ADVANCED MATERIALS & PROCESSES | MARCH 2023 33 7 FEATURE Cr, Cu, Mo, Ag, Au, Ta, Pt, Au, and Mo are produced using this method. There are a couple of radiopaque superelastic alloys in development. A frequent request for PVD technology is to evolve an existing approved self-expanding superelastic Nitinol stent design by making the contemporary device pattern at approximately half of the wall thickness, while retaining radial force and improving fatigue resistance (Fig. 5). The higher tensile plateaus and fatigue resistant microstructure allow for this end. Often the delivery system profile can be reduced as an added benefit. Other enabling devices use PVD for sensor or active device applications where accuracy and predictable performance are imperative. One approved medical device example of a critical Nitinol application is a cataract capsulotomy device used in ophthalmic surgery. An intricate and precise Nitinol ring, assembled into a silicone suction cup and attached to a handle, is connected to a pair of electrical leads that pass through the assembly and terminate to a power supply. The thin Nitinol ring is able to pass through a narrow slit, reopening itself and the surrounding suction cup once inside the eye. When energized using an electric pulse that passes through the circumference of the ring, the lens tissue is cut in a centralized circle by resistive heating. The suction cup fixes the position of the ring on the eye during the cut. This allows the lens to be removed and replaced by an artificial or cadaveric lens. In order to operate without fault, the ring component requires a wall thickness tolerance and feature tolerances of single digit microns. Although the ring is very thin, it needs to have a high recovery force to open the folded suction cup. It also needs to be cost effective and scalable to high volumes in order to meet procedure reimbursement limits. Regulatory bodies in the U.S. and worldwide are familiar with PVD Nitinol devices. Although these materials are currently used for approved implant and non-implant devices, there are potential applications in automotive, power, defense, microelectromechanical systems, and aerospace applications where similar needs for accurate, predictable, high-performance materials exist in the relevant size ranges. ~SMST For more information: Scott Carpenter, senior director of R&D; and Christian Palmaz, president & CEO, Vactronix Scientific, 5005 Brandin Ct., Fremont, CA 94538, 510.358.8400, scott.carpenter@ vactronixscientific.com, christian.palmaz@vactronixscientific.com, vactronixscientific.com. References 1. https://vaccoat.com/blog/physical-vapor-deposition-pvd/. 2. https://docs.google.com/presentation/d/1sW4ATeUm4USs09ZLNQ0RlNxeCE9E33Lzpsx-5WdOPa4/preview?slide=id.g735e9add31_2_42. 3. https://www.annualreviews.org/doi/pdf/10.1146/ annurev.ms.07.080177.001323. 4. https://acquandas.com/technology/technology-platforms. 5. https://www.semicore.com/news/102-what-is-co-sputtering-co-evaporation. Fig. 5 — (a) SEM image of a commercial NiTi stent at 250x; (b) SEM image of a Vactronix PVD-based NiTi stent at ~1000x. (a) (b)
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