Five years ago, DARPA announced their plans to undertake an initiative that promised to improve the lives of soldiers who had suffered upper extremity losses. In a speech given at the 24th Systems and Technology Symposium, COL Geoffrey Ling, M.D., Ph.D., manager of DARPA’s Revolutionizing Prosthetics program, detailed plans for fully integrated prosthetic limbs that would be controlled identically to the way biological arms are controlled. (DARPA)
Though the anticipated 2009 completion date has passed (and DARPA seems to have been beaten to the punch in the meantime), the end result provides some proof that good things really do come to those who wait. The project has now reached its third phase with a final design called the Modular Prosthetic Limb (MPL), and DARPA has backed the John Hopkins Applied Physics Lab in order to begin testing on human subjects.
Contrary to many of its earlier counterparts, the MPL offers an astonishing 22 degrees of motion (at the start of the program, the standard was 3). This includes independent movement of each finger and higher movement capabilities in the wrist, as well as simultaneous motion in joints. Engineers also hope the arm will be capable of bearing weight in a way that mimics the human arm, making it much more functional.
More striking than the improvements in mobility is the arm’s control: the MPL uses a technique called targeted muscle reeinnervation (TMR), in which a series of electrodes are connected to residual nerve fibers in the chest. When the patient thinks about moving their arm, the contracting chest muscles and nerve endings transmit information that’s interpreted by a microprocessor in the prosthesis and translated into physical motion. The Hopkins APL will be relying on studies like the one conducted by the University of Pittsburgh and Carnegie Mellon University, where they were able to train monkeys to control robotic arms by using their thoughts.
The arm also has a feedback system of sensors, which will transmit information about temperature and pressure back to the patient’s brain. With a bit of refinement, a replacement like this may get to the point where it’s almost indistinguishable from the real thing.
Seeing the video below of one of the earlier prototypes really took my breath away. I can’t possibly begin to imagine losing an arm or a hand, but I can believe that controlling a limb naturally after having lost it must be an emotional experience. The second video shows the more recent prototype being controlled remotely.
Human testing will begin within the year, according to the John Hopkins APL press release, and program manager Michael McLoughlin says of their plans: “Initially, we have targeted the quadriplegic patient population because they have the most to gain.”