The prosthetic arm that gave up on the hand

What it was

In December 2010, a prosthetic arm without a hand made the rounds of tech sites and TV news. Kaylene Kau, a recent graduate of the industrial design program at the University of Washington, had replaced the hand with a single tapering limb that curled around objects the way a tentacle does.

The mechanism was simple. A small motor pulled two cables that ran through the length of the limb. Two switches sat on the upper part of the arm. One made it curl, the other let it go. The wearer placed the limb against an object, pressed a switch, and it wrapped around the object. Kau described its jobs as holding things down, grasping and gripping, with control over how far it curled.

The reasoning came from research, not from looks. Her finding was that a prosthetic arm usually acts as an assistant to the remaining hand, which does the fine work. So the device did not need five fingers. It needed to hold things steady and adapt to different shapes. Fewer motors also meant a device that would be cheaper to produce.

The question was never how to copy a hand, but what the other hand needs help with.

Where the idea went

The tentacle itself went no further. When Core77 revisited it in 2012, the writer wondered how it would manage a pencil, and Kau was working as a designer in consumer electronics. We found no sign of a production version.

The industry kept building hands. Touch Bionics had launched the i-LIMB in 2007, with five individually powered fingers controlled by signals from the wearer’s own muscles. The prosthetics company Össur bought Touch Bionics in 2016 for £27.5 million. In 2018 Open Bionics, a Bristol company, began selling the Hero Arm in the UK: a 3D-printed bionic arm for below-elbow amputees, made to the wearer’s measurements, with several grip patterns, a wrist that rotates 180 degrees and covers that snap on with magnets.

What it means now

Kau’s question still stands. Should a prosthetic imitate a hand, or should it do the specific jobs the remaining hand needs help with? Commercial bionic arms chose imitation, but they absorbed part of her argument. Instead of trying to copy every movement, they offer a handful of grips that the wearer switches between for different tasks.

The Hero Arm also took on the attitude that made the tentacle memorable. It does not pretend to be skin. It is designed to be looked at, with swappable covers that treat the arm as a visible object. A tentacle is still a provocation. The brief behind it, design for the task rather than the silhouette, is the same brief inclusive designers work from today.