The development and characterization of soft robotic contractile actuators

Abstract

In this paper, I describe the development of a soft-robotic myocardium and pneumatic artificial muscles (PAMs) that replicate the physiological motion of the heart. We were able to generate physiological twisting motion in a confined geometry, but additional actuators would be required to generate physiological force for blood ejection. However, McKibben PAMs with thermoplastic polyurethane (TPU) bladders were too bulky and prevented the embedding of additional actuators. Therefore, multiple alternate PAM designs which occupy minimal unpressurized volume were explored. Of the various bladder and mesh pairings for traditional McKibben PAMs, latex bladders with nylon braided mesh proved the most promising. 2D PAMs with zero volume bladders were also developed: 2D McKibben, 2D Pleated, and 2D Cardiac Geometry PAMs. Candidate PAMs were characterized and compared to the physiological linear contraction (14.7%) and force generation (60N) of the heart. The 2D PAMs successfully reduced the volumetric footprint and were able to generate a maximum force of 0.46 N/cm3 (7mm-width five channel 2D McKibben PAM matrix), close to the amount generated by the baseline TPU PAMs (0.53 N/cm3), and up to 10.1% linear contraction (3mm-width nine channel 2D McKibben PAM matrix). However, none of the PAM matrices characterized were able to meet both linear contractile and force generation targets. With more characterization and iteration, the 2D PAMs seem promising for the biomimetic soft-robotic myocardium application.