Tannic acid (TA), a high molecular weight polyphenol of natural origin, was assembled in alternation with chitosan (CH) using a layer-by-layer technique. The deposition of tannic acid and chitosan layers on flat supports was monitored by quartz crystal microbalance, UV-vis spectroscopy, and electrophoretic mobility measurements on microparticles. Hollow (TA/CH)4 capsules were built and their permeability as a function of pH and molecular weight of a penetrating compound was investigated. The pH-permeability threshold for TA/CH capsules is shifted to lower pH for 2 pH units, as compared with commonly used polyallylamine/polystyrene sulfonate capsules. A more pronounced dependence of the TA/CH capsules' permeability on molecular weight of encapsulated substances allows better control over their release properties. Bovine serum albumin was loaded into (TA/CH)4 capsules using a pH-driven method and released by decreasing pH. Biocompatible tannic acid/chitosan films and capsules have advantages toward capsules made of synthetic polyelectrolytes for drug encapsulation and as delivery and depot systems. Incorporating a layer of tannic acid with proved antioxidant and antimicrobial properties into capsule walls, provides defense for encapsulated materials.
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Shutava et al. (2006) studied this question.