Ceramic Replaces Titanium With Machining Assistance
Coated titanium was to be replaced as the material for the stator housing in a right ventrical assist device. Zirconia ceramic was the material selected and expert machining met the needs for very tight tolerances to fabricate the component.
|Precision thin-walled zirconia ceramic stator housing portion of the right ventricular assist device. Shown here the O.D. of the round head portion has an offset bore configuration requiring very specific machining features and tolerances to ±0.0001 inch.
The Cleveland Clinic was investigating the use of ceramic materials for potential use in a right ventrical assist device (DexAide RVAD) to replace the current coated titanium stator housing used in the pump assembly. Zirconia ceramic was ultimately selected due to its hemocompatability and excellent material properties for journal bearing applications, including high hardness, low coefficient of friction, 0% water absorption, and noncorrosivity in saline environments. Because the zirconia is a non-conductor, there was also an improvement in power consumption due to the elimination of electrical eddy currents in the stator housing wall.
With the material selection completed, the next step in determining if this would become an effective replacement for coated titanium would center on the ability to effectively machine the zirconia ceramic to the extremely tight tolerances required for the pump assembly. The zirconia ceramic stator housing had to maintain the same goemetry as the titanium housing and not necessitate any changes to the other pump components.
The Cleveland Clinic consulted with engineers from AstroMet – a producer of highest quality zirconia material – and Insaco Inc. – a precision machining and polishing fabricator of parts from all technical ceramics, sapphire, glass, and quartz with over 65 years of expertise in the field. Insaco was able to easily comply with the engineering specs and provide the machining capabilities to achieve necessary tight tolerances. The company routinely machines these materials to very precise tolerances for dimension, flatness, wedge, and roundness/cylindricity. Its customer profile is centered on applications where tight tolerances on ultra hard materials are critical to the end-use application. Insaco has extensive inspection and documentation procedures so parts are always to print.
Dave Horvath, senior engineer at the Cleveland Clinic commented, “The machining of such a thin walled part in zirconia, while still maintaining tight tolerances and fine surface finish, is difficult at best. However, the material selected seems to have the potential to be a good match for our implantable blood pump applications."
After a series of side-by-side comparisions with the titanium housed assembly, the zirconia ceramic replacement assembly showed a 19% reduction in power consumption, no device-induced increase in platelet activity, and no biologic deposition in any of the implants.
Klaus A. Burckhardt, PE is a sales engineer with Insaco. He is responsible for market analysis, engineering expertise, and supporting quotation and account management responsibilities. Burckhardt can be reached at 215-536-3500 or KAB@insaco.com.