Researchers Develop a Fully Biodegradable Smart Tag for Temperature and Humidity Monitoring
"Ecoresorbable" tag composts safely in just nine weeks once its lifespan is up, and can warn when shipments get too hot.
Researchers from EPFL, the Swiss Federal Laboratories for Materials Science and Technology (Empa), CSEM SA, and ETH Zurich have designed chip-free temperature-monitoring smart sensors that, they say, are fully biodegradeable — requiring neither a battery nor a transmitter to operate.
"Researchers […] have developed a smart sensor tag that measures the temperature and relative humidity, and can 'remember' when a certain temperature threshold has been exceeded," Empa's Anna Ettlin explains of the team's work. "The small sticker is not only silicon-free, but also completely biodegradable. The project was funded by the Swiss National Science Foundation (SNSF) and Innosuisse as part of the BRIDGE Discovery program."
The chip, which operates without a battery or a transmitter, is constructed from printed paths of conductors that form resistive and capacitive circuit elements — inspired, the team says, by radio-frequency identification (RFID) tags, which harvest radio-frequency energy from a nearby transmitter to power a return signal. Where the breakthrough comes in is that the circuit elements are dynamic: their capacitive and resistive properties change depending on environmental conditions.
Using this property, the smart tags are able to feed back information about the current temperature and humidity — but that was only one part of the team's goal. The other comes in giving the tags "memory," whereby if the temperature of the tag exceeds 25°C (77°F) at any point a part of the circuit made from solidified oil permanently melts. "Talking about vaccinations, for example, this could mean that the shipment can no longer be used or that the expiry date is invalid," notes project lead Gustav Nyström.
While commercial temperature sensors already exist, they're not the most eco-friendly things. The smart tag designed by the team, though, is said to be fully "ecoresorbable" — meaning it's biodegradable and made exclusively of materials, including cellulose, zinc, beeswax, and frozen olive, jojoba, and coconut oils, which can be simply composted with full disintegration recorded within nine weeks of the tags' end-of-life.
The team's work has been published in the journal Nature Communications under open-access terms; two EPFL researchers are working on commercializing the technology through a startup called Circelec.
Main article image courtesy of Empa.