Wirelessly Powered Pacemaker Implanted In A Pig

Advances in technology engineered at the National University of Singapore (NUS) and Stanford University have improved the efficiency of energy transfers of electromagnetic power through tissue, effectively powering a pacemaker implanted in an adult pig. A phased array antenna, placed directly against the skin, focuses the electromagnetic energy to a specific location at efficiencies greater than what has been achieved with ultrasound or internal kinetically-sourced power, said the researchers.

There are several advantages to eliminating batteries from implanted devices. A battery-free device can be much smaller, lowering the risk of adverse events caused by an immune response. Also, batteries tend to be made from toxic substances, and even the most advanced battery will eventually have to be replaced through invasive surgery.

In 2014, researchers from Stanford introduced a wireless technique they claimed safely transmitted electromagnetic energy to implants. Their approach blended near-field waves with far-field waves to generate a specific kind of energy that could adjust its characteristics as it encounters different materials.  In a study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), Poon’s team demonstrated successful implantation of its device in a rabbit.

John Ho, a member of the research team and NUS professor, told Stanford News that the proposed system could “safely transmit power to tiny implants in organs like the heart or brain, well beyond the range of current near-field systems.”

Three years later, the same team has further optimized its technology by making two key changes. First, they developed a phased array that allows the energy to target a specific location, ensuring more energy reaches the device. Their second adjustment applied the antenna directly to the tissue, allowing the skin to “suck in” the energy. In a study published in Nature Biomedical Engineering, the team demonstrated its ability to effectively power a pacemaker in a pig using an external stimulator 2 mm in diameter.

Recent developments in alternative power sources for pacemakers have used ultrasound; one example is a non-invasive pacing system from Drexel University that is entirely external and convenient for short-term or emergency cardiac patients. Additionally, research from the University of Buffalo has proposed a piezoelectric  pacemaker that is powered by the patient’s own heartbeat.

According to Stanford researchers in a press release,   internal kinetic power sources typically are unable to generate the power required by most implants. Also, scientists said electromagnetic power is more successful in penetrating bone than currently available ultrasound technology, though they noted that their techniques could also be useful with energy generated with ultrasound.

“To make the system practical for continuous use, more improvements in the long-term reliability of the system will be needed,” wrote Ho in an article published concurrently with the study, noting that the most promising potential applications are biosensors, neuromodulation, and precision cancer therapies where the device needs only be activated periodically.

“The ability of the phased surfaces to wirelessly power devices that are small and deeper than currently possible may pave the way for new approaches to treat disease,” said Ho.