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Preview: Die Angewandte Makromolekulare Chemie

Macromolecular Materials and Engineering



Wiley Online Library : Macromolecular Materials and Engineering



Published: 2018-02-01T00:00:00-05:00

 



Flexible and UV Resistant Films Based on Thiophene-Substituted Conjugated Microporous Polymers Bearing Alkyl Chains: Tuning of Rigidity into Soft

2018-02-22T04:11:23.818981-05:00

Conjugated microporous polymers (CMPs) are usually formed as rigid π-conjugated networks and insoluble in common solutions which in turn have limitations in molding or process for applications due to its unprocessability. In this work, a series of CMPs containing thiophene-moieties (SCMPs) are obtained by dibromothiophene with carbon branched chain and ethynylbenzene monomers. The solubility of the SCMPs would be significantly improved by tuning the length of alkyl chains in alkyl-substituted dibromothiophene monomers. SCMPs products bearing different alkyl-substituted dibromothiophene moiety exhibit an interesting transition from insolubility to solubility in most common organic solvents, which would greatly improve its processability. Taking advantage of its solubility, freestanding SCMPs films and flexible and transparent UV resistant PDMS films based on SCMPs coatings can be easily fabricated by simple coating methods. These finding may provide a possibility for future design and fabrication of soluble and processable CMPs by rational design and tuning alkyl-substituted aromatic monomers. Conjugated microporous polymers (CMPs) bearing different alkyl-substitutions are synthesized which exhibit interesting transition from insolubility to solubility in most common organic solvents. Taking advantage of its solubility, freestanding films and flexible and transparent UV resistant PDMS films based on CMPs can be easily fabricated, which will greatly improve their processability.



Altering Silk Film Surface Properties through Lotus-Like Mechanisms

2018-02-21T02:37:18.1395-05:00

The nonwetting and self-cleaning properties of the lotus depend on microscale and nanoscale roughness provided in part by a covering of epicuticular waxes that crystalize on the surface of its leaves. Wax deposition is driven by the evaporation of water, which carries waxes to the surface as it moves through the epidermis and cuticle. If the wax layer is damaged, repair occurs through the same mechanism. The experiments described herein have exploited this principle to establish a completely biologically derived system based on silk and lotus epicuticular wax, showing that it is possible to coat silk surfaces with waxes and thereby change their wetting characteristics and tensile properties. The robustness of the material is also documented by crystal regrowth after damage to the wax layer through abrasion (scratching and rubbing), resistance to water-jetting, and UV exposure. To further characterize this system, the diffusion of natural and synthetic waxes through two types of silk films, Bombyx mori fibroin and engineered spider silk are studied, showing that the extent of wax diffusion through silk membranes depends upon wax type and protein structure, which remains unchanged through the process. Making use of the simple passive phenomenon of advection, these studies represent a method of low-energy fabrication of completely biological, lotus-inspired membranes with tunable surfaces. A completely biologically based, lotus-inspired system for modifying silk film surfaces is presented. The advection of water through films is used to coat silk film surfaces with wax to change their wetting characteristics. Tensile properties are altered, while the protein structure remains the same. The wax coating is easily restored after damage and the films perform well as a biopolymer material.



Antiplasticizing Behaviors of Glucarate and Lignin Bio-Based Derivatives on the Properties of Gel-Spun Poly(Vinyl Alcohol) Fibers

2018-02-21T02:32:23.534904-05:00

Petrol and biochemical plasticizers are added to poly(vinyl alcohol) (PVA) to improve its processability while tuning its moisture sensitivity. But those additives often reduce the mechanical performance of PVA products. In this study, the antiplasticization and properties of PVA containing additives from biorenewable sources are studied. PVA fibers are gel-spun having up to 3 wt% glucarate salts and 30% lignin. Glucarate lowers the gel melting temperature of PVA and increases fiber draw ratio. Further, glucarate enhances the mechanical performance of PVA beyond that of neat fibers. Interestingly, the combination of lignin and glucarate causes phase separation among fiber—a PVA/glucarate phase as the fiber core and lignin/PVA phase as the fiber shell. Neat PVA partially dissolves in 85 °C water; whereas, fibers containing glucarate and/or lignin resist dissolution. Thus, the combination of glucarate and lignin can induce high strength and moisture resistance, which are desirable industrial fiber properties. Lignin and ammonium glucarate are poly(vinyl alcohol) (PVA) antiplasticizers. Additives give stiff PVA fibers due to intermolecular hydrogen bonding and PVA crystallization. Glucarate crystallizes with PVA in a new form.



3D Printing/Interfacial Polymerization Coupling for the Fabrication of Conductive Hydrogel

2018-02-19T09:51:01.741482-05:00

In this study, 3D printing is coupled with interfacial polymerization to obtain electroactive hydrogels with complex and defined geometry. Conductive hydrogels are created through a two-step procedure: first a digital light processing 3D printing system is used to fabricate poly(ethylene glycol)diacrylate 3D structure and then pyrrole is oxidized to polypyrrole (PPY), exploiting an interfacial polymerization mechanism through which PPY can be formed in the poly(ethylene glycol) matrix, thus creating a conductive phase. 3D printing is coupled with interfacial polymerization to obtain electroactive hydrogels with complex and defined geometry. Conductive hydrogels are created through a two-step procedure: first a digital light processing 3D printing system is used to fabricate 3D structures and then pyrrole is oxidized to polypyrrole, exploiting an interfacial polymerization mechanism, thus creating a conductive phase directly in 3D-printed structure.



Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior

2018-02-19T09:46:05.557445-05:00

Biobased and open cell polyurethane (PU) foams are produced from a synthesized sorbitol-based polyester polyol. Different formulations are developed with various blowing agent systems (chemical vs physical blowing). Synthetized foams are fully characterized and compared. The cell morphology is carefully investigated by tomography and scanning electron microscopy. The chemical nature of the primary compounds, foaming kinetics, density, thermal behavior, and conductivity are fully studied, with also the main transition materials temperatures. It is shown that blowing agents especially impact the foaming kinetics. In the case of chemically blowing foams, higher foaming rate and temperatures are obtained. The mechanical behavior is particularly analyzed using quasi-static compression tests, according two main axes compared to the rise direction. A direct relationship is observed between the formulation, foam structure, foam morphology, and corresponding mechanical properties. Results clearly highlight unexpected properties of biobased PU foams with unveil anisotropic mechanical properties. Novel biobased polyurethane foams are elaborated from a synthetized sorbitol-based polyester polyol. The obtained foams' kinetic and mechanical properties are thoroughly investigated. A direct relationship between the foams' elaboration components and the mechanical properties is observed. Unexpected results are obtained, such as unveil anisotropic mechanical properties for these biobased foams.



Adaptive Polymeric Coatings with Self-Reporting and Self-Healing Dual Functions from Porous Core–Shell Nanostructures

2018-02-07T02:16:53.049826-05:00

In biological system, early detection and treatment at the same moment is highly required. For synthetic materials, it is demanding to develop materials that possess self-reporting of early damage and self-healing simultaneously. This dual function is achieved in this work by introducing an intelligent pH-responsive coatings based on poly(divinylbenzene)-graft-poly(divinylbenzene-co-methacrylic acid) (PDVB-graft-P(DVB-co-AA)) core–shell microspheres as smart components of the polymer coatings for corrosion protection. The key component, synthesized PDVB-graft-P(DVB-co-AA) core–shell microspheres are porous and pH responsive. The porosity allows for encapsulation of the corrosion inhibitor of benzotriazole and the fluorescent probe, coumarin. Both loading capacities can be up to about 15 wt%. The polymeric coatings doped with the synthesized microspheres can adapt immediately to the varied variation in pH value from the electrochemical corrosion reaction and release active molecules on demand onto the damaged cracks of the coatings on metal surfaces. It leads simultaneously to the dual functions of self-healing and self-reporting. The corrosion area can be self-reported in 6 h, while the substrate can be protected at least for 1 month in 3.5 wt% NaCl solution. These pH-responsive materials with self-reporting and self-healing dual functions are highly expected to have a bright future due to their smart, long-lasting, recyclable, and multifunctional properties. Adaptive polymer coatings on metals can address scientific challenges, such as corrosion detection and self-healing capability to increase materials durability on metal surfaces. Herein, adaptive polymer coatings on metal surfaces that are capable of self-reporting and self-healing dual functions for metal anticorrosion applications are reported.



Single Solvent-Based Film Casting Method for the Production of Porous Polymer Films

2018-02-07T02:10:52.780048-05:00

A single solvent-based film casting process for fabricating porous polymer films is developed in this study. The porous film is produced by mixing concentrated polylactic acid (PLA)/chloroform solution (20 wt%) and fresh chloroform solvent is followed by film casting. The average pore sizes of the films produced are seen to increase from 2.1 (±0.1) µm to 6.4 (±0.2) µm with increasing ratio of concentrated PLA solution and fresh solvent from 1:2 to 1:4. Functional groups of PLA after casting into porous film are confirmed via Fourier transform infrared spectroscopy analysis. Cytocompatibility studies (via Alamar Blue assessment) utilizing MG-63 cells on the porous PLA films reveal an increase in cell metabolic activity up to 8 d postseeding. In addition, these direct cell culture studies show that the porous membranes support cell adhesion and growth not only on the surface but also through the porous structures of the membrane, highlighting the suitability of these porous films in tissue engineering applications. A simple, straightforward, and quick method is demonstrated for preparing porous polymer films using a single solvent-based film casting process. PLA porous film is found to be cytocompatible and can be used as a porous coating on bioresorbable phosphate-based glass fibers to provide a 3D integrity to produce scaffold constructs.



Thermoresponsive Microspheres as Smart Pore Plugs: Self-Venting Clothing Membranes for Smart Outdoor Textiles

2018-02-07T02:05:53.89156-05:00

Rapidly changing temperature and precipitation conditions are challenging for clothing textiles when required to keep us warm under harsh weather. A smart functional outdoor membrane based on thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microspheres embedded into a polyurethane matrix is developed. Selective dissolution of two-particle composite precursors affords porous membranes with PNIPAM microspheres located within the pore walls. Adjusting the mean size of the thermoresponsive microplug permits us to switch membrane breathability depending on outdoor temperature. In cold conditions, the textile fabric closes off pores and reduces heat loss, as to keep a person warmer. Under hot conditions, the PNIPAM microplugs open up, and self-vent the jacket, allowing for high breathability and heat transfer. The resulting smart membranes are tested according to international standards. The principle of phase separation based microplug positioning within pores, and selective opening and closing of pores may enable other smart applications in material sciences, biology, and other consumer products. Rapidly changing weather conditions are challenging for clothing when required to keep us warm. A smart functional outdoor membrane based on thermoresponsive PNIPAM microspheres embedded into a polyurethane matrix is developed. In cold conditions, the membrane closes pores and reduces heat loss. Under hot conditions, the pores open up allowing for high breathability and heat transfer.



Thermoplastic Polyurethane Elastomers with Aliphatic Hard Segments Based on Plant-Oil-Derived Long-Chain Diisocyanates

2018-02-05T02:21:04.787441-05:00

Novel plant-oil-derived long-chain (C19 and C23) α,ω-diisocyanates, optionally in combination with the corresponding long-chain diols, provide entirely aliphatic hard segments in segmented thermoplastic polyurethane elastomers (TPUs), with carbohydrate-based poly(trimethylene glycol) soft segments. Compared to materials based on a mid-chain monomer analog, phase separation is higher due to an increased flexibility of the aliphatic segments. Although melting points are slightly lower than for HDPE, the long-chain TPU's solid-state structure is still dominated by hydrogen-bonding. Novel plant-oil-based long-chain α,ω-diisocyanates together with sugar-based polyether soft segments form thermoplastic polyurethane elastomers with a distinct phase separation.



Thermally Resistive Electrospun Composite Membranes for Low-Grade Thermal Energy Harvesting

2018-01-31T02:50:55.852703-05:00

In this work, thermally insulating composite mats of poly(vinylidene fluoride) (PVDF) and polyacrylonitrile (PAN) blends are used as the separator membranes. The membranes improve the thermal-to-electrical energy conversion efficiency of a thermally driven electrochemical cell (i.e., thermocell) up to 95%. The justification of the improved performance is an intricate relationship between the porosity, electrolyte uptake, electrolyte uptake rate of the electrospun fibrous mat, and the actual temperature gradient at the electrode surface. When the porosity is too high (87%) in PAN membranes, the electrolyte uptake and electrolyte uptake rate are significantly high as 950% and 0.53 µL s−1, respectively. In such a case, the convective heat flow within the cell is high and the power density is limited to 32.7 mW m−2. When the porosity is lesser (up to 81%) in PVDF membranes, the electrolyte uptake and uptake rate are relatively low as 434% and 0.13 µL s−1, respectively. In this case, the convective flow shall be low, however, the maximum power density of 63.5 mW m−2 is obtained with PVDF/PAN composites as the aforementioned parameters are optimized. Furthermore, multilayered membrane structures are also investigated for which a bilayered architecture produces highest power density of 102.7 mW m−2. Thermally resistive fibrous membranes within thermocells minimize the heat transport across the cell elevating the power output as high as 102 mW m−2. The thermocells are electric generators which harvest electricity out of thermal gradient. The charm of converting the waste heat energy into clean and scalable electricity has attracted immense research attention toward thermocells.



A Comparison of Electric-Field-Driven and Pressure-Driven Fiber Generation Methods for Drug Delivery

2018-01-31T02:50:27.25803-05:00

Polymeric fibers are prepared by using electric field driven fiber production technology—electrospinning and pressure driven fiber production technology—pressurized gyration. Fibers of four different polymers: polyvinylidene fluoride (PVDF), poly(methyl methacrylate (PMMA), poly(N-isopropylacrylamide), and polyvinylpyridine (PVP), are spun by both techniques and differences are analyzed for their suitability as drug carriers. The diameters of electrospun fibers are larger in some cases (PVDF and PMMA), producing fibers with lower surface area. Pressurized gyration allows for a higher rate of fiber production. Additionally, drug-loaded PVP fibers are prepared by using two poorly water-soluble drugs (Amphotericin B and Itraconazole). In vitro dissolution studies show differences in release rate between the two types of fibers. Drug-loaded gyrospun fibers release the drugs faster within 15 min compared to the drug-loaded electrospun fibers. The findings suggest pressurized gyration is a promising and scalable approach to rapid fiber production for drug delivery when compared to electrospinning. Optimized multiple polymer solutions are spun to make fibers, by both electrospinning and pressurized gyration. Electron microscopy is used to analyze morphology. Polyvinylpyridine fibers are loaded with poorly water-soluble drugs and undergo dissolution testing. Comparisons in drug release capability of the fibers spun by the two techniques are performed. This is the first time these two vital fiber manufacturing processes are compared.



Characterization and Finite Element Analysis of the Tensile Behavior of Electrospun Polymer Single Fibers

2018-01-31T02:49:47.035207-05:00

In this paper, polymer single fibers are prepared by electro-spinning technology with different solvent rations, and the micromechanics properties are investigated together with the finite element analysis. It is found that the tensile stress–strain curves of single fibers can be attributed to two kinds of trends, which are independent of the solvent ratios. A possible arrangement model of polymer chains within the electrospun fibers is proposed according to the tensile stress–strain curves and the mechanics theories. The effect of polymer chains arrangement on the mechanical properties of the fibers is explored by the finite element analysis. This research shows a practical reference to predict the relationship between orientation degree of polymer chains and mechanical properties within the fibers. Two kinds of typical polymer single fiber tensile behavior are discovered. The arrangement model of polymer chains in the single fiber is given. The three-stage fracture mechanism of polymer single fibers is explored.



The Tunable Porous Structure of Gelatin–Bioglass Nanocomposite Scaffolds for Bone Tissue Engineering Applications: Physicochemical, Mechanical, and In Vitro Properties

2018-01-25T05:58:48.585713-05:00

Unidirectional freeze-casting method is used to fabricate gelatin–bioglass nanoparticles (BGNPs) scaffolds. Transmission electron microscopy (TEM) images show that sol–gel prepared BGNPs are distributed throughout the scaffold with diameters of less than 10 nm. Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetric are used to evaluate the physicochemical properties of BGNPs. Scanning electron microscopy (SEM) micrographs present an oriented porous structure and a homogeneous distribution of BGNPs in the gelatin matrix. The lamellar-type structure indicates an improvement of mechanical strength and absorption capacity of the scaffolds. Increasing the concentration of BGNPs from 0 to 50 wt% have no noticeable effect on pore orientation, but decreases porosity and pore size distribution. Increase in BGNPs content improves the compressive strength. The absorption and biodegradation rate reduces with augmentation in BGNPs concentration. Bioactivity is evaluated through apatite formation after immersion of the nanocomposites in simulated body fluid and is verified by SEM–energy-dispersive X-ray spectroscopy (EDS), an element map analysis, X-ray powder diffractometer, and FTIR spectrum. SEM images and methyl thiazolyl tetrazolium assay confirm the biocompatibility of scaffolds and the supportive behavior of nanocomposites in cellular spreading. The results show that gelatin–(30 wt%)bioglass nanocomposites have incipient physicochemical and biological properties. Gelatin–bioglass scaffolds with unidirectional pores are obtained by freeze-casting technique. Therefore, bioactive–glass nanoparticles are synthesized by the sol–gel method and induce bioactive behavior to the constructs. Improvement of compression strength is assessed by lamellar-type microstructure. Betterment of mechanical stability and bioactivity are provided by increasing bioglass content. Cellular spreading is ameliorated by the addition of bioglass to pure gelatin.



Fabrication of 3D Microfluidic Channels and In-Channel Features Using 3D Printed, Water-Soluble Sacrificial Mold

2018-01-23T08:26:02.126795-05:00

Recent advent of additive manufacturing potentiates the fabrication of microchannels, albeit with limitations in resolution of printed structures, freedom of geometry, and choice of printable materials. Herein, a method is developed by sacrificial molding to fabricate microchannels in various polymer matrices and geometries. This method allows for rapid fabrication of 3D microchannels and channels harboring intricate in-channel features. The method uses commercially available fused deposition modeling 3D printer and filament made of polyvinyl alcohol (PVA). Mechanically stable molds are fabricated for 3D microchannels that can be completely removed in water. Importantly, the PVA mold is stable and resilient in hydrogels despite being hygroscopic. Perfusion channels are fabricated in biocompatible substrates such as gelatin and poly(ethylene glycol) diacrylate. Fabrication of the network of 3D multilayer microchannels is demonstrated by preassembling sacrificial molds from modular pieces of molds. Intricate staggered-herringbones grooves (SHGs) are also fabricated within microchannels to produce micromixers. The versatility and resilience of the method developed here is advantageous for biological and chemical applications that require 3D configurations of microchannels in various matrices, which would not be compatible with fabrication by direct 3D printing and softlithography. Digital fabrication confers wide freedom of design and provides a rapid route to prototype intended structures. Microchannels with intricate patterns are fabricated by sacrificial molding of water-soluble mold consisting of polyvinyl alcohol patterned with a fused deposition modeling 3D printer. This method allows for fabrication of complex 3D microchannels in seven polymer matrices including biocompatible hydrogels.



Morphology Development via Static Crosslinking of (Polylactic Acid/Acrylic Rubber) as an Immiscible Polymer Blend

2018-01-22T03:27:42.649725-05:00

The interrelation between crosslinking and morphology is investigated for an immiscible blend of polylactic acid (PLA) and acrylic rubber (ACM). The blends are prepared by solution mixing and static crosslinking is used to avoid the simultaneous effect of the flow field that occurs in dynamic vulcanization. It is carried out at different temperatures, times, and curing agent contents. Scanning force microscopy (SFM) and polarized optical microscopy are used to determine the morphology of the blends. The chemical interactions and viscoelastic properties of the blends after crosslinking are also studied using infrared spectroscopy and rheological tests, respectively. Before crosslinking, SFM shows matrix-droplet morphology for the samples that it is retained after that for the blend with 30 wt% ACM; however, it is changed to cocontinuous one in the blend with 50 wt% ACM. Partially, grafting of PLA on the crosslinked ACM is confirmed by Fourier transform infrared spectroscopy. The rheological results show that the incorporation of ACM to the PLA slows down the chain relaxation and vulcanization intensifies this effect. A model is proposed to explain the morphology evolution during static crosslinking of an immiscible blend. Static crosslinking of polylactic acid (PLA)/acrylic rubber (ACM) as an immiscible polymer blend is studied. Before crosslinking, a matrix-droplet morphology is observed for the samples that after crosslinking is changed to a cocontinuous one in the blend with 50 wt% ACM. It is explained by formation of a self-generated elastic force. In addition, a partially grafting of PLA chains on the ACM is detected.



Controllable Cross-Linking Anion Exchange Membranes with Excellent Mechanical and Thermal Properties

2018-01-19T05:31:49.473995-05:00

A new monomer called 2,2′-(4,4′-oxydiphenol-4,4′-diyl)bis(2-methyl-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoisoindol-2-ium) iodide (d3) is synthesized possessing both cross-linker and functional groups. The membranes are formed by copolymerizing d3 with norbornene and (3aR,4S,7R,7aS)-2-methyl-2-(3-(trimethylammonio)propyl)-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoisoindol-2-ium iodide (a3) at varying ratios. The water uptake is 41.35% at 60 °C, and ion exchange capacity is 2.35 mequiv g−1 for a mole ratio of a3, norbornene, and d3 (1:6:3). The conductivity is 12, 37, and 40 mS cm−1 when d3 is decreased. Meanwhile, the conductivity increases quickly with increasing the temperature. Furthermore, the mechanical properties and thermal properties are improved, attributed to the increased cross-linker. The membrane has a tensile strength of 41.3 MPa and the elongation at break of 38.0 %, and the 5 wt% loss temperature for membrane is ≈159 °C. The H2/O2 single fuel cells with this membrane show a maximum power density of 124 mW cm−2 at 50 °C. The cross-linked membranes demonstrate high-dimensional stability in alkaline solution. A kind of polymers for anion exchange membranes (AEMs) with different compositions is synthesized. These AEMs show good mechanical strength. Meanwhile, ion exchange capacity, conductivity, water uptake, swelling and thermal properties are all good enough for practical applications such as fuel cells arising from the high cross-linkers of the modified system.



Nanostructured Biopolymer/Few-Layer Graphene Freestanding Films with Enhanced Mechanical and Electrical Properties

2018-01-17T05:21:18.861548-05:00

In the present work, novel freestanding multilayered films based on chitosan (CHI), alginate (ALG), and functionalized few-layer graphene are developed through layer-by-layer assembly. First, functionalized few-layer graphene aqueous suspensions are prepared from graphite by a stabilizer-assisted liquid phase exfoliation process, using a pyrene derivative as stabilizer. Afterward, the films are produced and their physical, morphological, thermal, and mechanical properties are evaluated. Furthermore, their degradation and swelling profiles, as well as their biological behavior, are assessed. The incorporation of functionalized few-layer graphene results in films with a nanolayered structure, lower roughness than the control CHI/ALG films, and hydrophilic behavior. The mechanical characterization reveals an increase of the Young's modulus, ultimate tensile strength, and elongation at break due to the incorporation of the graphene derivative. A decrease in the electrical resistivity of the multilayered films is also observed. The biological assays reveal improved cytocompatibility toward L929 cells when functionalized few-layer graphene is incorporated in the CHI/ALG matrix. Therefore, these new graphene-reinforced multilayered films exhibit interesting properties and great potential for biomedical applications, particularly in wound healing and cardiac and bone tissue engineering. Novel freestanding multilayered films based on chitosan, alginate, and functionalized few-layer graphene are developed through layer-by-layer assembly. Graphene aqueous suspensions are prepared from graphite by stabilizer-assisted liquid phase exfoliation. An enhancement of the mechanical properties, a decrease in the electrical resistivity, and improved cytocompatibility due to graphene incorporation are found. These new films exhibit great potential for distinct biomedical applications.



Novel Making of Bacterial Cellulose Blended Polymeric Fiber Bandages

2018-01-17T02:02:00.835558-05:00

Bacterial cellulose (BC) is a very promising biological material. However, at present its utilization is limited by difficulties in shape forming it. In this Communication, it is shown how this can be overcome by blending it with poly(methylmethacrylate) (PMMA) polymer. BC:PMMA fibers are produced by pressurized gyration of blended BC:PMMA solutions. Subsequently, BC:PMMA bandage-like scaffolds are generated with different blends. The products are investigated to determine their morphological and chemical features. Cell culture and proliferation tests are performed to obtain information on biocompatibility of the scaffolds. Bacterial cellulose (BC) is used with poly(methylmethacrylate) (PMMA) polymer and pressurized gyration to successfully mass produce bandage-like scaffolds. Fibers in the range of 690 nm to 25 µm are formed at different BC:PMMA concentrations. 5 wt% BC containing scaffolds show best cell attachment and proliferation.



A Tough Composite Hydrogel can Controllably Deliver Hydrophobic Drugs under Ultrasound

2018-01-16T07:41:17.771882-05:00

Hydrogels are promising materials for biomedical uses, but they usually lack the ability to encapsulate hydrophobic drugs with proper drug-releasing stimulating method. Here a composite hydrogel with ultrasound controllable hydrophobic drug release behavior is reported, hydrophobic drug-loaded silicone oil were dispersed in poly(vinyl alcohol) hydrogel as microdroplets, which not only act as drug reservoirs but also notably enhance the toughness of the hydrogel. Ultrasound is used to trigger the hydrophobic drug release from the hydrogel, high on–off drug release ratios are obtained in the surveyed samples. Mechanism of ultrasound controlled drug release is studied, and the results indicate the mechanical effect is the main reason. The facile and general method of encapsulation and controlled release of hydrophobic drugs from hydrogels proposed in this contribution can be readily extended to other hydrogel system and can potentially broaden the application scope of hydrogel drug delivery. A hydrophobic drug loaded composite hydrogel is prepared by mixing hydrophobic drug loaded silicone oil with poly(vinyl alcohol) aqueous solution before conducting the freezing/thawing treatment. Ultrasound is successfully applied to control the release of loaded hydrophobic drugs, experimental results indicate that the mechanical effect of ultrasound is the main reason.



Biaxial Orientation of Poly(ethylene 2,5-furandicarboxylate): An Explorative Study

2018-01-16T07:41:01.413922-05:00

The biaxial orientation behavior of poly(ethylene 2,5-furandicarboxylate) (PEF) is studied in comparison to poly(ethylene terephthalate) (PET). PEF is a polyester that can be produced through similar steps as PET but using 100% biobased 2,5-furandicarboxylic acid instead of terephthalic acid. This work highlights the stress–strain behavior of PEF during biaxial orientation at various temperatures. Strain hardening and strain-induced crystallization in the oriented PEF samples generally appeared at higher stretch ratios for PEF than for PET at comparable molecular weight, while somewhat lower degrees of crystallinity are reached in PEF. Shrinkage in oriented PEF is found to be on par with PET in the region of the glass transition. Higher modulus and improved barrier properties, compared to PET, are found in the oriented materials when sufficiently high stretch ratios are applied in biaxial orientation. Biaxial stretching of poly(ethylene 2,5-furandicarboxylate) (PEF) and its influence on thermal, mechanical, and barrier properties is explored in comparison to poly(ethylene terephthalate). Characteristics of the stretching behavior are forces being off-set by PEF's higher T g and strain hardening occurring at higher stretch ratios.



A Novel Approach to Design Nanoporous Polyethylene/Polyester Composite Fabric via TIPS for Human Body Cooling

2018-01-15T10:53:59.771684-05:00

In this study, in order to obtain a wearable infrared-transparent material based on nanoporous polyethylene, a newly ultrahigh molecular weight polyethylene (UHMWPE)/polyester composite fabric with nanoporous structure is developed via thermally induced phase separation (TIPS) method. A polyester mesh with loose warp/weft weaves is chosen as the intermediate to enhance the fabric mechanical strength and air permeability. Meanwhile, methoxy-poly(ethylene glycol)-aminoethyl/polydopamine particles (mPPDAPs) are used to improve the hydrophilicity of UHMWPE. The fabric is composited with mPPDAPs/UHMWPE/liquid paraffin mixture at high temperature. Then the nanoporous structure is formed via TIPS in UHMWPE phase in the composite fabric. This newly UHMWPE/polyester composite fabric possesses a unique connective nanoporous structure with the pore sizes distributed from 50 to 100 nm and it also has many disconnected honeycomb pores that are ≈1000 nm in diameter. These characteristics endow the composite fabric with excellent properties of wearability and optical properties, including sufficient moisture wicking rate, air permeability, and mechanical strength, high infrared-transparent and ultraviolet/visible-opaque properties. It is an effective, economical, and practical novel composite textile for human body cooling. The ultrahigh molecular weight polyethylene/polyester composite fabrics with nanoporous structure are developed via thermally induced phase separation method. A polyester mesh is used to enhance the composite fabric mechanical strength and air permeability. Methoxy-poly(ethylene glycol)-aminoethyl/polydopamine particles are used to improve the hydrophilicity of the composite fabric. It is an effective, economical, and practical textile with infrared-transparent visible/UV-opaque property and sufficient wearabilities.



Facile Fabrication of Mussel-Inspired Multifunctional Polymeric Membranes with Remarkable Anticoagulant, Antifouling, and Antibacterial Properties

2018-01-15T10:53:05.688345-05:00

Herein, a facile one-step surface modification technique of coating functional biopolymer conjugated mussel-inspired catechol (CA) onto substrate is applied to confer polyethersulfone (PES) membranes with remarkable blood compatibility, antifouling property, and antibacterial property, respectively. CA conjugated poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS), poly(sulfobetaine methacrylate) (PSBMA), and poly(methacryloxyethyltrimethyl ammonium chloride) are synthesized via free radical polymerization in the presence of CA, and simultaneously coated onto PES membrane surface. The surface chemical compositions, surface zeta-potential convince the successful preparation of the modified PES membranes. PAMPS-coated membrane exhibits excellent blood compatibility, especially anticoagulation property; PSBMA-coated membrane displays excellent antifouling property and blood compatibility; meanwhile, PDMC-coated membrane shows robust bactericidal property. In general, this work demonstrates that the mussel-inspired surface modification protocol provides a facile and versitile method to confer the substrate with excellent blood compatibility, antifouling property, and antibacterial property, respectively, which has great potential for multibiomedical applications, such as blood purification, hemodialysis, and organ implantation. A facile one-step surface modification technique of coating functional biopolymer conjugated mussel-inspired catechol onto substrate is applied to confer polyethersulfone membranes with remarkable blood compatibility, antifouling property, and antibacterial property, respectively.



Aqueous Solution-Processable, Flexible Thin-Film Transistors Based on Crosslinked Chitosan Dielectric Thin Films

2018-01-15T10:52:32.980482-05:00

The hydrophilic character of chitosan (CS) limits its use as a gate dielectric material in thin-film transistors (TFTs) based on aqueous solution-processable semiconductor materials. In this study, this drawback is overcome through controlled crosslinking of CS and report, for the first time, its application to aqueous solution-processable TFTs. In comparison to natural CS thin films, crosslinked chitosan (Cr-CS) thin films are hydrophobic. The dielectric properties of Cr-CS thin films are explored through fabrication of metal–insulator–metal devices on a flexible substrate. Compared to natural CS, the Cr-CS dielectric thin films show enhanced environmental and water stabilities, with a high breakdown voltage (10 V) and low leakage current (0.02 nA). The compatibility of Cr-CS dielectric thin films with aqueous solution-processable semiconductors is demonstrated by growing ZnO nanorods via a hydrothermal method to fabricate flexible TFT devices. The ZnO nanorod-based TFTs show a high field-effect mobility (linear regime) of 10.48 cm2 V−1 s−1. Low temperature processing conditions (below 100 °C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e-waste problem. Crosslinked chitosan thin films are introduced as gate dielectric material for aqueous solution-processable, flexible thin film transistors. Low temperature processing conditions (below 100 °C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e-waste problem.



Mechanical Reinforcement of Low-Concentration Alginate Fibers by Microfluidic Embedding of Multiple Cores

2018-01-15T10:51:38.028269-05:00

This paper presents mechanically reinforced low-concentration alginate fibers by embedding inner cores of high-concentration alginate. 3D structures by stacking multiple polydimethylsiloxane (PDMS) layers allow the microfluidic formation and control of the isolated cores in the continuous flow. The alginate hydrogel fibers are simply spun, and the compartments, central core, surrounding cores, and outer shell layer are successfully verified. The results demonstrate the great potential for the development of complex fibrous materials, particularly for biological applications, which require specific morphology and composition of the fibers. Mechanical reinforcement of low-concentration alginate fiber by embedding multiple inner cores of high-concentration alginate is reported. 3D PDMS structure and flow control allow one-step formation of the complex and precise fiber morphology.



Water-Processable Multiwalled Nanotube: Phenol-Induced Reversible Oxidation Process and Ambipolar Charge Transport Property

2018-01-15T04:20:58.506893-05:00

Due to the fascinating electronic, thermal, and mechanical properties of single-walled carbon nanotubes (SWCNTs), extensive efforts have been devoted to the development of SWCNT-based materials. These materials' semiconducting properties and related applications, such as field-effect transistors (FETs), have been investigated by researchers for many years. However, despite the significant progress achieved, it remains challenging to separate semiconducting and metallic nanotubes from the mixtures of as-grown SWCNTs. In a few studies, composites of water-processable phenol formaldehyde resin/multiwalled carbon nanotubes (MWCNTs) have been found to exhibit a quasireversible oxidation process and to behave as semiconductors or field-effect transistors. This finding has rarely been reported for MWCNTs, and it differs greatly from findings regarding intrinsic semiconductive SWCNTs. Significantly, field-effect transistors fabricated with MWCNT composites as their semiconductor active layers have shown ambipolar charge transport characteristics. The results provide a high value-added application pathway for the application of polymer/MWCNTs as the FET materials for electronic devices that offer higher performance at a lower cost. A multiwalled carbon nanotube (MWCNT) suspension is doped with water-soluble sulfobutylated phenol formaldehyde resin (BSPF), for the first time. BSPF shows highly enhance dispersion stability and the BSPF-MWCNT composites display a reversible oxidation process. More significantly, the field-effect transistor devices using BSPF-MWCNTs film as an active layer exhibit both p-type and n-type field-effect characteristics.



Electrospun Antimicrobial PVDF-DTAB Nanofibrous Membrane for Air Filtration: Effect of DTAB on Structure, Morphology, Adhesion, and Antibacterial Properties

2018-01-15T04:20:33.450482-05:00

Antimicrobial polyvinylidene fluoride (PVDF) membrane modified by dodecyltrimethyl ammonium bromide (DTAB) has been electrospun using simple one-step technology, where the modifying agent DTAB is dissolved in spinning solution. X-ray photoelectron spectroscopy and electrokinetic analysis confirm reliably the presence of DTAB on the nanofibers surfaces; electrokinetic analysis shows the changes of zeta potential due to modification by DTAB. X-ray diffraction shows that electrospinning converts the part of α phase (≈40%) present in PVDF powder into β phase with all trans (TTT) zigzag chains conformation in PVDF electrospun membrane. Surface modification does not affect the phase composition of PVDF nanofibers, just only leads to lower crystallinity (smaller size of crystallites) in PVDF nanofibers. DTAB causes the curling of fibers and their aggregation, what completely changed the membrane structure. DTAB-modified membrane exhibits antibacterial properties against Staphylococcus aureus subsp. Aureus. Concentration of 0.5 wt% DTAB in spinning solution causes partial inhibition of bacterial growth only, while 1.0 wt% concentration leads to complete inhibition. Simple one-step synthesis is used for preparation of electrospun antimicrobial polyvinylidene fluoride membranes. Polyvinylidene fluoride is modified by antibacterial agent 1-dodecyltrimethyammonium bromide, which is dissolved directly in the spinning solution. The presence of antibacterial agent and the changes in polymer surface chemistry and structure are determined by electrokinetic measurement, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. All the modified membranes are antibacterially active.



Tough and Tear-Resistant Double-Network Hydrogels Based on a Facile Strategy: Micellar Polymerization Followed by Solution Polymerization

2018-01-09T05:55:49.297514-05:00

How to prepare a hydrogel with high strength and excellent tearing fracture energy is a problem faced by researchers. Here, tough and tear-resistant double-network hydrogels (Cx-SMy gels) are successfully prepared via a facile strategy: micellar polymerization followed by solution polymerization. The strength and fracture energy of these hydrogels are up to 13 MPa and 26500 J m−2, respectively, which are attributed to the synergy of quatra-crosslinking interactions inside the double-network. The quatra-crosslinking interactions include hydrophobic interaction, crystallization, electrostatic attraction, and hydrogen bonding. Moreover, it is confirmed that the facile strategy is a general way to prepare tough hydrogels by using electrolytic monomers and hydrophobic acrylates. How to prepare a hydrogel with high strength and excellent tearing fracture energy is a problem faced by researchers. Here, tough and tear-resistant double-network hydrogels (Cx-SMy gels) are successfully prepared via a facile strategy: micellar polymerization followed by solution polymerization. The strength and fracture energy of these hydrogels are up to 13 MPa and 26500 J m−2, respectively.



Macromol. Mater. Eng. 2/2018

2018-02-14T03:11:51.638624-05:00

Front Cover: Screw-assisted melt extrusion 3D printing has been developed for tissue engineering applications. The cover page image illustrates the in situ characterization of the polycaprolactone crystal structure evolution during the scaffold printing process via time-resolved synchrotron X-ray diffraction. This is reported by Fengyuan Liu, Cian Vyas, Gowsihan Poologasundarampillai, Ian Pape, Sri Hinduja, Wajira Mirihanage, and Paulo Bartolo in article number 1700494.



Macromol. Mater. Eng. 2/2018

2018-02-14T03:11:49.706808-05:00

Back Cover: Interconnected fiber arrays are incorporated into thin membranes using near-field electrospinning. This patterning approach may find uses in creating mechanically robust thin membranes, tailoring structural and functional properties for tissue engineering scaffolds and beyond. This is reported by Rox Middleton, Xia Li, Jenny Shepherd, Zhaoying Li, Wenyu Wang, Serena M. Best, Ruth E. Cameron, and Yan Yan Shery Huang in article number 1700463.



Masthead: Macromol. Mater. Eng. 2/2018

2018-02-14T03:11:46.598857-05:00




Structural Evolution of PCL during Melt Extrusion 3D Printing

2017-12-27T04:23:14.401602-05:00

Screw-assisted material extrusion technique is developed for tissue engineering applications to produce scaffolds with well-defined multiscale microstructural features and tailorable mechanical properties. In this study, in situ time-resolved synchrotron diffraction is employed to probe extrusion-based 3D printing of polycaprolactone (PCL) filaments. Time-resolved X-ray diffraction measurements reveals the progress of overall crystalline structural evolution of PCL during 3D printing. Particularly, in situ experimental observations provide strong evidence for the development of strong directionality of PCL crystals during the extrusion driven process. Results also show the evidence for the realization of anisotropic structural features through the melt extrusion-based 3D printing, which is a key development toward mimicking the anisotropic properties and hierarchical structures of biological materials in nature, such as human tissues. In situ X-ray diffraction for melt extrusion-based additive biomanufacturing of polycaprolactone is reported, revealing the evolution of crystal anisotropy and an increasing crystal fraction during the printing process. The main crystal orientation is consistent with the material flow direction. The results are promising for applications in the field of bioengineering where the fabrication of parts with designed anisotropy is relevant.



Near-Field Electrospinning Patterning Polycaprolactone and Polycaprolactone/Collagen Interconnected Fiber Membrane

2017-12-27T04:22:50.097401-05:00

Solution-based near-field electrospinning is employed to construct polymeric network membranes, made of orderly arranged and interconnected fibers. The narrow tip-to-nozzle separation of the direct-writing process leads to solvent enriched fibers being deposited on the substrate, despite the use of a low boiling point solvent. This results in fibers with low cross-sectional aspect ratio (flattened appearance), but providing a unique opportunity to produce interconnected fiber junctions through in situ, localized solvent etching by subsequent fiber overlays. Orthogonal networks of polycaprolactone (PCL) fibres, or PCL/collagen composite fibres, are fabricated, and then characterized by microscopy and spectroscopy techniques. This study presents a direct approach to strengthen interfiber junctions, and further the feasibility to interweave and interconnect fibers of different properties, leading to networked membranes with potentially tailorable functions for tissue engineering applications and beyond. Orderly and interconnected fiber arrays are incorporated into thin membranes using near-field electrospinning. Orthogonal networks of polycaprolactone fiber membranes demonstrate superior mechanical properties arisen from the strong fiber junctions. Interconnecting polycaprolactone and polycaprolactone/collagen fibers are also demonstrated. This patterning approach may find uses in creating mechanically robust thin membrane, tailoring structural and functional properties for tissue engineering scaffolds and beyond.



Biological Degradation and Biostability of Nanocomposites Based on Polysulfone with Different Concentrations of Reduced Graphene Oxide

2017-12-21T03:06:04.734357-05:00

Increasing incorporation of rGO in the polysulfone polymer generates materials with improved chemical and mechanical stability and less prone to biodegradation at the end of the nanocomposite life cycle. The results of attenuated total reflection infrared (ATR-IR) and mechanical strength, after exposure to wastewater influent, show that the increasing concentrations of rGO into the polymer matrix reduce changes in the nanocomposite properties. The increasing incorporation of rGO also increases growth inhibition of the wastewater microbial population on the surface of nanocomposites. Highest biofilm inhibition and material stability are observed with nanocomposites containing 3 wt% rGO. These results suggest that reduction in the material biodegradation is linked to the inhibition of biofilm growth on the nanocomposite surface due to the antimicrobial properties of rGO. This study demonstrates, for the first time, that the amount of rGO incorporated in the nanocomposite impact the biodegradability and end of life of polysulfone nanocomposites. The study of the biodegradability and stability of rGO/PSU nanocomposites in the presence of diverse microorganisms shows that these materials can potentially be more persistent, robust, and resistant in the environment for applications requiring biostability over long periods of time.



Honeycomb Surface with Shape Memory Behavior Fabricated via Breath Figure Process

2017-12-04T03:46:28.47413-05:00

A bio-inspired honeycomb pattern that exhibits shape memory behavior is successfully fabricated via the breath figure process. By the surface modification along with a chemical crosslinking process to enhance the recoverability, this honeycomb-like structure with shape memory behavior is realized. The surface wettability is dependent on the surface topography controlled by the deformation of temporary shape (elliptical circle) and recovery of the permanent shape (round circle) at the microscopic scales without the need of micromolding or expensive lithography strategy. This approach opens a facile route to an efficient, inexpensive, and versatile method to prepare films with switchable wettability. A bio-inspired honeycomb pattern that exhibits shape memory behavior is successfully fabricated via the breath figure process. The surface wettability is dependent on the surface topography controlled by the deformation of temporary shape (elliptical circle) and recovery of the permanent shape (round circle) at the microscopic scales.



Chemical Vapor Deposition of Polymer Thin Films Using Cationic Initiation

2017-12-04T03:46:55.502507-05:00

Chemical vapor deposition (CVD) is an attractive technique for the fabrication of high-quality polymer thin films. The scheme used to initiate polymer chain growth is fundamental to controlling polymer thin film chemistry. A new initiation scheme for polymer CVD utilizing cationic initiation with a strong Lewis acid, TiCl4, in combination with a hydrogen donor, H2O, is presented. This coinitiation scheme results in polystyrene deposition rates of 139 nm min−1, relative to just 34 nm min−1 when TiCl4 is used alone. Characterization by Fourier transform infrared spectroscopy shows that the polymer structures of polystyrene films prepared by conventional solution-based techniques and cationic CVD are similar. Synthesis of cross-linked polymer thin films is also demonstrated by depositing poly(divinylbenzene) and showing its insolubility in a range of solvents. The practical utility of these poly(divinylbenzene) films as corrosion resistant coatings is demonstrated. In 1 n HCl, 200 nm thick films on stainless steel increase the polarization resistance by a factor of 44 relative to bare, untreated stainless steel. A cationic initiation scheme for polymer chemical vapor deposition (CVD) is demonstrated. Combining a strong Lewis acid (TiCl4) with H2O results in deposition rates of 139 nm min−1 for polystyrene—a substantial enhancement over other CVD approaches. The ability to cross link polymer thin films for solvent resistance is also demonstrated, and corrosion resistance of the coatings is evaluated.



Facile Fabrication of Electrohydrodynamic Micro-/Nanostructures with High Aspect Ratio of a Conducting Polymer for Large-Scale Superhydrophilic/Superhydrophobic Surfaces

2017-11-29T02:50:49.476477-05:00

This communication describes a straightforward, cost-effective, and contactless lithography technique, electrohydrodynamic patterning, for fabricating the high-aspect-ratio micro-/nanostructures of the conducting polymer (CP) films directly on a conductive substrate with high integrity and throughput. Meanwhile, the superhydrophilicity/superhydrophobicity of the final CP films can be obtained by modulating the ON/OFF-state of the circuit of the assembly in the structure formation process. The final patterned CP films are hydrophilic/superhydrophilic when the circuit of the assembly is ON-state in the structure formation process, while they are hydrophobic/superhydrophobic when the circuit of the assembly is OFF-state. The high-aspect-ratio micro-/nanostructures of the CP films with the superhydrophilic/superhydrophobic surface are important in both fundamental research and practical applications such as photovoltaics, sensors, supercapacitors, actuators, low friction surfaces, and water harvesting. The high-aspect-ratio micro-/nanostructures of the conducting polymer films can be fabricated directly on a conductive substrate with high integrity and throughput via electrohydrodynamic patterning and, meanwhile, the superhydrophilicity/superhydrophobicity of the final patterned conducting polymer films can be achieved by variating the upper/lower electrode of the capacitor-like experimental installation and thus modulating the ON/OFF-state of the circuit in the structure formation process.



Enhanced Thermoelectric Performance of PEDOT:PSS Films by Sequential Post-Treatment with Formamide

2017-11-22T03:51:11.158144-05:00

This paper reports a series of sequential post-treatments using a polar solvent formamide to enhance the thermoelectric performance of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) anions (PEDOT:PSS). The electrical conductivity of PEDOT:PSS films significantly increases from 0.33 S cm−1 for the pristine film to ≈2929 S cm−1 for the treated film and meanwhile the Seebeck coefficient maintains as high as 17.4 µV K−1, resulting in a power factor of 88.7 µW m−1 K−2. Formamide is a polar solvent with a high boiling point of 210 °C and high dielectric constant of 109, and PSS has a good solubility in it. Post-treatment with formamide causes not only the phase segregation of PEDOT and PSS but also the removal of insulating PSS, therefore leading to the reorientation of PEDOT chains and enhancement in mobility without altering the doping level considerably. The cross-plane thermal conductivity also reduces from 0.54 to 0.19 W m−1 K−1 after the post-treatment, leading to a figure of merit (ZT) value of 0.04 at room temperature. The sequential post-treatment with formamide increases the electrical conductivity of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) film to ≈2929 S cm−1 without deteriorating the Seebeck coefficient. Hence, the power factor of the film increases by four orders of magnitude, reaching up to 88.7 µW m−1 K−2. The treatment also reduces the cross-plane thermal conductivity of the film from 0.54 to 0.19 W m−1 K−1.



Macromol. Mater. Eng. 2/2018

2018-02-14T03:11:50.154422-05:00

Frontispiece: Poly(ε-caprolactone) matrices reinforced with well distributed nanofibers of a polyglycolide rich copolymer have been prepared by molding multilayered assemblies of alternate PCL films and electrospun scaffolds. Efficient encapsulation of chlorhexidine and short and long term tunable release were achieved. This is reported by Yolanda Márquez, Lourdes Franco, Pau Turon, Luís J. del Valle and Jordi Puiggalí in article number 1700401.



Tunable Drug Loading and Reinforcement of Polycaprolactone Films by Means of Electrospun Nanofibers of Glycolide Segmented Copolymers

2017-12-27T04:21:58.961368-05:00

Electrospinning of a segmented copolymer having polyglycolide hard segments is successfully performed from 1,1,1,3,3,3-hexafluoroisopropanol solutions. During the process, a bactericidal agent, i.e., chlorhexidine (CHX), is effectively loaded, which results in nanofibers with a smaller diameter because of the change in solution conductivity. New fabrics based on molding of alternate layers of poly(ε-caprolactone) (PCL) films and the electrospun scaffolds of the segmented copolymer are prepared and characterized. The thermal molding process renders a PCL matrix homogeneously reinforced with nanofibers that compensate for the loss of mechanical properties caused by incorporation of CHX. Release of CHX is evaluated in different media. Results vary depending on the layer where the drug is incorporated. Thus, systems with an immediate bacteriostatic effect, as well as systems with a potential long term antimicrobial effect, are obtained. Growth inhibition and adhesion assays demonstrate the fast bactericidal effect of samples with CHX loaded in its outer layers. Poly(ε-caprolactone) (PCL) matrices reinforced with well distributed nanofibers of a polyglycolide rich copolymer are easily prepared by molding multilayered assemblies of alternate PCL films and electrospun scaffolds. Drugs are loaded in specific layers, giving rise to a tunable release. Short and long term bactericidal effects are interestingly derived as demonstrated by growth inhibition and cell adhesion experiments.



Macromol. Mater. Eng. 2/2018

2018-02-14T03:11:49.751296-05:00

Frontispiece: DOPO-containing polyesters as new flame retardants for biobased polyesters are reported. Their fire behavior is evaluated by cone calorimetry. The cover image shows the residues of five different polyesters with varied phosphorus content after forced-flaming combustion (left) and the chemical structure of selected species found in the gas phase. This is reported by Madeleine Schwarzer, Andreas Korwitz, Hartmut Komber, Liane Häußler, Bettina Dittrich, Bernhard Schartel, and Doris Pospiech in article number 1700512.



Phosphorus-Containing Polymer Flame Retardants for Aliphatic Polyesters

2017-12-27T04:23:38.820382-05:00

Polyesters with 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide-containing comonomers are synthesized aiming to improve the flame retardancy of aliphatic polyesters such as poly(butylene succinate) and poly(butylene sebacate). The influence of the chemical structure on the thermal decomposition and pyrolysis is examined using a combination of thermogravimetric analysis (TGA), TGA-Fourier transform infrared (FTIR) spectroscopy, pyrolysis-gas chromatography/mass spectrometry, and microscale combustion flow calorimetry. Thermal decomposition pathways are derived and used to select suitable candidates as flame retardants for PBS. The fire behavior of the selected polymers is evaluated by forced-flaming combustion in a cone calorimeter. The materials show two modes of action for flame retardancy: strong flame inhibition due to the release of a variety of molecules combined with charring in the solid state. Phosphorus-containing polyesters with itaconyl units are synthesized to improve the flame retardancy of aliphatic polyesters like poly(butylene succinate) (PBS). The thermal decomposition processes are analyzed and the fire behavior is evaluated in a cone calorimeter. 9,10-Dihydro-9-oxy-10-phosphaphenanthrene-10-oxide-substituted polyesters show reductions in effective heat of combustion, total heat evolved, and peak of heat release rate by more than 50% compared to PBS.



Influence of Topology of Highly Porous Methacrylate Polymers on their Mechanical Properties

2017-11-22T03:58:35.567358-05:00

Porous polymer monoliths are prepared using glycidyl methacrylate and methyl methacrylate as monomers, in both cases crosslinked with ethylene glycol dimethacrylate. Up to 75% porous samples are produced using either emulsion templating or bulk polymerization with porogens. In the case of emulsion templating, a cellular topology with cavities between 3.1 and 5.5 µm is observed for both monomers, while a cauliflower-like topology is formed in the case of bulk polymerization. The influence of topology features of monoliths on the mechanical properties is studied and for both polymers a dramatic influence, on both compressive moduli and compressive strength, is found. The mechanical parameters, namely elastic modulus and compressive strength are significantly higher for emulsion templated samples. Methacrylate based highly porous polymer monoliths are prepared using either emulsion templating or solution polymerization with included porogenic solvents. Comparison of compression properties reveals advantages of poly(high internal phase emulsion) monoliths prepared from emulsion precursors over solution polymerized analogs.



A Simple Strategy to Achieve Mussel-Inspired Highly Effective Antibacterial Coating

2017-11-29T02:51:13.071513-05:00

Although significant progress has been made in the preparation of mussel-inspired antibacterial coatings, continual challenges still remain in pursuing more facile and simpler fabrication methods to construct more robust and effective coatings. In this study, quaternized catechol (QCat), which is synthesized via a simple quaternization reaction from two commercially available materials, 2-chloro-3′,4′-dihydroxyacetophenone and N,N-dimethyldodecylamine, is used as a reactive antimicrobial agent to fabricate mussel-inspired antibacterial coatings. Specifically, QCat reacts with branched polyethyleneimine (PEI) in Tris-HCl solution through a cross-linking reaction between amino and catechol groups to form a homogeneous coating on various substrates via a simple co-deposition process. The formed PEI/QCat coating exhibits highly effective antimicrobial activity against both Staphylococcus aureus and Escherichia coli and good adhesion on glass, metal, and plastic substrates. Such a simple fabrication process makes it a potential candidate for industrial and medical applications. Quaternized catechol (QCat), which is synthesized via a simple quaternization reaction from two commercially available materials, 2-chloro-3′,4′-dihydroxyacetophenone and N,N-dimethyldodecylamine, is used as a reactive antimicrobial agent to fabricate mussel-inspired antibacterial coatings. The formed polyethyleneimine/QCat coating exhibits highly effective antimicrobial activity against both Staphylococcus aureus and Escherichia coli and good adhesion on glass, metal, and plastic substrates.



Ultralight and Low Thermal Conductivity Polyimide–Polyhedral Oligomeric Silsesquioxanes Aerogels

2017-12-04T03:48:53.780894-05:00

The research on rapid growing, organic, and ultralight cross-linking polyimide aerogels is receiving significant interest. In this work, poly(aminophenyl) silsesquioxanes (PAPSQ) are introduced as a cross-linker into the polymide (PI) aerogel. A comparative aerogel is prepared, using 1,3,5-triaminophenoxybenzene (TAB) as a cross-linker. The aerogels are characterized in terms of their micro- and nanostructures, density, shrinkage, thermal conductivity and insulation, and mechanical properties. It is found that the PI-PAPSQ aerogel have lower density, smaller shrinkage, lower thermal conductivity, higher thermal stability and insulation, and higher compression strength than the PI-TAB aerogel. The 1.1 wt% PI-PAPSQ shows the lowest aerogel density (0.010 g cm−3) and the 2.2 wt% PI-PAPSQ has a lower thermal conductivity (22.90 mW (m K)−1 than air. A model of the PI-TAB and PI-PAPSQ cross-linking networks are proposed to explain the excellent performance of the PI-PAPSQ aerogel. Polyimide aerogels cross-linked by multi-functional cyclic-ladder Polyhedral Oligomeric Silsesquioxane (POSS) have ultra-low density, ultra-high strength and superior insulation capacity. The difference in molecular scale is reflected on the macro scale so that PI-PAPSQ (Poly (aminophenyl) Silsesquioxanes) exhibits extremely superior performance. The prospects for the application of this ultra-light high-strength adiabatic organic aerogels are promising.



Preparation of Novel Fluorinated Copolyimide/Amine-Functionalized Sepia Eumelanin Nanocomposites with Enhanced Mechanical, Thermal, and UV-Shielding Properties

2017-12-04T03:42:16.176237-05:00

Novel fluorinated copolyimide/amine-modified sepia eumelanin (ASE) nanocomposites are successfully fabricated via covalent bonds. To achieve this, the polyimide (PI) is synthesized by random co-polycondensation. The effects of ASE on the structure and properties of the PI are investigated. A multilinked network is formed with ASE acting junctions in the nanocomposites. The mechanical properties of the PI are significantly improved by the addition of ASE, and the optimal tensile strength and elongation at break are 79.7 MPa and 85.42%, respectively. UV–vis transmittance, methylene blue (MB) photodegradation, and recyclability measurements confirm that the PI/ASE nanocomposites are transparent to visible light at low ASE loadings and show outstanding UV-shielding properties and lifetimes under intense UV irradiation owing to the synergistic absorption of UV light by the PI matrix and ASE. Furthermore, the PI/ASE nanocomposites have enhanced thermal properties with initial degradation temperatures above 500 °C. These properties endow the nanocomposites with great potential for UV-shielding in the conditions with high temperature and intense ultraviolet light. The polyimide/amine-functionalized sepia eumelanin (PI/ASE) nanocomposites with different content of ASE are successfully prepared via covalent bonds. The mechanical properties of PI are significantly enhanced with the addition of ASE, especially for toughness. Meanwhile, the synergistic UV absorption capacities of PI matrix and ASE endow the PI/ASE nanocomposites with the potential to serve as UV-shielding materials.



A Dual-Crosslinked Strategy to Construct Physical Hydrogels with High Strength, Toughness, Good Mechanical Recoverability, and Shape-Memory Ability

2017-12-04T03:41:36.887401-05:00

A novel type of physical hydrogel based on dual-crosslinked strategy is successfully synthesized by micellar copolymerization of stearyl methacrylate, acrylamide, and acrylic acid, and subsequent introduction of Fe3+. Strong hydrophobic associations among poly(stearyl methacrylate) blocks form the first crosslinking point and ionic coordination bonds between carboxyl groups and Fe3+ serve as the second crosslinking point. The mechanical properties of the hydrogel can be tuned in a wide range by controlling the densities of two crosslinks. The optimal hydrogel shows excellent mechanical properties (tensile strength of ≈6.8 MPa, elastic modulus of ≈8.0 MPa, elongation of ≈1000%, toughness of 53 MJ m−3) and good self-recovery property. Furthermore, owing to stimuli responsiveness of physical interaction, this hydrogel also shows a triple shape memory effect. The combination of two different physical interactions in a single network provides a general strategy for designing of high-strength hydrogels with functionalities. A physical hydrogel with excellent mechanical performances and shape-memory effect is successfully synthesized via two crosslinkings of strong hydrophobic associations and ionic coordination bonds. The reinforcement mechanism, energy dissipation, and mechanical recoverability processes of the hydrogel are systematically investigated. Furthermore, the responsiveness of physical interactions endows the hydrogel with a triple shape memory effect.



Electrospun Sandwich-Structure Composite Membranes for Wound Dressing Scaffolds with High Antioxidant and Antibacterial Activity

2017-12-06T08:11:38.369973-05:00

In this study, the sandwich-structured composite (SSC) membranes with well-antibacterial and antioxidant properties, which have the promising application as wound dressing, are successfully fabricated by combining an electrospinning process. The SSC membranes are composed of three layers, including the bottom polyvinylidene fluoride fibrous layer, the middle curcumin/polylactic acid (PLA) microsphere layer, and the top enrofloxacin/PLA fibrous layer, respectively. The obtained SSC membranes are characterized in terms of morphology, component, and mechanical property using scanning electronic microscope, X-ray diffractometer, Fourier transform infrared spectroscopy, and universal electronic testing machine, respectively. Moreover, in vitro drug release, antioxidant activity, antimicrobial activity, and biocompatibility of the SSC membranes are also evaluated. The results showed that the obtained composite membranes indeed possess the sandwich structure, where the middle microsphere layer is located between two fibrous surface layers. It is found that the drug-loaded SSC membranes show excellent antioxidant activity against •OH and DPPH free radicals and antibacterial activity against Staphylococcus aureus, Escherichia coli, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Candida albicans. The combination of electrospinning and electrospraying opens up a new way to fabricate a variety of composite membranes with a sandwich structure, which have promising potential application as wound dressing scaffolds. Sandwich-structured composite (SSC) membranes are successfully fabricated by combining an electrospinning process. The prepared SSC membranes show a hydrophobic surface and a hydrophilic surface, and possess well antibacterial and antioxidant properties. This study demonstrates an innovative strategy for creating SSC membranes, which have promising application prospects as wound dressings.



UV-Triggered Optical Response and Oxygen Scavenging Ability of a Water-Soluble Poly(N,N-dimethylacrylamide-co-2-vinylbenzylanthraquinone) Copolymer

2017-12-06T08:11:05.853691-05:00

A vinyl-modified anthraquinone (AQ) derivative (Vinyl-AQ) is synthesized through a palladium-mediated Suzuki coupling reaction between vinylphenylboronic acid and 2-chloromethylanthraquinone and, subsequently, copolymerized with N,N-dimethylacrylamide (DMAM) through free radical copolymerization in organic solvent. The chemical structure of the resulting water-soluble copolymer, P(DMAM-co-AQ), is verified using techniques such as proton nuclear magnetic resonance, attenuated total reflection-infrared spectroscopy, thermogravimetric analysis, and UV–vis spectroscopy. The evolution of the oxygen scavenging abilities of aqueous P(DMAM-co-AQ) solutions after UV irradiation is monitored as a function of UV irradiation time, concentration of AQ moieties, and pH. The copolymer is proved an effective UV-triggered oxygen scavenger, leading to dissolved oxygen contents below 1 ppm for the optimized experimental conditions. This behavior is related with the appearance of novel chemical species with interesting optical properties, as suggested by the respective evolution of the UV–vis absorption and photoluminescence spectra after UV irradiation. The water-soluble anthraquinone-based polymeric oxygen scavenger, P(DMAM-co-AQ), exhibits dramatic reduction in dissolved oxygen of aqueous solutions upon UV-triggering. Depending on the copolymer concentration, the irradiation time and the pH, the dissolved oxygen concentration can reach values less than 1 ppm. At the same time novel chemical species with interesting optical properties are appeared.



Thrombin-Loaded Poly(butylene succinate)-Based Electrospun Membranes for Rapid Hemostatic Application

2017-12-05T08:40:41.37098-05:00

Poly(butylene succinate) (PBS) and gelatin-coated PBS electrospun membranes are evaluated for use as support materials to immobilize thrombin, an effective hemostat for topical injury, and three methods differing in whether and when gelatin is included are envisaged to prepare thrombin-loaded PBS-based electrospun membranes for use as rapid hemostatic materials. Both PBS and gelatin-coated PBS membranes have high porosity, excellent wettability, rapid water penetration rate, and high water uptake, and thus are suitable support materials for thrombin. The thrombin immobilized onto gelatin-coated PBS membrane has both high initial enzyme activity and high storage stability ascribed to the stabilizing effect of gelatin on thrombin activity. The hemostasis performance of thrombin-immobilized membrane is evaluated in a rat liver model, showing shorter hemostasis time and less blood loss than clinically used gelatin sponge. The hemostasis mechanism is attributed to combined effects of thrombin and porous structure of electrospun membrane. Rapid hemostatic materials with easy handling, simple application, and long shelf life are prepared by immobilizing thrombin, an effective hemostat for topical injury, onto gelatin-coated poly(butylene succinate) electrospun membranes. They show shorter hemostasis time and less blood loss than clinically used gelatin sponge in a rat liver model and have a great potential to be used in first aid.



Thermal and Lithographic Performance of Silsesquioxane with Cycloaliphatic Epoxy-Siloxane Hybrid Spacer for Soft Lithography

2017-12-22T06:22:52.400618-05:00

Pattern replication and fidelity are crucial during soft lithography process. The flexibility and surface energy of the resist with that of the master mold are among the factors in determining such an effect. In this work, polysilsesquioxane bearing cycloaliphatic-epoxy spacer of different chain length at tethered positions is synthesized. Pattern replication using soft lithography is made using polymethylmethacrylate (PMMA) as master mold. The thermal and UV-cured lithographic performances are studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). It shows that chain length of spacer induces flexibility and thermal stability. Despite chain flexibility, increase in spacer length results in poor lithographic performance. This can be attributed to the behavior of spreading parameter with different surface energy between the PMMA mold and the polysiloxane resist surfaces. Different length of polysiloxane spacer is designed to understand the thermal and lithographic behaviors of silsesquioxane macromer. Cycloaliphatic epoxy is incorporated to the spacer for the crosslinking process upon ultra-violet (UV) radiation. The study gives an understanding that the increasing of spacer increases thermal property and reduces the capability of micro-pattern to be replicated with high fidelity.



Structural Evolution of UHMWPE Fibers during Prestretching Far and Near Melting Temperature: An In Situ Synchrotron Radiation Small- and Wide-Angle X-Ray Scattering Study

2017-12-27T04:22:14.663531-05:00

Combining a homemade extension apparatus and the in situ synchrotron radiation small- and wide-angle X-ray scattering methods for measurement, the structural evolutions of gel-spun ultrahigh molecular weight polyethylene (UHMWPE) fibers during prestretching at temperatures of 25 and 100 °C are investigated, respectively. Lamellar rotation toward the stretching direction occurs before strain hardening, while the folded-chain crystal destruction and extended-chain fibril formation processes occur in the strain hardening zone at 25 °C. While at 100 °C, stretching induced crystal melting before the stress plateau region and formation of fibrous crystals at the onset of the stress plateau are observed. Further stretching results in shear displacement of crystal blocks and, finally, destruction of the folded-chain crystals and formation of extended-chain fibrils. Prestretching UHMWPE fibers at 100 °C within a certain strain range can produce highly oriented fibrous crystals, which may provide an ideal precursor structure for the poststretching process. Combining a homemade extension apparatus and the in situ synchrotron radiation small- and wide-angle X-ray scattering methods for measurement, the structural evolutions of gel-spun ultrahigh molecular weight polyethylene (UHMWPE) fibers during prestretching at different temperatures are investigated. At 25 °C, lamellar rotation and amorphous extension occur at first, and then the crystals are fragmented through chain unfolding. The final structure consists of some lamellae and a small number of fibrils. At 100 °C, the melting reconstruction process happens. Further stretching results in shear displacement of the crystal blocks, unfolding of the chains, and forming extended-chain fibrils.



An Alternating Skin–Core Structure in Melt Multi-Injection-Molded Polyethylene

2017-12-22T06:23:59.134074-05:00

Shish-kebab, which is endowed with superior strength and modulus, provides the potential to fabricate self-reinforced polymer products. However, the injection-molded product usually exhibits a typical skin–core structure, and the shish-kebab is only located in an extremely thin shear layer. Therefore, the controlling and tailoring of crystal structures in complex flow field to improve the mechanical properties of the injection-molded sample are still a great challenge. Herein, for the first time, high-density polyethylene sample with a novel macroscopic alternating skin–core structure is achieved using a melt multi-injection molding technique. Results show that, with increasing the amount of melt injection, the layers of skin–core structure increase in the form of arithmetic progression, and therefore the tensile strength of the samples progressively increases due to an increase of shish-kebab content. This study demonstrates a new approach to achieve multilayer homogeneous materials with excellent tensile strength via macroscopic structural design during the practical molding process. The hierarchical crystalline morphologies of high-density polyethylene samples molded by melt multi-injection molding technique are investigated. For the first time, a distinct macroscopic alternating skin–core structure across the whole thickness of the samples can be observed.



Synthesis of Polyaniline Nanowires and Nanorods in the Presence of NaF under an Electric Field and Their Characterization

2017-12-27T04:21:16.933554-05:00

In this work, polyaniline nanowires and nanorods are synthesized through adjusting and controlling the concentration of D-camphor-10-sulfonic acid (CSA) and NaF salt under the application of an electric field. The morphologies and structures of as-synthesized polyaniline (PANI) are characterized through various methods, including transmission electron microscopy, UV–vis, Fouier transform infrared spectroscopy, and X-ray diffraction. The results demonstrate that the introduction of an electric field can improve the crystallinity of PANI, and PANI nanowires/nanorods are fabricated through changing the amount of NaF or CSA in the presence of the electric field. Besides, the 1H NMR experiments are executed to investigate the structures of final products. Polyaniline nanowires and nanorods are synthesized through adjusting the concentration of NaF or/and D-camphor-10-sulfonic acid (CSA) under the application of the electric field (30 V), when inorganic salt NaF is introduced into the initial solution containing aniline and CSA. The different morphologies of as-prepared polyaniline are characterized by transmission electron microscopy and displayed as follows.