Raphael Thys
Illustration showing an anatomical heart, blood vessel and a small implantable battery.
Implantable electronic devices have been a lifechanging development for so many people with cardiac issues; pacemakers can treat slowed heart rhythms while implantable cardioverter defibrillators (ICDs) can halt dangerously fast heartbeats.
But these miracle devices are limited by their battery life. Current devices are generally powered by small lithium batteries that need to be replaced via invasive surgical procedures roughly every 5-15 years.
In a bid to create a new generation of implantable devices that aren’t so limited, scientists are designing innovative new batteries that can be powered by the body itself.
In a new study, published in Chem, a research team led by experts at the Tianjin University of Technology successfully demonstrated a proof-of-concept battery system that can be implanted in the body and deliver stable power by reacting with oxygen in the body to produce electricity.
Implantable battery delivers stable power
The battery at the focus of this new research is a sodium—oxygen battery that has been specially designed to maximize its biocompatibility.
The battery electrodes are made from a sodium-based alloy and nanoporous gold, containing tiny pores thousands of times smaller than the width of a human hair. Both these compounds are naturally biocompatible. The entire battery system is also protected by a soft, thin, porous polymer coating that helps to improve biocompatibility even further.
The battery uses an alloy of sodium, gallium and tin as its anode. The nanoporous gold catalytic cathode is able to draw in oxygen from body fluids to fuel the necessary electrochemical reactions in the battery.
“When you think about it, oxygen is the source of our life,” said study author Xizheng Liu, a professor in the Institute for New Energy Materials and Low-Carbon Technologies at the Tianjin University of Technology. “If we can leverage the continuous supply of oxygen in the body, battery life won’t be limited by the finite materials within conventional batteries.”
In this new paper, Liu and colleagues implanted their battery under the skin on the backs of lab rats and measured the resulting electricity output for two weeks post-implant.
After this period, the batteries implanted were producing stable voltages between 1.3-1.4 volts, with a maximum power density of 2.6 µW/cm2.
These values fall shy of the requirements needed to power the current generation of implantable medical devices. However, the researchers believe that the stable production of electricity by their battery in this experiment demonstrates a successful proof-of-concept for battery designs that harness the oxygen in bodily fluids to work.
Proof-of-concept design appears safe to implant
In addition to monitoring the output of the implanted batteries, the research team also monitored the physical health of the lab rats. This included evaluation of the inflammatory response, metabolic changes and the extent of tissue healing/regeneration around the implant site.
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Immunohistochemical testing showed no significant inflammatory reactions, while tissue staining tests confirmed that there were no adverse effects on the rats’ main organs, such as the heart, liver and kidneys. Blood serum tests revealed no abnormalities. Blood vessels around the battery implantation site also appeared to regenerate quickly. This healing was seemingly linked to the battery’s performance.
“We were puzzled by the unstable electricity output right after implantation,” said Liu. “It turned out we had to give the wound time to heal, for blood vessels to regenerate around the battery and supply oxygen, before the battery could provide stable electricity. This is a surprising and interesting finding because it means that the battery can help monitor wound healing.”
Towards perpetual pacemakers
While the intended purpose for these batteries would be to power implantable medical technologies, the research team are open to investigating other uses.
“Because tumor cells are sensitive to oxygen levels, implanting this oxygen-consuming battery around it may help starve cancers. It’s also possible to convert the battery energy to heat to kill cancer cells,” Liu suggested. “From a new energy source to potential biotherapies, the prospects for this battery are exciting.”
But before these batteries can be used for any purpose, the team wants to explore ways of improving their efficiency and power generation by, for instance, incorporating other high-performance materials and optimising the battery structure. Picking materials that are cost-effective and can be easily scaled during manufacturing will also be key factors, they say.
Reference: Lv Y, Liu X, Liu J et al., Implantable and bio-compatible Na-O2 battery. Chem. 2024. doi: 10.1016/j.chempr.2024.02.012
This article is a rework of a press release issued by Cell Press. Material has been edited for length and content.
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