POLY(L-LACTIC ACID) PLURONIC BLENDS - CHARACTERIZATION OF PHASE-SEPARATION BEHAVIOR, DEGRADATION, AND MORPHOLOGY AND USE AS PROTEIN-RELEASING MATRICES

A new series of degradable polymeric matrices were prepared by blending poly(L-lactic acid) (PLA) and nonionic Pluronic surfactants, triblock copolymers of poly(ethylene oxide) (PEO) and poly-(propylene oxide) (PPO). The water content of the polymer blend films was controlled by mixing different types of block copolymers and by adjusting their amount. Physicochemical and morphological properties such as phase separation behaviors, degradation rates, and surface properties of PLA/Pluronic blend films have been characterized by differential scanning calorimetry (DSC), infrared spectroscopy (IR), gel permeation chromatography (GPC), and scanning electron microscopy (SEM). DSC studies suggested that blends with some degree of Pluronic miscibility in the amorphous region of PLA can be obtained by selecting polymer surfactants with suitable hydrophobicities. This resulted in the formation of films with an overall intact surface morphology (SEM). In aqueous solution, the blends revealed the typical liquid-crystalline phase transition of Pluronic polymers, suggesting the formation of a gellike structure within the PLA skeleton. PLA degradation rates were not affected by the blending procedure although the hydration degree in these matrices was higher, suggesting a complex mechanism of hydrogen bond formation between the carboxylic groups of PLA and the ethers of the surfactant polymers. When used as drug-releasing matrices, these blends extended protein release and minimized the initial protein burst compared to the pure polymer.