# Artificial Heart Valve Scaffold Based on Electrospun PCL/PU Three-Layer Composite Fibers
## 1 Introduction  
Now, heart valve disease has gradually become a prevalent heart disease. According to statistics, about 209 million people worldwide suffer from heart valve disease [1]. In the United States, approximately 20,000 people die directly from valve dysfunction and 60,000 valve replacements are performed each year [2]. According to the 2023 Summary of Chinese Cardiovascular Health and Disease Report, there are currently 330 million cardiovascular patients in China [3]. Usually, valvular disease is more common in the elderly, because age has a great impact on the incidence rate of valvular disease. It is expected that the number of valvular diseases will gradually increase with the further aging of the Chinese population in the future. Valvular heart disease is a kind of structural heart disease that affects the quality of life of patients and can be life-threatening in severe cases. In traditional treatment, mechanical valves, biogenic valves, and even allogeneic valves are often used to replace the diseased heart valves [4]. Each of these methods has its own advantages and disadvantages. The mainstream materials for mechanical heart valves are pyrolytic carbon, titanium alloys, stainless steel, etc. [5]. Mechanical valve preparation is simple and inexpensive, but its disadvantages are also obvious, such as poor blood compatibility [6]. In order to reduce the risk of thrombosis, patients need to take anticoagulant drugs for a long time, which can affect the body's coagulation function and increase the risk of bleeding, such as gum bleeding, skin bruising, etc. In severe cases, cerebral hemorrhage may even occur [7]. Bioderived heart valves have good biocompatibility and excellent mechanical properties, but the disadvantage is that they have a low service life [8]. The characteristics of the biomaterial itself determine that under long-term cardiac hemodynamic pressure, tissue degradation, calcification, and other phenomena will gradually occur, and allografts such as porcine heart valves or bovinepericardium last only 10-15 years [9]. Allogeneic transplantation lacks a stable source, and organ transplantation requires more prevention of immune rejection. So, it is particularly important to develop a new and efficient method for treating heart valves. The tissue-engineered heart valve has been a promising heart valve in recent years. It can mimic the characteristics of the original tissue and has the ability to grow, repair, and remodel in vivo. Of course, many methods have been invented to prepare tissue-engineered heart valves. Techniques such as weaving and 3D printing can be applied in this direction [10]. However, compared with these methods, we need a fast, fine, and tunable structure preparation method [11], which shows great significance in the research and development of new treatment strategies for heart valve diseases. As a typical technology, electrospinning is a method of using electrostatic force to stretch polymer solutions or melts into nanofibers. In the electrospinning process, polymer solutions or melts form Taylor cones under the action of a high-voltage electric field. When the electric field force overcomes the surface tension of the solution, the polymer solution or melt is ejected from the tip of the Taylor cone, and then ultrathin fibers are obtained. Electrospinning technology has the advantages of a simple preparation process, low cost, small fiber diameter, and large specific surface area; therefore, it is widely used in biomedical and tissue engineering fields [12]. Due to the smaller diameter of nanofibers, it can support and attach cells and can be used to simulate the structure and biological function of the natural extracellular matrix. Nanofibers show attractive potential for tissue and organ repair because most tissues and organs in the human body have similar morphology and structure to nanofibers. They can also realize the functions of bionic design and drug delivery.