Highly Selective Biomimetic Flexible Tactile Sensor for Neuroprosthetics

Biomimetic flexible tactile sensors endow prosthetics with the ability to manipulate objects,similar to human hands.However,it is still a great challenge to selectively respond to static and sliding friction forces,which is crucial tactile information relevant to the perception of weight and slippage during grasps.Here,inspired by the structure of fingerprints and the selective response of Ruffini endings to friction forces,we developed a biomimetic flexible capacitive sensor to selectively detect static and sliding friction forces.The sensor is designed as a novel plane-parallel capacitor,in which silver nanowire-3D polydimethylsiloxane(PDMS)electrodes are placed in a spiral configuration and set perpendicular to the substrate.Silver nanowires are uniformly distributed on the surfaces of 3D polydimethylsiloxane microcolumns,and silicon rubber(Ecoflex^(■))acts as the dielectric material.The capacitance of the sensor remains nearly constant under different applied normal forces but increases with the static friction force and decreases when sliding occurs.Furthermore,aiming at the slippage perception of neuroprosthetics,a custom-designed signal encoding circuit was designed to transform the capacitance signal into a bionic pulsed signal modulated by the applied sliding friction force.Test results demonstrate the great potential of the novel biomimetic flexible sensors with directional and dynamic sensitivity of haptic force for smart neuroprosthetics.

Next-Generation Prosthetic Hand:from Biomimetic to Biorealistic

Integrating a prosthetic hand to amputees with seamless neural compatibility presents a grand challenge to neuroscientists and neural engineers for more than half century.Mimicking anatomical structure or appearance of human hand does not lead to improved neural connectivity to the sensorimotor system of amputees.The functions of modern prosthetic hands do not match the dexterity of human hand due primarily to lack of sensory awareness and compliant actuation.Lately,progress in restoring sensory feedback has marked a significant step forward in improving neural continuity of sensory information from prosthetic hands to amputees.However,little effort has been made to replicate the compliant property of biological muscle when actuating prosthetic hands.Furthermore,a full-fledged biorealistic approach to designing prosthetic hands has not been contemplated in neuroprosthetic research.In this perspective article,we advance a novel view that a prosthetic hand can be integrated harmoniously with amputees only if neural compatibility to the sensorimotor system is achieved.Our ongoing research supports that the next-generation prosthetic hand must incorporate biologically realistic actuation,sensing,and reflex functions in order to fully attain neural compatibility.