Additive Manufacturing Fused Filament Fabrication Three-Dimensional Printed Pressure Sensor for Prosthetics with Low Elastic Modulus and High Filler Ratio Filament Composites

Presented here are thermoplastic fused filament fabrication (FFF) three-dimensional (3D) printed piezo-resistive pressure sensors for daily activities utilized on a prosthetic feedback system. The 3D printed pressure sensors were manufactured from various low elastic modulus composites comprising a compressible thermoplastic elastomer and conductive carbn. Carbon is in graphite form and added in high filler ratios. The printed sensors were compared to sensors that were fabricated in a gravity mold to highlight the difference in printed sensors to molded sensors. The design is an improvement on the current prosthetic pressure sensors that are either strain gage or thick/thin film-based sensors. The 3D printed pressure sensor has a thickness and feel similar to human skin, has a simple fabrication technique, and can be manufactured into user-specific geometries. Being FFF 3D printed, the sensor can be easily printed in smaller or larger sizes to create custom layouts or patterns for pressure sensor feedback systems. Where strain gage sensors are bulky and expensive and thick/thin film sensors do not provide aesthetic comparability and require complex manufacturing techniques, result in higher costs. The material was first characterized to establish the operating applied constant voltage and to demonstrate the low elastic modulus. The results from the cyclic voltammetry showed an ideal operating voltage of -0.2 V, and the modulus of the different composite types ranged from 1.83 × 10^-4 to 6.01 × 10^-4 GPa. After characterizing the composites, each was tested under a force to measure the change in current with an applied load. The FFF 3D printed sensors are able to detect pressure levels between 340.63 Pa and 51.09 kPa, and the molded sensors are able to detect pressure levels between 17.03 Pa and 47.69 kPa. The work presented here shows that a 3D printed prosthetic pressure sensor can be fabricated for daily activities and how 3D printing can impact the medical field.