MORPHOLOGICAL CHARACTERIZATION OF BIOERODIBLE POLYMERS .3. CHARACTERIZATION OF THE EROSION AND INTACT ZONES IN POLYANHYDRIDES USING SCANNING ELECTRON-MICROSCOPY

This paper describes the morphological changes which occur during the preparation and degradation of polyanhydrides composing different solvent- and melt-cast devices. The following monomers were used to synthesize the various polymers: sebacic acid (SA); 1,3-bis(p-carboxyphenoxy)propane (CPP); 1,6-bis(p-carboxyphenoxy)hexane (CPH); (carboxyphenoxy)methane (CPM); and 5-(p-carboxyphenoxy)-valeric acid (CPV). The morphology of the films and the eroding and intact zones that developed during degradation were examined by scanning electron microscopy (SEM). Amorphous and semicrystalline polymers fabricated by melt-casting displayed well-defined eroding zones with specific spherulitic or lamellar structures typical for each copolymer composition. Solvent-cast devices displayed porous spherulitic structures and, in most cases, did not display any obvious erosion zone, as judged by SEM. Aromatic copolymers were found to have liquid crystalline regions and SEM displayed spherical morphology that is specific to these phases. Crystalline and liquid crystalline regions were found to be more resistant to hydrolysis and degradation than amorphous regions.