Symbiotic cardiac pacemaker

Self-powered implantable medical electronic devices that harvest biomechanical energy from cardiac motion, respiratory movement and blood flow are part of a paradigm shift that is on the horizon. Here, we demonstrate a fully implanted symbiotic pacemaker based on an implantable triboelectric nanogenerator, which achieves energy harvesting and storage as well as cardiac pacing on a large-animal scale. The symbiotic pacemaker successfully corrects sinus arrhythmia and prevents deterioration. The open circuit voltage of an implantable triboelectric nanogenerator reaches up to 65.2 V. The energy harvested from each cardiac motion cycle is 0.495 μJ, which is higher than the required endocardial pacing threshold energy (0.377 μJ). Implantable triboelectric nanogenerators for implantable medical devices offer advantages of excellent output performance, high power density, and good durability, and are expected to find application in fields of treatment and diagnosis as in vivo symbiotic bioelectronics.


Principle and process of contact electrification
Contact electrification is main caused by the transfer of surface electrons 21 (Fig.1 g).
When an external force was applied, two triboelectric layers contacted to each other, resulting in the generation of free electrons between two triboelectric layer surfaces moving to a single potential well. With distance of two triboelectric layers increasing, a smaller barrier was formed and electrons kept moving between the surfaces. Along with the distance continued to increase, the probability of electrons jumping to the opposite surface became quite small, thus the electrons resided on one surface. When the distance reached far enough, the barrier was high to trap the electrons on different triboelectric layer surfaces (Fig. 1h, i). Here, the potential energy of transferring electrons between the two surfaces contained two short-range interactions and remote coulomb interaction. The energy difference ΔE was the electrostatic contribution, which also included the local interaction between electrons and the near surface 22 .

Supplementary Note 2
Electrical output of iTENG with different supporting structures.
The V-Q-x relationship of contact-mode iTENG can be derived based on electrodynamics 23 . Since the area size (S) of the metals is several orders of magnitude larger than their separation distance ( ) in the experimental case, it is reasonable to assume that the two electrodes are infinitely large. Under this assumption, the charges on the metal electrodes will uniformly distribute on the inner surfaces of the two metals.
Inside the dielectrics and the air gap, the electric field only has the component in the direction perpendicular to the surface, with the positive value pointing to Metal 23 .
OC 0 The keel structure significantly strengthened the mechanical property of the overall structure and effectively guaranteed the contact and separation process of the iTENG 10 .
Thus, the iTENG with keel structure will possess higher V(t) and x to improve ISC and VOC.
3D sponge spacer supporting structures could effectively increase the contact area Thus, the iTENG with 3D sponge spacer possessed higher S and σ to improve output Voltage. However, the V(t) may decrease with application of 3D sponge spacer which lead to a lower ISC.

Relationship between electrical output of iTENG and cardiac cycle
We studied the relationship between electrical output of iTENG and cardiac cycle  Fig. 5c, f). It implied that iTENG can not only be used as an energy harvesting device but also as self-powered active sensor for identifying cardiovascular events. The proposal was expected to further which is expected to get rid of relying on amplifying circuits in the traditional ECG mode of cardiac pacemaker.

Supplementary Note 4 Calculation of the energy harvested during each cardiac motion cycle
The generated energy during per cycle was an important parameter that iTENG as energy harvesting device apply to implantable electronics. The iTENG was driven by heart beat to do continuous periodic mechanical motion. The electrical output was also periodically time-dependent. The average output power was related to the load resistance. Given a certain period of time T, the maximum energy output per cycle of iTENG can be derived by the following equation 24 .
Here, Emax is the maximal output energy per cycle. Through the statistical analysis of the measurement results in vivo, the maximal short-circuit transferred charge QSC,max = 13.6 nC, the voltage difference ΔV = 72.9 V (Fig. 4f, g). So it could be inferred that

Pacing threshold energy
Pacing threshold energy is important to evaluate the feasibility of a self-powered cardiac pacing system from the energy perspective. Here, pacing threshold energy can be derived from the follow equation.
Since the pacing pulse is a square wave, the equation can be simplified as follow.
Here Et is the pacing threshold energy. Vt represents the pacing threshold voltage. R represents the pacing resistance. T stands for stimulus pulse durations.
As recent research visit for the 60 patients shows that the mean pacing capture threshold measured at 0.24 ms. the mean electrical values for R-wave sensing amplitude, pacing impedance, and pacing capture threshold at 0.24 ms were, respectively: 11.7 ± 4.5 mV, 719 ± 226 Ω, 0.57 ± 0.31 V at implant 25  The output power can be derived from the following equation: Here, the CiTENG is the capacitance of the iTENG. Thus the output power of iTENG were as follows: Therefore, all energy harvested from the heart is: Thus, the stored energy is 630.1 μJ and the energy efficiency is 8.3 %.

Commercial pacemaker drived by iTENG
The iTENG was connected to a 100 μF capacitor through a rectifier. Within 190 min, the voltage of capacitor be charged from 0 to 3.55 V. The electric energy was driving the commercial pacemaker (Adapta, ADDR03, Medtronic) produce the stimulus pulses signals. The voltage was detected by an electrometer (Keithley 6517B) and recorded by oscilloscope (Teledyne LeCroy HD 4096).