Biodegradable and stimuli sensitive amphiphilic graft copolymers and their sol-gel phase transition behavior

Abstract

pH and temperature-sensitive biodegradable poly(β-aminoester)-graft-poly(ε-caprolactone)-block-methoxy poly(ethylene glycol) (PBAE-g-PCL-b-mPEG) amphiphilic graft copolymers with different molecular weights were synthesized. The structure of these copolymers was adjusted by varying the feed ratios of ε-caprolactone to methoxy poly(ethylene glycol)s (mPEG), amine and diacrylate monomer amounts and the molecular weight of mPEG. Aqueous solutions of these copolymers formed micelles at lower concentrations; however, the concentrated solutions showed a reversible sol-gel transition property depending on both pH and temperature changes under representative physiological conditions (pH7.4, 37°C). The effects of the molecular weight of pH-sensitive poly(β-aminoester) block and mPEG group, the hydrophobic to hydrophilic block ratio (PCL/mPEG) and the concentration of the copolymer on the sol-gel transition were investigated. Proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography measurements were used to characterize the structure of the synthesized copolymers. The self-assemble behavior and critical micelle concentration of the amphiphilic copolymers were estimated in phosphate buffer solution using fluorescence spectroscopy. The gelling behavior was measured by using tube inversion method. At pH7.4, all copolymer solutions prepared 20wt% concentration indicated sol-gel transition with increasing temperature. In vitro degradation experiments displayed that the synthesized graft copolymers mostly degraded hydrolytically within 20days under physiological conditions. In order to investigate the potential application of synthesized hydrogels in drug delivery, Methylene Blue was used and approximately 70% of the loaded amount was released in 120hr. The findings indicate that obtained graft copolymers can be used as injectable biodegradable carriers for pharmaceutical drugs.