Skin-integrated stretchable actuators toward skin-compatible haptic feedback and closed-loop human-machine interactions

Abstract Skin-Integrated haptic interfaces that can relay a wealth of information from the machine side to the user side, leveraging the skin’s versatile haptic perception capabilities, are of great interest. Haptic feedback facilitates a deeper level of human-machine interactions, improves the efficiency, productivity, and safety of machine control, and enables a more immersive engagement in the virtual environment. However, existing haptic devices are not yet able to produce haptic cues that are compatible with the functionality and mechanical properties of the skin. In this work, we present the materials, structures, and applications of stretchable soft actuators for haptic feedback, which can match the perception range, spatial resolution, and stretchability of the skin. Pressure-amplification structures are fabricated using a scalable self-assembly process to ensure an output pressure beyond the skin perception threshold. Due to the minimized device size, the actuator array can be fabricated with a sufficiently high spatial resolution, which makes the haptic device applicable for all skin locations, including locations with the highest spatial acuity. The actuators can be stretched up to the elastic range of the skin without sacrificing the actuation performance. A haptic feedback system is demonstrated by employing the developed soft actuators and highly sensitive pressure sensors. Two proof-of-concept applications are developed to illustrate the capability of transferring information related to surface textures and object shapes acquired at the robot side (using sensing elements) to the user side (using haptic stimulation to the skin surface). The developed haptic feedback system lays the ground for bilateral human-machine interactions in industrial robotics, prosthetics, teleoperation, VR/AR, and other fields where haptic feedback can be beneficial.