SMA-based soft actuators with electrically responsive and photoresponsive deformations applied in soft robots

As a heat-triggered smart material, shape memory alloy (SMA) has been widely used in soft actuators and bioinspired robots. Coupled SMA wires are commonly chosen to achieve reversible actuation, while segment assembling methods are the main solutions for complicated bending modes. To address this, dual-stimulus responsive SMA/PDMS soft actuators were proposed in this research. As exerted by electrical current, the SMA/PDMS actuators showed a reversible bending process, which was beneficial for elastic energy storage and the release effect of PDMS elastomers wrapped around one-way shape memory SMA wires. The optimization of the current intensity and the PDMS thickness could be used to control bending amplitude, response time, and deformation recovery. This provided a reversible actuation manner with only single SMA wires instead of coupled SMA wire arrangements. In addition, photomechanical bending could be observed as the SMA/PDMA actuators were stimulated by near-infrared (nIR) light, which could be attributed to the localized photothermal effect of the SMA wires with nIR light illumination. Localized and continuous deformations were obtained that were dependent on the light intensity and the PDMS thickness and width. This demonstrated the ease of control that was beneficial with only a light stimulus instead of commonly utilized segment assembling. Two kinds of SMA/PDMS actuator-based soft grippers were used to grasp different shaped objects. Grasping and release actions could be achieved in electrically actuated conditions, while conformal grasping functions could be achieved as the light source illuminated. Our proposed SMA/PDMS actuators show potential applications in bioinspired soft hands and expand soft robots application areas.