Bionic Made Better

Engineers develop a mind-controlled prosthetic arm dexterous enough to play piano

by Marc Dey

Learning to live without a limb is an extremely daunting challenge. Many of us take the awesome tools that are our arms for granted, but without them even the most mundane tasks become struggle. For the longest time artificial limbs have served little purpose, other then astecticly faking an arm. However now there is an exciting alternative to the old prostectics: a bionic arm.

Prompted by the fact that hundreds of US veterans of the Iraq war have lost a limb, the Defense Advanced Research Projects Agency, or Darpa, has launched a $55-million project. The project consisted of a number prosthetics experts whose goal was to create a thought-controlled bionic arm that duplicates the functions of a natural limb.

These experts first developed Proto 1, which could bend at the elbow, rotate its wrist and shoulder, and open and close its fingers. Compared to most other prosthetics this was a huge leap forward.

The team has just finished Proto 2, a thought-controlled mechanical arm, complete with a hand and articulated fingers, that can perform 25 joint motions. The shoulder and wrist are capable of roll, pitch and yaw, the elbow can flex, and the fingers and thumbs bend at each knuckle. Each joint brings together two lightweight artificial bones made of carbon fiber and aluminum alloys.This type of dexterity closely resembles that of a real arm, which can make 30 motions. A person wearing a Proto 2 has enough dexterity that they could conceivably play the piano.

The bionic arm works with injectible myoelectric sensors (IMES) that detect muscle activity and wirelessly transmit commands to the prosthetic arm. A wire coil wrapped over the shoulder supplies wireless power to the implants and relays signals to computers in the arm that decipher the commands and tell the arm to move. The team eventually plan to implant electrodes directly on the nerves, or in the brain itself, to achieve more natural neural control.

Obviously a robotic device would need some form of power source, however many of our current sources would be rather impracticle and heavy. Researchers are experimenting with a hydrogen-peroxide pneumatic system to replace bulky, slow electric motors. The hydrogen peroxide reacts with an iridium catalyst to drive the arm's movements. The wearer would have to install a fresh hydrogen-peroxide canister each morning.

The bionic arm is not ready yeat and the team still have some work to do. The next steps are to shrink the battery, develop more-efficient motors, and refine the bulky electrodes used to read electrical signals in muscles. The final version of the hand will apparently be able to sense pressure, temperature and differences in the surfaces of objects.

If all goes well, by 2009, the agency will petition the Food and Drug Administration to put the arm through clinical trials.

bigeyeddeer@yahoo.co.uk