In vitro release of model compounds with different hydrophilicity from poly(ester-anhydride) microspheres.

Poly(ester-anhydride) microspheres were prepared using emulsion solvent evaporation technique from two copolymers obtained by polycondensation of sebacic acid (SBA) and oligo(3-allyloxy-1,2-propylene succinate) terminated with carboxyl groups (OSAGE). The SBA content in copolymers was 90 or 70 w/w %, respectively. The size of microspheres obtained was in the range of 2-4 microm (small microspheres) or 12-31 microm (large ones) and depended on stirring conditions used in emulsion formulation process, as well as on concentration of polymer solution used. Poly(ester-anhydride) microspheres were loaded with three model compounds (rhodamine B, p-nitroaniline and piroxicam) with different water solubility. The loading efficiency was dependent on kind of model compound, polymer composition and size of microparticles. Each of three model compounds also exhibited different release profiles. Rhodamine was released very quickly. The release of p-nitroaniline was more prolonged, but showed only little dependence on microsphere size and polymer composition, whereas the piroxicam-loaded microspheres exhibited the most interesting release profile, showing that release rate as well as transport mechanism can be adjusted by changing microsphere size and poly(ester-anhydride) compositions.