3D printing has notched up some mind-boggling accomplishments in its relatively short lifespan. We've seen 3D-printed bridges and 3D-printed buildings. Scientists have even managed to produce 3D-printed brain-scaffolding, if you can get your head around that (and if you can't, at least you now know who to see about it).

But this is something new, and the potential applications could be massive. For the first time, researchers have demonstrated that 3D printing is capable of producing fully functional electrical components, including resistors, inductors, capacitors, and even integrated wireless electrical sensors. Researchers at the University of Berkeley, California in the US have 3D-printed a wireless 'smart cap' for milk bottles that can tell you whether your milk is fresh by detecting signs of spoilage via embedded sensors.

The researchers, in collaboration with a team from the National Chiao Tung University in Taiwan, created their 3D-printed electronic circuitry by fusing traditional polymer materials with 'sacrificial structures' composed of wax. When the wax structures were removed, a liquid silver suspension was injected into the paths that were left. Once cooled, this formed the necessary metallic framework for the electronic circuitry to function.

The design of the sensor enabled the smart cap to detect changes in electrical signals stemming from increased levels of bacteria in a carton of milk, which the researchers left unopened at room temperature for 36 hours.

It's a cute little proof-of-concept showing what 3D-printed electrical components can do for us - and yes, we definitely want one for our kitchen - but as far as the researchers are concerned, their milk bottle smart cap is just the beginning. The ability to produce sensitive electrical components on demand will change people's lives (and isn't a million miles away from what used to be just science fiction).

"Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor," said Liwei Lin, senior author of the study, in a press release. "One day, people may simply download 3D-printing files from the Internet with customised shapes and colours and print out useful devices at home."

While advanced electronics like smartphones and computers might be beyond the scope of the researchers' current study (due to the extreme miniaturisation involved in today's high-tech components), the research paves the way for all kinds of basic electronics that could help us out in our day-to-day lives.

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

The research is published in Microsystems & Nanoengineering.