Study On The Preparation, Structure And Properties Of PH/Temperature-Sensitive Sodium Alginate/Poly(N-isopropylacrylamide) Hydrogels

In recent years, considerable research attention has been focused on the environment-sensitive hydrogels(intelligent hydrogel) 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 was prepared based on the poly(N-isopropylacrylamide) (PNIPAAm) with the excellent temperature sensitivity and the natural material, sodium alginate (SA) 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 approaches for improving the response rate of the hydrogel have been presented and 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 hydrogels based on sodium alginate and cross-linked poly (N-isopropylacrylamide) was prepared by semi-interpenetrating network (semi-IPN) technique. The swelling behaviors of the SA/PNIPAAm semi-IPN hydrogel, which response both temperature and pH value of the medium, were investigated in detail. Experimental results showed that the swelling ratios of the SA/PNIPAAm semi-IPN hydrogel at pH 1.2 are lower than those of pure PNIPAAm hydrogel, whereas the swelling ratios of the SA/PNIPAAm semi-IPN hydrogel at pH 7.4 are higher than those of pure PNIPAAm hydrogel; the higher the SA 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 SA/PNIPAAm semi-IPN hydrogel decrease with increasing temperature. The influence of pH on the swelling ratios of the hydrogel revealedthat pH-response of the hydorgel below the lower critical solution temperature (LCST) (25℃) is more significant than that of above the LCST(37℃).2. The swelling and deswelling kinetics of SA/PNIPAAm semi-IPN hydrogel were studied. The results indicated that at 25℃ (below the LCST) and pH=7.4 the swelling rate increased with increasing SA content in the semi-IPN hydrogel which may ascribe to the relaxation rate of macromolecular chains in the hydrogel network. In addition, the effect of pH value on the swelling rate was dependent on temperature while the effect of temperature on the swelling rate was also associated with pH value, the deswelling behaviors of SA/PNIPAAm semi-IPN hydrogel under at 45℃ or pH 1.2 conditions could be well described with the first-order kinetic equation, and the deswelling rate increase significantly with increasing SA content in the semi-IPN hydrogel.3. The effect of SA molecular weight and its amount used on the swelling behaviors of SA/PNIPAAm semi-IPN hydrogel were studied. The results showed that the molecular weight of SA and its amount used had hardly effect on the volume phase transtion temperature of the semi-IPN hydrogels; the equilibrium swelling ratio of the semi-IPN hydrogels increased with increasing the molecular weight of SA and its amount used; the swelling rate of the semi-IPN hydrogels decreased with the increase in molecular weight of SA and its amount used under acidic condition (pH=1.0), but the case was inverse under basic condition (pH=7.4); As the amount of SA used was small, the molecular weight of SA had great effect on the deswelling rate of the semi-IPN hydrogels while with increasing the amount of SA, the effect was decreased.4. The Cr-PNIPAAm/(SA/PNIPAAm) semi-IPN-II hydrogels were prepared by addition of the linear sodium alginate and PNIPAAm into the cross-linked PNIPAAm hydrogel network. The results indicated that the ratios of SA to linear PNIPAAm had less effect on the swelling ratios of the Cr-PNIPAAm/(SA/PNIPAAm) sem...