Soft Variable Resistance Material for Pressure Sensing Platform

Herein, we present the mechanical response of two porous and conductive foams made of polydimethylsiloxane (PDMS) and polyurethane (PU). A coating of carbon nanotubes (CNTs) renders the foams with positive piezo-conductivity, which is useful for sensing mechanical loads. Such materials are useful as sensors to improve the fitting process of a prosthetic socket for lower limb amputees, PDMS and PU are used commonly in prosthetic liners; here, we modify them with CNTs to convert these soft foams to sensor elements. When PU foam was pressed 60 times, it could not recover its original shape, whereas PDMS foam could maintain its elastic properties. After selecting PDMS foam with CNT coating as the base material, we demonstrated that the localized mechanical load could reduce resistance, which led to a color change via Joule heating of a thermochromic dye.

I. Introduction

Approximately 1.7 million people were reported with limb loss in the US [1]. A prosthetic socket is the main option to connect the prosthetic leg of a limb amputee with their residual limbs [2], [3], [4]. If the socket does not fit well with the residual limb, patients may experience uncomfortable loads. This is a very serious issue for lower limb amputees, whose residual limbs have to support body weight during locomotion and can lead to various skin breakdowns. In addition, ill-fitted socket may lead to abnormal gait and secondary injuries, such as back pain [5], [6].