The idea being trialed is a “smart cap” — a device to be placed inside a milk carton to sense the quality of the milk inside. This represents a breakthrough in terms of three dimensional printing of electronic circuits.
Polymers are poor conductors of electricity and 3D printing is based primarily around a set range of plastics. To overcome this, Controlled Environments reports that the research group designed materials based around polymers and wax. This created hollow tubes suitable for the addition of a liquid metal. For initial studies, silver was used to fill the tubes via nano-injection.
Various experiments found the shape and design of the material affected how it performed and its suitability in different applications. For instance, thin wires functioned well as resistors; whereas flat plates made for useful capacitors.
The basis of this led to the production of the sensor cap for milk cartons. The sensor functioned by detecting an increase in level of electrical signal as would be accompanied by a growth in bacterial population. When this occurs a signal can be sent wirelessly.
The sensor was tested on various cartons of milk, some held at room temperature and some in a refrigerator. It was found that the cartons kept at room temperature produced the electrical signal far earlier, which was consistent with bacterial growth (or the rate at which milk goes off).
The potential for such technology goes beyond milk cartons. As lead researcher Liwei Lin notes: “One day, people may simply download 3D-printing files from the Internet with customized shapes and colors and print out useful devices at home.”
The study was conducted at UC Berkeley (the Berkeley Sensor and Actuator Center) together with Taiwan’s National Chiao Tung University. The research has been published in the journal Microsystems & Nanoengineering, in an article headed “3D-printed microelectronics for integrated circuitry and passive wireless sensors.”
