PAL - hybrid prosthesis

What it does

PAL is a concept for a new, hybrid alternative to costly modern electric prostheses and outdated mechanical prostheses. It addresses the problems of low accessibility, low acceptance rate and social stigma associated with prostheses.

Your inspiration

While modern electric prostheses are fascinating pieces of engineering, only few people have access to them. Talking to users and experts revealed that for their high price, they are not even that practical. Mechanical, body-powered prostheses on the other end are more affordable and very functional, but their design is outdated and has not improved much in the last decades. These insights and the desire to help people inspired me to dive deeper, which led me to the creation of a more affordable, yet still desirable hybrid prosthesis that combines advantages of both electric and mechanical prostheses in a way that strongly benefits the users.

How it works

The prosthesis can be tailor-made using a configurator software. It is cable-actuated by body movements using a breathable undershirt that is locally reinforced to equally distribute the pulling forces. The detachable shirt is worn under the regular clothing. Using body power eliminates the need for heavy batteries and motors, allows for intuitive and fast control and creates natural force feedback. A lock-switch can be triggered myoelectrically by tensing the muscles in the stump. It locks and unlocks the grip, which facilitates moving around with a grasped object. The energy needed for the switch can be harvested from the users’ movements. The hand can perform the three most important grips in a reliable way, and it can be cleaned using a washing machine or a dishwasher. Users can also attach inexpensive, 3D-printed modules for specific activities to the prosthesis. When turning the wrist, the flexible socket creates a natural form transition to the arm.

Design process

In my research, I looked at the topic from various stakeholder angles: the amputees, the clinical prosthetists, the orthopedic technicians, education and researchers view. I conducted both online interviews and on-site visits to hear from the stakeholders themselves and learn from their experiences with prosthetic devices. With this background, I explored a broad variety of ideas that concerned not only the device itself, but the whole process before getting a prosthesis as well. I built a wide range of prototypes to test mechanisms, the overall construction and the materiality. This for example included prototyping and testing a simplified version of the harness undershirt, constructing and testing multiple iterations of 3D-printed, flexible finger mechanisms and sewing fabric parts. I stayed in conversation with both users and experts over the remaining concept development process and continuously assessed and validated the potential of my ideas. This helped to make the right decisions and improve crucial parts of the concept.

How it is different

PAL is the result of a human-centred design process that put the users’ needs above the industry interests. This led to a concept that has the potential of profoundly improving accessibility, functionality and acceptance. Existing 3D-printed prostheses are often just fragile, hard plastic versions of their high-end electronic counterparts, and therefore not very beneficial. This concept is unique in several ways. The configurator software together with an open-source manufacturing approach makes both professionals and users more independent, which improves overall accessibility. It fully utilizes the power of 3D-printing by using compliant mechanisms and flexible materials. It combines body power with myoelectric switching, which is a novelty that creates many benefits such as easy control. Contrary to other sockets, its socket is flexible and together with the fabric sleeve and the soft hand contributes to giving the prosthesis a friendly look and feel.

Future plans

Developing a prosthesis is very complex, and after this phase, I see the need to involve specialists of other disciplines such as mechanical engineering, electrical engineering, rehabilitation medicine and material science. The next steps would be to further refine the concept, and to make fully functional prototypes for the next phase of tests and validation. Going from this to a finished product that meets the medical standards is a big challenge, but I would like to take it. An alternative to building my own team would be to involve an experienced prosthesis manufacturer to help to realising this concept.

Awards