THE PREPARATION AND CHARACTERIZATION OF POLY(LACTIDE-CO-GLYCOLIDE) MICROPARTICLES .3. MICROPARTICLE/POLYMER DEGRADATION RATES AND THE IN-VITRO RELEASE OF A MODEL PROTEIN

Poly(lactide-co-glycolide) (PLG) polymers may be used to entrap antigens for the development of controlled release vaccines, which may be designed to obviate the need for booster doses. Four commercially available PLG polymers (co-polymer compositions and molecular masses: 50:50, 33 kDa; 50:50, 58 kDa; 50:50, 84 kDa and 75:25, 83 kDa) were used to prepare microparticles and their in vitro degradation rates were assessed by three methods: (1) assessment of surface morphology by scanning electron microscopy, (2) weight loss and (3) molecular mass determinations by gel permeation chromatography. Each method confirmed that degradation was more rapid for polymers with a lower molecular mass and a higher glycolide content. Some parameters affecting the rate of release of a model protein (ovalbumin) from microparticles prepared with the polymers were assessed in vitro. The rate of release of the protein was shown to depend on at least three parameters: (1) the molecular mass of the polymer, (2) the co-polymer composition and (3) the protein loading of the microparticles. Generally, the rate of polymer degradation showed good correlation with the rate of protein release and it was shown that the polymers investigated may be appropriate for the development of controlled release vaccines.