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

Abstract

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.

Soft robotic sleeve supports heart function

“…To create three dimensional and conformal devices that could be tested in animal models, we exploited fabrication techniques that allowed the integration of custom-designed soft pneumatic artificial muscles (PAMs) into a soft matrix that approximated and conformed to the outer surface of the heart. The PAMs' self-limiting load-length curves (27)(28)(29) provide a physiological, atraumatic strategy to assist and increase native cardiac muscle function. We oriented these PAMs in helical and circumferential patterns, similar to the outer two layers of the myocardial fibers of the heart, to replicate cardiac motion while providing synchronized mechanical assistance.…”

Mechanically programmable bend radius for fiber-reinforced soft actuators

“…These works and many others [8], [9], [10], [11], [12], [13] present methods for creating bending soft actuators; however, no one has yet -to our knowledge -presented a method for rapidly programming the bend radius and bending axis of a soft bending actuator by modifying the mechanical structure. This has relevance towards improving the agility of soft actuators -the ability to create intricate movements -by enabling the user to adjust the placement and magnitude of a bending actuator's radius of curvature [2].…”

An Intracardiac Soft Robotic Device for Augmentation of Blood Ejection from the Failing Right Ventricle

“…19,22,23 The PAM actuators are lightweight, have fast response times, and are tunable to match physiologic requirements of the heart. 19,21 In contrast to previous designs that provide biventricular support using an enclosing sleeve, 22,23 the RVED is specifically conceived to address the structural changes that are seen in advanced right heart failure.…”

“…19,22,23 The PAM actuators are lightweight, have fast response times, and are tunable to match physiologic requirements of the heart. 19,21 In contrast to previous designs that provide biventricular support using an enclosing sleeve, 22,23 the RVED is specifically conceived to address the structural changes that are seen in advanced right heart failure. 6,10,20,27 In this study, by employing a combination of soft robotics and precision engineering we developed a device that is small enough to be safely deployed inside the beating heart.…”

“…19 Roche et al described the use of non-compliant thermoplastic polyurethane (TPU) bladders to improve reliability while providing up to 34% linear contraction in a 120 mm long PAM for cardiac assist. 21 To meet the specifications of the required intracardiac use, the PAM was customized to a 10 mm maximum width and 40 mm length which was the lower limit of a dilated human RV.…”