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Designed to reduce the symptoms of tremors by detecting muscle signals and providing electrical stimuli in response, the human-machine interface is in development at the Fraunhofer Institute for Biomedical Engineering (IBMT) in Sulzbach, Germany.
The implants are made from biocompatible platinum-iridium and silicone, and are injected into the muscle through a catheter. Just three centimetres long and a millimetre in diameter, the tiny implant has an electrode at each end that functions as either a sensor or an actuator. External electrodes sewn into a textile ribbon supply the module with energy, sending pulsed alternating current through the muscle tissue.
Once implanted, the sensors register the first signs of muscle tremors and pass the information on to the external components. The controller evaluates the data and sends signals through the textile electrodes to stimulate the muscle. This closes a ‘control circuit’ of sensor and actuator components, counteracting the tremor.
The stimulus signal is not strong enough to trigger a muscle contraction directly. Instead, the nervous system registers the stimulation in the muscle tissue and responds by stopping the commands that trigger the muscle tremor.
The finer details of the relationship between tremors and signals from the nervous system are yet to be researched. “In clinical trials, however, our method is working astonishingly well. Initial trials have shown that providing the patient with stimuli for one or two hours is enough to reduce tremor symptoms for a longer period of time,” said Andreas Schneider-Ickert, project manager for active implants and innovation manager. “We have managed to reduce muscle tremors significantly in trials with patients.”
Since tremors often occur in both arms and both legs, implants can be injected and external textile electrodes placed in all the affected muscle groups, creating a distributed sensor network.
The controllers keep track of all the implanted and external electrodes at the same time and control them in coordination with each other. All this happens in real time, with the patient reportedly experiencing no delay.
The system is part of the EU-funded Extend project, in which nine partners from five countries are developing a versatile platform of distributed neural interfaces. The technology is aimed at helping people with neuromuscular disorders, such as tremors or symptoms of paralysis.
The platform uses external controllers to link implanted electrodes into an intelligent network. The components communicate with each other wirelessly, exchanging data, detecting muscle signals and sending targeted stimuli into the muscles.
Technology being developed in the Extend project is minimally invasive, so could be easier to implement than conventional implanted systems.
The technology platform could also help people with spinal cord injuries, if used alongside motorised exoskeletons. Sensors would register stimuli sent to nerves from the brain, transmitting them to the controller, which would then activate the right prosthesis to support the muscles to execute the movement.
Following initial successful tests, the concepts and technologies used in Extend have been developed, miniaturised, optimised and subjected to further implementation studies. The project has now been completed, with a successful proof of concept of the miniaturised system in humans.
Fraunhofer IBMT will use the knowledge gained from Extend to develop its expertise in the field of neuromuscular and neural interfaces.
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