Eric Dietsch is the Nitinol Product Manager at Fort Wayne Metals, a leading manufacturer of precision medical wire and components for the world’s most critical applications. Eric holds a BS in Industrial and Systems Engineering from Ohio State University. His diverse work experience includes the medical device industry, particularly Nitinol-supported devices, and roles in operation management, program management, engineering, and sales. In collaboration with the Fort Wayne Metals Engineering team, Eric focuses on supporting customers with material recommendations, product development, and education. Eric is available to help you and your company with any Nitinol-related questions or needs that you may have.
What are the primary benefits of Nitinol wire compared to other materials?
Nitinol is selected for its unique superelastic and shape memory properties. The superelastic properties allow material to see up to 6–8 percent strain with little permanent set or plastic deformation. This enables the wire to perform functions like following tortuous pathways through arteries or being compressed for delivery through catheters, then recovering to original form. These properties are useful in enabling less-invasive procedures and the application of devices such as guidewires, stents, and structural heart occluders. Whatever the desired shape of the material, Nitinol can help meet the needs of complex design requirements.
Why does Nitinol come in different colors and oxides?
The amount of heat, its duration, and the level of exposure to oxygen during the heat treatment process determines the thickness and color of the oxidation. But while the oxide color may have some value, ultimately, we aim for the desired mechanical and/or thermal properties as the determining specification. Nitinol can also be produced with an oxide-free surface. Oxide-free options include:
- pickled surface finish with a rougher matte gray appearance
- etched and mechanically polished with a brighter silver appearance
- etched with a duller silver appearance
- and Silk® NiTi
Silk® NiTi is bright silver and is the smoothest oxide-free Nitinol available with a roughness. ≤ 0.0762 µm [3 µin] 3D RMS. The smooth surface of Silk® NiTi has been found to work well in braiding applications.
What do I need to consider when specifying Nitinol?
It is important to consider what thermal properties, mechanical properties, material condition, and surface condition are best suited for an application. Nitinol goes through a phase transformation between martensite and austenite depending on temperature. Because the properties of Nitinol rely heavily on temperature, it is critical to keep in mind the environment that the material will be tested and applied. Mechanical properties to consider are the upper plateau strength and lower plateau strength as well as the residual elongation or permanent set, which can be measured using the standard test method for tension testing as defined in ASTM F2516.
Can you “tune” Nitinol to perform for my particular application?
Yes. Nitinol processing can be modified to achieve desired thermal and mechanical properties outside of normal ranges. Adjustments to one property can impact others, so a review of the targets is necessary to determine feasibility. We’ve developed some specialty products to specifically enhance certain characteristics. Our DPS® wire is designed to have higher plateau strength for applications requiring between 1.5 and 8 percent strain. Our USN® wire is processed to exhibit a higher modulus, which provides increased resistance to initial bends. Linear elastic wire is a straight wire with stiffness like an as-drawn Nitinol, while sustaining up to 4 percent recovery.
Can Nitinol be seen under X-Ray?
Yes. However, medical devices are only getting smaller in size, making them harder to see under x-ray. Our Nitinol DFT® wire can greatly improve visibility and is available in diameters down to 0.01905 mm [0.00075 in.]. Nitinol DFT® wire is a drawn filled tube product that is constructed with a Nitinol sheath and a dense core material, such as platinum or tantalum, which improves radiopacity. Standard fills of 40 percent or lower are typically recommended as the superelastic and shape memory properties of the Nitinol sheath begin to be overcome by the dense core when the ratios exceed this level.
Can I use Nitinol to perform work?
Nitinol is especially useful in actuator applications. The shape memory effect of the wire can be utilized by stretching and contracting the wire with a change in temperature to perform work, such as moving a load, flipping a switch, or opening a valve. The benefits of using Nitinol actuator wire over other standard actuators is that it is lighter weight and silent during operation. While primarily used for non-medical applications, we have also seen Nitinol actuators used in the medical industry.