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

Abstract

Non-aqueous protocols to encapsulate pharmaceutical proteins into biocompatible polymers have gained much attention because they allow for the minimization of procedure-induced protein structural perturbations. The aim of this study was to determine if these advantages could be extended to a semi-aqueous encapsulation procedure, namely the solid-in-oil-in-water (s/o/w) technique. The model protein bovine serum albumin (BSA) was encapsulated into poly(lactide-co-glycolide) (PLG) microspheres by first suspending lyophilized BSA in methylene chloride containing PLG, followed by emulsification in a 1% aqueous solution of poly(vinyl alcohol). By variation of critical encapsulation parameters (homogenization intensity, BSA:PLG ratio, emulsifier concentration, ratio of organic to aqueous phase) an encapsulation efficiency 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 release profiles were observed when using different encapsulation protocols. These differences were related to differences in the microsphere erosion observed using scanning electron microscopy. Release of BSA was mainly due to simple diffusion or to both diffusion and microsphere erosion. Fourier-transform infrared studies were conducted to investigate the secondary structure of BSA during the encapsulation. Quantification of the alpha-helix and 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 did not cause detrimental structural perturbations in BSA. In summary, the results demonstrate that the s/o/w technique is an excellent alternative to the water-in-oil-in-water technique, which is still mainly used in the encapsulation of proteins in PLG microspheres.

Poly(D,L-Lactide-Co-Glycolide) microspheres containing 5-fluorouracil: Optimization of process parameters

“…The decrease in the particle size of microspheres associated with an increase in the volume of the external phase of the secondary emulsion may be attributed to a decrease in the droplet size of the secondary emulsion. Castellanos et al 15 have reported similar observations. …”

Improved Enzyme Activity and Stability in Polymer Microspheres by Encapsulation of Protein Nanospheres

“…The encapsulation parameters chosen were the optimum parameters identified for the incorporation of proteins in PLGA microspheres by a s/o/w technique (see Supplemental material for details) (14). SEM micrographs of the HRP protein nanoparticles of the PLGA microsphere loaded with HRP nanoparticles and lyophilized HRP (for comparison) are shown in Fig.…”

“…PLGA microspheres were prepared by a s/o/w encapsulation procedure developed in our laboratory (14). Briefly, 40 mg of lyophilized HRP powder or HRP nanoparticles were suspended in a solution of PLGA in 2 ml of ethyl acetate.…”

“…The protein concentration was determined by measuring UV absorbance at 280 nm. The encapsulation efficiency was determined as described (14).…”

Encapsulation of protein nanoparticles into uniform-sized microspheres formed in a spinning oil film

“…When these droplets are created by emulsifying in water (eg, the solidin-oil-in-water [s/o/w] technique), the protein product can leak out into the bulk water phase resulting in low encapsulation efficiencies. 6,8,9 In addition, the drug can become partially wetted and rendered unstable in the organic solvent. 9 These pitfalls are overcome by using nonaqueous techniques such as the Prolease spray-freeze process or solid-in-oil-in-oil (s/o/o) emulsions.…”