Diffusion of camptothecin immobilized with cationic surfactant into agarose hydrogel containing anionic carrageenan

Abstract

Camptothecin (CPT) is a hydrophobic antitumor drug. Controlled release of CPT from hydrogel has not been satisfactorily achieved because of its poor compatibility and weak interaction with a hydrophilic hydrogel matrix. A new approach has been attempted in this work to solve these problems. In our approach, CPT was first solubilized in a micellar solution of cetyltrimethylammonium bromide (CTAB), a cationic surfactant. It was found that the solubility of CPT could be enhanced by CTAB (10 mM) to 0.17 mg/mL, which is 127 times higher than that in pure water, providing a great feasibility of drug loading. The micellar drug solution of CTAB-CPT was subsequently used to prepare agarose hydrogels containing a small content (<or= 0.3 wt %) of kappa-carrageenan, an anionic water-soluble polysaccharide. The release of CPT from so fabricated hydrogel-surfactant systems has been investigated by varying the content of kappa-carrageenan in the hydrogel. It was observed that the presence of kappa-carrageenan in the hydrogel system resulted in a significant decrease in the release rate of the drug. This effect was ascribed to the ionic interaction between the positively charged surfactant micelles and the negatively charged kappa-carrageenan. The release profiles were fitted to two mathematic models of diffusion and the diffusion coefficients of the drug were obtained as a function of kappa-carrageenan content.