Medical polymers have become an important branch, and are widely used in medical fields centered on diagnosis and treatment. Although the uses of medical polymer materials vary widely, they have in common that the use of medical polymer materials to achieve the purpose of treatment. These materials can be fully implanted in the body, or partly implanted in the body and partially exposed to the outside; they can be placed in the cavity of the body, or they can be placed in the body and act on tissues in the body in some way. Shengjiu Mold introduces the selection of medical plastics here.
1. Material selection principle
Regardless of which type of environment the materials used should have two basic properties, namely medical functionality and biocompatibility. In order to achieve the effect of diagnosis or treatment, it is necessary to purposefully design and utilize various artificial organs and medical products. In order for the material to fully perform its medical functions, it must also have good biocompatibility.
Biocompatibility refers to the ability of a material to continuously perform the required function in vivo or in vitro within a required time. Obviously, in most cases, the criteria for material selection and the reasons for the failure of materials are generally considered in terms of biocompatibility.
Biocompatibility is a complex subject, which includes histocompatibility and blood compatibility. It describes the changes caused by materials in the physiological environment. When materials are required to come into contact with biological tissues, not only will the materials not cause the body The side reaction of the material itself can also perform its function normally, that is, biocompatibility involves the material's response to the body and the body's response to the material.
The materials make the body's reactions include short-term local reactions, systemic toxicity, allergic reactions, and long-term carcinogenic, teratogenic, mutagenic reactions, the adaptability of the organism and the process of protein adsorption in the blood. The body's reactions to materials include corrosion, degradation, abrasion, and failure of materials in the body, as well as the material's adsorption of formed components in the blood.
From the perspective of materials, the factors affecting biocompatibility are: the purity of the material, the presence or absence of bacterial contamination on the surface of the material, the surface roughness of the material, and the geometry of the material. These are just external factors. The intrinsic factors are the properties of the material itself, including surface chemistry, surface energy, surface charge, chemical stability, and chemical and physical properties of degradation products.
In summary, although medical polymer materials are in different environments and have different requirements for materials, generally speaking, medical polymer materials should have the following properties:
1) Good physical and mechanical properties, can meet the requirements of physiological functions and use environment;
2) can withstand the sterilization process without affecting its biological and mechanical properties;
3) Good forming and processing performance, easy to be processed into products of various shapes, and low cost;
4) The polymer is medical grade, the content of heavy metals is small, and the content of extractables and solubles is low;
5) Non-toxic to the body, no pyrogenic reaction, no "three causes" (carcinogenic, teratogenic, genetic mutation) effect, does not damage adjacent tissues, does not interfere with the body's immune mechanism, and does not cause surface calcification;
6) When the material is in contact with blood, it has better anticoagulant properties, does not cause blood cells to decrease after hemolysis, does not cause protein denaturation in the blood, and does not damage the blood's constituents;
(7) When the material is implanted in the body, it has sufficient chemical stability and physiological inertia, and the physical and mechanical properties do not change significantly (excluding degradation materials).
2. Selection of plastic varieties and use requirements
Artificial organ
When human organs cannot perform their functions because the patient cannot recover, modern medicine provides two ways to restore their functions: one is to perform an allogeneic organ transplant, and the other is to replace or replace the lesion with an artificial organ. Organs to compensate for all or part of their functions. Due to the difficulty of the origin of the former organs, and the problems of preservation, immunity, and rejection of transplanted organs have not yet been solved, artificial organs, as another approach, have received rapid development in the medical community in recent years.
Generally speaking, the main requirements for artificial organs made of polymer materials are: sterility, non-toxicity, no "three effects", no allergy, non-immunity; except for artificial blood vessels, it is not desirable to form fibrosis The tissue is enveloped or grown inward to prevent the collagen tissue from losing its function; if it is an implanted artificial organ, it should be close to soft tissue in terms of flexibility and physical properties of the texture structure.
Plastic for restoration and implantation
In the past 20 years, the repair and replacement of bones, joints, skin, eyes, ears, nose, teeth, periodontal tissues, alveolar ridges, jaw joints, tumor resections, etc. have improved the quality of life for thousands of people. Given that the clinical purpose of repair and replacement technology is to relieve pain and treat defects, its design goal should be to make the prosthetic material complete and functional under normal physiological conditions for a considerable period of time.
Generally speaking, plastics used as repairs and implants should be well accepted by the body and able to withstand periodic loads in aggressive environments. Therefore, these plastics should have the following properties:
(1) Good biocompatibility;
(2) Good mechanical properties;
(3) The implant has a surface state suitable for tissue attachment, including the surface void size, morphology and distribution;
(4) the stability of the material in the physiological environment is good;
(5) Ability to attach, grow and grow into tissues;
(6) The elasticity of the material matches the elasticity of the organization;
(7) Easy molding.
Plastic medical supplies mainly refer to disposable medical supplies, such as syringes, blood storage bags, blood transfusion bags, blood vessels, drainage tubes and various intubations, inspection appliances, nursing appliances, anesthesia and surgical appliances, diagnostic appliances, family planning appliances, And medical products such as bandages, coverings, pessaries, etc. Plastics used as medical supplies should mainly meet the following properties:
(1) Non-toxic, easy to sterilize and easy to store;
(2) Lightweight and not easily broken;
(3) Good mechanical strength.
3.Applicable plastic varieties and characteristics
Polyester
The polyesters used as medical plastics are mainly polyethylene terephthalate and polybutylene terephthalate. These materials are made of fibers and have high elastic strength, heat resistance, flex resistance, corrosion resistance, and water absorption. It has low sex and good biocompatibility, so its braid is widely used in medicine, such as artificial blood vessels, artificial esophagus, artificial tendon, wound covering protection material, cardiovascular repair material, etc. However, when such materials come in contact with blood, the surface of the materials needs to be treated to further improve their anticoagulant properties.
Polyurethanes
In the current medical field, polyurethanes used in artificial organs and medical devices are polyether polyurethanes. Because this type of polyurethane has a microphase separation structure, it has good anticoagulant properties, mechanical properties, elasticity, chemical stability, biocompatibility, flex resistance, fatigue resistance, water resistance, abrasion resistance and resistance. Radiation. Because of this excellent performance of polyurethane, it has been widely used in the medical field.
Polyurethanes, which are being used as medical materials, are currently being researched for rapid popularization and application in cell engineering, immunoengineering, biological testing, and bioreaction engineering. It is believed that polyurethanes with excellent characteristics can occupy an important position in these fields.
Research data show that silicon has a very close relationship with life. Organosilicon compounds have excellent bioacceptability, physiological inertness, and resistance to biological aging. They are extremely versatile medical materials. For example, silicone oil is used as a blood defoamer, silicone gel is used for the treatment of skin scars, and silicone resin is used as a surface treatment agent for medical devices.
Polyolefin
Polyolefin is another large variety of medical plastics. It mainly includes polyethylene, polypropylene, polyvinyl chloride, acrylates and their copolymers.
Because polyethylene and polypropylene have excellent physical and mechanical properties, their chemical stability, water resistance and biocompatibility are good, odorless, non-toxic, odorless, no adverse reactions implanted in the body, low density, and easy processing and molding, so It is widely used in the field of medical polymers and is the most consumed variety in medical plastics. Ultra-high molecular weight polyethylene has strong abrasion resistance, small friction coefficient, small peristaltic deformation, high chemical stability and hydrophobicity. It is an ideal material for making artificial pulp, elbow, and knuckle. High density polyethylene and polypropylene can also be used to make artificial lungs, artificial trachea, artificial larynx, artificial kidney, artificial urethra, artificial bone, orthopedic repair materials and disposable medical supplies.
Polyvinyl chloride has good chemical stability, good chemical resistance and organic solvent resistance, good mechanical and electrical properties, and poor light and heat stability. The performance of polyvinyl chloride can be improved by adding plasticizers. Plasticizers can increase the stretchability and elasticity of polyvinyl chloride, but reduce the tensile strength. In addition to the poor thermal stability of polyvinyl chloride products, it is difficult to heat and sterilize, and other properties are good. It is widely used as a blood storage bag, a blood transfusion bag, and a blood catheter, an artificial peritoneum, an artificial urethra, a bag-type artificial lung, a heart catheter, and an artificial heart.
Polymethyl methacrylate is light, has high mechanical strength, good moisture resistance, and can be used under humid conditions for a long time. It has certain stability to water-soluble inorganic salts, alkalis and some dilute acids. It has good resistance to biological aging and biocompatibility, excellent optical properties and high light transmittance. Medically used as skull repair materials, artificial bones, artificial joints, thoracic cavity filling materials, human upper joint bone cement, especially in the application of dentures and trays. The modified hydrophilic polymethyl methacrylate is also widely used in ophthalmology, burn dressings, and drug microcapsules.
Fluoroplastic
The fluoroplastics used in medicine are mainly polytetrafluoroethylene. Polytetrafluoroethylene is a highly crystalline polymer with high density, low friction coefficient, excellent chemical stability, good biocompatibility and anticoagulant properties, does not decompose, has no adverse reactions in the human body, and has excellent heat resistance. , Can be used continuously above 200 ℃, can use high temperature disinfection.
Therefore, polytetrafluoroethylene is widely used in medicine, such as artificial heart, lung, blood vessel, heart valve, various tubular organs, such as artificial trachea, esophagus, bile duct, urethra and artificial peritoneum, cerebral dura mater and artificial skin.
4. Application examples of artificial blood vessels for transplantation
A vascular prosthesis is a flexible, tubular prosthesis that replaces a patient's weakened or blocked blood flow and bypass bypass caused by atherosclerosis or other rare degenerative diseases.
For artificial blood vessels, the materials used must have the following basic requirements:
(1) The material should have sufficient mechanical strength to withstand the pulse of blood pressure for a long time in absolute safety;
(2) the material has good biocompatibility and anticoagulation;
(3) the material has the ability to resist the attachment of bacteria and prevent infection;
(4) The flexibility and elasticity of the material are matched with the human diabetic blood vessels;
(5) the material is porous to facilitate the growth of endothelial cells;
(6) Easy to operate.
Generally speaking, polyester, Teflon or polyurethane materials can be used for medical artificial blood vessels. Polyester artificial blood vessels are knitted or plain woven with polymer multi-fiber filaments that are melt extruded with a diameter of a few microns. This fabric is extremely strong, has good tear resistance, and is easy for the surgeon to sew and operate. Uncoated artificial blood vessels can be safely sterilized by high-pressure steam, ethylene oxide, and gamma rays. Significant changes have taken place. Polyester artificial blood vessels are currently mainly used to replace aorta or hip arteries, and have reliability, durability and patency.
Teflon is a hydrophobic, chemically inert polymer. It needs to be made into a porous, flexible tube shape for application in artificial blood vessels. Because the material is very soft, it is easy to sew and handle, and can withstand a pressure of 0.48 MPa. Its anticoagulant performance is better than polyester, and it is generally used for small diameter blood vessels.
Polyurethane has high elasticity, high modulus, and good blood compatibility. As a prosthesis material, it can be adapted to the host artery. Although polyurethane has a certain degree of hydrolyzability and calcification can occur inside and outside the material, it is still an ideal material for small diameter artificial blood vessels.
Yuhuan Shengjiu Mould Co., Ltd. specializes in manufacturing and supplying Laboratory Plastic Ware Mould in China. And provide customers with a complete mold configuration program to help and improve the production of disposable medical equipment. Product details are welcome to visit: https://www.medicalmould.net