Synthesis And Phase Transition Mechanism Of Temperature-sensitive Hydrogel

Hydrogels are a class of polymeric materials, generally cross-linked, that swell inwater or in biological fluids without dissolving. They are organized asthree-dimensional networks of polymeric chains, physically and chemically bounded,and partially solvated by water molecules. Intelligent or smart hydrogels are a class ofpolymers which undergoing a volume phase transition in response to environmentalstimulus, such as pH, temperature, electric fields and so on. Temperature sensitivehydrogels are the most extensively studied stimuli-sensitive materials.Poly(N-isopropylacrylamide)(PNIPAAm) hydrogel is temperature sensitive, whichexhibits a lower critical solution temperature (LCST) at around32oC. They have beenused in various biomedical fields, including protein-ligand recognition, drug controlledrelease, recovered and cultured cells and immobilization enzymes.In this paper, in order to make much study on the characterizations ofpoly(N-isopropylacryamide) hydrogel, a hydrophilic monomer acrylic acid (AA),hydrophobic monomer ethyl acrylate (EA) or butyl acrylate (BA) and naturalpolysaccharides sodium alginate (SA) was introduced into the PNIPAAm backbone. Aseries of temperature and pH sensitive hydrogels were synthesized. Temperaturesensitivity, pH dependence of swelling and the swelling/deswelling behaviors ofhydrogels were investigated, respectively, which could improve the characterizationsof intelligent hydrogel.1. The contents of the N-maleyl chitosan (N-MACH) cross-linker and SA did notinfluence the lower critical solution temperature (LCST) of hydrogels evidently.2. Poly(N-isopropylacryamide-co-acrylic acid)[P(NIPAAm-co-AA)] hydrogelsexhibited LCST at34~39°C, with decreasing NIPAAm/AA from96/4to92/8and90/10, the LCST increased from34°C to37°C and39°C. 3. Poly(N-isopropylacryamide-co-ethyl acrylate)(P(NIPAAm-co-EA)) hydrogelsand poly(N-isopropylacryamide-co-butyl acrylate)(P(NIPAAm-co-BA)) hydrogelsexhibited LCST at29~31°C, increasing the amount of EA or BA in the hydrogelgradually decreased the LCST.4. The swelling ratio of the PNIPAAm, P(NIPAAm-co-AA), P(NIPAAm-co-EA)or P(NIPAAm-co-BA) hydrogels in acid/alkaline buffer solutions was higher than thatin the neutral solution. The pH sensitive behavior of SA/PNIPAAm semi-IPNhydrogels was different from other hydrogels because of the introduction of SA.5. All the hydrogels exhibited fast swelling in distilled water at25°C, theswelling ratio of the hydrgels was increased with the increase of SA or AA content, butdecreased with the increase of N-MACH cross-linker, EA or BA content.6. In the swelling/deswelling kinetics, all the dried hydrogels exhibited fastswelling/deswelling behavior, which might be attributed to macroporous structures ofthe hydrogels. The deswelling ratio of the hydrgels was decreased with the increase ofSA or AA content, but increased with the increase of N-MACH cross-linker, EA or BAcontent.