In the future, 3-D printers may be able to print living tissues like lungs, livers, hearts and other key organs. As a first step in that process, researchers are attempting to print knee cartilage with a 3-D printer.

Dr. Darryl D'Lima is a physician at the Scripps Clinic in San Diego, CA. As of now, he has already designed bioartificial cartilage from cow tissue. To do this, he modified a used ink jet printer to extrude a living gel made of cells. Dr. D'Lima also printed cartilage that was removed from patients who had undergone joint replacement operations.

Eventually, Dr. D'Lima hopes that the technology could be used to custom-print cartilage for a joint replacement. This cartilage could be custom-shaped and bio-engineered to avoid compatibility issues. Potential patients could include those with arthritis, physical trauma or other injuries.

As of now, 3-D printers are used to design products from a wide variety of materials. While most 3-D printers use powders or plastics to create an object layer by layer, bioprinters print cells in the form of a gel or liquid.

One of the challenges of bioprinting is finding effective ways to extrude living cells without killing them. In a regular inkjet printer, drops of ink are heated to very temperatures, forcing them onto a sheet of paper. Heat is also used with many traditional 3-D printers. However, heat can be a significant issue when printing living cells.

As of now, researchers are trying to design skin, blood vessels, bone, cartilage, liver and other tissues through 3-D printing. When researchers engineer tissues, they usually create a bioresorbable scaffold, adding cells to it later on. However, a bioprinter would allow healthcare workers to directly control cell placement to accurately mimic natural anatomical structures in the body.

While bioprinting has made significant progress over the past decade, it still faces significant challenges. "Nobody who has any credibility claims they can print organs, or believes in their heart of hearts that that will happen in the next 20 years," notes Brian Derby, researcher from the United Kingdom.

Organovo (San Diego, CA) is one startup that is making significant strides in the bioprinter field. For now, the company has developed a 3-D printer that can create strips of liver tissue. While the maximum thickness of a strip is 20 cells, the company believes the test could be used to test different pharmaceuticals.

Other initiatives are taking place around the globe. In Germany, one lab has created printed sheets of a patient's heart cells. Armed with these cells, physicians might be able to repair vascular damage from a heart attack. At the Hannover Medical School, researchers are exploring the viability of skin cell 3-D printing.

Another research team is working on bioprinters for fat. One potential use for this technology could be post-lumpectomy cosmetic procedures.

As of now, the technology is still in its infancy. However, 3-D printers have made great strides over the past decade. With thousands of researchers around the world exploring this exciting new technology, bioprinters could be coming to hospitals in the next few decades.