Shortcut – The Digital Prosthesis

EXPOSÉ When having to rely on a prosthesis, using digital devices is difficult: mouse, keyboard and touchscreens are designed for organic hands only. Yet amputees are often capable of using muscular gestures with their phantom hand, which can be read out. We have created an interface between these signals and the digital world that opens up new possibilities. Shortcut is a digital wristband that translates phantom hand gestures and planar movements into a wireless computer control. It facilitates a quick re-entry into the profession and unrestricted digital interaction.

We’re part of the DesignFarmBerlin Accelerator program and we were recently awarded the STARTS prize by Ars Electronica and the Mart Stam Förderpreis.

The design is mainly based on a repertoire of gestures that most amputees can still address neurologically. These were mapped to the most relevant computer in a sensible way. We have developed a catalogue of gestures that includes both basic functions such as cursor movement, left- and right-click and scroll, as well as quick access to functions such as zoom and quit. Thanks to a user-centered design approach the controls can be learned quickly and intuitively.

Shortcut 3-D printed model

Its main body consists of two injection moulded interlocking parts that are rotatable. To activate the sensor, the upper part is rotated counterclockwise and locks into place, while the opening thus slides over the sensor.

Main body close–up

The silicone wristband itself is detachable allowing for combinations with a variety of different bands.

Detachable band close–up

These include different circumferences as well as different colours and potentially materials to match user needs and individual taste.

Customizing options


Losing hands illustration
Heavy machinery illustration

Fifteen people per day loose a hand in Germany alone on average. About 25% of these happen while working with heavy machinery. Myoelectric prostheses are the most common form of artificial hand replacement. Electrodes are inserted in the shaft of the prosthesis which read muscle signals in the stump of the arm. Motors in the hand and wrist can translate these signals into mechanical movements. For this functionality users need to learn how to use flexor/extensor gestures in different combinations to operate the system. Bending the Phantom Hand upwards opens the fingers of the prosthesis, bending it downwards closes them. By co-contraction, i.e. by clenching a fist, it switches into rotating mode, where the same bending gestures from before now trigger the two directions of rotation. The functions are connected in series, the gestures are used twice. Therefore the two types of movements cannot be carried out simultaneously.

Many people that were formerly doing manual labour have to be retrained, so that the number of those working in office jobs increases by six times after the amputation. And although this is the biggest group, the percentage of people using their prosthesis during work is alarmingly low. A major problem is working with desktop computers. When it comes to operating these, the prosthesis itself is practically useless because it lacks the fine motor skills and the tactile feedback required. In most cases this means that all operations have to be adapted to using only one hand, which moreover will statistically be the weak hand of the user. It takes considerable time and effort to learn and besides things simply take much longer than before. This complicates daily work considerably.

Office jobs illustration

Use of prosthetics statistic

Source: Heintel, Wolf-Dietrich: Akzeptanz von Armprothesen, Eine retrospektive Studie an 454 Betroffenen: Patienten aus der TO Münster, Versicherte gesetzlicher Unfall- und Krankenversicherungen und der Versorgungsverwaltung, Pforzheim, 2006


Working prototype

The project was started with an intense research and ideation phase. We tried to get as close to the user as possible, to be able to identify core problems and frame first ideas. We interviewed patients and medics and we for example spent a day using only one hand. Many playful quick’n’dirty prototypes helped to get a better feel of how to approach different aspects.

Early ideation sketches

To test our concept as quickly as possible, we developed a first working prototype early on. We used a gaming bracelet with similar electrodes as those used in myoelectric prostheses to register muscle signals. In order to read the planar motion on the tabletop surface we included an optical sensor of a common computer mouse. We used a micro-controller and Arduino programming to translate the data into mouse commands and send them to the computer via USB cable. The technological package was placed in a 3D-printed housing.

Hacking a mouse

In order to make the product as suitable for everyday use as possible, we developed many different approaches to materials, shape, and handling. We focused on making it a friendly, modest, reliable and forgiving helper, while iterating towards a final shape. Testing usability and evaluating formal decisions included everything from sketching, paper models and renderings up to 1:1 scale 3D prints.

3D-printed prototypes

We decided to go with a robust rotund shape. The visual resemblance to wristwatches fits unobtrusively in different use cases.

Desgin sketches

Who we are

Maximilian Mahal

Max is a product designer with a background in craftsmanship and a strong expertise in rapid prototyping.

David Kaltenbach

David is an interaction designer. He has a great sense for generating wild ideas and turning them into reality. He has a strong eye for visuals.

Lucas Rex

Lucas is an interaction designer and a committed user advocate. He’s a fan of pragmatic solutions and design sprints.

Uli Maier

Uli is a prosthetics expert with many years of experience as an orthpedic technician for Ottobock Healthcare AG and Charité Berlin.

If you're curious to learn more or if you want to say hi, please drop us a mail :)