Soft Pneumatic Artificial Muscles with Low Threshold Pressures for a Cardiac Compression Device

In this paper, I present the design, fabrication and characterization of fully soft pneumatic artificial muscles (PAMs) with low threshold pressures that are intended for direct cardiac compression (DCC). McKibben type PAMs typically have a threshold pressure of at least lOOkPa and require rigid end fittings which may damage soft tissue and cause local stress concentrations, and thus failure points in the actuator. The actuator design I present is a variant on the McKibben PAM with the following key differences: the nylon mesh is embedded in the elastomeric tube, and closure of the end of the tube is achieved without rigid ends. The actuators were tested to investigate the effects of mesh geometry and elastomer material on force output, contraction, and rise time. Lower initial braid angles and softer elastomer materials provided the best force, contraction, and rise times; Up to 50N of force, 24% contraction, and response times of 0.05s were achieved at 100kPa. The actuators exhibited low threshold pressures (<5kPa) and high rupture pressures (138kPa 720kPa) which suggest safe operation for the DCC application. These results demonstrate that the actuators can achieve forces, displacements, and rise times suitable to assist with cardiac function. Thesis Supervisor: Daniel D. Frey Tile: Professor of Mechanical Engineering and Engineering Systems