P (NVP-co-¦Â-HPAT) / CS Interpenetrating Polymer Network Gel Synthesis And Environmental Response Characteristics

Chitosan was obtained by alkaline deacetylation of chitin from the shell of shrimp,crab and insects etc, is an alkaline polymer, one of the abundant and reproducible natural polymers in the world. Due to the biocompatibility, biodegradable, no toxicity and environmental friendship, chitosan and its ramifications are potentially be widely applied especially in biomedical applications such as in drug delivery system and artificial soft tissues and so on. In recent years, considerable research attention has been focusedon the environment-sensitive hydrogels(intelligent hydrogels) because they possess great potential applications in many aspects, including drug delivery system, enzyme immobilization and biomaterials separation and purification, etc. Among them, temperature and pH responsive hydrogels have attracted great interest from both fundamental and application fields at present. Therefore, a series of novel type of temperature and pH responsive semi-IPN and full-IPN (NVP-co-β- HPAT) / CS hydrogels were prepared based on the chitosan(CS) and N-vinyl-pyrrolidone-co-β-hydropropylacrylate(NVP-co-β-HPAT). The effect of the structure on the swelling and deswelling properties of these hydrogels have been systematically studied. Themechanism of the response has also been discussed. In addition, thepreliminary study of the hydrogel as a drug delivery system has been performed. The main results obtained are as follows:Firstly, A new kind of the semi-IPN hydrogel based on chitosan and cross-linked NVP-co-β-HPAT was prepared by semi-interpenetrating network (semi-IPN) technique. The effects of various factors such as temperature,pH,ionic strength and monomer mass ratios on the degree of equilibrium swelling were investigated.The results showed that the semi-IPN hydrogel had excellent temperature and pH-sensitivity, and the ionic strength had little influence on the swelling behaviour of the semi- IPN hydrogel in the range of I<2.0M. the degree of equilibrium swelling ratio of the semi-hydrogel increased with increasing of the concent ration of NVP. The semi-IPN hydrogel showed swelling reversibility when soaked in 20℃and 45℃distilled water, pH =3.0 and pH=8.0 buffer solutions alternately. The results imply that the semi-IPN hydrogel could be potential carrier for drug delivery system. The deswelling ratios of the semi-IPN hydrogels are higher than those of the NVP-co-β-HPAT hydrogel.Secondly, Based on the NVP-co-β-HPAT/CS semi-IPN hydrogels, the (NVP-co-β-HPAT)/CS full-IPN hydrogels were prepared by crosslinking CS with glutaraldehyde(GA). At room temperature, the equilibrium swelling ratios and swelling rates of the full-IPN hydrogels are lower than those of the semi-IPN hydrogels. The deswelling rates of the full-IPN hydrogels are higher than those of the semi-IPN hydrogels.Lastly, A preliminary study of the conventional (NVP-co-β-HPAT/CS) semi-IPN hydrogels as the drug delivery system for the model drug, salicylic acid was performed. It was found that at 20℃and pH=7.4 the release rate and amount of salicylic acid increase with increasing NVP content in the (NVP-co-β-HPAT)/CS semi-IPN hydrogels and below the VPTT(at 20℃),the little effect of pH on the drug release rate was observed, while above the VPTT(at 45℃), the effect is remarkable.