CONTROLLED DELIVERY OF THERAPEUTICS FROM MICROPOROUS MEMBRANES - II -IN-VITRO DEGRADATION AND RELEASE OF HEPARIN-LOADED POLY(D,L-LACTIDE-CO-GLYCOLIDE)

In vitro degradation and release of five types of heparin/surfactant-l oaded poly(D,L-lactide-co-glycolide 50:50) (PLG) microspheres alone an d also incorporated within microporous polyurethane tubes were studied over a 3-month period. Degradation was studied with scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Heparin release was characterized using a modified Azure A ass ay. SEM suggests that microspheres may be entrapped within polyurethan e fibrils of the polyurethane tubes, thereby reducing contact with the ir hydrated environment. FTIR transmittance spectra confirm microspher e incorporation within the polyurethane tubes and PLG ester hydrolysis occurring over the 3-month period. A correlation was observed between decreasing molecular weights and glass transition temperatures (T-g). The microspheres alone exhibited a change in T-g but not when incorpo rated within the microporous tubes. Release profiles revealed a burst effect occurring during the first 4 h and total release of the heparin from the microspheres by 12 weeks. (C) 1998 Elsevier Science Limited. All rights reserved.