Gelatin/Montmorillonite and Gelatin/Polyvinyl Alcohol/Montmorillonite Bionanocomposite Hydrogels: Microstructural,Swelling and Drying Properties

Abstract

Gelatin/montmorillonite bionanocomposite hydrogels containing 0, 5 and 10?wt.% of montmorillonite were prepared via two different techniques, either a cooling or drying method. In addition, gelatin/polyvinyl alcohol/montmorillonite bionanocomposite hydrogels having gelatin/polyvinyl alcohol ratios of 1/1, 1/2 and 2/1, loaded with 0, 5 and 10?wt.% of montmorillonite, were prepared via a cyclic freezing-thawing technique. The microstructural properties of both types of the prepared bionanocomposite hydrogels were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The gel fraction, swelling behavior and drying kinetics of all prepared bionanocomposite hydrogels were also studied. The XRD and SEM results showed a porous structure with a possible exfoliated morphology for both types of the prepared bionanocomposite hydrogels. In addition, the gel fraction of the bionanocomposite hydrogels increased and a more entangled and crosslinked network with a decreased pore size was obtained by increasing the loading level of montmorillonite for both types of the bionanocomposite hydrogels. The swelling ratio and drying rate of both types of the bionanocomposite hydrogels could be increased by decreasing the PVA portion or MMT loading level, while the swelling and drying ability of the gelatin/montmorillonite bionanocomposite hydrogels prepared via the cooling method was higher than those of the corresponding samples prepared via the drying method.     

Synthetic–Natural Bionanocomposite Hydrogels on the Basis of Polyvinyl Alcohol and Egg White

A series of bionanocomposite hydrogels composed of polyvinyl alcohol, a synthetic polymer, and egg white, a natural protein containing material, were prepared by the freezing- thawing cyclic method. Na-montmorillonite nanoclay (Na-MMT), as a crosslinker and reinforcing agent, with 0, 5, 10, and 15 wt% loadings (based on the dried mass of the bionanocomposite hydrogel) was incorporated in the polyvinyl alcohol and egg white hydrogel matrix. The microstructural characteristics of the prepared bionanocomposite hydrogels were characterized by the X-ray diffractometry, transmission electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and gel fraction measurements. Thermal and mechanical properties of the samples were also studied using differential scanning calorimetry and dynamic mechanical-thermal analysis. The swelling and drying kinetics and mechanisms of the bionanocomposite hydrogels were also studied. The bionanocomposite hydrogels had an exfoliated Na-MMT morphology with an appropriate dispersion of nanoclay layers in the hydrogel matrix. The results showed that the Na-MMT platelets acted as crosslinkers and created a hydrogel network with a smaller pore size in the bio-nanocomposite hydrogels, compared with the clay-free hydrogel. The obtained thermal and mechanical properties confirmed the reinforcing effect of the nanoclay in the bionanocomposite hydrogels. The swelling and drying rates of the bionanocomposite hydrogels exhibited an inverse dependency on the nanoclay loading. In general, it was concluded that the prepared bionanocomposite hydrogels could be used as appropriate biomaterials in biomedical applications, especially in drug delivery, tissue engineering and wound care.     

Polyvinyl Alcohol/Na-Montmorillonite Nanocomposite Hydrogels Prepared by Freezing–Thawing Method: Structural,Mechanical, Thermal,and Swelling Properties

Physically crosslinked nanocomposite hydrogels based on polyvinyl alcohol (PVA) containing Na-montmorillonite were prepared by the cyclic freezing–thawing method. The primarily exfoliated morphology of prepared nanocomposite hydrogels was confirmed by X-ray diffractometry (XRD) and transmission electron microscopy (TEM) as complementary techniques. It is shown that some interactions developed between the hydroxyl groups of PVA chains and Na-montmorillonite silicate layers in the nanocomposite hydrogels. Differential scanning calorimetry (DSC) results indicated some shifting in the glass transition temperature of the PVA hydrogel in the presence of the nanoclay. Swelling measurements showed that the swelling ratios of the nanocomposite hydrogels were increased either by decreasing the Na-montmorillonite content or by increasing the swelling medium temperature. Dynamic mechanical–thermal properties results showed higher storage modulus for nanocomposite hydrogels in temperature ranges both below and above 0°C. It was also found that the hardness of the nanocomposite hydrogels increased by increasing the nanoclay loading level.     

Preparation and Swelling Behavior of Partially Hydrolyzed Polyacrylamide Nanocomposite Hydrogels in Electrolyte Solutions

In this research, nanocomposite hydrogels were prepared by cross‐linking of partially hydrolyzed polyacrylamide/sodium montmorillonite aqueous solutions with chromium triacetate. The gelation process and influence of nanoclay content and salt concentration on swelling behavior were investigated. Study of gelation behavior using dynamic rheometry method showed that increasing the nanoclay content decreases the storage modulus, due to the partial adsorption of polymer chains onto the clay surface and ionic interaction between negative layers of sodium montmorillonite and Cr.³⁺ By increasing the cross‐linker concentration of the gelation system, the viscous energy dissipation properties of the nanocomposite gel decreases. Swelling ratio of the nanocomposite gels in distilled water decreased as the concentration of the nanoclay increased. However, nanocomposite gels showed lower salt sensitivity in electrolyte media compared with unfilled gels.     

Nanoporous Nanocomposite Hydrogels Composed of Polyvinyl Alcohol and Na-montmorillonite

Polyvinyl alcohol nanoporous nanocomposite hydrogels containing various levels of Na-montmorillonite were prepared by a cyclic freezing–thawing technique. An exfoliated morphology of silicate layers was observed for the nanocomposite hydrogels. The uniaxial tensile test indicated that the tensile modulus and tensile strength of the nanocomposite hydrogels increased with increasing Na-montmorillonite content, while their elongation-at-break values decreased. The results showed that by adding 15 wt% of montmorillonite to polyvinyl alcohol hydrogels, the molecular weight of polymer chains between two adjacent cross-links decreased to 56% and the effective cross-linking density increased up to 353%. It is also indicated that all nanocomposite hydrogel samples had nanoscale pore diameters and network mesh sizes less than 30 nm. The nanoporous structure of the nanocomposite hydrogels was confirmed by transmission electron microscopy observations and mercury intrusion porosimetry tests.     

Characterization of Polyvinyl Alcohol/ZnO Nanocomposite Hydrogels for Wound Dressings

Polymeric hydrogels, as novel soft biomaterials, have found various applications in the medical field; for instance, as wound dressings and wound care management. In this study, in order to achieve wound dressings with improved properties, nanocomposite hydrogels using incorporation of nano zinc oxide (ZnO) in polyvinyl alcohol (PVA), were prepared by a freezing-thawing method. The effect of ZnO loading on the mechanical, structural, physical and antibacterial properties of the samples was investigated and the morphology of the prepared nanocomposite hydrogels was determined by field emission scanning electron microscopy (FESEM). The results of mechanical tests of the nanocomposite hydrogels, using compressive and hardness tests, indicated that by adding increasingly amounts of the ZnO nanoparticles, the mechanical properties of the nanocomposite hydrogels were improved. Structure-related properties of the hydrogels, such as swelling and gel fraction measurements, showed that the increase in ZnO content lead to a decrease in the swelling rate and increase in the gel fraction of the nanocomposites. Antibacterial and biocompatibility analysis revealed that, with increasing nano ZnO content, the antibacterial properties of the nanocomposite significantly increased and the cells viability rose, leading to slightly reduced toxicity. The results of this work indicated that the presence and quantity of added ZnO in the PVA hydrogels were very influential factors to obtain the desirable characteristics of wound dressings, such as absorbing the wound fluids and exudates, being biocompatible, anti-bacterial and nontoxic, and having mechanical stability and flexibility.     

Study on the Dynamic Rheometry and Swelling Properties of the Polyacrylamide/Laponite Nanocomposite Hydrogels in Electrolyte Media

Polyacrylamide/laponite/chromium triacetate nanocomposite (NC) hydrogels were prepared by incorporation of the laponite nanoparticles in partially hydrolyzed polyacrylamide followed by cross-linking of their aqueous solutions with chromium triacetate. Influence of nanoparticle, cross-linker, polymer concentrations, and gelation media (water) temperature, salinity, and rheometer frequency on the viscoelastic behavior of the NC hydrogels were studied by probing the network properties. In addition, swelling behaviors of these NC gels in tap and oil reservoir water were evaluated. According to dynamic rheometry of the gelation process, the limiting storage modulus of the NC gels increased with increasing laponite content. The addition of laponite into the polyacrylamide gelling system increased their viscous properties more strongly than the elastic properties. The ultimate elastic modulus of the NC gels increased with increasing water salinity and temperature. Increasing rheometer frequency during gelation retarded the sol–gel transition and decreased the ultimate elastic modulus. The equilibrium swelling ratio of the NC hydrogels in tap water decreased with increasing laponite content. The salt sensitivity of the NC gels in oil reservoir water slightly decreased with increasing laponite content. These results suggest the superiority of the hydrolyzed polyacrylamide (HPAM)/chromium acetate/laponite NC hydrogels for water shut-off applications in oil reservoirs as compared with unfilled HPAM gels.     

Influence of Mass Ratio of Polyols on Properties of Polycaprolactone-Polyethylene Glycol/Methylene Diphenyl Diisocyanate/Diethylene Glycol Hydrogels

Polyurethane (PU) hydrogels with good hydrophilicity and biocompatibility have been applied as biomedical materials. A series of polyurethane prepolymers based on methylene diphenyl diisocyanate (MDI), polycaprolactone (PCL) and polyethylene glycol (PEG), using diethylene glycol (DEG) as the chain-extender, were synthesized; then the polyurethane hydrogels were obtained from the prepolymers using benzoyl peroxide (BPO) as a cross-linker by free radical polymerization. The influences of the ratio of polyols (PCL and PEG) on the contact angle, swelling ratio and morphology of the polyurethane hydrogel were investigated. The loading capacity and release behavior of chloramphenicol from the PCL-PEG/MDI/DEG hydrogels with different compositions were also studied. The contact angle and swelling degree results showed that the PCL-PEG/MDI/DEG hydrogel with PCL/PEG mass ratio of 3:1 had higher hydrophilicity than that with PCL/PEG mass ratios of 1:1 and 1:3. All PCL-PEG/MDI/DEG hydrogels showed three dimensional porous structures; however, the pore size increased with increasing PEG content. The chloramphenicol release kinetics from PCL-PEG/MDI/DEG hydrogels indicated Fickian diffusion, and the drug release rate increased with increasing PEG content in the PU hydrogels.     

Gelation Rheology and Water Absorption Behavior of Semi-Interpenetrating Polymer Networks of Polyacrylamide and Carboxymethyl Cellulose

Gelation rheology and swelling behavior of novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on polyacrylamide are described. These hydrogels were prepared by solution cross-linking of partially hydrolyzed polyacrylamide and carboxymethyl cellulose (CMC), using chromium triacetate. Effects of CMC content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels increased with increasing CMC content. Enhancement of storage modulus was more than two times for the semi-IPN gels containing 50 wt% CMC. It was also found that increasing the CMC content decreased the loss factor, indicating that the elastic properties of this gelling system increase more strongly than the viscous properties. The swelling ratio of the semi-IPN gels in tap water, NaCl and CaCl₂ solutions, and synthetic oil reservoir water slightly decreased as the concentration of the CMC increased. The improved storage modulus and slightly decreased swelling capacity in oil reservoir water make these semi-IPN hydrogels potentially good candidates for excess water treatment in oil recovery applications.     

液态簧振动力学谱在蛋白质水凝胶脱水变性过程的应用研究

本文用液态簧振动力学谱(RMS-L)方法, 对典型蛋白质水凝胶鸡蛋清的脱水变性过程进行了测量, 结果表明, 随水含量的减少, 鸡蛋清至少存在4个力学谱的显著变化过程. 基于此结果并结合力学谱的理论分析, 作者推测, 随水含量的减少, 鸡蛋清可能依次存在下述4个状态: 1) 类体水(bulk-likewater) 的蛋白质水凝胶态; 2) 键合水 (bond water) 的蛋白质水凝胶态; 3) 键合水和键合蛋白质(bonding protein) 的混合态; 4) 键合蛋白质态. 而蛋白质的空间构型(spatial configuration)转变即变性, 主要发生在拥有键合水的蛋白质通过失水向键合蛋白质转变的混合态. 这表明RMS-L对鸡蛋清脱水变性过程的检测是有效的, 所得结果对蛋白质变性机理、以及蛋白质水凝胶态的深入研究也应具有参考价值. 关键词： 力学谱 蛋白质水凝胶 蛋白质变性     

Hydroxyethyl Cellulose-Based Hydrogels with Various Pore Sizes Prepared by Freeze-Drying

Porous hydrogels were prepared from hydroxyethyl cellulose (HEC) using citric acid (CA) as a cross-linker with the pores formed by a freeze-drying technique prior to the cross-linking reaction. The pore size increased with the increase of the mass ratio of water to HEC during the preparation of the hydrogels. The porous structure of the hydrogels was in favor of the protein adsorption. The results of thermogravimetry demonstrated that the thermal stability of HEC was improved by cross-linking with CA. The data of percent weight remaining in buffer solution with different pH indicated that the hydrogels were stable in both weak acid and base media. The data of the swelling ratio demonstrated a fast swelling property of the hydrogel.     

Synthesis and Properties of Tannic Acid-Based Hydrogels

Hydrogels were synthesized by using tannic acid (TA) as a chemical cross-linker for the copolymer of allylglycidyl ether and acrylamide. The swelling ratio of the hydrogels increased with increasing amount of TA and decreased with increasing amounts of allylglycidyl ether. The hydrogels exhibited pH sensitivity; the swelling ratio increased with pH. Adsorption experiments of the hydrogel for Cu (II) ions suggested that the hydrogels can be used as an adsorbent for removal of Cu (II) heavy metal ions from dilute aqueous solutions.     

Effect of κ-carrageenan on volume phase transition for polyacrylamide (PAAm) hydrogel using the fluorescence technique

Steady-state fluorescence (SSF) technique was employed for studying swelling of polyacrylamide (PAAm) gels with various content of κ-carrageenan (κC). Disc shaped composite hydrogels were prepared by free-radical crosslinking copolymerization of acrylamide (AAm) with various amounts κC. N,N′-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and initiator, respectively. Pyranine was introduced as a fluorescence probe. Fluorescence intensity of pyranine was monitored during in situ swelling processes of composite gels. It was observed that fluorescence intensity values decreased as swelling is proceeded. Li–Tanaka equation was used to determine the swelling time constants, τ and cooperative diffusion coefficients, D from intensity variations during the swelling processes. It was shown that swelling time constants, τ decreased and diffusion coefficients, D increased as the κC content in the composites are increased.     

High-intensity ultrasound-assisted formation of cellulose nanofiber scaffold with low and high lignin content and their cytocompatibility with gingival fibroblast cells

Cellulose nanofiber (CNF) hydrogels with low lignin (8%) (LL-CNF) and high lignin (18%) (HL-CNF) content were produced at nominal powers of 240, 720 and 1200 W using high-intensity ultrasound technology (HIUS). Freeze-dried CNF hydrogels were evaluated as scaffolds for gingival fibroblast cells proliferation aiming biomedical applications. HIUS processing improved the dispersibility of the CNF and increased the water retention value by more than 5 times. The LL-CNF had a maximum fibrillation yield of 46 wt.%, whereas the HL-CNF had a maximum fibrillation yield of 40 wt.% at nominal power of ≥720 W. Regardless of the lignin content, the CNF hydrogels exhibited a typical elastic gel-like behavior with the highest elasticity of 263 Pa. After freeze-drying, the CNF aerogels had porosity ≥ 96.8%, and swelling capacity up to 42.1 g PBS/g aerogel. Moreover, the cell proliferation assay showed no differences in proliferation among the LL-CNF and HL-CNF scaffolds up to 11 days. Therefore, CNF scaffolds prepared with lignin content up to 18% present promising application in the biomedical field.     

Drying of heterogels swollen in organic vapor

Fast transient fluorescence technique (FTRF), which uses a Strobe Master System (SMS), is used to study swelling and drying of disc shape heterogels. Disc shape heterogels are prepared by free radical copolymerization (FCC) of methyl (methacrylate) (MMA) and styrene (S) with ethylene glycol dimethacrylate (EGDM). Pyrene (P_y) is introduced as a fluorescence probe during polymerization and lifetimes, τ, of P_y are measured during the in-situ swelling process. Chloroform was used as an organic vapor agent to induce gel swelling. It is observed that τ values decrease as swelling proceeds. The Li-Tanaka equation is used to determine the time constant, τ_c, and cooperative diffusion coefficients, D _c, for the swelling processes. Lifetimes of pyrene increase during drying. An empirical equation is introduced to determine the desorption coefficient, D, for drying. Heterogels with high S content swell and dry much more slowly than heterogels with low S content.     

Correlation of Diffusional Exponent with Structural Sequence of (N-Vinylpyrrolidone-alt-Acrylic Acid) Hydrogels: A Predictive Hydrogel Design Approach

Correlation of diffusional exponent of water into (N-Vinylpyrrolidone-alt-Acrylic acid) hydrogels with the structural sequence of hydrogel repeating units (i.e. hydrophilic and/or hydrophobic moieties) through a scaling law relationship has been investigated. The diffusional exponent (n) was found to depend linearly on Y/X² , where X equals to molar ratio of monomers in the feed (i.e. ([M₁ ]/[M₂ ])_feed) and Y equals to molar ratio of repeating units in the copolymer (i.e. ([M₁ ]/[M₂ ])_copolymer). Copolymers rich in hydrophilic acrylic acid (i.e. larger Y/X² ) were found to form more coiled polymeric chains as acrylic acid content increased due to H-bonding interactions, and hence results in lower diffusion coefficients and linear lowering of the n-value. On the other hand copolymers rich in partially hydrophobic N-vinylpyrrolidone (i.e. smaller Y/X²) formed more uncoiled polymeric chains as N-vinylpyrrolidone content increased due to larger amounts of positively charged protonated nitrogen atoms at pH 5.5 that tend to repel each other, which eventually lead to higher diffusion coefficients and a linear increase in n-value. These characteristic findings could be significant in sustained drug release studies, where the structural sequence of a hydrogel plays a dominant role in the release kinetics of a drug at certain positions and/or times.     

Rheological Properties and Microstructures of Hydroxyethyl Cellulose/Poly(Acrylic Acid) Blend Hydrogels

A simple in-situ method was introduced to prepare hydroxyethyl cellulose/poly(acrylic acid) (HEC/PAA) blend hydrogels by forming an interpenetrating network (IPN). Storage modulus (G′) and loss modulus (G″) were improved dramatically compared to HEC. To prove that hydrogen bonds and chemical crosslinking played major roles in improving the hydrogel strength and toughening, and to optimize the components of HEC/PAA blend hydrogels, a series of blend hydrogels with different ratios of HEC to PAA were designed and the corresponding Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), rheological tests, and swelling properties were compared. Crosslinked HEC/PAA blend hydrogel (mol/mol = 1:1) showed the best properties appropriate for opening up biomedical applications of the hydrogel.     

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.     

Preparation and Properties of Polyurethane Hydrogels Based on Methylene Diphenyl Diisocyanate/Polycaprolactone-Polyethylene Glycol

Polyurethane (PU) hydrogel is an important biomedical material for drug controlled release systems, wound dressings and medical bandages. Three series of polyurethane prepolymers based on methylene diphenyl diisocyanate (MDI), polycaprolactone (PCL) and polyethylene glycol (PEG), using diethylene glycol (DEG), N-methyldiethanolamine (MDEA) or dimethylolpropionic acid (DMPA), as the chain-extender, were prepared. Then the polyurethane hydrogels were obtained from the prepolymers, using benzoyl peroxide (BPO) as a cross-linking agent, by free radical polymerization. The influences of the types of chain-extenders and polyols on the contact angle, swelling ratio and morphology of the polyurethane hydrogels were investigated. The effect of the variety of the chain-extenders in the PU hydrogel on the drug release behavior was also studied. The FT-IR results showed that the PU hydrogels were successfully synthesized. The introduction of PEG improved the hydrophilicity of the PU hydrogels. The MDI/PCL-PEG/DEG hydrogel was hydrophobic, and there were small micropores on its surface; while the MDI/PCL-PEG/DMPA and MDI/PCL-PEG/MDEA hydrogels had high hydrophilicity and a micropouous structure on their surface due to the existence of carboxyl and tertiary amino functional groups. The change of chain-extenders had no significant effect on the cumulative drug release of chloramphenicol from the PU hydrogels. However, the introduction of PEG increased the drug release rate. The chloramphenicol release kinetics from the MDI/PCL-PEG hydrogels indicated non-Fickian diffusion.     

Novel pH-Sensitive Lactic Acid Oligomer Grafted Chitosan Hydrogel for Controlled Drug Release

A pH-sensitive hydrogel, using chitosan as hydrophilic segment and lactic acid oligomer (LAO) as hydrophobic segment, was successfully synthesized through a dehydration reaction between amino and carboxyl groups. Scanning electron microscope (SEM) images revealed that the channel-like network structure of the as-prepared hydrogels, which plays an important role in controllable drug release behavior, was gradually collapsed with increasing content of lactic acid. Fourier-transform infrared (FTIR) spectra were obtained to demonstrate the occurrence of the dehydration reaction. Furthermore, the swelling ratio measurement and release study were performed, and the results showed that the chitosan/LAO hydrogel had an outstanding pH-sensitive property, and thus has high potential for usage in controlled-drug release.