Transferable tattoos and decals are a fond piece of my childhood. Anyone my age still remembers how many "Transferelli" we could put on paper to invent scenarios and adventures. Later the password was “R41”, the transfers were used to label things. Today the technique lives again in step with technology. The era of edible electronics is approaching thanks to the developments of an IIT project led by Giorgio Bonacchini.
These components are now used to create intelligent tattoos that serve various applications. One of these, completely emerging and very interesting, is edible electronics. “Transfers” now consist of a thin film of ethyl cellulose polymer attached to a sheet of paper by a layer of water-soluble starch or dextrin.
Placing “Transferelli” (sorry, I can't call them anything else) in water dissolves the dextrin layer, allowing the sheet to be “transferred” to human skin or other objects. Images and text can be printed on them simply using a regular inkjet printer.
Edible electronics
It is this combination that sparked the imagination in a study at theItalian Institute of Technology in Genoa (IIT), with George Bonacchini as first author. The team is led by Dr. Mario Caironi, holder of a prestigious grant (ERC Consolidator) intended to further develop the field of edible electronics.
The team recently used the technology to print edible electronics on transfer paper. He then tested the electronic circuits and transferred them to edible items such as pharmaceutical pills and fruit.
Electronic devices that operate inside the digestive tract are not new at all. For many years, medical professionals have been studying so-called smart pills containing devices (for example these ingestible microsyringes, which distribute the drug more accurately). Up to now devices made exclusively with silicon-based components, which are expensive and inflexible.
The Italian team used inkjet printing to create electronic circuits on transfer paper.
The first question is easy: is it biocompatible?
We have to ingest it, it is important to know. Caironi and colleagues point out that ethyl cellulose film has long been used as an edible coating, including on pharmaceutical pills.
But the circuits also have other components. For example, transistors contain metallic materials. A single transistor requires only 4 micrograms of silver, so simple circuits should contain well below people's daily limit for silver. Printed in microparticles it should be biocompatible according to research already done. Of the other four semiconducting polymers used by the team, two are biocompatible, P3HT and polystyrene, and two not yet tested, 29-DPP-TVT and P(NDI2OD-T2).
Although these are used in picogram quantities, they still raise obvious questions about how safe they are. Caironi, Bonacchini and colleagues know this well and are taking on the task of evaluating how polymers interact with the human body. The results have been positive so far, but more research is needed.
The team uses these materials to print a variety of organic transistors and logic inverters onto transfer paper, then test their properties.
New challenges for edible electronics
There are other checks to do, in addition to those of biocompatibility. For example, the transfer process exposes the circuits to air, light and water, which can partially compromise the circuits. The team was able to mitigate this effect by mixing polymers and semiconductors. Stability is still variable, but the first steps towards edible electronics are more than encouraging.
“This result paves the way for the creation of robust complementary circuits,” say the researchers. “This system provides a simple and versatile platform for the integration of fully printed organic circuits on foods and drugs.”
The possible applications are many
For me this is exciting work. These circuits could instantly monitor the degree of ripeness of a fruit, or the edibility and perishability of foods and products. It would be a mortal blow to the food waste. Edible electronics could also allow drugs to be delivered in more targeted ways, or analyzes of various types directly into the digestive system.
Of course, there is still a lot of work to be done, particularly on the edible batteries that should provide the power for these types of circuits. They could probably be powered by piezoelectric energy systems that generate energy from body movement, or even sound. In any case, as mentioned, it is a big step forward for the future of edible and printed electronics, as well as for product traceability and supply chain transparency.
