The application of nitinol in the field of heart stents
In the field of cardiovascular stents, the reason why "nickel-titanium alloy tubes" are commonly used instead of "nickel-titanium alloy wires" lies in the strict requirements of mechanics and technology: thin-walled tubes (with a wall thickness of 0.1 to 0.2 mm and a diameter of 2 to 10 mm) after being laser-cut into grids such as rhombuses can provide uniform and powerful radial support, far superior to wire-like braiding; at the same time, the tube billets of nickel-titanium alloy can be engraved with drug storage chambers, chamfers, and other micro-geometries in the same process, meeting the clinical requirements of reducing intimal hyperplasia in closed units, while the wire-like structure is difficult to balance strength and precision.
The standard manufacturing process of nitinol tubes begins with 50.8% Ni-49.2% Ti medical tubing that complies with ASTM F2063: First, the predetermined patterns are cut out using femtosecond laser with an accuracy of ±5 µm. Then, the shape memory heat treatment is carried out at 500-600 °C to fix the expanded state. Subsequently, electrolytic polishing is performed to remove burrs and apply titanium nitride or rapamycin coatings. Finally, the finished scaffolds with super elasticity, biocompatibility, and drug release function are obtained.
Although the main component is a nitinol tube, nitinol wire still plays a "supporting role" in cardiovascular devices: the small-diameter anchoring hooks at both ends of the stent, the braided framework of the left atrial appendage occluder, and the super-elastic core wire of the interventional guidewire all utilize the flexibility and memory properties of nitinol wire, but due to insufficient radial support, they cannot replace the tubular main structure.
By comparison, nickel-titanium tubular stents have emerged as the gold standard for peripheral arteries due to their high support capacity and precise release. However, the nickel-titanium filament-woven peripheral venous filter, although flexible and reusable, has inherent flaws such as low support capacity and easy displacement. This explains why the clinical mainstream has always chosen "nickel-titanium tubes" as the core form for supporting blood vessels.
The cardiac stent industry is evolving towards a "nitinol tube + nitinol wire" hybrid structure, ultra-thin nanocrystalline tubes (with a wall thickness of less than 50 µm), and degradable nickel-titanium alloys. This is to further reduce the outer diameter of the delivery tube, enhance flexibility, and gradually degrade and disappear after the support task is completed, achieving another upgrade in materials science and precision medicine.
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