Edible electronics created by IIT's Center for Nano Science and Technology (CNST) in Milano. Credit: Istituto Italiano di Tecnologia.
Scientists in Italy have developed the world's first rechargeable edible battery, building the device entirely from everyday food ingredients and additives1. Having shown that the battery can be used to power a light-emitting diode, they reckon the technology could one day be an energy source for monitoring drug delivery, diagnosing disease and keeping tabs on food quality.
Available tiny devices that can be ingested to peer inside the body, rely on electronics which are toxic and must therefore be carefully wrapped up inside inert materials. If the packages get stuck, they have to be removed surgically.
The latest work addresses methods to provide power for edible electronics. Mario Caironi and colleagues at Istituto Italiano di Tecnologia (IIT) in Milan, looked for pairs of materials that could serve as the device's electrodes — an anode that releases electrons when the device discharges, and a cathode that soaks the electrons up.
Their aim was to find materials that undergo suitable reactions while being safe to swallow. Guided by the kinds of chemicals used to provide energy for miniscule biochemical machines such as enzymes, lead author, Ivan Ilic, tried out several combinations of possible edible molecules to arrive at the most stable voltage. He and his colleagues concluded that riboflavin (vitamin B2) would be best for the anode, while quercetin, a substance present in capers, could serve as the cathode.
Having settled on these molecules, the researchers mixed each of them with activated charcoal from coconuts, to enable electrons to flow. They then bound the electrodes with ethyl cellulose covered with very thin strips of gold, of the type used by pastry makers, to collect current and form external contacts. Inserting a water-based electrolyte and a separator made from nori algae, they finally encapsulated the device in beeswax.
Putting the 1cm2 battery through its paces, Caironi and colleagues found that it could operate at 0.65V, yielding 48 microAmps for at least 12 minutes. Achieving this performance over 100 charging and discharging cycles, they also showed they could power simple electronic components such as a light-emitting diode.
According to Christopher Bettinger of Carnegie Mellon University in the US, the research provides "another important step" in developing safe and useful ingestible devices. But he cautions that more work is needed to maximise the charge from a certain volume of battery – given the very small size of such devices.
Caironi points out that being rechargeable – it could convert mechanical processes within the gut into electrical charge – the battery might not need to hold as much charge for a given application. Nevertheless, he and his colleagues are looking to increase the battery's charging area by rolling up the electrodes. They will need to increase it by around a factor of ten to implement one specific application they are interested in, a ‘smart’ edible pill that would use a battery to emit regular signals indicating progress with drug delivery.
Caironi estimates that it will take at least a decade before such devices could reach the market. A closer application could be for sensors embedded in produce, to monitor their temperature or freshness. "In that case certification would be quicker," he says. "You don't need to eat these things, you just want to make sure they don't leave traces of toxic materials."
