Implantable and biocompatible Na-O2 battery (credit: Chem/Lv et al.)

Implantable medical devices rely on batteries (such as pacemakers, which keep the heart on beat). But batteries eventually run low and require invasive surgeries to replace.

So researchers at Tianjin University of Technology, China devised an implantable battery that runs on oxygen in the body. Their study with rats, published in the journal Chem, shows that the proof-of-concept design can deliver stable power and is compatible with the body’s biological system.

Biocompatible electrodes

To build a safe and efficient battery, the researchers made its electrodes out of a sodium-based alloy and nanoporous gold, a material with pores thousands of times smaller than a hair’s width. Gold is compatible with living systems and sodium is an essential and ubiquitous element in the human body.

The electrodes undergo chemical reactions with oxygen in the body to produce electricity. To protect the battery, the researchers encased it within a porous polymer film that is soft and flexible.

The researchers implanted the battery under the skin on the backs of rats and measured its electricity output. Two weeks later, they found that the battery can produce stable voltages between 1.3 V and 1.4 V. Although the output is insufficient to power medical devices, the design shows that harnessing oxygen in the body for energy is possible.

No inflammatory reactions

The team also evaluated inflammatory reactions, metabolic changes, and tissue regeneration around the battery. The rats showed no apparent inflammation.

Byproducts from the battery’s chemical reactions, including sodium ions, hydroxide ions, and low levels of hydrogen peroxide, were easily metabolized by the body and did not affect the kidneys and liver. The rats healed well after implantation, with the hair on their back completely regrown after four weeks. Blood vessels also regenerated around the battery.

The team plans to increase the battery’s energy delivery by exploring more efficient materials for electrodes and optimizing battery structure and design.

Beyond powering medical devices

Corresponding author Xizheng Liu, who specializes in energy materials and devices, noted that the battery is easy to scale up in production; and choosing cost-effective materials can further lower the price. The team’s battery may also find other purposes beyond powering medical devices.

“Because tumor cells are sensitive to oxygen levels, implanting this oxygen-consuming battery may help starve cancers. It’s also possible to convert the battery energy to heat and kill cancer cells,” says Liu.

This work was financially supported by the National Key Research and Development Program of China, the National Science Fund for Distinguished Young Scholars, and the National Natural Science Foundation of China.

Citation: Lv et al. Implantable and Bio-compatible Na-O2 battery. Chem (Cell Press. https://cell.com/chem/fulltext/S2451-9294(24)00074-3 (open access)

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