In-vitro release characteristics of tetracycline HCl, khellin and nicotinamide adenine dineculeotide from halloysite; a cylindrical mineral

The use of halloysite clay as a low cost alternative to more traditional mi croencapsulation systems is reported. Halloysite is an alumino-silicate cla y which demonstrates a predominately cylindrical geometry, uniquely charact erized by a hollow core or series of voids with diameters ranging from 16-5 0 nm. These nanoscale-to-mesoscale microcylinders are capable of entrapping active agents within the core lumen as well as within any void spaces cont ained in the multilayered walls of the cylinder. Some of the active agents associated with the clay are also bound to the external surfaces of the cla y. Delivery of the active agent is first by desorption of the active agent from the exterior surfaces and exposed ends of the microcylinders, and is f ollowed by a second more prolonged phase dominated by pore diffusion from t he ends of the cylinders. Halloysite is capable of retaining and releasing a range of active ingredients. Both hydrophilic and hydrophobic agents may be entrapped following appropriate pre-treatment of the clay to render it l ipophilic. Here, a unique low cost alternative microcylindrical delivery sy stem: the clay mineral halloysite, is investigated.