Precision parts for smart prosthesis

Weinheim. July 12, 2013. 17-year-old Tom uses an artificial leg. Walking with a prosthesis is different to walking with an "ordinary" leg. No artificial ankle joint can actively push the body away from the ground. The force normally provided by the muscles in the foot is missing and needs to be replaced by other groups of muscles. The brain has to learn and control a new sequence of motion. New smart prostheses with integrated sensors now make it possible to control walking as a natural sequence of movement. Freudenberg's Helix Medical Business Group produces medical silicone moldings for sophisticated prostheses for numerous applications. "We are a development partner to innovative companies in the field of implantation technology and use our many years of experience with the processing of implantable platinum-cured silicones," says Dr. Kai Opdenwinkel, Head of Development at Helix Medical Europe in Kaiserslautern.

Previous prostheses have a significant disadvantage: If the wearer unintentionally tenses a leg muscle, the knee joint stretches the prosthesis. As a result, unwanted movements may pose a hazard. Obstacles such as steps pose a problem if they appear suddenly. Wearers can only adapt their movement and control the prosthesis precisely if the obstacle is identified in good time. In contrast, the new smart prostheses use sensors to detect the direction in which movement needs to be controlled. This gives wearers of artificial legs like Tom an almost natural walking feeling.

How does this work precisely? Sensors that measure all activity signals of the leg muscles and convert them into prosthesis movement are incorporated in the shaft of the artificial leg. The system determines the ideal muscle signal from the data measured. It detects the wish of the wearer to move in a specific direction. At the same time, the sensors also register the wearer's movement status. In other words, the prosthesis "knows" whether the wearer is sitting, lying or running.

Pressure sensors located directly under the electronic sensors help in this process by detecting the transfer of weight to the prosthetic limb. The system then converts these two pieces of information into the appropriate movement of the prosthesis. The special feature is that the signal is determined on a real-time basis, providing a feeling of movement that is almost natural.

To ensure that the sensors remain reliably in place, the cables are precisely guided and the seals are impermeable, each prosthesis contains several medical silicone moldings. Helix Medical Europe is a development partner to innovative companies in the medical technology field. The Helix Medical specialists support customers on new projects by designing customer-specific, highly specialized sealing solutions. The special materials used reduce the cost to prosthesis producers and simplify the processes. Implantable precision moldings and tubing by Helix Medical Europe are used e. g. for pace makers, ear implants or port catheters.