Pharmaceutical Research

, Volume 18, Issue 6, pp 878–885 | Cite as

Stabilization and Controlled Release of Bovine Serum Albumin Encapsulated in Poly(D, L-lactide) and Poly(ethylene glycol) Microsphere Blends

  • Wenlei Jiang
  • Steven P. Schwendeman


Purpose. The acidic microclimate in poly(D, L-lactide-co-glycolide) 50/50 microspheres has been previously demonstrated by our group as the primary instability source of encapsulated bovine serum albumin (BSA). The objectives of this study were to stabilize the encapsulated model protein, BSA, and to achieve continuous protein release by using a blend of: slowly degrading poly(D, L-lactide) (PLA), to reduce the production of acidic species during BSA release; and pore-forming poly(ethylene glycol) (PEG), to increase diffusion of BSA and polymer degradation products out of the polymer.

Methods. Microspheres were formulated from blends of PLA (Mw 145,000) and PEG (Mw 10,000 or 35,000) by using an anhydrous oil-in-oil emulsion and solvent extraction (O/O) method. The polymer blend composition and phase miscibility were examined by FT-IR and DSC, respectively. Microsphere surface morphology, water uptake, and BSA release kinetics were also investigated. The stability of BSA encapsulated in microspheres was examined by losses in protein solubility, SDS-PAGE, IEF, CD, and fluorescence spectroscopy.

Results. PEG was successfully incorporated in PLA microspheres and shown to possess partial miscibility with PLA. A protein loading level of 5% (w/w) was attained in PLA/PEG microspheres with a mean diameter of approximately 100 μm. When PEG content was less than 20% in the blend, incomplete release of BSA was observed with the formation of insoluble, and primarily non-covalent aggregates. When 20%-30% PEG was incorporated in the blend formulation, in vitro continuous protein release over 29 days was exhibited. Unreleased BSA in these formulations was water-soluble and structurally intact.

Conclusions. Stabilization and controlled relaease of BSA from PLA/PEG microspheres was achieved due to low acid and high water content in the blend formulation.

poly(D, L-Lactide) poly(ethylene glycol) bovine serum albumin microspheres 


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Copyright information

© Plenum Publishing Corporation 2001

Authors and Affiliations

  • Wenlei Jiang
    • 1
    • 2
  • Steven P. Schwendeman
    • 2
  1. 1.Division of Pharmaceutics, College of PharmacyThe Ohio State UniversityColumbus
  2. 2.Department of Pharmaceutical SciencesThe University of MichiganAnn Arbor

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