Introduction
Nitinol, an unusual alloy of nickel and titanium that shows properties of shape memory and superelasticity, has found widespread applications in the medical field and is transforming healthcare. Nitinol's unique properties allow it to be designed into minimally invasive medical devices that can navigate the human body in remarkable ways.
What is Nitinol?
Nitinol refers to the nickel titanium alloy commonly referred to by its acronym - NiTi. When NiTi reaches its transformation temperature, it undergoes a crystal structure change which allows it to revert to a preformed shape. This phenomenon is called shape memory. Additionally, NiTi displays superelasticity or pseudoelasticity, where it can withstand high amounts of strain and still revert to its original undeformed shape upon unloading. These properties make Nitinol light, flexible and able to be designed into intricate small diameter medical devices.
Applications in Cardiology
Cardiology has seen some of the most revolutionary applications of Nitinol Medical Devices. Stents, which are small mesh tubes used to open blocked arteries, were some of the earliest medical applications of Nitinol. Nitinol stents are self-expanding - when deployed in a blocked artery, their shape memory allows them to expand and press against the vessel wall to hold it open. This makes insertion and placement much simpler than earlier balloon expandable stents. Today, Nitinol stents are the standard of care worldwide for treating coronary and peripheral artery disease.
Another major application is filter devices to capture blood clots in the heart before they can travel to the brain and cause a stroke. Inferior vena cava (IVC) filters made of Nitinol are deployed in the large vein leading to the heart to trap thrombi. Their self-expanding superelastic mesh design allows them to securely anchor in place and function for years. Retrievable IVC filters have also been developed which can be easily removed once the risk of clot passes, using Nitinol's shape memory.
Neurovascular Applications
In the neurovasculature - the delicate blood vessels of the brain, Nitinol has enabled groundbreaking new procedures. Its flexibility and shape memory allows creation of self-expanding stents much smaller than previous designs to access vessels as small as 2mm in diameter. These neurovascular stents help treat aneurysms - weak bulging areas in arterial walls at risk of rupture.
Coiling technologies use platinum coils delivered through a microcatheter to fill an aneurysm, promoting clotting off from circulation. Newer flow diverter stents constructed of Nitinol are changing the game. These ultra-flexible stents are deployed across the neck of an aneurysm, diverting blood flow away from it and promoting faster, more complete healing. They have vastly superior outcomes to coiling for large and giant aneurysms.
As stroke remains a leading cause of death worldwide, continues expansion of neuroendovascular techniques presents hope. And it would not be possible without the enabling properties of Nitinol.
Sub-Sections and Sub-headings
Nitinol in Orthopedics
Joint replacement has traditionally relied on metal alloys like titanium and cobalt-chrome. However, Nitinol is showing promise for next generation implants. Its shape memory and superelasticity allows construction of self-expanding components that can conform to complex joint geometries better than static designs. Early research involves spinal fusion cages and total disc replacements that deploy via Nitinol's memory effect to properly space and support vertebral bodies. If long term testing proves successful, these passive conforming implants could greatly simplify surgery and recovery time.
Nitinol in Urology and Gastroenterology
Two areas seeing extensive use of Nitinol are urology and gastroenterology due to demands of navigating convoluted anatomies. Ureteral stents made of Nitinol self-guide from the kidney to the bladder, releasing its memory effect shape change once in proper position to drain urine. Similarly, esophageal stents allow eating and drinking by bracing open collapsed areas of the swallowing tube.
Retrievable biliary and pancreatic stents that help drain blockages of the liver and pancreas ducts over months would not be possible without Nitinol. Its shape memory and flexibility permit easy removal after therapy, instead of requiring a second surgery. Nitinol is also used for sutures, surgical meshes and staples in pelvic organ prolapse and hernia repair where superelasticity eases tissue handling.
Nitinol in Vascular Surgery
With Nitinol stents revolutionizing cardiology and neurovascular care, it was only a matter of time before orthopedic extremities work utilized shape memory technology. Nitinol self-expanding stents show promise to restore blood flow in advanced cases of peripheral arterial disease affecting lower limb circulation. Their flexible scaffolding can navigate tortuous superficial femoral and tibial arteries to open blockages where traditional balloon angioplasty and bare-metal stents have failed.
Other areas include aortic endografts for abdominal aortic aneurysm repair which rely on Nitinol superelastic frame and stent designs to conform to complex 3D anatomies of the aorta and iliac arteries. New retrievable formats also allow less invasive alternatives if future open surgery becomes necessary. With lifestyle limiting claudication on the rise, shape memory alloys offer new hope.
From simpleNitinol stents and filters to complex flow diverters, retrievable implants and next generation joint designs, shape memory technology is revolutionizing minimally invasive surgery. Millions of lives have already benefited from these novel applications with more on the horizon. As material property insights continue advancing, new frontiers in orthopedics, urology, vascular and even wider surgical specialties await. Ultimately, it is Nitinol's versatility that makes it so well suited to medical environments and drives ongoing innovation improving patient care worldwide.
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