Release of macromolecules from albumin-heparin microspheres

Hydrophilic microspheres based on albumin-heparin conjugates have been prepared as a macromolecular delivery system. The soluble albumin-heparin conjugate was synthesized and crosslinked in a water-in-oil emulsion with glutaraldehyde to form microspheres in the same manner as for albumin microsphere preparation. The microspheres were characterized in terms of their size and swelling properties. The loading of macromolecules into albumin-heparin microspheres was carried out concurrently and after microsphere preparation. FITC-dextran was applied as a model macromolecule. A higher loading content was achieved when loading was carried out concurrently with microsphere preparation than when loaded subsequently. Prolonged release of FITC-dextran from albumin-heparin microspheres was achieved and attributed to the high molecular weight of the macromolecule. The release of FITC-dextran was modulated by crosslinking density, loading content and the method of drug incorporation. Apparently, the mechanism of FITC-dextran release from albumin-heparin microspheres was dependent on the method of drug incorporation. For release of FITC-dextran from the microspheres, assuming negligible interactions, a diffusion coefficient of 1.7 X 10m9 cm2/s was determined.