Cyanoacrylate adhesives

Cyanoacrylate tissue adhesives are pale yellow or transparent liquid monomers that polymerize rapidly through an anionic mechanism in the presence of weak bases such as water, alcohol, or amino groups (from proteins) that come in contact with the tissue surfaces. It is an exothermic reaction that yields a strong flexible film that bonds the wound edges.

Methylcyanoacrylate was the first material tested but was ruled out because of its rapid in vivo degradation. Longer-chain alkylcyanoacrylates (Figure 9.3) such as n -butyl cyanoacrylate and octylcyanoacrylate were developed to avoid this problem. Butyl cyanoacrylates have poor tensile strength, a circumstance that limits their use to small lacerations and incisions. The development of a longer-chain (octylcyanoacrylate) improved the performance of these biomaterials as adhesives for wound repair.

Cyanoacrylates in contact with living tissues in a moist environment polymerize rapidly to create a thin elastic film of high tensile resistance which ch3

METHYLCYANOACRYLATE

H2 H2

n-BUTYLCYANOACRYLATE

CC II H

H2 C

H2 C

H2 C

C H2

C H2

H2 C

C H2

VCH3

OCTYLCYANOACRYLATE

Figure 9.3. Cyanoacrylates used in biological glues guarantees firm adherence, stronger than that obtained with fibrin glues. Cyanoacrylates provide a flexible, water-resistant coating that is not impaired by blood or organic fluids and that also inhibits microbial growth. Easy to apply, these adhesives do not require the use of local anesthetics. The polymerization time varies as a function of the type of tissue with which the glue comes in contact and the nature of the fluids present. Polymerization starts after 1-2 s and takes about 1-1.5 min. Some authors prefer the superior physical properties of octylcyanoacrylate compared with butyl cyanoacrylate to repair facial lacerations [17]. As advantages, cyanoacrylates slough off spontaneously within 5-10 days, eliminating the need for suture removal.

Thus, it can be said that they are more cost-effective than sutures or staples because of the reduced need for follow-up and practitioner time [17-19].

Some disadvantages of the cyanoacrylates are the decreased tensile strength and the requirement that the areas to be treated be dry. Moreover, the application of an excessive amount of product, in addition to prolonging setting time, increases the exothermal reaction associated with polymerization, with possible thermal damage to the tissue. Thus, the glue should never be applied inside a wound over mucous membranes. It should also be avoided over areas of frequent friction, such as hands or feet, because of the risk of detachment of the adhesive.

Singer and Thode reviewed the literature on octylcyanoacrylates and reported that the current generation of octylcyanoacrylates (high-viscosity formulations) can be used successfully in a wide variety of clinical and surgical settings for multiple types of wounds involving most of the surface of the human body [20]. In an experimental study in rats, using another formulation, ethyl-2-cyanoacrylate, the histopathological analysis of vascular, myocardial, and pulmonary tissue sections demonstrated that there were no significant differences between sutures and ethyl-2-cyanoacrylate in controlling hemorrhage and air leakage [21].

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