IN-VITRO DEGRADATION AND BOVINE SERUM-ALBUMIN RELEASE OF THE ABA TRIBLOCK COPOLYMERS CONSISTING OF POLY(L(-CO-GLYCOLIC ACID) A-BLOCKS ATTACHED TO CENTRAL POLYOXYETHYLENE B-BLOCKS()LACTIC ACID), OR POLY(L(+)LACTIC ACID)

The in-vitro degradation of copoly(L-lactic acid-b-oxyethylene-b-L-lac tic acid) (LPLA-PEO-LPLA) and copoly(L-lactic-co-glycolic acid-b-oxyet hylene-b-L-lactic-co-glycolic acid) (LPLG-PEO-LPLG) shows striking dif ferences compared to the respective homo- or co-polymers. Due to micro phase separation both types of polymers swell very rapidly. In the cas e of LPLA-PEO-LPLA cleavage of the PEO -ester bond occurs more rapidly , compared to the degradation of the A-block, leading to a biphasic pa ttern, whereas in the case of LPLG-PEO-LPLG in vitro degradation is fa st and continuous. Depending on the lactyl/glycolyl ratio and PEO cont ent, systems with life spans of 2 to 3 weeks can be attained. In-vitro release studies using bovine serum albumin as model compound demonstr ated that microspheres prepared from these polymers allow the design o f either continuous (LPLG-PEO-LPLG) or pulsatile (LPLA-PEO-LPLA) relea se which is controlled by the structure and properties of the ABA trib lock copolymer. These polymers have, therefore, potential for parenter al protein delivery systems.