pH Responsive Decomposable Layer-by-Layer Nanofilms and Capsules on the Basis of Tannic Acid

Abstract

Tannic acid (TA) was assembled in alternation with two different polycations, strong poly(dimethyldiallylamide) (PDDA) and weak poly(allylamine) (PAH), using a layer-by-layer technique. Their deposition at different pH was confirmed by QCM, UV−vis spectroscopy, and surface charge measurements. TA/polyelectrolyte multilayer films and capsules have pH-dependent structural properties different from those of commonly used poly(styrenesulfonate)/poly(allylamine) (PSS/PAH) compositions. The lowest speed of TA/polycation multilayer dissolution was found at the conditions close to those used for film preparation. Permeability for fluorescein-labeled dextrans into tannic acid/polycation capsules with a five bilayer wall composition was investigated as a function of pH using confocal microscopy. It was found that minimal permeability occurs at pH 5−7 and maximal permeability at very high and very low pH, providing new opportunities for capsule loading as compared with an established procedure for PSS/PAH microcapsules. For TA/PDDA layers, less soluble films and less permeable capsules were obtained as compared with TA/PAH layers.