The effect of Pluronic on the protein release kinetics of an injectable drug delivery system

A new class of injectable controlled release depots has been prepared by incorporating materials that preferentially segregate during phase inversion. These consist of blends of poly(ethylene oxide) (PEO)/poly(propylene oxide) (PPO)/poly(ethylene oxide) (PEO) triblock copolymers (Pluronics) with poly(D,L-lactide) (PDLA)/1-methyl-2-pyrrolidinone (NMP) solutions. The effects of preferential segregation on the phase inversion dynamics and in vitro protein release kinetics were examined using dark ground imaging, high performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and confocal microscopy. Variations in Pluronic concentration and molecular weight had an insignificant effect on the internal depot morphologies, however, increasing the concentration and molecular weight did result in increased phase separation rates and, surprisingly, a decrease in the magnitude of the protein burst, though the release profiles still retained a typical burst-type shape. Additionally, increasing the Pluronic concentration beyond a critical point resulted in a transition from a burst-type profile to an extended-release profile. An interpretation of these results in terms of a qualitative model for the protein release mechanism is also given.