Transferable tattoos and decals are a loving piece of my childhood. Anyone my age still remembers how many "transfers" we could put on paper to invent scenarios and adventures. Further on, the password was "R41", the transfers were used to label things. Today the technique relives in step with the 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 smart tattoos that serve different applications. One of these, completely emerging and very interesting, is edible electronics. The “Transferelli” now consist of a thin film of ethylcellulose polymer attached to a sheet of paper by a layer of water-soluble starch or dextrin.
Putting the "transfers" (sorry, I can't call them any other way) 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 by using a regular inkjet printer.
It is this combination that ignited the imagination in a studio at theItalian Institute of Technology in Genoa (IIT), with Giorgio 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 by no means new. 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 semiconductor 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 be made, 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 blending 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 realization of robust complementary circuits,” say the researchers. “This system constitutes a simple and versatile platform for the integration of fully printed organic circuits on food and pharmaceuticals”.
The possible applications are many
For me it is an exciting job. 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 fatal blow to the food waste. Edible electronics could also allow the administration of drugs in more targeted ways, or analyzes of various types directly into the digestive system.
Of course, much work remains to be done, particularly on edible batteries that are supposed to provide power for these types of circuits. They could likely 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 the traceability of products and the transparency of the supply chain.