Block copolymer micelles as vehicles for hydrophobic drugs

Abstract

The limited solubility of hydrophobic drugs may hamper their potential investigation. Vehicles that can incorporate and effectively deliver such drugs are of interest. To this end, we have prepared micelles based on AB block copolymers of poly(ethylene oxide) (PEO) and poly(β-benzyl l-aspartate) (PBLA). The distribution of hydrophobic molecules into PEO-PBLA micelles was investigated by UV spectroscopy and the fluorescence probe technique using pyrene as a model drug. Further, the effects of temperature and sonication on pyrene partitioning into PEO-PBLA micelles were studied. The solubility of pyrene was enhanced in a linear fashion with respect to PEO-PBLA concentration. Weight-average partition coefficients of about 10 4 were determined for pyrene distribution in PEO-PBLA micellar solutions. The photophysical properties of pyrene, which are modified upon uptake within PEO-PBLA micelles, indicate a low polarity and pyrene mobility in the solubilization site (i.e. core region). The polarity of micellar cores (i.e. micropolarity) is apparently important for solute partitioning into polymeric micelles. PEO-PBLA micelles offer micropolarities slightly higher than those of the well-studied AB block copolymer micelles based on PEO and polystyrene (PS) on the pyrene scale. Nonetheless, block copolymer micelles, having cores consisting of a poly(amino acid), can be chemically tailored to adjust micropolarities for enhanced drug loading.