Nitinol Tubing: Hypotubing Versus Precision Tubing—A Medtech Makers Q&A

By Sean Fenske, Editor-in-Chief

Tubing is pervasive throughout healthcare and an essential component for medical devices across all care environments, from the doctor’s office to hospitals to assisted living facilities. As such, there are plenty of types, styles, and materials associated with it. This results in the need for very specific information when developing a device that requires it.

While tubing is often thought of as made of plastic, there are critical areas where metal tubing is required, offering benefits not realized otherwise. Among the material options is Nitinol, which may be provided as hypotubing or precision tubing. Depending on the application, the best option needs to be specified, and the variables for that choice need to be clarified.

Since Nitinol tubing can be challenging to work with, it’s important to collaborate with a supplier that understands how to best manipulate it to gain the greatest benefits from its properties. Fortunately, Chris Ford, VP of Operations, Materials, at Confluent Medical Technologies, answered a series of questions around the use of the material for medical device tubing in the following Q&A.

Sean Fenske: What is hypotubing? When developed in Nitinol, what are the medical device/healthcare applications for it?

Chris Ford: Hypotubing, short for hypodermic tubing, is a thin-walled, precision metal tube originally developed for hypodermic needles. It’s widely used in medical devices and other commercial applications because of its tight tolerances and high strength. Hypotubes are typically used in electrophysiology catheters, ablation catheters, retrieval devices, steerable surgical instruments, delivery devices, and shape memory actuators.

Fenske: Where is Nitinol precision tubing used in medical device/healthcare applications? Why is Nitinol required?

Ford: Precision nitinol tubing is typically used in the manufacture of peripheral, venous, pediatric, and neurovascular stents, heart valve frames, and certain pulsed field ablation components. Nitinol tubing is used in many of the most critical medical devices because it combines mechanical properties that are difficult to achieve with conventional alloys like stainless steel or cobalt-chromium. In many applications, these properties directly improve the ability to deliver a device safely and reliably through the body.

Fenske: What makes Nitinol such a challenging metal to work with? What makes it unique compared to most other metals?

Ford: Nitinol is much more difficult to work with than stainless steel, titanium, or cobalt-chrome alloys because of its unique crystal structure and phase transformations. The same properties that make it valuable—shape memory and superelasticity—also make it challenging to manufacture.

Fenske: With Nitinol hypotubing, why are length tolerances so important? What is the challenge with these? How is Confluent addressing those challenges?

Ford: Controlling length tolerance is critical, whether it’s for fab-cut components that go directly into an assembly process or longer tubes that feed into a laser-cutting or machining process. Tight tolerance length control reduces scrap and associated downstream costs in manufacturing and assembly.

Fenske: With Nitinol precision tubing, what is the challenge with wall tolerance? How is Confluent addressing this issue?

Ford: Precision tubing is produced through a series of area reductions of the tubing. Tooling wear and separation of tubing from ID support tooling are critical to maintaining a tight wall tolerance and overall concentricity of the tube. Confluent starts with producing an exceptionally concentric tube hollow and has systems in place to monitor and effectively manage tool wear during the reduction process.

Fenske: When specifying Nitinol tubing—hypotubing or precision tubing—what are the most important variables to consider? What must be spelled out specifically?

Ford: Dimensionally speaking, the design engineer needs to consider what two areas are critical to device performance—OD, ID, or Wall thickness—as only two of the three can be achieved. Hypotubing is typically specified with an OD and an ID. Precision tubing is typically specified with a desired wall thickness and tolerance coupled with either an OD or ID specification.

Additionally, metallurgical/melt characteristics are also important to consider when specifying the material grade of Nitinol. Confluent manufactures precision and hypotubing from both standard grade Nitinol (SE508) and high-purity grade Nitinol (SE508 ELI). Confluent stocks both grades, and we are vertically integrated back to the melt source.

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 medical device manufacturers?

Ford: Medical device manufacturers need to involve their tubing supplier early. Nitinol is a highly specialized material, and design choices related to dimensions, tolerances, and processing can have a major impact on performance and manufacturability. A strong supplier should be a technical partner that helps optimize designs, reduce risk, and scale successfully from development to production. At Confluent, that’s exactly the role we strive to play for our customers.

Vertical integration is also an important factor to consider when selecting a supplier for Nitinol tubing. Vertical integration is important to overall quality because it gives a manufacturer direct control over the critical processes that determine a product’s performance, rather than relying on multiple outside suppliers. This is especially valuable in medical device manufacturing, where small variations in material properties or processing can affect device safety, performance, and regulatory compliance. Confluent’s vertical integration from Nitinol melting through finished device manufacturing allows us to carefully control the quality of the products we manufacture for our customers.

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