Erosion of composite polymer matrices.

The erosion of composite polymer matrices made of slow and fast eroding polymers was investigated. These matrices can be used as implants that release drugs in a preprogrammed way. To understand the mechanism of drug release, the erosion of cylindrical polymer matrices made of several layers of different polymers was investigated. A layer of poly(D,L-lactic acid) was used to separate a core and a mantle consisting of poly(1,3-bis[p-carboxyphenoxy]propane-co-sebacic acid) 20:80. The investigation of the erosion mechanism revealed that erosion is a two-phase process. Wide angle X-ray diffraction and differential scanning calorimetry proved that the crystalline polymer parts of the polyanhydride layers above and below the polylactide erode one after the other. Concomitantly, sebacic acid accumulates periodically inside the matrix and leaves it in two phases. This agrees well with the release of brilliant blue and carboxyfluorescein, two model compounds, from such implants when incorporated into the polyanhydride layers. It can be concluded that the core of the composite implant erodes with a delay of 10-14 days because the polylactide protects it against premature erosion. Theoretical erosion models that were developed to simulate erosion support the proposed mechanism.