Bioinert materials refer to a class of biomedical materials that can remain stable in the biological environment and have no or only weak chemical reactions, mainly inert bioceramics and medical metals and alloys. Since there are no completely inert materials in reality, bioinert materials basically do not react chemically in the body. The combination between them and tissues is mainly a mechanical connection formed by the growth of tissues into their rough and uneven surfaces, that is, morphological combination.

Classification

Oxide ceramics (A1203, zQ), Si3N4 ceramics, glass ceramics, medical carbon materials, medical metal materials, etc. Due to their biological inertness, these materials generally do not change in shape or structure after being implanted in the human body, and their mechanical properties are stable. Therefore, these materials are currently the most widely used materials in human body load-bearing materials.

Inert polymers

Some materials that need to exist in the body for a long time hope to be biologically inert, that is, the materials are stable in the body and do not produce harmful reactions to the host. Non-degradable medical polymer materials are mainly polyurethane, silicone rubber, polyethylene acrylate, etc., which are widely used in the repair and manufacture of soft and hard tissues and organs of the human body such as ligaments, tendons, skin, blood vessels, artificial organs, bones and teeth, adhesives, material coatings, artificial lenses, etc. Its characteristics are that most of them have no biological activity, are not easy to firmly bind to tissues, and are prone to toxicity, allergic reactions, etc. Common bio-inert polymers are as follows: Polyethylene (PE) Polyethylene is a chain-like non-polar molecule, which is extremely stable to chemical agents and is acid and alkali resistant. Polyethylene is very tough, has certain flexibility and high insulation. Because polyethylene has excellent physical and mechanical properties, its chemical stability, water resistance and biocompatibility are good, it is tasteless, non-toxic, odorless, and has no adverse reactions when implanted in the body. Therefore, it is widely used in the field of medical polymers and is the largest variety of medical polymer consumption. Ultra-high molecular weight polyethylene has strong wear resistance, small friction coefficient, small creep deformation, high chemical stability and hydrophobicity, and is an ideal material for making artificial hip, elbow and finger joints. High-density polyethylene can also be used as artificial lungs, artificial trachea, artificial larynx, artificial kidney, artificial urethra, artificial bone, orthopedic repair materials and disposable medical supplies.

Polyvinyl chloride (PVC)

The degree of polymerization of polyvinyl chloride is about 590.1500 (BP number average molecular weight is about 36,000-93,000), with good chemical stability, good resistance to chemicals and organic solvents, and stable to acids (hydrochloric acid of any concentration, 90% sulfuric acid, dilute nitric acid, alkali below 20%) and salts at room temperature. It is soluble in solvents such as dimethylformamide, cyclohexanone, and tetrahydrofuran, with good mechanical and electrical properties, poor light and heat stability, a softening point of 80буC, and begins to decompose and discolor at 130буC, precipitating hydrogen chloride. Polyvinyl chloride products are divided into two categories: soft products and hard products. The properties of polyvinyl chloride can be improved by adding plasticizers. Commonly used plasticizers include dibutyl phthalate, dioctyl phthalate, epoxy soybean oil and tricresyl phosphate. Plasticizers can increase the stretchability and elasticity of polyvinyl chloride, but reduce the tensile strength.

Since the 21st century, it has been found that monomer vinyl chloride is carcinogenic. Many countries stipulate that the vinyl chloride residue in polyvinyl chloride products for medical and food packaging must be less than 1 ppm. Polyvinyl chloride soft products with a dissolution amount of less than 0.05 ppm plasticizer must consider the hemolysis and toxicity of the plasticizer used when used as implants and in the production of blood transfusion, infusion bags and blood storage bags, and must be strictly screened according to material safety conditions. Polyvinyl chloride products have good properties except that their thermal stability is poor and difficult to heat and boil for disinfection. A large number of them are used for blood storage and blood transfusion bags, as well as for making infusion tubes, blood transfusion tubes, extracorporeal circulation devices, artificial peritoneum, artificial urethra, bag-type artificial lung barrier (combination bag) and heart. Acrylic resin Acrylic resin is made by polymerization or copolymerization of acrylate, methacrylate or substituted acrylate. The characteristics of acrylic resin are biological inertness, good tissue compatibility, no three hazards (carcinogenicity, teratogenicity, mutagenicity), non-toxicity, easy sterilization, good mechanical strength, strong bonding force, and room temperature curing. It is widely used in the fields of biomedicine and medical health. The most commonly used acrylic resin is polymethyl methacrylate (PMMA), commonly known as plexiglass, which has good biocompatibility, aging resistance, and high mechanical strength. It is used in medicine for skull repair materials, artificial bones, artificial joints, chest filling materials, adhesives for artificial joints and bone materials, as well as dentures and dental trays. Modified hydrophilic PMMA is used in ophthalmology, burn dressings, microcapsules, etc.

Polytetrafluoroethylene

Polytetrafluoroethylene is known as the "King of Plastics" and is obtained by polymerization of tetrafluoroethylene monomers: the initiator is mostly inorganic peroxides, and the polymerization pressure is divided into high-pressure method and low-pressure method.

Polytetrafluoroethylene is the best high-temperature resistant plastic with a crystal melting point of up to 327буC. It is almost completely chemically inert and has self-lubricating or non-stickiness. It is not easily infiltrated by tissue fluid and has excellent chemical resistance, electrical properties, surface properties and physical and mechanical properties. It is not easy to coagulate and has little tissue reaction after implantation. It is widely used in artificial organs and tissue repair materials, medical sutures, medical device materials, etc. Such as artificial ureters, bile ducts, trachea, larynx, ligaments and tendons, esophageal dilators, artificial blood, artificial heart valves, artificial blood vessels, heart valve suture rings, blood-compatible velvet, pulmonary artery and ventricular septum defect patches. Mandibular, hip joint materials, orbital bone repair, rhinoplasty materials

Expanded polytetrafluoroethylene is a special polytetrafluoroethylene material made of polytetrafluoroethylene resin through special processing methods such as stretching. It is white, elastic and flexible, and has a mesh structure formed by microfiber connection. These microfibers form countless pores, so that expanded PTFE can be bent arbitrarily (over 360бу), has good blood compatibility, and is resistant to biological aging. It is used to make artificial blood vessels, heart patches and other medical products. From a medical point of view, it is currently the most ideal biological tissue substitute. Due to its good biocompatibility and unique microporous structure, it is non-toxic, non-carcinogenic, non-allergenic and other side effects, and human tissue cells and blood vessels can grow into its micropores to form tissue connections, just like autologous tissues, and the effect of rhinoplasty is very satisfactory.

Limitations of polytetrafluoroethylene application: expensive; micropores on the surface of the expanded body can hide bacteria, some of which are conditional pathogens and will not cause infection under normal circumstances. However, due to its porous nature, once the infection occurs, it will be difficult to control. Generally, it can only be removed, and the removal operation is difficult.

Organic silicon polymer

Since 2000, organic silicon polymer materials have been widely used in medicine, such as organic silicon rubber, organic silicon quaternary ammonium salt antibacterial and antifungal agents, etc. Organic silicon refers to compounds composed of alternating Si-O bonds, among which the most important is a polymer compound with (SiR2-O-SiR2-O)n as the main chain and organic groups on the side chain. Due to its unique chemical structure, it has many excellent physical and chemical properties and biocompatibility.

Due to the characteristics of organic silicon being non-toxic, odorless, biocompatible, non-skin sensitizing, biologically inert, high and low temperature resistant, breathable, unique solution permeability and stable physical and chemical properties, it has made great progress in the medical field.

Silicone rubber is a major category of medical silicone polymer materials. It is non-toxic, non-corrosive, does not cause coagulation, is non-carcinogenic, and non-sensitizing. It does not cause inflammation and allergic reactions in surrounding tissues after being injected or used in the human body. It has good compatibility with the human body and can withstand harsh disinfection conditions. It is an ideal medical polymer material. Silicone rubber products do not lose their elasticity and tensile strength when implanted in the human body for a long time. For example, artificial valves and artificial hearts are required not to cause thrombosis; artificial blood vessels must have fine mesh; when dialysis is performed on artificial kidneys, small molecules such as urea must be able to pass through, but not macromolecules such as serum proteins. Silicone rubber can fully meet the above requirements. From internal medicine, surgery to ENT, gynecology, from artificial organs to medical materials, such as intravenous catheters, catheters, artificial heart-lung machine pump tubes, and various blood transfusion and infusion tubes,

most are made of silicone rubber.

Silicone oil dimethyl silicone oil is widely used in medical treatment due to its physiological inertness and good defoaming performance. Silicone blood defoaming agent has the advantages of non-toxicity, non-destructiveness to blood, fast and thorough defoaming, etc. It is used to treat artificial blood circulation devices and blood transfusion instruments, equipment, and utensils. It can eliminate oxygen bubbles in extracorporeal blood circulation to ensure normal blood circulation and the implementation of cardiopulmonary surgery.

Polyacrylamide

PAM can be divided into non-ionic, anionic and cationic types according to the electrical properties of its groups in aqueous solution. However, no matter which type of PAM, it is a homopolymer or copolymer formed by free radical polymerization of acrylamide (AM) monomer. Its synthesis methods include homogeneous aqueous solution polymerization, reverse emulsion polymerization and reverse suspension polymerization. According to the way AM free radicals are initiated, it can be divided into chemical initiation polymerization, radiation polymerization and UV light polymerization.

In medicine, acrylamide hydrogel can be used for controlled release of drugs and enzyme embedding, protein electrophoresis (testing), artificial organ materials and implants (artificial lenses, artificial corneas, artificial cartilages, urethral prostheses, soft tissue substitutes).

Polyurethane (PU)

Polyurethane (PU) is one of the most ideal materials in the medical field. Generally, diisocyanates react with diols, diamines or dicarboxylic acids containing active hydrogen, polyester or polyether macromolecular diols are used as raw materials to react with different diisocyanates, and different small molecule diols, diamines, and alcohol amines are used as chain extenders. By controlling the reaction conditions, materials with a wide range of properties can be obtained according to design requirements.

Polyurethane elastomers have good anti-coagulation properties, and have good physical and mechanical properties such as wear resistance, elasticity, and flex resistance. It has become one of the most widely studied and applied anti-coagulation polymer materials. In the past thirty years, people have made various improvements and modifications to the classic polyurethane elastomer (block polyurethane), and developed on this basis, forming various types of anticoagulant polyurethane materials such as grafted polyurethane, ionic polyurethane and polyurethane with anticoagulant active substances on the surface.

From a structural point of view, the carbamate group (-CONH-) of polyurethane can be regarded as a combination of phthalamide (-NH-) and carbonate (-CO-), so it has unique properties. It has high hardness and good elasticity, as well as outstanding wear resistance, tear resistance, radiation resistance, high strength and chemical stability.

The medical application of polyurethane has achieved many results, and a series of commercial polyether polyurethane biomedical materials with practical value have been formed. The main applications are as follows:

(1) Artificial organ membranes and medical devices. Polyether block polyurethane has a dominant position in medical elastomers because of its excellent hydrolytic stability and blood compatibility, and its strength is better than silicone rubber. Such as blood pumps (artificial hearts) and artificial blood vessels, heart assist devices, heart bypass, artificial kidney dialysis membranes, artificial ventricles, artificial heart valves, diagnostic and therapeutic catheters, pacemakers, etc.

(2) Artificial skin and prostheses. Polyurethane soft foam is not only elastic but also breathable, suitable for making artificial skin, which can promote the growth of human skin. In addition, polyurethane has excellent flexibility and is an ideal material for making the most advanced modern lightweight and durable prostheses.

(3) Fracture reduction and fixation materials. Human fractures need to be fixed after reduction treatment. In the past, plaster bandages were used, but because plaster is heavy, low in strength, poor in breathability, not water-resistant, irritating to the skin, and not transparent to x-rays, it brings many inconveniences to doctors and patients. Orthopedic bandages made of polyurethane are strong, lightweight, have good air permeability and water resistance, fast curing speed, easy operation, good X-ray transmittance, and can be repositioned and fixed under X-ray irradiation. The repositioning and fixation and fracture healing can be checked at any time without removing the bandage, which improves the treatment effect.

(4) Polyurethane soft tissue adhesives. ж┴-Cyanoacrylate soft tissue adhesives are highly toxic. Since 2000, rapid curing polyurethane soft tissue adhesives have made great progress and have been used in cardiovascular surgical coatings to prevent suture bleeding. A fluorinated aromatic isocyanate polyurethane adhesive can be cured within 2 minutes and is used for hemostasis of liver lacerations and skin incision bonding.

(5) Degradable polyurethane and polyurethane hydrogels Degradable polyurethanes based on oxalic acid ester are used to treat pediatric aneurysms and as medical adhesives. Polyurethanes based on polycaprolactone or natural products are also easily hydrolyzed and enzymatically hydrolyzed in the human body. The water content of polyurethane hydrogels prepared with hydrophilic polyethylene glycol is as high as 67%, and some can reach more than 80%.

In addition, polyurethane can also be used as artificial esophagus, air bag, membrane lung cannula for the treatment of patients with acute respiratory insufficiency, and subclavian double-lumen cannula for dialysis.

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