Synthesis And Characterization Of Thermosensitive Hydrogel With Improved Mechanical Properties

P(N-isopropylacrylamide)(PNIPAAm) is one of the most widely studied thermo-sensitive hydrogels, exhibiting a reversible phase transition in aqueous solutions at a lower critical solution temperature (LCST). Many investigators have reported on the potential of PNIPAAm hydrogels for use in several biomedical applications, including drug delivery, bioseparation and so on. However, an important limitation of PNIPAAm hydrogels for application is their poor mechanical properties. Preparation of interpenetrating polymer network (IPN) structure is an effective method to improve the mechanical strength of the hydrogel.In this paper, in order to improve the mechanical properties and biocompatibility of the thermosensitive PNIPAAm hydrogel, firstly natural polysaccharides sodium alginate (SA) was introduced into the PNIPAAm backbone to form SA/PNIPAAm semi-IPN hydrogel, then Ca-alginate polymer was prepared by crosslinking of SA with Ca2+ ions, and full-IPN hydrogel was synthesized by which Ca-alginate was entangled with PNIPAAm. The improvement of compressive strength, tensile strength and Elongation at Break of the semi-IPN and full-IPN hydrogels were studied. And temperature sensitivity, swelling/deswelling behaviors and the preliminary study of drug release of these two kinds of hydrogels were investigated respectively.1. The liner copolymer SA was entangled with PNIPAAm network, which had no obvious effect on the LCST of the semi-IPN hydrogel; The LCST of the full-IPN hydrogel with Ca-alginate and PNIPAAm increased to 34℃.2. All the hydrogels exhibited fast swelling in distilled water at 25 ℃,and the swelling ratio of the hydrgels was increased with the increase of SA content. The swelling ratio of full-IPN hydrogel was smaller than semi-IPN hydrogel slightly. The swelling properties of these two kinds of hydrogels in PBS were better than that in simulated gastric fluid.3. Ionic strength of the salt solution had a great influence on the swelling properties of these two kinds of hydrogels. The swelling ratio of the hydrogels was decreased sharply with increasing NaCl concentration to 0.07 mg/mL at 25 ℃.4. 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 SA and Ca2+ content.5. The compressive strength of semi-IPN hydrogel was higher than pure PNIPAAm, and the compressive strength of the hydrgels was increased with the increase of SA content. Full-IPN hydrogels had higher compressive strength and tensile strength, and the mechanical strength of the hydrgels was increased with the increase of Ca2+content.6. The thermodynamic stability of the hydrogels was characterized by thermogravimetry. The result showed that the hydrogel had a good thermal stability. The glass transition temperature (Tg) of full-IPN and semi-IPN hydrogels were higher than that of PNIPAAm hydrogels. It was intimated the successful introduction of SA and Ca-alginate.7. The morphology of hydrogels was estimated by field scan electron microscopy (SEM). The hydrogels contained open and well-structure orientated porous network.8. A preliminary study of IPN hydrogels as the drug delivery system for the model drug,5-fluorouracil (5-Fu) was performed. It was found that the release rate and amount of 5-Fu increase with increasing SA content in the semi-IPN hydrogel. The release of 5-Fu in full-IPN hydrogel was slower than that of semi-IPN hydrogel. Temperature and pH of the medium had effect on the release behaviors.