In the Netherlands, approximately four thousand people have an arm defect, of which two thousand have a prosthesis. Worldwide, there are many more people, including for example veterans. A good prostheses can be very valuable as it allows people to participate in society. Sports, working, cooking: just try buttering a slice of bread with one hand: it is extremely difficult!
Twenty to fifty percent of the prostheses end up unused, therefore we aim to develop a new type of prosthesis
Currently there are several types of prostheses. There are passive devices which are used for cosmetic reasons and active ones which can be controlled by the user. I focus on the latter type. Active prostheses can be divided into myo-electric and body–powered prostheses.
Myo electric prosthesis are controlled using the residual muscles. The activity of these muscles is recorded by electrodes on the skin. The main advantage is that the control does not required high forces and is intuitive as the muscles intended for hand movement are still used. The main drawback is that there is no feedback; you cannot feel what the artificial hand is doing; you rely on vision to control the prosthesis properly. This lack of feedback from the device increases the workload on the patient as it is difficult to see if a cup of coffee is slipping or if you are crushing an egg, until it is too late.
Body-powered prosthesis use a harness around the shoulder and/or arm to transfer force through a cable to an artificial mechanical hand. The main advantage is that the user can feel if an object is hard or soft without having to look at it. Moreover, by using shoulder and arm movements, sensors in the muscle and tendons are used which provide very fast feedback and control. The main drawback is that current mechanical devices require such high operating forces that the harness is very uncomfortable and some users are not able to grasp object for extended periods of time. In addition, the high forces result in unnatural compensatory movements and overuse injuries.
My objective is to combine the best of both worlds: provide feedback similar to a body-powered prosthesis with the ease of control of a myo-electric prosthesis. The prosthesis is controlled similarly to a body-powered prosthesis and feedback will be provided by a small flexible motor. Control and feedback signals will be transmitted wirelessly. The hand that grips the object remains the same, but the control and feedback system is new. The harness will be replaced by small comfortable skin anchors that house the sensors and provide feedback and the hand is controlled by moving your shoulders. The forces experienced by the hand are returned to the shoulder providing the user with an immediate sense of the object. My aim is to make the shoulder interface small enough so it can be worn underneath clothing.
More research is needed to answer the questions posed in this project: how to best attach the sensors and actuator to the shoulder? What strong but flexible actuator can give the best feedback? How do we minimize power consumption so we don’t need a large? At this stage, we focus on opening and closing the hand. We hope that this system can be extended to include flexing and extending the wrist, or adding wrist rotation. Ideally, we would move fingers independently, but this will be left to future projects.
Unfortunately, many users of upper limb prosthetics are disappointed in today's solutions. The prostheses are either too taxing on their shoulder leading to muscle and joint injuries, or people do not feel the object they grasp. As such, twenty to fifty percent of the prostheses end up unused, collecting dust in the closet. This is a tragedy as we are not able to help these users. In addition, fitting a prosthesis and learning to use it requires effort from team of people and a prosthesis can cost up to 35,000 euros. We aim to develop a new type of prosthesis that will prevent these complaints and increase quality of life for prosthesis users.
My name is Alistair Vardy and I am Postdoc at TU Delft at the Faculty of Mechanical Engineering and the Delft Institute of Prosthetics and Orthotics. My work is funded by Fonds NutsOhra. Through my research I hope to improve the current upper arm prostheses by combining the best features of currently available prostheses, body-powered or myo-electric. Similar to body-powered, shoulder movements will be used to control and receive feedback. However, these forces are digitally communicated to and from an electrical prosthesis so that forces are very low and thus less taxing on the shoulders. My background in human movement sciences, mathematic control theory and muscle modelling helps me a lot with this research.
A great future dream of mine is the use of implantable technology. Advances in the field of micro-electronics have spurred on implants for prosthetics. Different groups are investigating the control of multiple fingers and even provide tactile sensation. My goal is to be at the forefront of this research field and provide solutions that are as close to the healthy human hand as possible. I am confident we can develop a prosthesis that is so good, users will never want to put it down.
upper limb prostheses, implants, prosthetic arm, myo-electric prostheses, body-powered prosthesis