3D-printers can print just about anything these days: shoes, guns - and even bones. Scientists all over the world have been working on printing bone replacements for some time. Now researchers at the University of Freiburg in southern Germany are taking a major step forward. They want to use a 3D-printer to create bones that come complete with blood vessels. With this method chances are higher that the print-outs connect to the surrounding tissue faster.

"This should make a crucial difference timing-wise," Günter Finkenzeller, head of the Tissue Engineering Department at the Plastic- and Hand-surgery center at the University of Freiburg, told DW. "Then the printed blood vessels only need to connect with the other vessels directly bordering on the implant and the natural tissue."

Other methods well documented in medical literature require blood vessels to grow into the implant from the surrounding tissue, which can take up to two weeks. By then, many artificial bones would have died off.

Hydro-gels as ink cartridges

It's going to be a while before Finkenzeller, the project's co-leader Peter Koltay and their colleagues will actually be able to print these bones and vessels. They have only just received a 460,000 euros ($526,000) research stipend from the German Research Foundation (DFG) that will fund their work for three years.

The first step will be to develop a suitable printer. So far, one of the problems with using 3D-printing in medicine is that most of the materials that the machine can use are synthetics. They are highly functional and resilient, but the human body doesn't take well to them.

"We want to build a printer that uses certain liquids called hydro-gels that can be equipped with appropriate cells so we can print three-dimensional bone tissue," Finkenzeller told DW. "We plan on printing osteoblasts - that are cells that synthesize bone - as well as endothelium cells. Those are cells that line the interior of blood vessels."

In short, the researchers are working on a 3D-printer that uses hydro-gels where regular printers use ink cartridges. In order for the machine to generate bone tissue complete with blood vessels that a patient's body won't reject, the hydro-gels should ideally be laced with his or her own cells.

Finkenzeller said that in the future, stem cells could be used for this. They are found everywhere in the human body and could be extracted from fatty tissue. In the lab, scientists would then "turn" these stem cells into bone cells to be added to the hydro-gels for printing.

Huge step forward for individualized medicine

The researchers in Freiburg don't expect to reach the point where they can print fully functioning bones in their exploratory three-year project. Getting there and making the method available to doctors and hospitals on a large-scale is a long-term goal that could be reached in seven to ten years, Finkenzeller estimates.

But once the time has come, 3D-printing could give new meaning to the concept of individualized medicine. Through x-ray and computed tomography (CT), doctors can get exact pictures of a patient's bone parts that need to be replaced. The 3D-printers of the future could then exactly replicate the shape of these parts and, using the patient's stem cells, print a perfect replacement.

This could be used in the treatment of bone cancer, for example, where tumor cells infest bone tissue. The hope is that in the future, a print-out could replace the affected bone. But there's a lot more where 3D-printers could make a big difference.

"This has incredibly high potential, not just for bones but for any other tissue that needs replacing," Finkenzeller said. "You could print skin tissue or cartilage, which would be very helpful for arthrosis patients, for example."

An efficient print-out liver

John Hunt takes it a step further. The director of the Liverpool-based UK Centre for Tissue Engineering says that one day, 3D-printers will be able to print entire organs.

"You can print absolutely anything, which is the most wonderful thing about 3D-printing," Hunt told DW. "We might start thinking about a pancreas, a liver, things like that."

It sounds like straight out of science fiction novel: printing a human liver. And Hunt does admit the print-out would likely not be 100 percent equivalent to an organ a patient would get from the transplant list.

"You have to think a little outside the box," he said. "We don't need to print a whole liver as you know it. We can print something that functions metabolically in the same way as a liver, but it doesn't have to look like a liver."

Patients wouldn't have to wait for years for an organ donation. It would likely take a while for the print-out organ to start working properly in the body, but that's a finite period, Hunt says - when you're on the waiting list for a transplant, you don't know when you'll get a new organ.

So the fact that a print-out liver might not look exactly like the original organ is not all that important. The focus on the essential features could even lead to an improvement:

"It doesn't have to be that complicated," Hunt said. "The maps of old cities for instance are a mess, with complicated, intertwined streets and such. The maps of new cities are all linear, with straight right angles, and it's all tremendously efficient."

The same could become true for print-out organs. We'll likely know more in seven to ten years.