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.