A 3-D-Printed Elastomeric Strain Sensor With Mechanical and Thermal Characterization for Restoring Proprioception in Lower Limb Amputees

Lower limb amputation (LLA) causes a loss of motor and proprioceptive abilities in affected individuals. Different prostheses have been created to compensate for this deficit. However, most of these devices are passive and provide no sensory feedback to the amputee. Several solutions have been proposed to restore different typologies of sensation, driven by mechanical information obtained through sensors positioned on the anatomical district of interest, with specific limitations. This article presents the mechanical and thermal characterization of a novel 3-D-printed elastomeric strain sensor filled with liquid metal. It is designed to measure the strain on the cosmetic cover of a transtibial prosthesis to provide information to a feedback system. Static and dynamic tests were performed on the sensor, providing a graduation curve with satisfactory sensitivity, repeatability, linearity, and no signal attenuation over the 1–10-Hz frequency range. Thermal tests demonstrated an increase in the electrical resistance of the sensor up to 2.5% in the temperature range of
$20~^{\circ }$
C–
$40~^{\circ }$
C.