Natural Products Condensed Tannins as both co-Initiator and Crosslinker to Prepare Highly Stretchable Polyacrylamide Hydrogel

Inspired by the function of condensed tannins (TA) in protecting tissue from the attack of free radicals, a simple and novel method was designed to prepare chemically crosslinked and highly tough hydrogels with homogeneous network with the presence of condensed tannins.During the process of polymerization, condensed tannins could capture free radicals from the initiator and become the starting point for the growth of polymer.By this way, condensed tannin could act as both co-initiator and crosslinking center to prepare highly stretchable hydrogels (TIC-gel) via radical polymerization.The mechanism that using TA to form crosslinking structure was put forward and confirmed by ¹H-NMR, FT-IR and immersing the TIC-gel in urea solution.The mechanical properties of TIC-gels were studied by a series of tensile measurements and rheological tests.As a result, these hydrogels could be stretched up to 2 250% with a maximal fracture energy 3.51 MJ/m³.This novel hydrogel has homogeneous network structure which is quite different from the heterogeneous network structure of conventional chemically crosslinked hydrogels (PAM-MBA-gel).Such good homogeneous network could effectively transfer the load among the network to endow the hydrogel with high elongation.