Researchers at the University of Wisconsin–Madison have developed an implantable pacemaker that does not require a traditional battery. The prototype draws the electricity it needs from the movement of the beating heart. The researchers’ ultimate aim is to develop a pacemaker that can continue to function throughout a patient’s lifetime.
Such a self-sustaining energy source could offer significant advantages, particularly for wireless pacemakers. At present, the battery takes up a large proportion of the implant and will eventually need replacing. An energy supply that utilises the heartbeat could potentially prevent the need for further surgical procedures whilst also allowing for smaller or more sophisticated implants.
Battery remains a limiting factor
Pacemakers have become increasingly smaller and more advanced over recent decades. Traditional systems consist of a pacemaker placed under the skin, which is connected to the heart via electrodes. For several years now, wireless intracardiac pacemakers have also been available. These compact devices are delivered to the heart via a catheter and placed directly into the right ventricle.
The absence of electrodes and an implant in the chest reduces certain complications and can speed up recovery. However, the battery remains a limitation. In a device such as the Micra, it accounts for more than half of the volume and weight, and has a lifespan of between seven and fourteen years.
When the battery runs out, removing the pacemaker from the heart is difficult. The old implant is therefore often left in place and a new one is inserted alongside it. This is not ideal, particularly for young patients, who may require multiple replacements over the course of their lives. Researchers have therefore been experimenting for some time with alternative energy sources, including piezoelectric and triboelectric nanogenerators. However, until now, miniaturised systems have failed to provide sufficient energy for an intracardiac pacemaker.
Heartbeat provides energy
The team of materials scientists Pengfei Chen and Xudong Wang developed a triboelectric nanogenerator small enough to fit into the battery compartment of an existing Micra pacemaker. This means the overall size of the implant does not need to increase. Above and below the electronics are special oscillating structures. These consist of electrode plates with a positive copper coating on one side and a negatively charged layer of fluorinated ethylene propylene on the other.
With every heartbeat, the structures are set in motion. In the process, oppositely charged surfaces are pressed together and then separated again. The resulting electrical charge can be used directly to power the pacemaker or stored in a small capacitor.
The design presented the researchers with a significant technical challenge. The structure must be flexible enough to move effectively, whilst at the same time remaining mechanically stable as it endures millions of heartbeats. Among other things, the position and width of the wiring and the thickness of the electrodes and substrates were therefore optimised.
Higher energy density
In laboratory tests, the nanogenerator achieved a power density of 276.6 microwatts per cubic centimetre. According to the researchers, this is sufficient to power the pacemaker. Furthermore, the power density is an order of magnitude higher than that of previous miniaturised nanogenerators.
A prototype was then tested in a pig for one month. During functional tests, the nanogenerator supplied sufficient energy to enable electrical stimulation of the heart. Furthermore, no adverse reactions were observed beyond those typically seen with conventional battery-powered intracardiac pacemakers. This marks a first step towards in-vivo application. However, the researchers emphasise that the system is not yet ready for clinical trials in humans.
Energy yield remains a challenge
A key point to note is that the energy yield in the pig’s heart was lower than during laboratory tests. Heart tissue is soft and therefore dampens part of the generator’s mechanical movement. Furthermore, the heart does not simply move up and down; whilst beating, it also performs a rotational movement. The current generator, however, operates most efficiently with a more linear movement.
The researchers therefore wish to further adapt the design to convert these complex movements more efficiently into mechanical oscillations and subsequently into electricity. In doing so, energy production must not only be sufficient but also stable over the long term. If this proves successful, the technology could extend beyond pacemakers alone. According to the research team, a compact energy source that continuously extracts energy from the body could also pave the way for a new generation of smaller implants with more extensive diagnostic and therapeutic functions.
The move towards clinical application is expected to take several more years. The ultimate prospect, however, is clear: an intracardiac pacemaker that is no longer limited by the lifespan of its battery, but draws its energy from the organ it supports.
AI extends pacemaker lifespan
Earlier this year, researchers from the University of Leeds, Université Grenoble Alpes and Grenoble-Alpes University Hospital developed an AI algorithm that can help extend the battery life of pacemakers. The software predicts how much energy individual functions and settings consume, enabling cardiologists to better tailor the configuration to the medical needs of individual patients.
The model uses real-world data from pacemaker manuals and clinical records and calculates, amongst other things, the energy consumption of functions such as rate responsiveness, ventricular synchronisation and activity tracking. The results have been validated using patient data. Pacemakers typically have a lifespan of seven to fourteen years. By disabling functions that a patient does not need, the battery may last several years longer. This could reduce the number of replacement operations and the associated healthcare costs. Furthermore, the model allows for direct comparisons between different devices, settings and manufacturers.
References
Science Advances (research)
