Bionic prosthesis: easy to put on, intuitive to use

Patients who receive a prosthesis after the amputation of a limb often have to train for weeks or months until they can control the technology and use it in everyday life without problems. At the Medical University of Vienna, the world's first bionic prosthesis has now been developed that has a closed control loop and enables immediate, intuitive use.

In an interview with MEDICA-tradefair.com, Prof. Oskar Aszmann talks about what bionic reconstruction actually means, how the novel prosthesis works and why the system can not only help patients after an amputation.

Prof. Aszmann, your newly developed prosthesis works according to the principle of bionic reconstruction. Can you explain this in more detail?

Prof. Oskar Aszmann: The word bionics is an acronym derived from biology and technics. In bionic reconstruction, we deal with the processing of biological signals to control a piece of technology – the prosthesis. These are nerve signals that we have to process in such a way that the prosthesis understands and implements them.

If a person has lost an arm, for example, all the corresponding nerves are still present but useless. We then have to perform a nerve transfer in a surgical procedure. In the process, we relocate the nerves to other muscles in the amputation stump so that they regain a certain functionality and the biosignals can be usefully used to control the prosthesis. With the help of a sensor – which can be placed on the skin or implanted – these signals are recorded and transmitted to the prosthesis. We have developed a system that is self-contained. The prosthesis also contains sensors that provide feedback to the patient.

We have currently found a technically useful solution to two important feedback problems: The patient knows when the prosthesis is in contact with an object. And he knows how intensive the force transmission is, i.e. how firmly he holds the object. There is therefore a closed feedback loop, which is made possible by a cuff electrode – a cuff that is placed around a nerve to stimulate it and thus in turn close the feedback loop. We call such a system bionic prosthesis.

How is the process when a patient receives such a prosthesis – from surgery to use?

Aszmann: Our engineers have succeeded in developing a system in which the individual components are modular so that the entire system can be implanted in one operation. After the nerve transfer, the individual sensors are attached to the muscles. The cuff electrodes are placed around the most important nerve tracts to enable a sensitive signal. The whole thing is then passed through a thin cable through a metal implant – a titanium pin implanted in the humerus – into the prosthesis. In this way the bio-signals from the nerves reach the prosthesis. The system does not require an external energy source.

The four patients we present in our publication did not all have a bone implant. In the patients who had this implant placed only recently, it took about three months for it to heal sufficiently. It takes about another three to six months until the signals are stable enough for the sensors on the muscle to conduct them well. In most patients it takes about six months from the time of surgery to the final application, in those with an existing implant a little less.

What are the advantages for the patient?

Aszmann: Basically, it's the same principle as with a Windows system for the computer: there's a lot of technology behind it, but you as a user don't see it. You don't have to think much about what actually happens there. The system has to do what you want it to do – and it has to do it as simply and directly as possible. The advantage for users of our prosthesis is that they do not have to worry about where the signals are and what to think about. He attaches the prosthesis to the titanium implant using a bayonet lock and can control it immediately. Moreover, the connection between the human being and the prosthesis works very reliably and precisely. The signals are transmitted to the prosthesis without delay.

In which direction is bionic limb reconstruction developing?

Aszmann: The most common cause of limb loss is accidents with agricultural machinery. Of course, in our industrialized society this affects only very few people. The biggest development that I see and am following scientifically at the moment is the expansion of the concept itself. We are currently conducting a large study with patients who are unable to move their hand after a stroke. Such a loss of function is equivalent to an amputation.

We have contributed some concepts here on how we can implement bionic reconstruction in this scenario. This is challenging in terms of signal technology because the patient's brain has been damaged during the stroke. However, we have already reached a point today where we can compensate for this neurological deficit and establish solid signals with which a prosthesis can be properly controlled. We can therefore actually offer bionic reconstruction for neurological patients and have already treated two patients in Vienna with great success. Technological progress and the possibility of making the interface between man and machine more fluid will add a few nuances to the concepts for treating physical defects in the 21st century, and I am convinced that a great deal can still be expected in this area.