Swelling behavior and biocompatibility of Carbopol‐containing superporous hydrogel composites

Carbopol‐containing superporous hydrogel composites (SPHCc) with fast swelling and high swelling ratio were prepared using free radical copolymerization. Swelling behavior of the SPHCc was studied in various salt and pH solutions and their biocompatibility was evaluated using tissue damage and cytotoxicity studies. The swelling ratio of the SPHCc decreased with the increase of Carbopol/monomer ratio and was sensitive to pH and ionic strength of the swelling medium. The release of insulin from the SPHCc was rapid in 0.01M phosphate buffered saline (PBS, pH 7.4). In the jejunum mucosal membrane toxicity studies in rat, no significant morphological damage was observed after application of SPHCc. Besides, no damage of the Caco‐2 monolayers was detected after incubation with SPHCc in the trypan blue and propidium iodide tests. On the basis of these results, it was concluded that the SPHCc might be a safe and effective carrier for peroral delivery of peptide and protein drugs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

CPE／P（AA-HEMA）吸水膨胀弹性体共混体系的性能研究

采用机械共混将氯化聚乙烯（CPE）、增容剂CPE接枝甲基丙烯酸-β-羟乙（CPE—g—HE—MA）与自制的吸水树脂甲基丙烯酸-甲基丙烯酸-口-羟乙酯共聚N[-P（AA—HEMA）]共混合成了CPE／P（AA—HEMA）／（CPE—g—HEMA）吸水膨胀弹性体。讨论比较了未添加和添加增容剂CPE—g—HEMA2种共混体系的吸水性能（吸水率、吸盐水率和质量损失率）。     

Reswelling behavior of polycation hydrogels carrying charges on the chain backbone by two‐step surfactant bindings

Chemically crosslinked polycations carrying charges on the chain backbone, that is, x,y‐ionene hydrogels (x = 2 or 6, y = 3 or 6), were successfully synthesized, and their swelling and surfactant binding behaviors were studied. A two‐step surfactant binding that produced swollen, complex hydrogels occurred for ionene hydrogels with a lower charge density. The reswelling of the hydrogels was associated with an excessive amount of surfactant binding, which mainly occurred through a hydrophobic interaction with a one‐to‐one complex. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3791–3794, 2006     

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     

Ionization‐induced ultrarapid response behavior of fibrous and porous electrospun hydrogels containing carboxyl groups

Fibrous porous membranes composed of poly(N‐isopropylacrylamide‐co‐acrylic acid) and poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) were prepared by electrospinning. The membranes behaved like hydrogels in water after being crosslinked at elevated temperatures. Investigations of the swelling and deswelling behavior indicated that the response rates significantly increased after the carboxyl and/or anhydride groups in the hydrogel membranes were ionized or neutralized with NaOH. It took them less than 60 s to reach equilibrium swelling and about 90 s to reach equilibrium deswelling. The response rates were much higher than those of the parent un‐ionized membranes; this indicated that ionization played an important role in the ultrarapid response behavior. The response rate was also higher than that of most hydrogel materials previously reported and was even comparable to superporous hydrogels with high moisture contents. The mechanism of the ultrarapid response behavior of the ionized membranes was qualitatively analyzed. We believe that the fine fiber diameter, high porosity, and improved wettability with water contributed to the ultrarapid response behavior. This study presents a new and facile method for improving the response rate of hydrogel materials made by electrospinning. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Swelling behavior of thermoreversible poly(N‐isopropylacrylamide‐co‐N‐vinylimidazole) hydrogels

Thermoresponsive hydrogels based on N‐isopropylacrylamide and N‐vinylimidazole were synthesized, and their swelling–deswelling behavior was studied as a function of the total monomer concentration. For copolymeric structures with better thermoresponsive properties with respect to poly(N‐isopropylacrylamide‐co‐N‐vinylimidazole) hydrogels, these hydrogels were protonated with HCl and HNO₃, and the copolymer behaviors were compared with those of the unprotonated hydrogels. The temperature was changed from 4 to 70°C at fixed pHs and total ionic strengths. The equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all the hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1619–1624, 2004     

Swelling behavior and diffusion studies of high‐water‐retaining acrylamide/potassium methacrylate hydrogels

Poly(acrylamide‐co‐potassium methacrylate) hydrogels were prepared by free‐radical simultaneous polymerization with aqueous solutions of acrylamide (AAm) and potassium methacrylate (KMA) with a redox initiator. The copolymerization was performed with eight different compositions of KMA at a fixed concentration of oil‐soluble crosslinkers, including 1,4‐butanediol diacrylate and ethylene glycol dimethacrylate (EGDMA). For every composition of AAm/KMA copolymer, the percentage swelling, swelling equilibrium, and diffusion characteristics were investigated. The copolymers were further studied for deswelling properties. The power law relationships of the hydrogels were evaluated for variation in terms of saline concentration. The AAm/KMA copolymers were confirmed by IR spectroscopy. Thermal studies of hydrogels were performed with differential scanning calorimetry and thermogravimetric analysis. EGDMA was found to be a better crosslinker for obtaining higher swelling and deswelling properties for the AAm/KMA hydrogels. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1153–1164, 2005     

Equilibrium swelling behavior and elastic properties of polymer–clay nanocomposite hydrogels

Nanocomposite hydrogels were prepared by free‐radical polymerization of the monomers acrylamide (AAm), N,N‐dimethylacrylamide (DMA), and N‐isopropylacrylamide (NIPA) in aqueous clay dispersions at 21°C. Laponite XLS was used as clay nanoparticles in the hydrogel preparation. The hydrogels based on DMA or NIPA monomers exhibit much larger moduli of elasticity compared with the hydrogels based on AAm monomer. Calculations using the theory of rubber elasticity reveal that, in DMA‐clay or NIPA‐clay nanocomposites, both the effective crosslink density of the hydrogels and the functionality of the clay particles rapidly increase with increasing amount of Laponite up to 10% (w/v). The results suggest that DMA‐clay and NIPA‐clay attractive interactions are stronger than AAm‐clay interactions due to the formation of multiple layers on the nanoparticles through hydrophobic associations. It was also shown that, although the nanocomposite hydrogels do not dissolve in good solvents such as water, they dissolve in dilute aqueous solutions of acetone or poly(ethylene oxide) of molecular weight 10,000 g/mol, demonstrating the physical nature of the crosslink points. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of super‐absorbent hydrogels based on hemicellulose

A kind of novel hemicellulose‐based hydrogel with excellent water absorbency was synthesized by the graft copolymerization of acrylic acid (AA), acrylic amide (AM) with hemicellulose. The various factors that influenced the water absorbency of the modified hemicellulose were studied, including AA content, hemicellulose content, neutralization degree of AA, and weight ratio (to monomer) of cross‐linker and initiator. The optimal conditions were found as follows: m(AA) : m(AM) : m(hemicellulose) = 15 : 3.5 : 1, the neutralization degree of AA was 75%, and weight ratio (to monomers) of the cross‐linker and the initiator was 0.03% and 1.0%, respectively. The maximum absorbencies toward distilled water and 0.9 wt % NaCl solution were 1128 g/g and 132 g/g, respectively. The characteristics of the hydrogels were also investigated by Fourier Transform InfraRed (FT‐IR), scanning electron microscope (SEM), and atomic force microscope (AFM). The results indicated that the undulant surface and broad network structure offer the hydrogels excellent water absorbency. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42441.     

Swelling behavior of protein-based superabsorbent hydrogels treated with ethanol

A fish protein-based superabsorbent hydrogel has been synthesized by modifying 80% of the ϵ-amino groups of the protein with ethylenediaminetetraacetic dianhydride followed by crosslinking the remaining ϵ-amino groups with glutaraldehyde. The hydrogel thus prepared was capable of absorbing about 200 g water per g dry gel after centrifuging at 214g. Denaturation of the gel by treatment with absolute ethanol increased the equilibrium water uptake of the gel from 200 to 425 g water per g of dry gel. The saline uptake of the gel also increased from 24 g saline (0.1M NaCl) for the control gel to 35 g saline per g dry gel for the ethanol-treated gel. Analysis of the structural state of protein chains in the crosslinked swollen gel network using circular dichroism spectroscopy showed that, whereas the protein chains in the control gel were predominantly in β-turn form, those in the ethanol-treated sample were mainly in the α-helical form. In addition to improving the swelling properties, the ethanol treatment offered the following advantages: 1. It dehydrated the gel and thereby eliminated the need for drying the gel. 2. It extracted low molecular weight off-odor compounds from the protein gel. 3. It could also extract any residual unreacted glutaraldehyde (believed to be carcinogenic) that might be present in the gel. The ethanol used in the process can be easily recovered and recycled in the process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2190–2196, 2001     

Novel hydrogels based on itaconic acid and citraconic acid: Synthesis,metal ion binding,and swelling behavior

Several copolymer hydrogels were prepared from radical copolymerization of 2‐hydroxypropyl methacrylate (HPMA) with itaconic acid (IA) and also with citraconic acid (CA) by using different feed ratios. The copolymers were characterized by FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopy as well as by thermal analysis. The swelling process of the different hydrogels immersed in water at different pH has been studied, and also the swelling of the hydrogels loaded with metal ions (Pb²⁺, Cd²⁺) was investigated. The metal‐binding properties were studied by using the liquid‐phase polymer‐based retention technique, including studies on the influence of pH on the binding process. The efficiency of these hydrogels for the recovery of metal ions in solution was determined by atomic absorption spectroscopic analysis. The thermal characteristics of these copolymers were studied by using differential scanning calorimetry and thermogravimetric analysis in nitrogen atmosphere. Accordingly, the gels loaded with metal ions showed a slight increase of the thermal decomposition temperature when compared with the pristine gels. The copolymer gel HPMA‐co‐CA showed a single glass transition temperature, whereas for the copolymer systems, HPMA‐co‐IA, only the copolymers loaded with Cd²⁺ ions showed a glass transition temperature. The morphology of film produced from the copolymers was investigated by scanning electron microscopy, revealing generally smooth surfaces. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

遇水膨胀橡胶的吸水膨胀和力学性能研究

以天然橡胶和吸水树脂（聚丙烯酸钠）为主要原料，以含聚氧化乙烯嵌段的亲水亲油型多嵌段共聚物为增容剂，活性陶土为补强剂，利用多组分机械共混技术，制备了遇水膨胀橡胶，从吸水动力学数据出发，研究了重量吸水率与增容剂含量，吸水树脂含量之间的关系；对遇水膨胀橡胶吸水前后的力学性能进行了测试。结果表明，增容剂的加入能显著改变遇水膨胀橡胶的吸水性能和力学性能。     

Novel biodegradable superabsorbent hydrogels derived from cotton cellulose and succinic anhydride: Synthesis and characterization

The synthesis of novel superabsorbent hydrogels was investigated with the reaction of cotton cellulose and succinic anhydride (SA) in the presence of 4‐dimethylaminopyridine as an esterification catalyst in a mixture of lithium chloride (LiCl) and N‐methyl‐2‐pyrrolidinone (NMP) or in a mixture of tetrabutylammonium fluoride (TBAF) and dimethyl sulfoxide (DMSO), followed by NaOH neutralization. Interestingly, a hydrogel was obtained without any crosslinking agent, and this indicated the partial formation of a diester between the cellulosic hydroxyl group and SA. The products obtained in LiCl/NMP exhibited superior absorbency to these obtained in TBAF/DMSO. The former absorbed an amount of water about 400 times its dry weight, and this was comparable to a conventional sodium polyacrylate superabsorbent hydrogel. Furthermore, in an aqueous NaCl solution, the absorbency of the product hydrogels was higher than that of the sodium polyacrylate superabsorbent hydrogel. The formed hydrogels biologically degraded almost completely after 25 days, and this showed their excellent biodegradability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3251–3256, 2006     

Synthesis and characterization of hydroxyethyl methacrylate/acrylamide responsive hydrogels

Hydrogels based on an aqueous solution of hydroxyethyl methacrylate (HEMA) and acrylamide (AM) in the presence of trithioglycolic acid (TTGA) were prepared under the effect of gamma irradiation. These hydrogels were characterized by IR spectroscopy and thermogravimetric analysis and investigated for temperature‐ and pH‐responsive materials. It was found that TTGA is essential for the formation of HEMA/AM hydrogels at different compositions, in which the gel fraction depends on composition. A binary mixture of HEMA and AM at equal ratios was the critical composition that forms hydrogels, even in the presence of TTGA. The IR spectroscopic analysis showed that the formation of hydrogels depends on hydrogen bonding and crosslinking. The TGA investigations with respect to mass loss and the temperatures of the maximum value of the rate of reaction showed that HEMA/AM hydrogels possess higher thermal stability than that of pure HEMA and this stability increases with increasing ratio of the AM component. Also, it was observed that the temperature of the maximum value of the rate of thermal decomposition reaction depends on hydrogel composition. However, calculations of the activation energy showed that the hydrogel composed of 90% HEMA and 10% AM exhibits the highest thermal stability during the increasing or decreasing rate of reaction. Kinetic studies of swelling in water showed that HEMA/AM hydrogels displayed a temperature‐responsive character within the temperature range 25–30°C, and showed a stepwise swelling behavior in the pH range 2–10, depending on composition. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1105–1115, 2005     

Swelling behavior and structural characteristics of polyvinyl alcohol/montmorillonite nanocomposite hydrogels

A series of nanocomposite hydrogels based on polyvinyl alcohol containing 0–10 wt % of the organically modified montmorillonite clay were prepared by freezing‐thawing cyclic method. The morphology of the nanocomposite hydrogels was observed by the scanning electron microscopy technique. The structural properties were determined by measuring the network mesh size, crosslinking density, and average molecular weight of polymer chains between crosslinks. The swelling behavior and the effect of swelling medium temperature on the swelling kinetics and characteristics of the nanocomposite hydrogels were also investigated. The results showed that two structural characteristics i.e., network mesh size and average molecular weight of polymer chains between crosslinks have inverse dependence on the clay loading level in the nanocomposite hydrogel, while crosslinking density shows completely direct dependence. Swelling measurements demonstrated a linear relation between the degree of swelling and the square root of immersion time at all swelling medium temperatures. The results indicated that the swelling characteristics of the nanocomposite hydrogels including the equilibrium degree of weight and volume swelling and the equilibrium water content were decreased by increasing the quantity of the clay incorporated into the hydrogel as well as by decreasing the temperature of swelling medium. While, the time required to reach to the equilibrium condition, as another swelling characteristic of the hydrogels, exhibited a completely opposite behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Swelling behavior of hydrogels for colon‐site drug delivery

Hydrogels based on n‐alkyl methacrylate esters (n‐AMA), acrylic acid, and acrylamide crosslinked with 4,4′‐di(methacryloylamino)azobenzene were prepared. Swelling behavior of the hydrogels was studied by the immersion of slabs in buffered solutions at pH 2.2–7.4. The diffusion of water into the slabs was discussed on the stress relaxation model of polymer chains. The results obtained are in good agreement with Schott's second‐order diffusion kinetics. The constants A and B of Schott's kinetics equation depend on the balance of hydrophobicity/hydrophilicity, the rigidity/flexibility, and the degree of crosslinking. The factors that exert the greatest influence on the swelling behavior of the gels include the degree of crosslinking, the lengths of the n‐AMA side chains, and pH values. By adjusting these factors, the degree of swelling of the hydrogels in the small intestine can be controlled, and consequently the drugs may avoid being released before arriving in the colon. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2835–2842, 2002; DOI 10.1002/app.10259     

Synthesis of poly(acrylamide‐co‐4‐vinylpyridine) hydrogels and their application in heavy metal removal

A series of poly(acrylamide‐co‐4‐vinylpyridine) hydrogels having varied acrylamide/4‐vinylpyridine content and different crosslink ratios of N,N′‐methylene‐bisacrylamide was prepared by using solution polymerization. The prepared hydrogel polymers were characterized by their elemental analysis, infrared spectroscopy, and equilibrium water content. The polymers were investigated toward metal ion uptake of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The polymers were more sensitive to Cu(II) and Ni(II) and the order of metal ion binding was Ni(II), Cu(II) > Zn(II) > Co(II) > Mn(II). Metal ion uptake by the polymers was reduced as the pH of the medium decreased. Recycling of the resins resulted in high recovery of the metal ions from their aqueous solutions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2522–2526, 2003     

Swelling behavior and determination of diffusion characteristics of acrylamide–acrylic acid hydrogels

In this study, a random copolymer of acylamide and acrylic acid [poly(AAm‐co‐AA)] was prepared by a redox copolymerization method of their aqueous solutions. The effects of initial AAm/AA mole ratio, PEG 4000 content, and N,N′‐methylenebisacrylamide concentration on swelling behavior were investigated in water. Average molecular weights between crosslinks, percentage swelling, swelling equilibrium values, and diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant) were evaluated for every hydrogel systems. The hydrogels showed mass swelling capabilities in the range 789–1040% (for AAm/AA hydrogels), 769–930% (for AAm/AA hydrogels in the presence of PEG 4000), and 716–1040% (for AAm/AA hydrogels containing different concentrations of the crosslinker). The swelling capabilities of the hydrogels decreased with the increasing AA, PEG 4000, and crosslinker concentrations. The diffusion of water into AAm/AA hydrogels was found to be a non‐Fickian type. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1289–1293, 2004     

Preparation of polyacrylamide hydrogels at various charge densities by postmodification

In this study, first polyacrylamide hydrogels were synthesized by free‐radical crosslinking polymerization of acrylamide monomer with N,N′‐methylenebis(acrylamide) as a crosslinker in an aqueous solution at 22°C. Then, a series of hydrogels at various charge densities were prepared by partial hydrolysis of polyacrylamide precursors in a 0.1M sodium hydroxide solution at 60°C. The hydrolysis time was varied between 20 and 180 min. The chemical structures and internal morphologies of the hydrogels before and after alkaline hydrolysis were characterized with attenuated total reflectance/Fourier transform infrared and scanning electron microscopy measurements. The swelling ratio of the hydrolyzed hydrogels was measured in buffer solutions at various pHs. From differential curves of dQ_v/dpH versus pH (where Q_v is the equilibrium swelling ratio of the hydrogels), the volume phase transition pH of the hydrogels was found to be 4.33 ± 0.05, regardless of the charge density of the hydrogels. In water at 22°C, the hydrogels with greater charge density showed a more rapid swelling rate because of their higher porosity and hydrophilicity. Moreover, in buffer solutions with the pH changing from 9.0 to 2.0 at 22°C, the hydrogels with greater charge density also exhibited a more rapid deswelling rate than the hydrogels with less charge density. In conclusion, the postmodification method is a good way of preparing pH‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009