Preparation and characterization of pH-sensitive hydrogel microparticles as a biological on–off switch

The pH-responsive swelling and release behaviors of anionic P(MAA-co-EGMA) hydrogel microparticles having various MAA and EG contents were investigated as a biological on–off switch for the design of an intelligent drug delivery system triggered by external pH changes. When DC was used as a dispersion stabilizer, well-dispersed hydrogel microparticles having an average diameter of approximately 4 μm were obtained. There was a drastic change of the equilibrium weight swelling ratio of P(MAA-co-EGMA) hydrogels at a pH of around 5, which is the pK _a of PMAA. When the MAA content in the hydrogel increased, the swelling ratio increased at a pH above 5 due to the more electrostatic repulsion between the charged groups of MAA. The P(MAA-co-EGMA) hydrogel microparticles showed a pH-responsive release behavior. At low pH (pH 4.0) small amounts of Rh-B were released while at high pH (pH 6.0) relatively large amounts of Rh-B were released from the hydrogels. The difference in the released amount of Rh-B from the hydrogels between pH 4.0 and 6.0 decreased when the MAA content in the hydrogels decreased, which means that the pH-responsive release behavior of the P(MAA-co-EGMA) hydrogel microparticles is closely related to the pH-responsive swelling property of the hydrogel.     

pH‐responsive hydrogel microparticles as intelligent delivery carriers for α‐MSH antagonists

For a first step in the development of an intelligent delivery system for a nonapeptide as an α‐MSH antagonist, pH‐responsive P(MAA‐co‐EGMA) hydrogel microparticles were prepared and their feasibility as intelligent delivery carriers was evaluated. There was a drastic change in the swelling ratio of P(MAA‐co‐EGMA) microparticles at a pH of around 5 and as the MAA amount in the hydrogel increased, the swelling ratio increased at a pH above 5. The loading efficiency of the nonapeptide at pH 7 increased with the amount of Methacrylic acid (MAA) in the hydrogel and at pH 2, where the electrostatic attraction was greatest, a high loading efficiency was not obtained because of the low swelling ratio of the hydrogel. The P(MAA‐co‐EGMA) microparticles demonstrated a pH‐sensitive release behavior for the nonapeptide. In addition, the P(MAA‐co‐EGMA) microparticles showed a protective ability for the nonapeptide and preserved the stability of the nonapeptide. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Swelling and hydrolytic degradation behaviour of pH‐responsive hydrogels of poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] crosslinked by biodegradable polycaprolactone chains

BACKGROUND: Stimuli‐responsive hydrogels are typically obtained from non‐biodegradable monomers. The use of biodegradable crosslinkers can overcome this limitation. In this context, the main aim of this work was to use modified polycaprolactone as a crosslinker in the preparation of pH‐responsive hydrogels based on N‐isopropylacrylamide and methacrylic acid to give poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(N‐iPAAm‐co‐MAA)). RESULTS: Poly(caprolactone) dimethacrylate macromonomer was synthesized and successfully employed as crosslinker with various ratios in the synthesis of well‐known pH‐responsive hydrogels of P(N‐iPAAm‐co‐MAA). The swelling properties of these degradable hydrogels were investigated. They practically do not swell at pH = 2, but exhibit a very high swelling capacity in distilled water and in solutions of pH = 7. In addition, degradation studies at pH = 12 showed that the hydrolysis of the ester groups in the polycaprolactone chains produces, after a relatively short time, the total solubilization of the polymer chains. CONCLUSION: The hydrogels under study have certain characteristics that could make them good candidates for use as matrices in controlled drug delivery. On the one hand, they do not swell in acid pH solution (stomach conditions) but they swell extensively at neutral pH. On the other hand, they became rapidly water soluble following degradation. Copyright © 2009 Society of Chemical Industry     

Release behavior of freeze‐dried alginate beads containing poly(N‐isopropylacrylamide) copolymers

Beads composed of alginate, poly(N‐isopropylacrylamide) (PNIPAM), the copolymers of N‐isopropylacrylamide and methacrylic acid (P(NIPAM‐co‐MAA)), and the copolymers of N‐isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM‐co‐MAA‐co‐ODA)), were prepared by dropping the polymer solutions into CaCl₂ solution. The beads were freeze‐dried and the release of blue dextran entrapped in the beads was observed in distilled water with time and pH. The degree of release was in the order of alginate bead < alginate/PNIPAM bead ≈ alginate/P(NIPAM‐co‐MAA) bead < alginate/P(NIPAM‐co‐MAA‐co‐ODA) bead. On the other hand, swelling ratios reached steady state within 20 min, and the values were 200–800 depending on the bead composition. The degree of swelling showed the same order as that of release. Among the beads, only alginate/P(NIPAM‐co‐MAA‐co‐ODA) bead exhibited pH‐dependent release. At acidic condition, inter‐ and intraelectrostatic repulsion is weak and P(NIPAM‐co‐MAA‐co‐ODA) could readily be assembled into an aggregate due to the prevailing hydrophobic interaction of ODA. Thus, it could block the pore of bead matrix, leading to a suppressed release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radiation synthesis of poly(N‐vinylpyrrolidone‐co‐methacrylic acid) hydrogels and their usability in uranyl ion adsorption

In this study, N‐vinylpyrrolidone(VP)/methacrylic acid (MAA) mixtures have been prepared at three different mole percents which the methacrylic acid composition around 5, 10, and 15%. Poly(N‐vinylpyrrolidone‐co‐methacrylicacid) P(VP/MAA) hydrogels irradiated at 3.4 kGy have been used for swelling and diffusion studies in water and uranyl ion solutions. The influence of dose, pH, relative amounts of monomers in MAA/VP monomer mixtures on the swelling properties have been investigated. P(VP/MAA) hydrogels were swollen in distilled water at pH 7.0. P(VP/MAA)1 hydrogel containing 36% (mole percent) methacrylic acid showed the maximum percent swelling in water. Adsorption isotherms were constructed for uranyl ions and P(VP/MAA) hydrogel systems. It has been found that P(VP/MAA) hydrogels have very high uptake of the uranyl ions succesfully in water containing uranyl ions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Control release of some pesticides from starch/(ethylene glycol‐co‐methacrylic acid) copolymers prepared by γ‐irradiation

Starch/(Ethylene glycol‐co‐Methacrylic acid) [Starch/(EG‐co‐MAA)] hydrogels were designed for controlled delivery of pesticides, such as Fluometuron (FH); Thiophanate Methyl (TF) and Trifluralin (TI) which are use in the agricultural field. The delivery device was prepared by using γ‐irradiation and was characterized by FTIR, DSC, and SEM. The swelling behavior of hydrogels as a function of copolymer composition and irradiation dose was detected. This article discusses the swelling kinetics of polymer matrix and release dynamics of Trifluralin from hydrogels for the evaluation of the diffusion mechanism and diffusion coefficients. The values of the diffusion exponent ‘n’ for both the swelling of hydrogels and the release of Trifluralin from the hydrogels have been observed between 0.56 and 0.86 when the MAA content in the polymers was varied from 20 to 80 wt %, respectively. It is inferred from the values of the ‘n’ that non‐Fickian diffusion mechanism has occurred for different EG/MAA compositions. The release rate from matrices prepared under different conditions was studied to determine which factors have the most affect and control over the hydrogel matrix release property. The preparation conditions such as EG/MAA hydrogel composition, pesticide concentration, type of pesticide and irradiation dose greatly affect the pesticide release rate, which also influenced by the pH and temperature of the matrix‐surrounding medium. The pesticide release rate decreased as the irradiation dose and pH increased, but it increased as the MAA content, pesticide concentration and temperature increased. The release rate of Trifluralin is the highest one, whereas the Fluometuron is the lowest. The properties of the prepared hydrogels may make them acceptable for practical use as bioactive controlled release matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A novel temperature and pH dual‐responsive hybrid hydrogel with polyhedral oligomeric silsesquioxane as crosslinker: synthesis,characterization and drug release properties

Octavinyl polyhedral oligomeric silsesquioxane (OVPS) is used as the crosslinker instead of N,N′‐methylenebisacrylamide (BIS) to copolymerize with 2‐(dimethylamino)ethyl methacrylate (DMAEMA) or DMAEMA and N‐isopropylacrylamide (NIPAM) to prepare hybrid hydrogels: P(OVPS‐co‐DMAEMA) and P(OVPS‐co‐DMAEMA‐co‐NIPAM). The prepared hydrogels are transparent and show dual response to temperature and pH. The hydrogels were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis and tensile tests. Their mechanical properties, swelling ratio, deswelling and reswelling behaviors as well as drug release properties were investigated. The results indicate that OVPS can be incorporated into polymer networks in proportion to feed ratios. The P(OVPS‐co‐DMAEMA) hydrogel exhibits more homogeneous interior structure, higher swelling ratio and faster response than the conventional hydrogel prepared with BIS. Moreover, the incorporation of OVPS enhances the compression and tensile properties of the hydrogels. The feed ratios of OVPS and NIPAM have a great effect on volume phase transition temperature, thermal sensitivity, swelling behavior, mechanical properties and drug release properties of the hybrid hydrogels. The prepared dual‐responsive OVPS‐containing hydrogels are expected to be used as biomedical materials in drug release and tissue engineering. © 2014 Society of Chemical Industry     

Thermo‐ and pH‐sensitive hydrogels based on 2‐(2‐methoxyethoxy)ethyl methacrylate and methacrylic acid

Hydrogels based on commercially available 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA), with methacrylic acid (MAA) as comonomer, are studied. The incorporation of an ionizable monomer, such as MAA, in a thermosensitive system leads to the formation of hydrogels able to respond to pH and temperature according to their monomeric composition. Thus, at low pH, the acid groups of MAA are protonated, and they do not contribute to increase the hydrophilic balance, and collapse of the hydrogels occurs around room temperature. For temperatures below that of collapse, the degree of swelling increases with increasing MEO₂MA content. In contrast, at neutral or basic pH, the ionization of the acid groups contributes to increase the hydrophilicity and the osmotic pressure, leading to polyelectrolyte behaviour. In this regime, the swelling capacity increases and the thermosensitivity decreases with increasing MAA content in the hydrogels. These properties make poly(MEO₂MA‐co‐MAA) hydrogels suitable candidates for use in oral controlled delivery of hydrophobic drugs. This possibility is explored using ibuprofen as a model drug, after a complete study of the swelling kinetics. Copyright © 2010 Society of Chemical Industry     

Analysis of the swelling dynamics of crosslinked P(N‐iPAAm‐co‐MAA) copolymers,the corresponding homopolymers and their interpenetrating networks. Kinetics of water penetration into the gel above the pKaof MAA comonomeric units

The effect of composition on the swelling kinetics of a series of crosslinked poly(N‐isopropylacrylamide)s [P(N‐iPAAm)] and poly(methacrylic acid)s [P(MAA)], their statistical copolymers P(N‐iPAAm‐co‐MAA), and some sequential interpenetrating networks (IPNs) has been studied at pHs above the pK_a of MAA comonomeric units. The swelling process of the hydrogels upon immersion in buffer solutions was monitored by the weight change as a function of time. First‐order kinetics apply better than second‐order kinetics which fail, especially for predicting swelling equilibrium values. However, hydrogels presenting hydrogen bonding between MAA and N‐iPAAm units do not obey either first‐order or second‐order kinetics. The high n values found indicate that the swelling process is mostly controlled by polymer relaxation. Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of novel pH‐sensitive chitosan‐poly(acrylamide‐co‐itaconic acid) hydrogels

Novel pH‐sensitive chitosan‐poly(acrylamide‐co‐itaconic acid) hydrogels were prepared by free radical copolymerization of acrylamide and itaconic acid (IA) in chitosan solution. The hydrogels were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and the swelling ratios of the hydrogels in water (pH 6.8) and pH 1.2. The influence of composition on the thermal properties of the hydrogels was assessed. The glass transition temperatures of the samples increased with IA content, ranging from 110 to 136 °C. Swelling of the hydrogels was found to obey second‐order kinetics with respect to the remnant swelling, indicating that diffusion is controlled by the relaxation of chains. The equilibrium swelling degree was strongly dependent on pH and composition. At both pH values the highest water uptake was obtained for the IA‐free sample M1. From the equilibrium swelling results the average molar mass between crosslinks, M_c, and the crosslink density of the chitosan‐poly(acrylamide‐co‐itaconic acid) samples were calculated. The results evidenced the reinforcing effect of IA on the hydrogel structure. It is concluded that these highly swellable pH‐sensitive hydrogels can be useful for applications in biomedicine and pharmacy. © 2013 Society of Chemical Industry     

Stimuli-Responsive Hydrogels Based on Random Copolymers of the Sucrose Methacrylate

Poly(sucrose methacrylate-co-acrylic acid), P(SMA-co-AA), and poly(sucrose methacrylate-co-diethylene glycol methyl ether methacrylate), P(SMA-co-EG₂MA), are synthesized by free radical polymerization using sucrose dimethacrylate as a crosslinker. The copolymers present one glass transition suggesting a random distribution of the comonomers. The copolymers–water interaction parameter χ is around 0.5, while M_c increases with SMA molar fraction. The kinetics of water swelling show a Fickian behavior for P(SMA-co-AA) richer in acrylic acid. The swelling is driven by the ionic character of the P(SMA-co-AA), except at pH = 2, and by the hydrophilicity of the SMA for the P(SMA-co-EG₂MA). The temperature influences the swelling behavior of the P(SMA-co-EG₂MA) due to the lower critical solution temperature (LCST) behavior. The pH- and thermoresponsiveness of the P(SMA-co-AA) and P(SMA-co-EG₂MA) hydrogels are maintained by replacing the sensitive comonomers with SMA up to mass fractions of 85 and 20 wt%, respectively, ≈71 and 17 wt% of sucrose, a product from a renewable resource. The hydrolytic degradation of the hydrogels is more pronounced for copolymers richer in SMA and resulted in sucrose release. Hydrogels present viscoelastic behavior, and the P(SMA-co-AA) series is more resistant to compression. The xerogels of the copolymers richer in SMA show a foam-like morphology with open cells.     

Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent. RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy. CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry     

pH and thermo‐responsive poly(N‐isopropylacrylamide) copolymer grafted to poly(ethylene glycol)

pH and thermo‐responsive graft copolymers are reported where thermo‐responsive poly(N‐isopropylacrylamide) [poly(NIPAAm), poly A ], poly(N‐isopropylacrylamide‐co‐2‐(diethylamino) ethyl methacrylate) [poly(NIPAAm‐co‐DEA), poly B ], and poly(N‐isopropylacrylamide‐co‐methacrylic acid) [poly(NIPAAm‐co‐MAA), poly C ] have been installed to benzaldehyde grafted polyethylene glycol (PEG) back bone following introducing a pH responsive benzoic‐imine bond. All the prepared graft copolymers for PEG‐g‐poly(NIPAAm) [ P‐N1 ], PEG‐g‐poly(NIPAAm‐co‐DEA) [ P‐N2 ], and PEG‐g‐poly(NIPAAm‐co‐MAA) [ P‐N3 ] were characterized by ¹H‐NMR to assure the successful synthesis of the expected polymers. Molecular weight of all synthesized polymers was evaluated following gel permeation chromatography. The lower critical solution temperature of graft copolymers varied significantly when grafted to benzaldehyde containing PEG and after further functionalization of copolymer based poly(NIPAAm). The contact angle experiment showed the changes in hydrophilic/hydrophobic behavior when the polymers were exposed to different pH and temperature. Particle size measurement investigation by dynamic light scattering was performed to rectify thermo and pH responsiveness of all prepared polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Heterogeneous and homogeneous structure dextran–poly(methacrylic acid) interpenetrating network hydrogels: synthesis and an application study

pH‐sensitive dextran–poly(methacrylic acid) (Dext–pMeAc) full interpenetrating network hydrogels (INHs) were prepared by simultaneous radical polymerization of methacrylic acid monomer (MeAc) and Dext polymer chains in the presence of N,N‐methylenebisacrylamide (MBA) as crosslinker in aqueous solution. These hydrogels were investigated as a drug carrier. The influence of MeAc and MBA contents in the network hydrogels on the swelling behaviour and mechanical strength of prepared Dext–pMeAc INHs was evaluated. Dext–pMeAc INHs were characterized by Fourier transform IR spectroscopy, and kinetic swelling measurements were carried out in deionized water and in simulated gastric fluids (pH 1.1 and pH 7.4). Dext–pMeAc/1‐1, Dext–pMeAc/3‐1 and Dext–pMeAc/5‐1 hydrogels with molar ratios of n_Dext/n_MeAc = 10 and n_MBA/n_Dext = 10, 30 and 50 respectively showed a core–shell structure when they swelled. This phenomenon was not observed in Dext–pMeAc/5‐2, Dext–pMeAc/5‐3 and Dext–pMeAc/5‐5 hydrogels containing a higher amount of Dext in the gels. The swelling data proved the formation of INHs with pH‐sensitive behaviour. A drug release study was performed using Rhodamine 6G fluorescent dye as a model hydrophilic bioactive molecule. The in vitro release rate of Rhodamine 6G from Dext–pMeAc/5‐3 hydrogel was dependent on the pH of the release medium. Copyright © 2012 Society of Chemical Industry     

Multi‐responsive polymeric microcontainers for potential biomedical applications: synthesis and functionality evaluation

Temperature and pH responsive poly(N‐isopropylacrylamide‐co‐methacrylic acid) (P(NIPAAm‐co‐MAA)) microcontainers with encapsulated magnetic nanoparticles in the shell were prepared by a two‐stage distillation precipitation polymerization. PMAA@Fe₃O₄/P(NIPAAm‐co‐MAA) core–shell nanoparticles were synthesized by the second‐stage polymerization of NIPAAm, MAA and N, N′‐methylenebisacrylamide as crosslinker in the presence of magnetic nanoparticles and PMAA as core. These novel triple‐functional microcontainers were prepared by selective removal of the PMAA core in water. Daunorubicin hydrochloride (DNR) was loaded into the microcontainers and the release profile was studied by UV–visible spectroscopy. The synthesized nanostructures were characterized with transmission and scanning electron microscopy, X‐ray diffraction and Fourier transform infrared spectroscopy. The magnetic properties were evaluated by vibrating sample magnetometry. The shrink and swelling behavior was studied by dynamic light scattering. Copyright © 2012 Society of Chemical Industry     

Novel dually responsive hydrogel with rapid deswelling rate

Hydrogels based on 2‐hydroxyethyl methacrylate (HEMA), methacrylic acid (MAA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were prepared by free radical polymerization. The prepared hydrogels were characterized using Fourier transform infrared spectrometry. The states of water in the hydrogels were probed using differential scanning calorimetry and three types of water (free, freezing bound and non‐freezing bound) were detected, the contents of which were calculated. Compared with conventional poly(HEMA‐co‐MAA) hydrogels, the deswelling rate of the poly(HEMA‐co‐PEGMA‐co‐MAA) hydrogels is significantly improved, owing to the introduction of PEGMA. The deswelling process can be well described with a first‐order kinetics equation. Moreover, the swelling ratio of poly(HEMA‐co‐PEGMA‐co‐MAA) hydrogels exhibits a temperature dependence. Based on the analysis of the components of the hydrogels, a brushed core/shell structure is proposed for these, and confirmed by transmission electron microscopy observations. Copyright © 2006 Society of Chemical Industry     

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     

Temperature and pH responsive hydrogels based on polyethylene glycol analogues and poly(methacrylic acid) via click chemistry

A novel temperature responsive copolymer, poly[2‐(2‐methoxyethoxy)ethyl methacrylate‐co‐oligo(ethylene glycol)methacrylate‐co‐N‐hydroxymethyl acrylamide] [P(MEO₂MA‐co‐OEGMA‐co‐HMAM)], was synthesized by atom transfer radical polymerization. pH responsive poly(methacrylic acid) (PMAA) was synthesized by reversible addition‐fragmentation chain transfer polymerization. After the hydroxyl groups on P(MEO₂MA‐co‐OEGMA‐co‐HMAM) were transformed into azide groups and the carboxyl groups on PMAA were transformed into alkyne groups respectively, a novel temperature and pH responsive hydrogel was fabricated by click chemistry between the azide‐P(MEO₂MA‐co‐OEGMA‐co‐HMAM) and alkyne‐PMAA in the presence of CuSO₄ and sodium ascorbate in aqueous solution. The rheological kinetics of gel formation demonstrated that gelation had commenced within 5 min at 25 °C, since then the storage modulus (G′) was higher than the loss modulus (G″). SEM images of hydrogel morphology and the swelling ratios of hydrogel at different temperatures and pH proved that the formed hydrogel had temperature and pH sensitivities. Bovine serum albumin was used as a model to evaluate the sustained release of the hydrogel; the results indicated that the hydrogel was a promising candidate for controlling protein drug delivery. © 2015 Society of Chemical Industry     

Preparation and drug‐release behavior of minocycline‐loaded poly[hydroxyethyl methacrylate‐co‐poly(ethylene glycol)–methacrylate] films

In this work, biocompatible hydrogel matrices for wound‐dressing materials and controlled drug‐release systems were prepared from poly[hydroxyethyl methacrylate‐co‐poly(ethylene glycol)–methacrylate] [p(HEMA‐co‐PEG–MA] films via UV‐initiated photopolymerization. The characterization of the hydrogels was conducted with swelling experiments, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis (differential scanning calorimetry), and contact‐angle studies. The water absorbency of the hydrogel films significantly changed with the change of the medium pH from 4.0 to 7.4. The thermal stability of the copolymer was lowered by an increase in the ratio of poly(ethylene glycol) (PEG) to methacrylate (MA) in the film structure. Contact‐angle measurements on the surface of the p(HEMA‐co‐PEG–MA) films demonstrated that the copolymer gave rise to a significant hydrophilic surface in comparison with the homopolymer of 2‐hydroxyethyl methacrylate (HEMA). The blood protein adsorption was significantly reduced on the surface of the copolymer hydrogels in comparison with the control homopolymer of HEMA. Model antibiotic (i.e., minocycline) release experiments were performed in physiological buffer saline solutions with a continuous flow release system. The amount of minocycline release was shown to be dependent on the HEMA/PEG–MA ratio. The hydrogels have good antifouling properties and therefore are suitable candidates for wound dressing and other tissue engineering applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling behavior of poly(acrylamide‐co‐N‐vinylimidazole) hydrogels under different environment conditions

A series of random copolymers of acrylamide and N‐vinylimidazole, poly(AAm‐co‐NVI), with various compositions were prepared using redox copolymerization. The influence of environmental conditions such as pH, temperature, and ionic strength on the swelling behavior of the copolymeric hydrogels was investigated. The hydrogels exhibited the highest equilibrium swelling in basic medium at high temperature. Equilibrium swelling decreased with rising ionic strength at pH 5.0. As pH increased, equilibrium swelling of the hydrogels increased at pH 11.0 and I = 0.20 M. Swelling kinetics of the hydrogels was found to be non‐Fickian at 25°C. The process tended to be Fickian at higher pH and temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1783–1788, 2005