By Sean Fenske, Editor-in-Chief

When developing a device, material selection is a critical early step. In an ideal situation, a new product will gain advantages from the inherent properties provided by the choice of metal, plastic, ceramic, or whatever option is chosen. As such, it’s important to be familiar with the potential alternatives available that would make the best match for the device.

Unfortunately, not all materials are commonly used and there’s a lack of familiarity with them. For example, Nitinol is a metal that isn’t often selected for many orthopedic applications, however, it provides a unique set of properties that would make it ideally suited for specific situations. With this in mind, it’s vital to work with an expert on the metal or material, such as Nitinol, you are considering.

Fortunately, a Nitinol expert from Resonetics took time to respond to questions about the material. In the following Q&A, Eric Veit, Vice President, Nitinol Business Development, addressed what makes Nitinol unique, what orthopedic applications it’s ideal for, and what manufacturers need to keep in mind when using it (or whether they should be using it).

Sean Fenske: What is Nitinol? What makes it a unique metal?

Eric Veit: Nitinol is a metal alloy composed of nickel (Ni) and titanium (Ti). The name itself is derived from the Nickel Titanium Naval Ordnance Laboratory, where it was first developed in the 1960s. Nitinol is a shape memory alloy (SMA) with two extraordinary properties that set it apart from most metals: shape memory effect and superelasticity (also called pseudoelasticity).

Shape memory effect is a thermally induced phase transformation. Nitinol must be in its martensitic phase to exhibit the shape memory effect. Superelasticity is a stress-induced phase transformation. Both phenomena arise from the same underlying material property, the martensitic phase transformation, but they occur under different conditions. The superelastic property, allowing the metal to “spring back to its shape,” is the property most Nitinol devices take advantage of, but they are often confused.

Fenske: What’s the confusion involving these properties?

Veit: Both properties involve recoverable deformation. In both cases, Nitinol appears to “remember” its shape and return to it after deformation. This can make it difficult to distinguish when one mechanism is at play versus the other.

They each present with the same phase transformation, but these occur due to different triggers. Both behaviors rely on the reversible transformation between austenite (i.e., high-temperature phase) and martensite (i.e., low-temperature phase).

The key difference is how the phase change is triggered. Superelasticity occurs due to mechanical stress, while shape memory occurs due to temperature changes. Some Nitinol devices utilize both properties, making it unclear which mechanism is responsible at a given time. For example, a self-expanding stent uses superelasticity to recover its shape when deployed in a blood vessel, but during manufacturing, shape memory may be used to set its form.

Fenske: What physical properties does Nitinol offer that make it suitable for certain orthopedic applications?

Veit: The super elastic property of nitinol allows it to absorb significant amounts of strain without permanent deformation, making it ideal for devices that need to withstand mechanical stresses, such as stents and bone anchors. The following table lists some of the advantages of Nitinol over other common orthopedic metals—titanium and stainless steel.

Fenske: Where is Nitinol being used in orthopedic implants? Why?

Veit: Nitinol’s compatibility with the human body, coupled with its corrosion resistance, adds to its appeal for use in orthopedic implants such as bone staples or as a durable material for bone drills or reaming devices. In orthopedic applications, nitinol devices can apply constant force to bones and joints to aid in correction or healing, while in cardiovascular applications, nitinol stents can adapt to the movements of blood vessels, providing support without causing damage or irritation.

Bone staples used primarily in foot and ankle surgery are, by far, the most common application of Nitinol in the orthopedic space. Bone staples are used to a much lesser degree in hand surgery and spinal surgery. Other orthopedic Nitinol uses include fracture fixation devices, suture anchors, shape-memory plates for bone realignment, and potentially orthodontic (maxillofacial) implants. Beyond implants, the flexibility and shape memory can be advantageous for delivery systems as well.

Fenske: For what types of instrumentation in orthopedics is Nitinol being used? Why?

Veit: Bone drills and dental drills are types of instrumentation using Nitinol because it can withstand high amounts of strain without breaking.

Nitinol retractors and tissue spreaders are self-expanding and can hold soft tissue apart during surgery. The superelasticity allows flexibility and resilience, reducing the need for mechanical locking or adjustment.

Arthroscopic instruments, such as graspers, probes, or shavers that must pass through narrow joint spaces, benefit from Nitinol’s torqueability and kink resistance, which make it ideal for tools used in constrained environments.

Nitinol is also used more and more in robotic surgery because the ability to bend and the shape memory effect enable deployment or correction once inside the body, especially with robotic or endoscopic approaches.

Nitinol guidewires and alignment jigs are used to guide drilling or screw placement in trauma and reconstructive procedures because the superelasticity and recoverable deformation are ideal for curved trajectories in bones.

Core benefits of using Nitinol for Instrumentation:

• Self-actuation (via temperature change or pre-stressing)
• Flexibility and fatigue resistance
• Reduced need for mechanical parts
• Improved minimally invasive capabilities

Fenske: What are the important considerations to keep in mind when selecting Nitinol for an orthopedic application? Are there reasons or situations for which it shouldn’t be used?

Veit: Since most orthopedic applications are bone staples, they typically start from a very different material form than most interventional applications, which start from a Nitinol tube or sheet. A block of Nitinol is milled or machined to create the 3D shape of the staple. There are not very many places in the world that offer the material form needed for this application, but Resonetics is one of them. Processing these blocks of material can change their mechanical properties if not performed correctly. The result could be two parts that look identical visually and dimensionally but perform completely differently. That is true for all Nitinol; the complexity of the material means it is easy to change the properties at each processing step so process control and material know-how are critical to repeatable results.

As far as situations where it should not be used, it is typically more expensive than other metals. Nitinol is significantly more expensive than stainless and slightly more expensive than titanium, so the use case has to justify the additional cost. If the application will not require flexibility or fatigue, and the application works with other materials, Nitinol should not be used.

Fenske: What aspects are often overlooked when a company is selecting Nitinol (or perhaps with material/metal selection in general) for orthopedic devices?

Veit: When selecting Nitinol (or any material) for orthopedic devices, companies often focus on the headline benefits (e.g., shape memory, superelasticity, biocompatibility), but several critical aspects are frequently overlooked, especially in the context of manufacturability, regulatory compliance, and long-term performance.

• Processing Sensitivity of Nitinol—As mentioned earlier, Nitinol is highly dependent on precise processing, especially at the heat treatment steps. Poor control can lead to loss of desired transformation temperatures, poor fatigue performance, or inconsistent device behavior.
• Fatigue and Fracture Behavior—While in theory, Nitinol has high fatigue resistance, in practice, it can suffer from microscopic inclusions, cracking, or surface defects that reduce fatigue. This can lead to premature failure under cyclic loading if not properly processed and inspected.
• Joining and Machining Challenges—Nitinol is very difficult to laser weld, braze, or machine compared to stainless steel or titanium. It’s super hard on tooling and, therefore, can dramatically affect yield, cost, and design flexibility, especially when complex shapes or tight tolerances are needed.
• Surface Chemistry and Finishing—Surface oxides created during processing and nickel leaching are concerns that can affect biocompatibility and corrosion performance. Improper surface treatment (e.g., electropolishing, passivation, or coating) can trigger regulatory flags or lead to inflammatory responses.
• Design for Shape Memory vs. Superelasticity—As already mentioned, these concepts are often confused, and designers often mix the two properties, but they require different engineering approaches.
• Cost and Supply Chain Complexity—Nitinol is more expensive and has fewer high-precision suppliers globally, so choosing a vertically integrated supplier with deep technical capabilities, like Resonetics, will ensure consistent supply, shorter lead times, and flexible order quantities.
• Regulatory Scrutiny and Validation—Nitinol devices may face stricter validation for fatigue life, nickel release, and thermal performance compared to traditional metals, especially if used in a novel application. The FDA has a guidance document specifically covering Nitinol. You need a supplier that can anticipate these to reduce delayed FDA or CE approvals and help minimize increased test costs.

Fenske: Do you have any additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell orthopedic device manufacturers?

Veit: The smartest use of Nitinol isn’t where it replaces traditional metals, it’s where it enables new procedures, instruments, or therapies that weren’t possible before. The opportunity exists for novel applications using Nitinol that exceed the norms of traditionally stainless or titanium applications. I urge companies to explore what they might be able to accomplish with Nitinol either as an implant or perhaps as a delivery system component. We have the expertise to help bring your concept from a napkin sketch to production. Variability in heat treatment, surface finish, or raw Nitinol quality can cause dramatic shifts in device behavior. Work only with experienced Nitinol suppliers and validate every step in the process, from ingot to final form.

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