Biodegradable thermogelling poly(ester urethane)s consisting of poly(1,4-butylene adipate), poly(ethylene glycol), and poly(propylene glycol)

Abstract

New biodegradable and thermoresponsive amphiphilic multiblock poly(ester urethane) copolymers consisting of poly(1,4-butylene adipate) (PBA), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) were synthesized. The chemical structures and molecular characteristics of the copolymers were confirmed by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy. The copolymers had relatively high molecular weights ranging from 40k to 46k with narrow molecular weight distributions. The amphiphilic block copolymers could form micelles in water with very low critical micellization concentration (CMC) values that are dependent on the PBA content and temperature. The copolymers with higher PBA contents showed lower CMC values because the PBA segments increased the hydrophobicity of the copolymers. The thermodynamic parameters of the micellization process were studied through CMC dependence on temperature, and it was concluded that the micellization process is a spontaneous and entropy-driven process. The aqueous solutions of the copolymers could form thermosensitive hydrogels with very low critical gelation concentrations (CGCs) ranging from 5 to 8 wt%. Higher PBA contents resulted in lower CGCs and higher strength of the hydrogels, again because of the hydrophobicity of the PBA segments. The hydrolytic degradation studies showed that these hydrogels could degrade rapidly within a period of 40 days, which resulted in the mass loss of the hydrogels and the molecular weight decrease of the copolymers. The copolymer hydrogels could sustain the release of the bovine serum albumin (BSA) model protein drug up to a few weeks, and the protein release rate could be controlled by the PBA contents in the copolymers. The cell viability assay showed that the poly(PEG/PPG/PBA urethane)s did not elicit cytotoxic response against the L929 cells with the copolymer concentration up to 0.63 mg mL⁻¹. The PBA-based polyurethane copolymers may be candidate biomaterials for promising biomedical applications.