Mr. Kreitz et al., CONTROLLED DELIVERY OF THERAPEUTICS FROM MICROPOROUS MEMBRANES - II -IN-VITRO DEGRADATION AND RELEASE OF HEPARIN-LOADED POLY(D,L-LACTIDE-CO-GLYCOLIDE), Biomaterials, 18(24), 1997, pp. 1645-1651
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.
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