Thermosensitive sol-gel phase transition behavior of methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) diblock copolymers

Poly(ethylene glycol)-based diblock and triblock polyester copolymers stimulating to temperature were studied as injectable biomaterials in drug delivery system because of their nontoxicity, biocompatibility and biodegradability. We synthesized the diblock copolymers consisting of methoxy poly(ethylene glycol) (MPEG) (M_n = 750 g/mole) and poly(ε-caprolactone) (PCL) by ring opening polymerization of ε-CL with MPEG as an initiator in the presence of HCl·Et₂O. The aqueous solution of synthesized diblock copolymers represented sol phase at room temperature and a sol to gel phase transition as the temperature increased from room temperature to body temperature. To confirm the in vivo gel formation, we observed the formation of gel in the mice body after injection of 20 wt% aqueous solution of each block copolymer. After 2 months, we observed the maintenance of gel without dispersion in mice. In this study, we synthesized diblock copolymers exhibiting sol-gel phase transition and confirmed the feasibility as biomaterials of injectable implantation.