Stnthesis And Characterization Of Temperature And PH Dual Sensitive Hydrogels Cross-linked With Chitosan

Hydrogels are insoluble, cross-linked three dimensional network structure composed of hydrophilic polymer, which do not dissolve in water but absorb a great deal of water. Intelligent or smart hydrogels are a class of polymers which undergoing a volume phase transition in response to environmental stimulus, such as pH, temperature, electric fields and so on. Intelligent hydrogels have promising potential application in the field of drug delivery system, biomaterial culture and tissue engineering because of their biocompatibility,flexibility and similarity to natural tissues,etc. Poly(N-isopropylacryamide) (PNIPAAm) is a thermosensitive hydrogel that has received much attention and application because of its lower critical solution temperature (LCST) behavior at around 32°C in an aqueous solution, which is close to the physiological temperature.In this paper, the cross-linker N-maleyl chitosan (N-MACH) was synthesized with chitosan (CS) and maleic anhydride (Ma) as materials. Poly(N-isopropylacryamide) (PNIPAAm) hydrogels, Poly(N-isopropylacryamide-co-acrylamide) [P(NIPAAm-co-Am)] hydrogels and Poly(N-isopropylacryamide)/Sodium carboxymethyl cellulose (PNIPAAm/CMC) semi-interpenetrating polymer network (semi-IPN) hydrogels have been synthesized by the free radical polymerization in distilled water, with the soluble and biodegradable N-MACH cross-linker. The temperature and pH sensitive behavior, swelling/deswelling kinetics, swelling ratio in NaCl solution, the thermodynamics and the morphology of the hydrogels were investigated. At last, the biodegradable behaviors of P(NIPAAm-co-Am) hydrogels in simulated intestinal fluid (SIF) and simulated gastric fluid (SGF) were investigated.1. The content of the N-MACH cross-linker and CMC did not influence the lower critical solution temperature (LCST) of hydrogels evidently, but it was significantly influenced by monomer ratio of the NIPAAm/Am. The LCST increased with the increase of the content of Am.2. All the hydrogels exhibited fast swelling kinetics in DW at 25°C, the swelling ratio of the hydrgels was increased with the increase of Am and CMC content, but decreased with the increase of N-MACH cross-linker content.3. The hydrogels deswelled fast in DW when the temperature was above their LCSTs. The deswelling rate of the hydrogels was decreased with the increase of N-MACH cross-linker,Am and CMC content.4. The swelling ratio of the hydrogels was decreased sharply with increasing NaCl concentration to 0.05 mg/mL at 25°C.5. The swelling ratio of the hydrogels was strongly dependent on the pH of the swelling medium. The swelling ratio of the PNIPAAm and P(NIPAAm-co-Am) hydrogels in acid/alkaline buffer solutions was higher than that in the neutral solution. The pH sensitive behavior of PNIPAAm/CMC semi-IPN hydrogels was different from PNIPAAm and P(NIPAAm-co-Am) hydrogels because of the introduction of CMC.6. The thermodynamic stability of the hydrogels was characterized by thermogravimetry. The result showed that the hydrogel had a good thermal stability.7. The glass temperature (Tg) of P(NIPAAm-co-Am) and PNIPAAm/CMC semi-IPN hydrogels was higher than that of PNIPAAm hydrogels. It was intimated the successful introduction of Am and CMC.8. The morphology of hydrogels was estimated by field scan electron microscopy (SEM). The hydrogels contained open and well-structure orientated porous network. 9. In enzymatic degradation studies, the weight loss of the P(NIPAAm-co-Am) hydrogels was strongly dependent on the cross-linking density, the content of Am, and the concentration of the lysozym and pepsin.