Triterpenoid-Based Self-Healing Supramolecular Polymer Hydrogels Formed by Host-Guest Interactions

Pentacyclic triterpenoids, a class of naturally bioactive products having multiple functional groups, unique chiral centers, rigid skeletons, and good biocompatibility, are ideal building blocks for fabricating versatile supramolecular structures. In this research, the natural pentacyclic triterpenoid glycyrrhetinic acid (GA) was used as a guest molecule for β-cyclodextrin (β-CD) to form a GA/β-CD (1:1) inclusion complex. By means of GA and β-CD pendant groups in N,N'-dimethylacrylamide copolymers, a supramolecular polymer hydrogel can be physically cross-linked by host-guest interactions between GA and β-CD moieties. Moreover, self-healing of this hydrogel was observed and confirmed by step-strain rheological measurements, whereby the maximum storage modulus occurred at a [GA]/[β-CD] molar ratio of 1:1. Additionally, these polymers displayed outstanding biocompatibility. The introduction of a natural pentacyclic triterpenoid into a hydrogel system not only provides a biocompatible guest-host complementary GA/β-CD pair, but also makes this hydrogel an attractive candidate for tissue engineering.