(New Scientist) -- Good news for injured athletes. Damaged knee ligaments heal better if patched with a scaffold made from pig's intestine.

Tearing the medial collateral ligament, or MCL, is one of the most common sporting injuries. The ligament tends to heal by itself, so doctors don't usually resort to surgery. But afterwards it can be weaker and prone to further injury.

So Volker Musahl and his postdoc Savio L-Y Woo at the University of Pittsburgh in Pennsylvania tried patching up MCL injuries in rabbits with the material derived from pig gut. The patched ligaments were stronger than those left to heal by themselves, Musahl told the Engineering Tissue Growth International Conference last week in Pittsburgh. "We have clearly shown that the quality of the tissue is better after treatment," he says.

Musahl and Woo used material developed by Stephen Badylak of Purdue University in Indiana. To make his patches, Badylak takes the middle layer of pig intestine, removes all the cellular material and sterilises what is left. The result is a thin and strong biological mesh.

Intestinal tissue contains an abundance of healing factors that promote cell growth, and the mesh retains many of these. When implanted into an injury, the scaffold attracts cells such as fibroblasts and blood vessels into the area, inducing an impressive healing response.

And it's not just knees that can be treated. The scaffolds help the body grow new skin, cartilage and bones with little scarring. "We get site-specific remodelling of injuries and defects," says Badylak. "Many of the patients successfully treated have had life-threatening problems."

Already, these treatments have moved out of the lab and into hospitals. The US Food and Drug Administration has approved the material and it has been used to treat 70,000 patients in the US for a variety of injuries, including knees and shoulders, as well as skin wounds.

Badylak has also developed alternative scaffolds derived from different tissues. And Arnold Caplan of Case Western Reserve University in Cleveland, Ohio, works with a common biological material called hyaluronic acid, which is normally found in the spaces between cells. He seeds the sponge-like material with stem cells from bone marrow, before implanting it in deep holes drilled in rabbit knees. "It regenerates cartilage at the surface of the joint, and then brings in blood vessels at the bottom to regenerate bone," says Caplan.

Although these results are exciting, much needs to be done to truly understand whether function, not just structure, is properly restored. At the conference, David Butler of the University of Cincinnati in Ohio talked about the need to design implants that can withstand the unique loads different joints encounter. "It's important to meet the functional demands of the tissue," he says.