Bifunctional Phenol-Enabled Sequential Polymerization Strategy for Printable Tough Hydrogels

Hydrogels are promising material candidates in engineering soft robotics, mechanical sensors, biomimetic regenerative medicine, etc. However, developing multinetwork hydrogels with high mechanical properties and excellent printability are still challenging. Here, a bifunctional phenol-enabled sequential polymerization (BPSP) strategy is reported to fabricate high-performance multinetwork hydrogels under the orthogonal catalysis of efficient ruthenium photochemistry. Benefiting from this bifunctional design, phenols can sequentially polymerize with typical monomers and themselves to fabricate various phenol-containing polymers (Ph-Ps) and Ph-Ps-based multinetwork tough hydrogels, respectively. The as-prepared hydrogels have maximum stress of 0.75 MPa and toughness of 2.2 MJ m^{- 3} under the critical strain of 800%. These property parameters are a maximum of 16 times higher than those of the phenol-postmodified and phenol-free hydrogels. Moreover, the rapid coupling polymerization of phenols can shorten the gelation times of hydrogels to as low as ≈4 s, which enables its printable property for customizable applications. As a proof of concept, a 3D scaffold-like structure is optimized as highly sensitive mechanical sensors for detecting various human motions.