Biocompatible electrolyte could enable safer implantable batteries

Implantable batteries that run on the type of saline used in intravenous drips or on a cell culture medium that contains compounds already found in the body could provide a safer and more easily shaped alternative to the lithium ion batteries most commonly used for miniaturised electronic devices, whether these are medical devices surgically implanted into the body or wearables for medical or other applications, according to research published by chemists at Fudan University in Shanghai.

"Current batteries like the lithium-ion ones used in medical implants generally come in rigid shapes," explained Prof Yonggang Wang of the university’s Collaborative Innovation Centre of Chemistry for Energy Materials, co-senior author on the paper in the journal Chem.

"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."

The rigidity of these batteries is generally caused by the addition of protective materials to prevent leakage of electrolytes, Wang’s team explains. Replacing these potentially hazardous materials with biocompatible fluids allows sodium-ion batteries to be made, which are slimmer and more flexible than lithium ion versions. The team tested two biocompatible electrolytes: simple saline, of the same types used in intravenous treatments as a solvent for active drug ingredients, and a cell-culture solution that contains amino acids, sugars and vitamins, designed to mimic the fluid that surrounds living cells in the body. They also tested sodium sulphite, which is non-biocompatible but stable and inert, as an electrolyte for batteries for external wearable devices.