Here we reported a novel ultrasound-induced polymerization to achieve a polyacrylamide–sodium alginate (SA) dual network hydrogel via a redox reaction with MXene (Ti₃C₂) as a reductant and potassium persulfate (KPS) as an oxidant.

Gait abnormalities have been widely investigated in the diagnosis and treatment of neurodegenerative diseases. However, it is still a great challenge to achieve a comfortable, convenient, sensitive and high-pressure resistant flexible gait detection sensor for real-time health monitoring. In this work, a polyaniline (PANI)@(polyacrylic acid (PAA)–polyvinyl alcohol (PVA)) (PANI@(PVA–PAA)) ternary network hydrogel with a uniaxially oriented porous featured structure was successfully prepared using a simple freeze–thaw method and in situ polymerization. The PANI@(PVA–PAA) hydrogel shows excellent compressive mechanical properties (423.44 kPa), favorable conductivity (2.02 S m⁻¹) and remarkable durability (500 loading–unloading cycle), and can sensitively detect the effect of pressure with a fast response time (200 ms). The PANI@(PVA–PAA) hydrogel assembled into a flexible sensor can effectively identify the movement state of the shoulder, knee and even the sole of the plantar for gait detection. The uniaxially oriented porous structure enables the hydrogel-based sensor to have a high rate of change in the longitudinal direction and can effectively distinguish various gaits. The construction of a hydrogen bond between PANI and the PVA–PAA hydrogel ensures the uniform distribution of PANI in the hydrogel to form a ternary network structure, which improves the pressure resistance and conductivity of the PANI@(PVA–PAA) hydrogel. Thus, PANI@(PVA–PAA) hydrogel flexible sensor for gait detection can not only effectively monitor some serious diseases but also detect some unscientific exercise in people's daily life.