Formulation optimization of serratiopeptidase-loaded PLGA microspheres using selected variables

Serratiopeptidase-loaded poly (D,L-lactic-co-glycolic acid) (PLGA) microspheres were prepared using the modified double emulsion method. The effect of polymer concentration and external aqueous phase volume on microsphere size and entrapment efficiency was studied by 3(2) full factorial experiments. The results of analysis of variance test for measured responses indicated the test's significance (P < 0.05). The contribution of PLGA concentration on microsphere size and percentage yield was found to be higher than that of external aqueous phase volume, which produced a significant effect on entrapment efficiency. Microspheres demonstrated spherical particles in the size range of 19.08-41.14 microm and entrapment efficiency between 15.37 and 79.86%. The formulation using a medium level of polymer and a low level of external aqueous phase (PLGA: 300 mg; EAP: 100 mL) showed maximum entrapment (75.86 +/- 2.31%). The in vitro release profile of all formulations demonstrated a similar sustained release showing an initial burst followed by diffusion. The bioactivity of the peptide remained intact after microencapsulation as assayed by in vitro proteolytic activity. Response surface graphs are presented to examine the effects of independent variables on the responses studied. In conclusion, controlled-release serratiopeptidase-loaded PLGA microspheres demonstrating maximum entrapment were successfully prepared by an experimental design methodology with a minimum number of runs, representing an economical approach.