Globalization has increased the standard of living in many countries, and people are living longer. Lifestyle-related disorders, such as cardiovascular diseases, are on the rise as people’s living standards and options rise. Companies are racing to develop medical devices that can treat difficult physical disorders and diseases. Novel materials play a crucial role in enabling such design and development. Nitinol (NiTi) is one such material, discovered by William J. Buehler in 1959 while conducting research at the US Naval Ordnance Laboratory in White Oak, MD. Nickel Titanium Naval Ordnance Laboratory, or Nitinol, was first used in medical devices in the late 1980s.
Nitinol is one of several shape memory alloys (SMAs) that may revert to their original shape after being deformed. Wire, tube, sheet, foil, and machined or molded geometries are all options for Nitinol components. Nitinol shape memory sheet have developed a solid foothold in a variety of industries, from consumer appliances to automotive to aerospace and medical equipment because they provide designers with remarkable flexibility in substituting conventional materials. Nitinol is prominent in medical devices because of its biocompatibility and super-elasticity. Stents, guide wires, stone recovery baskets, filters, needles, dental files, and other surgical devices are made of nitinol.
The Shape Memory Effect
The shape memory effect is most commonly demonstrated by deforming a piece of metal—for example, by winding a piece of straight wire into a tight coil—and then entirely removing the deformation by heating the metal with a modest amount of heat, such as dipping it in hot water. When heated, the metal “remembers” its previous shape and springs back into a straight wire shape. The shape memory effect occurs when a material’s crystal form changes when it cools or heats beyond its characteristic transformation temperature. Above its transformation temperature (austenite), the crystal structure of NiTi alloys changes from an ordered cubic crystal form to a monoclinic crystal phase.
Applications of Nitinol Sheet
The most well-known application of Nitinol tubes is the laser cutting of self-expanding stents. It is a popular choice in peripheral vascular applications. When producing stents, concentration control and a good surface polish on the tube’s inner diameter are critical. Nitinol tubes are employed in a variety of applications, including biopsy, endoscopy, and orthopedics.
Catheters are guided into difficult-to-reach areas of the body using Nitinol guidewires. They are preferred because, unlike stainless steel, they do not kink. The wire is flexible and can go through the body in a sinuous course without causing damage. Nitinol rotates smoothly and distributes torque. Braided stents and filters are also routinely made with nitinol wires.
Nitinol sheet is popular because it allows designers to design goods flat before shaping them into devices, which is not possible with other forms. The sheet can be manufactured with extremely fine thickness tolerances and consistent thickness control throughout the entire surface. This strong process capability aids downstream process optimization and automation—predictable final dimensions will result from constant beginning sheet thickness and controlled post-processing.
Nitinol has the disadvantage of not being radio-opaque, which is required for accurate stent placement and the ability to find the device in the body. To improve radio-opacity, several precious metals marking methods, such as platinum and palladium, are widely utilized in conjunction with Nitinol-based devices.
Close collaboration with the supply chain, as with other materials and development initiatives, allows the team to assess cost implications and other engineering issues early on. When the material properties and limits are fully understood and recognized, Nitinol can provide a straightforward, elegant solution to a problem where past solutions were extremely complex or expensive.