Supramolecular networks with high shear stiffening enabled by metal ion-mediated hydrogen bonding enhancement strategy.

Shear stiffening gel (SSG) with prominent rate-dependent mechanical properties is promising for impact protection, but conventional boron-based SSG suffers from toxicity and corrosion arising from boric acid. Here, we design a boron-free supramolecular dynamic reversible network of polytitanosiloxane (PTS) based on the metal-ion-mediated hydrogen bonding enhancement strategy. Different oxidation states of Ti atoms in the network influence the charge distribution of the adjacent hydroxyl groups (Ti-OH). The electrostatic potential of the H-bond donor and acceptor could be effectively modulated by the Ti4+ and Ti3+ cations, thereby enhancing the H-bond strength. The resulting PTS SSG exhibits exceptional shear stiffening (~2800 times, 0.1-100 Hz), negligible corrosion, and low cytotoxicity (Grade 1). The PTS SSG is further explored for impact protection materials and flexible mechanical sensors in practice. The hydrogen bonding enhancement strategy also paves the way for developing dynamic reversible networks to fabricate next-generation smart materials.