Cyanoacrylate applications

Fig. 1. Cyanoacrylate application to close a skin incision (aiTow points to adhesive).

Cyanoacrylates would normally have a relatively short open time as they are very sensitive to surface moisture and to a lesser extent atmospheric moisture. In most cyanoacrylate applications, the joint shonld be closed within a few seconds and certainly not more than a few minutes. 

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In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Because of their ability to bond a wide variety of substrates, cyanoacrylate instant adhesives are now produced in multi-ton quantities for both industrial and consumer applications [3]. 

Ethyl cyanoacrylate is the monomer which is most widely used in both consumer and industrial applications, because of its combination of fast cure speed and ease of manufacture. 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

The homopolymers, which are formed from alkyl cyanoacrylate monomers, are inherently brittle. For applications which require a toughened adhesive, rubbers or elastomers can be added to improve toughness, without a substantial loss of adhesion. The rubbers and elastomers which have been used for toughening, include ethylene/acrylate copolymers, acrylonitrile/butadiene/styrene (ABS) copolymers, and methacrylate/butadiene/styrene (MBS) copolymers. In general, the toughening agents are incorporated into the adhesive at 5-20 wt.% of the monomer. 

At present there is only one commercially available tissue adhesive with approved on-label indications for skin closure. 2-Octyl-cyanoacrylate (Dermabond, Ethicon, Inc., Somerville, NJ) is presently indicated for skin closure in wounds which are not under extreme tension. This tissue adhesive is approved for topical skin application only. It is not indicated for internal use. The material is useful in closing traumatic skin lacerations [4,5] after wounds have been thoroughly cleaned as well as for minimally invasive surgical incisions and even larger surgical incisions in elective cases. The cyanoacrylate is applied while the skin... 

Cyanoacrylates. Fast curing cyanoacrylates are used for holding shims in place during assembly of components and other applications where fast cure is useful. 

Reactive adhesives Reactive adhesives are either low molecular weight polymers or monomers that solidify by polymerization and/or cross-linking reactions after application. Cyanoacrylates, phenolics, silicon rubbers, and epoxies are examples of this type of adhesive. Plywood is formed from impregnation of thin sheets of wood with resin, with the impregnation occurring after the resin is placed between the wooden sheets. 

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The largest application of methyl and ethyl cyanoacetale is the production of the cyanoacrylate adhesives widely used within the ear and electronic industries. 

Formulations of 2-octyl cyanoacrylate (Liquid Bandage12), polyvinyl acetate, poly-butryal were successful in rat studies, however, a spray-on bandage is recommended for ease-of-use and, especially for one-hand application such as with a pump-type spray bottle. Aerosol cans are under pressure and may not be allowed to be carried on aircraft. 

Both of these formulations can be applied to tissue by pouring or spraying on wounds. Both formulations are particularly conducive for pressure-spray or pump-spray applications. They both form continuous impermeable films over moist tissue, are water-proof after application, have long shelf stability, and are biocompatible. The siloxane-based material appears to have no stinging effect on excised tissue, and it does possess a very low surface energy that is difficult for environmental contamination and bacteria to attach. These materials are inexpensive compared to cyanoacrylates. 

Cyanoacrylate is not usable for in-dwelling applications, because the by-products of decomposition within the body are harmful to healthy tissue. Therefore, this material, although useful for sealing skin incisions with sutures, is not a viable candidate for repairing internal organs or vessels. 

The outermost skin layer, the stratum corneum (SC), consists of corneocytes embedded in lipid layers and represents the main barrier for skin penetration of xenobiotics. Its thickness in healthy adults may vary from 5 to 20 /um, except in the palm and sole where it is much thicker. SC can be removed sequentially by repeated application of appropriate adhesive tapes.1 This technique, commonly known as SC tape stripping, is a relatively noninvasive method to investigate the structure, properties, and functions of SC in vivo2 and is the most frequently used for such purposes. Other techniques to remove SC are skin surface biopsy using cyanoacrylate strips and skin scraping. 

Many cyanoacrylates give rather rigid bonds which may in consequence be brittle and not able to resist peeling forces. However, in recent years more flexible toughened grades have been developed for applications in which resistance to peeling is required. 

The application of UV absorbers, i.e. compounds absorbing the harmful solar radiation, represents an effective solution of the problem (Rabek, 1990). The absorbed radiation is deactivated by intramolecular radiative and radiationless processes. The ideal UV absorber is expected to absorb all terrestrial UV-A and UV-B radiation but no radiation having wavelengths higher than 400 nm. Different classes of commercialized UV absorbers fulfil requirements on effective plastics protection. A group of UV absorbers acting by excited state intramolecular proton transfer (ESIPT) mechanism (Pospfsil and Nespurek, 1997) includes phenolic derivatives of benzophenone (37), various benzotriazoles, such as 38 or 39, and 1,3,5-triazine 40. Non-phenolic UV absorbers are represented by oxamide 41 and a-cyanoacrylate 42. 

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