HBS is a consortium of 4 European companies (Sorin Group, Tronics, Cedrat, Easii IC) and 2 research centers (CEA-LETI, TIMA) (figure 2) that decided to combine their expertise in 2010 to:
(i) Develop an EH-powered pacemaker by harvesting the mechanical energy produced by the movements of the heart and eliminating the need for batteries that must be replaced every five to ten years.
(ii) Reduce the size of a cardiac pacemaker by a factor of eight, from 8 cm3 to 1 cm3. This reduction will make it possible to attach the pacemaker directly to the endocardium, eliminating the need for intravenous introduction of cardiac leads.
Figure 2: HBS consortium to develop the pacemaker of the future
3. Heartbeats Energy harvesters
HBS Heartbeats energy harvesters belong to the family of Vibration Energy Harvesters that have been increasingly studied since the 2000s. Yet, due to the strong constraints in terms of size (<1cm³) and frequency (a few Hz), developing such devices is quite challenging.
1. Harvesting vibrations from heartbeats
Harvesting energy from vibrations consists in developing mass-spring resonant devices that turn vibrations into a relative movement between two elements (mechanical-to-mechanical converter) that is then turned into electricity thanks to a mechanical-to-electrical converter (piezoelectric, electrostatic, electromagnetic devices) [5
] (figure 3
Figure 3: (a) Two-steps conversion to turn vibrations into electricity and (b) general model of a vibration energy harvester
The output power of these devices is low, generally in the order of 10µW per gram of mobile mass, but this is enough to power basic actions such as detecting vibration peaks or delivering energy pulses to the heart.
But, the heart is a tough environment for the mechanical-to-mechanical converter. The global size of the device must be small (1cm³) and the resonant frequency of the mass-spring system low (in theory, equal to heartbeats frequency, that is to say 1-3Hz). Such constraints lead to large mass displacements and fragile devices that are not compatible with pacemakers' requirements (size, lifetime, reliability).
Fortunately, while beating at 1-3Hz, in-vivo acceleration measurements (figure 4a
) showed that significant power can be harvested on the 20Hz range (figure 4b
) turning HBS into a challenging but viable project.
Figure 4: (a) Typical vibration spectrum in the right atrium and (b) theoretical available power per gram of mobile mass in the ventricle as a function of the resonant frequency of the device
As for the mechanical-to-electrical converter, two transduction technologies are currently under investigation: piezoelectric devices are studied at TIMA while CEA-LETI focuses on electrostatic devices using electrets (electrically charged dielectrics, equivalent to magnets in electrostatic). It is also noteworthy that electromagnetic devices cannot be used due to MRI incompatibilities.