This 3D-printed smart cap can sense spoiled milk

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Researchers have 3D-printed a smart cap for a milk carton that detects signs of spoilage using embedded sensors.

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3D printing has grown by leaps and bounds in recent years, ranging from affordable prosthetics and medical implants to on-demand toys and cars. However, a group of UC Berkeley engineers have pointed out, one thing that was missing up until now was the ability to produce sensitive electronic components. So in collaboration with researchers at Taiwan’s National Chiao Tung University, the team has set out to expand the already impressive portfolio of 3D printing technology to include electrical components, like resistors, inductors, capacitors and integrated wireless electrical sensing systems. In order put this advancement to the test, they have printed a wireless smart milk carton cap capable of detecting signs of spoilage using embedded sensors.

(Source: Sung-Yueh Wu)

“Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor,” explained Liwei Lin, a professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Center. These findings were published in a new open-access journal in the Nature Publishing Group entitled “Microsystems & Nanoengineering. “One day, people may simply download 3D-printing files from the Internet with customized shapes and colors and print out useful devices at home.”

While polymers are typically used in 3D printing given their ability to be flexed into a variety of shapes, they are poor conductors of electricity. To get around this, the researchers devised a system using both polymers and wax. They removed the wax, leaving hollow tubes into which liquid metal was injected and then cured. The team used silver in their latest experiments.

The shape and design of the metal determined the function of different electrical components. For instance, thin wires acted as resistors, and flat plates were made into capacitors. The electronic component was then embedded into a plastic cap to detect signs of spoilage in a milk carton. A capacitor and inductor were added to the smart cap to form a resonant circuit. The engineers flipped the carton to allow a bit of milk into the capacitor, and left the carton unopened for 36 hours at room temperature.

(Source: Sung-Yueh Wu)

From there, the circuit sensed the changes in electrical signals that accompany increased levels of bacteria. These changes were monitored with a wireless radio-frequency probe at the start of the experiment and every 12 hours thereafter. Upon completion, the smart cap found that the peak vibration frequency of the room-temperature milk dropped by 4.3% after 36 hours. In comparison, a carton of milk kept at 4°C saw a relatively minor 0.12% shift in frequency over the same time period.

“This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers,” Lin added. “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.”

Looking ahead, the researchers are hoping to further develop this technology for use in health applications, such as implantable devices with embedded transducers that can monitor blood pressure, muscle strain and drug concentrations.

Interested? Read more about the study here.