Encapsulation of bovine serum albumin in poly(lactide-co-glycolide) microspheres by the solid-in-oil-in-water technique

Non-aqueous protocols to encapsulate pharmaceutical proteins into biocompat ible polymers have gained much attention because they allow for the minimiz ation of procedure-induced protein structural perturbations. The aim of thi s study was to determine if these advantages could be extended to a semi-aq ueous encapsulation procedure, namely the solid-in-oil-in-water (s/o/w) tec hnique. The model protein bovine serum albumin (BSA) was encapsulated into poly(lactide-co-glycolide) (PLG) microspheres by first suspending lyophiliz ed BSA in methylene chloride containing PLG, followed by emulsification in a 1% aqueous solution of poly(vinyl alcohol). By variation of critical enca psulation parameters (homogenization intensity, BSA:PLG ratio, emulsifier c oncentration, ratio of organic to aqueous phase) an encapsulation efficienc y of > 90 % was achieved. The microspheres obtained showed an initial burst release of < 20 %, a sustained release over a period of about 19 days, and a cumulative release of at least 90 % of the encapsulated BSA. Different r elease profiles were observed when using different encapsulation protocols. These differences were related to differences in the microsphere erosion o bserved using scanning electron microscopy. Release of BSA was mainly due t o simple diffusion or to both diffusion and microsphere erosion. Fourier-tr ansform infrared studies were conducted to investigate the secondary struct ure of BSA during the encapsulation. Quantification of the <alpha>-helix an d beta -sheet content as well as of overall structural changes showed that the secondary structure of encapsulated BSA was not more perturbed than in the lyophilized powder used initially. Thus, the encapsulation procedure di d not cause detrimental structural perturbations in BSA. in summary, the re sults demonstrate that the s/o/w technique is an excellent alternative to t he water-in-oil-in-water technique, which is still mainly used in the encap sulation of proteins in PLG microspheres.