Stimuli-Responsive Tannin–FeIII Hybrid Microcapsules Demonstrated by the Active Release of an Anti-Tuberculosis Agent

A simple and facile strategy for the creation of ferric tannin microcapsules around a liquid, non-sacrificial core is described. The assembly of the capsules occurs rapidly once ferric tannin complexes are subjected to ultrasonic treatment. The driving forces for the rapid capsule assembly reside in the strategy of adding ferric ions into the initial emulsion, which promotes shell formation and stability through well-known complexation effects. This is the first time that microcapsule assemblies of monomeric tannins like epigallocatechin-3-O-gallate has been demonstrated, which are reportedly unable to form dispersing microcapsules in the absence of a templating metal. The efficacy of the approach is demonstrated by the complete release of a hydrophobic molecule that is active against M. tuberculosis by using Acacia tannin capsules. The release kinetics of the active molecule were of zeroth order over a 12 h time frame.