Page Outline
This page first introduces the Nitinol in the beginning of the invention purpose, the current application and future development potential. Later, typical applications of Nitinol in medical, industrial, aviation and daily life were described in detail.
History
Nitinol was discovered in the Naval Ordnance Laboratory (NOL), used to make tools for dismantling magnetic mines. However, because the Nitinol was too difficult to melt and process, the commercialization was difficult until the 1990s
Figure 1. The initial sample of Nitinol.
Current
Nitinol has proved to be widely used in various fields, including biomedicine and medicine, novel products, heat engine, sensors, low temperature activation of mold and memory slot and lifting equipment.
Figure 2. Nitinol basket used in medical field.
Future
Nitinol is a rare thin film form with strong binding and rapid endothelialisation. Porous Nitinol, as a very flexible material, has the potential to promote bone growth.
Figure 3. Electron microscopy of Nitinol.
Typical Application in Various Fields
The numerous applications of Nitinol are described below according to different fields.
These applications focus on its shape memory effect (SME), superelasticity, and biocompatibility, which will also be reflected in the brackets after the title of each application.
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.
Industrial Applications
In the industrial field, the Nitinol devices are used to control the system, including temperature control and coupling.
1. Temperature control (SME)
Nitinol's shape change characteristics can be used for temperature control switches in industrial production, which realize temperature control by activating variable resistors or switches. When the nitinol spring is heated above the reverse transformation temperature, the shaft moves to the right because the restoring force of the spring overcomes the force exerted on the biasing spring. When the Nitinol spring cools below the martensitic transformation temperature, the shaft returns to its original position.[5]
Figure 9. Nitinol spring for temperature control.
2. Cryofit coupling (SME)
Low temperature nitinol hollow cylinder with inner diameter smaller than pipe diameter is first expanded and stored in martensite state until assembly. After installing the expansion coupling on the oil pipe, when the temperature rises to the ambient temperature, the inner diameter of the coupling returns to the original size and forms a firm connection with the oil pipe. The device can be applied to hydraulic systems in petrochemical and other industries.[5]
Figure 10. Nitinol cryofit coupling.
Aerospace
In the aerospace field, the shape memory ability of Nitinol is used to serve the delivery of relative equipment and device.
1. Nitinol tire (SME)
When the structure is the same, the deformation of Nitinol tire is 30 times that of steel tire compared with spring steel tire without permanent deformation. [6] The surface of the tire can be deformed to match the contour of the ground surface to produce a strong grip, then return to the original tire shape and the wheel rotates. This can deal with dangerous terrain such as the surface of Mars. [7]
Figure 11. Nitinol tire.
2. Antenna of spacecraft (SME)
Nitinol is processed into an expanded antenna shape in the parent phase state, and then cooled to completely become martensite. Then it is folded within the recovery range and becomes a very small shape to facilitate loading into the carrier rocket. After taking it into space, due to the radiation heating of the sun, its shape gradually expands during the heating process until it reaches the temperature of the parent phase and becomes a complete antenna. [8]
Figure 12. Nitinol Antenna.
3. Temperature control (SME)
Nitinol can be used to prepare heat sink with bidirectional memory function for spacecraft temperature control system. [9] When the temperature changes, the two-way memory blade can spontaneously turn to different angles to open or close the heat dissipation device, so as to meet the requirement of rapidly emitting or storing heat and maintain a constant temperature.
Daily Life
Nitinol is also widely used in daily life due to its super elasticity and shape memory.
1. Eyeglass frame (superelasticity)
The use of Nitinol components for the eyeglass frame, nose piece (bridge) and ear pieces (temples) provide improved wearer comfort as well as great resistance to accidental damage. [10]
Figure.13 Nitinol eyeglass frame.
2. Golf insert (SMA)
Nitinol Super-elastic sheet for Golf Head hitting surface plate.[10]
Figure.14 Nitinol golf insert.
3. Spoon for magic show (SMA)
Be used for making self-bending Nitinol spoons in magic shows. [10]
Figure.15 Nitinol self-bending spoon.
References
[1] S. A. Shabalovskaya. (1996), “On the nature of the biocompatibility and on medical applications of NiTi shape memory and superelastic alloys,” Bio-Medical Materials and Engineering, 6(4): 267–289.
[2] Kapoor, D. (2017). Nitinol for Medical Applications: A Brief Introduction to the Properties and Processing of Nickel Titanium Shape Memory Alloys and their Use in Stents. Johnson Matthey Technology Review, 61(1), 66-76.
[3] Wadood, A. (2016). Brief Overview on Nitinol as Biomaterial. Advances in Materials Science and Engineering, 1-9.
[4] Bansiddhi, A., Sargeant, T., Stupp, S., & Dunand, D. (2008). Porous NiTi for bone implants: A review. Acta Biomaterialia, 4(4), 773-782.
[5] Duerig, T., Pelton, A., & Stöckel, D. (1999). An overview of nitinol medical applications. Materials Science and Engineering: A, 273-275, 149-160 [cited 10 June 2020]. Accessed from: https://doi.org/10.1016/s0921-5093(99)00294-4
[6] Nancy Smith Kilkenny(2017). "Reinventing the Wheel." Accessed on 5 June 2020 from https://www.nasa.gov/specials/wheels/
[7]"Mars Rover Specifications." NASA. Accessed on 9 June 2020, from: https://mars.nasa.gov/mars2020/mission/rover/wheels/
[8] Costanza, G., & Tata, M. (2020). Shape Memory Alloys for Aerospace, Recent Developments, and New Applications: A Short Review. Materials, 13(8), 1856.
[9] Hartl, D., & Lagoudas, D. (2007). Aerospace applications of shape memory alloys. Proceedings of The Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 221(4), 535-552.
[10] W. M. Huang, Z. Ding, C. C. Wang, J. Wei, Y. Zhao, and H. Purnawali, “Shape memory materials,” Materials Today, 13,(7-8), pp. 54–61, 2010.