While commercial manufacturers did not start using the metal alloy nitinol until the 1980s, it actually has been around since 1959. In that year, scientists were working to create a heat and corrosive resistant alloy and discovered that combining nickel and titanium did the trick. They named it “nitinol” to represent the atomic symbols for nickel and titanium (“ni” and “ti”) and to commemorate the name of their laboratory, Naval Ordinance Laboratory (NOL).
Nitinol’s Unique Properties
Nitinol is an especially valuable alloy because it is extremely elastic and has the ability to change shape depending on temperature. When it is cool, it is bendable and very soft, and when it is warm, it is rigid and springy. This alloy is useful for manufacturing coils because it allows them to “remember” their previous shape when they are heated. This makes them both more flexible than stainless steel and kink resistant.
In particular, nitinol is an excellent material to use when creating components for minimally invasive medical devices, such as guidewires, catheters and stents. When medical professionals need to navigate in particularly tight areas, nitinol has both the flexibility to change shape as needed, and the durability to endure high amounts of strain.
Benefits of Nitinol
There are so many good reasons to use nitinol, it’s difficult to find reasons not to use it. Here are some of the many benefits of this amazing substance:
- It has very good thermal conductivity. This means it is able to conduct heat extremely well.
- It has high corrosion resistance. Nitinol is difficult to damage. Once a component has been created using this alloy, it lasts for a long time, like titanium and stainless steel.
- It has biocompatibility, which means it can safely be used in the human body. This is especially important, of course, for the medical industry. Manufacturers of medical equipment must be certain that the materials they use will not only last for many years, but also not cause adverse reactions in patients.
Because nitinol is such a versatile substance, it is used for a wide variety of applications—each of which has a unique set of specifications. Manufacturers can process nitinol to achieve thermal and mechanical properties outside of the normal range. Depending on the strain of the specific application, the alloy can be tuned to have greater strength, resistance, or elasticity. The most skilled nitinol product manufacturers are able to make it do whatever they want it to do.
Nitinol in the Medical Field
In recent decades, medical product manufacturers have been using nitinol more and more. Here are just a few of the many ways this substance helps medical professionals do their jobs:
- Stents – Doctors use stents to open arteries and keep them open, so the material used to make them must be both strong and flexible. Nitinol is the perfect alloy to use because it has both those properties; additionally, it is also kink-resistant.
- Dentistry – Orthodontists, in particular, have need for many wires and brackets that hold braces together and perform the function of moving teeth. Nitinol’s shape memory is particularly helpful in this situation.
- Colorectal surgery – Gastroenterologists use this material to reconnect intestines after they remove a suspected malignancy.
- Orthopedic implants – When surgeons are replacing patients’ joints, they need components that will help patients regain flexibility and range of motion—as well as easily adapt to an individual patient’s tissue. Nitinol is the preferred material for these components.
The Importance of Superelasticity in Stents
Stents are perhaps the most obvious example of why the superelasticity of nitinol can be so beneficial. As previously stated, doctors use stents to keep arteries open. When these devices are inserted into the body, they can be compressed down to a minuscule size so as to be used in minimally invasive procedures. When the stents reach their destination, however, they expand to fill the necessary space and brace the inside circumference of a tubular passage in the body. Nitinol stents are superelastic and have shape memory, which means they are able to automatically return to their former shape once they are deployed.
Compared with stainless steel stents, which reach their destination during balloon angioplasty, nitinol stents can be much safer to use. When the balloon accomplishes its purpose, it is deflated, which can cause the stent to spring back toward its smaller state and possibly damage the blood vessel. On the other hand, nitinol has dynamic interference which causes it to expand directly to its preconditioned diameter with no recoil. It continues to push against the blood vessel and do the job it is supposed to do.
It has been more than 60 years since nitinol was first discovered, and during that time, it has revolutionized the medical device industry. This alloy’s unique properties have allowed doctors to save many lives.