Synthesis and Characterization of Surface‐Hydrophobic Ion‐Exchange Microspheres and the Effect of Coating on Drug Release Rate

Abstract

Biodegradable, dextran‐based ion‐exchange microspheres (IE‐MS) have been used for localized delivery of anticancer drugs and chemosensitizers. Because of their hydrophilic nature, the IE‐MS release their payload quickly. The purpose of this work was to develop an IE‐MS system that could provide a broad range of release rates for in vitro and in vivo applications. Sulfopropylated dextran microspheres (SP C25 MS) were surface‐modified by acylation. These hydrophobically modified sulfopropylated dextran microspheres (HM‐MS) were further coated with the cationic acrylic polymer Eudragit RL100 (EU‐MS). The changes in chemical composition after the surface modification and coating were characterized by X‐ray photoelectron spectroscopy. The effects of the modification and coating on the surface hydrophobicity, equilibrium swelling, surface morphology, and drug loading capacity were investigated. The HM‐MS showed little change in swelling and functionality, despite significantly increased affinity to oil and carbon content on the surface. The coated microspheres (EU‐MS) exhibited a profoundly decreased swelling ratio, an even higher affinity to oil, a higher loading capacity, and a lower drug release rate. Through further coating of the EU‐MS with different amounts of corn oil, the rate of drug release could be tailored to cover a relatively wide range. These results suggest that a versatile delivery system with various release profiles can be prepared by a combination of hydrophobic modification, polymer coating, and oil coating. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 807–817, 2000