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Titanium human “spare parts”

September 09, 2002

Heart valves bred from a patient’s own cells would be a big progress. Meanwhile, surgeons have to make do with other methods and materials: tissue grafts, modified heart valves from human or animal donors. Valves made from artificial materials have the advantage of lasting longer. But they have the unfortunate drawback to intensify the coagulation of blood, tend to corrode and are more easily contaminated by pathogenic bacteria.

This applies to the shutters and the ring used to support them, which is surgically sewed to the heart’s wall. This ring-shaped part measuring about two centimeters in diameter is usually made of pyrolitic carbon. This lightweight material similar to graphite is produced through thermal degradation of carbon-based compounds. It is well compatible with blood and tissue. But being brittle and difficult to form causes problems. This limits the extent to which the whole valve can be adapted to the heart without impeding the flow of blood. It was this problem that prompted scientists at the company Tricumed Medizintechnik into action. They developed an improved type of cardiac valve made of titanium. Their research partners at the Fraunhofer Institute for Manufacturing and Advanced Materials IFAM developed a suitable metal-powder injection molding manufacturing process.

Apart from the choice of the most suitable titanium alloy, the design of the ring and shutters is a vital factor, as Dr. Thomas Hartwig of the Near-Net-Shape Production Technologies Department explains: “Our techniques offer greater scope to modify the design parameters of the valve than before. It is so streamlined that the blood flow is minimally affected and there is a very low probability of the formation of deposits.” The fabrication of a part like this is the culmination of a considerable wealth of expertise: The IFAM researchers started by verifying the feasibility of processing the alloy by metal injection molding (MIM). Then they optimized the sintering process of the valve’s coponents. One of the points they took into account was that the parts shrink during the baking of the metal powder, thus altering their shape. Moreover: The final polishing process implies a loss of material. The project partners performed tests on the prototypes to verify the mechanical properties of the valves. The IFAM engineers subsequently optimized the production process and transferred the know-how to Tricumed, who is now manufacturing the parts to the required specifications.

Fraunhofer-Gesellschaft