Tuning the thermoresponsive properties of poly(oligo(propylene glycol) methacrylate) hydrogels via gradient copolymerization with 2-hydroxyethyl methacrylate

Gamma radiation was used to prepare copolymer hydrogel libraries based on oligo(propylene glycol) methacrylate (OPGMA) and 2-hydroxyethyl methacrylate (HEMA); a complete screening in composition of P(OPGMA/HEMA) copolymers was elaborated from 0% to 100% of OPGMA. Determination of gel fraction was performed as the first step after radiation induced synthesis. Tuning of the volume phase transition temperature (VPTT) of P(OPGMA/HEMA) copolymeric hydrogels was investigated by swelling study. Additional characterization of structure and properties was conducted by FTIR, DSC, and UV-Vis spectroscopy. All results indicate that new P(OPGMA/HEMA) copolymeric hydrogels have wide diversity in thermoresponsive properties which strongly depend on their composition.     

Influence of N-vinyl-2-pyrrolidone and methacrylic acid on thermal curing process of 2-hydroxyethyl methacrylate hydrogel

This study investigated the effects of N-vinyl-2-pyrrolidone (NVP) and methacrylic acid (MA) comonomers on the curing characteristics and properties of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel for soft contact lenses. A real-time temperature measurement system was devised and the exothermic behaviors of hydrogel contact lenses comprising PHEMA, P(HEMA/NVP), and P(HEMA/MA) during oven-curing condition were analyzed. The results of the real-time temperature measurement were compared with the experimental analysis by using differential scanning calorimetry at different heating rates. NVP and MA content changes affected the HEMA-based hydrogel's equilibrium water content (EWC), contact lens diameter, and gel fraction. HEMA-based hydrogel sheets with varying NVP and MA contents were fabricated and mechanically characterized. The temperature at which the exothermic reaction occurred varied depending on the type of added comonomer and the exothermic reaction of HEMA containing NVP was delayed. When NVP was added, the mechanical strength and EWC were lower than when MA was added. In order to maintain the mechanical properties while improving the equilibrium moisture content of the lens, it was found that the use of MA is more advantageous than the use of NVP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48622.     

Equilibrium swelling properties of weakly lonizable 2-hydroxyethyl methacrylate (HEMA)-based hydrogels

Hydrogles, sensitive to pH, were prepared by copolymerizing 2-hydroxyethyl methacrylate (HEMA) with 2-dimethylaminoethyl methacrylate (DMA). The mole fraction of the DMA monomer present during synthesis was fixed at 0.3, while the volume fraction of total monomer varied from 0.29 ( I ) to 1.0 ( II ). Swelling equilibria were measured in citrate of phosphate buffer for pH from 3.0 to 7.6 Swelling of the hydrogels depends on the volume fraction monomer present during synthesis, solution, pH, and identity of the buffer, Hydrogel I reached a four-fold larger swelling ratio (g swollen hydrogel/g dry hydrogel) in pH 3.0 citrate buffer, as compared to hydrogel II . Experimental results are interpreted on the basis of ideal Donnan equilibria. © 1994 John Wiley & Sons, Inc.     

Ultrasonic characterization of water sorption in poly(2-hydroxyethyl methacrylate) hydrogels

A complex mechanism characterizes the water uptake kinetics in hydrogels, as a consequence of the strong structural changes occurring in the material during the sorption process. The water sorption involves the transformation of a glassy, moderately crosslinked polymer in a rubbery material. In this study, the changes in the ultrasonic attenuation and velocity in crosslinked poly(2-hydroxyethyl methacrylate) [poly-(HEMA)] hydrogel films during water sorption are measured by scanning laser acoustic microscopy (SLAM) and a pulse–echo system. In particular, the pulse–echo technique provides additional valuable information, thanks to its capability for monitoring the position of the swollen/unswollen fronts during water sorption. The evolution of the attenuation observed by SLAM is analyzed in terms of reflections on macroscopic discontinuities and absorption mechanisms. Finally, the propagation of ultrasonic waves acts as a dynamic mechanical test of the material; and, therefore, the measured longitudinal velocity and ultrasonic attenuation are applied to the calculation of the storage bulk longitudinal modulus of the poly(HEMA) hydrogels during water sorption. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:823–831, 1998     

Immobilization of lipase on poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) hydrogel for the synthesis of butyl oleate

Lipase from Candida rugosa was immobilized by entrapment on poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) [poly(VP-co-HEMA)] hydrogel, cross-linked with ethylene glycol dimethacrylate (EDMA). The immobilized enzyme was used in the esterification of oleic acid with butanol in hexane. The activities of the immobilized enzyme preparations and the leaching of the enzyme from the hydrogel supports with respect to composition were investigated. The thermal, solvent, and storage stability of the immobilized preparations also were determined. Increasing the percentage VP from 0 to 90, which corresponds to the increase in the hydrophilicity of the hydrogels, increased the activity of the immobilized enzyme. Lipase immobilized onto VP(%):HEMA(%), 90:10 hydrogel had the highest activity. Increasing the hydrophobicity of the hydrogel (increasing the percentage HEMA) seemed to decrease leaching of the enzyme from the support. Immobilized lipase on 100% HEMA hydrogel indicated highest entrapment and lowest leaching by hexane washing. The lipase immobilized on VP(%):HEMA(%), 50:50 hydrogel showed highest thermal, solvent, and storage stability compared to lipase immobilized on other hydrogel compositions as well as the native lipase.     

Hydrophilic gels based on copolymers of 2-hydroxyethyl methacrylate with methacrylamide and acrylamide

Copolymerization of 2-hydroxyethyl methacrylate with methacrylamide or acrylamide and a crosslinking agent in the presence of water or other diluents yielded transparent hydrogels with a varying degree of swelling and varying sorption properties. The equilibrium degree of swelling increases with increasing content of amide groups and exhibits a maximum at ca. 60 wt-% methacrylamide. The temperature dependence of swelling at 25–50°C changes from negative to positive with growing content of methacrylamide in the copolymer. The effect of the introduction of the amide groups can be interpreted by a weakening of the extent of hydrophobic interactions and by an increase in the role played by the hydrogen bonds. At the same time, the swelling-in effect of the salting-in anions decreases and the sensitivity to the sorption of metal cations increases. The increasing content of methacrylamide is reflected in an increase in the modulus, tensile strength, and elongation-at-break in gels swollen to the same degree. In gels swollen in water to equilibrium, the positive effect of methacrylamide units is compensated for by the negative effect of the increasing degree of swelling, so that the mechanical properties of these gels do not depend too much on the composition of the copolymer. The increasing content of acrylamide in the copolymer strongly raises the degree of swelling, which is reflected in poorer mechanical properties compared to poly(2-hydroxyethyl methacrylate).     

Sugar-dependent solubility and fluorescence property of copolymers consisting of phenylboronic acid and 2-hydroxyethyl methacrylate moieties

Copolymers consisting of N-3-acrylamidophenylboronic acid (APBA) and 2-hydroxyethyl methacrylate moieties (HEMA) were synthesized and their solubility and fluorescence properties were evaluated in the presence of sugar. The APBA–HEMA copolymer composed of 25 mol% of APBA moiety was found to be poorly soluble in water at pH 7.4. However, the water solubility of APBA–HEMA was improved in the presence of fructose in solution. The solubility of APBA–HEMA was influenced by fructose in a concentration-dependent manner, due to the formation of boronate ester of APBA moiety with fructose added. In addition, APBA–HEMA was modified with fluorescein isothiocyanate (FITC) for the fluorometric detection of sugars. The fluorescence intensity of FITC-modified APBA–HEMA was dependent on the type and concentration of sugars in solution. The fluorescence intensity of FITC-modified APBA–HEMA was highly enhanced by the addition of fructose, while the fluorescent response was negligibly small when other sugars were added. Thus, usefulness of FITC-modified APBA–HEMA for the selective determination of fructose was demonstrated.     

Solute diffusion in swollen membranes. Part V: Solute diffusion in poly(2-hydroxyethyl methacrylate)

Studies with phenylalanine diffusing in well-characterized poly(2-hydroxyethyl methacrylate) (PHEMA) membranes swollen in water at 37°C were conducted. Films were prepared by reaction of HEMA monomer with the cross-linking agent ethylene glycol dimethacrylate (EGDMA) at cross-linking ratios, X, of 0.005, 0.01, 0.0128, 0.025, and 0.050 mole EGDMA/mole HEMA in the presence of 40 weight percent water at 60°C for 12 hours. These membranes were subsequently swollen in water at 37°C and their structure analyzed using a modified Gaussian distribution equation of swelling. The calculated values of M?_c varied between 1,700 and 3,425 daltons, which corresponded to a correlation length of the mesh size, egr, of 24 to 35 A. The phenylalanine solute diffusion coefficient varied from 0.17 × 10^?6 to 0.97 × 10^?6 cm²/s, and depended on the aforementioned structural parameters of the membranes.     

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     

Ultrasonic wave attenuation during water sorption in poly(2-hydroxyethyl methacrylate) hydrogels

A scanning laser acoustic microscope (SLAM) was used to measure the acoustic attenuation during water sorption in a film of crosslinked poly(2-hydroxyethyl methacrylate) [poly(HEMA)] hydrogel. The contribution of reflection, scattering, and absorption of acoustic waves to the measured attenuation is evaluated. The analysis of a model accounting only for the possible reflection of the acoustic waves at the swollen/unswollen boundaries indicates that the time dependence of the attenuation during water sorption cannot be explained simply by accounting for the presence of two additional interfaces. A predominant contribution of acoustic wave absorption during the glass transition, occurring at the two swollen/unswollen interfaces, is assumed. Also, microvoids cannot be excluded as contributors to craze growth in the glassy matrix at the penetrant/polymer interface.     

Intra and intermolecular relaxations 2,3-dihydroxypropyl methacrylate and 2-hydroxyethyl methacrylate hydrogels

The dynamic mechanical transitions present in the 2-hydroxyethyl methacrylate (HEMA) and 2,3-dihydroxypropyl methacrylate (DHPMA) homopolymers and two random copolymers, with one-to-one and three-to-one HEMA-to-DHPMA molar ratios, were examined by analyzing the dry xerogels and hydrogels at various states of hydration. The temperatures of the primary α transition and the secondary β and γ transitions were determined in the tension mode; the storage modulus and loss modulus as a function of temperature and frequency were recorded. The results were compared to the results obtained from dielectric analysis at low hydration using tan δ. The frequency dependence of the dispersions was calculated for the dry and hydrated states, using mechanical and dielectric data. The information obtained was used to elucidate the interaction between the polymer and the sorbed water. Analysis of the low temperature secondary γ transition and secondary transitions resulting from polymer-water interactions was emphasized. During the initial hydration, the temperature maxima of the dielectric and mechanical secondary γ transitions, and the transitions that appear in the presence of absorbed water increased as the DHPMA content increased. The apparent activation energy associated with the secondary transitions increased as well. All of this is the result of stronger intermolecular interactions due to the increased density of hydrophilic moieties in DHPMA.     

Physico-chemical characterization of hybrid polymers obtained by 2-hydroxyethyl(methacrylate) and alkoxides of zirconium

Hybrid monolithic materials were prepared through polymerisation of 2-hydroxyethyl methacrylate (HEMA) mixed with zirconium alkoxides (Zr(OBuⁿ)₄, Zr(OPrⁿ)₄ and Zr(OEt)₄), modified by acetylacetonate groups. The molar ratio HEMA/Zr varied between 1 and 4. Thermo-Gravimetry coupled with Mass Spectroscopy (TG-MS) analyses, ¹³C MAS NMR and Dynamical Mechanical Thermal Analysys (DMTA) indicated the polymeric chains were interconnected by the inorganic component.The presence of zirconium alkoxides modified substantially the poly-HEMA properties. Glass transition temperature of hybrid materials derived from butoxy and propoxy was found in the range 50-80 °C, depending on the composition. The typical swelling of p-HEMA in the water, was suppressed by the presence of zirconium compounds. After immersion in distilled water, hybrid polymers showed an initial slight weight increase, followed by a small mass loss, which increases proportionally to the length of alkoxyl group (ethoxide(propoxide(butoxide) and reaches a constant value after about 40 days. The hybrids remained always rigid and transparent. Flexural modulus and strength of about 400-900 and 4-8 MPa were measured.     

Swelling and mechanical properties of crosslinked hydrogels containing N-vinylpyrrolidone

Copolymers of 2-hydroxyethyl methacrylate/N-vinyl-2-pyrrolidone (HEMA/NVP) and methyl methacrylate (MMA)/NVP were prepared in the presence of varying amounts of ethylene glycol dimethacrylate (EGDMA) and methylene diacrylamide (MDA) as crosslinkers by photopolymerisation. The resultant solid polymers were swollen to equilibrium in water at 293 K to produce hydrogels. These hydrogels were characterised by soluble fraction and equilibrium water content. The gels were also characterised by compression—strain measurements, which enabled the calculation of Young's modulus and effective crosslink density. The differences in these properties of HEMA/NVP and MMA/NVP polymer series and the effects of MDA versus EGDMA as a crosslinker were explained in terms of compositional drift of polymerisation, heterogeneous crosslinking and hydrophilicity/hydrophobicity of the components involved. In comparison with EGDMA, MDA was found to be more effective in reducing the soluble fraction of the polymers studied and to produce less rigid networks when swollen.     

温度及pH敏感共聚/粘土纳米复合水凝胶的合成与性能研究

以无机粘土为交联剂制备了具有温度、pH双重敏感性的聚（N-异丙基丙烯酰胺-co-甲基丙烯酸-β-羟乙酯）/粘土纳米复合水凝胶（P（NIPA-co-HEMA）/clay）,并用红外和X衍射对其结构和形态进行了表征。在弱碱性（pH=7.4）和25℃条件下,分别研究了温度和不同pH缓冲溶液对该凝胶溶胀度的影响,测定了纳米复合水凝胶的力学性能。结果表明：水凝胶的粘土已被剥离成单片层,且均匀分散在凝胶网络中,起交联作用;P（NIPA-co-HEMA）/clay具有良好的温度、pH双重敏感特性;凝胶的断裂伸长率〉1000%。     

2,3-Dihydroxypropyl methacrylate and 2-hydroxyethyl methacrylate hydrogels: gel structure and transport properties

The drying kinetics were examined in four cross-linked polymers that form hydrogels: 2,3-Dihydroxypropyl methacrylate (DHPMA) and 2-hydroxyethyl methacrylate (HEMA) and two random copolymers, with one-to-one and three-to-one HEMA-to-DHPMA molar ratios. The hydrogels were saturated with buffered, isotonic saline solution and deionized water; weight loss kinetics were monitored at temperatures from 16 to 37 °C at 30 and 60% relative humidity under air flow. While there are numerous studies of diffusion in hydrogels, this is one of few studies examining the initial evaporative drying period. The analyses of this short time data revealed that increasing the DHPMA content decreased water volatility; the percent water loss rate decreased with DHPMA content. Long time desorption data coupled with differential scanning calorimetry (DSC) results suggest that departure from Fickian desorption kinetics coincides with the onset of non-freezing water desorption. Dynamic mechanical analysis (DMA) revealed that changes in stiffness accompanying desorption are much more pronounced in HEMA containing polymers. Preliminary results indicate that the ion transport rate is greater in DMPMA containing hydrogels.     

Elastic and swelling behavior of 2-hydroxyethyl methacrylate,diethylene glycol methacrylate,and methacrylic acid copolymers

The elastic and swelling behavior of copolymers of 2-hydroxyethyl methacrylate, diethylene glycol methacrylate, and methacrylic acid crosslinked with ethylene glycol dimethacrylate has been studied. In the range of copolymer composition studied, Young's modulus of the swollen networks increases with the content of methacrylic acid, and its dependence on the content of diethylene glycol methacrylate passes through a maximum. The concentrations of the elastic network chains and determined from Young's moduli of swollen networks are much higher than those calculated from stoichiometry. This effect is attributed to the presence of additional physical crosslinks due to water-induced ordering of the hydrophobic backbone chains. Both the elastic and swelling behavior of the polymers mentioned above are decisive for their application in the preparation of soft contact lenses. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2141–2148, 1997     

Radiation-grafted polymers for biomaterial applications. II. The morphology and structure of 2-hydroxyethyl methacrylate and ethyl methacrylate homopolymer grafts

The 2-hydroxyethyl methacrylate (HEMA)/ethyl methacrylate (EMA) graft copolymer system has been found to be a useful model for investigating blood/polymer interactions. Studies of the structure of both HEMA and EMA radiation-grafted regions were conducted using extraction methods and transmission electron microscopy of selectively stained HEMA grafts. The effect of the extraction procedure on the surface topography of HEMA- or EMA-grafted films was studied by means of scanning electron microscopy. The existence of internal cells in the bulk of the HEMA network was demonstrated, and their osmotic nature was investigated. As grafting proceeds, the HEMA network becomes increasingly porous. The extraction studies carried out on EMA grafted showed that with this system an increasingly dense structure is obtained as grafting proceeds.     

Temperature effect on the permeation through poly(2-hydroxyethyl methacrylate) membrane

The temperature dependence of permeability through highly syndiotactic poly(2-hydroxyethyl methacrylate) [P(HEMA)] membrane is reported for highly polar organic solutes such as ureas, methyl substituted ureas and amides, and for NaCl and Na₂SO₄. The membranes used were equilibrated in distilled water at each temperature before measurements. From the linear correlationship between the excess heat capacities, ?C_p^o(excess) in aqueous solution at infinite dilution and the permeability parameter PM^1/3, it is found that the water structure perturbing capability of the polar organic solutes is a controlling factor in the permeation mechanism at relatively low temperature, where P(HEMA) membrane has higher water content and more structured water. In addition, it is found that the poor separation for urea of cellulose acetate membrane in the reverse osmosis practice is due to the higher water structure-breaking capability of urea.     

Radiation-grafted polymers for biomaterial applications. I. 2-hydroxyethyl methacrylate: Ethyl methacrylate grafting onto low density polyethylene films

Studies were conducted on the radiation grafting of 2-hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) by the mutual irradiation technique onto low density polyethylene. Four different solution concentrations were used, and radiation doses ranged from 0.03 to 0.05 Mrad. Four copolymer compositions having different HEMA:EMA ratios were also studied using two total monomer concentrations. The kinetics of the grafting process demonstrated by the two monomers were basically different. While EMA showed a typical diffusion-controlled kinetic pattern, HEMA exhibited a more complex behavior, the main features of which were an induction period, a slight autoacceleration and a significant drop in graft level after a maximum is reached. The difference in behavior was interpreted in terms of partitioning of monomers into the polyethylene substrate. The surface topography of the grafted films was studied by means of scanning electron microscopy. A mechanism based on osmotic cell formation was suggested for the HEMA graft system. The copolymer systems investigated showed that the graft reaction is faster in the initial stages for higher percentages of EMA in the monomer mixtures; as grafting proceeds the trend is reversed.     

Poly(2-hydroxyethyl methacrylate-co-sulfobetaine) hydrogels. II. Synthesis and swelling behaviors of the [2-hydroxyethyl methacrylate-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate] hydrogels

A series of the 2-hydroxyethyl methacrylate/3-dimethyl-(methacryloyloxyethyl)ammonium propane sulfonate (HEMA/DMAPS) copolymeric gels was prepared from various molar ratios of HEMA and the zwitterionic monomer DMAPS. The influence of the amount of the zwitterionic monomer in the copolymeric gels on the swelling behaviors in water, various saline solutions, and temperature was investigated. The results indicate that the PHEMA hydrogel (D0) and lower DMAPS content of the HEMA/DMAPS copolymeric gel (D1) exhibit overshooting phenomena in the dynamic swelling behavior. The maximum overshooting value decreases with increase in temperature. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55°C. Then, the minimum swelling ratio diminishes gradually with increasing of the DMAPS content in the HEMA/DMAPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/DMAPS copolymeric gels increase rapidly with increasing of concentration of the salt with a smaller ratio of the charge/radius. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2021–2034, 1998