Fig. 4

Mechanism and performance of the power assist unit. a Electrochemical actuation mechanism of the power assist unit. b Typical CV curves of one actuator petal at different scan rates. c, d Representative cyclic performance of an actuator petal with voltage window of (c) ± 2.5 V and (d) ± 2.0 V at the scan rate of 5 V s^− 1, respectively. e Illustration of the systole and diastole of a failed heart post-infarction. Dotted line represents the systolic state and demonstrates the infarcted area with dyskinesis and bulging. The arrow indicates the direction of myocardial movement during contraction. f Stress contribution map of the power assist unit conducted by computer simulation. g Contraction performance of the power assist unit under increased voltage change frequency: 5, 10, 15, 20 and 25 V s^− 1, corresponding to a heart systolic-diastolic behavior of 30, 60, 90, 120 and 150 bpm