Interventional Radiologist at WorkNitinol Properties Affecting Uses in Interventional Radiology
Section snippets
BACKGROUND
Nitinol is an alloy comprised of approximately 50% nickel and 50% titanium. Nitinol has properties of superelasticity and shape memory. Superelasticity refers to the enhanced ability of a material to be deformed without irreversible change in shape. Shape memory is the ability of a material to regain its shape after plastic deformation at a lower temperature. These physical properties of nitinol allow complex device configurations and high expansion ratios enabling percutaneous delivery through
• Structural Basics
Superelasticity and shape memory are based on the ability of nitinol to exist in several crystal forms or phases. Phase transitions between liquid and solid phases are commonly known phenomena, such as water freezing to ice or solid metal melting into liquid. What makes nitinol unique is its ability to exist in two distinctly different, reversible crystal phases in its solid state at clinically useful temperatures. The alignment of crystals at the higher temperature is called austenite (A)
BIOCOMPATIBILITY
Nitinol is a highly biocompatible and nontoxic material (8, 9), although nitinol alloys contain approximately 50% nickel, which is considered toxic. However, assessment of nickel metabolism in humans indicates that the body burden on nickel in normal adults averages 0.5 mg (7 micrograms per kg for a 70-kg adult person). The maximum recommended permissible amount of nickel administered to a human as a contaminant in intravenous fluids should not exceed 0.5 micrograms per kg per day (35
GENERAL CONSIDERATIONS
Nitinol devices can generate tremendous force (up to 80 kg/mm2)if they meet resistance during their recovery. Varying the thickness of the nitinol wire, the overall shape of the device, and the spatial arrangement of the nitinol wire within this shape can regulate the force. These design features, as well as the characteristics of the nitinol alloy used, should be taken into account when designing, selecting, and deploying interventional devices for specific clinical applications.
Self-expanding
CONCLUSION
The features of superelasticity and shape memory make nitinol an excellent material for interventional devices. These physical characteristics permit manufacture of complex shapes of devices and introduction through low-profile delivery systems. Familiarity with the characteristics of nitinol aids in selecting the most suitable device for a specific clinical indication.
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X-ray visibility and metallurgical features of NiTi shape memory alloy with erbium
2014, Materials LettersCitation Excerpt :Radiopacity generally refers to the ability of a material to absorb X-rays, which contrasts it against other materials surrounding it in an X-ray image [3]. A high X-ray visibility of surgical devices is critical during minimally invasive surgery for the exact placement of the minimally invasive surgical devices within the targeted anatomical site while keeping the X-ray exposure of the patient to a minimum [6,7], yet radiopacity of common biomedical materials are generally low [3–5]. NiTi usually has the lowest radiographic contrast among these alloys (Fig. 1a) and poses a problem in particular in smaller size devices made of NiTi [6,7].
Micro-CT-compatible Technique for Measuring Self-expanding Stent Forces
2010, Journal of Vascular and Interventional RadiologyCitation Excerpt :For a successful long-term clinical prognosis, optimization of stent design, including thermo-mechanical processing, by using a testing device as described in this study will play a key role. The stress-strain curves obtained during testing of the nitinol stent used in this study (Fig 7) demonstrate the unique hysteresis properties previously attributed to nitinol (14,19,22). The stress-strain curves exhibit two distinct sections, depending on the direction of the deformation.
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2009, BiomaterialsCitation Excerpt :These results suggest that the cyclic crosslinking structures formed within the genipin stent matrix were beneficiary to the improvement of its mechanical property. Elastic deformation refers to changes in shape that disappear completely after the release of external forces [28]. When external forces exceed the limit of elastic deformation, test stents become plastically deformed (or fractured) resulting in a permanent change of shape.
Monitorizing nitinol alloy surface reactions for biofouling studies
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