Synthesis, self-assembly, and formation of polymer vesicle hydrogels of thermoresponsive copolymers

A series of N-isopropylacrylamide and methacrylate derivative random copolymers with various contents of cholic acid groups in the side chain are synthesized by free radical polymerization. These thermoresponsive random copolymers can organize themselves into large vesicles in water upon heating, accompanied by gradual phase transitions from transparent polymer solutions to turbid solutions and then to white hydrogels. The white vesicle hydrogels display non-elastic deformation and shrink. They can re-dissolve directly upon cooling. Further, X-ray diffraction results indicate the existence of crystalline regions on the vesicle membrane. Based on these results, the possible formation mechanism of the fiber-layer structures on the vesicle membrane is also discussed. It is noteworthy that the gel-forming temperatures of the resultant copolymers below 37 °C which indicate the vesicle gels may find applications as injectable implant systems for sustained drug delivery.