Metal Injection Molding Produces Tiny Inner Ear Implants

The stirrup, a small bone in the human ear, can be accurately replicated using established production processes. By means of injection molding, researchers can now produce such tiny implants from biocompatible materials such as titanium.

“We make exact copies of this delicate ossicle. Injection molding with very fine metal powder enables us to replicate these tiny structures,” explains Philipp Imgrund of the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research IFAM in Bremen. Until now, the production of tiny metal parts using techniques such as etching or milling has been a very complex and time-consuming process, and not suitable for many types of metal. With micro metal powder injection molding (micro-MIM), however, the scientists are able to combine and shape different types of material. It has been possible for a long time to produce tiny parts from stainless steel. Now the researchers are in a position to make such small, delicate components out of biocompatible materials such as titanium and titanium alloys.

In a pilot series, the researchers manufactured 300 miniature parts with a weight of 5.4 milligrams each and a wall thickness of only 0.3 millimeters. “We are now ready to start series production with the micro-MIM process,” Imgrund stresses. “Using the stirrup as an example, we are demonstrating the limits and possibilities of the process and of the new materials.” The injection mold for the demonstrator was designed and built by Krämer Engineering in Rendsburg.

Before injection-molding miniature parts, the researchers mix the fine metal powder with an organic binding agent. The mixture can then be processed on an injection molding machine in the same way as a plastic. Following this, the binding agent is expelled from the component, which is then sintered to a high density. “We vary the powder and binding agent and are developing suitable injection-molding and sintering processes. Our objective is to achieve reproducibly high quality for very complex micro-components and to equip these components with additional functions as required,” explains Imgrund. Components could be reinforced with higher-strength material in areas subject to particularly high stress, for example, or a part could be given special magnetic properties.

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