Cartilage-inspired hydrogel strain sensors with ultrahigh toughness, good self-recovery and stable anti-swelling properties

Conventional hydrogels inevitably "swell" under liquid or physiological conditions, which drastically destroys their mechanical properties, severely limiting their practical applicability. Here, a cartilage-inspired tough, anti-swelling and conductive hydrogel was designed and successfully fabricated. The hydrogel exhibits splendid mechanical strength of 2.75 MPa and good self-recovery, with a recovery efficiency of 96%. In addition, the hydrogel also has anti-swelling properties in different solutions, including H2O, DMSO, physiological saline, seawater and aqueous solutions with different pH values from 3 to 11. Surprisingly, the mechanical strength of the hydrogel is significantly improved (up to 4.05 MPa) after swelling in H2O for 24 h. Moreover, the presence of dynamic ions (Fe3+, Na+, Cl-) in the system also imparts superior conductivity to the hydrogel, which could accurately monitor human motions (bending of neck, elbow, wrist and knee) as a flexible strain sensor. Therefore, this biomimetic hydrogel should have broad application in various fields in complex environments, for example in electric skin, biosensors, tissue engineering, etc.