Engineers 3D print ‘smart cap’ for detecting spoilt milk

The research, published this week in Microsystems & Nanoengineering, reveals how the team 3D printed resistors, inductors, capacitors and integrated wireless electrical sensing systems using a combination of polymers and wax. The wax is then removed, leaving hollow tubes into which liquid silver is injected and cured to create circuits.

“Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor,” said senior author Liwei Lin, a professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Centre.

“One day, people may simply download 3D printing files from the internet with customised shapes and colours and print out useful devices at home.”

To demonstrate the technology, the engineers embedded 3D printed electrical components into the cap of a milk carton to monitor bacteria levels. The ‘smart cap’ was fitted with a capacitor and an inductor to form a resonant circuit. The unopened carton was then upended to allow some milk to get trapped in the cap’s capacitor gap, and left at room temperature for 36 hours.