Four years ago, we heard how researchers had created a microwave-oven-sized 3D printer that could produce sheets of skin for treating burns. Now, some of the same scientists have developed a handheld device that prints skin directly onto deep wounds.

The shoebox-sized gadget was built by a team from the University of Toronto, led by PhD student Navid Hakimi under the supervision of associate professor Axel Guenther.

It's described as working like a white-out tape dispenser, except instead of dispensing tape, it lays down sheets of alginate-based tissue. On the underside of each sheet are stripes of bio ink containing biological materials such as skin cells and collagen, which is the most abundant protein in the skin, along with fibrin, which is a protein that's instrumental in wound healing.

Weighing less than a kilogram (2.2 lb), the device reportedly requires little training to use, it eliminates the washing and incubation stages required by some conventional bioprinters, and it can cover a wound with skin within two minutes or less. It's already been tested on rats and pigs.

The scientists now plan on expanding the size of coverable wound areas, and hope to eventually begin clinical trials on humans.

"Our skin printer promises to tailor tissues to specific patients and wound characteristics," says Hakimi. "And it's very portable."

A paper on the research was recently published in the journal Lab on a Chip.