Synthesis and swelling behavior of thermosensitive IPN hydrogels based on sodium acrylate and N‐isopropyl acrylamide by a two‐step method

A series of interpenetrating polymer network (IPN) hydrogels having higher swelling ratio (SR) and thermosensitivity were synthesized from sodium acrylate (SA) and N‐isopropyl acrylamide (NIPAAm) by a two‐step method. A series of the porous poly(sodium acrylate ‐co‐1‐vinyl–2‐pyrrolidone) [poly(SA‐co‐VP)], (SV), hydrogels were prepared from acrylic acid having 90% degree of neutralization and VP monomer in the first step. The second step is to immerse the SV dried gels into the NIPAAm solution containing initiator, accelerator, and crosslinker to absorb NIPAAm solution and then polymerized to form the poly(SA‐co‐VP)/poly(NIPAAm) IPN hydrogels (SVN). The effect of the different molar ratios of SA/VP and the content of NIPAAm on the swelling behavior and physical properties of the SVN hydrogels was investigated. Results showed that the SVN hydrogels displayed an obviously thermoreversible behavior when the temperature turns across the critical gel transition temperature (CGTT) of poly(NIPAAm) hydrogel. The pore diameter distributions inside the hydrogel also indicated that the pore sizes inside the SVN hydrogels were smaller than those inside the SV hydrogels. At the same time, the more proportion of SA was added into the hydrogel, the larger pore diameter of the SV hydrogel was formed. The results also showed that the SR decreased with an increase of the VP content in the SV hydrogel and more obviously decreased in the SVN hydrogels. The SVN networks also showed stronger shear moduli than SV hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of chitosan characteristics on the physicochemical properties,antibacterial activity,and cytotoxicity of chitosan/2‐glycerophosphate/nanosilver hydrogels

The effects of molecular weight (MW) and the degree of deacetylation (DD) of chitosan (CS) on the physicochemical properties, antibacterial activity, and cytotoxicity of CS/2‐glycerophosphate (GP)/nanosilver hydrogel in the development of a thermosensitive in situ formed wound dressing are examined herein. The gelation temperatures for the hydrogels were measured in the range of 32–37°C by manipulating the MW and DD of CS and the GP concentration. The structure of 88% DD CS hydrogel was more porous, uniform, and connective than that of the 80% DD CS hydrogel. The superior water vapor transmission rates of hydrogels with 80% and 88% DD CS were 7150 ± 52 and 9044 ± 221 gm^?2 d^?1, respectively. The skin permeations of nanosilver by the 80% and 88% DD CS hydrogels were 3.82 and 4.99 μg cm^?2, respectively, in 24 h tests. Both the hydrogels with 6 and 12 ppm nanosilver showed cytotoxicity for HS68 cells. The diameters of the hydrogel's inhibition zones for Pseudomonas aeruginosa and Staphylococcus aureus increased when the concentration of nanosilver increased and the MW of the CS decreased. Therefore, the hydrogel could be prepared with lower MW CS and lower concentration of nanosilver in order to reduce the cytotoxicity of nanosilver, while maintaining similar antibacterial activity for a hydrogel prepared with higher concentration nanosilver and higher MW CS. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Adsorption of methylene blue on hemicellulose‐based stimuli‐responsive porous hydrogel

A stimuli‐responsive porous hydrogel was synthesized from wheat straw hemicellulose using CaCO₃ as the porogen, and its application for the removal of methylene blue was studied. The porous structure of the prepared hydrogel was confirmed by SEM analysis. The effects of pH and polyelectrolyte on the swelling of the hydrogels were discussed, and the porous hydrogels showed excellent sensitivity to pH and salt. The deswelling kinetic study indicated that the hydrogels exhibited rapid shrinking in NaCl aqueous solutions. The methylene blue adsorption on the hydrogels was investigated, and the obtained adsorption data was fitted to the pseudo‐first‐order, pseudo‐second‐order and intra‐particle diffusion kinetics models, and the pseudo‐first‐order kinetic model could describe the adsorption process, and the adsorption process of methylene blue on the hydrogels was controlled by external film diffusion. This study reported that the hemicellulose‐based porous hydrogel is promising for water treatment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41606.     

A promising porous polymer-nanoclay hydrogel nanocomposite as water reservoir material: synthesis and kinetic study

A porous hydrogel nanocopmposite based on biodegradable salep and montmorillonite (MMT) was synthesized by in-situ free radical graft polymerization of salep chains with acrylic acid (AA) monomers. The chemical structure and morphological properties of the prepared hydrogels was evaluated by FTIR spectroscopy, X-ray diffraction and SEM techniques. The effect of reaction variables such as crosslinker, initiator, monomer and clay contents on equilibrium water absorption capacity and swelling kinetic of hydrogel were investigated and optimized. Swelling behavior of the hydrogels in various pH and saline solutions was also studied. Incorporation of MMT into hydrogel matrix caused the formation of porous hydrogel network. These porous structures resulted in higher water uptake capacity and swelling rate in hydrogel nanocomposite in comparison to neat hydrogel sample. Moreover, hydrogel nanocomposite sample exhibited proper salt and pH-sensitive behavior. High swelling capacity and rate, porosity, salt and pH sensitivity make hydrogel nanocomposite a profitable candidate in agricultural and horticultural applications, such as water reservoir system.     

Preparation and properties of PEG hydrogel from PEG macromonomer with sulfonate end group

A novel PEG macromonomer with methacryloyl and sulfonate group at each chain end was prepared, and new PEG‐based hydrogels were prepared by crosslinking polymerization of this PEG macromonomer in the presence of PEG dimethacrylate. Their swelling properties are measured and compared with those of reference hydrogel from methoxy PEG methacrylate to elucidate the effect of the sulfonate end group. The prepared sulfonated PEG hydrogels exhibited water absorbency in the range of 19 ～ 42 g water/g dry‐gel depending on the composition. These hydrogels with anionic sulfonate group showed swelling behavior varying with salt type, concentration, and also with pH of aqueous solution. The morphology of the sulfonated PEG gels by SEM showed irregular porous network structure varying with the composition. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 56–61, 2005     

Novel approach to highly porous superabsorbent hydrogels: synergistic effect of porogens on porosity and swelling rate

A novel practical strategy for preparing highly porous superabsorbent hydrogels (HPSHs) was invented. HPSHs were quantitatively prepared through an optimized rapid convenient solution polymerization of partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Acetone and sodium bicarbonate were used as porosity generators (porogens) during the polymerization process to create highly porous structures. Time and sequence of addition of the porogens, as well as the gelation time of the polymerization, were recognized to affect the efficiency of the porogens. Sodium bicarbonate produced the more porous hydrogels with a higher rate of swelling. In comparison with a hydrogel prepared under porogen‐free conditions (control), acetone and sodium bicarbonate enhanced the swelling rate as high as 43–55% and 111–131% of the control, respectively. When both the porogens were used consecutively in the process, a remarkable synergistic effect was observed in the swelling rate of the products. Nearly all the two‐porogen processes resulted in foamy products from the polymerization system. With the single‐porogen systems, however, the foam formation stage was observed only in a part of the total process time. The apparent volume of the as‐synthesized foamy products prepared from the two‐porogen system was more than that of the single‐porogen systems by up to fourfolds. Morphological studies using scanning electron microscopy (SEM) showed that the two‐porogen systems created highly porous structures. The density of all the HPSHs synthesized was about 1.5 g cm^?3 and no distinct differences were observed in their equilibrium swelling. These superabsorbent hydrogels exhibited a very high rate of swelling, so that their swelling time was measured to be less than one minute. Copyright © 2003 Society of Chemical Industry     

Synthesis and properties of radiation‐induced acrylamide–acrylic acid hydrogels

Acrylamide (AAm)/acrylic acid (AAc) hydrogels in the cylindirical form were prepared by γ‐irradiating binary systems of AAm/AAc with 2.6–20.0 kGy γ‐rays. The effect of the dose and relative amounts of AAc and pH on the swelling properties, diffusion behavior of water, diffusion coefficients, and network properties of hydrogel systems was investigated. The swelling capacities of AAm/AAc hydrogels were in the range of 1000–3000%, while poly(acrylamide) (PAAm) hydrogels swelled in the range of 450–700%. Water diffusion into hydrogels was found to be non‐Fickian‐type diffusion. Diffusion coefficients of AAm/AAc hydrogels were found between 0.79 × 10^?5 and 2.78 × 10^?5 cm² min^?1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3570–3580, 2002     

Novel superabsorbent materials from bacterial cellulose

A novel process for the production of superabsorbent materials (hydrogels) from bacterial cellulose (BC) was developed. Prior to crosslinking with a water‐soluble polyethylene glycol diacrylate (PEGDA), BC was first carboxymethylated and functionalized with glycidyl methacrylate. The degree of crosslinking influenced the swelling properties of the hydrogels. The use of greater amounts of PEGDA enhanced the formation of a thicker macromolecular network containing fewer capillary spaces in the crosslinked gel. The maximum water retention value of the hydrogels containing 2.5–3.5 mmol of carboxyl groups per gram of gel reached 125 g g^?1 in distilled water, and 29 g g^?1 in saline (0.9% NaCl solution). The highly porous hydrogel architecture with a pore size of 350–600 µm created a high specific surface area. This enables rapid mass penetration in superabsorbent applications. The superabsorbent hydrogels reached 80% of their maximum water absorption capacity in 30 min. © 2018 Society of Chemical Industry     

Preparation and swelling behaviors of porous hemicellulose‐g‐polyacrylamide hydrogels

Novel porous hydrogels were successfully synthesized from hemicelluloses (HCs) and acrylamide (Am) with poly(ethylene glycol) (PEG) as the porogen. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy (SEM). The results show that the used PEG was not involved in the formation process of the hydrogels, and the HC‐g‐polyacrylamide hydrogels displayed a higher thermal stability than the hemicellulosic polymer. SEM analysis confirmed that the prepared hydrogels had porous structures. The effects of the Am/HC ratio, the amount and molecular weight of PEG and the amount of the crosslinker N,N‐methylene bisacrylamide on the swelling ratio of the prepared hydrogels were investigated in detail. The experimental data were fitted with the exponential heuristic equation and the Schott second‐order dynamic equation. The diffusion of water molecules into the hydrogel network was found to be non‐Fickian in behavior, and the swelling kinetics could be described by the Schott second‐order dynamic equation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Swelling and dye sorption studies of AAm/SA hydrogels crosslinked by glutaraldehyde and divinylbenzene

Highly swollen acrylamide (AAm)/sodium acrylate (SA) hydrogels were prepared by free radical solution polymerization in aqueous solution of AAm with SA as comonomer and two multifunctional crosslinkers such as glutaraldehyde (GL) and divinylbenzene (DVB). Water absorption and percentage swelling were determined gravimetrically. The influence of SA content in hydrogels was examined. Percentage swelling ratio of AAm/SA hydrogels was increased up to 2946–12,533%, while AAm hydrogels swelled up to 1326–1618%. The values of equilibrium water content of the hydrogels are between 0.9297–0.9921. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Adsorption properties of AAm/SA hydrogels in aqueous thionin solution have been investigated. Finally, the amount of sorbed thionin per gram of dry hydrogel (q_e) was calculated to be 4.81 × 10^?6?11.69 × 10^?6 mol thionin per gram for hydrogels. Removal efficiency (RE%) of the AAm/SA hydrogels was changed range 37.03–68.82%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

pH sensitivity and swelling behavior of partially hydrolyzed formaldehyde-crosslinked poly(acrylamide) superabsorbent hydrogels

Poly(acrylamide) superabsorbent hydrogel was synthesized through crosslinking method. Formaldehyde was used as a crosslinking agent. To achieve a hydrogel with high swelling capacity, the resulted hydrogels were saponified using NaOH solution at high temperature. During saponification, ammonia gas is produced from hydrolysis reaction of amide groups. The arising of ammonia produces porous structure in hydrogels, which is confirmed using scanning electron microscopy. The conversion of amide groups to carboxylate groups was identified by FTIR spectroscopy. The reaction variables in both crosslinking and hydrolysis reactions that affect the swelling of hydrogels were optimized. The swelling of the hydrogels in various salt solutions with various valencies and radii was studied. Also, the absorbency under load was measured. The hydrogels exhibited pH-sensitivity characteristics. A sharp swelling change was observed in lieu of pH variations in a wide range (1–13). The swelling variations were explained according to the swelling theory based on the hydrogel chemical structure. The pH-reversibility and on–off switching behavior makes the intelligent hydrogels as good candidates for considering as potential drug carries. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of biodegradable hydrogels of κ-carrageenan grafted acrylic acid-co-2-acrylamido-2-methylpropanesulfonic acid as candidates for drug delivery systems

Novel types of highly swelling hydrogels were prepared by grafting crosslinked polyacrylic acid-co-poly-2-acrylamido-2-methylpropanesulfonic acid (PAA-co-PAMPS) chains onto κ-carrageenan through a free radical polymerization method. Here, we propose a mechanism for κ-carrageenan-g-PAA-co-PAMPS formation and confirm the hydrogel structure using FTIR spectroscopy. The effect of grafting variables (i.e. concentration of methylenebisacrylamide (MBA), acrylic acid/-2-acrylamido-2-methylpropanesulfonic acid (AA/AMPS) weight ratio, ammonium persulfate (APS), κ-carrageenan, neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with a maximum swelling capacity. The maximum water absorbency of the optimized final product was 1238 g/g, while poly-2-acrylamido-2-methylpropanesulfonic acid-g-κ-carrageenan and polyacrylic acid-g-κ-carrageenan hydrogels swelled to a range of 135–800 g/g. The swelling of superabsorbent hydrogels was measured in various solutions with pH values ranging from 1 to 13. In addition, the pH reversibility, on–off switching behavior and swelling kinetics in distilled water were preliminarily investigated.     

Conductive double-network hydrogel for a highly conductive anti-fatigue flexible sensor

Improving the mechanical properties of hydrogels is a prime example of their large-scale, diverse applications. Herein, we report a one-pot method for preparing a double network system hydrogel where the polyvinyl alcohol served as the first polymer backbone, acrylamide as the second network, and N, N′-Methylenebisacrylamide as the cross-linker, and the prepared hydrogels presented excellent mechanical properties with 1168% tensile strain and 598 kPa compressive strength. Through the metal–ligand bonds, an electrolyte solution containing Cu²⁺ was introduced into the hydrogel, which exhibits higher water retention than other electrolyte-containing hydrogels. Specially, the hydrogel was able to retain water for 8 h under extreme dry conditions at 60°C. The GF value was calculated to be 0.124 when the strain was 0%–64.2%. Furthermore, the hydrogel flexible sensor can detect changes in ambient temperature. When the ambient temperature rises, its relative resistance also tends to rise. In conclusion, this hydrogel sensor offers great potential applications in flexible sensors.     

Fluconazole release through semi‐interpenetrating polymer network hydrogels based on chitosan,acrylic acid,and citraconic acid

Semi‐interpenetrating polymer network hydrogels with different compositions of chitosan (Cs), acrylic acid, and citraconic acid were synthesized via free‐radical polymerization with ethylene glycol dimethacrylate as a crosslinker. The variations of the swelling percentages of the hydrogels with time, temperature, and pH were determined, and Cs–poly(acrylic acid) (PAA) hydrogels were found to be most swollen at pH 7.4 and 37°C. Scanning electron micrographs of Cs–PAA and Cs–P(AA‐co‐CA)‐1 (Cs‐poly(acrylicacid‐co‐citraconir acid)^?1) were taken to observe the morphological differences in the hydrogels. Although the less swollen hydrogel, Cs–P(AA‐co‐CA)‐1, had a sponge‐type structure, the most swollen hydrogel, Cs–PAA, displayed a uniform porous appearance. Fluconazole was entrapped in Cs–P(AA‐co‐CA)‐1 and Cs–PAA hydrogels, and the release was investigated at pH 4.0 and 37°C. The kinetic release parameters of the hydrogels (the gel characteristic constant and the swelling exponent) were calculated, and non‐Fickian diffusion was established for Cs–PAA, which released fluconazole much more slowly than the Cs–P(AA‐co‐CA)‐1 hydrogel. A therapeutic range was reached at close to 1 h for both hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electroresponsive and spinnable hydrogels from xanthan gum and gelatin enhanced by Fe3+ ions coordination

Polyelectrolyte hydrogels with spinnability and electroresponsive were prepared from xanthan gum (XG) and gelatin. Oscillatory rheological measurements were utilized to explore mechanical properties and thermal stability of the resultant XG-Gelatin5 hydrogels. The XG-Gelatin5 hydrogels possessed higher strength and larger critical strain than these of the XG hydrogels, demonstrating existence of synergistic interactions. The XG-Gelatin5 hydrogels were stable in temperature range of 20–60°C, and gradually release drug with controlled manner in neutral and acid medium at 37°C. The self-recoverable and thixotropic XG-Gelatin5 hydrogels were extruded to form hydrogel fibers, and the dried hydrogel fibers rapidly bend towards cathode under applied voltage. Long hydrogel fibers were harvested with enhancement by Fe³⁺ ions, and were weaved and braided to obtain hydrogel fiber constructs. The XG-Gelatin5 hydrogel fibers with electroresponsive and controlled drug release possess potential applications in biomaterials, tissue engineering, and drug carrier fields.     

Preparation and Characterization of Porous Poly (N-isopropylacrylamide) /Clay Nanocomposite Hydrogels

Summary  A novel porous PNIPA/Clay nanocomposite hydrogel (NC hydrogel) was prepared by in situ free-radical polymerization using inorganic clay as a crosslinker and calcium carbonate (CaCO₃) particle as a pore-forming agent and subsequent extraction of CaCO₃ with acid. The structure and morphology of the hydrogels were characterized by means of FTIR, TEM and SEM. The temperature responsive behaviors, the deswelling behaviors and the mechanical properties of the NC hydrogels were investigated in detail. The results showed that the swelling ratios below VPTT and the deswelling rates of the NC hydrogels were significantly improved as compared with the hydrogels without introduction of CaCO₃. Moreover, the NC hydrogels thus prepared also exhibited good mechanical properties.     

Novel metronidazole-loaded hydrogel as a gastroretentive drug delivery system

A metronidazole-loaded hydrogel was synthesized by free radical polymerization using dimethylaminoethyl methacrylate (DMAEMA) monomer and triethyleneglycol dimethacrylate (TEGDA) and methylene bisacrylamide (MBA) as cross-linkers. The DMAEMA hydrogels were cross-linked with 5 and 10% MBA or with 0.1, 0.5, 1 and 4% TEGDA as cross-linking agents. Ammonium persulfate and tetramethyl ethylene diamine were used as initiator and catalyst, respectively. The prepared hydrogels were characterized, and the effect of cross-linking agent content on the swelling behavior and in vitro drug release of hydrogels was investigated. The results of X-ray diffractometry, differential scanning calorimetry and Fourier transform infrared spectroscopy studies indicated that the prepared hydrogels possessed an amorphous morphology and there was not any interaction between the hydrogel polymers and metronidazole as drug, which resulted in the dependence of drug release on the physicochemical characteristics of hydrogel such as swelling, polymer erosion, and surface morphology. According to the results, the hydrogel containing 0.5% TEGDA which was prepared by freeze-drying method exhibited a porous structure with a high swelling ratio and displayed a sustained and complete drug release. It could be concluded that the hydrogel developed by this facile method is a good candidate with a potential for use in gastroretentive drug delivery systems.     

Preparation and swelling behavior of biodegradable hydrogels based on α,β‐poly(N‐2‐hydroxyethyl‐DL‐aspartamide)

Biodegradable polymers and the hydrogels have been increasingly applied in a variety of biomedical fields and pharmaceutics. α,β‐Poly(N‐2‐hydroxyethyl‐DL ‐aspartamide), PHEA, one of poly(amino acid)s with hydroxyethyl pendants, are known to be biodegradable and biocompatible, and has been studied as an useful biomaterial, especially for drug delivery, via appropriate structural modification. In this work, hydrogels based on PHEA were prepared by two‐step reaction, that is, the crosslinking of polysuccinimide, the precursor polymer, with oligomeric PEG or PEI‐diamines and the following nucleophilic ring‐opening reaction by ethanolamine. Soft hydrogels possessing varying degrees of gel strength could be prepared easily, depending on the amount of different crosslinking reagents. The swelling degrees, which were in the range of 10–40 g–water/dry gel, increased somewhat at higher temperature, and also at alkaline pH of aqueous solution. A typical hydrogel remained almost unchanged for 1 week, at 37°C in phosphate buffer of pH 7.4, and then seemed to degrade slowly as time. A porous scaffold could be fabricated by the freeze drying of water‐swollen gel. The PHEA‐based hydrogels have potential for useful biomaterial applications including current drug delivery system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3741–3746, 2003     

Sustained delivery of hydrocortisone acetate by CS/N‐vinyl‐2‐pyrrolidone/CaCO3 microparticle hybrid hydrogels

The goal of this research is to develop a composite hydrogel system for sustained release of therapeutic agents. The hybrid hydrogels were prepared by radiation crosslinking on aqueous solution of Chitosan (CS)/N‐vinyl‐2‐pyrrolidone (NVP) with different loads of CaCO₃ in the presence of hydrocortisone acetate (HCA), an anti‐inflammatory drugs. Physical characteristics of CS/NVP/CaCO₃ were studied using X‐ray diffraction (XRD) and infrared spectrophotometery (IR). The porous structure of resulted hydrogel was confirmed by SEM micrographs. The effect of doses and calcium carbonate amount on the swelling of the hydrogels was investigated. The ability of the prepared CS/NVP/CaCO₃‐based hybrid hydrogels to be used as drug carriers for anti‐inflammatory‐specific drug delivery system was estimated using HCA as a model drug. POLYM. COMPOS., 35:1176–1183, 2014. © 2013 Society of Plastics Engineers     

Gelatin based pH‐sensitive hydrogels for colon‐specific oral drug delivery: Synthesis,characterization, and in vitro release study

Based on gelatin (Gltn) and acrylic acid (AAc), biodegradable pH‐sensitive hydrogel was prepared using gamma radiation as super clean source for polymerization and crosslinking. Incorporation of PAAc in the prepared hydrogel was confirmed by Fourier transform infrared spectroscopy (FTIR). The effect of PAAc content on the morphological structure of the prepared hydrogel swollen at pH 1, 5, and 7 was examined using scanning electron microscopy (SEM). The results showed the dependence of the porous structure of the prepared hydrogels on AAc content and the pH of the swelling medium. Swelling properties of gelatin/acrylic acid copolymer hydrogels with different AAc contents were investigated at different pH values. Swelling data showed that the prepared hydrogels possessed pronounced pH sensitivity. In vitro release studies were performed to evaluate the hydrogel potential as drug carrier using ketoprofen as a model drug. Experimental data showed that the release profile depends on both hydrogel composition and pH of the releasing medium. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010