It wasn’t long ago that a typical prosthesis was little more than a hunk of plastic. Fortunately, the technology has developed rapidly in the past couple of decades. Now there are a wide range of prosthetic designs that are getting closer and closer to true biomimicry, meaning they provide capabilities comparable to their biological counterparts. The most difficult kind of prosthesis to design is the human hand, because it is so incredibly versatile; it’s no accident that you can go from doing a pull-up to writing with a pencil without missing a beat. This new biomimetic prosthetic hand replicates the human hand more closely than previous designs.
This prosthetic hand, called Hannes, was developed by engineers from the Italian Institute of Technology and Centro Protesi INAIL, and was reported in the most recent issue of Science Robotics. Their goal was simple: create the most advanced prosthetic hand possible. While this doesn’t quite reach the capability of a biological human hand, it does get closer than just about any other design we’ve seen. It can be worn by people with a wide range of remaining residual limb length, and is fully robotic. It’s controlled via a myoelectric system that is able to detect the contractions of the user’s residual limb. By flexing a forearm muscle, for example, they can cause the grip to close. These sensors can be adapted to work with whatever muscles are still present.
One of the keys to the performance of this design is the use of a single powerful motor, which is used to flex all of the fingers via tensile cables. This lets it exert more force than similar designs that utilize multiple smaller motors. It does limit the ability to flex a single finger independently, but that’s something that can be difficult even for human hands. In their testing, they found that the movement of the hand and fingers very closely replicates that of a biological hand. It is able to achieve a grasp force of 150 N, and the team claims that the battery can last an entire day on a single charge. The design has already been tested very extensively and the results are quite remarkable. Test users were able to perform delicate actions like picking up and moving small items, and then seamlessly switch to more forceful activities like using tools. While this is an iterative advance rather than a revolutionary one, Hannes shows a great deal of promise and could dramatically improve the lives of amputees and those born without hands.