The human blood circulatory system includes three parts: blood, blood vessels, and heart. The blood vessels serve as bridges to connect organs and the heart in series, and provide channels for the flow of blood to transport nutrients to various parts of the body. Therefore, they are often collectively referred to as the cardiovascular system. Lesions that occur in these areas are called cardiovascular diseases. Cardiovascular disease is the most common disease threatening human health, and its incidence ranks first among various diseases in the world. At present, there are about 2.6 million deaths due to cardiovascular and cerebrovascular diseases in my country each year, with an average of about 300 deaths per hour. As the population of our country enters an aging population, the incidence, recurrence and mortality of these diseases will continue to rise. It has caused a heavy economic and spiritual burden to the society and family.
The causes of cardiovascular diseases are mainly divided into two categories:
1. The pathological changes of blood vessel function caused by physiological aging of human organs.
For example, atherosclerosis leads to narrowing and occlusion of arteries, strokes caused by carotid atherosclerosis, heart disease caused by coronary atherosclerosis, etc. These diseases mostly occur in the elderly;
2. Vascular disease caused by human tissue damage or disease.
For example, cutting with sharp tools leads to damage and rupture of arteries and veins, renal aortic aneurysm, iliac aneurysm, and vasodilation caused by expansion of descending thoracic aortic aneurysm. When blood vessels cannot function normally due to arteriosclerosis, aging or damage, surgical procedures such as transplantation, bypass, or intervention are needed to use blood vessel substitutes for treatment.
An ideal artificial blood vessel material, as a permanent implant for the human body, must first have good biocompatibility, including:
1. Can not cause abnormal immunity, rejection and allergic reactions;
2. No adverse reaction to cell growth function, no teratogenic or twinning effect;
3. It is non-toxic, does not damage neighboring tissues, does not induce tumors, does not cause coagulation, hemolysis, denaturation of blood proteins, and damage platelets, etc.;
4. It is chemically inert, does not cause denaturation due to the influence of blood and body fluids, and has no abnormal biodegradation leading to loss of strength;
5. After implantation, the function of the material will not be damaged, will not be affected by biological influence and aging, can withstand physical changes caused by exercise, and will not absorb sediment.
6. Secondly, in order to be able to withstand the force received during and after implantation, ensure the long-term patency of blood vessels, and withstand the periodic pulsating pressure caused by systolic and diastolic pressure, the graft should also have Corresponding mechanical properties, sufficient fatigue resistance, and the artificial blood vessel should have similar with the replaced blood vessel.
The anastomosis between the artificial blood vessel and the host blood vessel is made by sutures. Therefore, the artificial blood vessel must have a certain seam strength to ensure that the edge can withstand the tensile load of the surgical thread during the transplantation operation, and it will neither break nor loosen.
The finished product of artificial blood vessel is required to have various shapes and sizes, can be sterilized, and is easy to handle and suture during surgery. Its size and shape are required to be stable, resistant to traction, bending and compression, and can quickly return to its original shape after being deformed by external force. The outer surface of the artificial blood vessel should have a certain degree of roughness to facilitate the attachment and growth of surrounding cells. At the same time, the wall of the tube should have a suitable porosity, which can not only prevent blood penetration, but also allow small molecules to pass through.
In summary, for artificial blood vessels. The materials used must have the following basic requirements:
(1) The material should have sufficient mechanical strength and be absolutely safe to withstand the pulsation of blood pressure for a long time;
(2) The material has good biocompatibility and anticoagulant properties;
(3) The material has the ability to resist bacterial adhesion and prevent infection;
(4) The flexibility and elasticity of the material match the human blood vessel;
(5) The material is porous to facilitate the growth of endothelial cells;
(6) Easy operation.
At present, the artificial blood vessel materials that have been used in clinical medicine mainly include polyester, polytetrafluoroethylene, polyurethane and natural silk. Among them, the pure natural mulberry silk material is not stable enough due to its spiral shrinkage, which is easy to cause vascular collapse and poor shape retention. It is no longer used alone in clinical practice.
When polyester is used as a biomedical material, its biomechanical properties, chemical stability and biocompatibility are better than other polymer materials, but its blood compatibility is poor, the surface is easy to coagulate, and its decomposability is poor, and it is difficult to be completely decomposed and digested by the body. absorb. The polyester material has a smooth surface, tightly arranged internal molecules, good wear resistance and light resistance, acid and alkali corrosion resistance, high strength, good elasticity, heat resistance and thermal stability are better than other synthetic fibers. Due to the symmetrical molecular structure and high crystallinity, there is no high-polarity group in the macromolecular structure, so the hydrophilicity and moisture absorption are poor. Although the low-hydrophilic structure has high permeability to human body fluids, it can limit the direction of tissue fluid. The material penetrates inside, but it is easy to cause adverse reactions such as coagulation and thrombosis.
When Dacron artificial blood vessels come into contact with blood, in addition to the adsorption of soluble proteins by the tube wall, the adhesion of platelets, the formation of clots and the intervention of fibrin will become a new interface in the graft material cavity.
This special blood flow interface is not only not conducive to tissue healing, it is also a fluid surface prone to thrombosis, and the risk of long-term use at low blood flow rates is higher. Therefore, the polyester artificial blood vessel is suitable for the replacement of large blood vessels, but it is not the best material for replacing or replacing small blood vessels in the body.
PTFE has excellent chemical resistance, high and low temperature resistance, aging resistance, low friction, dielectric properties, non-stick properties, and physiological inertness, making it used in many fields such as chemical industry, machinery, electrical, construction, and medical treatment. Become an indispensable special material. Due to its excellent biocompatibility, it rarely produces blood clots and is suitable for implanting in human artificial blood vessels. They can be combined with human tissues for a long time, have good blood permeability, and have a microporous structure that allows natural tissues to grow and grow. Cell metabolism. In the middle and small diameter artificial blood vessels, in the past, the integrally molded expanded polytetrafluoroethylene (ePTFE) was mostly used.
Polyurethane (PU) materials have attracted much attention in recent years because they have good compliance and elasticity, and have excellent anti-thrombotic properties. Compared with ePTFE blood vessels, experiments show that PU blood vessels realize endothelialization in a shorter time, and the thickness of the neointima is obviously thicker than ePTFE blood vessels. Polyurethane has high elasticity, high modulus and good blood compatibility. As a prosthetic material, it can be compatible with the host artery. Although polyurethane has a certain degree of hydrolysis, and calcification may occur inside and outside the material, which affects elasticity, it is still an ideal material for small-diameter artificial blood vessels.