Engineers at UC Berkeley in the US, and National Chiao Tung University in Taiwan have developed a wireless smart cap for milk cartons that can detect signs of spoilage.
The smart cap incorporates technology that allows electrical components to be incorporated into 3D-printed plastics using embedded sensors. These components typically include resistors, inductors, capacitors, and wireless electrical sensing systems.
Once fitted, the container can be tilted upside-down to quickly test for the changes in electrical signals that will indicate high levels of bacteria.
Commenting on this, Berkeley Sensor and Actuator Center co-director and senior author of the paper Liwei Lin said: "Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor.
"One day, people may simply download 3D-printing files from the internet with customised shapes and colours and print out useful devices at home."
The researchers used polymers owing to their flexibilit, which allows them to be formed into a variety of shapes.
To make them good candidates for electronic devices, a system of polymers and wax was built, where the wax, which was replaced later with liquid metal, was injected.
The electronic components were then integrated with a plastic milk carton cap to monitor signs of spoilage. The 'smart cap' was fitted with a capacitor and an inductor to form a resonant circuit.
A bit of milk was trapped in the cap's capacitor gap, and the entire carton was then left unopened at room temperature (about 71.6 degrees Fahrenheit) for 36 hours. Changes in electrical signals were monitored and reported.
"This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers.
"You could imagine a scenario where you can use your cellphone to check the freshness of food while it's still on the store shelves," Lin added.
Lin said besides milk, the technology can be easily extended to food items.
The team is also working on developing this technology for health applications, such as implantable devices with embedded transducers that can monitor blood pressure, muscle strain, and drug concentrations.
