Hierarchical supermolecular structures for sustained drug release.

In this study, we report the formation of a hierarchical supermolecular structure, a fiber-shaped block copolymer/ paclitaxel complex, from the self-assembly of stereoregular amphiphilic block copolymer mixtures with paclitaxel, a wellknown anticancer drug. The behavior of the unusual selfassembled structure in drug loading and in vitro release is explored for potential biomedical applications such as a localized and sustained drug delivery system. Paclitaxel, which is extracted from the bark of the Pacific Yew tree (Taxus brevifolia), is a natural taxane effective against various tumors like ovarian and breast cancer. It prevents cancer cells from dividing by binding and stabilizing the microtubes and inhibiting the disassembly into tublins at the end of the mitosis process. However, it has limited solubility in water (0.3mg L 1 at 37 8C), making application of paclitaxel in cancer therapy difficult. Currently, Taxol is the only formulation available for clinical use, where paclitaxel is dissolved in a 50:50 mixture of Cremophore EL (polyethoxylated castor oil) and dehydrated alcohol. Unfortunately, the organic medium Cremophore EL has been reported to cause a migration of suspected carcinogens such as di-(2-ethylhexyl)phthalate (DEHP) from the infusion bags frequently used in hospitals, and severe side effects such as hypersensitivity reactions, nephrotoxicity, neurotoxicity, and cardiotoxicity have been documented. Thus, various polymer-based carriers like microspheres, nanoparticles, micelles,