Soft Robotic Heart Formed with a Myocardial Band for Cardiac Functions.

The myocardial contracting ratio is approximately 20%, whereas ejection fraction exceeds 60%. Understanding the structure and kinetic mechanisms of the heart that enable this high ejection fraction is crucial in both basic and clinical medicine. However, these mechanisms remain incompletely elucidated. The authors have developed a functional model based on the unique myocardial band theory, which posits that the ventricle is formed by a single myocardial band winding into a spiral. According to this theory, a muscle band, which incorporated thin McKibben artificial muscles embedded within a soft elastomer, was formed, and it was subsequently rolled to replicate the ventricle's structure. Thin McKibben muscles are well-suited for mimicking cardiac muscles due to their longitudinal contraction, radial expansion, and ability to operate in a curved position. In general, animal hearts exhibit approximately 20% myocardial contracting ratio, a 1.2-fold change in myocardial band thickness, and an ejection fraction in the range 50-70%. In comparison, soft robotic hearts demonstrated values of 17.3%, a 1.28-fold thickness change, and a 47.8% ejection fraction, respectively, which closely approximated those of real hearts. Water ejection experiments conducted using a soft robotic heart revealed that the maximum pressure during contraction reached 200 mmHg, generating a pressure-volume loop similar to that observed in the human heart. Thus, soft robotic hearts hold the potential for a wide range of clinical applications, including the elucidation of heart failure pathophysiology and the development of surgical treatments.