By studying the wound healing mechanism of tunicate's tunic, scientists have identified the key role of pyrogallol structures in the cross-linking of biomacromolecules. Inspired by this, researchers have developed a variety of multifunctional hydrogels decorated by pyrogallol groups that mimic the tunic of tunicate. Owing to the presence of abundant pyrogallol groups, tannic acid can coordinate with various metal ions to form multifunctional hydrogels. Herein, this review summarizes the pyrogallol-modified multifunctional biomacromolecular hydrogels crosslinked by the coordination with metal ions and introduces the research progress of tannin-based hydrogels formed by the metal coordination cross-linking. The involved biomacromolecules contain chitosan and chitin. Focus is on the modification of biomacromolecules by pyrogallol groups, and fabrication method, gelling mechanism, multifunctionality and potential applications of these formed biomacromolecules hydrogels.
