New sensors improve mind-controlled prosthetics

Theresa Roland (c) Johannes Kepler Universität Linz

By Hildegard Suntinger

Biomechatronic engineers at the Linz Institute of Technology (LIT) have developed capacitive sensors for mind-controlled prosthetics, thereby significantly improving their quality. The prosthetics fit better and are less prone to failure.

Prosthetics give those patients who have lost limbs more independence in everyday life and a higher quality of life. The technology is very advanced. Mind-controlled prostheses are setting trends. As Theresa Roland from the Institute of Biomedical Mechatronics at the Johannes Kepler University Linz explains, mind control is based on the still-existent muscle tissue. A thought process inside the brain is ultimately an electrical signal that is transmitted by nerve fibres to muscle fibres and which can be measured on the surface of the skin.

Sensor technology

What this research is working on is the technical approach to the natural use of limbs. Sensor technology constantly opens up new possibilities. However, these are often accompanied by a number of obstacles in their application. Up until now, the following aspects have been problematic for sensor-based prosthetics:

Common sensors require a conductive connection to the skin and are sensitive to perspiration. For the sensor to be able to function smoothly, the skin must be prepared with an electrolytic gel or a skin preparation.
To ensure a conductive connectivity, the sensors must be pressed firmly onto the skin. This can lead to unpleasant pressure points and is particularly stressful for people with circulatory disorders.
Each shift and every vibration of the prosthetic triggers malfunctions.

Flexible capacitive sensors

The biomechatronic engineers at the Linz Institute of Technology have used flexible capacitive sensors in mind-controlled prosthetics for the first time and have been able to make crucial improvements:

Flexible sensors adapt to the anatomy of the human forearm, are very comfortable to wear, and also ensure stability and protection against interference.
Capacitive sensors react without contact to the approach of a conductive or non-conductive object and are therefore independent from skin conductivity.

The adaptability of the flexible sensors means that interference is reduced. Most importantly, however, the team developed a relatively simple algorithm with which the sensors can distinguish between thought signals and interference impulses, explains Roland. The system runs without an app. The algorithms are integrated directly into the sensor. Overall, the innovation brings a substantial improvement in the way a prosthetic works, as it is only activated during actual muscle contraction. Otherwise, a prosthetic might move if, for example, a mobile phone is activated nearby.

Cooperation with Otto Bock Healthcare

The flexible, capacitive sensors were developed in cooperation with Otto Bock Healthcare and supported by the Linz Center of Mechatronics. An article about the project was published in the science and technology journal Sensors, which you can read here.

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Roland also wants to integrate artificial intelligence at a further stage of development. Neural networks are to be used above all to improve the robustness of the sensor. This system should be able to distinguish between interference and useful signals even more effectively.

About mind-controlled prosthetics

The first mind-controlled prosthetic was developed in 1964 in the USA. In Europe, the system was used for the first time in 2007 – in a collaboration between Otto Bock Healthcare (Vienna) and US scientists. The system uses nerves, which were initially responsible for controlling limbs, to transmit thoughts.

The prerequisite for this function, however, is a nerve transfer. This is a surgical procedure in which nerves leading to the amputated limbs are relocated. In the process, existing nerves of the body part are connected to the same muscle groups. Once the nerves have settled in, the patient is required to train the various movement patterns until sufficiently strong electrical impulses are produced by the muscle groups during contraction.

Myoelectric prostheses

These are complicated biochemical processes in the muscle cells that generate electrical voltage within the microvolt range. The technical term for this is myoelectric. Myoelectric prosthetics are battery-operated prosthetics which are set in motion by muscle contraction. These detect muscle movements via electrodes or sensors and convert them into impulses which control movement.