There was a time not so long ago that my inkjet printer saw a lot of action. Nowadays, however, it can sit idle for weeks or even months before being called into service. But when it is called upon, the long break between print jobs means the print heads are usually clogged and an ink-wasting head clean needs to be performed. Taking inspiration from the human eye, researchers at the University of Missouri (MU) have developed a print nozzle that prevents the ink inside from drying out when not in use.

To keep the surface of our eyeballs moist, our eyelids spread a film of oil that prevents a thin layer of tears from evaporating. Recognizing that the same principle could be used to keep ink from drying out in the print nozzle opening, Jae Wan Kwon, associate professor in the College of Engineering, and MU engineering student Riberet Almeida, developed a system that uses a droplet of oil to block air from getting to the ink in the nozzle and drying it out.

Because mechanical shutters like eyelids would not work at the small scale of the inkjet nozzle, as the droplet would stay in place thanks to surface tension, Kwon’s system uses an electric field to move the droplet of oil in and out of place.

Kwon says his technology could be adapted for use in other devices in which the material being sprayed through the nozzle is even more valuable and expensive than ink – hard as that may be to believe, such substances do exist.

“Other printing devices use similar mechanisms to ink jet printers,” Kwon said. “Adapting the clog-free nozzle to these machines could save businesses and researchers thousands of dollars in wasted materials. For example, biological tissue printers, which may someday be capable of fabricating replacement organs, squirt out living cells to form biological structures. Those cells are so expensive that researchers often find it cheaper to replace the nozzles rather than waste the cells. Clog-free nozzles would eliminate the costly replacements.”

Rapid prototyping systems are another potential application suggested by Kwon for the technology. These devices emit streams of liquid plastic through nozzles like those on an ink jet printer, but the thick, sticky liquid can clog quite easily. This means that the whole nozzle, which can cost thousands of dollars, will often have to be replaced.

“The nozzle cover we invented was inspired by the human eye,” said Kwon. “The eye and an ink jet nozzle have a common problem: they must not be allowed to dry while, simultaneously, they must open. We used biomimicry, the imitation of nature, to solve human problems.”

The video below shows a microscopic view of the nozzle operating.