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Medical nickel-titanium shape memory alloys, mainly used to manufacture implantable or interventional medical devices, are widely used in cardiothoracic surgery, neurosurgery, urology, digestive surgery and orthopedic surgery. Nitinol is a shape memory alloy that automatically returns to its original state after plastic deformation over a specific temperature range. Nitinol has good biocompatibility and corrosion resistance, so it can be used as a medical implant material, and has the advantages of high damping, super elasticity, wear resistance, shock resistance, fatigue resistance and so on. Among them, superelasticity is its outstanding advantage, and most nickel-titanium medical devices rely on superelasticity (Figure 1) to function.

01. Nitinol currently has the largest market share in medical applications

Nitinol can be applied in a wide range, of which the application of medical devices is the fastest development, the current market size is the largest, accounting for more than 60% of the share of nickel-titanium raw materials, China's annual nickel-titanium equipment market size of nearly 400 billion yuan. Medical nitinol can be used to manufacture implantable medical devices such as heart occluders, aortic stents, guidewire products, kidney micropumps, vascular stents, esophageal stents, bone fixators, surgical sutures, dental correction wires, etc.; Medical nitinol has a wide range of clinical applications, including general surgery, minimally invasive surgery, medical cosmetology, dental orthodontics, etc.

02. Medical nitinol is widely used in the preparation of various non-vascular stents and vascular stents with its excellent superelasticity

Compared with other medical implant materials, medical nitinol has shape memory function and has outstanding advantages of superelasticity. Taking advantage of this feature, non-vascular, self-expanding metal stents made of medical nitinol, such as non-vascular gastrointestinal and airway stents, can be used to help patients with occlusion or stenosis in various areas of the anatomy, including the bile duct tree, pancreatic duct, esophagus, colon, and duodenum. In the vast majority of cases, stent placement is a minimally invasive procedure, and patients recover quickly with less trauma than general open surgery. For example, the HANAROSTENT™ technology features a unique hook-shaped cross nitinol design (Figure 2) designed to provide a natural and flexible fit to the patient's anatomy, and is equipped with open ends to prevent stent displacement.

Medical nitinol lower extremity arterial stent is mainly used to treat iliac artery, femoral artery, lower extremity artery stenosis or occlusion, restore the blood supply of distal blood vessels. Self-expanding stents are currently the most commonly used stents in peripheral interventional therapy. The stent material is generally nitinol, which is most widely used in lower limb arterial stent because of its strong elasticity and deformation resistance. Lower limb muscle activity is frequent, peripheral blood vessels are subjected to forces in many directions, such as axial stretching, axial compression, twisting rotation, radial compression, bending, etc., especially the bending and folding near the joint makes the stent easy to deform, break and affect the patency of blood vessels. Generally, the greater the radial compression resistance of the stent, the smaller the resistance to axial compression, bending and torsion, and the stent can also conform to the movement of the limb under the premise of maintaining a certain diameter of the diseased blood vessel. In addition to the above vascular force considerations, the key parameters of the stent also include radial support force RRF, chronic expansion force COF, compliance, positioning accuracy, etc. The ideal stent should have as large a RRF as possible, a small COF, good compliance, and accurate positioning.

Generally, the braided bracket has better compliance and fatigue resistance than the laser engraved bracket, and the stent also presents better support when released to the standard pipe diameter, but the braided bracket is easy to shorten the displacement, and there are disadvantages of inaccurate positioning. Through a series of mechanical property design of the raw material nickel titanium wire, combined with the subsequent unique weaving and structural design, it is expected to realize a product solution that combines the advantages of the two and bring stent products that are more in line with clinical needs.

03. The guidewire core still faces the "stuck neck"

The excellent elasticity and torsional resistance of nitinol wire are also widely used as the core wire of guide wire and other pathway products. The core products of the pathway category mainly include microcatheter wire, contrast, intermediate and guide wire, sheath and blocking compression equipment. Although it is a seemingly inconspicuous wire, the access class may account for more than half of the cost of consumables for an operation. Although coronary stents have been replaced by domestic products, coronary access products are still dominated by foreign brands such as Termao, Medtronic, and Abbott.

Figure 4 Guidewire

The process design of the guidewire, including the gradation of the core wire, the spring winding and the subsequent welding and coating process, is of course the top priority. As a guide wire supported by metal, its pushability, torque, maneuverability and development are particularly important, and these properties are also closely related to the mechanical properties of nickel-titanium wire or stainless steel wire as a core wire, and the core technology of these high-precision raw material wires is almost all in Japan, the United States and other Western countries. The guidewire is morphologically like a "metal" complex, so its underlying material technology occupies a large share of it. The core reason why Japanese companies such as Terumo and Asahi can thrive on guidewires comes from their strong foundation of metal substrates. The research on metal material technology, large investment in fixed assets, high processing barriers, is a science that completely relies on time and investment accumulation, and "overtaking on curves" is very difficult.

04. Medical nitinol alloys are still monopolized by imports, and domestic substitution is underway

Industry analysts said that the phase change behavior and mechanical properties of nitinol alloy are complex, and for medical device raw materials that need to take into account dimensional accuracy and stable performance, the production is difficult, the cycle is long and the cost is high, and the number of mass production enterprises in the world is limited. Medical nitinol is a high-tech product in nitinol, with higher technical barriers to production and fewer global mass production enterprises. In China, medical nitinol manufacturers mainly include Pell Technology, Youyan Yijin, Haolu, Seth, etc., but there is still a huge gap with imported nickel-titanium raw materials, so downstream interventional device manufacturers are still based on purchasing imported nickel-titanium raw materials, and they are still stuck in this key raw material. At present, China's medical nitinol implant related terms, specification requirements, test methods and other standards are basically perfect, and the national medical expenditure capacity is continuously enhanced, which is conducive to the development of China's medical nitinol industry.