Mineral Tanning-Inspired Metal Ions Coordination Hydrogels with Outstanding Mechanical Strength and Toughness for Flexible Force Sensors

By virtue of reversible energy dissipation and good ionic conductivity, metal ions have been extensively introduced to construct hydrogels. However, the traditional soaking method to prepare metal ions coordination hydrogels (MI-HG) faces the challenge of diffusion and combination of metal ions, leading to weak mechanical properties. Inspired by the leather mineral tanning mechanism, a strategy that controls the accessibility of hydrogels by pickling and basifying processes thus significantly improving the strength and toughness of MI-HG is proposed. To achieve this, polyvinyl alcohol/poly(acrylamide-co-acrylic acid) (PVA/PAM-co-PAA) hydrogels-bearing ligands similar to those of leather collagen are fabricated. Zr4+, Cr3+, Al3+, and Fe3+ commonly used for mineral tanning are chosen as the metal source. The results demonstrate that the mechanical properties of the products (MI-HGTanning) are significantly promoted, especially for Cr3+ and Zr4+. For example, the tensile strength of Zr-HGTanning and toughness of Cr-HGTanning reach 7.79 +/- 0.41 Mpa and 28.01 +/- 3.1 MJ m-3, approximately three and seven times that of their soaking samples. From macro to micro characterization and by theoretical simulation, the mineral tanning mechanism of metal ions first permeating and then effectively combining with carboxylates, thus improving the mechanical performance of MI-HGTanning is deciphered, the products of which are promised applications in flexible force sensors. Inspired by the leather mineral tanning mechanism that metal ions first fully permeate then effectively combine with the functional ligands of hydrogels, a series of metal ions coordination hydrogels (MI-HGTanning) with microstructure bearing a large number of pores are successfully constructed, which demonstrate significantly improved mechanical properties compared with those of traditional soaking samples (MI-HGSoaking). image