(87f) Controlled Release From Halloysite – Polymer Composite Films

Both polymethyl methacrylate and polyvinyl alcohol films impregnated with drug loaded halloysite were evaluated as controlled release systems. Two methods for loading the drug, tetracycline, into the halloysite tubes were evaluated and resulted in similar levels of loading and release kinetics. One method is simpler and has the advantage that the loading level can be directly calculated. A "burst" effect was observed, in which there is an initial rapid release of tetracycline from loaded tubes. The origin of this burst effects was explored by evaluating washing protocols. For prepared films drug loaded into halloysite was released at a significantly reduced rate compared to films that were prepared using either free tetracycline or free tetracycline and unloaded halloysite. The release profile remains Fickian and is well described by a simple Higuchi model. However, the addition of montmorillonite to these films results in anomalous transport indicating that for montmorillonite absorption desorption kinetics affects the transport, while for halloysite adsorption desorption kinetics on the tubes outside wall does not affect transport.