In 2012, scientist John Rogers from the University of Illinois at Urbana Campain introduced a series of biodegradable silicon chips, who could control the temperature or mechanical deformation, transmitting the results by radio to external devices. Some of them could even carry out treatment by heating surrounding tissues to prevent infections. To provide wireless power of these chips from an external source was proposed use induction coils.
A photo from open sources
But wireless power transmission is problematic for devices located deep inside tissues or bones. And for solutions to this problem, Dr. Rogers and his colleagues have completely created biodegradable battery.
Their devices described last week in the journal Advanced Materials, use magnesium foil anodes and iron cathodes, molybdenum or tungsten. All these metals dissolve slowly in body, and their ions are biocompatible in low concentrations. Battery electrolyte is saline solution with by adding phosphates and the whole system is packaged in biodegradable polymer polyanhydride.
Battery currents and voltages may vary depending on cathode metal used. For example, one square centimeter batteries with a magnesium anode and a molybdenum cathode produces stable 2.4 mA current. After the battery is dissolved in the body less than 9 milligrams of magnesium gets in – about twice as much from a coronary artery shunt, and such concentrations do not cause problems.
All battery versions can support steady current output. more than a day. Team hopes to improve density current power by increasing the surface area of the magnesium foil, which should increase reactivity. According to the authors, 0.25 sq. battery cm and a thickness of just one micrometer could would power the wireless implant throughout the day.
At the same time, biosoluble magnesium batteries are by no means only decision. Last year Christopher Bettinger from Carnegie Mellon University of Pittsburgh, PA introduced Sodium-ion battery with electrodes made of pigment melanin. But magnesium batteries have a relatively large current power and charge density, and last longer.
