Introduction
Nitinol is a nickel titanium alloy that exhibits the unique property of shape memory and superelasticity. This allows the material to undergo large deformations but return to its pre-deformed shape making it ideal for use in various medical devices. Over the past few decades, Nitinol has spawned a revolution in the medical field with the development of innovative minimally invasive surgical tools and implants.
Stents
One of the earliest and most widely used applications of Nitinol is in coronary stents. Stents are small mesh like tubes that are inserted into narrowed or blocked blood vessels via a catheter to open up the blockage. Early metal stents made from stainless steel were prone to restenosis or renarrowing of the artery post procedure. Nitinol stents, on the other hand, are highly flexible and expandable allowing them to be tightly pressed against the vessel wall. Furthermore, upon heating to body temperature in the vessel, they regain their pre-formed shape maintaining the patency of the vessel. This property combined with improvements in drug eluting coatings on the stents has significantly reduced restenosis rates revolutionizing the treatment of cardiac diseases.
Filters
Nitinol Medical Devices filters are commonly used in patients at a high risk of developing pulmonary embolism or blood clots in the lungs. The filter is placed via catheter in the inferior vena cava - the large vein that drains into the heart from the lower body. Any clots that break loose from the deep veins of the legs would get trapped in the filter preventing them from reaching the lungs. The self-expanding Nitinol filter assumes the shape of an umbrella or basket on deployment and continues to securely fix itself in position in the vessel. This has provided an effective alternative to blood thinners in high risk patients.
Guidewires
Guidewires play a crucial role in modern interventional procedures by helping the catheter or device reach the target location in a minimally invasive fashion. Nitinol guidewires are highly kink resistant, steerable and trackable over their entire length due to the shape memory and superelastic properties. They are used for crossing chronic total occlusions in angioplasty, navigating complex arterial and venous structures during various interventions as well as aiding device delivery. Their unique performance attributes have facilitated many previously impossible procedures to be performed routinely now.
Retrievable IVC Filters
Nitinol is now enabling new functionalities in IVC filters with the development of retrievable filters. Traditional permanent filters remained implanted long term even after the clot risk subsided posing their own risks. Retrievable filters on the other hand can be safely removed following the risk period through an invasive snare procedure. They self-center and anchor securely in the IVC during deployment but can be resheathed into the slender catheter for removal. This prevents long term filter related complications while still addressing short term clot risks optimally.
Orthopedic Implants
In the orthopedic field, Nitinol is revolutionizing the treatment of fractures, spine problems and joint replacements. Nitinol bone plates allow minimally invasive plate osteosynthesis where the coated plate is compressed to pass through a small incision but regains its original shape to securely fix the bone fragments. Nitinol bone screws exhibit high pullout strength due to interfacial bone ingrowth minimizing screw loosening risks. In spinal applications, Nitinol rods, hooks and pedicle screws help stabilize fractures or correct deformities with shape changing capabilities. Furthermore, Nitinol meshes and scaffolds can be used for bone regeneration in fractures. On the joint replacement front, Nitinol alloys are being investigated for use in minimal incision total hip and knee implants as well as augmented surgical tools.
Future Prospects
While Nitinol has had a tremendous impact already, ongoing research continues to broaden its applications. Areas being explored include self-expanding vascular stents with drug reservoirs, endovascular aneurysm sealing devices, retrievable vena cava filters for longer term protection, active catheter navigation systems, superelastic sutures and more. Combinations with other materials using techniques like 3D printing also hold promise. Considering the unique versatility offered, Nitinol is certain to keep transforming patient care through innovative medical devices going forward. Its ability to aid minimally invasive procedures while withstanding the rigors of the human body makes it a technology to watch out for in the healthcare products industry.
The shape memory and superelastic properties of Nitinol have provided medical innovators a revolutionary biomaterial to develop sophisticated yet simple solutions. From improving access with guidewires to delivering localized drug therapies with stents to re-opening blocked vessels, Nitinol has had far reaching impact. Its applications continue to broaden and enable previously difficult interventions to be performed routinely. Going forward, ongoing research will undoubtedly give rise to newer kinds of life changing Nitinol based medical devices that further enhance patient outcomes.
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