Study On The Preparation, Structure And Properties Of PH/Temperature-Sensitive Natural Polymer Hydrogels

In recent years, considerable research attention has been focused on 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, from the point of view of molecule design, a series of novel type of temperature and pH responsive hydrogels were prepared based on the poly (N-isopropylacrylamide) (PNIPAAm) with the excellent temperature sensitivity and the natural material, carboxymethyl chitosan (CMCS) or sodium carboxymethylcellulose (CMC) with pH sensitivity in this dissertation. The effect of the structure on the swelling and deswelling properties of these hydrogels has been systematically studied. The mechanism of the response has also been discussed. In addition, the preliminary study of the hydrogel as a drug delivery system has been performed. The main results obtained are as follows:1. A new kind of the semi-IPN hydrogel based on carboxymethyl chitosan and cross-linked poly (N-isopropylacrylamide) was preparedby semi-interpenetrating network (semi-IPN) technique. The swelling behaviors of the CMCS/PNIPAAm semi-IPN hydrogels, which response both temperature and pH value of the medium, were investigated in detail. Experimental results showed that the changes of the equilibrium swelling ratios of CMCS/PNIPAAm semi-IPN hydrogels are larger than those of the pure PNIPAAm hydrogel below and above the VPTT. The deswelling ratios of the semi-IPN hydrogels are higher than those of the pure hydrogel. Around the CMCS isoelectric point (pH=2.71), the volume phase transition temperatures (VPTT) of CMCS/PNIPAAm semi-IPN hydrogels reduce sharply. The swelling ratios of CMCS/PNIPAAm semi-IPN hydrogels at pH=2-4 are lower than those at other conditions.2. Based on the CMCS/PNIPAAm semi-IPN hydrogels, the CMCS/PNIPAAm full-IPN hydrogels were prepared by crosslinking CMCS with glutaraldehyde (GA). Changes of the network structure don't affect the VPTT of the interpenetrating network hydrogels, which is about 33℃. 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 at different pH value of the medium.3. Another semi-IPN hydrogels with temperature and pHresponsive based on sodium carboxymethylcellulose (CMC) and cross-linked poly (N-isopropylacrylamide) were prepared by semi-interpenetrating network (semi-IPN) technique and their swelling behaviors were investigated in detail. Experimental results indicated that the swelling ratios of the CMC/PNIPAAm semi-IPN hydrogels at pH 1.2 are lower than those of pure PNIPAAm hydrogel, whereas the swelling ratios of the CMC/PNIPAAm semi-IPN hydrogels at pH 7.4 are higher than those of pure PNIPAAm hydrogel; the higher the CMC content in the semi-IPN hydrogels, the stronger the tendency; whether at acidic condition (pH=1.2) or weak alkaline condition (pH=7.4), the swelling ratios of the CMC/PNIPAAm semi-IPN hydrogels decrease with increasing temperature. The influence of pH on the swelling ratios of the hydrogels revealed that pH-response of the hydorgel below the volume phase transition temperature (VPTT) (25℃) is more significant than that of above the VPTT(37℃). The deswelling rates of the semi-IPN hydrogels are higher than those of the pure hydrogel, and the deswelling rates increased with increasing the amount of CMC.4. The swelling kinetics of CMC/PNIPAAm semi-IPN hydrogels was studied. The results indicated that at weak alkaline condition, the transport mechanism of the hydrogels is non-Fickian transport. And at acid condition, the transport mechanism belongs to non-Fickiantransport for the hydrogels below the VPTT; the transport mechanism belongs...