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Bendy, non-toxic batteries could improve biological implants


New battery technology using saline solution instead of toxic chemicals could open new frontiers in wearable and implantable electronics


An artist's impression of flexible, implantable batteries using biocompatible electrolytes.
An artist's impression of flexible, implantable batteries using biocompatible electrolytes.
Guo et al.

Bendable batteries that run off saline solution could soon power wearable electronic devices and medical implants if a proof-of-concept created by a Chinese team proves robust enough.

The bendy batteries, which can also run using a cell culture medium, would not only overcome the mechanical stress issues associated with wearables such as smart watches, but also represent a much safer alternative to the current industry-standard lithium-ion batteries.

A team led by Yonggang Wang of Fudan University in Shanghai created flexible batteries powered by biocompatible sodium-ion solutions. In a paper published in the journal Chem, the team explains that the approach means wearable batteries will no longer need to also contain bulky protective structures that function to isolate the flammable and corrosive electrolytes associated with lithium-ion models from contact with the body.

The need for protective barriers means that most batteries designed for wearables and implants are both comparatively heavy and rigid.

The researchers note that in any battery design electrolyte leakage is undesirable, but in the case of sodium-ion versions its advent will not cause damage. Saline solution is inert in the body, and cell culture medium simply contains amino acids and sugars and vitamins that are already part of the metabolic process.

Taking advantage of the absence of enclosing structures, Wang and colleagues designed both two-dimensional and one-dimensional prototypes for use in implanted devices such as pacemakers.

The 2D battery, described as “belt-shaped”, take the form of a thin electrode film connected to supporting steel strands. The 1D version uses nanoparticles embedded in a carbon steel backbone.

In addition, the battery designs were replicated using sodium sulfate solution as the electrolyte source, to produce a version that was more suitable for external wearables.

In testing, the sodium sulfate produced better charge holding and power output capacity than equivalent size lithium ion models. These values were slightly lower for the saline and cell culture medium versions, probably – the researchers suggest – because the two solutions contain fewer sodium ions.

The research was not without problems. The team discovered that the carbon nanotubes that make up the 1D battery accelerated the conversion of dissolved oxygen into hydroxide ions, which reduced overall effectiveness.

However, in a prime example of seeing positive potential in a negative outcome, Wang suggests that this conversion – divorced from considerations of battery longevity – could be adapted into treatments for bacterial infection or cancer.

“We can implant these fibre-shaped electrodes into the human body to consume essential oxygen, especially for areas that are difficult for injectable drugs to reach,” says Wang.

“Deoxygenation might even wipe out cancerous cells or pathogenic bacteria since they are very sensitive to changes in living environment pH. Of course, this is hypothetical right now, but we hope to investigate further with biologists and medical scientists.”

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Andrew Masterson is news editor of Cosmos.
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