Facile preparation of low swelling,high strength,self-healing and pH-responsive hydrogels based on the triple-network structure

A polyacrylic acid(PAA)/gelatin(Gela)/polyvinyl alcohol(PVA)hydrogel was prepared by copolymerization,cooling,and freezing/thawing methods.This triplenetwork(TN)structure hydrogel displayed superior mechanical properties,low swelling ratio and self-healing properties,The superior mechanical properties are attributed to the triple helix association of Gela and PVA crystallites by reversible hydrogen bonding.The characterization results indicated that the fracture stress and the strain were 808 kPa and 370% respectively,while the compression strength could reach 4443 kPa and the compressive modulus was up to 39 MPa under the deformation of 90%.The hydrogen bonding in PVA contributed to maintain and improve the self-healing ability of hydrogels.Every type of hydrogels exhibited a higher swelling ratio under alkaline conditions,and the swelling ratios of PAA,PAA/PVA and PAA/Gela hydrogels were 27.71,12.30 and 9.09,respectively.The PAA/Gela/PVA TN hydrogel showed the lowest swelling ratio(6.57)among these hydrogels.These results indicate that the novel TN hydrogels possess good environmental adaptability and have potential applications in the biomedical engineering and sensor field.     

Biomimetic patterning of polymer hydrogels with hydroxyapatite nanoparticles

We report here an in situ process to produce nano-composite polymer hydrogels having surfaces patterned with hydroxyapatite (HA) nanoparticles (100 nm). Poly (vinyl alcohol) (PVA) has been used as a hydrogel forming medium. A three step process, comprising precipitation of HA nanoparticles in presence of PVA molecules and freeze thawing of obtained PVA-HA emulsion, followed by critical point drying, has been devised to produce three dimensional nanocomposite hydrogels. Interaction of Ca²⁺ with oxygen atoms of PVA and the hydrogen bonding characteristic of the polymer have been exploited to have controlled size distribution of HA in a continuous and macroporous network of PVA. A systematic variation in the polymer concentration could be correlated with microstructural features of the hydrogel.     

Development of a novel porous cryo-foam for potential wound healing applications

This body of work describes the development of a porous hydrogel for wound healing applications. In the present study poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) based hydrogels were prepared, and their properties were examined. Varying concentrations of the polymers and distilled water were used to prepare the hydrogels. The use of a high shear mixer, for foaming the PVA and PVA/PAA gels, and how this physical change can affect the structure and porosity of the hydrogel in question, represents a key feature of this work. The mechanical and thermal properties were determined by parallel plate rheometry and modulated differential scanning calorimetry (MDSC) respectively. The results indicated that the hydrogels containing low concentration of PVA and high volume of H₂O are significantly weaker than those synthesised with higher concentrations of PVA. The thermal analysis shows distinct endotherms and provides evidence of crystallisation. The chemical structure of the hydrogels was confirmed by means of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).     

Composite Microgels Created by Complexation between Polyvinyl Alcohol and Graphene Oxide in Compressed Double‐Emulsion Drops

Microgels, microparticles made of hydrogels, show fast diffusion kinetics and high reconfigurability while maintaining the advantages of hydrogels, being useful for various applications. Here, presented is a new microfluidic strategy for producing polymer‐graphene oxide (GO) composite microgels without chemical cues or a temperature swing for gelation. As a main component of microgels, polymers that are able to form hydrogen bonds, such as polyvinyl alcohol (PVA), are used. In the mixture of PVA and GO, GO is tethered by PVA through hydrogen bonding. When the mixture is rapidly concentrated in the core of double‐emulsion drops by osmotic‐pressure‐driven water pumping, PVA‐tethered GO sheets form a nematic phase with a planar alignment. In addition, the GO sheets are linked by additional hydrogen bonds, leading to a sol–gel transition. Therefore, the PVA–GO composite remains undissolved when it is directly exposed to water by oil‐shell rupture. These composite microgels can be also produced using poly(ethylene oxide) or poly(acrylic acid), instead of PVA. In addition, the microgels can be functionalized by incorporating other polymers in the presence of the hydrogel‐forming polymers. It is shown that the multicomponent microgels made from a mixture of polyacrylamide, PVA, and GO show an excellent adsorption capacity for impurities.     

Graphite/poly (vinyl alcohol) hydrogel composite as porous ringy skirt for artificial cornea

Graphite/poly (vinyl alcohol) (PVA) hydrogel composites, which were designed as the porous ringy skirt surrounding the transparent core of a novel artificial cornea, were prepared by using the freeze/thawing process and the particle-leaching technique. The properties of the composites, including the water content, the mechanical strength, the porous architecture and the interactions between the graphite and PVA, were investigated. The tissue responses to the composite and pure PVA hydrogel were studied by in vivo implantation in the dorsal muscles of mice. The results showed that chemical interactions were present between the graphite and PVA in the composite, which benefited the combination of the two phases and enhanced the uniform distribution of graphite particles in the PVA matrix. However, the present of graphites in the PVA hydrogels reduced the tensile strength, elongation at break and water content of the composite. Moreover, the porous graphite/PVA hydrogel composite had interconnective pore structure with high porosity and enough mechanical strength. According to the histological analysis of 1 week and 12 weeks post-implantation, the graphite/PVA hydrogel composites showed less inflammatory reactions than the PVA hydrogels at the 1 week post-implantation. Moreover, compared to pure PVA hydrogel, the graphite/PVA hydrogel composite exhibited enhanced migration and infiltration of cells, and more neovascularization and tissue ingrowth. These in vivo characteristics will be beneficial for the long-term biofixation of artificial cornea. Therefore, the porous graphite/PVA hydrogel composite has a potential to be used as novel artificial cornea skirt.     

PVA-PAAIPN水凝胶的制备及其溶胀性质研究

利用化学交联和循环冰冻-解冻相结合的顺序逼近法，制备了由和聚乙烯醇（PVA）和聚丙烯酸（PAA）复合的具有互穿聚合物网络（IPN）结构的高分子水凝胶。研究了交联剂含量，PAA含量和温度对水凝胶溶胀性质的影响，实验结果表明，30℃时，交联剂含量为1.0mol%的凝胶溶胀度最大，凝胶中PAA含量越大，凝胶的溶胀度越大；具有IPN结构的凝胶具有温度敏感性质；调节凝胶中PAA和交联剂的含量，可以控制凝胶突变体系的大小。     

FTIR spectroscopy characterization of poly (vinyl alcohol) hydrogel with different hydrolysis degree and chemically crosslinked with glutaraldehyde

In this work, poly (vinyl alcohol) (PVA) hydrogels with different degree of hydrolysis (DH) were prepared by chemical crosslinking with glutaraldehyde (GA). The nanostructure of the resulting hydrogels was investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Synchrotron small-angle X-ray scattering characterization (SAXS). In vitro tests were performed by swelling ratio assays in different pH solutions. The infrared spectra of the crosslinked PVA showed absorption bands of the acetal bridges resulted from the reaction of the GA with the OH groups from PVA. Also the FTIR spectroscopy was used to determine the crystallinity of the PVA film based on the relative intensity of the vibration band at 1141 cm^− 1. The results have showed an increase of hydrogel crystallinity with higher DH of PVA. SAXS patterns have clearly indicated important modifications on the PVA semicrystalline structure when it was crosslinked by GA. The swelling ratio was significantly reduced by chemically crosslinking the PVA network. PVA-derived hydrogel with chemically modified network was found to be pH-sensitive, indicating a high potential to be used in drug delivery polymer system.     

Preparation and characterization of keratin-based biocomposite hydrogels prepared by electron beam irradiation

The biocompatible and highly porous keratin-based hydrogels were prepared using electron beam irradiation (EBI). The conditions for keratin-based hydrogel formation were investigated depending on several conditions, including the presence of poly(vinyl alcohol) (PVA), concentration of keratin solution, EBI dose, and poly(ethylene imine) (PEI) additives. The pure keratin (human hair and wool) aqueous solution was not gelled by EBI, while the aqueous keratin solutions blended with PVA were gelled at an EBI dose of more than 90 kGy. Furthermore, in the presence of PEI, the aqueous keratin solution blended with PVA could be gelled at a considerably lower EBI dose, even at 10 kGy. This finding suggests that the PEI additives significantly influence the rate of gelation and that PEIs function as an accelerator during gelation. The resulting keratin-based hydrogels were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), gel fraction, degree of swelling, gel strength, and kinetics of swelling analyses.     

Novel PVP/PVA hydrogels for articular cartilage replacement

Poly(vinyl alcohol) (PVA) hydrogel has been considered as a very interesting and promising material for articular cartilage replacement. The most vital shortcoming of PVA hydrogels is that their mechanical properties are difficult to meet the requirements of articular cartilage. In the present work, blend hydrogels based on PVA and poly (vinyl pyrrolidone) (PVP) were prepared by repeated freezing and thawing method. Such hydrogel had similar internal three-dimensional structure and water content (approximately 75%) as nature articular cartilage. The mechanical and tribological properties were investigated to find out that change of mechanical and tribological properties of PVP/PVA hydrogels were significantly dependent on PVP content and freezing–thawing cycles. The blend hydrogel with 1 wt.% PVP had the best mechanical properties and the friction system consisting of such blend hydrogel and stainless steel ball exhibited a mixed lubrication regime especially under bovine serum lubrication. The results established that such hydrogel would be a novel attractive material for articular cartilage replacement.     

Swelling and mechanical behaviors of carbon nanotube/poly(vinyl alcohol) hybrid hydrogels

In this paper, carbon nanotubes (CNTs) were added into poly(vinyl alcohol) (PVA) hydrogels to modify their mechanical properties. A series of CNT/PVA hybrid hydrogels were prepared by freezing/thawing method. The mechanical and swelling properties of all hybrid hydrogels are better than those of the original PVA hydrogel. Especially, for CNTP-0.5 specimen with 0.5% w/w CNTs, its tensile modulus, tensile strength and strain at break are increased by 78.2%, 94.3% and 12.7%, respectively. And its swelling behavior is different from that of the pure PVA hydrogel. Its final swelling ratios at room temperature and 310 K are increased by 35.7% and 44.9%, respectively.     

Radiation preparation of PVA/CMC copolymers and their application in removal of dyes

Copolymer hydrogels composed of poly(vinyl alcohol) (PVA) and carboxymethyl cellulose (CMC) was prepared by using electron beam irradiation as crosslinking agent. The copolymers were characterized by FTIR and the physical properties such as gelation. The thermal behavior and swelling properties of the prepared hydrogels were investigated as a function of PVA/CMC composition. The factors effecting adsorption capacity of acid, reactive and direct dyes onto PVA/CMC hydrogel, such as CMC content, pH value of the dye solution, initial concentration and adsorption temperature for dyes were investigated. Thermodynamic study indicated that the values the negative values of ΔH suggested that the adsorption process is exothermic. The value of ΔH (38.81 kJ/mol) suggested that the electrostatic interaction is the dominant mechanism for the adsorption of dyes on hydrogel.     

Evaluation of poly(vinyl alcohol) hydrogels as a component of hybrid artificial tissues

Hydrogels are three-dimensional polymeric networks very similar to biological tissues. Many synthetic polymers can be used in preparing hydrogels. Among them poly(vinyl alcohol) (PVA), physically crosslinked by repeated freeze-thawing cycles of polymer aqueous solutions, is widely employed to make hydrogels for biomedical applications. To increase the similarity between hydrogels and natural tissues and to obtain polymeric hybrid tissues, we attempted to incorporate 3T3 cells, from a mouse fibroblast cell line, into PVA hydrogels obtained by one freeze-thawing cycle using as a solvent complete culture medium. Hydrogels were also made using eight freeze-thawing cycles from PVA solutions prepared using as a solvent either complete culture medium or water. Cell adhesion experiments were performed by seeding 3T3 and human umbilical vein endothelial cells (HUVEC) on to the hydrogel surface. The effect of the solvent and of the different number of freeze-thawing cycles on the mechanical characteristics of the PVA hydrogels were investigated by dynamic-mechanical techniques. A scanning force microscope analysis of the hydrogel surface viscoelastic properties was also carried out. Our results show that PVA is not cytotoxic. Although PVA hydrogel surface characteristics do not seem to favour the adhesion of substrate-dependent cells, encouraging results were obtained with the 3T3 cells incorporation. DMA analysis indicates that the networks prepared by eight freeze-thawing cycles possess a mechanical consistency comparable, even slightly better, than the ones prepared by only one freeze-thawing cycle and used for the cell incorporation studies.     

三维结构聚丙烯酰胺/聚乙烯醇水凝胶的合成及其在超级电容器中的应用

分别以过硫酸铵(APS)和N-N二甲基双丙烯酰胺(NMBA)作为引发剂和交联剂引发交联具有三维网络结构的聚丙烯酰胺/聚乙烯醇(PAM-PVA)水凝胶,将该水凝胶浸泡在6mol/L的KOH溶液中不同时间,制备凝胶聚合物电解质,并组装成双电层超级电容器。采用循环伏安、恒流充放电、交流阻抗等电化学测试技术对组装的超级电容器进行全面的性能研究,采用蓝电监测系统测试组装的超级电容器的稳定性。结果表明,以2.0g聚乙烯醇和10.0g丙烯酰胺反应制得的凝胶基体在吸收72h电解质溶液后组装的超级电容器性能最优,其比电容可达230F·g~(-1),5 000次充放电之后其循环保持率仍高达98%。     

Tough,Transparent, and Slippery PVA Hydrogel Led by Syneresis

Slippery and transparent polyvinyl alcohol (PVA) hydrogels with mechanical robustness exhibit broad applications in artificial biological soft tissues, flexible wearable electronics, and implantable biomedical devices. Most of the current PVA hydrogels, however, are unable to integrate these features, which compromises its performance in biological and engineering applications. To achieve such purpose, herein, a novel tactic is proposed, salting-out-after-syneresis of PVA, to realize a mechanically robust and highly transparent slippery PVA hydrogel. The syneresis of PVA sol is first conducted to form highly dense and transparent PVA polymer networks, then the salting-out effect tunes the aggregation of the polymer chains to rapidly induce the phase separation and crystallization. The resultant hydrogels show the transparency up to 98% in the visible region, the tribological coefficient down to 0.0081, and the excellent mechanical properties with strength, modulus, and toughness of 26.72 ± 1.05, 6.66 ± 0.29 MPa, and 55.21 ± 1.62 MJ m⁻³, respectively. To reveal the potentials, PVA contact lens that combine remarkable lubrication, anti-protein adhesion, biocompatibility, and drug-loading functions are demonstrated. This strategy provides a simple and new avenue for developing the mechanically robust, transparent, and hydrated hydrogels, showing the potential in biomedicine and wearable devices.     

纳米细菌纤维素/聚乙烯醇复合水凝胶在模拟体液中的疲劳行为

聚乙烯醇(PVA)复合水凝胶作为半月板及软骨等长期承重植入体,在生理环境中的疲劳行为关系到植入体的持久性和稳定性。采用弥散增强的方法将纳米细菌纤维素(BC)均匀分散在PVA水凝胶基体中,制备了纳米BC/PVA复合水凝胶。在模拟体液(SBF)环境中,采用压缩疲劳过程分析、疲劳前后刚度变化分析及疲劳前后尺寸稳定性分析3种方法,测试和评价了复合水凝胶的抗疲劳性能和力学稳定性。结果表明:纳米BC/PVA复合水凝胶在模拟人体环境中具有良好的抗疲劳性能,能够满足体内植入物的抗疲劳性能需求;纳米BC的加入可以有效提升复合水凝胶的力学稳定性和抗疲劳性能,但随着纳米BC含量的进一步升高,复合水凝胶的抗疲劳性能有所减弱,当PVA与纳米BC质量比为30∶1时,纳米BC/PVA复合水凝胶疲劳前期与后期最大位移变化量最小(0.002mm),疲劳前后刚度变化最小(5.41%),且疲劳前后尺寸稳定性最强,变形量仅为0.427mm,抗疲劳性能达到最佳。     

Hydrogel-based piezoresistive pH sensors: investigations using FT-IR attenuated total reflection spectroscopic imaging

The strong swelling ability of the pH-responsive poly(acrylic acid)/poly(vinyl alcohol) (PAA/PVA) hydrogel makes the development of a new type of sensor possible, which combines piezoresistive-responsive elements as mechanoelectrical transducers and the phase transition behavior of hydrogels as a chemomechanical transducer. The sensor consists of a pH-responsive PAA/PVA hydrogel and a standard pressure sensor chip. However, a time-dependent sensor output voltage mirrors only the physical swelling process of the hydrogel but not the corresponding chemical reactions. Therefore, an investigation of the swelling behavior of this hydrogel is essential for the optimization of sensor design. In this work, Fourier transform infrared (FT-IR) spectroscopic imaging was used to study the swelling of the hydrogel under in situ conditions. In particular, laterally and time-resolved FT-IR images were obtained in the attenuated total reflection mode and the entire data set of more than 80,000 FT-IR spectra was evaluated by principal component analysis (PCA). The first and third principal components (PCs) indicate the swelling process. Molecular changes within the carboxyl groups were observed in the second and fourth PC and identified as key processes for the swelling behavior. It was found that time-dependent molecular changes are similar to the electrical sensor output signal. The results of the FT-IR spectroscopic images render an improved chemical sensor possible and demonstrate that in situ FT-IR imaging is a powerful method for the characterization of molecular processes within chemical-sensitive materials.     

Viscoelastic behavior of nano-hydroxyapatite reinforced poly(vinyl alcohol) gel biocomposites as an articular cartilage

Nanohydroxyapatite reinforced poly(vinyl alcohol) gel (nano-HA/PVA gel) composites has been proposed as an articular cartilage repair biomaterial. In this paper, nano-HA/PVA gel composites were prepared by in situ synthesis nano-HA particles in PVA solution and accompanied with freeze/thaw method. The influence of nano-HA content, PVA concentration, test frequency and freeze/thaw cycle times on the viscoelastic behavior of nano-HA/PVA gel composites were evaluated using dynamic mechanical thermal analysis (DMTA). The results showed that both storage modulus and loss modulus firstly increased and then presented decreasing trend with the rise of nano-HA content. Their maximum values were obtained while nano-HA content was 6%. Furthermore, the G′ and G″ of the composites improve with the increase of PVA concentrations and freeze/thaw cycle times. This effect was more distinct at low freeze/thaw cycles. The phase angle (tan δ) of the pure PVA gel is larger than that of the nano-HA/PVA composites at the test frequency spectra, but all the phase angle values of the tested composites were close to that of nature bone.     

多重氢键增强的带乙烯基二氨基三嗪水凝胶的记忆性能与药物的选择吸附

制备了多重氢键增强的水凝胶聚(丙烯酰胺-co-2-乙烯基-4,6-二氨基-1,3,5-三嗪)/单宁酸(P(Am-co-VDT)/TA).通过对力学性能、微观形貌和红外光谱的测试和分析,发现TA通过氢键交联了水凝胶,使其结构更加致密,且水凝胶具有高的拉伸强度(2.34MPa)和断裂伸长率(410％).这是由于聚合物链上的...     

Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface

Physical parameters (such as crosslinking density, crystallinity and mechanical properties) have been found to largely affect cellular behavior on polymer scaffolds. This study demonstrated that transparent pure Poly (vinyl alcohol) hydrogels prepared via a freeze–thaw method can be made to support cell adhesion by controlling physical parameters such as concentration and the number of freeze–thaw cycles. For a given number of freeze–thaw cycles, (specifically 45), polymer concentration dependent structural and mechanical properties (such as tensile strength and stiffness) were correlated with cell adhesion. The maximum cell attachment occurred on the hydrogels with the greatest mechanical properties, crystallinity and crosslinking density. The hydrogel surfaces were more favorable to human dermal fibroblasts than human lens epithelial cells and retained their transparency as well as dimensional stability with only a small degree of swelling. Fibroblast laden hydrogels showed extensive alkaline phosphatase activity which confirmed their healthy proliferation and function. In this manner, this study suggests that transparent Poly (vinyl alcohol) hydrogels prepared by the freeze thaw method described here should be further studied for numerous tissue engineering applications.     

Thermoresponsive hyperbranched copolymer with multi acrylate functionality for in situ cross-linkable hyaluronic acid composite semi-IPN hydrogel

Thermoresponsive polymers have been widely used for in situ formed hydrogels in drug delivery and tissue engineering as they are easy to handle and their shape can easily conform to tissue defects. However, non-covalent bonding and mechanical weakness of these hydrogels limit their applications. In this study, a physically and chemically in situ cross-linkable hydrogel system was developed from a novel thermoresponsive hyperbranched PEG based copolymer with multi acrylate functionality, which was synthesized via an ‘one pot and one step’ in situ deactivation enhanced atom transfer radical co-polymerization of poly(ethylene glycol) diacrylate (PEGDA, M_n = 258 g mol⁻¹), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M_n = 475 g mol⁻¹) and (2-methoxyethoxy) ethyl methacrylate (MEO₂MA). This hyperbranched copolymer was tailored to have the lower critical solution temperature to form physical gelation around 37°C. Meanwhile, with high level of acrylate functionalities, a chemically cross-linked gel was formed from this copolymer using thiol functional cross-linker of pentaerythritol tetrakis (3-mercaptopropionate) (QT) via thiol-ene Michael addition reaction. Furthermore, a semi-interpenetrated polymer networks (semi-IPN) structure was developed by combining this polymer with hyaluronic acid (HA), leading to an in situ cross-linkable hydrogel with significantly increased porosity, enhanced swelling behavior and improved cell adhesion and viability both in 2D and 3D cell culture models.