Encapsulation, stabilization, and release of BSA-FITC from polyanhydride microspheres

In order to determine the efficacy of using polyanhydrides as a carrier for therapeutic proteins, the model protein bovine serum albumin labeled with fluorescein isothiocyanate (BSA-FITC) was encapsulated in microspheres of poly sebacic anhydride (poly(SA)), and random copolymers of poly(SA) and poly(1,6-bis- p-carboxyphenoxy)hexane (poly(CPH)). The microspheres were fabricated via the double emulsion (water/oil/water) technique and were characterized using scanning electron microscopy, gel permeation chromatography, confocal microscopy, and a Coulter counter. The effect of protein loading, protein distribution, and change in polymer composition was examined in an in vitro release study. The secondary structure of the encapsulated BSA-FITC was determined with Fourier transform infrared spectroscopy. The primary structure of the released protein was analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Poly(SA) and 20:80 (CPH:SA) microspheres were found to conserve the primary structure of the released protein and the secondary structure of the encapsulated protein, and showed a sustained delivery for approximately 15 and 30 days, respectively. As the CPH content in the copolymer increased, the secondary structure of FITC-BSA was not conserved, as indicated by the steep decrease in the α-helix content.