Insulin release behavior of poly(N-isopropylacrylamide-co-N-vinyl-2-pyrrolidone) hydrogel based on modified melamine crosslinkers

Novel hydrogels based on poly(N-isopropylacrylamide-co-N-vinyl-2-pyrrolidone) (PNIPAAm/PNVP), were synthesized by solution radical polymerization using water as solvent and different weight percentage of crosslinkers ranging from 0.5 to 4%. The monomer mol ratios of NIPAAm/VP (0.9/0.1, 0.5/0.5, and 0.1/0.9) were used in all cases. N,N′-methylenebisacrylamide (MBA) and the new synthesized N,N,N-triacrylamido melamine (MAAm) were used as crosslinkers. The swelling parameters such as the swelling ratio Q, equilibrium water content (EWC), volume fraction of polymer φ_p and volume fraction at crosslinking φ_r were calculated from swelling measurements at different temperatures. The lower critical solution temperatures (LCST) of the prepared hydrogels were measured using DSC technique. The data of LCST indicated that the NIPAAm/VP crosslinked with MAAm or MBA showed reversible swelling and shrinking with temperature changes. The temperature dependence of swelling ratio and response kinetics upon heating or cooling was also investigated to understand the smart properties, i.e., temperature sensitive properties of these smart hydrogels. The in vitro release experiments were carried out at 22 and 37°C, respectively, to investigate the effect of temperature-sensitive property of these PNIPAAm/PNVP hydrogels crosslinked with MAAm and MBA crosslinkers on insulin release profiles.     

Observations on the swelling characteristics of the zwitterionic hydrogel of poly(1-3-sulfopropyl)-2-vinyl-pyridinium-betaine hydrogel

Samples of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (PSPV) have been synthesized to high conversion by free radical polymerization in aqueous solution of the zwitterionic monomer SPV with several concentrations of the crosslinker N,N′-methylene-bis-acrylamide (MBA). The densities of the resultant xerogels increased regularly with the content of MBA. Hydrogels obtained by swelling them in water and aqueous KSCN solution were examined by gravimetric and dimensional analysis. The water contents increased with decreasing content of MBA, the value of 92.7 wt% at the lowest MBA content being higher than that for other zwitterionic hydrogels. Enhanced swelling occurred in 1 M aq. KSCN at each MBA content, the total swelling being 98.1 wt% at the lowest crosslinker content. Swelling increased with increasing temperature. An approximate procedure to formulating swelling equilibrium in term of the volume fraction of water in hydrogel, in conjunction with the van’t Hoff equation, yields a small positive value for the enthalpy of swelling. This is compared with values derived similarly for other hydrogels.     

The Influence of Preparation Methods on the Swelling and Network Properties of Acrylamide Hydrogels with Crosslinkers

Abstract

Using different types and concentrations of crosslinkers, acrylamide (AAm) hydrogels have been prepared with chemical initiation and gamma irradiation techniques. The effects of the preparation method, crosslinkers type and concentration on swelling behavior of AAm hydrogels were investigated. Swelling was performed in distilled water and followed gravimetrically. Swelling parameters such as equilibrium swelling degree, equilibrium water content (EWC), maximum swelling, initial swelling rate, diffusion exponent and coefficient, and network parameters such as molecular mass between crosslinks, crosslink density, mesh size, and porosity were calculated and evaluated. The range of equilibrium swelling degree of AAm hydrogels was varied from 255% to 1450% depending upon the preparation method, crosslinker type, and crosslinker concentration. The diffusion of water into AAm hydrogels was found to be nonFickian.     

pH and temperature responsive hydrogels of poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-methacrylic acid): Synthesis and swelling characteristics

Temperature and pH sensitive 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and methacrylic acid (MAA) homopolymer and copolymer hydrogels have been prepared using N,N′-methylenebisacrylamide (MBA) and ethylene glycol dimethacrylate (EGDMA) as crosslinkers. Swelling of these hydrogels has been studied in terms of monomer ratio, type and concentration of the crosslinkers and in various concentrations of mono, di and trivalent salt solutions. Though swelling of the EGDMA crosslinked poly(AMPS-co-MAA) hydrogels is found to be higher than those based on MBA crosslinker, strength of the latter system has been found to be better. Swelling behavior of these hydrogels in different salt solutions at different concentrations has shown a drop in swelling from monovalent to trivalent cations and also at higher salt concentrations. The results have indicated the possibilities of developing tailor made hydrogels combining optimum swelling with better strength characteristics that will suit different physiological and biological environments.     

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of composite and nanocomposite hydrogels were synthesized by copolymerization reaction of partially neutralized acrylic acid (SA) on bentonite micropowder (BT) using N,N′-methylenebisacrylamide (MBA) as a crosslinker and potassium persulfate (I) as an initiator in aqueous solution. The influences of Na⁺-BT, organoBT (O-BT), and the content of the BT in the copolymeric gels on the swelling behaviour in deionized water and saline solution (0.2 wt.% NaCl_(aq)) were investigated. Results showed that the equilibrium swelling (W_∞) was decreased by adding a small amount of the BT, however, at higher BT contents, the W_∞ increased with the increase of the amount of clay. It was found that a concentration of 14 wt.% Na⁺-BT gave the best results absorption (955 g/g). Moreover, the amount of swelling for these absorbents in saline solution was smaller than that in deionized water. These hydrogels were characterized by X-ray diffraction and scanning electron microscopy. Finally, the thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability.     

Preparation and characterization of poly(acrylic acid)‐iron rich smectite superabsorbent composites

A novel poly(acrylic acid)‐iron rich smectite (IRS) superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) in the presence of N,N‐methylenebisacrylamide (MBA) as a crosslinker. IRS was used to strengthen the hydrogel products in the polymerization process. Water absorbencies for these superabsorbent composites in water and saline solutions were investigated. IRS caused a reduced equilibrium swelling as low as 8–26%. However, grafted IRS particles resulted in improved gel strength as high as 66% compared to the IRS‐free sample. IRS modified superabsorbent hydrogel composites exhibited higher thermal stability compared to the IRS‐free sample. The pH dependent reversible swelling behavior of hydrogels was also investigated. It is found that the swelling process is pH dependent and reversible for synthesized superabsorbent. Superabsorbent hydrogel composites were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR spectroscopy was confirmed grafting of acrylic chains onto the surface of IRS particles. From the standpoint of these results, these strengthened and thermostabilized hydrogels may be considered as good candidates for a controlled release study and agricultural applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Radiation synthesis and characterization of poly(N,N-dimethylaminoethyl methacrylate-co-N-vinyl 2-pyrrolidone) hydrogels

In this study, radiation synthesis and characterization of swelling behavior and network structure of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), and poly(N,N-dimethylaminoethyl methacrylate-co-N-vinyl 2-pyrrolidone) (P(DMAEMA-co-VP)), hydrogels were investigated. PDMAEMA and P(DMAEMA-co-VP) hydrogels in the rod forms were prepared by irradiating the ternary mixtures of DMAEMA/VP/cross-linking agent, ethyleneglycol dimethacrylate (EGDMA), by gamma rays at ambient temperature. In composition ranges where the three components were completely miscible, water was also added to the ternary mixture to provide the formation of homogeneous polymerization and gelation. The influence of irradiation dose, comonomer, VP, and cross-linking agent, EGDMA, content on the total percentage gelation and monomer conversion were investigated. The effect of pH and temperature on the swelling behavior of hydrogels have also been examined. Hydrogels showed typical pH response and temperature responses, such as low-pH and low temperature swelling and high-pH and high temperature deswelling. Polymer-solvent interaction parameter (χ) and enthalpy and entropy changes appearing in the χ parameter for the P(DMAEMA-co-VP)-water system were determined by using Flory-Rehner theory of swelling equilibrium. The negative values for ΔH and ΔS indicate that prepared pure PDMAEMA and P(DMAEMA-co-VP) hydrogels have lower critical solution temperature (LCST) and Flory-Rehner theory of swelling equilibrium provides a satisfactory agreement to the experimental swelling data of the hydrogels.     

Synthesis and characterization of thermoresponsive isopropylacrylamide-acrylamide hydrogels

In this study, hydrogels of poly(N-isopropylacrylamide-co-acrylamide) having a thermoresponsive character were prepared by a redox polymerization method. NIPAM-co-AAm hydrogels with different thermoresponsive properties were obtained by changing the initial NIPAM/AAm mole ratio and crosslinker concentration.Equilibrium-swelling ratio, dynamic swelling ratio and dynamic deswelling ratio were evaluated for all hydrogel systems. The fast shrinking was observed with all gels. The time required for equilibrium shrinking increased with the increase of acrylamide content in the gel.     

Collagen-based highly porous hydrogel without any porogen: Synthesis and characteristics

In this contribution we have developed a collagen-based highly porous hydrogel by neutralizing the grafted poly(acrylamide-co-acrylic acid) after gel formation. Preparation of the hydrogels involved free radical polymerization of a combination of hydrolyzed collagen, acrylic acid (AA), acrylamide (AAm) and distilled water, in appropriate amounts and contained a crosslinking agent called N,N′-methylene bisacrylamide (MBA). The chemical structure of the hydrogels was characterized by means of FTIR spectroscopy, DSC and TGA thermal methods. Morphology of the samples was examined by scanning electron microscopy (SEM). Systematically, the certain variables of the graft copolymerization were optimized to achieve maximum swelling capacity. The absorbency under load (AUL) and centrifuge retention capacity (CRC) were measured. The swelling ratio in various salt solutions was also determined and additionally, the swelling of hydrogels was measured in solutions with pH ranged 1-13. The synthesized hydrogel exhibited a pH-responsiveness character so that a swelling-collapsing pulsatile behavior was recorded at pH 2 and 8.     

Modified carrageenan. 5. Preparation,swelling behavior,salt‐ and pH‐sensitivity of partially hydrolyzed crosslinked carrageenan‐graft‐polymethacrylamide superabsorbent hydrogel

The polysaccharide, kappa‐carrageenan (κC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N′‐methylene bisacrylamide (MBA) were used as a free‐radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either κC‐g‐PMAM or hydrolyzed κC‐g‐PMAM (PMAM: polymethacrylamide) was characterized by FT‐IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling capacity of these hydrogels was also measured in various salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Absorbency of superabsorbing hydrogels was examined in buffer solutions with pH range 1–13. Also, the pH reversibility and on–off switching behavior, at pH values 3.0 and 8.0, makes the synthesized hydrogels good candidates for controlled delivery of bioactive agents. Finally, swelling kinetics in distilled water and various salt solutions was preliminary investigated. Results showed that the swelling in water was faster than in saline solutions. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis and swelling behavior of thermosensitive hydrogels based on N-substituted acrylamides and sodium acrylate

A series of hydrogels based on N-isopropylacrylamide, sodium acrylate, and N-tert-butylacrylamide were synthesized by free radical polymerization in a mixture of dioxane and water with tetra(ethylene glycol) diacrylate as the crosslinker and benzoyl peroxide as the initiator. The swelling behavior including the swelling rate of the crosslinked gels in water was studied with gravimetric method. The swelling ratio of the gel (0.1 mol% crosslinking) can reach 420 g/g at 20 °C and such a gel can release 96% of the water absorbed at 40 °C. The lower critical swelling temperature (LCST) of the copolymers can be adjusted by changing the chemical composition of the polymers. Such crosslinked gels can be potentially used as thermosensitive superabsorbent because of their high water uptake and thermal sensitivity.     

Acrylamide Hydrogels Preparation via Free Radical Crosslinking Copolymerization: Kinetic Study and Morphological Investigation

The simultaneous gravimetric and dilatometric techniques have been used to study the kinetics of aqueous free radical crosslinking copolymerization of acrylamide (AAm) and N,N^'-methylenebisacrylamide (MBA) at different crosslinker ratios, and reaction temperatures. In this study, the gel properties were investigated using swelling measurements and microscopic techniques. Based on the data, it was proposed that the deviation point of the results of dilatometric technique from those of the gravimetric one can be a new criterion for gel point. The monomer conversion and the equilibrium swelling ratio of the hydrogels were measured as a function of the reaction time. Experimental data showed an inverse dependence of the critical gel point on crosslinker concentration. As the MBA/AAm ratio was decreased to 0.1?wt%, the product appearance changed. In addition, the effects of temperature on the reaction rate and critical gel point were studied. At higher temperatures, the equilibrium swelling ratio reached to its minimum value earlier. Besides, the hydrogel surface became smoother.     

Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) hydrogels: Synthesis, swelling and interaction with ionic surfactants

Thermosensitive hydrogels were prepared by free-radical polymerization in aqueous solution from N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N-Methylenebis(acrylamide) (MBAAm) was used as a crosslinker. A kinetic study of the absorption determined the transport mechanism. The diffusion coefficients of these hydrogels were calculated for the Fickian mechanism. It was shown that the swelling behavior of the P(NIPA-co-AAm) hydrogels can be controlled by changing the amount of MBAAm. The swelling equilibrium of the P(NIPA-co-AAm) hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In SDS and DTAB solutions, the equilibrium swelling ratio of the hydrogels increased, this is ascribed to the conversion of non-ionic P(NIPA-co-AAm) hydrogel into polyelectrolyte hydrogels due to binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method, it was found that the electric conductivity of the P(NIPA-co-AAm)—surfactant systems depended strongly on both the type and concentration of surfactant solutions.     

不同交联剂对甲基丙烯酸-β-羟乙酯/E-51双甲基丙烯酸酯聚合物水凝胶性能的影响

以水溶性单体甲基丙烯酸-β-羟乙酯(HEMA)与大分子交联剂E-51双甲基丙烯酸酯(E-51-DMA)(质量比HEMA/E-51-DMA=90/10)为主要原料,分别引入了5种小分子交联剂:N,N′-亚甲基双丙烯酰胺(MBA)、二乙烯基苯(DVB)、双甲基丙烯酸乙二醇酯(EDMA)、1,1,1-三(丙烯酰氧甲基)丙烷(TAP)和2,2,2-三(丙烯酰氧甲基)乙醇(TAE),采用本体聚合方法合成了5个系列的聚合物水凝胶.研究了小分子交联剂的类型及用量对水凝胶溶胀性能、杨氏模量以及有效交联密度ve和聚合物-水相互作用参数χ的影响,并比较了不同交联剂的交联效率.结果表明,随着小分子交联剂用量的增大,水凝胶平衡含水量EWC逐渐降低,聚合物体积分数2逐渐增大,反映聚合物网络结构的有效交联密度ve以及热力学参数聚合物-水相互作用参数χ值也随之增大.通过理论交联密度和有效交联密度的线性拟合,得到所选用的5种小分子交联剂在E-51-DMA10/HEMA90水凝胶体系中的交联效率,其顺序为DVB>EDMA>TAE>MBA≈TAP.     

Chemically Crosslinked pH- and Temperature-Sensitive (N-isopropylacrylamide-co-1-vinyl-2-pyrrolidone) Based on New Crosslinker: I. Swelling Behavior

Novel pH- and temperature-sensitive polymer matrices based on N-isopropylacrylamide have been developed. The hydrogels were prepared by bulk radical polymerization of N-isopropylacrylamide and 1-vinyl-2-pyrrolidinone in appropriate amounts of distilled water using different mol% of traditional N,N-methylene bisacrylamide (MBA) and the new synthesized N,N,N-tris acryloyl melamine (MAAm) crosslinkers. Lower critical solution transition temperatures (LCST) were measured by differential scanning calorimetry. The synthesized hydrogels have LCST lower than 40°C. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. The crosslinked NIPAAm/VP with MAAm hydrogels exhibited more rapid deswelling rate than NIPAAm/VP hydrogels crosslinked with MBA in pure water in response to abrupt temperature changes from 20°C to 50°C.     

Surfactant-bound monolithic columns for separation of proteins in capillary high performance liquid chromatography

A surfactant-bound monolithic stationary phase based on the co-polymerization of 11-acrylamino-undecanoic acid (AAUA) is designed for capillary high performance liquid chromatography (HPLC). Using D-optimal design, the effect of the polymerization mixture (concentrations of monomer, crosslinker and porogens) on the chromatographic performance (resolution and analysis time) of the AAUA–EDMA monolithic column was evaluated. The polymerization mixture was optimized using three proteins as model test solutes. The D-optimal design indicates a strong dependence of chromatographic parameters on the concentration of porogens (1,4-butanediol and water) in the polymerization mixture. Optimized solutions for fast separation and high resolution separation, respectively, were obtained using the proposed multivariate optimization. Differences less than 6.8% between the predicted and the experimental values in terms of resolution and retention time indeed confirmed that the proposed approach is practical. Using the optimized column, fast separation of proteins could be obtained in 2.5 min, and a tryptic digest of myoglobin was successfully separated on the high resolution column. The physical properties (i.e., morphology, porosity and permeability) of the optimized monolithic column were thoroughly investigated. It appears that this surfactant-bound monolith may have a great potential as a new generation of capillary HPLC stationary phase.     

Preparation,swelling, and stimuli‐responsive characteristics of superabsorbent nanocomposites based on carboxymethyl cellulose and rectorite

Utilization of naturally available raw materials for the fabrication of eco‐friendly functional materials has long been desired. In this work, a series of superabsorbent nanocomposites were prepared by radical solution copolymerization of sodium carboxymethyl cellulose (CMC), partially neutralized acrylic acid (NaA), and rectorite (REC) in the presence of initiator ammonium persulfate (APS) and crosslinker N,N'‐methylene‐bis‐acrylamide (MBA). The optimal reaction variables including the mass ratio of acrylic acid (AA) to CMC, MBA concentration, and REC content were explored. FTIR spectra confirmed that NaA had been grafted onto CMC and REC participated in polymerization. REC was exfoliated and uniformly dispersed in the CMC‐g‐PNaA matrix without agglomeration as shown by XRD, TEM, and SEM analysis. The thermal stability, swelling capabilities, and rate of the nanocomposites were improved after introducing REC, and the gel strength greatly depended on the concentration of crosslinker MBA. The nanocomposite showed excellent responsive properties and reversible On–Off switching characteristics in various saline, pH, and hydrophilic organic solvent/water solutions, which provided great possibility to extend the application domain of the superabsorbent nanocomposites such as drug delivery system. Copyright © 2010 John Wiley & Sons, Ltd.     

Gel formation in atom transfer radical polymerization of 2‐(N,N‐dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate

Copolymers of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA) were synthesized via atom transfer radical polymerization using ethyl 2‐bromoisobutyrate as the initiator, Cu(I)Br as the catalyst, and 1,1,4,7,10,10‐hexamethyltriethylene tetramine as the ligand. At low crosslinker levels, the polymerizations followed the first‐order kinetics. However, when the crosslinker level was above 10 mol %, the ln([M]₀/[M]) versus time curves showed deceleration at medium conversions because of the higher reactivity of EGDMA than that of DMAEMA. An acceleration at high conversions was also observed and probably caused by the diffusion limitations of catalyst/ligand complex in the polymer network. The hydrogels were characterized by swelling experiments, and the sol polymers were characterized by the size exclusion chromatographic technique to determine the number‐average molecular weight and polydispersity. The gel data were analyzed and, via a comparison to Flory's gelation theory, found to be more homogeneous than similar hydrogels prepared by conventional free‐radical polymerization methods. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3780–3788, 2001     

Synthesis,characterization, and swelling behaviors of chitosan‐g‐poly(acrylic acid)/poly(vinyl alcohol) semi‐IPN superabsorbent hydrogels

A series of granulated semi‐interpenetrating polymer network (semi‐IPN) superabsorbent hydrogels composed of chitosan‐g‐poly(acrylic acid) (CTS‐g‐PAA) and poly(vinyl alcohol) (PVA) were prepared by solution polymerization using ammonium persulfate (APS) as an initiator and N,N′‐methylenebisacrylamide (MBA) as a crosslinker. The effects of reaction conditions such as the concentration of MBA, the weight ratio of AA to CTS, and the content of PVA on water absorbency were investigated. Infrared (IR) spectra and differential scanning calorimetry (DSC) analyses confirmed that AA had been grafted onto CTS backbone, and PVA semi‐interpenetrating into CTS‐g‐PAA networks. SEM analyses indicated that CTS‐g‐PAA/PVA has improved porous surface and PVA was uniformly dispersed in CTS‐g‐PAA network. The semi‐IPN hydrogel containing 10 wt% PVA shows the highest water absorbency of 353 and 53 g g^?1 in distilled water and 0.9 wt% NaCl solution, respectively. Swelling behaviors revealed that the introduction of PVA could improve the swelling rate and enhance the pH stability of the superabsorbent hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.     

TEMPERATURE AND pH RESPONSE, AND SWELLING BEHAVIOR OF POROUS ACRYLONITRILE-ACRYLIC ACID COPOLYMER HYDROGELS

Macroporous acrylonitrile-acrylic acid （AN-AA） copolymer hydrogels were synthesized by flee-radical solution polymerizations, using ammonium persulfate （APS）/N,N,N＇,N＇-tetramethylethylenediamine （TEMED） redox initiator system and alcohols porogens. The morphology, temperature and pH sensitive swelling behavior, and swelling kinetics of the resulting hydrogels were investigated. It was found that alcohol type and concentration had great influences on the pore structure and porosity of hydrogels. The pore size of hydrogel increases with the moderate increase of the length of alcohol alkyl chain. However, a further increase of alkyl length would result in the formation of cauliflower-like structure and the decrease of pore size. The porosity of hydrogels increases with the increase of porogen concentration in the polymerization medium. The hydrogels with macroporous structure swell or shrink much faster in response to the change of pH in comparison with the conventional hydrogel without macroporous structure. Furthermore, the response rate is closely related to the porosity of the hydrogels, which could be easily controlled by modulating the concentration of the porogen in the medium. The circular swelling behavior of hydrogels indicated the formation of a relaxing three-dimensional network.