Production and characterization of biodegradable microparticles for the controlled delivery of proteinase inhibitors

An in-liquid drying process, based on the use of a water-in-oil-in-water (w/o/w) emulsion, for the microencapsulation of soybean trypsin inhibitor (SBTI) and basic pancreatic trypsin inhibitor (BPTI) is described. For the microparticle production, three different polymers were used, namely: poly(L-lactide), L-PLA; poly(DL-lactide), DL-PLA and poly(DL-lactide-co-glycolide) 50:50, DL-PLG. Optical and scanning electron microscopy were employed in order to study the external and internal morphology of microparticles. Rather different structures were observed, depending on the polymer and peptides employed. Swelling kinetics of microparticles and polymer degradation were also determined. Swelling analysis was carried out by an in vitro method based on the use of a viscous medium enabling the study of changes of individual microparticles. Peptide encapsulation and release kinetics from microparticles were determined by evaluating their in vitro inhibitory activity on trypsin. These experiments demonstrated that both SBTI and BPTI are still active after microencapsulation. Taken together our results indicate that the microparticles produced can be proposed as a non-parenteral controlled release system for trypsin inhibitors.