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An MHH cooperation project is investigating how muscle function can be stimulated again after nerve injuries. To this end, the researchers are developing a plastic-based magnetic fleece that is implanted under the skin and is designed to stimulate the muscle tissue directly with low-voltage current. The German Research Foundation is funding the project with around 800,000 euros.
Motorcycle accidents, serious falls, amputations or deep cuts can cause significant damage to the nerve tissue in the arms and legs. In the worst case, the spinal cord is affected. However, injuries to the peripheral nervous system following damage to the nerve plexus in the upper and lower extremities can also have serious consequences for those affected. This is because the nerve fibres of various spinal nerves are arranged, regrouped and bundled there, similar to power lines in a domestic fuse box. If the nerve fibres are severed, they cannot perform their function and sensory disturbances occur in the affected areas of the body. At the same time, the muscles are affected because the electrical signal can no longer be transmitted to its destination due to the interrupted nerve conduction.
A research team led by Dr. Doha Obed, assistant physician at the Clinic for Plastic, Aesthetic, Hand and Reconstructive Surgery at Hanover Medical School (MHH), is addressing this problem. In cooperation with the Institute for Multiphase Processes at Leibniz University Hannover (LUH), the researchers want to develop a novel piezoelectric fibre fleece that is placed under the skin on the paralysed muscle and then stimulates the muscle through the skin from the outside using a magnetic field. The project is being funded by the German Research Foundation (DFG) with around 800,000 euros over three years.
Electrical nerve impulse missing
In the case of simple injuries, a nerve can be surgically restored. This option is not available for direct injuries to the spinal cord. ‘However, repairing the signal pathway does not restore nerve function itself,’ emphasises PD Dr. Obed. ‘The nerve fibres must regenerate along the entire length from the point of severance to the respective target muscle.’ This can take several months. During this time, many of the affected muscles lose their function due to the lack of electrical nerve impulses. The longer the paralysis lasts, the worse the muscle functions in the long term. The impairment is even more severe in cases of injuries close to the spinal cord. Until now, muscle paralysis has been treated with methods such as functional electrical stimulation (FES). This involves attaching electrodes to the skin and applying an electrical current to them, causing the underlying muscle to contract. However, this procedure does not cure paralysis; at best, it helps to strengthen the muscle. Electrodes implanted under the skin also have disadvantages. ‘On the one hand, there is the problem of cables hanging out of the affected skin area, and on the other hand, the systems are prone to malfunction and infection,’ says the prospective plastic surgeon.
Ultra-thin, stable plastic fleece
The researchers are therefore pursuing a different, completely new approach. They want to produce a special fibre fleece made of polyvinylidene fluoride (PVDF). PVDF is a thermoplastic fluoroplastic that is largely insensitive to heat and chemical influences and is used, among other things, as a lining for pipes or exterior components. At the Institute of Multiphase Processes at LUH, this raw material is extensively processed and transformed into an ultra-thin but very stable fibre fleece that can be implanted as easily as possible under the skin, where it promotes interaction with the paralysed muscle tissue. ‘The magnetic fibre fleece is piezoelectric, meaning it deforms when an electrical voltage is applied,’ says PD Dr Obed. This voltage is generated externally by a magnetic field. The deformation of the fibre fleece in turn generates an electric current that can stimulate the muscle.
Activation by mini MRI
‘We are still working out how best to activate the fibre fleece, for example by using a handy device that works like a kind of mini magnetic resonance imaging tube,’ says the physician. The researchers are currently working on how to objectively measure the voltage generated in the paralysed muscle without cables. At LUH, engineers are developing small measuring probes for this purpose, which will also be implanted under the skin as microchips. The fibre fleece implant will then be tested in animal models. If the muscle stimulation works, the model could be used not only after nerve injuries, but also for muscle stimulation after a stroke.
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For further information, please contact Dr Doha Obed, obed.doha@mh-hannover.de.
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