BIOLOGICAL-ACTIVITY OF LYSOZYME AFTER ENTRAPMENT IN POLY (D,L-LACTIDE-CO-GLYCOLIDE)-MICROSPHERES

Purpose. The purpose of this study was to investigate the process of p reparing microspheres for maximising entrapment efficiency (EE) and re tained biological activity (RBA) of peptides and proteins. Methods. A controlled-release formulation based on poly(d,1-lactide-co-glycolide) was designed and produced using a small-scale double emulsion method. These PLG microspheres contained a model peptide, lysozyme. The retai ned bioactivity of the incorporated lysozyme was determined by bacteri al assay. The size distributions and the morphology of the microsphere s were characterized. Results, The RBA and EE improved when the PLG co ncentration in the organic phase of the emulsion was increased. A high lysozyme concentration in the inner water phase of the emulsion resul ted in decreased EE and an increase in the proportion of fragmented pa rticles. The RBA of lysozyme in the microspheres varied between 30 and 80% with changes to the process. Conclusions, The study shows that th e RBA of lysozyme in PLG microspheres is strongly dependent on the exp erimental conditions for preparing the microspheres. Measurement of th e EE alone, without the RBA is insufficient to evaluate the efficacy o f the designed delivery system.