Low-temperature 3D printing of conductive hydrogel-based soft sensors for quantitative strain and load monitoring

A conductive hydrogel sensing material and its corresponding soft strain sensor were successfully fabricated by integrating low-temperature 3D printing technology with in situ reduction of silver particles on the surface of a polyvinyl alcohol (PVA) hydrogel matrix reinforced with sodium lignosulfonate (LS) and sodium alginate (SA). The PVA–LS–SA hydrogel matrix prepared via low-temperature 3D printing possessed stable mechanical strength and controllable structural morphology. After being conductively functionalized, the hydrogel exhibited reliable strain sensing performance based on the synergistic mechanism of microcracks in the silver particle layer and the tunneling effect within the soft matrix, which was effectively used to monitor various human motion signals including finger, wrist and knee joint movements. A clear polynomial relationship was identified between the relative change in resistance and the applied strain. When connected in the form of an array to a resistance acquisition and display system, the sensor was able to accurately provide real-time feedback with small errors on the magnitude and location of the applied load in practical measurement. The low-temperature 3D printing offered strong supports for the customized preparation and practical application of soft sensing materials and provided a feasible approach for developing conductive hydrogel sensors suitable for micro-strain detection.