Stereocomplexed 8-armed poly(ethylene glycol)-poly(lactide) star block copolymer hydrogels: Gelation mechanism, mechanical properties and degradation behavior

Mixing aqueous poly(ethylene glycol)-poly(D-lactide) and poly(ethylene glycol)poly(L-lactide) star block copolymer solutions resulted in the formation of stereocomplexed hydrogels within 1 min. A study towards the mechanism of the temperature dependent formation of stereocomplexes in the hydrogels using rheology and nuclear magnetic resonance experiments revealed that the formation of stereocomplexes is facilitated at higher temperatures, due to rearrangement in the micellar aggregates thereby exposing more PLA units available for stereocomplexation. The formed gels became temperature irreversible due to the presence of highly stable semi-crystalline stereocomplexed PLA domains. An enantiomeric mixture of 8-armed star block copolymers linked by an amide group between the poly(ethylene glycol) core and the poly(lactide) arms (PEG (NHCO) (PLA)(8)) yielded hydrogels with improved mechanical properties and stability at 37 degrees C in PBS compared to 8-armed star block copolymers linked by an ester group. The possibility to be formed in situ in combination with their robustness make PEG-(NHCO)-(PLA)(8) hydrogels appealing materials for various biomedical applications. (C) 2012 Elsevier Ltd. All rights reserved.