Operation of implants in the body: Battery prototype generates electricity from oxygen in the blood

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Cable (symbolic image): Previously, batteries used in pacemakers had to be replaced after a certain period of time

Photo: Amyna Paloha/Getty Images

Pacemakers ensure that the heart does not go out of rhythm. But the systems require power and cannot simply be plugged into a power outlet or charged. Until now, doctors have had to replace the batteries in one operation. Researchers want to change that: They have developed a battery that uses oxygen from the blood as an energy source.

Tests on rats show that the new battery is biocompatible, meaning it does not harm the organism around it, and delivers constant power after two weeks. This is what the Chinese group led by Xizheng Liu from the Tianjin University of Technology reports in the specialist journal “Chem”. However, more research is needed before a model can also be used for humans.

"If we can use the body's continuous oxygen supply, battery life will not be limited by the limiting materials in conventional batteries," Liu is quoted as saying in a statement from the specialist publisher. The most important challenge for such a battery, however, is that it does not pose a danger to the body, write the study authors.

For the device, they used gold with tiny pores and a body-safe plastic (PLCL) that encases the battery. As tests show, the battery is biocompatible even if it is damaged and components such as solids or other substances enter the body.

In a battery chamber, the anode - one of the electrodes - is made of copper foam with an alloy of sodium, gallium and tin. From the anode to a Nafion membrane, sodium plus ions move back and forth as active components during loading and unloading. In the second chamber, with nanoporous gold as the cathode, body fluid including blood is the electrolyte and oxygen is the active component. The oxygen is constantly replenished, so theoretically there is no need to change the battery.

Prototype with weaknesses

Liu and colleagues tested the battery in the laboratory and, in a proof of concept, implanted it under the skin of rats on their backs. The animals tolerated the battery and wound healing was normal. But initially the battery did not provide a constant voltage, so current did not flow regularly through the small wires protruding from the rat's back.

“It turned out that we needed to give the wound time to heal so that the blood vessels around the battery could regenerate and deliver oxygen,” explains Liu. That took about two weeks.

Then the battery provided 1.3 volts of voltage and continuous current. Although this is not yet enough to operate a pacemaker, the researchers are confident that they can achieve higher current output through other materials and an improved design.

They can also imagine other applications for the battery, for example in cancer treatment: “Since tumor cells are sensitive to oxygen levels, implanting this oxygen-consuming battery could help starve cancer,” says Liu.

ani/dpa