Ultrasonic monitoring of the network formation in superabsorbent cellulose based hydrogels

Biodegradable hydrogels are finding increasing interest in the academic and industrial field due to their high swelling capacity and the potential for many novel applications enabled by their biodegradability. The monitoring of the hydrogel cross-linking process is a crucial step for predicting hydrogel performances in terms of degree of swelling and viscoelastic properties.In this work, the chemical cross-linking of cellulose based hydrogels has been monitored during synthesis in water by means of ultrasonic wave propagation and low frequency dynamic mechanical analysis (DMA). The effect of the cross-linker concentration on the hydrogel acoustic behaviour has been also analysed and correlated with the different elastic response developed by the macromolecular hydrogel.The results demonstrate the reliability of the ultrasonic wave propagation in the following network formation process of a superabsorbent hydrogel, being capable of following the limited changes in the physical properties of the reacting solution.     

Radiation crosslinking and sorption properties of hydrogels based on 1‐vinyl‐2‐pyrrolidone,hydroxyethyl methacrylate,and their copolymers

This work has been concerned with the synthesis of the hydrogels of poly (vinyl pyrrolidone) (NVP), poly (hydroxy ethylmethacrylate) (HEMA), and their copolymer under the effect of gamma radiation in the presence of N,N‐methylenebisacryl‐amide (MBAm) as a crosslinking agent. The effect of the different factors that may affect the gelation and yield product, such as solvent composition and irradiation dose, was investigated. The formed hydrogels were characterized in terms of swelling in water and different organic solvents, X‐ray diffraction (XRD), and IR spectroscopic analysis. The sorption capability of these hydrogels towards some commercial basic and acid dyesstuffs was also studied. The results showed that a solvent mixture composed of equal contents of water and methanol is the most suitable to afford the minimum sol fraction and the highest yield product at a minimal irradiation dose of 10 kGy. It was observed that NVP hydrogel displayed the highest swelling in water, alcohols, and dimethyformamide of ～1300% and a lower tendency to swell in nonpolar solvents. The results showed that HEMA hydrogel has a high affinity to absorb basic dyes while NVP has a tendency for acid dyes. Also, the sorption of either the basic or acid dyes by the different hydrogels was found to greatly depend on the concentration of dye in solution and the mass of the used hydrogel. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3274–3280, 2004     

Highly Stretchable,Compressible, Resilient,and Equilibrium Swelling Hydrogels with Elastic Nano Junctions

In this work, a flexible and polymerizable polyurethane‐urea (PUU) nanoparticle is used for the first time to prepare hydrogels showing highly stretchable, compressible, and resilient properties in their equilibrium swelling state. The PUU nanoparticles are prepared by reported interfacial polycondensation of O/W nanoemulsions followed by surface modification with acrylate groups. The hydrogels are prepared by simple free‐radical copolymerization of acrylamide and the polymerizable PUU nanoparticles. These PUU nanoparticles are expected to act as polyfunctional nanocrosslinkers and elastic junctions of the hydrogel’s network. The obtained hydrogels show high water containing character (94–97 wt%) in their equilibrium swelling state. The equilibrium swelling hydrogels can still be stretched and compressed up to 430–1170% and 95%, respectively, without fracture. Furthermore, cyclic tensile tests with a maximum strain of 500% or 700% show that the resilience of these equilibrium swelling hydrogels is as high as 95–97%. This work provides a new strategy and some new insights into the fabrication of fully swelling hydrogels with both extraordinary ductility and resilience, which is of critical importance for many of their practical applications.     

Functionalized galactoglucomannan‐based hydrogels for the removal of metal cations from aqueous solutions

New types of hydrogels derived from O‐acetyl galactoglucomannan (AcGGM) hemicellulose have been synthesized and characterized. The objective of this work was to analyze the sorption capacity (S) of three types of hydrogels containing AcGGM derivatives incorporated into the carboxylic groups of the polymer chain in the AA hydrogel, sulfonic groups in the APA hydrogel, and amide groups in the acrylamide (Aam) hydrogel. These hydrogels are capable of interacting and removing ions such as cadmium [Cd(II)], copper [Cu(II)], lead [Pb(II)], nickel [Ni(II)], and zinc [Zn(II)]. The results show that AA and Aam hydrogels had a lower sorption capacity of ions compared to the APA hydrogel, which had a high sorption capacity. The maximal sorption capacity was determined by the successive enrichment method, obtaining Pb(II) amount of 48.3 mg/g of AA hydrogel, 65.8 mg/g of APA hydrogel, and 40.8 mg/g of Aam hydrogel. Hence, Pb(II) ions are greatly retained by the three hydrogels. These results are promising for the development of new materials with potential applications in metal ion removal. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44093.     

Preparation and Controlled Drug Release Characteristics of Thermoresponsive PEG/Poly (NIPAM-co-AMPS) Hydrogels

Thermosensitive hydrogels were prepared by free radical polymerization of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropanesulphonic acid (AMPS) in presence of polyethylene glycol (PEG) as macroinitiator. The incorporation of functional monomer in the hydrogel was confirmed by infrared spectroscopy. The equilibrium swelling ratio (ESR), deswelling rate, volume transition temperature, and surface morphology of synthesized hydrogels are found to be dependent on concentration of AMPS monomer in the feed composition. The equilibrium swelling ratio (ESR) and water retention properties increase with increasing AMPS concentration in hydrogels and decrease with increasing salt concentration in external medium. The hydrogel with high dose of AMPS has high loading efficiency of theophylline drug, whereas the in-vitro release of the drug is delayed for a prolonged period in swollen gels above LCST of PNIPAM.     

Water and dye sorption studies of novel semi IPNs: Acrylamide/4‐styrenesulfonic acid sodium salt/peg hydrogels

In this study, it has been investigated that the incorporation of poly(ethylene glycol), (PEG) and 4‐styrenesulfonic acid sodium salt, (NaSS) into acrylamide, (AAm) hydrogel during free radical solution polymerization synthesis. Poly (ethylene glycol)dimethacrylate, (PEGDMA) was used as a multifunctional crosslinker in polymerization. The main purpose of this study was to combine both monomers and a polymer in a new polymeric system. Dye sorption properties of hydrogels and semi IPNs were investigated by using cationic dye such as Union Green B (Janus Green B, UGB). Swelling and sorption studies were carried out at 25°C. For structural characterization, FTIR analysis was made. The equilibrium percentage swelling (S_eq%) ranges are 660–1330% for AAm/NaSS hydrogels and 580–1310% for AAm/NaSS/PEG semi IPNs. To determine the sorption behaviors of cationic dye UGB, some sorption parameters such as sorption capacity (q), adsorption percentage (Ads%) and partition coefficient (K_d) of the hydrogels were investigated. Binding characterization has been studied by Langmuir linearization method. The sorption capacity values of the hydrogel systems were changed between 1.24 × 10^?4 and 4.05 × 10^?4 mol g^?1. The values of Ads% of the hydrogels were changed among 18?67%, and the values of K_d of the hydrogels were between 0.22 and 2.02. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

镁离子对PVA/GG-Mg2+复合水凝胶的结构和物理化学性质的影响

聚乙烯醇(PVA)和结冷胶(GG)构成的复合水凝胶(PVA/GG)有助于提高材料的生物相容性,在生物材料方面得到广泛的关注和应用。为进一步改善其结构和力学性质,在PVA/GG中引入Mg²⁺参与高分子链的交联,合成了PVA/GG-Mg²⁺复合水凝胶。通过分析其网络结构、力学性质、溶胀和热失水动力学,研究了Mg²⁺对分子间作用、水凝胶结构和性质的影响。结果表明在PVA/GG-Mg²⁺水凝胶中,Mg²⁺对重组网络结构、增强力学性能、强化离子与高分子的静电和氢键作用、改进水凝胶的保水性能等方面起到了很重要的作用。系统中Mg²⁺所产生的影响与PVA/GG-Ca²⁺和PVA/GG-Al³⁺复合水凝胶中Ca²⁺和Al³⁺的影响相似。研究有助于复合水凝胶在生物材料领域的应用。     

Effect of the incorporation of a low amount of carbohydrate-containing monomer on the swelling properties of polyacrylamide hydrogels

In this work, the influence of the incorporation of a small amount of carbohydrate-containing monomer N-acryloyllactosylamine (LAM) on the swelling behavior of covalently-crosslinked polyacrylamide hydrogels in water has been reported. The incorporation of LAM into the copolymer was assessed by ATR–FTIR and thermogravimetric experiments. The main result is that the equilibrium water uptake was significantly decreased as soon as the hydrogel contained LAM considering a constant amount of crosslinking agent. The greatest difference of water uptakes between carbohydrate-free hydrogel and carbohydrate-containing hydrogel occurred for the lowest crosslinker amount of 1 mol%. In that case, the value of the water uptake reached 56-fold for the carbohydrate-free hydrogel and decreased down to 41-fold for the 10 mol% LAM hydrogel. Additional NMR experiments were used to measure the amount of non-crystallizable water which was higher for carbohydrate-free hydrogel than that for lactose-containing hydrogel confirming the water uptake results.     

Role of solvent on structure,viscoelasticity, and mechanical compressibility in nanocellulose-reinforced poly(vinyl alcohol) hydrogels

Cellulose nanocrystals (CNCs) reinforced polyvinyl alcohol (PVA)-based hydrogels with high water content and tunable mechanical properties that can be molded in to any desired shape are presented in this work. Freeze thawing of PVA-CNC solutions in a mixed solvent system of dimethyl sulfoxide and water enabled to produce a set of physically crosslinked hydrogels with tunable mechanical properties. It was observed that the composition of the solvent altered the mechanical properties and network structure in the hydrogel systems. Differential scanning calorimetry was used to understand the thermal events behind solvent effect on the properties of the hydrogel. Optical microscopy results suggest that these hydrogels possess a macroporous structure. Furthermore, dynamic viscoelastic analysis and axial compression tests have shown that the viscoelastic and mechanical compression properties of the hydrogels improved upon reinforcement with CNC. Overall, the hydrogel enjoys appealing properties as a synthetic biomaterial for soft tissue applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47044.     

High performances of dual network PVA hydrogel modified by PVP using borax as the structure-forming accelerator

A dual network hydrogel made up of polyvinylalcohol (PVA) crosslinked by borax and polyvinylpyrrolidone (PVP) was prepared by means of freezing-thawing circles. Here PVP was incorporated by linking with PVA to form a network structure, while the introduction of borax played the role of crosslinking PVA chains to accelerate the formation of a dual network structure in PVA/PVP composite hydrogel, thus endowing the hydrogel with high mechanical properties. The effects of both PVP and borax on the hydrogels were evaluated by comparing the two systems of PVA/PVP/borax and PVA/borax hydrogels. In the former system, adding 4.0% PVP not only increased the water content and the storage modulus but also enhanced the mechanical strength of the final hydrogel. But an overdose of PVP just as more than 4.0% tended to undermine the structure of hydrogels, and thus deteriorated hydrogels’ properties because of the weakened secondary interaction between PVP and PVA. Likewise, increasing borax could promote the gel crosslinking degree, thus making gels show a decrease in water content and swelling ratio, meanwhile shrinking the pores inside the hydrogels and finally enhancing the mechanical strength of hydrogels prominently. The developed hydrogel with high performances holds great potential for applications in biomedical and industrial fields.     

Self-assembly and metal ions-assisted one step fabrication of recoverable gelatin hydrogel with high mechanical strength

ABSTRACT

Gelatin hydrogel has been widely applied in bio-applications due to their good biocompatibility and high water content. However, poor mechanical properties of gelatin hydrogel greatly limit their application. Here we present a facile one-step soaking method to fabricate a recoverable gelatin hydrogel with high mechanical property, which is based on hydrogen bonds and metal ionic interaction. The mechanical properties of gelatin hydrogels can be tuned with different metal ions, temperatures and soaking times. Especially, gelatin-Fe³⁺ hydrogel can reach to 65 MPa compression stress with the compressive strain over 99% and possess good fatigue resistance under cyclic loadings. Besides, hydrogels crosslinked with metal ions show better antibacterial ability against Escherichia coli and Staphylococcus aureus. This work suggested an alternative for the design of tough gelatin-based hydrogels with desirable properties, which may hold promising for potential bio-applications under physiological conditions.     

Separation and preconcentration of some heavy‐metal ions using new chelating polymeric hydrogels

Two new chelating polymeric hydrogels, crosslinked polyacrylamide/triethylenetetraamine/CS₂Na (hydrogel I) and crosslinked polyacrylamide/diethylenetriamine/CS₂Na (hydrogel II), were prepared by the transamidation and dithiocarbamylation of crosslinked polyacrylamide. The products were characterized with elemental analysis and IR spectroscopy. In both polymeric hydrogels, the optimum pH for the removal of Cd(II), Pb(II), and Zn(II) ions ranged from 7 to 8, from 6 to 7, and from 7 to 8, respectively. The sorption isotherms of the investigated metal ions on the prepared hydrogels were developed, and the equilibrium data fitted the Langmuir and Freundlich isotherm models well. At the optimum pH for each metal ion, the maximum sorption capacities of hydrogel I toward Cd(II), Pb(II), and Zn(II) ions, estimated from the Langmuir model, were 5.3, 0.63, and 1.27 mmol/g, respectively, and those of hydrogel II were 4.1, 0.59, and 0.89 mmol/g, respectively. The experimental sorption capacities of hydrogel I toward Cd(II), Pb(II), and Zn(II) ions were 4.5, 0.6, and 1.2 mmol/g, respectively. In the case of hydrogel II, the capacities were 3.7, 0.52, and 0.88 mmol/g in the same prescribed order. The thermodynamic parameters (the free energy of sorption, enthalpy change, and entropy change) for cadmium, lead, and zinc sorption on the prepared polymers were also determined from the temperature dependence. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A New Sorbent Chemically Cross-linked Highly Swollen Copolymeric Hydrogels for Dye Uptake

Water uptake and the sorption properties of polyelectrolyte hydrogels made by the polymerization of acrylamide (AAm) with maleic acid (MA) were investigated as a function of composition to find materials with swelling and dye sorption properties. Highly swollen acrylamide/maleic acid (AAm/MA) hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with MA as comonomer and two multifunctional cross-linkers such as trimethylolpropane triacrylate (TMPTA) and 1,4-butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. Chemically cross-linked AAm/MA hydrogels were used in experiments on sorption of water-soluble monovalent cationic dyes such as “Nil blue” (NB) and “Methyl violet (MV)”. Weight-swelling ratio values of AAm/MA hydrogels were calculated range 8.88–61.46. Some swelling kinetic parameters were found. Diffusion behavior of water and water sorption rate constant were investigated. Water diffusion into hydrogels was found to be non-Fickian in character. For sorption of cationic dyes, NB and MV into AAm/MA hydrogels were studied by batch sorption technique at 25°C. AAm/MA hydrogels in the dye solutions showed coloration. However, the AAm hydrogel did not show sorption of any dye from solution. The amount of the dye sorbed per unit mass of AAm/MA hydrogels was investigated.     

Gamma radiation synthesis and swelling properties of hydrogels based on poly(ethylene glycol)/methacrylic acid (MAc) mixtures

In this work, gamma radiation was used to prepare hydrophilic hydrogels based on different mass ratios of poly(ethylene glycol) (PEG) and methacrylic acid (MAc) monomer. The thermal stability of hydrogels was characterized thermogravimetric analysis (TGA). The effect of temperature and pH, as external environments, on the equilibrium swelling of PEG/MAc hydrogels was also studied. The results showed that the gel fraction of PEG/MAc hydrogels is lower than that of PMAc hydrogel, in which the gel fraction of PMAc hydrogel was decreased greatly with increasing the mass ratio of PEG polymer in the initial solutions. The results showed that PEG/MAc hydrogels reached the equilibrium swelling state in water after 6 hours. It was found that the equilibrium swelling of PEG/MAc hydrogels displayed a transition change within the temperature range 30–40°C. This change in equilibrium swelling was illustrated by differential scanning calorimetry (DSC). However, it was observed that the equilibrium swelling of PEG/MAc hydrogels increases progressively with increasing the pH value from 4 up to 8. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Introduction of molecular spacers between the crosslinks of a cellulose‐based superabsorbent hydrogel: Effects on the equilibrium sorption properties

The possibility to modulate cellulose‐based hydrogel sorption properties through the insertion of molecular spacers between the crosslinks was investigated. Starting polymers were the sodium salt of carboxymethyl cellulose, a polyelectrolyte cellulose derivative, and hydroxyethyl cellulose, a nonpolyelectrolyte derivative. Poly(ethylene glycol) with various molecular weights was linked by its free ends at two divinyl sulfone (DVS) crosslinker molecules, to increase the average distance between two crosslinking sites and thus to act as a spacer. Both the effect of the concentration and the molecular weight of the spacer on the hydrogel final sorption properties in water and water solutions were investigated. The presence of the spacer allowed us also to perform hydrogel synthesis with higher concentrations of cellulose in the reactive mixture, and the effect of the polymer concentration in the batch was analyzed. Hydrogels obtained in the presence of spacers displayed significantly higher equilibrium sorption properties than those of the ones obtained without spacers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 168–174, 2003     

The Role of Permeability and Related Properties in the Design of Synthetic Hydrogels for Biomedical Applications

Synthetic hydrogels are a versatile range of materials which are of value in several biomedical applications, particularly those where permeability is important. Because the equilibrium water content of the gel governs permeability processes and has a marked influence on other important properties, the permeability requirements of a material often influence other aspects of its behaviour. The design of hydrogels for contact lenses demands an understanding of these interrelationships and thus provides a valuable basis for extending hydrogel design to other applications.     

Porous boron nitride nanofibers/PVA hydrogels with improved mechanical property and thermal stability

Polyvinyl alcohol (PVA) hydrogel is a promising material possessing good chemical stability, high water absorption, excellent biocompatibility and biological aging resistant. However, the poor mechanical performance of PVA hydrogel limits its applications. Here we report the utilization of one-dimensional (1D) BN nanofibers (BNNFs) as nanofillers into PVA matrix to prepare a novel kind of BNNFs/PVA composite hydrogel via a cyclic freezing and thawing method. For comparison, the composite hydrogels using spherical BN nanoparticles i.e. BN nanospheres (BNNSs) as fillers were also prepared. The mechanical properties, thermal stabilities and swelling behaviors of the composite hydrogels were investigated in detail. Our study indicates that the mechanical properties of the hydrogels can be improved by adding of BNNFs. After loading of BNNFs into PVA with content of 0.5?wt%, the compressive strength of the composite hydrogel increases by 252% compared with that of pure PVA hydrogel. The tensile performance of BNNFs/PVA composite hydrogels has also been improved. Impressive 87.8% increases in tensile strengths can be obtained with 1?wt% BNNFs added. In addition, with the increase of BNNFs content, the thermal stability and the swelling ratio of hydrogels are increased gradually. The swelling ratio of hydrogel increases by 56.3% with only 1?wt% BNNFs added. In comparison, the improvement effects of the BNNS fillers on the mechanical strengths and swelling ratios are much weaker. The enhanced effects of BNNFs can be ascribed to the strong hydrogen bond interaction between BNNFs and PVA. The high aspect ratios of the nanofibers should also be took into account.     

Polyelectrolyte CASA hydrogels for uptake of uranyl ions from aqueous solutions

In this study, uranyl ion adsorption from aqueous solutions has been investigated by chemically crosslinked acrylamide/sodium acrylate (CASA) hydrogels. Adsorption studies were investigated by the spectroscopic method. CASA hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), sodium acrylate (SA), and water by free radical polymerization in aqueous solution, using multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA). Uranyl ion adsorption from aqueous solutions was studied by the batch sorption technique at 25°C. The effect of uranyl ion concentration and mass of adsorbent on the uranyl ion adsorption were examined. In experiments of sorption, L‐type sorption in the Giles classification system was found. Some binding parameters, such as initial binding constant (K_i), equilibrium constant (K), monolayer coverage (n), site‐size (u), and maximum fractional occupancy (Ô) for the CASA hydrogel–uranyl ion binding system, were calculated using the Langmuir linearization method. Finally, the amount of sorbed uranyl ion per gram of dry hydrogel (q) was calculated to be 4.44 × 10^?4–14.86 × 10^?4 mol uranyl ion per gram for CASA hydrogels. Adsorption of uranyl ion (percentage) was changed within a range of 12.86–46.71%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 200–204, 2007     

Spin coating cellulose derivatives on quartz crystal microbalance plates to obtain hydrogel‐based fast sensors and actuators

Cellulose based superabsorbent hydrogels were spin coated and chemically crosslinked on Quartz Crystal Microbalance plates to obtain a thin superabsorbent layer. The hydrogel network was obtained by crosslinking hydroxiethylcellulose (HEC) and Carboxymethylcellulose (CMC) by the difunctional Divinylsulfone (DVS). The presence of the polyelectrolyte CMC was found to be responsible for the material high sorption sensitivity to changes in ionic strength and pH of the external solution, due to the Donnan type equilibrium established between the internal of the gel and the external solution. Since the hydrogel was synthesized in the form of a thin layer, there is negligible barrier to water diffusion through the material, which results in a fast swelling response to changes in the external solution properties. The device was immersed in a flux of water solution, where the ionic strength was continuously changed. The fast change in the equilibrium sorption capacity of the spin coated hydrogel were converted to an electrical signal by the apparatus. The time lag of the response was comparable to the inverse of the quartz oscillation frequency (approximately 10^?7 s), and the accuracy in the weight change measurement was of the order of the nanogram. FTIR microscope analysis was used to determine the presence of hydrogel and its distribution on the QCM plate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Controllable properties and microstructure of hydrogels based on crosslinked poly(ethylene glycol) diacrylates with different molecular weights

This work describes a comprehensive study of hydrogels based on polyethylene glycol diacrylates (PEGDAs) with the molecular weight (MW) range of 400–2000. The blends of low‐ and high‐molecular weight PEGDA macromers with different ratios were photopolymerized under visible light irradiation, using a blue light sensitive photoinitiator Irgacure819, at the total polymer concentration of 60 wt %. Swelling ratios, wetting property, elastic moduli, transparency, and the microstructure of the resulting hydrogels were investigated. Among them, equilibrium water contents, hydrophilicity, and mesh size of the hydrogels increased while the elastic moduli decreased when increased the PEGDA MW or the content of higher MW PEGDA in the blends. Most of the hydrogels possessed excellent transparency in visible region. The viability of L929 cells on the surface of hydrogel was also estimated. All the selected hydrogels exhibited a relatively high proliferation rate, which demonstrated this hydrogel system with photoinitiator Irgacure819 had good biocompatibility. These results show the properties of PEGDA hydrogel could be easily adjusted by varying PEGDA MW or the ratios of low‐ and high‐MW macromers in the composites. It could be helpful for the design of proper PEGDA hydrogels in the applications as tissue engineering or drug delivery system. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011