Medical Applications

In the medical field, Nitinol is widely used not only because of its shape memory properties and hyperelasticity, but also because of its good biocompatibility and corrosion resistance. Nitinol has been used in everything from simple orthodontic wire to sophisticated heart stents.

1. Stenting in an artery (SME)

Ballooning made of Nitinol can effectively improve blood flow when stented in cardiovascular. In the operation, a balloon is placed in the diseased blood vessel to reopen the stenosis clogged lumen. Figure 4 shows the application of Nitinol stent in artery. Figure 4(a) shows a state in which blood flow in an artery is normal, Figure 4(b) presents a state in which blood flow is reduced due to platelets, and Figure 4(c) is the state in which blood flow is restored by opening an artery through a stent.[2]

Figure 4. The application of Nitinol stent in artery.

2. Biomedical implant (SME, biocompatibility)

Nitinol's low elastic modulus is close to that of natural aggregate, and its compressive strength is higher than that of natural bone material. [3] At the same time, its high recovery strain (due to shape memory or superelastic effect) and low rigidity can promote the integration of Nitinol and bone structure. These characteristics make it an ideal material for biomedical implants. In recent years, it is also a hot issue to study the application of porous Ni-Ti foam to bone tissue scaffolds and intervertebral fusion devices.

Figure 5. Photograph of commercially available porous Nitinol.

3. Supporting grafts (SME)

Stents are also used to support grafts, such as in the treatment of aneurysms. Weakening of arterial wall leads to the appearance and ballooning out of aneurysm, which is at risk of rupture. The graft is placed through the interlayer and anchored to the healthy part of the aneurysm near the carotid artery to exclude blood from the aneurysm sack. The graft is typically supported and anchored by a self-expanding nitinol stent structure.

Figure 6. Sketch of Nitinol support graft in artery.

4. Orthodontic wire (superelasticity)

As the pitting corrosion of nitinol in saliva solution is better than SS304 stainless steel, low-temperature nitinol wire can be used as orthodontic arch wire for dental sleeve.[3] When the nitinol wire is connected to the bracket attached to each tooth, the nitinol wire provides a low constant force at the temperature of the human body, and the teeth can move in a controlled manner while reducing the need to retighten the wire. The transition temperature of these wires generates force at the temperature of the human mouth (about 37 degrees Celsius (98.6 degrees Fahrenheit)). [5]

Figure 7. Nitinol orthodontic wire.

5. Surgical catheters (SMA, superelasticity)

Nitinol tube can be used as surgical catheter, which is easier to bend than steel catheter, thus facilitating the surgeon to enter the catheter into difficult parts of the human body.

Figure 8. Nitinol surgical catheters.

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Applications

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