What is Nitinol and How is it Leveraged in Medical Device Design?

Nitinol is a nickel-titanium shape memory alloy widely used in the medical industry due to its numerous desirable properties. One of those is that the metal has a shape-memory capability, so it will return to its original form after being bent while in a spring-like shape. It works well for specific medical devices because it can compress to fit into areas where conventionally sized devices do not and then expand to the desired appearance. Nitinol medical applications are often products inside the body.

How Is Nitinol Made?

Making nitinol requires working with extremely high temperatures since both the respective metals have some of the highest melting points among all materials of their type. Nitinol is reactive at high temperatures, so the melting of nickel and titanium must occur in a vacuum or inert environment. Otherwise, oxide inclusions can form that compromise structural integrity through the appearance of thin, film-like insoluble skins.

The two main melting options are vacuum induction melting and vacuum arc remelting. However, some fabricators use double-melting processes, which rely on both those methods. The two metals must combine at an approximately 1:1 atomic ratio. Additionally, regulations surrounding medical applications of nitinol require the material to be 54.5% titanium to 57% nickel.

Additionally, vacuum arc remelting requires numerous melting and remelting cycles to achieve the composition, but vacuum induction melting gets those results after one melt. Moreover, vacuum induction melting only suits people who need nitinol in small quantities.

Once molten nitinol cools in a cast, it forms a block called an ingot. Finally, hot forging and rolling methods get it into the desired shapes.

What Are Examples of Nitinol Medical Applications?

Nitinol, one of the most prominent shape memory alloys, has existed since 1959, and it happened unintentionally. The individuals associated with its first creation were trying to make a corrosion and heat-resistant alloy. Once people began exploring the material more intensively, they found it suited many medical needs and supported the production of innovative devices.

Many medical device manufacturers have pursued technological advancements in other, complementing ways, such as through automation. Such options improve resource utilization and quality control, keeping production costs competitive. Automation can also improve patient safety by enabling better consistency. Whether factories use automated technologies to make the devices used for nitinol medical devices, these products offer numerous advantages.

Some more well-known medical devices that leverage nitinol include:

Heart valves/valve repair devices (Medtronic’s Evolut, Abbott’s TriClip, Edwards’ Mitris Resilia)
Cardiac pulsed field ablation (PFA) catheters (Medtronic’s Sphere-360, Biosense Webster’s Varipulse, Boston Scientific’s Farapulse, Abbott’s Volt)
Stents and stent retrievers (Johnson & Johnson MedTech’s Embotrap)
Intramedullary nails (Enovis’ DynaNail)
Guidewires
Vena cava filters
Bone staples
Self-locking orthopedic devices
Dental devices

Making Catheter Ablation More Personalized

Catheter ablation techniques selectively destroy heart tissue abnormalities to correct arrhythmias. Nitinol is a commonly chosen material for the ablation tip, which delivers concentrated energy to the desired area.

A 2023 study involving patients in the European Union investigated how effectively a Medtronic Sphere-9 nitinol-tipped catheter treated individuals with two types of atrial fibrillation. The outcomes showed atrial arrhythmias did not return for 78% of patients across two groups after their procedures. Additionally, 85% of those receiving a commercialized and optimized waveform during their catheter ablation procedures had one year without atrial arrhythmias.

The outcomes also showed that Sphere-9’s nine-millimeter nitinol ablation tip may shorten overall procedure times by allowing for fewer focal ablation lesion applications. The ablation tip supports personalized procedures by supporting two energy types with a single catheter, depending on what the patient and treatment require.

Preventing Muscle Atrophy During Healing

As designers and engineers find the most appropriate nitinol medical applications, they must maintain a problem-solving mindset, understanding various challenges and how creative, thoughtful solutions could address them. That was the approach of a doctor who invented blood banks in the 1930s after realizing people could store the fluid the same way they did when keeping medicines.

Nitinol offers superb elasticity, and that characteristic made it of interest to researchers who adopted similarly forward-thinking attitudes when designing a system to prevent muscle atrophy in limbs as they healed in casts.

While exploring the potential of devices that stretch and contract muscles to keep them in good condition during healing, researchers created a mechanically active adhesive that functions as a soft robotic device. One of its primary components is a nitinol spring that makes the device move once it reaches a certain temperature. The team wired the spring to a microprocessing unit, allowing them to program the movement.

When the group tested their device by implanting it into the calf muscles of mice, they found it exerted approximately 15% mechanical strain on those body parts, mimicking the muscular deformation caused by exercise.

Another part of the experimentation involved encasing the rodents’ legs in tiny casts for two weeks after implanting the muscle stimulation device. The outcomes showed that the nitinol-enabled product reduced wastage and could prompt some of the major pathways to foster regrowth and protein synthesis.

Promoting Better Fracture Recovery

Some nitinol medical applications increase the chances of patients returning to full functionality after suffering bone fractures. Orthopedic specialists often use lag screws to compress bone fragments, tightening these components as needed to cause the bone to heal in the appropriate position.

A commercially available product makes lag screws more dynamic by utilizing nitinol’s shape-memory and elasticity capabilities. This system includes a disc that sits over the lag screw shafts and—once the screws are correctly tightened and seated—becomes deformed.

However, the deformation resistance engineered into the disc results in continuous compression for the bone fragments. The manufacturer’s internal study showed this approach could enable gap closures up to 4 millimeters, offering the pressure and durability needed to give people healthy recoveries after broken bones.

Achieving Progress with Nitinol Medical Applications

The most successful medical applications of nitinol are those where the involved parties thoroughly understand the material’s properties and how they will facilitate specific requirements. A good starting point is to consider things from the perspectives of patients, providers and others who will directly engage with the newly designed medical devices. Since many people prefer familiarity, they need compelling reasons to switch to new products. Getting them to do it is easier when they see clear benefits from making the change.

Those engineering medical applications with nitinol components should also plan numerous efforts that will allow them to see the pros and cons of a product’s performance in labs and real-world settings. Information about the associated outcomes lets them verify a device’s safety, suitability for intended applications and other particulars. Such insights could make it easier to get innovative products approved, especially when it is time to engage with regulators and show them carefully collected data about how well they work.

Article source：MPO