Application and Classification of Medical Adhesives

At present, medical adhesives play a very important role in clinical practice. In surgery, medical adhesives are used for local adhesion and repair of certain organs and tissues; microvascular oozing of sutures at the suture site after surgery; bone and joint jointing and positioning in orthopedic surgery; dental surgery for teeth repair. In the field of family planning, medical adhesives have unparalleled advantages over other methods: Adhesion of the vas deferens or fallopian tubes with adhesives is simple, painless, and free of side effects, and can be easily reopened if necessary.

1 The classification of medical adhesives can be divided into dental adhesives and surgical (or in-vivo) adhesives from the object and performance requirements of medical adhesives; and can be divided into soft tissue adhesives, dental adhesives, bone cements, and skins according to applications. Adhesives and so on. No matter which type of adhesive, the ideal medical adhesive should meet:
1 Safe, non-toxic, non-carcinogenic, teratogenic, mutagenic;
2 good adhesive strength;
3 at room temperature and pressure can be quickly glued with the organization;
4 good biocompatibility;
5 is aseptic and antibacterial;
6 Less heat when curing, so as not to burn tissue;
7 Difficult to form thrombi;
8 can be gradually degraded, absorbed, excreted, etc. within the tissue.

2 Application of medical adhesives
2.1 Soft Tissue Adhesives The purpose of soft tissue bonding is to promote the natural healing of the tissue itself, so it is usually only about 1 week to 10 days. But it must be able to bond quickly and coexist with moisture and fat. At present, soft tissue adhesives widely used in clinics mainly include cyanoacrylates, fibrin, and the like.
2.1.1 α-cyanoacrylate adhesive α-Cyanoacrylate is a type of instant adhesive, single-component, solvent-free, no pressurization when bonding, curing at room temperature, no special treatment after bonding. Due to its low viscosity, good spreadability, colorless and transparent after curing, it has a certain degree of heat resistance and solvent resistance, especially it can be strongly combined with relatively moist human tissues. The adhesive is based on alpha-cyanoacrylic acid alkyl ester as a main component, and a small amount of higher polyhydric alcohol ester (such as dioctyl sebacate, etc.) is added as a plasticizer, and a soluble polymer (such as polymethacrylate) is added. ) As a tackifier, hydroquinone and dioxane* as stabilizers. Since the cyano group at the α-position is a strong electron-withdrawing gene, the β-carbon atom can exhibit a strong positive charge, so that there is a great tendency to polymerize when the α-cyanoacrylate comes into contact with the anion. Anion polymerization occurs immediately upon the attack of anions. Therefore, OH ions rapidly initiate their polymerization when exposed to air or in contact with a wet surface. This is why it can act as an instant adhesive. The rate of polymerization of α-cyanoacrylates and their effect on human tissue are strongly related to the type of alkyl group.
Methyl α-cyanoacrylate has the fastest polymerization rate, but also has the greatest irritation to human tissues. As the length of the alkyl group and the number of carbon atoms in the side chain increase, the polymerization rate decreases, and the irritation decreases. The toxicological evaluation of α-cyanoacrylate was organized and its adult acute toxicity test results showed that: LD50>13g•kg-1, which is a practical non-toxic grade; the results of carcinogenic teratogenicity test: No carcinogenic teratogenicity. In addition, it also has the characteristics of decomposition and excretion in the body. Its superior performance makes it widely used in skin wounds, joining and hemostasis of the liver, kidney, spleen, lung or blood vessels. The surgical mesh anastomosis does not leave significant scars. At present, the foreign adhesives are AD/here, Cyanobond, Eastman910, and Aro nAlpla. The domestic famous 504 hemostatic glue (main glue is n-butyl α-cyanoacrylate) and 508 medical adhesive (main glue is α-cyanoacrylate).
2.1.2 Fibrin adhesive The main components are fibrinogen, thrombin, factor VIII of blood coagulation, Ca2+, aprotinin and so on. The adhesive is a physiologically functional adhesive, and the adhesion is not affected by blood coagulation disorders such as thrombocytopenia, and it is rapid, without excessive heat or pressure, without the influence of moisture at the adhesion site, and the biocompatibility is good. Moderate absorption. It is mainly used for hemostasis of soft tissue trauma, nerve and pancreatic blood vessel adhesion.

2.2 Hard Tissue Adhesives
2.2.1 Dental Adhesives The history of dental adhesives can be traced back more than half a century ago. In 1940, the first polymer used for dental repair was polymethyl methacrylate. This dental restoration adhesive is not high enough in hardness and adhesion and was quickly eliminated. In 1965, a composite adhesive with polyfunctional methacrylate as a base material and inorganic powder as a filler emerged, and its performance was greatly improved. It is still widely used in dental restorations. Dental adhesives are used in the oral cavity, and the conditions are harsh. The main reasons are: a lot of water exists; the complexity of the tooth surface properties; temperature changes; mechanical stress, etc. Therefore, the bonding and repair of teeth is much more difficult than expected. . Although people have developed a large number of products after long-term efforts, the effect is not very satisfactory.
Traditional cements belong to inorganic materials, commonly known as cements, such as zinc phosphate, and have been used for more than 100 years. This cement is divided into two parts, one is a powder and the other is a liquid, and it is mixed when used.
This cement is non-toxic and non-irritating, but it has poor adhesion to enamel and is mainly located by mechanical fitting force. Its biggest disadvantage is that the solidified cement slowly dissolves in saliva or water and its lifetime is short.
In order to overcome the drawbacks of this cement, zinc phosphate cements were modified to develop carboxylated cements. When used, 1.4-1.5 grams of powder was mixed with 1 g of liquid. During the curing process, the carboxyl group in the liquid agent is chelated with zinc oxide Zn2+ in the powder to form a cross-linked structure, resulting in an organic salt that is hardly soluble in water. At the same time, the carboxyl groups can also be chelated with Ca2+ in the dentin, so the cohesion is greatly increased. Adding tannic fluoride compound to the carboxylated cement not only improves the mechanical properties, but also has the effect of inhibiting the decay of teeth. Synthetic resin has many clinical applications in dentistry, and it mainly assumes the role of mechanical force. It is mostly acrylic esters and derivatives containing active double bonds. Polymethyl methacrylate, the earliest used in dental adhesives, was eliminated due to poor bonding. Since the 1970s, many kinds of polymethacrylate dental adhesives have been developed and their performance has been improved. Representative products include: 2-Hydroxy-3-methyl-propyl methacrylate (HNPM) and ethoxy alkyl methacrylate (Rhenyl P) synthesized by Zhong Lin et al., Bowen (R. Bowen) invented bisphenol A bis(3-methacryloxy-2-hydroxypropyl)ether (Bis GMA). These substances have both hydrophilic and hydrophobic groups in their molecules, so they have excellent adhesion properties and can be used as dental filling compound filling resins.
2.2.2 Adhesives for Orthopaedics The most common are cements, which consist of monomers, polymer particles (150-200 μm), polymerization inhibitors, accelerators, and the like. In order to facilitate X-ray imaging, contrast agent BaSO4 is sometimes added. Bone cement belongs to acrylics. Since a small amount of monomer released during the polymerization process of bone cement is likely to cause a cytotoxic reaction, the fibrous tissue at the interface between the bone cement and the bone tissue grows to form a thick combined tissue membrane with a decrease in blood pressure, so that the binding force is insufficient. problem. Porous implants and calcium phosphates are also commonly used clinically as orthopedic adhesives.

2.3 Medical Pressure Sensitive Adhesive The medical pressure sensitive adhesive consists of an elastomer and a tackifier resin. Raw materials used may be natural rubber, SIS, SBS, acrylic copolymers, silicone copolymers, polyurethanes, and the like. The earliest used in this field was rubber-based pressure-sensitive Tape. Because of the aging of natural rubber, it is often necessary to add a variety of adjuvants. It is oil-soluble. After application, it is often dissolved on the body's surface and internal fat components, causing skin irritation and decreased adhesion. SIS, SBS and other elastomer-based hot-melt pressure-sensitive adhesive tape, with colorless, transparent, non-toxic, tasteless, good adhesion, resistance to aging and other advantages, widely used in women's health products and infants diapers etc. Recently, acrylate hot melt pressure-sensitive adhesives developed by radiation cross-linking and metal cation cross-linking have been reported at home and abroad, and the adhesives have numerous advantages. At present, medical pressure-sensitive adhesives develop rapidly, and the demand is increasing day by day. An important direction for development is in the application of drug delivery and delivery systems. It can ensure that the system maintains close contact with the skin and allows the skin to penetrate the drug. The speed of the design is advanced. In addition, it can be used as a drug-loading reservoir skeleton or a viscous controlled release material, which plays an important role in directed drug application and controlled release. At present, there are many kinds of medical adhesives and they are widely used, but there are still various defects. For example, α-cyanoacrylates have a short adhesive time, but the adhesive layer has a large brittleness, and formaldehyde is unavoidably generated at the time of decomposing. Adhesives for teeth are easily affected by temperature, strength, and environmental factors, which may easily result in poor adhesion. As a biomedical adhesive, it must have good biodegradability and biocompatibility, and its decomposition products must take into account biological, chemical, clinical and physical factors. At present, the completely ideal medical adhesive has not yet been successfully developed. There are many problems to be solved, and people need to further explore and develop.