Nonionic Hydrogels Research Articles

Jute Stick-Derived Cellulose-Based Hydrogel: Synthesis, Characterization, and Methylene Blue Removal from Aqueous Solution.

In this work, microcrystalline cellulose (MCC) was isolated from jute sticks and sodium carboxymethyl cellulose (Na-CMC) was synthesized from the isolated MCC. Na-CMC is an anionic derivative of microcrystalline cellulose. The microcrystalline cellulose-based hydrogel (MCCH) and Na-CMC-based hydrogel (Na-CMCH) were prepared by using epichlorohydrin (ECH) as a crosslinker by a chemical crosslinking method. The isolated MCC, synthesized Na-CMC, and corresponding hydrogels were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electronic microscopy (SEM), and energy dispersive spectroscopy (EDS) for functional groups, crystallinity, surface morphology, and composite elemental composition, respectively. Pseudo-first-order, pseudo-second-order, and Elovich models were used to investigate the adsorption kinetics. The pseudo-second-order one is favorable for both hydrogels. Freundlich, Langmuir, and Temkin adsorption isotherm models were investigated. MCCH follows the Freundlich model (R2 = 0.9967), and Na-CMCH follows the Langmuir isotherm model (R2 = 0.9974). The methylene blue (MB) dye adsorption capacities of ionic (Na-CMCH) and nonionic (MCCH) hydrogels in different contact times (up to 600 min), initial concentrations (10-50 ppm), and temperatures (298-318 K) were investigated and compared. The maximum adsorption capacity of MCCH and Na-CMCH was 23.73 and 196.46 mg/g, respectively, and the removal efficiency of MB was determined to be 26.93% for MCCH and 58.73% for Na-CMCH. The Na-CMCH efficiently removed the MB from aqueous solutions as well as spiked industrial wastewater. The Na-CMCH also remarkably efficiently reduced priority metal ions from an industrial effluent. An effort has been made to utilize inexpensive, readily available, and environmentally friendly waste materials (jute sticks) to synthesize valuable adsorbent materials.

A Facilely Prepared Adhesive Dressing Derived from Non-Ionic Hydrogel for Accelerated Diabetic Wound Healing

Hydrogels are an important category of polymeric materials with physicochemical features such as moisturizability and biocompatibility that are ideal for developing dressings for diabetic wounds. However, conventional non-ionic hydrogel materials generally exhibit poor mechanical properties and poor adhesion, which compromise their ability to self-sustain in mechanically dynamic wound microenvironments. In this research, we developed a hybrid hydrogel as a highly biocompatible adhesive wound dressing that met the mechanical requirements of the skin to promote chronic wound healing in diabetic mouse models. A 7.5% (w/v) hydrogel corresponded to a Young’s modulus of 6.3 kPa. In vitro cell-based and subcutaneous implantation experiments in mice demonstrated the excellent biocompatibility and optimal biodegradability of hydrogel dressings. In a diabetic mouse splint wound model for evaluating wound healing in vivo, the hydrogel dressing showed robust adhesion to the wound and efficiently accommodated mechanical deformations around the wound, resulting in significantly improved healing rates of chronic diabetic wounds. Thus, our work illustrates a newly alternative strategy for the simple and efficacious treatment of chronic wounds in the context of diabetes care.

Utilizing the Hofmeister Effect to Induce Hydrogelation of Nonionic Supramolecular Polymers into a Therapeutic Depot

AbstractNonionic hydrogels are of particular interest for long‐term therapeutic implantation due to their minimal immunogenicity relative to their charged counterparts. However, in situ formation of nonionic supramolecular hydrogels under physiological conditions has been a challenging task. In this context, we report on our discovery of salt‐triggered hydrogelation of nonionic supramolecular polymers (SPs) formed by self‐assembling prodrug hydrogelators (SAPHs) through the Hofmeister effect. The designed SAPHs consist of two SN‐38 units, which is an active metabolite of the anticancer drug irinotecan, and a short peptide grafted with two or four oligoethylene glycol (OEG) segments. Upon self‐assembly in water, the resultant nonionic SPs can be triggered to gel upon addition of phosphate salts. Our 1H NMR studies revealed that the added phosphates led to a change in the chemical shift of the methylene protons, suggestive of a disruption of the water‐ether hydrogen bonds and consequent reorganization of the hydration shell surrounding the SPs. This deshielding effect, commensurate with the amount of salt added, likely promoted associative interactions among the SAPH filaments to percolate into a 3D network. The formed hydrogels exhibited a sustained release profile of SN‐38 hydrogelator that acted potently against cancer cells.

Utilizing the Hofmeister Effect to Induce Hydrogelation of Nonionic Supramolecular Polymers into a Therapeutic Depot.

Nonionic hydrogels are of particular interest for long-term therapeutic implantation due to their minimal immunogenicity relative to their charged counterparts. However, in situ formation of nonionic supramolecular hydrogels under physiological conditions has been a challenging task. In this context, we report on our discovery of salt-triggered hydrogelation of nonionic supramolecular polymers (SPs) formed by self-assembling prodrug hydrogelators (SAPHs) through the Hofmeister effect. The designed SAPHs consist of two SN-38 units, which is an active metabolite of the anticancer drug irinotecan, and a short peptide grafted with two or four oligoethylene glycol (OEG) segments. Upon self-assembly in water, the resultant nonionic SPs can be triggered to gel upon addition of phosphate salts. Our 1 H NMR studies revealed that the added phosphates led to a change in the chemical shift of the methylene protons, suggestive of a disruption of the water-ether hydrogen bonds and consequent reorganization of the hydration shell surrounding the SPs. This deshielding effect, commensurate with the amount of salt added, likely promoted associative interactions among the SAPH filaments to percolate into a 3D network. The formed hydrogels exhibited a sustained release profile of SN-38 hydrogelator that acted potently against cancer cells.

Force-induced ion generation in zwitterionic hydrogels for a sensitive silent-speech sensor

Human-sensitive mechanosensation depends on ionic currents controlled by skin mechanoreceptors. Inspired by the sensory behavior of skin, we investigate zwitterionic hydrogels that generate ions under an applied force in a mobile-ion-free system. Within this system, water dissociates as the distance between zwitterions reduces under an applied pressure. Meanwhile, zwitterionic segments can provide migration channels for the generated ions, significantly facilitating ion transport. These combined effects endow a mobile-ion-free zwitterionic skin sensor with sensitive transduction of pressure into ionic currents, achieving a sensitivity up to five times that of nonionic hydrogels. The signal response time, which relies on the crosslinking degree of the zwitterionic hydrogel, was ~38 ms, comparable to that of natural skin. The skin sensor was incorporated into a universal throat-worn silent-speech recognition system that transforms the tiny signals of laryngeal mechanical vibrations into silent speech.

Re-Entrant Conformation Transition in Hydrogels.

Hydrogels are attractive materials not only for their tremendous applications but also for theoretical studies as they provide macroscopic monitoring of the conformation change of polymer chains. The pioneering theoretical work of Dusek predicting the discontinuous volume phase transition in gels followed by the experimental observation of Tanaka opened up a new area, called smart hydrogels, in the gel science. Many ionic hydrogels exhibit a discontinuous volume phase transition due to the change of the polymer–solvent interaction parameter χ depending on the external stimuli such as temperature, pH, composition of the solvent, etc. The observation of a discontinuous volume phase transition in nonionic hydrogels or organogels is still a challenging task as it requires a polymer–solvent system with a strong polymer concentration dependent χ parameter. Such an observation may open up the use of organogels as smart and hydrophobic soft materials. The re-entrant phenomenon first observed by Tanaka is another characteristic of stimuli responsive hydrogels in which they are frustrated between the swollen and collapsed states in a given solvent mixture. Thus, the hydrogel first collapses and then reswells if an environmental parameter is continuously increased. The re-entrant phenomenon of hydrogels in water–cosolvent mixtures is due to the competitive hydrogen-bonding and hydrophobic interactions leading to flow-in and flow-out of the cosolvent molecules through the hydrogel moving boundary as the composition of the solvent mixture is varied. The experimental results reviewed here show that a re-entrant conformation transition in hydrogels requires a hydrophobically modified hydrophilic network, and a moderate hydrogen-bonding cosolvent having competitive attractions with water and polymer. The re-entrant phenomenon may widen the applications of the hydrogels in mechanochemical transducers, switches, memories, and sensors.

Therapeutic Hydrogel Lenses and the Antibacterial and Antibiotic Drugs Release

The aim of this research was to evaluate the effects of different lens types on the availability and efficacy of anti-inflammatory and antibiotic drugs. Three lens types were examined: (1) nonionic hydrogel lenses; (2) ionic hydrogel lenses; and (3) silicone hydrogel lenses. The lenses were incubated with (a) dexamethasone; (b) betamethasone; (c) bromophenacyl bromide; and (d) chloramphenicol. Drug availability was quantified by gradient HPLC, and chloramphenicol antibacterial activity was quantified by testing the inhibition of Salmonella typhimurium growth on agar. The lens allowing the most abundant passage of betamethasone was the ionic hydrogel lens, followed by the silicone hydrogel lens and nonionic hydrogel lens. The lens allowing the most abundant passage of dexamethasone was the ionic hydrogel lens, but only at 0.5 h and 1 h. Regarding chloramphenicol, the ionic hydrogel lens and silicone hydrogel lens allowed more abundant passage than the nonionic hydrogel lens. These results highlight the relevance of adapting lenses to anti-inflammatory therapy, thus allowing a personalized medical approach.

Release of Aloe vera Extracts from Therapeutic Lenses

Aloe vera extracts have been used for drug therapy due to their antimicrobial, anti-inflammatory, and epithelia-regenerative actions. Considering the possible adverse side effects on the corneal surface of anti-microbial agent administration after ocular surgery, it is of interest to identify the ability of Aloe vera extract release from a therapeutic lens to prevent ocular irritation. The aim of this research was to evaluate the effects of different lens types on the availability and efficacy of releasing Aloe vera extracts in which they are soaked. Two lens types were examined: (1) non-ionic hydrogel lenses and (2) ionic hydrogel lenses. Aloe vera availability was quantified by LC–MS, and activity was quantified by a spectrophotometer (Nanodrop) at different times: (a) 30 min, (b) 60 min, (c) 2 h, (d) 6 h, and (e) 24 h. The lens allowing for the most abundant passage of Aloe vera extracts was the ionic hydrogel lens, followed by the non-ionic hydrogel lens. The obtained results demonstrate that the best lens allowing for the high and stable release of Aloe vera extract to the corneal surface are those composed of ionic hydrogels.

Influence of Sodium Salts on the Swelling and Rheology of Hydrophobically Cross-linked Hydrogels Determined by QCM-D.

Hydrophobically modified copolymers provide a versatile platform of hydrogel materials for diverse applications, but the influence of salts on the swelling and material properties of this class of hydrogels has not been extensively studied. Here, we investigate model hydrogels with three different sodium salts with anions chosen from the classic Hofmeister series to determine how these counterions influence the swelling and mechanical properties of neutral hydrogels. The gel chosen was based on a statistical copolymer of dimethylacrylamide and 2-(N-ethylperfluorooctane sulfonamido) ethyl acrylate (FOSA). Our measurements utilize a quartz crystal microbalance with dissipation (QCM-D) to quantify both swelling and rheological properties of these gels. We find that a 1 mol/L solution of Na2SO4, corresponding to a kosmotropic anion, leads to nearly a 2.6-fold gel deswelling and correspondingly, the complex modulus increases by an order of magnitude under these solution conditions. In contrast, an initial increase in swelling and then a swelling maximum is observed for a 0.02 mol/L concentration in the case of a chaotropic anion, NaClO4, but the changes in the degree of gel swelling in this system are not directly correlated with changes in the gel shear modulus. The addition of NaBr, an anion salt closer to the middle of the chaotropic to kosmotropic range, leads to hydrogel deswelling where the degree of deswelling and the shear modulus are both nearly independent of salt concentration. Overall, the observed trends are broadly consistent with more kosmotropic ions causing diminished solubility ("salting out") and strongly chaotropic ions causing improved solubility ("salting in"), a trend characteristic of the Hoffmeister series governing the solubility of many proteins and synthetic water-soluble polymers, but trends in the shear stiffness with gel swelling are clearly different from those normally observed in chemically cross-linked gels and are correspondingly difficult to interpret. The salt specificity of swelling and mechanical properties of nonionic hydrogels is important for any potential application in which a wide range of salt concentrations and types are encountered.

Ionic Conductivity of Polyelectrolyte Hydrogels.

Polyelectrolytes have many important functions in both living organisms and man-made applications. One key property of polyelectrolytes is the ionic conductivity due to their porous networks that allow the transport of water and small molecular solutes. Among polyelectrolytes, zwitterionic polymers have attracted huge attention for applications that involve ion transport in a polyelectrolyte matrix; however, it is still unclear how the functional groups of zwitterionic polymer side chains affect their ion transport and swelling properties. In this study, zwitterionic poly(carboxybetaine acrylamide), poly(2-methacryloyloxyethyl phosphorylcholine), and poly(sulfobetaine methacrylate) hydrogels were synthesized and their ionic conductivity was studied and compared to cationic, anionic, and nonionic hydrogels. The change of the ionic conductivity of zwitterionic and nonionic hydrogels in different saline solutions was investigated in detail. Zwitterionic hydrogels showed much higher ionic conductivity than that of the widely used nonionic poly(ethylene glycol) methyl ether methacrylate hydrogel in all tested solutions. For both cationic and anionic hydrogels, the presence of mobile counterions led to high ionic conductivity in low salt solutions; however, the ionic conductivity of zwitterionic hydrogels surpassed that of cationic and ionic hydrogels in high salt solutions. Cationic and anionic hydrogels showed much higher water content than that of zwitterionic hydrogels in deionized water; however, the cationic hydrogels shrank significantly with increasing saline concentration. This work provides insight into the effects of polyelectrolyte side chains on ion transport. This can guide us in choosing better polyelectrolytes for a broad spectrum of applications, including bioelectronics, neural implants, battery, and so on.

Physicochemical properties of ionic and non-ionic biocompatible hydrogels in water and cell culture conditions: Relation with type of morphologies of bovine fetal fibroblasts in contact with the surfaces

Cationic, anionic and non-ionic hydrogels having acrylamide polymer backbones were synthesized via free radical polymerization with N,N-methylenebisacrylamide (BIS) as crosslinker. The chemical structures of the hydrogels were characterized by Fourier Transform Infrared Spectroscopy (FTIR). Physicochemical properties such as swelling kinetic, maximum swelling capacity, volume phase transition temperature (VPTT) and wettability (static water contact angle) of hydrogels swollen in aqueous and cell culture medium, at room and cell culture temperatures were studied. In order to correlate the surface properties of the hydrogels and cellular adhesivity of bovine fetal fibroblasts (BFFs), cellular behaviour was analyzed by inverted fluorescence optical microscopy and atomic force microscopy (AFM). MTT assay demonstrated that the number of viable cells in contact with hydrogels does not significantly change in comparison to a control surface. Flattened and spindle-shaped cells and cell spheroids were the adopted morphologies during first days of culture on different hydrogels. Cell spheroids were easily obtained during the first 5days of culture in contact with PNIPAM-co-20%HMA (poly (N-isopropylacrylamide-co-20%N-acryloyl-tris-(hydroxymethyl)aminomethane)) hydrogel surface. After 15days of culture all hydrogels showed high adhesion and visual proliferation. According to obtained results, non-ionic and hydrophilic surfaces with moderated wettability induce the formation of BFFs cell spheroids. These hydrogel surfaces could be used in clinical and biochemical treatments at laboratory level to cell growth and will allow generating the base for future biotechnologic platform.

Design and synthesis of nonionic copolypeptide hydrogels with reversible thermoresponsive and tunable physical properties.

Polypeptide-based formulations that undergo liquid to hydrogel transitions upon change in temperature have become desirable targets since they can be mixed with cells or injected into tissues as liquids, and subsequently transform into rigid scaffolds or depots. Such materials have been challenging to prepare using synthetic polypeptides, especially when reversible gelation and tunable physical properties are desired. Here, we designed and prepared new nonionic diblock copolypeptide hydrogels (DCH) containing hydrophilic poly(γ-[2-(2-methoxyethoxy)ethyl]-rac-glutamate) and hydrophobic poly(l-leucine) segments, named DCHEO, and also further incorporated copolypeptide domains into DCHEO to yield unprecedented thermoresponsive DCH, named DCHT. Although previous attempts to prepare nonionic hydrogels composed solely of synthetic polypeptides have been unsuccessful, our designs yielded materials with highly reversible thermal transitions and tunable properties. Nonionic, thermoresponsive DCHT were found to support the viability of suspended mesenchymal stem cells in vitro and were able to dissolve and provide prolonged release of both hydrophilic and hydrophobic molecules. The versatility of these materials was further demonstrated by the independent molecular tuning of DCHT liquid viscosity at room temperature and DCHT hydrogel stiffness at elevated temperature, as well as the DCHT liquid to hydrogel transition temperature itself.

Releasing property from surface polyion complex gel

ABSTRACTSurface polyion complex (sPIC) gels were prepared with a nonionic hydrogel interior core, composed of poly(N‐vinylformamide and poly(N‐vinylacetamide), and a chemically bounded polyion complex layer on the outer surface, composed of poly(vinylamine) and poly(acrylic acid). The gels were investigated as controlled drug release models based on electrostatic interactions depending on pH. Methylene blue and allura red were employed as cationic and anionic drug models, respectively, and resulted in the selective adsorption depending on pH conditions. Monovalent and multivalent anionic drug models, allura red and 1,3,6‐naphthalenetrisulfonate were observed for their releasing behavior from the sPIC gel. The results indicated that the multivalent anionic drug effectively controlled release depending on pH conditions. We further investigated sPIC gels regarding their ability to control the release of ionic molecules as a function of pH‐driven changes in electrostatic interactions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42081.

Swelling equilibrium of hydrogels of (N-isopropyl acrylamide + anionic and cationic comonomers) in aqueous solutions of sodium chloride: Experimental results and modeling

Experimental results are reported for the swelling equilibrium of some ionic hydrogels consisting of N-isopropyl acrylamide (N-IPAAm) and one or two comonomers – the anionic monomer 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and/or the cationic monomer 3-(methacrylamido)propyl trimethylammoniumchloride (MAPTAC) – in water and in aqueous solutions of sodium chloride at 298K. The degree of swelling of such ionic hydrogels increases with the net charge (i.e., the difference in the mole fractions of anionic and cationic comonomers) as well as with the charge density (i.e. the mole fraction of a single comonomer). The mole fraction of a single comonomer was varied between 0 and 0.05. The (absolute) difference between the mole fractions of the anionic and cationic comonomers was varied between 0 and 0.03. Two characteristic transitions in the degree of swelling of the hydrogels were observed when sodium chloride is added to the coexisting liquid phase. The first transition depicts the conversion of the ionic comonomer into the neutral state. In that transition the degree of swelling of a charged ionic hydrogel reduces to the degree of swelling of a nonionic hydrogel. For the investigated hydrogels, that transition occurs when the mass fraction of NaCl in the coexisting aqueous phase is increased beyond approximately 5×10−5. The second transition occurs at much higher sodium chloride mass fractions (around 5×10−3). In that transition the hydrogel collapses, i.e., that transition resembles the phase transition observed when non-ionic N-IPAAm hydrogels are dissolved in aqueous solutions of sodium chloride.The experimental results for the degree of swelling are quantitatively described by a thermodynamic framework that combines an expression for the Gibbs energy of a liquid phase (a chemical reactive, aqueous electrolyte solution of the non-crosslinked polymer chains) with an expression for the Helmholtz energy of an elastic network (that accounts for the crosslinking effects).

Depletion-Mediated Potentials and Phase Behavior for Micelles, Macromolecules, Nanoparticles, and Hydrogel Particles

We report a simple depletion potential that captures measured potentials and phase behavior for micrometer-sized colloids in the presence of unadsorbing charged micelles, charged nanoparticles, nonionic macromolecules, and nonionic hydrogel particles. Total internal reflection microscopy (TIRM) is used to measure net potentials between colloids and surfaces, and video microscopy (VM) is used to measure quasi-2D phase behavior in the same material systems. A modified Asakura-Oosawa (AO) depletion potential is developed to accurately quantify particle-wall potentials and interfacial crystallization via particle-particle potentials in Monte Carlo (MC) simulations. The modified AO potential includes effective depletant sizes, accurate osmotic equations of state, and partition coefficients. Partition coefficients are used as the sole adjustable fitting parameter, although an approach to their theoretical prediction from depletant density profiles is also presented. Our results demonstrate a model that accurately captures depletion interactions and phase behavior in a variety of material systems.

Diffusion and binding of 5-fluorouracil in non-ionic hydrogels with interpolymer complexation

Hydrogen-bonded interpolymer complexes can be used for development of novel dosage forms. In this study, two types of crosslinked hydrogels, copolymer networks of N-vinyl pyrrolidone and acrylamide (PVP-co-PAM) and interpenetrating polymer networks (IPN) composed of crosslinked PVP-co-PAM and poly(vinyl alcohol) (PVA), were synthesized at three different degrees of crosslinking. The side chain groups in such polymers can form non-ionic complexes through H-bonding, resulting in additional “crosslinks” in the hydrogels. Both kinds of hydrogels have significantly larger swelling sensitivities than the networks formed with ionizable side chains. In the IPNs, introduction of the PVA chains into the PVP-co-PAM networks raises the permeability, indicating more open pores. The permeability decreases with the increasing degree of crosslinking of the copolymer. For probing the drug binding in the hydrogels, Fourier transform infrared spectra (FTIR) difference spectroscopy indicated the presence of significant H-bonding interactions between 5-fluorouracil (5-FU) and the side chains of the polymers. Such interactions are larger in the PVP-co-PAM copolymers than in the IPN hydrogels, thereby causing an additional source of the slower release kinetics in the copolymer hydrogels as revealed by the Peppas model, albeit both types of the networks followed a non-Fickian transport mechanism.

Synthesis and Characterization of Water Soluble and Water Swelling Thermo-sensitive Copolymers based on 2- Hydroxyethylacrylate and 2-Hydroxyethylmethacrylate

Thermo-sensitive linear and cross-linked copolymers based on 2-hydroxyethylacrylate and 2-hydroxyethylmethacrylate were synthesized and their physicochemical properties were investigated. It was found that copolymer solutions have lower critical solution temperature (LCST) and copolymer hydrogels of certain composition undergoes sharp collapse at temperature increase. The interaction of copolymers with surfactants was studied. It was shown that swelling behavior of copolymers in surfactants aqueous solutions depend on several factors: copolymer composition, surfactant concentration. Its influence on copolymer hydrogels is discussed. Great enhancing of amplitude of thermo-induce collapse of cross-linked polymers are caused by interaction of some nonionic hydrogels with ionic surfactant in aqueous solutions.

The biological efficiency and bioavailability of human growth hormone delivered using injectable, ionic, thermosensitive poly(organophosphazene)-polyethylenimine conjugate hydrogels

We have endeavored to develop injectable, thermosensitive, biodegradable hydrogels that prolong human growth hormone (hGH) release, improving bioavailability through introducing balanced ionic interactions. Cationic poly(organophosphazene)-polyethylenimine (PEI, 1.8 kDa) conjugate hydrogels were synthesized as those hydrogels for sustained delivery of anionic hGH with proper ionic strength of association/dissociation. We have additionally prepared different chain lengths of α-amino-ω-methoxy-poly(ethylene glycol) (AMPEG550 and AMPEG750) for the synthesis of conjugates as a means to control hydrogel degradation rates. All Aqueous solutions of PEI-conjugates became hydrogels hydrolyzable in proportion to AMPEG molecular weight at body temperature; these PEI-conjugates complexed with hGH and extended hGH release in vitro. In pharmacokinetic studies of hGH behavior in SD rats, hydrogels of PEI-conjugate/hGH complexes could suppress the initial burst-phase, and extend the duration, of release, as well as increasing of area under the curve (AUC) compared to controls including hGH solution or non-ionic hydrogel. In a hypophysectomized rat model, the biological efficacy of hGH delivered from PEI-conjugate/hGH complex hydrogels was equivalent to that from daily administration over four days based on body weight gain and width of the tibial growth plate. These results suggest that ionic, thermosensitive, poly(organophosphazene)-PEI-conjugate hydrogel demonstrates potential as an injectable depot for sustained delivery of bioavailable hGH.

The removal of heavy metal ions from aqueous solutions by novel pH-sensitive hydrogels

Novel non-ionic hydrogels were synthesized by radical homopolymerization of N-vinyl-2-pyrrolidone (VP) or by radical copolymerization of VP with methylacrylate (MA). A macroinimer (MIM) was used as a crosslinker and initiator, as well. The percentage of mass swelling ratios ( S M), the molecular weight between crosslinks ( M c) and Young's modulus of the hydrogels were investigated. The hydrogels were used as binding materials for different heavy metal ions such as Cu 2+, Cd 2+, Ni 2+ and Zn 2+ under varying conditions. The binding capability of the hydrogels toward the metal ions decreases in the following order: Cu 2+ > Ni 2+ > Zn 2+ > Cd 2+.

Study of the properties of hydrolyzed polyacrylamide hydrogels with various pore structures and rapid pH-sensitivities

Nonionic polyacrylamide (PAAm) hydrogels were synthesized using three methods: room temperature polymerization, cryo-polymerization, and modified cryo-polymerization. Anionic PAAm hydrogels were obtained after hydrolyzing the nonionic hydrogels under alkaline conditions. The composition of anionic hydrogels was characterized by Fourier transform infrared (FT-IR) spectroscopy and element analysis. Morphological studies showed that the hydrogels exhibited various pore structures when they were synthesized using different methods. An additional mechanism for the formation of cryogels was proposed. Investigation of the swelling properties of the hydrogels and analysis of the swelling kinetics showed that the hydrolyzed PAAm hydrogels had rapid pH-sensitive rates.