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From patent to patient

During minimally invasive surgery, the doctor uses magnetic resonance imaging to monitor the operation. A puncture needle made of carbon-fiber-reinforced plastic offers a clear view as well as several treatment functions.

Sometimes it begins with a slight pulling sensation in the back, while at other times it can put a person completely out of action from one minute to the next: These are the symptoms of a slipped disk. An operation is not always necessary, as there are effective alternatives to surgery. One method is to puncture the spinal disks. This involves injecting medicine into the injured area of the body with a thin needle. To be able to monitor the operation at all times and position the instruments accurately, the surgeon requires an image of the affected area. This can be obtained using magnetic resonance imaging (MRI). “The problem so far, however, was that conventional metal instruments interfere with the magnetic field of the MRI and distort the picture,” explains Sebastian Schmitz of the Fraunhofer Institute for Production Technology IPT. “Our task was to develop instruments made out of fiber reinforced composite materials for use in the tomograph, as these materials afford a clear view.” But how to produce a carbon-fiber-reinforced plastic puncture needle that is just as firm and rigid as those made from stainless steel? The engineers have now developed a new manufacturing process. Up to eight thousand individual carbon fibers are treated in a miniaturized pultrusion process: The fibers are soaked in a thermosetting plastic, which is then heated until it sets. At the same time, high pressure is applied to press the fibers together and into the desired shape. Both processes must take place simultaneously without hindering each other. To incorporate a working channel into the needles, the engineers use hollow glass fibers that are processed together with the carbon fibers. The patented needles have now entered series production on the basis of this method. A finished needle with one working channel has a diameter of 0.8 millimeters. Needles with three channels are a little thicker, measuring 1.2 millimeters. One channel, for instance, contains an endoscope that illuminates the tissue to be treated. Via the same route, the reflected light reaches a camera, and the operator sees a moving image on the monitor. The fiber in the second channel conducts laser light, which the surgeon can use to cut or weld tissue. The third channel serves to induct rinsing liquids or medication. In this way, several stages of treatment can be carried out and monitored simultaneously. The needle is suitable for spinal pain therapy, to inject contrast medium into joints for arthrography, and for puncturing cysts.

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