Development and trends of coronary stents

(HY-industry technical centre)

According to World Health Organization, World Health Statistics 2018 released by WHO, about 17.9 million people worldwide died of cardiovascular disease in 2016, accounting for 44% of chronic non-communicable diseases. Among them, coronary heart disease is a major disease in cardiovascular disease, and percutaneous coronary intervention is one of the current mainstream clinical therapies. As a coronary stent that is essential for percutaneous coronary intervention, it plays a decisive role in the final treatment.

Coronary heart disease and clinical treatment plan

It is because of the tireless regular pulsation of our heart that maintains the continuous flow of blood in the body’s circulatory system, thus enabling the continuous delivery of oxygen and nutrients to all parts of our body and taking away metabolic waste. It can be said that the heart It is the “engine” that maintains our physical activity. However, the continuous operation of the “engine” also requires the continuous consumption of “fuel” and the discharge of “waste”. How is the “fuel” shipped and how is the “waste” shipped? The answer is “Coronary circulation”. Among them, the “fuel” is transported through the coronary artery, and the “waste” is transported through the coronary vein. It can be seen that the smooth circulation of the coronary circulation plays a vital role in maintaining the normal pulsation of the heart. Once the coronary circulation is blocked, the heart beat will soon stop and cause sudden death.

“Coronary heart disease”, CHD, referred to as coronary heart disease, is a common type of “cardiovascular disease, CVD” that blocks coronary circulation. It refers to myocardial dysfunction and/or organic matter caused by coronary artery stenosis and insufficient blood supply. Sexual lesions. Coronary heart disease originally belonged to “rich disease”, but with the improvement of social living standards, coronary heart disease has gradually “fly into the homes of ordinary people.”

At present, the mainstream clinical treatment programs are divided into three categories: drug therapy, “Percutaneous transluminal coronary intervention, PCI” and “Coronary artery bypass grafting, CABG”.

  • Drug therapy is the basic treatment for coronary heart disease. Once the coronary heart disease is diagnosed, regardless of the degree of coronary artery stenosis, or whether the stent or surgical bypass is implanted, it is necessary to adhere to the oral pro-prognosis for a long time. However, drug therapy is a conservative treatment that only relieves symptoms, stabilizes atheromatous plaque, prevents the occurrence of acute myocardial infarction, and does not substantially solve the problem of coronary artery stenosis, and eliminates or reduces the formed atheromatous plaque.

  • Percutaneous coronary intervention (PCI) usually sends a coronary stent to the coronary artery through the radial or femoral artery. The coronary stent supports the narrow or occluded blood vessels to achieve smooth blood flow, which can effectively improve the myocardium. Blood supply significantly relieves the onset of angina pectoris, improves exercise endurance, and improves quality of life.

  • Coronary artery bypass is the use of the patient’s own Great saphenous vein or other arteries to connect the distal coronary artery to the aorta, so that the narrow coronary artery can be bypassed and blood can be directly supplied to the distal end of the myocardium to improve the myocardium. Blood supply, improve symptoms of angina and improve life treatment.

Because PCI is less invasive and can accommodate most patients with coronary heart disease, it is currently the mainstream clinical treatment for coronary artery stenosis. As an indispensable coronary stent in PCI, it plays a decisive role in the final treatment.

Coronary stent and its technical development

Since the advent of the coronary stent invention, there are still many technical problems to be overcome. The two biggest challenges are the “in-stent restenosis” caused by excessive proliferation of smooth muscle inside the vessel after surgical implantation, ISR and after stent implantation. Long-term retention of “late stent/scaffold thrombosis, LST” may exist in the body.

One of the earliest invented coronary stents was the “bare metal stent, BMS”, which was actually an ordinary wire that played a supporting role. Subsequent studies found that after treatment of coronary heart disease with bare metal stents, the stenosis rate was significantly reduced. However, after one year, about 20% to 30% of the stents had restenosis. In a common sense, the blood vessels were blocked. The reason is that after the coronary stent is opened in the blood vessel, its thin wire/beam will cause damage to the inner wall of the blood vessel. During the self-repair process, the inner wall of the blood vessel has been working in a direction to completely cover the wrapped stent, thereby easily causing excessive proliferation of the smooth muscle of the inner wall of the blood vessel. In order to solve this problem, researchers have thought of loading a polymer coating of anti-cell proliferation drugs on the outer surface of the bare metal stent. The slow release of the drug in the body can continue to inhibit the smooth muscle of the blood vessel wall for a period of time after surgery. The proliferation of cells, resulting in the “drug eluting stent, DES”. It is simple to understand that a drug-eluting stent is equivalent to a “bare metal stent + drug coating.”

The drug-eluting stent can be subdivided into two generations according to the technical stage of drug coating. The drugs used in the first-generation drug-eluting stent coating are common chemotherapeutic drugs, mainly “sirolimus”, “paclitaxel”, and the coating uses a non-degradable polymer. The drug coating does effectively alleviate restenosis in the stent, but it raises additional problems. The drug can not only effectively inhibit the proliferation of smooth muscle cells in the inner wall of blood vessels, but also effectively inhibit the proliferation of vascular endothelial cells. The endothelium has been difficult to repair, so that the stent body and the polymer coating are exposed to the bloodstream for a long time, which is easy to induce platelet aggregation and lead to thrombosis. The thrombus production is equivalent to another myocardial infarction… This second-generation drug-eluting stent mainly improves the drug coating, changing the loaded drug to a derivative of sirolimus, such as “everolimus”, “zotarolimus”, At the same time, a degradable polymer is selected as the drug-loading coating. Currently, the second-generation drug-eluting stents have the advantage of maintaining drug-eluting stents (reducing the incidence of in-stent restenosis) while also reducing safety concerns (reducing the rate of late stent thrombosis).

At present, technical improvements for drug-eluting stents are still emerging, such as further reducing the drug loading, changing the drug loading method (abandoning the polymer coating, filling the micropores in the stent wire/beam), but the vast majority Most obtained non-inferior clinical outcomes with rare and more favorable clinical outcomes.

If the drug coating on the coronary stent is called “surface” innovation, the research and development workers have also done a lot of work in the “inner”, from the initial 316L stainless steel, gradually evolved to L605 cobalt chrome, MP35N Metal materials such as cobalt-nickel alloy, nickel-titanium alloy, platinum-chromium alloy, and high-nitrogen nickel-free stainless steel. For the current stent patients, a great benefit is that they can accept “magnetic resonance imaging (MRI) examinations below 3.0 T. However, these metals are not absorbed/degradable in the body, so once implanted in the body, they will accompany the patient for a lifetime. Especially for young patients, there is a long-term foreign body in the body, which is not a good thing.

The concept of “bioresorbable vascular stent, BVS” was proposed. According to the current research and development route, the fully degradable scaffold is divided into two major genres. One is to select the degradable polymer as the scaffold matrix material, and the main one is “polylactide, PLA”; the other is to select the degradable metal, mainly magnesium (Mg). , iron (Fe), zinc (Zn) or the corresponding alloy. The benefits of fully degradable stents are obvious: the late stent fracture does not have to worry, the blood vessels can be contracted and contracted normally, the original blocked position can be re-implanted, and the medical imaging examination can be arbitrary… Beautiful, but the fully degradable stents currently under research/approved are not perfect, and there is still much room for improvement.

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