New biodegradable polymers for injectable drug delivery systems.

Many biodegradable polymers were used for drug delivery and some are successful for human application. There remains fabrication problems, such as difficult processability and limited organic solvent and irreproducible drug release kinetics. New star-shaped block copolymers, of which the typical molecular architecture is presented, results from their distinct solution properties, thermal properties and morphology. Their unique physical properties are due to the three-dimensional, hyperbranched molecular architecture and influence microsphere fabrication, drug release and degradation profiles. We recently synthesized thermosensitive biodegradable hydrogel consisting of polyethylene oxide and poly(L-lactic acid). Aqueous solution of these copolymers with proper combination of molecular weights exhibit temperature-dependent reversible sol-gel transition. Desired molecular arrangements provide unique behavior that sol (at low temperature) form gel (at body temperature). The use of these two biodegradable polymers have great advantages for sustained injectable drug delivery systems. The formulation is simple, which is totally free of organic solvent. In sol or aqueous solution state of this polymer solubilized hydrophobic drugs prior to form gel matrix.