Tannic Acid as a Degradable Mucoadhesive Compound

To achieve site-specific delivery of pharmaceuticals, the development of effective mucoadhesive polymers is essential. Thus far, only a few polymers, such as thiolated ones and related variants, have been studied. However, their mucoadhesiveness varies depending on the type of polymer and the degree of chemical functionalization. Furthermore, the chemistry of tethering often requires harsh reaction conditions. Recently, pyrogallol-containing molecules have emerged as good tissue and hemostatic adhesives, but their in vivo mucoadhesive properties have not been demonstrated. Herein, we found that pyrogallol-rich tannic acid (TA) formulated with poly(ethylene glycol) (PEG), named TAPE, exhibits superior mucoadhesive properties. TAPE is prepared by a simple physical mixture of TA and PEG. It remained on esophageal mucus layers for at least several hours (8 h) after oral feeding. The mucoadhesion originated from intermolecular interaction between the polyphenols of TA and mucin, exhibiting pH dependency. TAPE adhered strongly to mucin in neutral conditions but bound weakly in acidic conditions due to different hydrolysis rates of the ester linkages in TA. Thus, TAPE might be useful as a long-lasting esophageal mucoadhesive composite.