Schematic of an electron battery for potential biological applications. An electron battery composed of metal anodes and corresponding high voltage cathodes can continuously generate ions and power the motion of ions in various biosystems. Internally, the electron battery is connected by an electrical conductor that allows the transport of electrons, and its external electrodes are connected with the human body through ionic cables.

Engineers at the University of Maryland (UMD) invented a new kind of battery – the bio-compatible battery – producing the same ion-based electrical energy used by all living things.

In human bodies, flowing ions (sodium, potassium, and other electrolytes) are the electrical signals that power the brain and control heart rhythm and muscle movement.

In traditional batteries, the electrical energy, or current, flows as moving electrons. Current is generated within the battery by moving positive ions from one end to the other. The new UMD battery does the opposite, moving negatively charged electrons inside the device to deliver energy as positive ions.

“Potential applications might include the development of the next generation of devices to micro-manipulate neuronal activities and interactions that can prevent and/or treat medical problems such as Alzheimer’s disease and depression,” says group member Jianhua Zhang, Ph.D., a staff scientist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health in Bethesda, Maryland. “The battery could be used to develop medical devices for the disabled, or for more efficient drug and gene delivery tools in both research and clinical settings, to more precisely treat cancers and other medical diseases.”

Bio-compatible, bio-material batteries

Because living cells work on ionic current and existing batteries provide an electronic current, scientists have previously tried to create biocompatibility between these two by patching an electronic current into an ionic current. The problem is an electronic current needs to reach a certain voltage to jump the gap between electronic systems and ionic systems. However, in living systems, ionic currents flow at very low voltage. With an electronic-to-ionic patch, the induced current would be too high to run a brain or muscle. This problem could be eliminated by using ionic current batteries which can run at any voltage.

The new UMD battery has another unusual feature – it uses grass to store its energy. To make the battery, the team soaked blades of Kentucky bluegrass in a lithium salt solution. The channels that once moved nutrients up and down the grass blade were ideal conduits to hold the solution.

“The microchannels in the grass can hold the salt solution, making them a stable ionic conductor,” says Chengwei Wang, first author of the paper and a graduate student in the Materials Science and Engineering department at UMD.

However, the team plans to diversify the types of ionic current electron batteries can produce.

“We are developing multiple ionic conductors with cellulose, hydrogels, and polymers,” Wang says.

University of Maryland
www.umd.edu

The research was funded by Nanostructures for Electrical Energy Storage, a DOE Energy Frontier Research Center, and by Intramural Research Program of the NIDDK (DK043304).