Regenerative medicine, which seeks to replace organs, tissues, and cells damaged by disease, injured by trauma, or worn by time (see my earlier posting on this subject, "Stem Cells and Beyond," March 9), holds much promise. But at present it is not possible to regenerate entire limbs lost to accident or war. Until the field of regenerative medicine advances further, artificial limbs offer the most hope for those who have lost an extremity. And thanks to remarkable progress in microelectronics, computer science, micro-engineering, and neurosurgery, we are nearing a time when artificial arms may move as spontaneously and naturally as the original.
A recent issue of the Journal of the American Medical Association* describes one notable advance by a team of neurosurgeons, engineers and rehabilitation specialists working in Chicago and Canada, funded by both the Defense Advanced Research Projects Agency and the National Institutes of Health. Their goal is to create an artificial arm that naturally responds to signals from the brain.
The first step of the process is to surgically relocate nerves that signal absent muscles. For example, the ends of severed nerves that would connect to the biceps or forearm are stitched to separate muscles of the chest. After the body heals, a signal from the brain that normally contracts a muscle in the arm now tightens one in the chest. An array of sensors placed over the chest to detect the slightest muscle tension relays signals to a computer, which in turn sends signals to a set of tiny motors that move the new limb.