An exciting new biodegradable battery unveiled by a team of scientists could have huge potential for biomedical devices. The tiny battery can be safely absorbed by the body within just three weeks and could be used in temporary devices intended to monitor tissue or deliver short term treatment. From Nature:
Their devices, described last week in Advanced Materials, use anodes of magnesium foil and cathodes of iron, molybdenum or tungsten. All these metals will slowly dissolve in the body, and their ions are biocompatible in low concentrations. The electrolyte between the two electrodes is a phosphate-buffered saline solution, and the whole system is packed up in a biodegradable polymer known as a polyanhydride.
Currents and voltages vary depending on the metal used in the cathode. A one-square-centimetre cell with a 50-micrometre-thick magnesium anode and an 8-micrometre-thick molybdenum cathode produces a steady 2.4 milliamps of current, for example. Once dissolved, the battery releases less than 9 milligrams of magnesium — roughly twice as much as a magnesium coronary artery stent that has been successfully tested in clinical trials, and a concentration that is unlikely to cause problems in the body, says Rogers. “Almost all of the key building blocks are now available” to produce self-powered, biodegradable implants, he says.
All versions can maintain a steady output for more than a day, but not much longer. The team hopes to improve the batteries’ power per unit weight — known as power density — by patterning the surface of the magnesium foil to increase its surface area, which should enhance its reactivity. The authors estimate that a battery measuring 0.25 cm2 and just one micrometre thick could realistically power a wireless implantable sensor for a day.
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