• Soft Robotics
• Artificial heart
• Heart failure
• FEM
• Hyperelastic

Over the years, due to pathological conditions, the heart can start losing its healthy contractile pumping functionality and its ability to satisfy the blood demand of the organs, leading to a dangerous condition known as heart failure. Today, this pathology has assumed an increasingly significant epidemiological dimension, becoming the world's leading cause of death. Heart transplantation is the gold standard treatment for end-stage heart failure. However, the paucity of donors makes the number of performed implants limited and, due to long waiting lists, 45% of patients die while waiting for a transplant. In recent years, successful alternatives to transplantation have been developed, such as the total artificial heart (TAH) systems. Currently, the only total artificial heart approved by the Food and Drug Administration (FDA) in 2004 and CE-marked in 1999 as a 'Bridge for Transplantation' is the Syncardia TAH. Although this device, designed on the base of traditional robotic principles, ensures a physiological blood flow, it continues to be extremely complicated to develop a device that is permanent and, above all, safe. In fact, there are numerous problems associated with its use, such as the formation of thrombi, the development of infections, caused by the presence of percutaneous tubes connected to bulky external drivers but also the alteration of the cardiac cycle and the necessity of continuous anticoagulant therapy. Despite the numerous alternatives developed, traditional robotic systems started to reach a technological plateau in the last decades, therefore researchers tackled the issue by designing a new generation of devices based on soft robotics technologies. This new field of robotics, indeed, paved the way towards the design and development of a completely new typology of biomedical devices, based on innovative features, such as high deformability, safe interaction with tissues, variable stiffness and self-repair capability.
An example of a soft artificial ventricle was developed at the BioRobotics Institute of the Scuola Superiore Sant'Anna in Pontedera. It consists of a deformable semi-ellipsoidal ventricular chamber surrounded by two layers of counteracting pneumatic actuators arranged in a helical manner. In particular, the basic actuating unit in this system is the McKibben actuator, which was selected both for its muscle-like behaviour and its high force-weight ratio. When the actuator is supplied with compressed air, it is able to simultaneously shorten and thicken thanks to a special reinforcing external structure guiding the motion. The pressurization of the actuators leads to the squeezing of the enclosed ventricular chamber, consequently causing the ejection of blood. In this work, Finite Element Method (FEM)-based simulations were run in ANSYS 2021 R1 as design tool able to guide the choice towards the most suitable blood chamber material. A preliminary study was carried out by comparing in the same working conditions three different silicone materials: Ecoflex 00-30, Dragon Skin 30 and Smooth-Sil 950 (Smooth On Inc.), elastomers of increasing stiffness. An ejection fraction of 68 ml, evaluated in relation to the design volume, and limited deformation during the diastolic phase led to the choice of Smooth-Sil 950 silicone for the fabrication of the chamber. Subsequently, to validate the model, prototypes with the same materials were fabricated and experimental tests were conducted to verify the behaviour observed in the FEM simulations.
The validation underlined the accuracy of the FEM simulations, with an observed maximum error of 3.4 ml and a mean error of 2.6 ml. This allowed the use of the ANSYS software as a powerful design tool to investigate also new chamber geometries, to further enhance the action of the actuators on the chamber. Four different pre-deformed geometries were investigated that, once compared to the initial semi-ellipsoidal one, required less energy to be deformed, while still ensuring an amplification of the ejection fraction.
Thanks to the results reported within this thesis, an important additional design step towards the development of a new generation of soft artificial hearts was made. A more efficient pumping action lays, indeed, the foundation for an innovative device and, hopefully, a definitive solution to heart failure.