Microneedles for Biological Sensors
The Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM) is working on the development of biological sensor to measure cell forces. With the aid of such sensors, the compatibility of substances with living cells can be investigated, for instance. The surface of the sensor consists of an array of several hundred thousand identical needles with a defined diameter between 1 and 5 µm and a length of up to 30 µm. The deflection of the needles correlates directly with the force exerted by the cell.
Until now, such needle arrays have usually been produced by means of casting. However, this time-consuming method permits production of only a few components per day. In the future, it should be possible to manufacture large quantities of sensors with micrometer-thin surface structures reproducibly by means of microinjection molding. Using a thermoplastic polyurethane, it was possible to mold 490,000 needles with a diameter of 5 µm, a height of 25 µm and a spacing of 10 µm. The needle arrays produced via microinjection molding are currently being tested for their suitability as cell force sensors and will be modified as necessary.
At the same time, an optical measuring system that can detect needle deflection is undergoing development. In addition, a further reduction in the size of the sensor structure is being planned. Structured nickel mold inserts with a hole diameter of only 4 µm (and a hole spacing of 4 µm as well) have already been produced at the IFAM. This provides a sensor surface with over 600,000 individual needles. The first molding trials for these microstructures are currently being conducted.
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