Nanocomposite Hybrid Biomass Hydrogels as Flexible Strain Sensors with Self-Healing Ability in Harsh Environments

The current challenges of wearable hydrogel sensors need to be addressed, especially how they are inevitably frozen at subzero temperature and are easily damaged. In this work, we present stretchable, antifreezing, and self-healing hydrogels by introducing Ag/TA@CNCs and l-proline into the guar gum (GG)/poly­(acrylic acid) (PAA) hybrid network. The existence of Ag/TA@CNCs provided enhanced conductivity, mechanical strength, and self-healing properties. The rupture stress of the hydrogels improved from 0.45 to 0.69 MPa, and the self-healing efficiency increased from 71.4% to 88.3%. Benefiting from zwitterionic l-proline as an emerging cryoprotectant, favorable flexibility and self-healing abilities were also achieved in subzero environments (the self-healing efficiency could reach 80.8% for 6 h at −15 °C). Resistive-type hydrogel strain sensors exhibited a high gauge factor (GF = 8.65 at strains of 350–550%) and fast response time (190 ms), as well as stable sensitivity even at low temperatures. Also, they could accurately monitor various human movements, including small (mouth opening and finger bending) and large changes (wrist bending, elbow bending, leg lifting, and squatting). The nanocomposite hybrid biomass hydrogels were promising for wearable flexible sensors with a long service time in a wide temperature range.