# A Review of Innovative Electromagnetic Technologies for a Totally Artificial Heart
## 2 Main TAH Projects  
The first experiences focus on fluid-driven (FD) TAHs actuated by pneumatic or hydraulic devices with external drivers. Figure 1a sketches a typical arrangement where the pump injects the fluid by an alternate rotating motion that is consistent with the filling and ejection of the respective blood chambers regulated by fluid valves [13]. Electro-pneumatic driving systems typically resemble such an approach. The Berlin Heart project that led to EXCOR(r)VAD was one of the first experiences of paracorporeal systems [1; 24]. A compressor generates the pulsatile air flow driven in a forward/reverse mode by the electric motor. The pumped, air conveyed by cannulas to the heart chambers, acts on multi-laminar diaphragms separating the air and blood chambers. Syncardia TAH-t operates according to a similar principle. Pneumatic drivelines connect the two ventricle chambers to an external pneumatic driver system, allowing coordinated but independent pumping with control over various driving parameters [14]. In [25], a small pneumatic actuator is proposed that can be used as an extracorporeal  
Figure 1: Main TAH types; (**a**) fluid driven; (**b**) electromechanical driven; and (**c**) continuous flow with integrated pump. biventricular assist device. A brushless direct current (BLDC) electric motor drives a ball screw system clockwise or counterclockwise, moving the ball screw system and then generating a two-way airflow through the airline connectors. Two air chambers located at the opposite ends of the moving unit are connected to pusher plates. If the external blood sacs are connected to the airline connectors of the actuator, the two-way airflow is converted to a blood pumping force that pushes and pulls flexible diaphragms in the blood sacs. Although this is based on well-assessed technology, this configuration has several drawbacks, such as its bulky arrangement, noisy operation, need for percutaneous air pressure hoses, poor durability, lack of self-regulatory feedback from the circulatory system, and reduced blood compatibility. Heavily affecting the patient's quality of life, it can therefore be considered a bridging solution prior to biological heart transplantation. A similar apparatus based on FD was implemented in the Carmat TAH (Aeson), where the external pneumatic drive is replaced by an internal electrical motor supplied by an abdominal cable connected to external batteries [1; 2; 18]. The main difference with the AbioCor TAH consists of the presence of four pericardial biomembranes. In every chamber, the flexible membrane acts as a divider and keeps hydraulic fluid and blood on each side. The electric motor-pump group pushes the fluid into and out of the chambers, making the membrane deflect and displace the blood. Four biological valves at the inlet and outlet provide unidirectional pulsatile blood flow. Embedded electronics, microprocessors, and integrated sensors allow auto-regulated responses for the physiological needs of the patient [19]. The large size and mass (1 kg) of the system as well as the need for a portable external power supply system continuously connected to the prosthesis represent its main disadvantages. Hand in hand with the development of innovative biocompatible materials for membranes and pumping components [26; 27], the introduction of more advanced electromagnetic devices in recent TAH projects significantly improved ergonomics, compactness, and control capability. Such features allow for a more accurate heart operation and limit the impact on daily life at the same time. Among the electromagnetic components, transcutaneous energy transmission (TET) systems represent a significant improvement, allowing the implant of long-lasting, small-size rechargeable batteries, paving the way for the prospective implantation of several types of electrical devices together with the main drive.