Eudragit S100-coated halloysite nanotube/chitosan microspheres for colon-targeted release of paeoniflorin

Paeoniflorin is a promising therapy for ulcerative colitis; however, a carrier is required for its localization and release in the colon. This study was conducted to investigate the colon-targeting potential of Eudragit S100 (EUS100)-coated halloysite nanotube (HNT)/chitosan (CTS) (HNT/CTS/EUS100) microspheres encapsulating paeoniflorin. HNT/CTS microspheres were prepared by emulsification cross-linking and were then coated by emulsification-solvent evaporation using EUS100 as the coating material. Fourier transform infrared spectroscopy and scanning electron microscopy were performed to study the structure and morphology of the microspheres. The HNT/CTS microspheres were mainly bound by physical adsorption. The microspheres had an average particle size of 26.7 +/- 7.5 mu m and a rough surface with a porous internal structure. Cumulative drug release in vitro was evaluated using different pH media and rat colonic content to simulate gastrointestinal and colonic conditions. HNT/CTS/EUS100 microspheres released approximately 70% of the drug in simulated colon fluid, which was approximately 20% higher than that released by HNT/CTS microspheres. Drug release by HNT/ CTS/EUS100 in simulated colon fluid was controlled by first-order diffusion mechanisms. Our results indicate that HNT/CTS/EUS100 microspheres can effectively deliver paeoniflorin to the colon with good colonic drug delivery characteristics.