Abstract:

The effect of PEG and PCL composition of thermosensitive PCL-PEG-PCL hydrogels on Sol-gel transition temperature and release rate of bovine serum albumin(BSA) were investigated. A series of thermosensitive PCL-PEG-PCL triblock copolymers with different PEG and PCL block lengths were synthesized via ring-opening polymerization of ε-CL using PEG1500/PEG1000 as the initiator and Sn(Oct)₂ as the catalyst. Their composition, structure, and molecular weight were characterized via ¹H NMR and GPC techniques. The Sol-gel transition temperature was determined with the test tube inverting method. TEM, ¹H NMR, and fluorescence probe technique were employed to identify formation of micelles of the triblock copolymers in aqueous solution. BSA was used as a model protein drug. Hydrogels of these PCL-PEG-PCL triblock copolymers loaded with BSA were prepared for in vitro release study, and BSA concentration in the released sample was determined with microBCA method. The effect of PCL and PEG block lengths on Sol-gel transition temperature and release rate of BSA was also discussed. The results obtained indicated that the Sol-gel transition temperature of copolymers was related to block lengths of PCL and PEG, increasing the PCL length at a fixed PEG central block led to a lower transition temperature at a given copolymer concentration, while with the enhancement of the PEG length at a similar hydrophobic PCL length, the transition temperature increases. And the protein release rate was independent of the hydrophobic PCL length, whereas the longer PEG length, the lower protein release rate.

Key words: PCL-PEG-PCL copolymer; Temperature-sensitive; Hydrogel; Sol-gel transition temperature; Controlled release of protein drug