MOST PROSTHETIC ARMS ARE CLUMSY THINGS: Range of motion is limited, and operation can be nonintuitive (for example, a flex of the bicep turns the wrist). But now an international team led by Johns Hopkins University Applied Physics Lab scientists is working to change all of that. Its Proto 1 prosthetic arm features eight motions (such as a grasping hand) and operates using a process called targeted muscle reinnervation, in which nerves from an amputated limb are transplanted to muscles near the amputation site. When the nerves excite the muscles, surface electrodes sense that energy and prompt movement.

Although researchers are still testing Proto 1 on patients, they are already at work on Proto 2. This prototype will feature more than 25 movements, such as individually bending and spreading the fingers, and as many as 80 sensors on the hand and fingertips that will detect pressure, vibration and temperature. An even more direct connection with the user’s residual nerves than that of Proto 1 will control the expanded, more precise motions.

Proto 2, slated for completion this summer, will also be a testing ground for various energy sources (electric, hydraulic and pneumatic) to determine which deliver the most power and weigh the least. Whether it will keep its current winning name remains to be seen.