Preparation and characterization of inulin ester microspheres as drug carriers

Acetylated and succinoylated inulin were synthesized by reacting inulin wit h acetic anhydride and succinic anhydride. The modified inulin was characte rized by FTIR, NMR, and potentiometric titration. The compositional depende nce of their properties, such as solubility, pKa, and melting point, was in vestigated. The results reveal that the solubility of the inulin derivative s in pH 7.4 buffer solution increases with the succinyl content, varying fr om negligible for fully acetylated inulin to over 54% for fully succinoylat ed inulin, whereas the corresponding pKa of the inulin derivatives decrease s with increasing succinyl content. In addition, the melting point is lower ed by acetylation and/or succinoylation. The influence of pH and ionic stre ngth on the solubility of inulin acetate succinate was also studied. The so lubility increases dramatically as the pH value approaches that of the pKa. Interestingly, in pH 7.4 buffer solutions of varying ionic strength, a max imum solubility appears at an ionic strength of 0.15M. This is interpreted as a result of a balance of the ion exchange process and the double layer s uppression. Microspheres of inulin acetate and inulin acetate succinate wit h and without drug were prepared by the solvent precipitation method. Catio nic compounds, chlorhexidine and chymotripsin, were used as model drugs. Th e size and morphology of microspheres were determined by scanning electron microscope. The microspheres range in diameters from 0.5 to 4 mu m for inul in acetate and inulin/chymotripsin microspheres, and from 90 to 130 mu m fo r inulin acetate/chlorhexidine microspheres. The cross-section of the micro spheres exhibits a porous interior. Preliminary results show that the micro spheres are able to release the incorporated drugs for an extended period o f time. (C) 2000 John Wiley & Sons, Inc.