Application of halloysite clay nanotubes as a pharmaceutical excipient
Halloysite nanotubes, a biocompatible nanomaterial of 50-60 nm diameter and ca. 15 nm lumen, can be used for loading, storage and sustained release of drugs either in its pristine form or with additional polymer complexation for extended release time. This study reports the development composite tablets based on 50 wt.% of the drug loaded halloysite mixed with 45 wt.% of microcrystalline cellulose. Powder flow and compressibility properties of halloysite (angle of repose, Carr's index, Hausner ratio, Brittle Fracture Index, tensile strength) indicate that halloysite is an excellent tablet excipient. Halloysite tubes can also be filled with nifedipine with ca. 6 wt.% loading efficiency and sustained release from the nanotubes. Tablets prepared with drug loaded halloysite allowed for almost zero order nifedipine release for up to 20 h. Nifedipine trapped in the nanotubes also protect the drug against light and significantly increased the photostability of the drug. All of these demonstrate that halloysite has the potential to be an excellent pharmaceutical excipient that is also an inexpensive, natural and abundantly available material.