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.