These bio-batteries are the future power source the world needs

Smartwatches might work well enough with ridgid, lithium-ion batteries, but more experimental wearable devices, such as smart clothing and implantable modules, need a new type of power source. It’s no good sticking an AAA Duracell into your arm to power a medical implant; what’s needed is a flexible battery, one that ideally doesn’t use toxic or flammable chemicals.

Researchers in China may have come up with a solution. A normal IV saline solution, to be exact. In their search for a nonhazardous alternative to Lithium-ion batteries, the scientists tested the use of cheap-to-produce sodium-ion solutions. They settled on two biocompatible chemicals: a normal saline solution, much like that pumped into the body during IV treatments, and a cellular fluid containing amino acids, sugars, vitamins and sodium ions.

“Current batteries like the lithium-ion ones used in medical implants generally come in rigid shapes,” said co-senior author of the research paper, Yonggang Wang, a chemistry professor at Fudan University and the Collaborative Innovation Center of Chemistry for Energy Materials. “Additionally, most of the reported flexible batteries are based on flammable organic or corrosive electrolytes, which suffer from safety hazards and poor biocompatibility for wearable devices, let alone implantable ones.”

Because both of the solutions chosen by the scientists pose no risk to human tissue, much less is needed in the way of bulky structural reinforcement. As they describe in a paper published in the journal Chem, the researchers were able to replace a rigid battery-casing with flexible forms. This included a “belt-shaped” battery that involved sticking thin electrode films to a net of steel strands, and a “fibre-shaped” battery build of electrode nanoparticles embedded around a carbon nanotube backbone.

The new biocompatible batteries were tested alongside one running on sodium sulfate, which is suitable for external wearable devices, but perhaps shouldn’t go inside your body. The charge-holding capacity on the saline and cell-culture batteries was only marginally less than the sodium sulphate-electrolyte, which outperformed many lithium-ion wearable batteries in terms of charge-holding capacity, even when they were folded and bent.

The scientists also discovered an undesired side reaction, which isn’t great for the battery but could be used to help treat cancer. It turns out the fibre-shaped battery’s carbon nanotubes can accelerate the conversion of dissolved oxygen into hydrogen ions. This won’t do favours for the battery’s effectiveness, but as a stand alone process it has the scope to be used in the treatment of cancer and bacterial infections.

“Deoxygenation might even wipe out cancerous cells or pathogenic bacteria”

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

Smart clothes and implantable devices may be at a nascent stage, but a fundamental key to their success will be how they power themselves. With flexible batteries powered by biocompatible chemicals, Wang and the other researchers could very well be pioneering technology that will one day find itself above and beneath under our skin.

Image: This is an artistic rendering of fiber-shaped implantable batteries using biocompatible electrolytes. Credit: Guo et al.

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