Don't cry over spilled milk when your food becomes spoiled. There is now a 3D printed "smart cap" that can sense when perishable liquids go rotten — so you never have to smell that awful aroma for yourself.

Engineers at UC Berkeley collaborating with Taiwan's National Chiao Tung University have developed a smart cap for milk cartons that uses wireless electrical sensors to detect whether the liquid has gone sour.

In a paper published in the journal Nature, the team reveals that they used polymers (popular in 3D printing) combined with wax (since polymers are a poor material for electricity) to create the cap. The wax was then removed, leaving behind a hollow tube that allowed them to inject silver.

The engineers then added electronics, including a capacitor and inductor, to create a circuit that could monitor if and when the milk would become spoiled. After flipping the milk carton over to get some milk into the capacitor, they left the carton unopened in a room around 72 degrees Fahrenheit for 36 hours.

In order to tell if the milk was spoiled, the engineers tracked changes in electrical signals associated with the increase of bacteria in the liquid. They were able to monitor the changes wirelessly using a radio-frequency probe, which found the peak vibration frequency of the milk decreased by 4.3 percent after 36 hours. For comparison, refrigerated milk would have 0.12 percent frequency change in 36 hours.

"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 Center. "One day, people may simply download 3D-printing files from the Internet with customized shapes and colors and print out useful devices at home."

This also means that 3D printing smart caps could one day be added to food packaging. "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 said.

Don't hold your breath (figuratively), though — this probably won't occur until the cost of 3D printers goes down.

Photo: Guy Montag | Flickr

Via: Berkeley News