Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content.However,due to the network defects of polymer gels,traditional hydrogels are usually brittle and fragile,which limits their practical applications.Herein,we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels.Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction.More importantly,based on the Hofmeister effect,the presence of(NH_(4))_(2)SO_(4)can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains'aggregation state and crystallinity.As a result,the as-prepared nanocomposite hydrogels possess unique physical properties,including robust mechanical and electrical properties.The as-prepared hydrogels can be further assembled into a high-performance flexible sensor,which can sensitively detect large-scale and small-scale human activities.The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Synthesis and properties of physically crosslinked poly (vinyl alcohol) hydrogels

The present study is an investigation of the properties of poly(vinyl alcohol),which would be a better contact lens mate- rial than conventional HEMA in some ways.A transparent PVA hydrogel was prepared from a PVA solution in a mixed solvent consisting of water and a water-miscible organic solvent,DMSO,by the freezing-thawing method.The water content,visible light transmittance,mechanical and swelling properties of the hydrogels were evaluated as a function of PVA concentration and number of freeze-thaw cycles.The results show that the properties of PVA hydrogels depend on the polymer concentration,the number of freeze-thaw cycles and the addition of the organic solvent.

Chemical and physical properties of poly (vinyl alcohol) hydrogel films formed by irradiation

Chemical and physical properties of poly(vinyl alcohol) (PVA) hydrogel films were investigated as a function of production factors. The experimental results show that the gel fraction depends strongly on the radiation dose, the degree of swelling is inversely dependent on the concentration of PVA solution, the tensile strength depends mainly on the PVA blending ratio and the elongation at break is inversely dependent on the radiation dose.

Controlled delivery of ibuprofen from poly(vinyl alcohol)-poly(ethylene glycol) interpenetrating polymeric network hydrogels

Hydrogels composed of poly(vinyl alcohol)(PVA) and poly(ethylene glycol)(PEG) were synthesized using glutaraldehyde as crosslinker and investigated for controlled delivery of the common anti-inflammatory drug, ibuprofen(IBF). To regulate the drug delivery, solid inclusion complexes(ICs) of IBF in β–cyclodextrin(β–CD) were prepared and added to the hydrogels. The ICs were prepared by the microwave irradiation method, which is more environmentally benign. The formation of IC was confirmed by various analytical techniques and the synthesized hydrogels were also characterized. Controlled release of drug was achieved from the hydrogels containing the ICs in comparison to the rapid release from hydrogels containing free IBF.The preliminary kinetic analysis emphasized the crucial role of β–CD in the drug release process that influences the polymer relaxation, thereby leading to prolonged release. The cytotoxicity assay validated the hydrogels as non-toxic in nature and hence can be utilized for controlled delivery of IBF.

Compatibility and Properties of Biodegradable Blend Films with Gelatin and Poly(vinyl alcohol)

The blend films with gelatin and poly（vinyl alcohol） （PVA） were prepared by a solution casting method. The compatibility between gelatin and PVA in the blend films was investigated. The transmittance, Fourier-transform infrared spectroscopy （FTIR）, x-ray diffraction （XRD）, thermogravimetry analysis （TG）, and differential scanning calorimetry （DSC） were employed to characterize the resultant blend films. According to optic result, the opacity of the blend film at the ratio of 20/80 （w/w, Gel to PVA） was the lowest, indicating the best compatibility between Gel and PVA at the ratio. The results oflR, XRD, DSC, and TG revealed an intensive interaction and good compatibility between them in the blend film at the ratio. The mechanical properties and solubility showed that PVA content in the blend films obviously affected the elongation at break and solubility. The mechanical properties and water resistance of gelatin film may be improved by the introduetion of PVA.

Research on the Long Time Swelling Properties of Poly (vinyl alcohol)/Hydroxylapatite Composite Hydrogel

Poly(vinyl alcohol)/hydroxylapatite(PVA/HA)composite hydrogel was prepared by repeated freezing and thawing.The water loss properties of the resultant hydrogel were investigated by using optical microscope.Long time immersion tests of PVA/HA composite hydrogel were carried out in the diluted calf serum solution to study the change laws of swelling properties with the freezing-thawing cycles and HA content.The micro-morphologies of PVA/HA composite hydrogel after long time immersion were observed by means of the high-accuracy 3D profiler.The results show that the swelling process of PVA/HA composite hydrogel is the converse process of its water loss.Long time swelling ratio curves of PVA/HA composite hydrogel in the calf serum solution are manifested as four stages of quick increase,decrease,slow decrease and stable balance,and its equilibrium swelling ratio decreases with the increase of freezing-thawing cycles and HA content.It is revealed that the network structure of the composite hydrogel immersed for a long period is significantly improved with the increase of HA content. Perfect network structures of PVA/HA composite hydrogel as well as full and equilibrium tissues after swelling equilibrium are obtained when the HA content is 3% and the number of freezing-thawing cycles is 7.

Preparation and Swelling Behavior of Physically Crosslinked Hydrogels Composed of Poly(vinyl alcohol) and Chitosan

The physically crosslinked poly（vinyl alcohol）/chitosan （CS） composite hydrogels were prepared by cyclic freezing/thawing techniques, and the microstructure and swelling behavior of the hydrogels in the simulated gastric （pH 1.0） and intestinal （pH 7.4） media were investigated. The experimental results of infrared spectra （IR）, scanning electron microscope （SEM） and differential scanning calorimetry （DSC） demonstrated that poly（vinyl alcohol） and chitosan had good miscibility in the composite hydrogels, and the addition of chitosan perturbed the formation of poly（vinyl alcohol） crystallites. The swelling kinetics results indicated that the composite hydrogels had good pH sensitive properties to the acidic environments, and with the increase of chitosan content in the blend, the maximum swelling degreed and the swelling rate both increased, but it led to more dissolution at pH 1.0. And the composite hydrogels also exhibited good reversible swelling behavior with pH value of the swelling medium altering between 1.0 and 7.4. In addition, the higher freezing/thawing cycle times resulted in the lower swelling rate. Therefore, the swelling behavior of the composite hydrogels could be adjusted by changing the chitosan contents and the freezing/thawing cycle times.

Facile preparation of methylcellulose/poly(vinyl alcohol)physical complex hydrogels with tunable thermosensitivity

Novel complex hydrogels of methylcellulose （MC） and poly（vinyl alcohol） （PVA） with wide-spectrum thermoresponsivity were prepared via physical and mild process. Thermal phase transition of MC/PVA hydrogels exhibited two forms including sol/sol to gel/sol and sol/gel to gel/gel. The phase transition temperature of MC/PVA solution ranged from 38,7 to 60.6 ℃ and was able to be adjusted by simply changing the feeding ratios of two components. The interior morphology of MC/PVA gels was examined with fluorescence analysis and scanning electron microscopy analysis, which showed that MC was well dispersed in matrix before and after thermally gelling.

Physicochemical Properties of Poly(Vinyl Alcohol)/Chitosan/Soluble Starch Composite Hydrogel

Fabricating of hydrogels based upon polymers and inorganic matter is an innovative replacement for the generation of adaptable matrices.In this study,the poly(vinyl alcohol)(PVA)/chitosan(CS)/soluble starch(SS)composite hydrogel was prepared by the solution blending method,in which SS was used as a cross-linking agent to cross-link with PVA in order to improve the stability of PVA in the tissue fluid.The composition and the thermal stability of hydrogels were characterized by Fourier transform infrared(FTIR)spectroscopy and thermo gravimetric analysis(TGA).The result shows that the PVA/CS/SS composite hydrogel possesses potentially morphological and thermal stability and can be used for tissue engineering.

Effect of Processing Parameters on Morphology and Mechanical Properties of Hollow Gel-Spun Lignin/Graphene Oxide/Poly(Vinyl Alcohol)Fibers

To investigate the influence of various processing parameters on the mechanical properties of fibers,lignin/graphene oxide(GO)/poly(vinyl alcohol)(PVA)fibers with different mass ratios of lignin and GO to PVA were prepared by gel spinning technique.Air drawing process and spinneret diameters were tuned as the main factors.The tensile strength increased up to 472 MPa with air drawing process applied in 30L0.05GO0.72D-A PVA fibers(air-drawn PVA fibers reinforced by 30%lignin and 0.05%GO spun with a spinneret diameter of 0.72 mm),indicating 17.4%higher than that of the fiber without air drawing process(402 MPa).Similarly,at least a 14.6%increase in Young's modulus has been achieved for 30L0.05GO0.72D-A fiber.In addition,a smaller spinneret diameter(0.72 mm)also led to a 24.9%increase in tensile strength and a 7.7%increase in Young's modulus in comparison with those of 5L0.05GO0.84D-A fibers.

Preparation and Properties of Poly(vinyl alcohol)/Chitosan Blend Bio-nanocomposites Reinforced by Cellulose Nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals（CNCs） on the mechanical, thermal and barrier properties of poly（vinyl alcohol）/chitosan（PVA/Cs） bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction（XRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, thermogravimetric analysis（TGA and DTG）, oxygen transmission rate（OTR）, and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.

Polyurethane/poly(vinyl alcohol) hydrogel coating improves the cytocompatibility of neural electrodes

Neural electrodes,the core component of neural prostheses,are usually encapsulated in polydimethylsiloxane（PDMS）.However,PDMS can generate a tissue response after implantation.Based on the physicochemical properties and excellent biocompatibility of polyurethane（PU）and poly（vinyl alcohol）（PVA）when used as coating materials,we synthesized PU/PVA hydrogel coatings and coated the surface of PDMS using plasma treatment,and the cytocompatibility to rat pheochromocytoma（PC12）cells was assessed.Protein adsorption tests indicated that the amount of protein adsorption onto the PDMS substrate was reduced by 92%after coating with the hydrogel.Moreover,the PC12 cells on the PU/PVA-coated PDMS showed higher cell density and longer and more numerous neurites than those on the uncoated PDMS.These results indicate that the PU/PVA hydrogel is cytocompatible and a promising coating material for neural electrodes to improve their biocompatibility.

Thermal aging behavior of high performance poly(vinyl alcohol) hydrogel

The thermal aging behavior of poly （ vinyl alcohol ） （ PVA ） hydrogel was studied at four different temperatures of 40 ℃, 50 ℃, 60 ℃ and 70 ℃ in one year. The samples of PVA hydrogel were closely covered by plastic film. The changes of their chemical structures and physical properties during aging were measured through different measurable techniques including tensile testing, gel permeation chromatography （ GPC ）, viscosity analysis, and Fourier transform infrared （FTIR） spec- trum. The results showed that the molecular weight of PVA in hydrogel changed little with time and temperature. FTIR spectra of PVA in all the samples were similar to those of the original samples. The tensile strength of PVA hydrogel didn＇t change until the 330th days.

Study of Pneumococcal Surface Protein, PspA, Incorporated in Poly(Vinyl Alcohol) Hydrogel Membranes

This study investigates poly(vinyl alcohol) (PVA) membranes as controlled release micro-matrices, which can be useful in therapeutic applications for optimizing the administration of drugs. Currently, the use of hydrogels is limited by protein size. This study investigates the delivery of PspA, a large protein of approximately 38 kD. Pneumococcal surface protein A (PspA) has been shown to provide protective immunity against pneumococcal infection and is considered as a pneumococcal vaccine. The protein release experiments demonstrated that from an initial pH 7.4, approximately 60% of PspA diffuse into a neutral environment with an initial burst and a declining rate reaching equilibrium. The results indicate that the protein was successfully incorporated and released from the membrane over time. The hydrogel and protein interaction is temporary, and the membrane system is ideal for protein drug delivery. The data confirm that the protein did not aggregate and was active after release. The protein release is promising and a step forward to develop microneedles to facilitate high molecular weight protein delivery as well as vaccine delivery.

Characterization of UV-curable Poly（ethylene glycol） Diacrylate Based Hydrogels

Poly（ethylene glycol） diacrylate/polyvinyl alcohoI（PEGDA/PVA） hydrogels were prepared from PEGDA and PVA as precurors by means of single UV radiation（UV ra.）, UV radiation followed by high energy electron beam irradiation（Irra.）, UV radiation followed by freeze-thawing（FT） or UV ra. and Irra. followed by FT, respectively. 2-Hydroxy-l-[4-（hydroxyethoxy）phenyl]-2-methyl-l-propanone（Irgacure 2959） was used as a photoinitiator. The effects of the various methods on the swelling and mechanical properties of the hydrogels were investigated. The results show that hydrogels made by UV ra. plus high energy electron beam irradiation followed by FT showed a higher crosslinking density and a larger tensile strength than those made by the other methods.

PVA/PEG Hybrid Hydrogels Prepared by Freeze-thawing and High Energy Electron Beam Irradiation

In this paper, poly（vinyl alcohol）（PVA） and PVA/poly（ethylene glycol）（PEG） hybrid hydrogels were synthesized by freeze-thawing or freeze-thawing followed by high energy electron beam irradiation. The influence of PEG molecular weight, mass ratios of PVA to PEG, thawing temperature and number of freeze-thawing（FT） cycles on the mechanical strength of PVA/PEG hydrogel was investigated. Also, the thermal behaviors were examined by differential scanning calorimetry（DSC） and the microstructttres were observed with scanning electron microscopy（SEM）. The results suggest that the addition of PEG improves the mechanical strength of PVA hydrogel and the irradiation reduces both the strength of PVA/PEG hydrogel slightly and the degree of crystallinity. The improved properties suggest that PVA/PEG hydrogel can be a good candidate for the application in the biomedical.

高分子实验中模具的制备及应用

高分子实验中很多时候要用到不同形状的聚四氟乙烯模具,比如,聚合物薄膜的制备及性能研究。不同的用途需要制备不同形状的模具,如,薄膜拉伸测试,需要长方形的模具以制备长方形的薄膜;薄膜耐水压测试,需要制备圆形的模具以制备圆形的薄膜;吸水率测试,需要方形的模具以制备方形的薄膜。模具的深度决定了薄膜的厚度,进一步决定了薄膜的不同性能。展示模具的应用,是通过制备不同形状和不同厚度的聚乙烯醇薄膜,来研究薄膜厚度对薄膜性能的影响。

聚丙烯腈对聚乙烯醇膜形貌和性能的改进

通过流延成膜的方法制备了聚乙烯醇/聚丙烯腈共混薄膜。通过扫描电镜分析了共混膜的形貌。通过差式扫描量热仪、热重分析、拉伸测试、表面接触角测试研究了共混膜的热力学性能、机械性能和化学性能。测试结果显示聚丙烯腈对聚乙烯醇膜的形貌和性能产生了显著的影响。

Research on the friction and wear mechanism of Poly(vinyl alcohol)/hydroxylapatite composite hydrogel

Poly(vinyl alcohol)/Hydroxylapatite(PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite as raw materials, using the method of repeated freezing and thawing.The morphologies of PVA/HA composite hydrogel were observed by means of high-accuracy 3D profiler and scanning electron microscope(SEM).The compressive elastic modulus and the stress relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter.The friction and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer.The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope(ESEM).The results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural bovine knee articular cartilages.With the increase of freezing-thawing cycles and the HA content, the degree of cross-link and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress relaxation is improved and the value of balance stress decreases.The friction coefficient decreases with the increase of the freezing-thawing cycles and the HA content.The more the freezing-thawing cycles are, the earlier the friction coefficient reaches the stable balance value.The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular cartilage is inversely proportional to freezing-thawing cycles and the HA content.The main wear mechanisms of PVA/HA composite hydrogel are plastic flowing and adhesive flaking.The wear severity degree decreases with the increase of freezing-thawing cycles and the HA content.

Responsive Hybrid Poly(vinyl alcohol)Hydrogel Membranes with Embedded Microgels as Valves

The research and application of responsive materials have long been hampered by their complicated designs and tedious construction processes.Besides,many current responsive materials show retard or weak responsiveness.In this study,responsive hybrid poly(vinyl alcohol)hydrogel membranes with embedded poly(N-isopropylacrylamide-acrylic acid)microgels as valves were constructed by simple mixing and subsequent freezing-thawing process.In the structure of the membranes,the matrix poly(vinyl alcohol)chains thread through and entangle with the microgels,and the microgels are firmly constrained within the hybrid hydrogel network.The fast and sharp temperature responsiveness of the embedded microgels was largely retained and endowed the hydrogel membrane with excellent temperature and pH responsiveness.Moreover,the hydrogel membrane showed excellent fatigue resistance in both temperature and pH-responsive flux examination.This study presented the great potential of these hybrid hydrogel membranes in biomedical applications and provided a new strategy for the future design and construction of responsive biomaterials.