Stnthesis And Characterization Of Thermoresponsive Hydrogels Cross-Linked With N-Malely Chitosan

Intelligent hydrogels are hydrophilic polymers that are crosslinked to form insoluble, water-swellable networks, which have the capability to respond to small external stimulus changes, such as temperature, pH, light, ionic strength, magnetic field and so on. Especially, the temperature- and pH- responsive hydrogels whose swelling and deswelling behaviors are controlled by temperature and pH, have promising potential application in the field of drug delivery system, biomaterial culture and tissue engineering. Poly(N-isopropylacrylamide) (PNIPAAm) hydrogel is the best known temperature responsive hydrogel that has received much attention for biomedical use because of its volume phase transition (VPT) behavior around 32°C in an aqueous solution, which is close to the physiological temperature. Due to the biocompatibility, biodegradable, no toxicity and environmental friendship, chitosan is potentially widely applied in biomedical application. In this paper, soluble and biodegradable cross-linker N-maleyl chitosan(N-MACH) was synthesized with chitosan (CS) and maleic anhydride (Ma) as materials. With N-MACH cross-linker, a series of cross-linked poly(N-isopropylacrylamide-co-itaconic acid) [P(NIPAAm-co-IA)] hydrogels were prepared, and their pH-and temperature-responsive behaviors, water contents, swelling/deswelling kinetics, the thermodynamics and the morphology of the hydrogels were investigated. At last, a preliminary study of the biodegradable behaviors of P(NIPAAm-co-IA) hydrogels was investigated.1. The amount of the N-MACH cross-linker did not influence the volume phase transition temperature (VPTT) behavior of hydrogels evidently, while the VPTT of hydrogels was significantly influenced by weight ratio of the NIPAAm/IA.2. The water content of N-MACH-cross-linked P(NIPAAm-co-IA) hydrogels was controlled by the weight ratio of NIPAAm/IA, swelling media, cross-linker content and the temperature of the media. The swelling ratio of the hydrgels was increased with the increase of IA content, while decreased with the increase of cross-linker content. The water content was higher in water than in other medium. The swelling ratio of the hydrgels was higher at 25°C than at 37°C.3. The swelling behavior of the P(NIPAAm-co-IA) hydrogels was strongly dependent on the pH of the swelling medium. The swelling ratio of the hydrogels in acid/alkaline buffer solutions was higher than that in the neutral solution.4. All the P(NIPAAm-co-IA) hydrogels exhibited fast swelling kinetics in DW and PBS at 25°C, and all of them could reached swelling equilibrium within 480 min. The swelling ratios of the hydrogel decreased with the increase of the cross-linker content.5. The deswelling kinetics of N-MACH cross-linked P(NIPAAm-co-IA) hydrogels were studied. The deswelling rates of the hydrogel were dependent on the content of IA and cross-linker.6. The thermodynamics stability was characterized by thermogravimetry. The result showed that the hydrogel had a good thermal stability.7. The morphology of the hydrogels was estimated by the field scan electron microscopy. The P(NIPAAm-co-IA) hydrogel had macroporous network structure which could make water easier to diffuse in or out of the matrix.8. The degradation of the N-MACH cross-linked P(NIPAAm-co-IA) hydrogels as a function of times in the PBS at 37°C were studied. The breakdown of the hydrogels was dependent on the cross-linking density, the weight ratio of NIPAAm/IA.9. In enzymatic degradation studies, breakdown of the N-MACH cross-linked P(NIPAAm-co-IA) hydrogels was dependent on the cross-linking density, the weight ratio of NIPAAm/IA.