| Popis: |
Three types of triblock copolymers, ABA, ABC and ACB, where A, B and C are poly (ϵ-caprolactone) (PCL), pply- dl -lactide (PLA) and polyglycolide (PGA), respectively, were synthesized by living polymerization of the purified monomers, ϵ-caprolactone (ϵ-CL), dl -lactide (LA) and glycolide (GA), in dry toluene at 90 °C in the presence of an Al/Zn bimetallic alkoxide complex. The composition of each block copolymer was determined by NMR spectrometry and corresponded to the monomer ratio. Microspheres containing levonorgestrel (LNG) were prepared from the triblock copolymers by the solvent evaporation process and possessed a non-porous surface and an appropriate size for injection. In vitro release of LNG from the copolymer matrices with different compositions and molecular weights was measured in deionized water at 37°C; a constant rate of release of LNG of about 0.4-1.0 /gmg/day/ mg of microspheres was maintained for 3 to 6 months. The release profiles depended on the block length and molecular weight of the block copolymer. It may be attributed to the increase of erosion-controlled release associated with PLA and PGA segments in the copolymer, which effectively compensated for the declining diffusional release from the PCL phase. |
