Influence of Amide versus Ester Linkages on the Properties of Eight-Armed PEG-PLA Star Block Copolymer Hydrogels

• DOI: 10.1021/bm901080d
• Publication Date: 2009-11-25T18:48:03Z
• Authors: Sytze J. Buwalda; Pieter J. Dijkstra; Lucia Calucci; Claudia Forte; Jan Feijen
• Keywords: Magnetic Resonance Spectroscopy; Polymers; Organic polymers; Copolymers; Polyesters; Biocompatible Materials; Esters; Hydrogels; PEG; Amides; 01 natural sciences; Polyethylene Glycols; 0104 chemical sciences; Biopolymers; drug delivery; PLA; Rheology; Plastics; hydrogels

Water-soluble eight-armed poly(ethylene glycol)-poly(l-lactide) star block copolymers linked by an amide or ester group between the PEG core and the PLA blocks (PEG-(NHCO)-(PLA)(8) and PEG-(OCO)-(PLA)(8)) were synthesized by the stannous octoate catalyzed ring-opening polymerization of l-lactide using an amine- or hydroxyl-terminated eight-armed star PEG. At concentrations above the critical gel concentration, thermosensitive hydrogels were obtained, showing a reversible single gel-to-sol transition. At similar composition PEG-(NHCO)-(PLA)(8) hydrogels were formed at significantly lower polymer concentrations and had higher storage moduli. Whereas the hydrolytic degradation/dissolution of the PEG-(OCO)-(PLA)(8) takes place by preferential hydrolysis of the ester bond between the PEG and PLA block, the PEG-(NHCO)-(PLA)(8) hydrogels degrade through hydrolysis of ester bonds in the PLA main chain. Because of their relatively good mechanical properties and slow degradation in vitro, PEG-(NHCO)-(PLA)(8) hydrogels are interesting materials for biomedical applications such as controlled drug delivery systems and matrices for tissue engineering.