In vitro degradation and protein release of transparent and opaque physical hydrogels of block copolymers at body temperature.

Poly( D,L-lactide- co-glycolide)- b-poly(ethylene glycol)- b-poly( D,L-lactide- co-glycolide) (PLGA-PEGPLGA) triblock copolymers were synthesized at 130 and 160 °C. The concentrated aqueous solutions of both specimens underwent reversible sol-to-(transparent gel)-to-(opaque gel) transitions upon heating but exhibited different critical gelation concentrations and transition temperatures, possibly due to the minor sequence differences between D,L-lactide (LA) and glycolide (GA) in the PLGA blocks. Aqueous solutions (20 wt%) of the copolymers synthesized at 130 and 160 °C spontaneously formed an opaque gel and a transparent gel at body temperature, respectively. The resulting hydrogels displayed similar in vitro degradation profiles in phosphate buffer saline solutions at 37 °C. Nevertheless, the late-stage releases of bovine serum albumin from the physical hydrogels differed. The present study reveals for the first time that transparent vs. opaque thermogel state influences some of their biomaterial-related properties via the 'overheat degree' of the thermogelling systems at a given working temperature, usually 37 °C. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]