Nitinol basics

Nitinol for medical application

Nitinol's unusual ability to accommodate large strains, combined with its compatibility with the human body, have made it one of the most commonly used materials in medical device for both reusable and disposable medical instruments, implants components. The shape memory alloy Nitinol is a made-up-word, derived from its place of discovery: Nickel Titanium Naval Ordnance Laboratory. The material, if deformed while cool, returns to its undeformed shape when warmed. A reversible, solid phase transformation known as martensitic transformation is the force behind Nitinol. The alloy material forms a crystalline structure, which is capable of undergoing a change from one form of crystalline structure to another. Temperature change or/and loading initiate this transformation. Above its transformation temperature, Nitinol is superelastic, able to withstand a small degree of deformation when a load is applied and returns to its original shape when the load is removed. Below its transformation temperature, it displays the shape memory effect. When it is deformed it will remain in that shape until heated above its transformation temperature, at which time it will return to its original shape. Nitinol is known to be highly biocompatible and its properties make it suitable for use in implants. These unique properties and tailorability of Nitinol makes it suitable for many applications in medicine.

Nitinol returns to its original shape ...

austenite and martensite ... this means, surgeons can shape an instrument on site to fit it to the patient's anatomy. Then after heat sterilization the device returns to its original shape (thermal shape memory effect). Example of this application are dilators and suction cannulaes.

Nitinol is superelastic ...

... which allows the material to be bent more significantly than stainless steel without taking a set. Small Nitinol wires and tubes will pass through tortous paths in the body and remain straight and torqueable. The superelastic plateau enables Nitinol devices that apply constant stress over a wide range of shapes, e.g. springs.

Nitinol is kink resistant and flexible ...

... which makes it the material of choice for endoluminal devices like retrieval baskets. The baskets are extremely flexible. They permit an easy access, combined with high kink resistance, high radial forces and one to one movement.

Nitinol with its biomechanical properties ...

... makes it the most similar to biologic materials from the mechanical point of view. In comparison, materials such as stainless steel and titanium are very rigid, yielding little in response to pressure from surrounding tissue. Nitinol with similar biomechanic properties as human tissue allows mechanical cycling and therefore is the most suitable for implants like bone staples, stents or markers.

Nitinol is non-ferromagnetic ...

... with a lower magnetic susceptibility than stainless steel and produces fewer artifacts than stainless steel, similar to pure titanium.

Top