Preparation Of Cyclotriphosphazene Hydrogel By Thiol-michael Addition

Phosphazene derivatives possess good biocompatibility and biodegradability. The degradation products are nontoxic, therefore phosphazene derivatives are promising in biomedicine, such as tissue engineering scaffold and drug controlling delivery.In this paper, hex[4-(monomethyl maleate) phenoxy]cyclotriphosphazene(HMCP) was synthesized from hexachlorocyclotriphosphazene, HMCP can rapidly crosslinked in situ with PEG-SH and pentaerythritol tetrakis(2-mercaptoacetate)(PTMA) under physiological conditions by thiol-Michael type addition. The reaction kinetics showed that the final conversion of double bonds was more than 90%. Moreover, compressive strength and compression modulus of the crosslinked products increased with the increasing of PTMA content. The swelling ratio and degradability of gel were sensitive to pH value. The largest swelling ratio of products was 672% in pH=7.4 solution, however, it hardly swell in pH=1.0 solution. Besides, the degradation rate of crosslinked products in pH=7.4 solution was faster than that of in pH=1.0 solution. The drug release rate of crosslinked products in pH=1.0 solution were slightly slower than that of in pH=7.4 solution.The gel was added into calcium phosphazene bone cement in order to improve the anti-washout capacity. The gel network did not hinder the formation of hydroxyapatite. But the mechanical strength reduced as the addition of gel system. However, degradation rate of composites in pH=7.4 solution was quite slow, the weight of the composites only dcreased about 5% after 90 days.