In this blog post, we will examine the changes and limitations brought by advances in stent technology to heart disease treatment, and explore the challenges that need to be addressed and future development possibilities.
To maintain the smooth functioning of the heart, often called the engine of the human body, the heart muscle must receive sufficient oxygen and nutrients. This is achieved through the supply of blood via the arteries surrounding the heart. These blood vessels supplying the heart are called coronary arteries. The heart beats approximately 100,000 times a day, pumping 7,500 liters of blood throughout the body. The role of the coronary arteries in this process is crucial, and even minor issues can immediately impact heart function.
If waste products like cholesterol and proteins build up in these coronary arteries, obstructing the smooth flow of blood, various heart diseases such as myocardial infarction and angina pectoris can occur. These heart diseases rank as the third leading cause of death among adults in Korea, following cancer and cerebrovascular disease. Particularly in modern society, the incidence of cardiovascular disease is rapidly increasing due to high-fat, high-carbohydrate diets and lack of exercise. Against this backdrop, the prevention and treatment of coronary artery disease have become even more critical challenges. With growing concern about adult diseases like diabetes and hypertension due to overconsumption, treatment methods for these conditions are of paramount interest.
In the past, even when narrowed coronary arteries were identified, there were few effective solutions. While methods like administering thrombolytic agents to dissolve accumulated debris existed, these provided only temporary relief and were not considered fundamental solutions. Even when heart surgery was necessary, factors like the patient’s physical condition and age often made surgery unfeasible. However, the invention of stents brought a new perspective to this problem.
A stent is a type of biomaterial used in treating circulatory system diseases. It is inserted into coronary arteries, cerebral vessels, etc., in the form of a metal mesh to expand the vessel and facilitate smooth blood flow. Its applications are gradually expanding beyond coronary artery disease to include peripheral vascular disease, aneurysms, and even urethral stricture treatment. The stent was first introduced in 1964 by Charles Theodore Dotter as a non-functional tube. Then, in 1986, Jacques Pue performed the first coronary stent implantation in a human. Stents are generally designed to expand elastically to reduce vascular stenosis. Based on their expansion method, they are categorized into self-expanding stents, which utilize the inherent expansion force of the metal itself, and balloon-expandable stents. Balloon-expandable stents are inserted by first placing a guidewire into the vessel, then inserting the balloon and stent. The balloon is inflated, and finally, the balloon and guidewire are removed. The inserted stent helps expand the vessel, facilitating better blood flow.
Early stents were made entirely of metal, but this led to problems. First, the vascular endothelial tissue grew through the mesh of the stents, causing restenosis. Additionally, it was discovered that the metal oxidized, causing metal ions to dissolve into the blood, altering the surrounding pH and potentially causing physical and chemical reactions with the surrounding tissue. This led to inflammation around the stents and recurrent stenosis, which became serious problems for patients. There was a possibility that ions could generate deformed nucleic acids, potentially creating carcinogenic substances. Stent thrombosis, where platelets, cholesterol, and other substances become entangled in the stent and obstruct blood flow, was also identified as a problem with metal stents. To address these issues, research into coating stents with drugs began in the mid-1990s. As research results showed drug-eluting stents to be more effective than standard metal stents, they became the mainstream choice. While there were initial concerns about the drug coating, their efficacy and safety were proven through clinical studies, leading to their widespread adoption. First-generation drug-eluting stents featured a type of biocompatible polymer coating on the stent surface to easily control the rate at which the drug was released into the body. Subsequent second-generation drug-eluting stents incorporated a polymer coating resembling the structure of human blood, resulting in a stent with enhanced stability. However, they did not completely resolve the problem of blood flow obstruction caused by stent thrombosis, an issue also present with conventional metal stents.
To address this, research is underway to modify the polymer structure on the stent surface to prevent proteins from adhering. Since proteins tend to adhere to hydrophobic surfaces and separate from hydrophilic ones, this research is focused on adding large amounts of hydrophilic substituents to the polymer. Additionally, research is underway on stents that dissolve within the body after maintaining their function for a certain period and completing their drug-eluting capabilities, replacing permanently implanted stents. These bioabsorbable stents are expected to be safer in the long term compared to conventional metal stents. Such dissolvable stents are garnering attention as a potential solution to the aforementioned stent thrombosis.
Treatment methods for heart disease are constantly evolving, with technological advances in stents at the forefront. The development of stents, which opened new horizons in heart disease treatment, remains an ongoing process. However, this progress faces numerous challenges. Since stents are used as biomaterials, they must consider biostability—related to the body’s immune response—and biocompatibility—related to the material’s properties. Biostability requires that stents do not cause fever, inflammation, antigenicity, or carcinogenic reactions after implantation. Biocompatibility requires that the stent achieves mechanical, volumetric, and biochemical integration with the surrounding tissue. Successful stent implantation necessitates patient-specific design, and a comprehensive treatment plan considering factors like genetic predisposition, lifestyle habits, and pre-existing conditions is crucial. What began as a simple metal mesh has now become a subject of research for countless scientists, feeling almost like an extension of the body itself. As quality of life improves, disease prevention and treatment methods will become a concern for everyone, and the need for safer and more effective treatments will emerge. The future development of stents, leading the way in heart disease treatment, is drawing significant attention.
