Elisavet D. Bartzoka

Synthesis of nano- and microstructures from proanthocyanidins, tannic acid and epigallocatechin-3-O-gallate for active delivery

Microcapsules (MCs) and nanoemulsions (NEs) were generated from both condensed and hydrolysable tannins, respectively, for controllable, stimuli-responsive active release. A rapid, simple and robust one step method based solely on the use of tannins, i.e., without the use of any additional cross-linking reagents, was developed via ultrasound treatment. The condensed tannins Schinopsis balansae wood extract (Sb) and Acacia mearnsii bark extract (Am) were studied for their potential use in microcapsule assembly, and the hydrolysable tannins tannic acid (TA) and epigallocatechin-3-O-gallate (EGCG) were studied for their potential use in forming nanoemulsions upon ultrasonic irradiation. Tannin microcapsules (TMCs) and tannin nanoemulsions (TNEs) were thoroughly characterized via cryo-SEM, as well as fluorescence and optical microscopy, to reveal their structural and morphological characteristics. GPC analyses revealed that microcapsules and nanoemulsions were formed due to efficient electronic interactions between the aromatic moieties present in the polyphenolic backbone of high molecular weight fractions of tannins, and apparently without any significant chemical modification. Both TMCs and TNEs were formed in high yields and their release efficiencies showed the higher stability of the MCs compared to the NEs. Active release from and the pH stability of both the TMCs and TNEs were evaluated. Tannins – and more specifically the polymeric structures of tannins – proved to be ideal scaffolds for ultrasound assisted capsule assembly with potential for the pH triggered delivery of hydrophobic active molecules.

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.