Microphase separation in bioerodible copolymers for drug delivery

This research examines the microstructure of bioerodible polyanhydrides wit h an eye towards precise design of drug delivery devices. Our main hypothes is is that the bioerodible copolymer poly(1,6-bis-p-carboxyphenoxyhexane-co -sebacic anhydride) (CPH:SA) undergoes micro-phase separation at certain co polymer compositions due to differences in relative hydrophobicity of the c o-monomers, resulting in thermodynamic partitioning of drugs incorporated i nto these copolymers. We investigate the thermal properties, degree of crys tallinity, and surface microstructure of several compositions of CPH:SA usi ng differential scanning calorimetry (DSC), wide-angle X-ray diffraction (W AXD), and atomic force microscopy (AFM). We observe that the degree of crys tallinity decreases, while the crystal lamellar thickness increases with CP H content. Phase-imaging using AFM indicates the presence of micro-domains in 20:80 and 80:20 CPH:SA, while poly(SA) and 50:50 CPH: SA show no micro-p hase separation. Finally drlulg-polymer interactions are studied by loading the polymers with different amounts of brilliant blue (hydrophilic) and p- nitroaniline (hydrophobic). DSC and WAXD analysis shows that loading hydrop hobic drugs into relatively hydrophobic polymers (poly(SA)) lowers melting point that becomes more pronounced with increased drug loading. (C) 2000 El sevier Science Ltd. All rights reserved.