as-printed LFP and LTO fibers together with gel polymer as the quasi-solid electrolyte. The all-fiber device exhibits a high specific capacity of ≈110 mAh g−1 at a current density of 50 mA g−1 and maintains a good flexibility of the fiber electrodes, which can be potentially integrated into textile fabrics for future wearable electronic applications. Printable all-fiber quasi-solid-state lithium-ion batteries are developed through an efficient, scalable, and cost-effective 3D printing approach. The all-fiber device demonstrates high mechanical flexibility, mechanical strength, and excellent electrochemical performance, holding great promise for flexible and wearable electronic applications.



Improvement and Regeneration of Perovskite Solar Cells via Methylamine Gas Post-Treatment

2017-09-14T07:21:30.389181-05:00

The control of film morphology is crucial in achieving high-performance perovskite solar cells (PSCs). Herein, the crystals of the perovskite films are reconstructed by post-treating the MAPbI3 devices with methylamine gas, yielding a homogeneous nucleation and crystallization of the perovskite in the triple mesoscopic inorganic layers structured PSCs. As a result, a uniform, compact, and crystalline perovskite layer is obtained after the methylamine gas post-treatment, yielding high power conversion efficiency (PCE) of 15.26%, 128.8% higher than that of the device before processing. More importantly, this post-treatment process allows the regeneration of the photodegraded PSCs via the crystal reconstruction and the PCE can recover to 91% of the initial value after two cycles of the photodegradation-recovery process. This simple method allows for the regeneration of perovskite solar cells on site without reconstruction or replacing any components, thus prolonging the service life of the perovskite solar cells and distinguishing from any other photovoltaic devices in practice. The crystals of the perovskite films are reconstructed by post-treating the MAPbI3 devices with methylamine gas, yielding high power conversion efficiency (PCE) of 15.26%, 128.8% higher than that of the device before processing. More importantly, the photodegraded perovskite solar cells are regenerated via crystal reconstruction and the PCE recovers to 91% of the initial value after two cycles of the photodegradation-recovery process.



Controlled Layer Thinning and p-Type Doping of WSe2 by Vapor XeF2

2017-09-13T01:03:45.931426-05:00

This report presents a simple and efficient method of layer thinning and p-type doping of WSe2 with vapor XeF2. With this approach, the surface roughness of thinned WSe2 can be controlled to below 0.7 nm at an etched depth of 100 nm. By selecting appropriate vapor XeF2 exposure times, 23-layer and 109-layer WSe2 can be thinned down to monolayer and bilayer, respectively. In addition, the etching rate of WSe2 exhibits a significant dependence on vapor XeF2 exposure pressure and thus can be tuned easily for thinning or patterning applications. From Raman, photoluminescence, X-ray photoelectron spectroscopy (XPS), and electrical characterization, a p-doping effect of WSe2 induced by vapor XeF2 treatment is evident. Based on the surface composition analysis with XPS, the causes of the p-doping effect can be attributed to the presence of substoichiometric WOx (x < 3) overlayer, trapped reaction product of WF6, and nonstoichiometric WSex (x > 2). Furthermore, the p-doping level can be controlled by varying XeF2 exposure time. The thinning and p-doping of WSe2 with vapor XeF2 have the advantages of easy scale-up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes, which is promising for applications of building WSe2 devices with versatile functionalities. A controllable layer thinning and p-doping of WSe2 by vapor XeF2 is demonstrated. The etching rate depends on XeF2 exposure pressure greatly. The etched depth and p-doping level can be tuned easily by varying XeF2 exposure time. This approach has the advantages of easy scale-up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes.



One-Pot Synthesis of Antimony-Embedded Silicon Oxycarbide Materials for High-Performance Sodium-Ion Batteries

2017-09-13T01:03:13.666257-05:00

Sodium-ion batteries have recently attracted intensive attention due to their natural abundance and low cost. Antimony is a desirable candidate for an anode material for sodium-ion batteries due to its high theoretical capacity (660 mA h g−1). However, the utilization of alloy-based anodes is still limited by their inherent huge volume changes and sluggish kinetics. The Sb-embedded silicon oxycarbide (SiOC) composites are simply synthesized via a one-pot pyrolysis process at 900 °C without any additives or surfactants, taking advantage of the superior self-dispersion properties of antimony acetate powders in silicone oil. The structural and morphological characterizations confirm that Sb nanoparticles are homogeneously embedded into the amorphous SiOC matrix. The composite materials exhibit an initial desodiation capacity of around 510 mA h g−1 and maintained an excellent capacity retention above 97% after 250 cycles. The rate capability test reveals that the composites deliver capacity greater than 453 mA h g−1, even at the high current density of 20 C rate, owing to the free-carbon domain of SiOC material. The electrochemical and postmortem analyses confirm that the SiOC matrix with a uniform distribution of Sb nanoparticles provides the mechanical strength without degradation in conductive characteristics, suppressing the agglomeration of Sb particles during the electrochemical reaction. Sb-embedded SiOC composites are synthesized by direct one-pot pyrolysis without any additional surfactants or chemicals. The crystalline Sb nanoparticles are homogeneously embedded into the amorphous SiOC. The mechanical strength of SiOC enhances its long-term performance. The free-carbon domain in SiOC provides the superior rate capability of the composite electrode.



An O2 Self-Supplementing and Reactive-Oxygen-Species-Circulating Amplified Nanoplatform via H2O/H2O2 Splitting for Tumor Imaging and Photodynamic Therapy

2017-09-13T01:02:36.486717-05:00

Conventional photodynamic therapy (PDT) has limited applications in clinical cancer therapy due to the insufficient O2 supply, inefficient reactive oxygen species (ROS) generation, and low penetration depth of light. In this work, a multifunctional nanoplatform, upconversion nanoparticles (UCNPs)@TiO2@MnO2 core/shell/sheet nanocomposites (UTMs), is designed and constructed to overcome these drawbacks by generating O2 in situ, amplifying the content of singlet oxygen (1O2) and hydroxyl radical (•OH) via water-splitting, and utilizing 980 nm near-infrared (NIR) light to increase penetration depth. Once UTMs are accumulated at tumor site, intracellular H2O2 is catalyzed by MnO2 nanosheets to generate O2 for improving oxygen-dependent PDT. Simultaneously, with the decomposition of MnO2 nanosheets and 980 nm NIR irradiation, UCNPs can efficiently convert NIR to ultraviolet light to activate TiO2 and generate toxic ROS for deep tumor therapy. In addition, UCNPs and decomposed Mn2+ can be used for further upconversion luminescence and magnetic resonance imaging in tumor site. Both in vitro and in vivo experiments demonstrate that this nanoplatform can significantly improve PDT efficiency with tumor imaging capability, which will find great potential in the fight against tumor. Enhanced and amplified photodynamic therapy: A multifunctional nanoplatform, UCNPs@TiO2@MnO2 core/shell/sheet nanocomposites, is designed to overcome the drawbacks of photodynamic therapy by generating O2 in situ, amplifying the content of singlet oxygen (1O2) and hydroxyl radical (•OH) via water-splitting, and utilizing 980 nm near-infrared light to increase penetration depth, which significantly improves PDT efficiency as well as reduces the side effects.



Fluorescent Protein Nanovessels: A New Platform to Generate Bio–Abiotic Hybrid Materials for Bioimaging

2017-09-13T01:01:33.677341-05:00

In this report, a new platform to generate fluorescent protein nanovessels is described. Based on systemic analyses and reconstitution experiments, a combination of protein scaffold and organic dye is identified. Briefly, certain proteins such as bovine serum albumin (BSA) can rapidly form cube-like scaffold upon heating. This protein scaffolds intrinsically interact with nonfluorescent dyes such as bromophenol blue (BPB), forming BSA-BPB nanocubes (BBNCs). Moreover, it turns out that the commercially available dye BPB contains aggregation-induced emission (AIE) properties, allowing the BBNCs emissive upon irradiation. The fluorescent protein nanovessels are highly biocompatible and can be readily internalized by different type of cells. The fluorescent signal of the materials is well-penetrable from mouse tissues and can be detected at near-infrared region, making it a useful tool for various biological imaging studies. This platform for making fluorescent protein nanovessels is green, rapid, and cost-effective and can be extended to other protein scaffolds and possibly other dye/AIE molecules. A new platform to generate fluorescent protein nanovessels for bioimaging is described. Certain proteins can rapidly form nanoscaffolds upon denaturation. These scaffolds intrinsically nature interact with certain nonfluorescent dyes, forming fluorescent protein nanovessels. The platform is green, rapid, and cost-effective and may be extended to diversified proteins and possibly various dye/AIE molecules.



Bone Marrow Dendritic Cells Derived Microvesicles for Combinational Immunochemotherapy against Tumor

2017-09-13T00:57:58.178508-05:00

Various types of cell can change the cytoskeleton and shed microvesicles (MVs) with biomimic properties as parent cells in response to stimuli. To take use of the drug package capability of MVs and the potent antigen presentation property of dendritic cells (DCs), DC-derived antigenic MVs are constructed by priming DCs with tumor-derived MVs and then encapsulating a chemotherapeutic drug during MVs shedding. This kind of MVs exhibit significant inhibition on melanoma tumor growth and metastasis. The MV-encapsulated chemotherapeutics can induce direct cytotoxicity and immunogenic cell death in tumor cells. Moreover, a robust antitumor immunity is induced in both, the tumor-draining lymph node and the tumor microenvironment as the infiltration and activation of T lymphocytes increases. This kind of MVs is further explored in a hepatic ascites model with remarkable prolonged overall survival of mice. More importantly, the MVs can extend the survival of 60% mice more than 150 d without ascites even after rechallenging the tumor twice. This study demonstrates that antigenic MVs with chemotherapeutics possess great potential in cancer immunochemotherapy. Dendritic cell (DC)-derived antigenic microvesicles (MVs) are prepared by priming DCs with tumor-derived MVs and then encapsulating a chemotherapeutic drug during MV shedding. The MVs exhibit significant inhibition on melanoma tumor growth and metastasis and can extend the survival to more than 150 d for 60% of the mice. The animals remain free of acites even after rechallenging tumor twice in a hepatic ascites model.



Laser Interference Lithography for the Nanofabrication of Stimuli-Responsive Bragg Stacks

2017-09-13T00:57:01.008086-05:00

Dynamic structural coloration in Tmesisternus isabellae beetle elytra is a unique example of Bragg stack-based wavelength tuning in response to external stimuli. The underlying principles could guide the design of quantitative optical stimuli-responsive polymers. Existing nanofabrication techniques to create such materials are costly, time-consuming, and require high expertise. This study reports a nanofabrication method to produce slanted Bragg stack structures in poly(acrylamide-co-poly(ethylene glycol) diacrylate) hydrogel films by combining laser interference lithography and silver halide chemistry in a cost-effective and rapid process (≈10 min). The Bragg stacks consist of silver bromide nanocrystal multilayers having a lattice spacing of ≈200 nm. Upon broadband light illumination, the Bragg stacks diffract a narrow-band peak at 520 nm at ≈10° with respect to the normal incidence. The lattice spacing of the hydrogel films can be modulated by external stimuli to shift the Bragg peak for dynamic quantitative measurements. To demonstrate the utility of this method, the Bragg stacks are functionalized with phenylboronic acid molecules. Bragg peak shift analysis allows reversible glucose sensing within a physiological dynamic range (0.0–20.0 mmol L−1) having a sensitivity of 0.2 mmol L−1. The developed Bragg stacks may have application in portable, wearable, and implantable real-time medical diagnostics at point-of-care settings. Laser-directed interference lithography involving silver halide chemistry is utilized as a rapid nanofabrication technique to create a slanted Bragg stack consisting of silver bromide nanocrystals in a hydrogel film. The lattice spacing of the Bragg stacks can be modulated by external stimuli to obtain dynamic diffraction peak shifts. The hydrogel functionalized with phenylboronic acid enables reversible quantitative measurements of glucose.



Highly Sensitive Low-Bandgap Perovskite Photodetectors with Response from Ultraviolet to the Near-Infrared Region

2017-09-13T00:56:06.620255-05:00

It is a great challenge to obtain broadband response perovskite photodetectors (PPDs) due to the relatively large bandgaps of the most used methylammonium lead halide perovskites. The response range of the reported PPDs is limited in the ultraviolet–visible range. Here, highly sensitive PPDs are successfully fabricated with low bandgap (≈1.25 eV) (FASnI3)0.6(MAPbI3)0.4 perovskite as active layers, exhibiting a broadband response from 300 to 1000 nm. The performance of the PPDs can be optimized by adjusting the thicknesses of the perovskite and C60 layers. The optimized PPDs with 1000 nm thick perovskite layer and 70 nm thick C60 layer exhibit an almost flat external quantum efficiency (EQE) spectrum from 350 to 900 nm with EQE larger than 65% under −0.2 V bias. Meanwhile, the optimized PPDs also exhibit suppressed dark current of 3.9 nA, high responsivity (R) of over 0.4 A W−1, high specific detectivity (D*) of over 1012 Jones in the near-infrared region under −0.2 V. Such highly sensitive broadband response PPDs, which can work well as self-powered conditions, offer great potential applications in multicolor light detection. Highly sensitive perovskite photodetectors (PPDs) with broadband response from ultraviolet to the near-infrared region are achieved with low-bandgap (≈1.25 eV) (FASnI3)0.6(MAPbI3)0.4 perovskite as active layer. The optimized PPDs with 1000 nm thick perovskite and 70 nm thick C60 electron transport layer exhibit an almost flat response from 350 to 900 nm with external quantum efficiency larger than 65% under −0.2 V bias.



Sub-Micrometer Structure Formation during Spin Coating Revealed by Time-Resolved In Situ Laser and X-Ray Scattering

2017-09-12T07:21:20.335047-05:00

Solution-processed thin polymer films have many applications, such as organic electronics and block-copolymer nanofabrication. These films are often made by spin coating a solution that contains one or more solids and can show different phase-separated structures. The formation mechanism of the droplet-like morphology is studied here by processing polystyrene (PS) and a fullerene derivative ([6,6]-phenyl-C71-butyric acid methyl ester, [70]PCBM) from o-xylene. The final structure consists of [70]PCBM droplets partially embedded in a PS-rich matrix showing interdomain distance of 100–1000 nm as determined from transmission electron microscopy and grazing incidence small angle X-ray scattering (GISAXS). To elucidate the formation of these morphologies in real time, ultrafast in situ GISAXS coupled with laser interferometry and laser scattering is performed during spin coating. In situ thickness measurements and laser scattering show that liquid–liquid phase separation occurs at ≈70 vol% solvent. Subsequently, in only 100–400 ms, almost dry [70]PCBM domains start to protrude from the swollen PS-rich matrix. These results are used to verify the ternary phase diagram calculated using Flory–Huggins theory. The discussed multitechnique approach can be applied to study fundamental aspects in soft matter such as phase separation in thin films occurring at very short time scales. Phase separation in droplet-forming polymer:fullerene mixtures is studied in real time by performing simultaneously in situ X-ray scattering, laser scattering, and thickness measurements. In situ observations combined with ex situ results and data modeling show how droplet formation involves stages like liquid–liquid phase separation and solvent partitioning, resulting in thin films featuring both embedded phase separation and surface topography.



Layered Simple Hydroxides Functionalized by Fluorene-Phosphonic Acids: Synthesis, Interface Theoretical Insights, and Magnetoelectric Effect

2017-09-11T10:15:25.722126-05:00

Copper- and cobalt-based layered simple hydroxides (LSH) are successfully functionalized by a series of fluorene mono- and diphosphonic acids, using anionic exchange reactions and a preintercalation strategy. The lateral functionalization of the fluorene moieties has only little impact on the overall structure of the obtained layered hybrid materials but it influences the organization of the molecules within the interlamellar spacing. For bulky fluorene (9,9-dioctyl derivative), luminescence is preserved when inserted into copper and cobalt hydroxydes, whereas it is completely quenched for the other fluorenes. Detailed characterization of the internal structure and chemical bonding properties for copper- and cobalt-based hybrids is performed via ancillary experimental techniques. For the copper-based LSH class, for which more elusive findings are found, first-principles molecular dynamics simulations unravel the fundamental stabilizing role of the H-bonding network promoted within the local environments of the fluorene mono- and diphosphonic acids. The cobalt series of compounds constitute a new class of hybrid magnets, with ordering temperatures ranging from 11.8 to 17.8 K and show a clear magnetoelectric effect. This effect appears above a threshold magnetic field, which is null below the magnetic ordering temperature, and it persists in the paramagnetic regime till about 110 K. Copper and cobalt layered simple hydroxides can be functionalized by a series of fluorene phosphonic acids. X-ray diffraction and first-principles molecular dynamics underline the role of water molecules at the organic–inorganic interface in the copper analogues. The cobalt analogues present a ferrimagnetic ordering at TC ranging from 11.8 to 17.8 K and a rare magnetoelectric effect, which extends till 110 K.



Living Bioelectronics: Strategies for Developing an Effective Long-Term Implant with Functional Neural Connections

2017-09-11T01:32:38.217614-05:00

Existing bionic implants use metal electrodes, which have low charge transfer capacity and poor tissue integration. This limits their use in next-generation, high resolution devices. Coating and other modification techniques have been explored to improve the performance of metal electrodes. While this has enabled increased charge transfer properties and integration of biologically responsive components, stable long term performance remains a significant challenge. This progress report provides a background on electrode modification techniques, exploring state-of-the art approaches to improving implantable electrodes. The new frontier of cell-based electronics, is introduced detailing approaches that use tissue engineering principles applied to bionic devices. These living bioelectronic technologies aim to enable devices to grow into target tissues, creating direct neural connections. Ideally, this approach will create a paradigm shift in biomedical electrode design. Rather than relying on unwieldy metal electrodes and direct current injection, living bioelectronics will use cells embedded within devices to provide communication through synaptic connections. This report details the challenge of designing electrodes that can bridge the technology gap between conventional metal electrode interfaces and new living electrodes through considering electrical, chemical, physical and biological characteristics. Bionic implants using metal electrodes have low charge transfer capacity and poor tissue integration. This progress report provides a background on electrode modification techniques, exploring state-of-the art approaches to improving implantable electrodes. The new frontier of cell-based electronics is introduced, detailing approaches that use tissue engineering principles applied to bionic devices. Living bioelectronics will ultimately create a paradigm shift in biomedical electrode design.



Enhancing the Stability of Perovskite Quantum Dots by Encapsulation in Crosslinked Polystyrene Beads via a Swelling–Shrinking Strategy toward Superior Water Resistance

2017-09-11T01:31:40.200386-05:00

Organic/inorganic hybrid lead halide perovskites are promising optoelectronic materials due to their unique structure, excellent properties, and fascinating potential applications in lighting, photovoltaic, etc. However, perovskite materials are very sensitive to moisture and polar solvent, which greatly hinders their practical applications. Here, highly luminescent perovskite–polystyrene composite beads with uniform morphology are prepared via a simple swelling–shrinking strategy. This process is carried out only in nonpolar toluene and hexane without the addition of any polar reagents. As a result, the as-prepared composite beads not only retain high luminescence but also exhibit superior water-resistant property. The composites emit strong luminescence after being immersed into water over nine months. Moreover, even in some harsh environments such as acid/alkali aqueous solution, phosphate buffer solution, and Dulbecco's modified eagle medium biological buffers, they still preserve high luminescence. The applications in light-emitting diodes and cellular labeling agents are also carried out to demonstrate their ultrastability. Highly luminescent perovskite–polystyrene composite beads with uniform morphology are prepared by packing perovskite quantum dots in crosslinked polystyrene beads via swelling in toluene and then shrinking the beads in hexane. The composite not only retains high luminescence but also exhibits superior water resistance.



Tuning of a Vertical Spin Valve with a Monolayer of Single Molecule Magnets

2017-09-11T01:30:55.289675-05:00

The synthesis and the chemisorption from solution of a terbium bis-phthalocyaninato complex suitable for the functionalization of lanthanum strontium manganite (LSMO) are reported. Two phosphonate groups are introduced in the double decker structure in order to allow the grafting to the ferromagnetic substrate actively used as injection electrode in organic spin valve devices. The covalent bonding of functionalized terbium bis-phthalocyaninato system on LSMO surface preserves its molecular properties at the nanoscale. X-ray photoelectron spectroscopy confirms the integrity of the molecules on the LSMO surface and a small magnetic hysteresis reminiscent of the typical single molecule magnet behavior of this system is detected on surface by X-ray magnetic circular dichroism experiments. The effect of the hybrid magnetic electrode on spin polarized injection is investigated in vertical organic spin valve devices and compared to the behavior of similar spin valves embedding a single diamagnetic layer of alkyl phosphonate molecules analogously chemisorbed on LSMO. Magnetoresistance experiments have evidenced significant alterations of the magneto-transport by the terbium bis-phthalocyaninato complex characterized by two distinct temperature regimes, below and above 50 K, respectively. Spinterface tuning of a vertical spin-valve is achieved by the chemical functionalization of the spin-injecting electrode with a terbium(III) bis(phthalocyaninato) monolayer grafted from solution. Comparing the results obtained with a similar device fabricated including a diamagnetic layer it is possible to evidence that the single molecule magnets film constitutes an additional spin-scattering layer able to control directly the magnetoresistance strength.



Scaling Effects on the Electrochemical Performance of poly(3,4-ethylenedioxythiophene (PEDOT), Au, and Pt for Electrocorticography Recording

2017-09-08T07:42:59.209555-05:00

Reduced contact size would permit higher resolution cortical recordings, but the effects of diameter on crucial recording and stimulation properties are poorly understood. Here, the first systematic study of scaling effects on the electrochemical properties of metallic Pt and Au and organic poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes is presented. PEDOT:PSS exhibits better faradaic charge transfer and capacitive charge coupling than metal electrodes, and these characteristics lead to improved electrochemical performance and reduced noise at smaller electrode diameters. PEDOT:PSS coating reduces the impedances of metallic electrodes by up to 18x for diameters <200 µm, but has no effect for millimeter scale contacts due to the dominance of series resistances. Therefore, the performance gains are especially significant at smaller diameters and lower frequencies essential for recording cognitive and pathological activities. Additionally, the overall reduced noise of the PEDOT:PSS electrodes enables a lower noise floor for recording action potentials. These results permit quantitative optimization of contact material and diameter for different electrocorticography applications. Electrode arrays are fabricated using metal (Pt, Au) and organic (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)) coatings. Their electrochemical sensing characteristics are studied and quantified as a function of diameter for different frequency bands and at different size regimes. The results can guide the design and operation of ECoG electrode arrays.



Self-Healing Graphene Oxide Based Functional Architectures Triggered by Moisture

2017-09-08T07:41:42.675297-05:00

Self-healing materials are capable of spontaneously repairing themselves at damaging sites without additional adhesives. They are important functional materials with wide applications in actuators, shape memorizing materials, smart coatings, and medical treatments, etc. Herein, this study reports the self-healing of graphene oxide (GO) functional architectures and devices with the assistance of moisture. These GO architectures can completely restore their mechanical-performance (e.g., compressibility, flexibility, and strength) after healing their broken sites using a little amount of water moisture. On the basis of this effective moisture-triggered self-healing process, this study develops GO smart actuators (e.g., bendable actuator, biomimetic walker, rotatable fiber motor) and sensors with self-healing ability. This work provides a new pathway for the development of self-healing materials for their applications in multidimensional spaces and functional devices. Self-healing graphene oxide (GO) functional architectures including 3D compressible foams, 2D flexible films, and 1D wearable fibers are demonstrated. These GO assemblies exhibit excellent and fast self-healing ability with moisture assistance. Apart from the construction of graphene macroblocks, this promising healing ability has been incorporated into GO smart actuators and sensors.



Carbon Nanotube Based Inverted Flexible Perovskite Solar Cells with All-Inorganic Charge Contacts

2017-09-08T07:40:56.192554-05:00

Organolead halide perovskite solar cells (PSC) are arising as promising candidates for next-generation renewable energy conversion devices. Currently, inverted PSCs typically employ expensive organic semiconductor as electron transport material and thermally deposited metal as cathode (such as Ag, Au, or Al), which are incompatible with their large-scale production. Moreover, the use of metal cathode also limits the long-term device stability under normal operation conditions. Herein, a novel inverted PSC employs a SnO2-coated carbon nanotube (SnO2@CSCNT) film as cathode in both rigid and flexible substrates (substrate/NiO-perovskite/Al2O3-perovskite/SnO2@CSCNT-perovskite). Inverted PSCs with SnO2@CSCNT cathode exhibit considerable enhancement in photovoltaic performance in comparison with the devices without SnO2 coating owing to the significantly reduced charge recombination. As a result, a power conversion efficiency of 14.3% can be obtained on rigid substrates while the flexible ones achieve 10.5% efficiency. More importantly, SnO2@CSCNT-based inverted PSCs exhibit significantly improved stability compared to the standard inverted devices made with silver cathode, retaining over 88% of their original efficiencies after 550 h of full light soaking or thermal stress. The results indicate that SnO2@CSCNT is a promising cathode material for long-term device operation and pave the way toward realistic commercialization of flexible PSCs. A novel, thermal- and photostable inverted perovskite solar cell is developed, employing a SnO2-coated carbon nanotube film as cathode (substrate/NiO-perovskite/Al2O3-perovskite/SnO 2@CSCNT-perovskite). The deposition of the electron-extracting SnO2 on the CSCNT cathode increases device efficiencies, eliminates device hysteresis, and suppresses charge combination. Solar cells fabricated with SnO2@CSCNT cathodes show power conversion efficiencies of 14.3 and 10.5% on rigid and flexible substrates, respectively.



Large-Area Chemical Vapor Deposited MoS2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics

2017-09-08T07:40:11.189665-05:00

2D semiconductors are poised to revolutionize the future of electronics and photonics, much like transparent oxide conductors and semiconductors have revolutionized the display industry. Herein, these two types of materials are combined to realize fully transparent 2D electronic devices and circuits. Specifically, a large-area chemical vapor deposition process is developed to grow monolayer MoS2 continuous films, which are, for the first time, combined with transparent conducting oxide (TCO) contacts. Transparent conducting aluminum doped zinc oxide contacts are deposited by atomic layer deposition, with composition tuning to achieve optimal conductivity and band-offsets with MoS2. The optimized process gives fully transparent TCO/MoS2 2D electronics with average visible-range transmittance of 85%. The transistors show high mobility (4.2 cm2 V−1 s−1), fast switching speed (0.114 V dec−1), very low threshold voltage (0.69 V), and large switching ratio (4 × 108). To our knowledge, these are the lowest threshold voltage and subthreshold swing values reported for monolayer chemical vapor deposition MoS2 transistors. The transparent inverters show fast switching properties with a gain of 155 at a supply voltage of 10 V. The results demonstrate that transparent conducting oxides can be used as contact materials for 2D semiconductors, which opens new possibilities in 2D electronic and photonic applications. Transparent conducting aluminum doped zinc oxide (AZO) is optimized and used, for the first time, as contact material to fabricate fully transparent circuits based on 2D monolayer molybdenum disulfide (MoS2). The circuits show a high visible-range transmittance of 85%. The transistors, rectifiers, and inverters show competitive performance to 2D devices that use opaque Si substrates and metal contacts.



Quantum Dots Emitting in the Third Biological Window as Bimodal Contrast Agents for Cardiovascular Imaging

2017-09-08T07:39:05.385739-05:00

Physicians are demanding innovative technologies for multimodal imaging of the cardiovascular system that would lead to the appearance of advanced diagnosis and therapy procedures. This implies the simultaneous development of new imaging techniques and contrast agents whose synergy would make it possible. Optical coherence tomography (OCT) has recently emerged as a versatile and high-resolution clinical technique for cardiovascular imaging. Unfortunately, the lack of adequate contrast agents impedes the use of OCT for intracoronary multimodal imaging. In this work, the hitherto unexplored capability of semiconductor quantum dots (IR-QDs) emitting in the third infrared biological window (1.55–1.87 µm) to act as multimodal agents for intracoronary imaging is demonstrated. Under single line laser excitation at 1.3 µm, IR-QDs are capable of providing simultaneous backscattering contrast and efficient luminescence at 1.6 µm. In this work, backscattered radiation is successfully employed to construct OCT images in both fluids and tissues whereas the infrared luminescence of the IR-QDs provides the possibility for simultaneous acquisition of high penetrating fluorescence images. The first multimodal (fluorescence + OCT) imaging of an artery using IR-QDs as contrast agents is provided herein demonstrating their outstanding potential for future clinical applications. Infrared-emitting quantum dots can behave as bimodal contrast agents for cardiovascular imaging based on their unique combination of scattering and fluorescence properties. In combination with intracoronary optical coherence tomography, infrared-emitting quantum dots emerge as unique candidates for advanced cardiovascular imaging.



An Amidine-Type n-Dopant for Solution-Processed Field-Effect Transistors and Perovskite Solar Cells

2017-09-08T07:35:44.724579-05:00

This study reports an effective amidine-type n-dopant of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) that can universally dope electron acceptors, including PC61BM, N2200, and ITIC, by mixing the dopant with the acceptors in organic solvents or exposing the acceptor films in the dopant vapor. The doping mechanism is due to its strong electron-donating property that is also confirmed via the chemical reduction of PEDOT:PSS (yielding color change). The DBU doping considerably increases the electrical conductivity and shifts the Fermi levels up of the PC61BM films. When the DBU-doped PC61BM is used as an electron-transporting layer in perovskite solar cells, the n-doping removes the “S-shape” of J–V characteristics, which leads to the fill factor enhancement from 0.54 to 0.76. Furthermore, the DBU doping can effectively lower the threshold voltage and enhance the electron mobility of PC61BM-based n-channel field-effect transistors. These results show that the DBU can be a promising n-dopant for solution-processed electronics. An effective solution-processed amidine-type n-dopant of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), which can universally dope electron acceptor materials, including PC61BM, N2200, and ITIC, is reported. The DBU doping can enhance the performance of the perovskite solar cells and the electron mobility of the field-effect transistors.



SiO2/TiO2 Composite Film for High Capacity and Excellent Cycling Stability in Lithium-Ion Battery Anodes

2017-09-08T07:31:40.444166-05:00

In this study, partially crystalline anodic TiO2 with SiO2 well-distributed througout the entire oxide film is prepared using plasma electrolytic oxidation (PEO) to obtain a high-capacity anode with an excellent cycling stability for Li-ion batteries. The micropore sizes in the anodic film become inhomogeneous as the SiO2 content is increased from 0% to 25%. The X-ray diffraction peaks show that the formed oxide contains the anatase and rutile phases of TiO2. In addition, X-ray photoelectron spectroscopy and energy-dispersive X-ray analyses confirm that TiO2 contains amorphous SiO2. Anodic oxides of the SiO2/TiO2 composite prepared by PEO in 0.2 m H2SO4 and 0.4 m Na2SiO3 electrolyte deliver the best performance in Li-ion batteries, exhibiting a capacity of 240 µAh cm−2 at a fairly high current density of 500 µA cm–2. The composite film shows the typical Li–TiO2 and Li–SiO2 redox peaks in the cyclic voltammogram and a corresponding plateau in the galvanostatic charge/discharge curves. The as-prepared SiO2/TiO2 composite anode shows at least twice the capacity of other types of binder-free TiO2 and TiO2 composites and very stable cycling stability for more than 250 cycles despite the severe mechanical stress. A porous SiO2/TiO2 composite film as an anode for Li-ion batteries is achieved via a plasma electrolytic oxidation process, containing amorphous/anatase/rutile TiO2 and well-distributed amorphous SiO2. It exhibits a noticeably high capacity (more than 700 µAh cm‒2 at 100 µA cm‒2) and stable capacity retention (over 250 cycles) with excellent cycle performance.



Transparent and Flexible Nacre-Like Hybrid Films of Aminoclays and Carboxylated Cellulose Nanofibrils

2017-09-08T07:31:11.674641-05:00

Nacre and other biological composites are important inspirations for the design and fabrication of multifunctional composite materials. Transparent, strong, and flexible hybrid films of aminoclays (AC) and carboxylated cellulose nanofibrils (CNF) with a nacre-like microstructure at AC contents up to 60 wt% are prepared. The high transmittance of visible light is attributed to the high homogeneity of the hybrid films and to the relatively small refractive index contrast between the CNF-based matrix and synthetic AC. The strength and strain to failure of the hybrids are significantly higher than biogenic nacre and other nacre-mimicking nanocellulose-based materials, e.g., montmorillonite-CNF and graphene oxide-CNF composite films. The excellent mechanical properties are related to the ionic bonds between the negatively charged carboxylic groups on the CNF and the positively charged amine groups on the AC nanoparticles. This work illustrates the significance of tailoring the interactions between small clay particles and biopolymers in multifunctional materials with potential applications as printable barrier coatings and substrates for optoelectronics. Inspired by nacre, cationic aminoclay (AC) and carboxylated cellulose nanofibril (CNF) are fabricated into strong, flexible, and highly transparent hybrid films. The combination of high tensile strength and large strain to failure of the ionically bonded AC-CNF films is significantly higher than biogenic nacre and other nacre-mimicking nanocellulose-based materials, e.g., montmorillonite-CNF and graphene oxide-CNF films.



Atomic-Level Coupled Interfaces and Lattice Distortion on CuS/NiS2 Nanocrystals Boost Oxygen Catalysis for Flexible Zn-Air Batteries

2017-09-08T07:27:07.23378-05:00

The exploration of highly efficient nonprecious metal bifunctional electrocatalysts to boost oxygen evolution reaction and oxygen reduction reaction is critical for development of high energy density metal-air batteries. Herein, a class of CuS/NiS2 interface nanocrystals (INs) catalysts with atomic-level coupled nanointerface, subtle lattice distortion, and plentiful vacancy defects is reported. The results from temperature-dependent in situ synchrotron-based X-ray absorption fine spectroscopy and electron spin resonance spectroscopy demonstrate that the lattice distortion of 14.7% in CuS/NiS2 caused by the strong Jahn–Teller effect of Cu, the strong atomic-level coupled interface of CuS and NiS2 domains, and distinct vacancy defects can provide numerous effective active sites for their excellent bifunctional performance. A liquid Zn-air battery with the CuS/NiS2 INs as air electrode displays a large peak power density (172.4 mW cm−2), a high specific capacity (775 mAh gZn−1), and long cycle life (up to 83 h), making the CuS/NiS2 INs among the best bifunctional catalysts for Zn-air battery. More remarkably, the flexible CuS/NiS2 INs-based solid-state Zn-air batteries can power the LED after twisting, making them be promising in portable and wearable electronic devices. The anomalous CuS/NiS2 interface nanocrystals (INs) with nanointerfaces, subtle lattice distortion with a degree of about 14.7%, and rich defects show excellent electrocatalytic performance for both oxygen evolution reaction and reduction reaction. A Zn-air battery with CuS/NiS2 INs as air-cathode demonstrates high performance, even after bending with various shapes. Flexible CuS/NiS2 INs-based solid-state Zn-air batteries can even power light-emitting diodes.



Programmable Macroporous Photonic Crystals Enabled by Swelling-Induced All-Room-Temperature Shape Memory Effects

2017-09-08T07:26:32.650162-05:00

This study reports unconventional, all-room-temperature shape memory (SM) effects using templated macroporous shape memory polymer (SMP) photonic crystals comprising a glassy copolymer with high-glass transition temperature. “Cold” programming of permanent periodic structures into temporary disordered configurations can be achieved by slowly evaporating various swelling solvents (e.g., ethanol) imbibed in the interconnecting macropores. The deformed macropores can be instantaneously recovered to the permanent geometry by exposing it to vapors and liquids of swelling solvents. By contrast, nonswelling solvents (e.g., hexane) cannot trigger “cold” programming and SM recovery. Extensive experimental and theoretical investigations reveal that the dynamics of swelling-induced plasticizing effects caused by fast diffusion of solvent molecules into the walls of macropores with nanoscopic thickness dominate both “cold” programming and recovery processes. Importantly, the striking color changes associated with the reversible SM transitions enable novel chromogenic sensors for selectively detecting trace amounts of swelling analytes mixed in nonswelling solvents. Using ethanol–hexane solutions as proof-of-concept mixtures, the ethanol detection limit of 150 ppm has been demonstrated. Besides reusable sensors, which can find important applications in environmental monitoring and petroleum process/product control, the programmable SMP photonic crystals possessing high mechanical strengths and all-room-temperature processability can provide vast opportunities in developing reconfigurable/rewritable nanooptical devices. Plasticizing effects induced by rapid diffusion of swelling solvent molecules, combined with a glassy shape memory polymer possessing high Tg and mechanical strength, enable programmable macroporous photonic crystals exhibiting unconventional all-room-temperature shape memory cycles. The striking color changes associated with reversible shape memory transitions lead to novel chromogenic sensors for selectively detecting trace amounts of swelling analytes in nonswelling solvents.



Dual Functionalization of Liquid-Exfoliated Semiconducting 2H-MoS2 with Lanthanide Complexes Bearing Magnetic and Luminescence Properties

2017-09-08T07:25:54.36248-05:00

Liquid exfoliated, atomically thin semiconducting transition metal dichalcogenides (TMDs), as inorganic equivalents of graphene, have attracted great interest due to their distinctive physical, optoelectronic, and chemical properties. Functionalization of 2D TMDs brings new prospects for applications in optoelectronics, quantum technologies, catalysis, and medicine. In this report, dual functionalization of 2D semiconducting 2H-MoS2 nanosheets through simultaneous incorporation of magnetic and luminescent properties is demonstrated. A facile method is proposed for tuning the properties of the TDM semiconductors and accessing multimodal platforms, consisting in covalent grafting of lanthanide complexes onto the surface of 2D TMDs. Dual functionalization of liquid-exfoliated MoS2 nanosheets is demonstrated simultaneously with both europium (III) and gadolinium (III) complexes to form a colloidally stable luminescent (with millisecond lifetimes) and paramagnetic MoS2-based nanohybrid material. This work is the first example of transition metal dichalcogenide nanosheets functionalized with preformed lanthanide complexes. These findings open new prospects for covalent functionalization of TMDs with molecular species bearing specific functionalities as a means to tune the optoelectronic properties of the semiconductors, in order to create advanced materials and devices with a wide range of functionalities. Semiconducting 2H-MoS2 nanosheets are functionalized simultaneously with europium (III) and gadolinium (III) complexes. The characteristic optical and paramagnetic behavior of the lanthanides is maintained postfunctionalization, in addition to the semiconductor phase of the 2H-MoS2. This work brings new and added functionality to MoS2 without resorting to refractory doping, thinning to monolayer, or other approaches.



Functional Polysaccharide Sutures Prepared by Wet Fusion of Interfacial Polyelectrolyte Complexation Fibers

2017-09-08T07:23:11.638795-05:00

This study reports polysaccharide-based fibers that can be utilized as biocompatible functional sutures. Fibers are spontaneously formed by spinning at the interface between two oppositely charged polysaccharide solutions. Unlike the common belief that polysaccharide fibers prepared by electrostatic interactions would exhibit weak mechanical strength, it is demonstrated that fibers spun at the interface between two droplets of positively charged chitosan and negatively charged heparin can exhibit high mechanical strength through spontaneous wet-state fusion of interfiber strands at a spinning wheel. Dry solidification results in multistranded fibers that were ≈100 µm in diameter with a tensile strength of ≈220 MPa. Post fibrous manipulation yields various morphology with straight or twisted fibers, fabrics, or springs. To demonstrate application of the fiber, it is applied as a medical suture. As heparin has a unique ability to bind adeno-associated virus (AAV), a therapeutic, biocompatible suture exhibiting localized AAV-mediated gene delivery function can be prepared. This study shows that multistrand fusion of fibers, formed by weak, electrostatic interactions and followed by drying solidification counterintuitively results in mechanically strong, functional fibers with various potential applications. The adeno-associated virus (AAV) immobilized chitosan/heparin suture is fabricated for localized gene delivery. Implantation of the AAV immobilized chitosan/heparin suture in subcutaneous tissue results in highly localized fluorescence signal expression at the implant site in the timeframe from three to five weeks. The developed chitosan/heparin suture holds great promise for clinical gene delivery.



Ligand Versatility in Supercrystal Formation

2017-09-08T07:21:45.237292-05:00

Supercrystals (SCs) offer the opportunity to integrate nanoparticles into current technologies without losing their unique and designable properties. In the past two decades, much research has been conducted, allowing the synthesis of differently shaped nanoparticles of various materials. Employing those building units, several methods have been developed enabling the preparation of an increasing number of different superstructures. In this review, an overview is given of the large versatility of surfactant molecules used for SC preparation. While SCs with uncharged organic ligands are by far the largest group, the use of charged or uncommon ligands allows the preparation of unique SCs and superlattices. Additionally, the influence of the ligands on the self-assembly and properties of the resulting SCs is highlighted. Herein, the influence of the surfactant species on supercrystal formation is discussed with regard to superlattice and structural diversity. The variety of different ligands is categorized into three groups, which are uncharged long-chain organics, charged organics, and unusual ligands. While the first category includes the mostly used ligands, uncommon surfactants enable the preparation of unique superstructures.



Direct Laser Writing of Superhydrophobic PDMS Elastomers for Controllable Manipulation via Marangoni Effect

2017-09-08T07:11:30.460337-05:00

Direct light-to-work conversion enables manipulating remote devices in a contactless, controllable, and continuous manner. Although some pioneering works have already proven the feasibility of controlling devices through light-irradiation-induced surface tension gradients, challenges remain, including the flexible integration of efficient photothermal materials, multifunctional structure design, and fluidic drag reduction. This paper reports a facile one-step method for preparing light-driven floating devices with functional surfaces for both light absorption and drag reduction. The direct laser writing technique is employed for both arbitrary patterning and surface modification. By integrating the functional layer at the desired position or by designing asymmetric structures, three typical light-driven floating devices with fast linear or rotational motions are demonstrated. Furthermore, these devices can be driven by a variety of light sources including sunlight, a filament lamp, or laser beams. The approach provides a simple, green, and cost-effective strategy for building functional floating devices and smart light-driven actuators. A facile fabrication of superhydrophobic polydimethylsiloxane (PDMS) elastomers structures that permit controllable manipulation via Marangoni effectthat permit controllable manipulation via Marangoni effect is reported here. Direct laser writing technology is employed to apply a light absorbing and superhydrophobic layer on the PDMS surface. By integrating the functional layer at the desired position or by designing asymmetric structures, typical light-driven devices with fast linear or rotational motions are demonstrated.



Table Salt as a Template to Prepare Reusable Porous PVDF–MWCNT Foam for Separation of Immiscible Oils/Organic Solvents and Corrosive Aqueous Solutions

2017-09-07T11:32:45.592344-05:00

Many advanced materials are designed for separation of immiscible oils/organic solvents and aqueous solutions, including poly(vinylidene fluoride) (PVDF)-based materials with superwettability. However, due to the limited solubility of PVDF, techniques (e.g., phase inversion and electrospinning) often involve the use of toxic organic solvents. Here a facile organic solvent-free method is described to prepare a porous PVDF–MWCNT (multiwalled carbon nanotube) foam using table salt as a sacrificial template. The porous PVDF–MWCNT foam is characterized as superhydrophobic–superoleophilic with good elasticity due to its 3D porosity and low surface energy. The foam exhibits high adsorption capacity to a variety of oils/organic solvents and can be easily reused by squeezing, heating, or releasing in other solvents. Moreover, the foam is highly resistant toward UV exposure, corrosive aqueous solutions such as acidic, alkaline, salty solutions, and turbulent environments, and shows effective oils/organic solvents removal in these complex environments. The continuous separation of immiscible oils/organic solvents and corrosive aqueous solutions with vacuum assistance is also presented. The organic solvent-free and reusable PVDF–MWCNT foam is a promising candidate for large-scale industrial separation of oils/organic solvents and water in corrosive and turbulent conditions. Porous poly(vinylidene fluoride)–multiwalled carbon nanotube foam with superwettability is fabricated by sacrificial template method without using any organic solvents. The foam exhibits high adsorption capacity to a variety of oils/organic solvents and can be easily reused by squeezing, heating, or releasing in other solvents. Continuous separations of immiscible oils/organic solvents and corrosive aqueous solutions are realized by vacuum assistance.



Surface Energy-Controlled SERS Substrates for Molecular Concentration at Plasmonic Nanogaps

2017-09-06T09:58:19.10676-05:00

Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surface-enhanced Raman spectroscopy (SERS) analysis. In this article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A large-area HAR plasmonic nanopillar array is generated using a nanolithography-free simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self-assembled monolayer of low surface-energy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary-force-induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars. Molecular concentration at the electromagnetic hot spots is achieved using surface-enhanced Raman spectroscopy (SERS) substrates with controlled surface energies. The surface energies of the high aspect ratio plasmonic nanostructures are precisely controlled via the selective removal of low-surface energy chemicals that is chemisorbed onto the structures.



High Performance Flexible Nonvolatile Memory Based on Vertical Organic Thin Film Transistor

2017-09-06T09:57:53.14365-05:00

Flexible floating-gate organic transistor memory (FGOTM) is a potential candidate for emerging memory technologies. Unfortunately, conventional planar FGOTM suffers from weak driving ability and insufficient mechanical flexibility, which limits its commercial application. In this work, a novel flexible vertical FGOTM (VFGOTM) is reported. Benefitting from new vertical architecture, VFGOTM provides ultrashort channel length to afford an extremely high current density. Meanwhile, VFGOTM devices exhibit excellent memory performance and outstanding retention property. The memory properties of VFGOTM devices are comparable or even better than traditional planar FGOTM and much better than the reported organic nonvolatile memory with vertical transistor structures. More importantly, organic nonvolatile memory with vertical transistor structures is investigated for the first time on a flexible substrate. The results show that VFGOTM architecture allows vertical current flow across the channel layer to effectively eliminate the effect of mechanical bending during current transport, which significantly improves the mechanical stability of the flexible VFGOTM. Hence, with a combination of excellent driving ability, memory performance, and mechanical stability, VFGOTM devices meet the practical requirements for high performance memory applications, which have great potential for the application in a wide range of flexible and wearable electronics. A novel vertical architecture floating gate organic transistor memory fabricated on a flexible substrate is reported. The unique vertical architecture enables memory devices with ultrashort channel length, which provides a large current density (excellent driving ability), fast operation and mechanical stability, showing great potential for the application in a wide range of flexible and wearable electronic applications.



Conducting Polymer Based Visual-Aided Smart Thermosensors on Arbitrary Substrates

2017-09-06T09:57:09.213134-05:00

Conducting polymers have shown appealing performances as sensing materials in various smart sensors such as gas, chemical and biological sensors, owing to their unique physical and electrical properties. This study reports a novel development for the fabrication of visual-aided smart thermal (VAST) sensors. The sensors are based on conducting polymers, temperature-sensitive resin, and liquid crystal molecules via direct scrawling and in situ solventless polymerization. In the VAST sensor, the thermochromism resins and liquid crystals form a visual-aided system with the real-time early warning function and the conducting polymers provide an ultrahigh resolution by the measure of the change of resistivity. Additionally, these VAST sensors also hold the advantages of low cost, using simple tools, high stability, excellent adaptability to arbitrary substrates, wide application fields, and facile large-scale fabrication. These properties are in favor of fabricating smart thermal sensors to satisfy the practical demands, such as the demonstrated temperature detecting system (especially flexible devices with nonplanar surface), thermodefect diagnostic system, smart battery monitoring system, and other environment monitoring. Visual-aided smart thermal (VAST) sensors are fabricated through the combination of direct scrawling and in situ solventless polymerization. Resulting VAST sensors possess real-time early warning function, ultrahigh resolution, high stability, and outstanding adaptability. These properties make VAST sensors ideal for many applications, not just as simple temperature detectors, but also as real-time intelligent monitoring system.



Morphology of a Ternary Blend Solar Cell Based on Small Molecule:Conjugated Polymer:Fullerene Fabricated by Blade Coating

2017-09-06T09:55:50.619195-05:00

Here, conjugated polymer is added as third component to tune the solution viscosity, morphology, and function of small molecule (SM) based bulk-heterojunction (BHJ) solar cells, which are fabricated using blade coating. Novel information about the effect of blade coating speed on the nanoscale morphology and function of ternary blend solar cells is provided. The crystal sizes increase with an increase of coating speed for both binary and ternary blends, while the addition of the third component tends to favor smaller SM crystal grains and improves the connectivity of SM crystals. Small angle neutron scattering experiments provide the first clear experimental evidence that the addition of the third component would significantly impact the fullerene phase separation, which is crucial for bimolecular recombination and charge transport. It shows that for both binary and ternary blends, the concentration and sizes of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) aggregates increase with an increase of coating speed, while addition of third component does not affect the volume fraction of PCBM aggregates but impacts the size of PCBM aggregates. It is demonstrated that the judicious selection of blade coating speed and addition of conjugated polymer optimize the morphology of SM-BHJ, providing guidelines for high performance SM-BHJs from roll-to-roll production. The crystallization of small molecules and fullerene phase separation in SM-BHJ blends are significantly impacted by the blade coating speed as well as the addition of a third component. The judicious selection of blade coating speed and the addition of a conjugated polymer optimizes the morphology of SM-BHJ, which will provide guidelines for high performance SM-BHJ from roll-to-roll production.



Nucleation and Crystallization Control via Polyurethane to Enhance the Bendability of Perovskite Solar Cells with Excellent Device Performance

2017-09-05T07:25:04.705594-05:00

Solar cells based on mixed organic–inorganic halide perovskites are promising photovoltaic technologies with low-cost and fantastic power conversion efficiency (PCE). Enhancing the nucleation and regulating the crystallization rate of perovskite films and improving the bendability of brittle hybrid grains are crucial to improving the photovoltaic performance of flexible perovskite solar cells (PVSCs). Here, a simple approach is first introduced for fabricating perovskite films with full coverage and larger crystalline size by incorporating the elastomer polyurethane (PU) into the perovskite precursor solution to both retard the crystallization rate and improve the bendability. Shiny, smooth perovskite films are obtained with compact, micrometer-sized crystalline grains that exhibit excellent photoelectric performances. The PVSCs fabricated by incorporating PU into the perovskite precursor offer an impressive PCE of 18.7% with almost no photocurrent hysteresis and excellent stability in ambient air. More importantly, the elastomer PU additive crosslinks the grain boundaries between neighboring perovskite crystals to form a PU network that effectively improves the bendability of the perovskite films. Polyurethane (PU) has been used as an effective additive to optimize the performance of perovskite solar cells by retarding crystallization rate and enhancing grain size of perovskite crystals. More importantly, elastomer PU can effectively improve the bendability of perovskite films due to denseness and high elasticity created by crosslinking grain boundaries between neighboring perovskite crystals to form a PU network.



Phenotypic Selection of Magnetospirillum magneticum (AMB-1) Overproducers Using Magnetic Ratcheting

2017-09-05T07:13:57.864057-05:00

Magnetosomes, magnetic nanoparticles (MNPs) encapsulated in lipid membranes produced by magnetotactic bacteria (MTB), have superior properties such as a narrow size distribution, making them of potential significant value for biomedical and industrial applications. However, the slow growth rate and genetic complexity of MTB have thus far limited large scale production of biologically synthesized MNPs. This problem is compounded by a lack of a platform to select MTB of interest. Here, the development of a magnetic ratcheting system that facilitates automated, live, and quantitative isolation of Magnetospirillum magneticum (AMB-1) based on their phenotype, i.e., number of MNPs is described. Using repeated (five) cycles of random chemical mutagenesis and magnetic selection, AMB-1 overproducers that biomineralize on average 2.2-fold more MNPs (≈25) than the widely available strain AMB-1 are generated. The size, shape, and magnetic properties of the MNPs of the overproducers are also similar to the control AMB-1, supporting the utility of the platform for enriching MTB with overproducer phenotypes. Magnetosomes, magnetic nanoparticles (MNPs) encapsulated in lipid membranes produced by magnetotactic bacteria, have superior properties such as a narrow size distribution, making them of potential significant value for biomedical and industrial applications. Here, the development of a magnetic ratcheting system that facilitates automated, live, and quantitative isolation of Magnetospirillum magneticum (AMB-1) based on their phenotype, i.e., number of MNPs is described.



Waveguide Encoded Lattices (WELs): Slim Polymer Films with Panoramic Fields of View (FOV) and Multiple Imaging Functionality

2017-09-05T07:13:33.875846-05:00

When encoded with a 3D network of interconnected and pentadirectional waveguides, an otherwise passive polymer film transforms into an intelligent optical element—a waveguide encoded lattice (WEL)—that combines a panoramic field of view, infinite depth of field and powerful capacity to perform multiple imaging operations such as divergence-free transmission, focusing, and inversion. The lattices are moreover operable with coherent and incoherent light at all visible wavelengths, both individually (e.g., narrow band sources such as lasers, light-emitting diodes) and collectively (e.g., incandescent sources). This combination of properties is unprecedented in single-component films and the WEL structures represent a new class of flexible, slim films that could confer advanced optical functionalities when integrated with light-based technologies (e.g., solar panels, smart phone cameras, and smart screens) and are amenable to the design and fabrication of new miniaturized optical and optoelectronic devices. Encoding a polymer film with a network of waveguides generates an intelligent element that possesses a panoramic field of view, an infinite depth of field, and can focus, invert, and transmit images without divergence. This unprecedented class of slim, flexible films could confer advanced functionalities to light-based technologies including solar panels, phone cameras and smart screens.



Mutually Synergistic Nanoparticles for Effective Thermo-Molecularly Targeted Therapy

2017-09-05T07:12:31.673252-05:00

Photothermal therapy (PTT) is of particular importance as a highly potent therapeutic modality in cancer therapy. However, a critical challenge still remains in the exploration of highly effective strategy to maximize the PTT efficiency due to tumor thermoresistance and thus frequent tumor recurrence. Here, a rational fabrication of the micelles that can achieve mutual synergy of PTT and molecularly targeted therapy (MTT) for tumor ablation is reported. The micelles generate both distinct photothermal effect from Cypate through enhanced photothermal conversion efficiency and pH-dependent drug release. The micelles further exhibit effective cytoplasmic translocation of 17-allylamino-17-demethoxygeldanamycin (17AAG) through reactive oxygen species mediated lysosomal disruption caused by Cypate under irradiation. Translocated 17AAG specifically bind with heat shock protein 90 (HSP90), thereby inhibiting antiapoptotic p-ERK1/2 proteins for producing preferable MTT efficiency through early apoptosis. Meanwhile, translocated 17AAG molecules further block stressfully overexpressed HSP90 under irradiation and thus inhibit the overexpression of p-Akt for achieving the reduced thermoresistance of tumor cells, thus promoting the PTT efficiency through boosting both early and late apoptosis of Cypate. Moreover, the micelles possess enhanced resistance to photobleaching, preferable cellular uptake, and effective tumor accumulation, thus facilitating mutually synergistic PTT/MTT treatments with tumor ablation. These findings represent a general approach for potent cancer therapy. This study reports a rational fabrication of the micelles that can achieve mutual synergy of photothernal therapy (PTT) and molecularly targeted therapy (MTT) for effective tumor ablation through enhanced PTT by blocking stressfully overexpressed HSP90 under irradiation using 17-allylamino-17-demethoxygeldanamycin (17AAG) and preferable MTT efficiency by reactive oxygen species mediated effective cytoplasmic translocation of 17AAG caused by Cypate under irradiation.



In Situ Construction of 3D Interconnected FeS@Fe3C@Graphitic Carbon Networks for High-Performance Sodium-Ion Batteries

2017-09-05T07:11:12.294154-05:00

Iron sulfides have been attracting great attention as anode materials for high-performance rechargeable sodium-ion batteries due to their high theoretical capacity and low cost. In practice, however, they deliver unsatisfactory performance because of their intrinsically low conductivity and volume expansion during charge–discharge processes. Here, a facile in situ synthesis of a 3D interconnected FeS@Fe3C@graphitic carbon (FeS@Fe3C@GC) composite via chemical vapor deposition (CVD) followed by a sulfuration strategy is developed. The construction of the double-layered Fe3C/GC shell and the integral 3D GC network benefits from the catalytic effect of iron (or iron oxides) during the CVD process. The unique nanostructure offers fast electron/Na ion transport pathways and exhibits outstanding structural stability, ensuring fast kinetics and long cycle life of the FeS@Fe3C@GC electrodes for sodium storage. A similar process can be applied for the fabrication of various metal oxide/carbon and metal sulfide/carbon electrode materials for high-performance lithium/sodium-ion batteries. 3D interconnected FeS@Fe3C@graphitic carbon networks are constructed via a chemical vapor deposition method followed by a sulfuration process. The unique nanostructure endows the FeS@Fe3C@GC composite with high discharge capacity, good rate capability, and excellent cycling stability as anode for sodium-ion batteries. The strategy can be extended to the fabrication of other metal oxide/carbon and metal sulfide/carbon electrode materials.



Intracellular Pathways Involved in Bone Regeneration Triggered by Recombinant Silk–Silica Chimeras

2017-09-04T07:26:41.417324-05:00

Biomineralization at the organic–inorganic interface is critical to many biology material functions in vitro and in vivo. Recombinant silk–silica fusion peptides are organic–inorganic hybrid material systems that can be effectively used to study and control biologically mediated mineralization due to the genetic basis of sequence control. However, to date, the mechanisms by which these functionalized silk–silica proteins trigger the differentiation of human mesenchymal stem cells (hMSCs) to osteoblasts remain unknown. To address this challenge, silk–silica surfaces are analyzed for silica–hMSC receptor binding and activation, and the intracellular pathways involved in the induction of osteogenesis on these bioengineered biomaterials. The induction of gene expression of αVβ3 integrin, all three mitogen-activated protein kinsases, as well as c-Jun, runt-related transcription factor 2, and osteoblast marker genes is demonstrated upon growth of the hMSCs on the silk–silica materials. This induction of key markers of osteogenesis correlates with the content of silica on the materials. Moreover, computational simulations are performed for silk/silica-integrin binding which show activation of αVβ3 integrin in contact with silica. This integrated computational and experimental approach provides insight into interactions that regulate osteogenesis toward more efficient biomaterial designs. This work describes the intracellular pathways leading to osteogenesis for recombinant silk-chimera proteins with potential in regenerative medicine. Using an integrated computational-experimental approach, insight into key interactions for control of osteogenesis is provided, demonstrating involvement of integrin αVβ3, and mitogen-activated protein kinase pathways in osteogenic markers induction promoted by silica surfaces. This is critical for optimized designs for mineralized materials.



Enhanced Reversible Sodium-Ion Intercalation by Synergistic Coupling of Few-Layered MoS2 and S-Doped Graphene

2017-09-04T07:26:14.130307-05:00

Sodium-ion batteries (SIBs) are regarded as the best alternative to lithium-ion batteries due to their low cost and similar Na+ insertion chemistry. It is still challenging but greatly desired to design and develop novel electrode materials with high reversible capacity, long cycling life, and good rate capability toward high-performance SIBs. This work demonstrates an innovative design strategy and a development of few-layered molybdenum disulfide/sulfur-doped graphene nanosheets (MoS2/SG) composites as the SIB anode material providing a high specific capacity of 587 mA h g−1 calculated based on the total composite mass and an extremely long cycling stability over 1000 cycles at a current density of 1.0 A g−1 with a high capacity retention of ≈85%. Systematic characterizations reveal that the outstanding performance is mainly attributed to the unique and robust composite architecture where few-layered MoS2 and S-doped graphene are intimately bridged at the hetero-interface through a synergistic coupling effect via the covalently doped S atoms. The design strategy and mechanism understanding at the molecular level outlined here can be readily applied to other layered transition metal oxides for SIBs anode and play a key role in contributing to the development of high-performance SIBs. Few-layered MoS2/S-doped graphene composites are successfully designed and developed with highly reversible Na+ storage capability and remarkably long cycling life owing to the unique and robust composite architecture providing a synergistic coupling effect at the hetero-interface via covalently doped S atoms. Such innovative design and development hold great promise for low-cost and high-performance sodium-ion batteries.



Nutlin-3a and Cytokine Co-loaded Spermine-Modified Acetalated Dextran Nanoparticles for Cancer Chemo-Immunotherapy

2017-09-04T07:24:10.862898-05:00

The combination of chemo- and immunotherapy represents one promising strategy to overcome the existent challenges in the present-day anticancer therapy. Here, spermine-modified acetalated dextran nanoparticles (Sp-AcDEX NPs), co-loaded with the non-genotoxic molecule Nutlin-3a (Nut3a), and the cytokine granulocyte–macrophage colony-stimulating factor (GM-CSF), are developed to induce cancer cell death and create a specific antitumor immune response. These polymeric NPs release Nut3a in a pH dependent fashion and induce endosomal escape. Due to Nut3a, the loaded NPs exert specific toxicity toward wild-type p53 cancer cells while avoiding toxicity in immune cells. Furthermore, the NPs show intrinsic immune adjuvancy on monocyte derived-dendritic cells, upregulating the expression of cell surface CD83 and CD86 costimulatory markers. Finally, it is examined that by inducing MCF-7 breast cancer cell death and acting as immune adjuvants, the NPs can downregulate the expression of IL-10 and upregulate IL-1β, leading to proliferation of CD3+ and cytotoxic CD8+ T cells. Overall, the study suggests that Sp-AcDEX NPs loaded with Nut3a and GM-CSF is a promising system for chemo-immunotherapy, capable of inducing tumor cell death and stimulating immune response. Nutlin-3a and granulocyte–macrophage colony-stimulator factor are co-loaded into spermine-modified acetalated dextran nanoparticles to produce a nanosystem for cancer chemo-immunotherapy. The nanosystem is biocompatible, exerts cancer cell death, has intrinsic immunoadjuvancy, induces upregulation of the costimulatory signals in dendritic cells, and changes the cytokine balance, leading to T-cell proliferation and development of CD8+ T-cell subset.



Nanoarchitectonics for Hybrid and Related Materials for Bio-Oriented Applications

2017-09-04T07:23:22.628953-05:00

Atom/molecular-level controls in nanotechnology are important for the precise placement of components in device applications. Despite many advances, nanotechnology still uses simple systems to make precise atom/molecule-scale changes. This is in contrast with the many phenomena observed in biological systems, where there appears to be a well-designed integrative approach involving molecular units to achieve atomic- and molecular-scale changes. Inspired by nature, we introduced a novel concept—nanoarchitectonics—to develop nanoscale functional materials for bio-oriented applications. Nanoarchitectonics is a unified concept combining nanotechnology and methodologies in related research fields, such as supramolecular chemistry, self-assembly, and self-organization, to satisfy the major features of nanosciences for the creation of functional materials or even devices and machines. This concept guides the harmonized assembly of nanoscale objects into higher order functional materials. In this Feature Article, recent research activities are introduced regarding the development of advanced functional materials of hybrid and related architectures on the basis of nanoarchitectonics from diverse contexts of organic and inorganic materials: i) from biology (DNA-based hybrid); ii) from geology (clay-based hybrid); iii) from 0D nanotechnology (fullerene-based hybrid); and iv) from other nanoarchitectonics. Therefore, this Feature Article showcases some examples of the nanoarchitectonic concepts at work in diverse material types. Developments of functional materials for bio-related applications are discussed on the basis of a novel concept—nanoarchitectonics—which guides the harmonized assemblies of nanoscale objects to higher order functional materials. In this feature article, examples are taken from biology (DNA-based hybrid), geology (clay-based hybrid), and nanotechnology (fullerene-based hybrid), as well as other nanoarchitectonics materials.



Highly Efficient Self-Healable and Dual Responsive Cellulose-Based Hydrogels for Controlled Release and 3D Cell Culture

2017-09-04T07:21:55.775145-05:00

To face the increasing demand of self-healing hydrogels with biocompatibility and high performances, a new class of cellulose-based self-healing hydrogels are constructed through dynamic covalent acylhydrazone linkages. The carboxyethyl cellulose-graft-dithiodipropionate dihydrazide and dibenzaldehyde-terminated poly(ethylene glycol) are synthesized, and then the hydrogels are formed from their mixed solutions under 4-amino-DL-phenylalanine (4a-Phe) catalysis. The chemical structure, as well as microscopic morphologies, gelation times, mechanical and self-healing performances of the hydrogels are investigated with 1H NMR, Fourier transform infrared spectroscopy, atomic force microscopy, rheological and compression measurements. Their gelation times can be controlled by varying the total polymer concentration or 4a-Phe content. The resulted hydrogels exhibit excellent self-healing ability with a high healing efficiency (≈96%) and good mechanical properties. Moreover, the hydrogels display pH/redox dual responsive sol-gel transition behaviors, and are applied successfully to the controlled release of doxorubicin. Importantly, benefitting from the excellent biocompatibility and the reversibly cross-linked networks, the hydrogels can function as suitable 3D culture scaffolds for L929 cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the cellulose-based self-healing hydrogels show potential applications in drug delivery and 3D cell culture for tissue engineering. New high-performance cellulose-based self-healing hydrogels are constructed through dynamic acylhydrazone crosslinking under 4-amino-dl-phenylalanine catalysis. These hydrogels have highly tunable gelation time and exhibit pH/redox controlled release behaviors. Importantly, they can serve as suitable 3D culture scaffolds for cells, as a result of their excellent biocompatibility and adaptable dynamic networks.



Understanding Thermal Insulation in Porous, Particulate Materials

2017-09-04T07:21:15.490992-05:00

Silica hollow nanosphere colloidal crystals feature a uniquely well-defined structure across multiple length scales. This contribution elucidates the intricate interplay between structure and atmosphere on the effective thermal diffusivity as well as the effective thermal conductivity. Using silica hollow sphere assemblies, one can independently alter the particle geometry, the density, the packing symmetry, and the interparticle bonding strength to fabricate materials with an ultralow thermal conductivity. Whereas the thermal diffusivity decreases with increasing shell thickness, the thermal conductivity behaves inversely. However, the geometry of the colloidal particles is not the only decisive parameter for thermal insulation. By a combination of reduced packing symmetry and interparticle bonding strength, the thermal conductivity is lowered by additionally 70% down to only 8 mW m−1 K−1 in vacuum. The contribution of gaseous transport, even in these tiny pores (<200 nm), leads to minimum thermal conductivities of ≈35 and ≈45 mW m−1 K−1 for air and helium atmosphere, respectively. The influence of the individual contributions of the solid and (open- and closed-pore) gaseous conductions is further clarified by using finite element modeling. Consequently, these particulate materials can be considered as a non-flammable and dispersion-processable alternative to commercial polymer foams. Colloidal assemblies represent a model platform to understand heat transport in nanostructured materials. Using the uniquely well-defined structure of monodisperse hollow silica particles, a material with an extremely low effective thermal conductivity of 8 mW m−1 K−1 in vacuum can be systematically designed. Control parameters are the particle geometry, the interparticle bonding strength, and the ensemble symmetry.



Development of a Dual-Modally Traceable Nanoplatform for Cancer Theranostics Using Natural Circulating Cell-Derived Microparticles in Oral Cancer Patients

2017-09-04T07:17:05.456491-05:00

Cell-derived microparticles (MPs), which are biogenic nanosized membrane vesicles that convey bioactive molecules between cells, have exhibited great potential to serve as therapeutic platforms. However, so far, all the MPs used as theranostic vectors in previous studies have been produced in vitro from cell culture supernatants, which is still associated with several concerns regarding practical applications. In this study, circulating MPs (CMPs), which are freshly purified from the peripheral blood of oral squamous cell carcinoma (OSCC) patients, are directly and efficiently embedded with ultrasmall near-infrared-fluorescent magnetic quantum dots (Ag2Se@Mn QDs) via electroporation. By virtue of the superior photostability, favorable biocompatibility, and dual-mode traceability of Ag2Se@Mn QD-labeled CMPs in vivo, the tissue distribution and natural tumor-targeting behavior of CMPs from OSCC patients are directly visualized in living mice for the first time. Moreover, by simultaneously embedding antitumor siRNA and Ag2Se@Mn QDs into CMPs derived from OSCC patients, a dual-modally traceable and actively tumor-targeted nanoplatform for cancer theranostics is developed. This study reports the first reliable conjugation-free labeling strategy for in vivo dual-mode tracking of CMPs harvested from the human body, and, more importantly, reports the development of traceable tumor-targeted theranostic vectors based on naturally occurring CMPs from cancer patients. Circulating microparticles (CMPs) purified from the plasma of oral cancer patients are simultaneously loaded with ultrasmall Mn-magnetofunctionalized Ag2Se quantum dots (Ag2Se@Mn QDs) and antitumor siRNA with the assistance of electroporation. Based on the dual-mode traceability of Ag2Se@Mn QDs and the inherent tumor-targeting and cargo-delivering abilities of CMPs, these real natural vectors are successfully transformed into multifunctional nanoplatforms for tumor-targeted theranostics.



Elastic Modulus Dependence on the Specific Adhesion of Hydrogels

2017-09-04T07:15:58.102627-05:00

Mechanosensitivity in biology, e.g., cells responding to material stiffness, is important for the design of synthetic biomaterials. It is caused by protein receptors able to undergo conformational changes depending on mechanical stress during adhesion processes. Here the elastic modulus dependence of adhesive interactions is systematically quantified using ligand–receptor model systems that are generally not thought to be mechanosensitive: biotin–avidin, mannose–concanavalin A, and electrostatic interactions between carboxylic acids and polycationic surfaces. Interactions are measured by microgel sensors of different stiffness adhering to surfaces presenting a corresponding binding partner. Adhesion is generally decreased for softer microgels due to reduced density of binding partners. Density-normalized data show that low-affinity carbohydrate ligands exhibit reduced binding in softer networks, probably due to increased network conformational entropy. However, in case of stronger interactions with large interaction range (electrostatic) and large lifetime (biotin–avidin) density normalized adhesion is increased. This suggests compensation of entropic repulsion for softer networks probably due to their increased mechanical deformation upon microgel adhesion and enhanced cooperative binding. In essence, experiments indicate that soft interacting polymer materials exhibit entropic repulsion, which can be overcome by strongly interacting species in the network harnessing network flexibility in order to increase adhesion. The relationship between material stiffness and specific interaction is analyzed using novel microgel adhesion sensors in combination with an interferometric technique. In general, adhesion of soft polymer network is found to be governed by entropic repulsion, however, strong biomolecular interaction harnesses “softness” in order to reinforce adhesion. Understanding of such mechanosensitivity phenomena is critical for biomaterial development.



Engineered Axonal Tracts as “Living Electrodes” for Synaptic-Based Modulation of Neural Circuitry

2017-09-04T07:12:17.27505-05:00

Brain–computer interface and neuromodulation strategies relying on penetrating non-organic electrodes/optrodes are limited by an inflammatory foreign body response that ultimately diminishes performance. A novel “biohybrid” strategy is advanced, whereby living neurons, biomaterials, and microelectrode/optical technology are used together to provide a biologically-based vehicle to probe and modulate nervous-system activity. Microtissue engineering techniques are employed to create axon-based “living electrodes”, which are columnar microstructures comprised of neuronal population(s) projecting long axonal tracts within the lumen of a hydrogel designed to chaperone delivery into the brain. Upon microinjection, the axonal segment penetrates to prescribed depth for synaptic integration with local host neurons, with the perikaryal segment remaining externalized below conforming electrical–optical arrays. In this paradigm, only the biological component ultimately remains in the brain, potentially attenuating a chronic foreign-body response. Axon-based living electrodes are constructed using multiple neuronal subtypes, each with differential capacity to stimulate, inhibit, and/or modulate neural circuitry based on specificity uniquely afforded by synaptic integration, yet ultimately computer controlled by optical/electrical components on the brain surface. Current efforts are assessing the efficacy of this biohybrid interface for targeted, synaptic-based neuromodulation, and the specificity, spatial density and long-term fidelity versus conventional microelectronic or optical substrates alone. A biohybrid brain–machine interface strategy is developed using neuron/axon-based “living electrodes” within microcolumnar encasement. The perikaryal segment remains quasi-externalized under optical/electrical arrays on a brain surface, while the axonal segment is microinjected for targeted, synaptic-based neuromodulation of deep host circuitry. This biohybrid approach is at the intersection of neuroscience and engineering to establish biological intermediaries between man and machine.



A Mesocrystal-Like Morphology Formed by Classical Polymer-Mediated Crystal Growth

2017-09-04T07:11:34.796506-05:00

Growth by oriented assembly of nanoparticles is a widely reported phenomenon for many crystal systems. While often deduced through morphological analyses, direct evidence for this assembly behavior is limited and, in the calcium carbonate (CaCO3) system, has recently been disputed. However, in the absence of a particle-based pathway, the mechanism responsible for the creation of the striking morphologies that appear to consist of subparticles is unclear. Therefore, in situ atomic force microscopy is used to investigate the growth of calcite crystals in solutions containing a polymer additive known for its ability to generate crystal morphologies associated with mesocrystal formation. It is shown that classical growth processes that begin with impurity pinning of atomic steps, leading to stabilization of new step directions, creation of pseudo-facets, and extreme surface roughening, can produce a microscale morphology previously attributed to nonclassical processes of crystal growth by particle assembly. The first mechanistic picture is presented of the process by which crystals develop exotic morphologies previously attributed to “mesocrystals.” The canonical mesocrystal of calcite grown in polystyrene sulfonate solution forms through completely classical processes of step advancement on faceted crystal surfaces, putting to rest the notion that a typical mesocrystal morphology is evidence for a growth pathway via particle assembly.



Self-Assembling Azaindole Organogel for Organic Light-Emitting Devices (OLEDs)

2017-09-04T07:11:03.763258-05:00

This study reports on the use of a self-assembling organogel, 5-(4-nonylphenyl)-7-azaindole (1), as a new emitter in small-molecule organic light emitting devices (OLEDs). The theoretical calculations along with the photophysical characterization studies suggest the coexistence of the monomer and dimer species at high concentration of compound 1. The presence of this type of dimer (formed via H-bonding) is responsible for the increased emission. However, the most notable feature is the 3D network of vastly interconnected fibers formed in the organogel that modifies the photophysical properties. Based on this, several OLED architectures are made in order to understand the mechanism involved in the electroluminescence (EL) behavior of 1. Although the position of the EL spectra differs from that of the photoluminescence (PL) spectra, the trends observed in the device properties perfectly match with dimer formation. In this framework a better device performance is associated to a higher efficiency of dimer formation, which optimizes in the OLED prepared from the organogel. Therefore, these results show that the rational combination of a moiety showing a strong PL intensity increased upon aggregation with organogel properties is an efficient strategy to create alternative emitters for OLED devices. A new emitter based on a self-assembled organogel, 5-(4-nonylphenyl)-7-azaindole, is proposed and tested for organic light emitting device (OLED) applications. The theoretical calculations along with the photo-electroluminescent characterization unravel the mechanism involved in the electroluminescence behavior and also point out that this kind of self-assembling molecule is an efficient strategy to create alternative emitters for OLED devices.



A Magnetoresistance Induced by a Nonzero Berry Phase in GeTe/Sb2Te3 Chalcogenide Superlattices

2017-08-31T11:10:59.096826-05:00

The chalcogenide alloy Ge–Sb–Te (GST) has not only been used in rewritable digital versatile discs, but also in nonvolatile electrical phase change memory as a key recording material. Although GST has been believed for a long time not to show magnetic properties unless doped with magnetic impurities, it has recently been reported that superlattices (SLs) with the structure [(GeTe)L(Sb2Te3)M]N (where L, M, and N are usually integers) have a large magnetoresistance at room temperature for particular combinations of L and M. Here it is reported that when [(GeTe)L(Sb2Te3)M]N chalcogenide SL films are thermally annealed at 470 K and cooled down to room temperature under an external magnetic field accompanied by current pulse injections, a large magnetoresistance change (>2500 Ω) is induced. This study shows that the phenomenon has a strong correlation with the GeTe thickness and the periodic structure of the SL films, and that it is induced by the structural phase transition between electrically nonpolar and polar phases in the GeTe layers in the SLs. This study proposes that the relationship between the polar (ferroelectric) phase and the Berry curvature in the SLs is responsible for the magnetoresistance change. A chalcogenide superlattice composed of GeTe and Sb2Te3 sublayers is usually nonmagnetic. However, once exposed to thermal annealing under a magnetic field accompanied by current injections, it generates a large magnetoresistance at specific GeTe film thicknesses of 0.4 and 0.8 nm.



Spatial Differences in Cellular and Molecular Responses as a Function of the Material Used in Conduit-Mediated Repair and Autograft Treatment of Peripheral Nerve Injuries

2017-08-31T11:06:11.93128-05:00

The treatment of peripheral nerve injuries remains a major problem worldwide despite the availability of a number of Food and Drug Administration (FDA) approved devices which fail to match the efficacy of autografts. Different strategies are used to improve regeneration and functional recovery using biomaterial nerve conduits. However, there is little investigation of the transcriptomic and proteomic changes which occur as a result of these interventions, particularly regarding transection injuries. This study explores differences between autograft-mediated repair and conduit-material-mediated repair of peripheral nerve injuries to understand fundamental differences in their repair mechanisms at the proteomics level at the proximal, middle, and distal components in the early stages of repair. Pathway analysis demonstrates that each material selectively activates different regenerative pathways and alters different biological functions spatially throughout the biomaterial conduits. The analysis highlights some of the deficiencies in conduit-mediated repair in comparison to autograft (e.g., recycling of myelin and cholesterol, reduction in reactive oxygen species, and higher expression of regenerative proteins). These findings thus suggest that by supplementing the expression of these proteins on the biomaterial of choice, this study can potentially attain regeneration equivalent to autograft. This approach paves the way for incorporating future biomaterial-specific functionalities in nerve guidance conduits. The proteomic changes that occur spatially throughout a natural or synthetic nerve guidance conduit or within an autograft during the treatment of peripheral nerve injuries are investigated in this study. Using pathway analysis tools, this study explores how different materials in conduit-mediated nerve repair, and how autografts, activate different biological functions during the early stages of regeneration.



Tuning Thermal Transport in Chain-Oriented Conducting Polymers for Enhanced Thermoelectric Efficiency: A Computational Study

2017-08-29T11:29:03.735583-05:00

Thermoelectric polymers should be electron-crystal and phonon-glass to efficiently interconvert heat and electricity. Herein, by using molecular dynamics simulations, it is demonstrated that engineering phonon transport in conducting polymers by tailoring its degree of polymerization can effectively improve the energy conversion efficiency. This is based on the separated length scales that charge carriers and phonons travel along the polymer backbone. By tuning the chain length and the crystallinity of chain-oriented poly(3,4-ethylenedioxythiophene) fibers, a dramatic decrease of the axial thermal conductivity to 0.97 W m−1 K−1 has been observed in rationally designed polymer fibers with the crystallinity of 0.49 and the relative molecular weight of 5600. The dimensionless thermoelectric figure of merit at 298 K has been enhanced to 0.48, which is approximately one order of magnitude higher than that in crystalline polymers. Tuning degrees of polymerization and crystallinity of conducting polymers have been demonstrated, by using molecular dynamics simulations, as effective strategies to engineer thermal transport along the polymer backbone for achieving a high zT. The essential reason behind this is the separation of length scales for charge carriers and phonons travelling along the polymer backbone.



High-Precision Temperature-Controllable Metal-Coated Polymeric Molds for Programmable, Hierarchical Patterning

2017-08-29T11:28:19.909356-05:00

Nanofabrication is an indispensable process in nanoscience and nanotechnology. Unconventional lithographic techniques are often used for fabrication as alternatives to photolithography because they are faster, more cost-effective, and simpler to use. However, these techniques are limited in scalability and utility because of the collapse of preprinted structures during step-and-repeat processes. This study proposes a new class of temperature-controllable polymeric molds that are coated with a metal such that any site-specific patterning can be accomplished in a programmable manner using selective contact-dewetting lithography. The lithography allows sub-100 nm patterning, step-and-repeat processing, and hierarchical structure fabrication. The programmable feature of the lithography can be utilized for the structural coloring and shaping of objects. Large-area programmable patterning, semiconductor device manufacturing, and the fabrication of iridescent security devices would benefit from the unique features of the proposed strategy. The surface temperature of the mold can be precisely and uniformly controlled by localized joule heating system. The characteristics of temperature-controllable metal-coated polymeric molds show great potential for unconventional lithographic techniques for sub-100 nm scale features, large-area programmable patterning, and 3D hierarchical structuring via step-and-repeat processes.



Structure Sorting of Large-Diameter Carbon Nanotubes by NaOH Tuning the Interactions between Nanotubes and Gel

2017-08-28T12:46:19.726189-05:00

The structure separation of synthetic single-wall carbon nanotube (SWCNT) mixture species with diameters larger than 1.2 nm still remains a challenge. Here, an NaOH-assisted gel chromatography method is used for the structure separation of the SWCNT mixture with a diameter range of 1.2–1.7 nm, in which NaOH is used to tune the interaction between distinct (n, m) SWCNTs and gel. Incrementally increasing NaOH concentration in SWCNT dispersion selectively enhances the adsorbability of different-structure SWCNTs and enlarges their interaction difference with gel, leading to their structure separation after applying into a gel column system. On this basis, a two-step method is developed for further improving the structure purity of the separated SWCNTs by combining overloading and stepwise elution. These results are well demonstrated by the optical spectra of the separated SWCNTs. This work paves a way for single-chirality separation of large-diameter SWCNTs using gel chromatography technique and is an advanced progress in the structure control of SWCNTs. A NaOH-assisted gel chromatography method is developed for the effective structure separation of large-diameter single-wall carbon nanotubes (SWCNTs) (>1.2 nm). In this technique, NaOH is used to tune the interaction between large-diameter SWCNTs and gel, and discriminates different-structure SWCNTs that have minute differences in their interactions with the gel.



Single Component Organic Solar Cells Based on Oligothiophene-Fullerene Conjugate

2017-08-28T12:13:52.512452-05:00

A new donor (D)–acceptor (A) conjugate, benzodithiophene-rhodanine–[6,6]-phenyl-C61 butyric acid methyl ester (BDTRh–PCBM) comprising three covalently linked blocks, one of p-type oligothiophene containing BDTRh moieties and two of n-type PCBM, is designed and synthesized. A single component organic solar cell (SCOSC) fabricated from BDTRh–PCBM exhibits the power conversion efficiency (PCE) of 2.44% and maximum external quantum efficiency of 46%, which are the highest among the reported efficiencies so far. The SCOSC device shows efficient charge transfer (CT, ≈300 fs) and smaller CT energy loss, resulting in the higher open-circuit voltage of 0.97 V, compared to the binary blend (BDTRh:PCBM). Because of the integration of the donor and acceptor in a single molecule, BDTRh-PCBM has a specific D–A arrangement with less energetic disorder and reorganization energy than blend systems. In addition, the SCOSC device shows excellent device and morphological stabilities, showing no degradation of PCE at 80 °C for 100 h. The SCOSC approach may suggest a great way to suppress the large phase segregation of donor and acceptor domains with better morphological stability compared to the blend device. Integration of donor and acceptor in a single molecule by a covalent linkage is a promising approach to overcome unfavorably large-phase separation in bulk heterojunction blend solar cells. A new all-in-one system forms a specific molecular arrangement which decreases energetic disorder and facilitates ultrafast charge separation.



Multifunctional Neural Interfaces for Closed-Loop Control of Neural Activity

2017-08-28T05:13:26.78141-05:00

Microfabrication and nanotechnology have significantly expanded the technological capabilities for monitoring and modulating neural activity with the goal of studying the nervous system and managing neurological disorders. This feature article initially provides a tutorial-like review of the prominent technologies for enabling this two-way communication with the nervous system via electrical, chemical, and optical means. Following this overview, the article discusses emerging high-throughput methods for identifying device attributes that enhance the functionality of interfaces. The discussion then extends into opportunities and challenges in integrating different device functions within a small footprint with the goal of closed-loop control of neural activity with high spatiotemporal resolution and reduced adverse tissue response. The article concludes with an outline of future directions in the development and applications of multifunctional neural interfaces. The capability to monitor and modulate neural activity in a closed-loop fashion is essential for studying the nervous system and managing neurological disorders. This feature article introduces the prominent technologies for interfacing with the nervous system via electrical, chemical, and optical means, followed by a discussion of opportunities and challenges in developing multifunctional interfaces that embody the three modalities.



Batteries: Shape-Reconfigurable Aluminum–Air Batteries (Adv. Funct. Mater. 35/2017)

2017-09-18T06:29:48.684356-05:00

In article number 1702244, Jooho Moon, Wooyoung Shim, and co-workers report a shape-reconfigurable battery that can polymorph while preserving its electrochemical functionality. The flexible and foldable aluminum–air cell composed of an aluminum foil and a carbon composite, combined with the concept of shape-reconfigurable materials, provides a new approach for realizing highly deformable aluminum–air batteries.



Flexible Electronics: A Bi-Sheath Fiber Sensor for Giant Tensile and Torsional Displacements (Adv. Funct. Mater. 35/2017)

2017-09-18T06:29:48.72543-05:00

A highly stretchable, resistive strain sensor composed of a bi-sheath structure is described by Jianning Ding, Linqi Shi, Zunfeng Liu, and co-workers in article number 1702134. Buckles of a carbon nanotube sheath contact with one another under compression of an underlying buckled elastomer sheath, which is co-axially coated on a rubber fiber. Stretching separates the buckles, resulting in linear increase of resistance with strain.



Masthead: (Adv. Funct. Mater. 35/2017)

2017-09-18T06:29:43.149059-05:00




Contents: (Adv. Funct. Mater. 35/2017)

2017-09-18T06:29:43.031071-05:00




Nanostructured Metal Chalcogenides for Energy Storage and Electrocatalysis

2017-08-04T01:08:36.143793-05:00

Energy storage and conversion technologies are vital to the efficient utilization of sustainable renewable energy sources. Rechargeable lithium-ion batteries (LIBs) and the emerging sodium-ion batteries (SIBs) are considered as two of the most promising energy storage devices, and electrocatalysis processes play critical roles in energy conversion techniques that achieve mutual transformation between renewable electricity and chemical energies. It has been demonstrated that nanostructured metal chalcogenides including metal sulfides and metal selenides show great potential for efficient energy storage and conversion due to their unique physicochemical properties. In this feature article, the recent research progress on nanostructured metal sulfides and metal selenides for application in SIBs/LIBs and hydrogen/oxygen electrocatalysis (hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction) is summarized and discussed. The corresponding electrochemical mechanisms, critical issues, and effective strategies towards performance improvement are presented. Finally, the remaining challenges and perspectives for the future development of metal chalcogenides in the energy research field are proposed. Metal chalcogenides including metal sulfides and selenides are intensively studied in the energy field due to their unique physicochemical properties. In this review, specific attention is given to the state-of-the-art research progress in sodium-ion batteries, lithium-ion batteries, and electrocatalysis hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction.



Shape-Reconfigurable Aluminum–Air Batteries

2017-08-07T07:13:58.743748-05:00

The battery shape is a critical limiting factor affecting foreseeable energy storage applications. In particular, deformable metal–air battery systems can offer low cost, low flammability, and high capacity, but the fabrication of such metal–air batteries remains challenging. Here, it is shown that a shape-reconfigurable-material approach, in which the deformable components composed of micro- and nanoscale composites are assembled, is suitable for constructing polymorphic metal–air batteries. By employing an aluminum foil and an adhesive carbon composite placed on a cellulose scaffold as a substrate, an aluminum–air battery that can be deformed to an unprecedented high level, e.g., via expanding, folding, stacking, and crumpling, can be realized. This significant deformability results in a specific capacity of 128 mA h g−1 (496 mA h g−1 per cell; based on the mass of consumed aluminum) and a high output voltage (10.3 V) with 16 unit battery cells connected in series. The resulting battery can endure significant geometrical distortions such as 3D expanding and twisting, while the electrochemical performance is preserved. This work represents an advancement in deformable aluminum–air batteries using the shape-reconfigurable-material concept, thus establishing a paradigm for shape-reconfigurable batteries with exceptional mechanical functionalities. Shape-reconfigurable batteries that lead to 2D and 3D polymorphed states while preserving electrochemical functionality are developed. Aluminum–air batteries composed of an aluminum foil and a carbon composite on a cellulose scaffold are adopted as a platform, which represents an advancement in deformable batteries using the shape-reconfigurable-material concept, establishing a paradigm for shape-reconfigurable batteries with exceptional mechanical functionalities.



A Bi-Sheath Fiber Sensor for Giant Tensile and Torsional Displacements

2017-07-19T01:48:58.413021-05:00

Current research about resistive sensors is rarely focusing on improving the strain range and linearity of resistance–strain dependence. In this paper, a bi-sheath buckled structure is designed containing buckled carbon nanotube sheets and buckled rubber on rubber fiber. Strain decrease results in increasing buckle contact by the rubber interlayer and a large decrease in resistance. The resulting strain sensor can be reversibly stretched to 600%, undergoing a linear resistance increase as large as 102% for 0–200% strain and 160% for 200–600% strain. This strain sensor shows high linearity, fast response time, high resolution, excellent stability, and almost no hysteresis. Novel bi-sheath strain sensors for tensile and torsional strain are fabricated by hierarchically buckling an aligned carbon nanotube sheath on a buckled elastomer-coated rubber fiber. The contact area between adjacent nanotube buckles decreases with increasing stretch to provide 160% increase in resistance during 600% sensor elongation, which is fast in response, low in hysteresis, and high in cycle life.



Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells

2017-07-28T01:31:27.126835-05:00

This study reports the development of copper(I) thiocyanate (CuSCN) hole-transport layers (HTLs) processed from aqueous ammonia as a novel alternative to conventional n-alkyl sulfide solvents. Wide bandgap (3.4–3.9 eV) and ultrathin (3–5 nm) layers of CuSCN are formed when the aqueous CuSCN–ammine complex solution is spin-cast in air and annealed at 100 °C. X-ray photoelectron spectroscopy confirms the high compositional purity of the formed CuSCN layers, while the high-resolution valence band spectra agree with first-principles calculations. Study of the hole-transport properties using field-effect transistor measurements reveals that the aqueous-processed CuSCN layers exhibit a fivefold higher hole mobility than films processed from diethyl sulfide solutions with the maximum values approaching 0.1 cm2 V−1 s−1. A further interesting characteristic is the low surface roughness of the resulting CuSCN layers, which in the case of solar cells helps to planarize the indium tin oxide anode. Organic bulk heterojunction and planar organometal halide perovskite solar cells based on aqueous-processed CuSCN HTLs yield power conversion efficiency of 10.7% and 17.5%, respectively. Importantly, aqueous-processed CuSCN-based cells consistently outperform devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate HTLs. This is the first report on CuSCN films and devices processed via an aqueous-based synthetic route that is compatible with high-throughput manufacturing and paves the way for further developments. Dissolution of copper thiocyanate (CuSCN) in aqueous ammonia enables processing of superior quality hole-transporting layers at low temperature in ambient air. Transistors based on these CuSCN layers exhibit mobilities close to 0.1 cm2 V−1 s−1, while solar cells incorporating CuSCN interlayers yield power conversion efficiencies of 10.7% and 17.5% for organic bulk heterojunction and organometal halide cells, respectively.



Water Splitting: Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity (Adv. Funct. Mater. 35/2017)

2017-09-18T06:29:48.599288-05:00

A highly-ordered and crystalline Fe2TiO5 honeycomb nanotube photoanode is described by Jae Sung Lee and co-workers in article number 1702428. Fabricated by hybrid microwave annealing using ultrathin anodic aluminum oxide as a template, the device shows an outstanding water splitting activity after triple modification. The strategy paves the way for significantly improving the performance of other photoelectrode materials.



Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity

2017-08-14T01:21:03.503967-05:00

Highly ordered iron titanate (Fe2TiO5) nanotube array photoanode is synthesized on F:SnO2 glass with ultrathin anodized aluminum oxide as a hard template. Highly crystalline, yet the nanotube array morphology-preserved Fe2TiO5 is fabricated by hybrid microwave annealing (HMA). The effects of the synthesis parameters on photoelectrochemical (PEC) water splitting activity under simulated sunlight are systematically studied including HMA time, pore size, wall thickness, and length of the nanotubes to optimize the nanotube array photoanode. In addition, triple modification strategies of TiO2 underlayer, hydrogen treatment, and FeNiOx cocatalyst loading effectively improve the PEC activity further. The systematically engineered nanotube array photoanode achieves a photocurrent density of 0.93 mA cm−2 at 1.23 VRHE under 1 sun (100 mW cm−2) irradiation, which corresponds to 2.6 times that of the previous best Fe2TiO5 photoanode. In addition, the photocurrent onset potential shifts cathodically by ≈280 mV relative to the pristine nanotube array electrode. A highly ordered Fe2TiO5 nanotube array photoanode with high crystallinity is synthesized with ultrathin anodic aluminum oxide as a template and hybrid microwave annealing, which achieves an excellent photoelectrochemical water splitting performance by additional triple modifications. The strategy paves a way for other photoelectrode materials to significantly improve their performance.



Biodegradable and Highly Deformable Temperature Sensors for the Internet of Things

2017-07-10T10:57:27.295409-05:00

Recent advances in biomaterials, thin film processing, and nanofabrication offer the opportunity to design electronics with novel and unique capabilities, including high mechanical stability and biodegradation, which are relevant in medical implants, environmental sensors, and wearable and disposable devices. Combining reliable electrical performance with high mechanical deformation and chemical degradation remains still challenging. This work reports temperature sensors whose material composition enables full biodegradation while the layout and ultrathin format ensure a response time of 10 ms and stable operation demonstrated by a resistance variation of less than 0.7% when the devices are crumpled, folded, and stretched up to 10%. Magnesium microstructures are encapsulated by a compostable-certified flexible polymer which exhibits small swelling rate and a Young's modulus of about 500 MPa which approximates that of muscles and cartilage. The extension of the design from a single sensor to an array and its integration onto a fluidic device, made of the same polymer, provides routes for a smart biodegradable system for flow mapping. Proper packaging of the sensors tunes the dissolution dynamics to a few days in water while the connection to a Bluetooth module demonstrates wireless operation with 200 mK resolution prospecting application in food tracking and in medical postsurgery monitoring. Advances in biomaterials and nanofabrication allow designing highly mechanically stable electronics that are biodegradable. This study demonstrates temperature sensors whose material composition enables full biodegradation while the layout and ultrathin format ensure fast response time and reliable operations upon stretching and folding. Wireless operation, achieved via an external Bluetooth module, prospects application in food monitoring and post-surgery implants.



Amorphous GaN@Cu Freestanding Electrode for High-Performance Li-Ion Batteries

2017-07-27T06:10:59.043705-05:00

GaN is demonstrated to be an ideal anode for Li-ion batteries (LIBs) for the first time. Amorphous GaN@Cu nanorods (a-GaN@Cu) freestanding electrode is designed via a low-temperature pulsed laser deposition method, which exhibits prominent rate capability and untralong lifespan as an anode for LIBs. With porous interconnected metal nanorods substrate to improve the structure integrity and electronic conductivity, the a-GaN@Cu electrode delivers a capacity recovery of 980 mAh g−1 after 150 cycles from 0.25 to 6.25 A g−1 and a high discharge capacity of 509 mAh g−1 after 3000 cycles at 10.0 A g−1. The lithium storage in the a-GaN is also systematically studied, which suggests a redox reaction mechanism. Pioneer research on GaN as anode for Li-ion batteries, a-GaN@Cu freestanding electrode, is designed via a facile pulsed laser deposition method and shows superior performance through a redox reaction mechanism.



Improved Performance in FeF2 Conversion Cathodes through Use of a Conductive 3D Scaffold and Al2O3 ALD Coating

2017-07-24T14:53:34.762671-05:00

FeF2 is considered a promising conversion compound for the positive electrode in lithium-ion batteries due to its high thermodynamic reduction potential (2.66 V vs Li/Li+) and high theoretical specific capacity (571 mA h g−1). However, the sluggish reaction kinetics and rapid capacity decay caused by side reactions during cycling limit its practical application. Here, the fabrication of Ni-supported 3D Al2O3-coated FeF2 electrodes is presented, and it is shown that these structured electrodes significantly overcome these limitations. The electrodes are prepared by iron electrodeposition on a Ni support, followed by a facile fluorination process and Al2O3 coating by atomic layer deposition. The 3D FeF2 electrode delivers an initial discharge capacity of 380 mA h g−1 at a current density of 200 mA g−1 at room temperature. The 3D scaffold improves the reaction kinetics and enables a high specific capacity by providing an efficient electron pathway to the insulating FeF2 and short Li diffusion lengths. The Al2O3 coating significantly improves the cycle life, probably by preventing side reactions through limiting direct electrode–electrolyte contact. The fabrication method presented here can also be applied for synthesis of other metal fluoride materials on different 3D conductive templates. Ni-supported 3D FeF2 electrodes are prepared by electrodeposition followed by fluorination. Atomic layer deposition coating of the FeF2 coated with Al2O3 improves its electrochemical properties. The electrode shows good cyclability under high current density and good rate performance, demonstrating that a 3D conductive scaffold, coupled with a thin oxide coating, significantly improves the performance of fluoride-based conversion cathodes.



An Interplay between Matrix Anisotropy and Actomyosin Contractility Regulates 3D-Directed Cell Migration

2017-07-24T06:24:23.72854-05:00

Directed cell migration is essential for many biological processes, such as embryonic development or cancer progression. Cell contractility and adhesion to the extracellular matrix are known to regulate cell locomotion machinery. However, the cross-talk between extrinsic and intrinsic factors at the molecular level on the biophysical mechanism of three dimensional (3D)-directed cell migration is still unclear. In this work, a novel physiologically relevant in vitro model of the extracellular microenvironment is used to reveal how the topological anisotropy of the extracellular matrix synergizes with actomyosin contractility to modulate directional cell migration morphodynamics. This study shows that cells seeded on polarized 3D matrices display asymmetric protrusion morphodynamics and in-vivo-like phenotypes. It is found that matrix anisotropy significantly enhances cell directionality, but strikingly, not the invasion distance of cells. In Rho-inhibited cells, matrix anisotropy counteracts the lack of actomyosin-driven forces to stabilize cell directionality suggesting a myosin-II-independent mechanism for cell guidance. Finally, this study shows that on isotropic 3D environments, cell directionality is independent of actomyosin contractility. Altogether, this study provides novel quantitative data on the biomechanical regulation of directional cell motion and shows the important regulatory role of matrix anisotropy and actomyosin forces to guide cell migration in 3D microenvironments. This work describes the generation of anisotropic cell-derived matrices for the study of physiopathological processes. Microfabricated guiding templates are combined with the confluent culture of fibroblasts to generate native-like 3D matrices with controlled architectures. This extracellular matrix model is allowed to unravel the critical interplay between matrix anisotropy with actomyosin contractility during directed 3D cell migration by modulating the locomotion strategy of cells.



Ultrafast Synthesis of Ultrasmall Poly(Vinylpyrrolidone)-Protected Bismuth Nanodots as a Multifunctional Theranostic Agent for In Vivo Dual-Modal CT/Photothermal-Imaging-Guided Photothermal Therapy

2017-07-21T06:02:45.352204-05:00

To elaborately fabricate real-time monitoring and therapeutic function into a biocompatible nanoplatform is a promising route in the cancer therapy field. However, the package of diagnosis and treatment into a single-“element” nanoparticle remains challenge. Herein, ultrasmall poly(vinylpyrrolidone)-protected bismuth nanodots (PVP-Bi nanodots) are successfully synthesized through an ultrafacile strategy (1 min only under ambient conditions). The nanodots are easy to synthesize in both laboratory and large scale using low-cost bismuth ingredients. PVP-Bi nanodots with ultrasmall size show good biocompatibility. Due to the high X-ray attenuation ability of Bi element, PVP-Bi nanodots have prominent performance on X-ray computed tomography (CT) imaging. Moreover, PVP-Bi nanodots exhibit a high photothermal conversion efficiency (η = 30%) because of the strong near-infrared absorbance, which can serve as nanotheranostic agent for photothermal imaging and cancer therapy. The subsequent PVP-Bi-nanodot-mediated photothermal therapy (PTT) result shows highly efficient ablation of cancer cells both in vitro and in vivo. PVP-Bi nanodots can be almost completely excreted from mice after 7 d. Blood biochemistry and histology analysis suggests that PVP-Bi nanodots have negligible toxicity. All the positive results reveal that PVP-Bi nanodots produced through the ultrafacile method are promising single-“element” nanotheranostic platform for dual-modal CT/photothermal-imaging-guided PTT. Ultrasmall poly(vinylpyrrolidone)-protected bismuth nanodots are successfully synthesized through an ultrafacile strategy (1 min only under ambient conditions). The nanodots with ultrasmall size (≈2.7 nm) show good biocompatibility both in vitro and in vivo, which can be used for X-ray computed tomography (CT) and photothermal imaging. These two imaging modalities can effectively guide the photothermal therapy process of nanodots.



Truly Electroforming-Free and Low-Energy Memristors with Preconditioned Conductive Tunneling Paths

2017-08-03T00:51:32.50741-05:00

1S1R (1 selector and 1 memristor) is a laterally scalable and vertically stackable scheme that can lead to the ultimate memristor density for either memory or neural network applications. In such a scheme, the memristor device needs to be truly electroforming-free and operated at both low currents and low voltages in order to be compatible with a two-terminal selector. In this work, a new type of memristor with a preconditioned tunneling conductive path is developed to achieve the required performance characteristics, including truly electroforming-free, low current below 30 µA (potentially <1 µA), and simultaneously low voltage ≈±0.7 V in switching operations. Such memristors are further integrated with two types of recently developed selectors to demonstrate the feasibility of 1S1R integration. This study proposes and experimentally demonstrates a truly electroforming-free device with both low switching current and voltage for the first time. The exemplary device with a Ta/Ta2O5:Ag/Ru-stack structure functions based on conductive tunneling paths. The low operation current and voltage make the memristors highly compatible with two-terminal selectors. 1S1R integrate cells are demonstrated with both ionic selector and electronic selector.



Spatially Separated CdS Shells Exposed with Reduction Surfaces for Enhancing Photocatalytic Hydrogen Evolution

2017-07-24T06:17:15.388555-05:00

To the photocatalytic H2 evolution, the exposure of a reduction surface over a catalyst plays an important role for the reduction of hydrogen protons. Here, this study demonstrates the design of a noble-metal-free spatially separated photocatalytic system exposed with reduction surfaces (MnOx@CdS/CoP) for highly solar-light-driven H2 evolution activity. CoP and MnOx nanoparticles are employed as the electron and hole collectors, which are selectively anchored on the outer and inner surface of CdS shells, respectively. Under solar light irradiation, the photogenerated holes and electrons can directionally move to the MnOx and CoP, respectively, leading to the exposure of a reduction surface. As a result, the H2 evolution increases from 32.0 to 238.4 µmol h−1, which is even higher than the activity of platinum-loaded photocatalyst (MnOx@CdS/Pt). Compared to the pure CdS with serious photocorrosion, the MnOx@CdS/CoP maintains a changeless activity for the H2 evolution and rhodamine B degradation, even after four cycles. The research provides a new strategy for the preparation of spatially separated photocatalysts with a selective reduction surface. Spatially separated CdS sphere shells with a selective reduction surface are synthesized by a novel strategy. In this case, the CoP and MnOx nanoparticles as the cocatalysts are located at the outer and inner surface of shells, respectively. The directional migration of photogenerated charges is responsible for the stable and enhanced photocatalytic H2 evolution and rhodamine B degradation under solar light irradiation.



Unprecedented Homoleptic Bis-Tridentate Iridium(III) Phosphors: Facile, Scaled-Up Production, and Superior Chemical Stability

2017-07-26T06:26:46.964261-05:00

Bis-tridentate Ir(III) metal complexes are expected to show great potential in organic light-emitting diode (OLED) applications due to the anticipated, superb chemical and photochemical stability. Unfortunately, their exploitation has long been hampered by lack of adequate methodology and with inferior synthetic yields. This hurdle can be overcome by design of the first homoleptic, bis-tridentate Ir(III) complex [Ir(pzpyph)(pzHpyph)] (1), for which the abbreviation (pzpyph)H (or pzHpyph) stands for the parent 2-pyrazolyl-6-phenyl pyridine chelate. After that, methylation and double methylation of 1 afford the charge-neutral Ir(III) complex [Ir(pzpyph)(pzMepyph)] (2) and cationic complex [Ir(pzMepyph)2][PF6] (3), while deprotonation of 1 gives formation of anionic [Ir(pzpyph)2][NBu4] (4), all in high yields. These bis-tridentate Ir(III) complexes 2–4 are highly emitted in solution and solid states, while the charge-neutral 2 and corresponding t-butyl substituted derivative [Ir(pzpyBuph)(pzMepyBuph)] (5) exhibit superior photostability versus the tris-bidentate references [Ir(ppy)2(acac)] and [Ir(ppy)3] in toluene under argon, making them ideal OLED emitters. For the track record, phosphor 5 gives very small efficiency roll-off and excellent overall efficiencies of 20.7%, 66.8 cd A−1, and 52.8 lm W−1 at high brightness of 1000 cd m−2. These results are expected to inspire further studies on the bis-tridentate Ir(III) complexes, which are judged to be more stable than their tris-bidentate counterparts from the entropic point of view. Homoleptic bis-tridentate Ir(III) complexes are synthesized using a facile and simplified methodology. One monomethylated derivative (i.e., a t-butyl emitter) exhibits very small efficiency roll-off and excellent efficiencies of 20.7%, 66.8 cd A−1, and 52.8 lm W−1, at a high brightness of 1000 cd m−2.



Proton Conduction in a Tyrosine-Rich Peptide/Manganese Oxide Hybrid Nanofilm

2017-08-04T01:13:00.989989-05:00

Proton conduction is an essential process that regulates an integral part of several enzymatic catalyses and bioenergetics. Proton flows in biological entities are sensitively controlled by several mechanisms. To understand and manipulate proton conduction in biosystems, several studies have investigated bulk proton conduction in biomaterials such as polyaspartic acid, collagen, reflectin, serum albumin mats, and eumelanin. However, little is known about the bulk proton conductivity of short peptides and their sequence-dependent behavior. Here, this paper focuses on a short tyrosine-rich peptide that has redox-active and cross-linkable phenol groups. The spin-coated peptide nanofilm is immersed in potassium permanganate solution to induce cross-linking and oxidation, simultaneously leading to hybridization with manganese oxide (MnOx). The peptide/MnOx hybrid nanofilm can efficiently transport protons, and its proton conductivity is ≈18.6 mS cm−1 at room temperature. This value is much higher than that of biomaterials and comparable to those of other synthetic proton-conducting materials. These results suggest that peptide-based hybrid materials can be a promising new class of proton conductor. A new class of hybrid proton conductor composed of tyrosine-rich peptide and manganese oxide is synthesized. Electrical measurements and isotope analysis reveal that the main charge carrier of the hybrid film is a proton from water vapor. Interestingly, cross-linking and oxidation of tyrosine simultaneously lead to hybridization with MnOx, resulting in strong synergetic effects on proton conduction.



Role of Ordered Ni Atoms in Li Layers for Li-Rich Layered Cathode Materials

2017-08-01T09:16:46.563483-05:00

Li-rich layered oxide materials are promising candidates for high-energy Li-ion batteries. They show high capacities of over 200 mAh g−1 with the additional occupation of Li in their transition metal layers; however, the poor cycle performance induced by an irreversible phase transition limits their use in practical applications. In recent work, an atomic-scale modified surface, in which Ni is ordered at 2c sites in the Li layers, significantly improves the performance in terms of reversible capacity and cycling stability. The role of the incorporated Ni on this performance, however, is not yet clearly understood. Here, the effects of the ordered Ni on Li battery performance are presented, based on first-principles calculations and experimental observations. The Ni substitution suppresses the oxygen loss by moderating the oxidation of oxygen ions during the delithiation process and forms bonds with adjacent oxygen after the first deintercalation of Li ions. These NiO bonds contribute to the formation of a solid surface, resulting in the improved cycling stability. Moreover, the multivalent Ni suppresses Mn migration to the Li-sites that causes the undesired phase transition. These findings from theoretical calculations and experimental observations provide insights to enhance the electrochemical performance of Li-rich layered oxides. The regularly ordered Ni substitution in the Li-rich layered oxide significantly improves the battery performance in terms of reversible capacity and cycling stability. The combinatorial study using first-principles calculations and experiments reveals that Ni substitution effectively suppresses the oxygen loss and cation mixing that induces the undesired phase transition for the Li-rich layered cathode materials.



Plasmonic Color Filters as Dual-State Nanopixels for High-Density Microimage Encoding

2017-07-31T06:12:57.722191-05:00

Plasmonic color filtering has provided a range of new techniques for “printing” images at resolutions beyond the diffraction-limit, significantly improving upon what can be achieved using traditional, dye-based filtering methods. Here, a new approach to high-density data encoding is demonstrated using full color, dual-state plasmonic nanopixels, doubling the amount of information that can be stored in a unit-area. This technique is used to encode two data sets into a single set of pixels for the first time, generating vivid, near-full sRGB (standard Red Green Blue color space)color images and codes with polarization-switchable information states. Using a standard optical microscope, the smallest “unit” that can be read relates to 2 × 2 nanopixels (370 nm × 370 nm). As a result, dual-state nanopixels may prove significant for long-term, high-resolution optical image encoding, and counterfeit-prevention measures. Using nanostructured metal surfaces to separate discrete colors from white light shows tremendous promise for enabling the next generational leap in image sensors, “printing” techniques, and display technologies. Here, the use of two-color nanopixels for optical image encoding is explored: employing them as dual-state nanopixels to generate surfaces encoded with two sets of optical information using just one set of pixels.