An innovative compliant mechanism for a soft pump: towards a soft robotic artificial heart ventricle

While mechanical instabilities were traditionally considered as failure events, triggering them in a controlled fashion recently paved the way to novel functionalities and improved performance, especially in systems made of compliant materials. In this work, we present an innovative soft robotic artificial heart ventricle whose pumping strategy is based on the triggering of torsional instability in a fluid-containing and passive soft-shell. During pumping, the soft-shell collapses, showing the formation of inward folds that strongly contribute to the volumetric reduction of the soft-shell, thus to the pumping functionality. The soft robotic artificial ventricle is a stand-alone system actuated by five inverse pneumatic artificial muscles, that are arranged in a helical fashion around the soft-shell. The actuation system is versatile, and can be realized with any actuator that can linearly contract and act helicoidally. A cable-driven soft pump demonstrated the concept and was used as a study platform to set the requirements for actuation, in hydraulic conditions of pressure typical of a human heart ventricle. The experimental results in a hybrid mock circulation demonstrated that our soft robotic artificial ventricle has a physiological stroke volume (59.8 ml) and generates pressures that meet the physiological requirements in the pulmonary circulation, with 26.2 mmHg and 25.4 mmHg generated maximum pressure in the artificial ventricle and in the simulated pulmonary aorta, respectively.