Aschoff’s team has followed the model of a tooth. The group theorizes that a well-anchored implant—in which the bone has grown into the metal—will prevent bacteria from migrating into the bone and causing dangerous infections. (The bacteria in our mouths, for example, typically stay on the surfaces of our teeth, tongue, and gums.) Gordon Blunn, head of the Centre for Bio-Medical Engineering at University College London, has taken a somewhat different tack, getting inspiration from deer, whose antlers provide a natural model for a healthy interface between skin and bone.
As part of normal wound healing after surgery, the edges of the sliced sections of skin will try to knit together, growing downward along the connector pin of the prosthetic implant in search of another piece of skin. But that produces a pocket that can collect dirt and increase the chances of infection. Blunn’s team has focused its efforts on encouraging the skin to form a tight seal around the implant, thereby decreasing the risk of infection. Deer seem to do this via large pores in the bone just beneath the skin. These pores encourage soft tissue to adhere. Blunn and colleagues mimicked this process by adding a porous flange, implanted just below the skin, encouraging the optimal skin seal to form. Blunn is a scientific consultant for Stanmore Implants, which aims to commercialize the technology.
So far his team has surgically attached implants to four people, one of whom was a lower-limb amputee who climbed Kilimanjaro with his prosthetic leg in September. (One of Blunn’s most famous subjects is Oscar the cat, who received two prosthetic hind limbs after an accident involving a combine harvester a year ago. Two months after receiving the implants, Oscar could run.)
To Matheny’s disappointment, human testing has not yet begun in the U.S. That’s in large part due to the high risk of infection, but Matheny says that’s a chance he is willing to take. McGough, who is Matheny’s surgeon, is part of a team working with European scientists and other groups in the U.S. to garner approval from the U.S. Food and Drug Administration to bring this technology stateside.
“I think this will change everything for amputees,” says McGough. The surgeon has traveled to Germany to learn the procedure and has already given one patient an implant there. He hopes that Matheny will be next; researchers there have already built him a custom-designed device. For legal reasons, the surgery needs to take place in Germany. “And I don’t have the money to go there yet,” says Matheny.