Usually modern pacemakers are powered by built-in batteries and you need to replace the pulse generator when the battery reaches end of life. What if the device gets charged itself using energy of cardiac contractions? That is exactly what a triboelectric pacemaker powered by cardiac contractions aims to achieve. Triboelectric effect is typically the static electricity which is generated when a plastic comb is used on dry hair. Researchers have tested a symbiotic cardiac pacemaker which uses an implantable triboelectric nanogenerator (iTENG) which harvests energy from cardiac contractions and stores in a capacitor .
The iTENG can harvest 0.495 μJ of energy during each cardiac contraction, while only 0.377 μJ is required for a pacing cycle for endocardial pacing. Nanostructured polytetrafluoroethylene (PTFE) thin film was one triboelectric layer in the patch applied over the left ventricle of the experimental animal to harvest energy. Spacer layer was a three dimensional (3D) elastic sponge (ethylene-vinyl acetate copolymer). Memory alloy ribbon made of highly resilient titanium was utilized as the keel. The whole assembly was enclosed in a flexible Teflon film and a polydimethylsiloxane layer.
The triboelectric nanogenerator was placed between the heart and pericardium with the PTFE layer facing the left ventricle. Cardiac contractions caused periodic contact and separation of the two triboelectric layers, generating energy, which was stored in a 100 μF capacitor through a rectifier. The capacitor could be charged from 0 to 3.55 V within 190 minutes in the large animal model. They could use the stored energy to pace the animal at 3 V with pulse width of 0.5 ms. This could be used to correct experimental sinus node dysfunction induced by local hypothermia.
An earlier study had used in vivo mechanical movement in breathing, harvested by iTENG to directly drive a pacemaker in a rat .
A study published in July 2021 reported on a self-rechargeable cardiac pacemaker system with triboelectric nanogenerators . It was a commercial coin battery sized iTENG based on body motion and gravity. The enclosed five-stacked iTENG converts mechanical energy into electricity at 4.9 μW/cm3 . The energy was able to charge a lithium-ion battery. This was successfully incorporated into a cardiac pacemaker and they confirmed ventricular pacing and sensing in a self-rechargeable system. In an adult mongrel, they could use this system for pacing the ventricle at 5 volts with 1 ms pulse width and lower rate interval of 90 beats per minute in VVI mode.
These are just proof of concept studies which are quite encouraging. We need much more technological developments to enable clinical use. Finally, the longevity of the device and biocompatibility of the materials used in the long term should be proved beyond doubt before we can ever dream of a triboelectric pacemaker for the heart.
Ouyang H, Liu Z, Li N, Shi B, Zou Y, Xie F, Ma Y, Li Z, Li H, Zheng Q, Qu X, Fan Y, Wang ZL, Zhang H, Li Z. Symbiotic cardiac pacemaker. Nature Communications. 2019;10:1821.