Influence of Formulation Methods on the In Vitro Controlled Release of Protein from Poly(Ester) Microspheres

Abstract

Poly (dl-lactide/glycolide, 50:50) microspheres containing bovine serum albumin (BSA) were pre-pared with and without Carbopol® 951 (a potential adjuvant agent) by o/o, o/w and (w/o) /w emul-sion methods. The protein loading of the microspheres reached 50%–70% of the theoretical amount of protein put into the formulation medium. The microsphere particle size was approximately 500 μm, 25–100μm, 10–20/nn using o/o, o/w, or (w/o)/w emulsion techniques, respectively. The release of BSA was dependent on the preparation method. The greatest burst of release was found for vacuum-dried microspheres formulated using the (w/o)/w method. This burst effect could be eliminated by lyophilizing the microspheres following their preparation. BSA was released at a higher initial rate from microspheres prepared by the o/w emulsion method that contained Carbopol® 951 than from micro-spheres not containing Carbopol® 951. Release studies also suggested that the release of BSA could be sustained for 54, 36, or 34 days for microspheres prepared by o/o, o/w, or (w/o)/w methods, respectively.