Study On PreParation And Properties Of Injectable Temperature Sensitive Hydrogels

The injectable block copolymer hydrogels, which are reversible polymer networks formed by physical interactions and exhibit a sol-gel phase transition in response to external stimuli, have great potential in biomedical and pharmaceutical applications, especially in site-specific controlled drug-delivery systems. The drug may be mixed with a polymer solution in vitro and the drug-loaded hydrogel can form in vivo after injection. Stimuli-sensitive block copolymer hydrogels have many advantages. This paper concerns the synthesis, characterization, and properties of the injectable polyester/polyether hydrogels and their potential applications. Temperature sensitive hydrogel is one of the important stimuli-sensitive hydrogels, because it is easy to control and has practical advantages.(1) Butanediol as the initiator, PLLA was synthesized by ring-opening polymerization of L-lactide. When the mole ratio of succinic anhydride and PLLA was 3:1, reaction time was 24h and reaction temperature was 28℃, the PLLA has the largest yield and the most number of carboxyl group. A Series of poly(L-lactic acid)/poly(ethylene glycol) multiblock copolymers was synthesized. which aqueous solution undergoing the sol-gel transition temperature from 15 to 42℃. The chemical stucture was characterized by 1H-NMR. The transition temperature and range of phase transition were affected by the molecular weight and composition of the multiblock copolymer.(2) Pentaerythritol and Glycerol as the initiator, star PLLA was synthesized by ring-opening polymerization of L-lactide. A Series of poly(L-lactic acid)/poly(ethylene glycol monomethyl ether) star multiblock copolymers was synthesized, which aqueous solution undergoing sol-gel transition from 20 to 66℃. The transition temperature and range of phase transition were affected by the molecular weight and composition of the multiblock copolymer. At low temperatures, block copolymer self-assembled in aqueous solution to form polymeric micelles. As the temperature increases, micelles aggregated to form larger size micellarclusters which should play a critical role in the sol-gel transition, and sol-gel phase transition took place. The hydrophobic force was the phase transforming driving force.(3) In vitro release profile of urapidil hydrochloride from star block copolymer hydrogels was performed. Experimental results showed the copolymer hydrogels exhibited better sustained-release capacity and the drug release lasted 30h. There were two drug release behavior in whole release process. The drug release followed zero-order kinetic.in the first stage, and then Ritger-Peppas kinetic.