Effect of Preparation Methods on Mechanical Properties of PVA/HA Composite Hydrogel

##正## Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out todiscuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA compositehydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and ninefreezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value andpresented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA compositehydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA compositehydrogel with 3% HA.     

基于壳聚糖的可控缓释型微针制备与性能评价

在临床应用上,一种能够持续递送药物的微针(microneedle,MN)系统对于一些疫苗、激素类药物的递送具有重要价值。本文研究设计了一种基于壳聚糖的可控缓释型微针阵列(PVA/CS-MN),将微针贴片与药物相结合用于药物的可控长效缓释。重点研究了PVA/CS-MN的制备优化工艺,并对MN阵列外观形貌、力学性能、溶解与溶胀性能以及体外刺入性能进行了表征。实验结果表明,使用最优工艺制备的PVA/CS-MN具有良好的形貌以及力学性能,可以顺利在皮肤上打开微通道,并实现可控的溶解与溶胀功能。同时,体外透皮扩散实验表明,以抗坏血酸(l-ascorbic acid)为模型药物制备的Vc-PVA/CS-MN在1 h内即释放了约57%的药物,随后12 h内缓慢释放了约66.7%的药物,7 d后最终释放了92%的药物。PVA/CS-MN具备可控的缓释特性以及优良的药物递送效率,为药物的持续透皮递送提供了一个新选择。     

The plasticizing mechanism and effect of calcium chloride on starch/poly(vinyl alcohol) films

Starch/poly(vinyl alcohol) (PVA) films were prepared with calcium chloride (CaCl(2)) as the plasticizer. The micro morphology of pure starch/PVA film and CaCl(2) plasticized starch/PVA film was observed by scanning electron microscope. The interaction between CaCl(2) and starch/PVA molecules was investigated by Fourier transform infrared spectroscopy. The influence of CaCl(2) on the crystalline, thermal and mechanical properties of starch/PVA films was studied by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and tensile testing, respectively. The results indicated that CaCl(2) could interact with starch and PVA molecules and then effectively destroy the crystals of starch and PVA. Starch/PVA films plasticized with CaCl(2) became soft and ductile, with lower tensile strength and higher elongation at break compared with pure starch/PVA film. The water content of starch/PVA film would increase with the addition of CaCl(2). This is an important cause of the plasticization of CaCl(2) on starch/PVA film.     

Biosorption of 2,4-dichlorophenol by immobilized white-rot fungus Phanerochaete chrysosporium from aqueous solutions

The fungus Phanerochaete chrysosporium was immobilized in several polymer matrices: Ca-alginate, Ca-alginate-polyvinyl alcohol (PVA) and pectin, and was then used as a biosorbent for removing 2,4-dichlorophenol (2,4-DCP) in wastewater. Immobilization of P. chrysosporium onto pectin was less efficient than that onto other matrices because of its poor mechanical strength and low adsorption efficiency. Ca-alginate immobilized fungal beads with biocompatibility exhibited good mechanical strength and adsorption efficiency over 60%. Among the different biomass dosages in Ca-alginate immobilized fungal beads, 1.25% (w/v) was the optimum. The adsorption data of 2,4-DCP on the blank Ca-alginate beads, free, and immobilized fungal biomass could be described by the Langmuir and Freundlich isotherms very well. Desorption operation was efficiently completed by using distilled water as eluant, and the desorption efficiency reached 82.16% at an optimum solid/liquid ratio of 14.3. The consecutive adsorption/desorption cycles studies employing the Ca-alginate immobilized fungal beads demonstrated that the immobilized fungal biomass could be reused in five cycles without significant loss of adsorption efficiency and adsorbent weight.     

Structure and optical properties of plant cell wall bio-inspired materials: cellulose-lignin multilayer nanocomposites

Interfacial affinity between lignin model compound (dehydrogenation polymer [DHP]) and cellulose nanocristals (CN) was studied before building a nanocomposite cellulose/lignin in multilayer form by spin-coating method. The adsorption isotherm of DHP was measured by ellipsometry at the liquid/CN film interface and showed that the surface concentration of adsorbed DHP increases with the bulk concentration in solution. The DHP appeared as globular structures on cellulosic film, as observed by AFM. Spreading a dense lignin layer on CN film gave rise to the disappearance of the InfraRed resonance bands related to the DHP aromatics. The film obtained from alternate layers of cellulose/DHP was transparent in visible light and had weak absorption in UV wavelengths. Optical properties measured in the visible wavelength range by ellipsometry and spectrophotometry indicated that beyond six bilayers (cellulose/DHP), the composite exhibits antireflexion properties.     

Physical, chemical and mechanical properties of pehuen cellulosic husk and its pehuen-starch based composites

Pehuen cellulosic husk was characterized and employed as reinforcement for composite materials. In this research, thermoplastic pehuen starch (TPS) and TPS/poly(lactic acid) (PLA)/polyvinyl alcohol (PVA) composites, reinforced with 5 and 10% of pehuen husk, were prepared by melt-blending. Comparative samples of pehuen TPS and TPS/PLA/PVA blend were also studied. Physical, thermal, structural and mechanical properties of composites were evaluated. Pehuen husk mainly consists of cellulose (50wt%), hemicellulose (30wt%) and lignin (14wt%). In respect to lipids, this husk has only a 0.6wt%. Its surface is smooth and damage-free and it is decomposed above 325°C. The incorporation of pehuen husk improved considerably the thermal stability and mechanical properties of the studied composites, mainly in TPS composites. Their thermal stability enhances since biofiber hinders the "out-diffusion" of volatile molecules from the polymer matrix, while mechanical properties could raise due to the natural affinity between husk and starch in the pehuen seed.     

Synthesis and Characterization of PVA-HA-Silk Composite Hydrogel by Orthogonal Experiment

PVA-HA-Silk composite hydrogel was synthesized with polyvinyl alcohol (PVA),nano-hydroxyapatite (HA) and natural silk by using the method of repeated freezing and thawing.A series of tests were performed to study water content,stress relaxation behavior,elastic modulus,and creep characteristics of PVA-HA-Silk composite hydrogel.Orthogonal experimental design method was used to analyze the influence degree of PVA,HA and silk (three kinds of raw materials) on mechanical properties and water content of the PVA-HA-Silk composite hydrogel to select the best material ratio according to their overall performance.The results demonstrate that the mass percentage of PVA has the greatest impact on the water content,followed by HA and silk.Compression stress-strain variation of PVA-HA-Silk composite hydrogel presents a nonlinear relationship,which proves that it is a typical viscoelastic material.Comparing the mechanical properties of 16 formulas,the formula of PVA-HA-silk composite hydrogel with mass percentage of PVA 15％,HA 2.0％ and silk 1.0％ is the best.     

Toward "strong" green nanocomposites: polyvinyl alcohol reinforced with extremely oriented cellulose whiskers

To exploit the maximum potential of cellulose whiskers (CWs), we report here for the first time the successful fabrication of nanocomposites reinforced with highly oriented CWs in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a colloidal suspension of cotton-derived CWs. The macroscopically homogeneous PVA-CW suspensions were extruded into cold methanol to form gel fibers followed by a hot drawing. Compared to the neat PVA fiber, the as-spun fiber containing a small amount of CWs (5 wt % of solid PVA) showed higher drawability, leading to an extremely high orientation of CWs with the matrix PVA. The stress-transfer mechanism, a prime determining factor for high mechanical properties of nanocomposites, was studied by X-ray diffraction. The stress on the incorporated CWs was monitored by applying an in situ nondestructive load to the composite fibers. The applied stress to the whole sample was found to be effectively transferred to the CWs inside the composites, suggesting strong interfacial bonding between the filler and the matrix. Effective stress transfer to the oriented whiskers resulted in outstanding enhancement in mechanical properties of the nanocomposites.     

Degradation of polyvinyl alcohol under mechanothermal stretching

Mechanical and thermal properties of polyvinyl alcohol (PVA) are characterized and analyzed using in situ X-ray photoelectron spectroscopy (XPS) and quantum chemistry calculations. It is found that the carbon peaks—commonly used as the reference for spectroscopic analysis—shift under mechanical and thermal stretching. Results also indicate that, at different temperatures and among the various functional groups present in PVA, the carbon in the C–O group is the most stable. Computational calculations showed that Hartree–Fock/10-31G (d) reproduces the binding energy of core carbon electrons with an accuracy of 95 %, which is enough to characterize bonds, allowing the results of the spectroscopic analysis to be corroborated.

Jabuticaba‐Inspired Hybrid Carbon Filler/Polymer Electrode for Use in Highly Stretchable Aqueous Li‐Ion Batteries

Stretchable electronics are considered as next‐generation devices; however, to realize stretchable electronics, it is first necessary to develop a deformable energy device. Of the various components in energy devices, the fabrication of stretchable current collectors is crucial because they must be mechanically robust and have high electrical conductivity under deformation. In this study, the authors present a conductive polymer composite composed of Jabuticaba‐like hybrid carbon fillers containing carbon nanotubes and carbon black in a simple solution process. The hybrid carbon/polymer (HCP) composite is found to effectively retain its electrical conductivity, even when under high strain of ≈200%. To understand the behavior of conductive fillers in the polymer matrix when under mechanical strain, the authors investigate the microstructure of the composite using an in situ small‐angle X‐ray scattering analysis. The authors observe that the HCP produces efficient electrical pathways for filler interconnections upon stretching. The authors develop a stretchable aqueous rechargeable lithium‐ion battery (ARLB) that utilizes this HCP composite as a stretchable current collector. The ARLB exhibits excellent rate capability (≈90 mA h g^?1 at a rate of 20 C) and outstanding capacity retention of 93% after 500 cycles. Moreover, the stretchable ARLB is able to efficiently deliver power even when under 100% strain.     

Preparation and characterization of surface crosslinked TPS/PVA blend films

Surface crosslinked thermoplastic starch (TPS)/PVA blend films were prepared by applying ultra violet (UV) irradiation. Sodium benzoate was used as photosensitizer and induced onto film surface layer by soaking the TPS/PVA films in the photosensitizer aqueous solution. The effects of concentration of photosensitizer aqueous solution, soaking time and UV irradiation dose on the surface photocrosslinking reaction were investigated. Physical properties, such as water contact angle, moisture absorption, swelling degree and solubility in water as well as mechanical properties of the films were measured to characterize the influence of the surface photocrosslinking modification. The obtained results showed that the surface modification considerably reduced the surface hydrophilic character of the TPS/PVA films, enhanced the film’s water resistance and also increased tensile strength and Young’s modulus but decreased elongation at break of the films.     

Development and in vitro evaluation of chitosan-Eudragit RS 30D composite wound dressings

The purpose of this research was to design and evaluate chitosan-based films intended for wound dressing application. Required properties for successful wound dressing, such as liquid uptake, vapor and oxygen penetration, bioadhesiveness, and film elasticity, were examined. Water uptake and vapor penetration of the films were determined gravimetrically, while oxygen penetration was determined by Winkler’s method. The bioadhesive properties were determined with an in-house pulley system instrument using a pig gut model. Film elasticity was determined with a stretch test using an Instron apparatus. The results showed that pure chitosan films exhibited relatively high liquid uptake and the adsorption tended to decrease with the addition of Eudragit RS 30D. Moisture vapor and oxygen were found to be able to penetrate through all film formulations in comparable amounts. The bioadhesiveness test tended to show lower bioadhesive properties with the addition of Eudragit RS 30D. The formulation containing only chitosan exhibited low elongation of the film at 2 N, but the film elasticity increased with the addition of Eudragit RS 30D. In conclusion, the addition of Eudragit RS 30D could improve a film’s mechanical properties but lower its bioadhesiveness. Published: March 24, 2006     

Modeling and experimental investigation of rheological properties of injectable poly(lactide ethylene oxide fumarate)/hydroxyapatite nanocomposites

Injectable multiphasic polymer/ceramic composites are attractive as bioresorbable scaffolds for bone regeneration because they can be cross-linked in situ and are osteoconductive. The injectability of the composite depends on the nanoparticle content and the energetic interactions at the polymer/particle interface. The objective of this research was to determine experimentally the rheological properties of the PLEOF/apatite composite as an injectable biomaterial and to compare the viscoelastic response with the predictions of a linear elastic dumbbell model. A degradable in situ cross-linkable terpolymer based on low molecular weight poly(L-lactide) and poly(ethylene oxide) linked by unsaturated fumarate groups is synthesized. The poly(L-lactide-co-ethylene oxide-co-fumarate) (PLEOF) terpolymer interacts with the surface of the apatite nanoparticles by polar interactions and hydrogen bonding. A kinetic model is developed that takes into account the adsorption/desorption of polymer chains to/from the nanoparticle surface. Rheological properties of the aqueous dispersion of PLEOF terpolymer reinforced with nanosized hydroxyapatite (HA) particles are investigated using mechanical rheometry. To this end, we performed a series of rheological experiments on un-cross-linked PLEOF reinforced with different volume fractions of HA nanoparticles. The results demonstrate that the observed nonlinear viscoelasticity at higher shear rates is controlled by the energetic interactions between the polymer chains and dispersed particle aggregates and by the rate of the adsorption/desorption of the chains to/from the surface of the nanoparticles.     

Correlating Stiffness,Ductility, and Morphology of Polymer:Fullerene Films for Solar Cell Applications

The development of flexible and physically robust organic solar cells requires detailed knowledge of the mechanical behavior of the heterogeneous material stack. However, in these devices there has been limited research on the mechanical properties of the active organic layer. Here, two critical mechanical properties, stiffness and ductility, of a widely studied organic solar cell active layer, a blend film composed of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) are reported. Processing conditions are varied to produce films with differing morphology and correlations are developed between the film morphology, mechanical properties and photovoltaic device performance. The morphology is characterized by fitting the absorption of the P3HT:PCBM films to a weakly interacting H‐aggregate model. The elastic modulus is determined using a buckling metrology approach and the crack onset strain is determined by observing the film under tensile strain using optical microscopy. Both the elastic modulus and crack onset strain are found to vary significantly with processing conditions. Processing methods that result in improved device performance are shown to decrease both the compliance and ductility of the film.     

Development and characterization of a novel bioactive polymer with antibacterial and lysozyme‐like activity

The development and characterization of a novel bioactive polymer based on the immobilization of glucose oxidase enzyme (GOx) in a polyvinyl alcohol (PVA) film showing antibacterial activity is presented. The PVA‐GOx composite material was extensively characterized by UV‐vis, X‐ray Photoelectron (XPS) spectroscopy and by Fourier Transform Infrared (FTIR) spectroscopy to verify the preservation of enzyme structural integrity and activity. The antimicrobial activity of this composite material against Escherichia coli and Vibrio alginolyticus was assessed. Furthermore the lysozyme‐like activity of PVA‐GOx was highlighted by a standard assay on Petri dishes employing Micrococcus lysodeikticus cell walls. The findings from this study have implications for future investigations related to the employment of PVA‐GOx system as a composite material of pharmaceutical and technological interest. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 461–470, 2014.     

Novel chitosan-based films cross-linked by genipin with improved physical properties

Novel cross-linked chitosan-based films were prepared using the solution casting technique. A naturally occurring and nontoxic cross-linking agent, genipin, was used to form the chitosan and chitosan/poly(ethylene oxide) (PEO) blend networks, where two types of PEO were used, one with a molecular weight of 20 000 g/mol (HPEO) and the other of 600 g/mol (LPEO). Genipin is used in traditional Chinese medicine and extracted from gardenia fruit. Importantly, it overcomes the problem of physiological toxicity inherent in the use of some common synthetic chemicals as cross-linking agents. The mechanical properties and the stability in water of cross-linked and un-crosslinked chitosan and chitosan/PEO blend films were investigated. It was shown that, compared to the transparent yellow, un-cross-linked chitosan/PEO blend films, the genipin-cross-linked chitosan-based film, blue in color, was more elastic, was more stable, and had better mechanical properties. Genipin-cross-linking produced chitosan networks that were insoluble in acidic and alkaline solutions but were able to swell in these aqueous media. The swelling characteristics of the films exhibit sensitivity to the environmental pH and temperature. The surface properties of the films were also examined by contact angle measurements using water and mixtures of water/ethanol. The results showed that, with the one exception of cross-linked pure chitosan in 100% water, the cross-linked chitosan and chitosan/PEO blends were more hydrophobic than un-crosslinked ones.     

Fabrication and characterization of biodegradable poly(3-hydroxybutyrate) composite containing bioglass

Bacterially derived poly(3-hydroxybutyrate) (P(3HB)) has been used to produce composite films by incorporating Bioglass particles (<5 microm) in 5 and 20 wt % concentrations. P(3HB) was produced using a large scale fermentation technique. The polymer was extracted using the Soxhlet technique and was found to have similar thermal and structural properties to the commercially available P(3HB). The effects of adding Bioglass on the microstructure surface and thermal and mechanical properties were examined using differential scanning calorimetry, dynamic mechanical analysis (DMA), X-ray diffraction, surface interferometry, electron microscopy, and nanoindentation. The addition of increasing concentrations of Bioglass in the polymer matrix reduced the degree of crystallinity of the polymer as well as caused an increase in the glass transition temperature as determined by DMA. The presence of Bioglass particulates reduced the Young's modulus of the composite. The storage modulus and the loss modulus, however, increased with the addition of 20 wt % Bioglass. A short period (28 days) in vitro bioactivity study in simulated body fluid confirmed the bioactivity of the composites, demonstrated by the formation of hydroxyapatite crystals on the composites' surface.     

Dichroic Optical Properties of Uniaxially Oriented Gold Nanorods in Polymer Films

Applications based on the optical excitation of the longitudinal surface plasmon resonance of gold nanorods (AuNRs) work at highest efficiency if all component AuNRs can be maximally excited simultaneously. This can be achieved in aligned AuNR structures, such as those embedded in uniaxially stretched polymer films. Since too high heating temperatures during film stretching cause reshaping and alteration of optical properties of the rods, a maximum allowable heating temperature is determined. The alignment of the rods is quantified by an orientational order parameter of 0.92 based on a statistically significant sample of assumed t distributed means and obtained by scanning electron microscopy. We show that a stretched AuNRs-PVA composite film has optical properties that approach the dichroic properties of an idealized ensemble of fully aligned, identical, and non-interacting AuNRs embedded in a PVA film. The idealized system is provided by FDTD simulations of a single AuNR, which we carried out using the size- and shape-adapted dielectric function of gold and the software RSOFT.     

Composite system based on chitosan and room-temperature ionic liquid: direct electrochemistry and electrocatalysis of hemoglobin

A novel polymer/room-temperature ionic liquid (RTIL) composite material based on chitosan (Chi) and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIM.BF(4)) was explored. The composite system can be readily used as an immobilization matrix to entrap proteins and enzymes. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. A pair of well-defined quasireversible redox peaks of hemoglobin were obtained at the Chi-BMIM.BF(4)-Hb composite-film-modified glassy carbon (GC) electrode by direct electron transfer between the protein and the GC electrode. Dramatically enhanced biocatalytic activity was exemplified at the Chi-BMIM.BF(4)-Hb/GC electrode by the reduction of oxygen and trichloroacetic acid. Thermogravimetric analysis (TGA) suggests that the Chi-BMIM.BF(4)-Hb composite has higher thermal stability than Chi-Hb itself. The Chi-BMIM.BF(4)-Hb film was also characterized by UV-visible spectra, indicating excellent stability in solution and good biocompatibility for protein. The unique composite material based on polymer and ionic liquid can find wide potential applications in direct electrochemistry, biosensors, and biocatalysis.     

The effect of chitosan on the in vitro biological performance of chitosan-poly(butylene succinate) blends

Chitosan blends with synthetic biodegradable polymers have been proposed for various biomedical applications due to their versatile mechanical properties and easier processing. However, details regarding the main surface characteristics that may benefit from the blending of these two types of materials are still missing. Hence, this work aims at investigating the surface properties of chitosan-based blends, illustrating the way these properties determine the material-proteins interactions and ultimately the behavior of osteoblast-like cells. The surface characteristics of modified and nonmodified blends were assessed using complimentary techniques such as optical microscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), contact angle measurements and surface energy calculations. The adsorption of human serum albumin (HSA) and human plasma fibronectin (HFN) onto the different surfaces was quantified by association of an indirect method with a colorimetric assay. It was found that the presence of chitosan on the surface promoted the adsorption of proteins. Moreover, a preferential adsorption of albumin over fibronectin was registered. The in vitro biological performance of the studied materials was further investigated by a direct contact assay with an osteoblastic-like cell line (SaOs-2). A synergistic effect of the two components of the blend was observed. While the synthetic polyester promoted the adhesion of SaOs-2, the presence of chitosan significantly enhanced the osteoblastic activity of these cells. This work further confirmed the interest in designing polymeric blends with natural polymers as a successful strategy to enhance the biological performance of a biomaterial.