A shape-memory soft actuator integrated with reversible electric/moisture actuating and strain sensing

Soft actuators are now required to be smarter to perceive the outside world besides mechanical deformation, which has broader applications in soft robotics, wearable devices and biomedical electronics. However, most of the sensory actuators in previous research were complicated because of the separation of sensing and actuating units. Here, a shape-memory soft actuator integrated with reversible electric/moisture actuating and strain sensing was prepared with a compact sandwich structure. Silver nanoparticles (AgNPs) were used to form a middle composite layer, connecting a hygroscopically deformable polyvinyl alcohol (PVA) layer with a high-performance flexible shape memory polymer (FSMP) layer. With the electrothermal AgNP layer, the PVA-AgNPs-FSMP (PAF) composite shows quick recovery (within 10 s) under ultralow voltage (2 V), high strain-sensing sensitivity (1.56 Gauge Factor) and fast response to deformation (110 m s). What is more, the compact construction endows the PAF composite with electrical stability in 1000 bending cycles. Due to the novel combination of PVA, FSMP and AgNPs, the low-power PAF actuator can efficiently load and unload target objects without additional cooling process, and distinguish the presence and weights of them in real time. The results suggest that the soft PAF actuator has great potential applications in soft robotics and biomimetic devices, especially in automated packaging production lines of food, medicine, logistics sorting and other industries.