Biological adhesives

Abstract

The need to effectively manage very important problems like hemostasis and tissue sealing has had a strong influence on the development of modern surgical techniques. A group of chemical products (natural and synthetic materials) known as sealants, glues, or tissue adhesives has been developed to reduce bleeding and promote tissue sealing. For example, it has been shown that the use of a cyanoacrylate adhesive contains the bleeding from gastric varices with a higher rate of success and a lower rate of mortality than the administration of ethanolamine oleate, a sclerosing agent [1]. In blepharoplasty, an eye surgery technique, octyl-2-cyanoacrylate, a cyanoacrylate approved by the U.S. Food and Drug Administration (FDA) has been used with excellent results in terms of quality when compared with the use of sutures [2]. Three types of adhesives have been utilized in cardiovascular surgery: fibrin glues, which are resorbable but do not provide strong adhesion and require rapid healing of the tissue; enbucrilates, which have been used successfully for left ventricular free wall rupture [3] but produce a marked exothermic reaction and are unstable; and biological glues. The latter have been employed to bond pericardial patches and reinforce sutures. In aortic dissection, a very serious clinical situation, a bioadhesive is used to bond the proximal and the distal edges of the dissected aorta, which are then sutured. The mechanical behavior of the bioadhesive in this clinical situation has yet to be characterized and the association of sutures appears to be indispensable [4]. Chemically, tissue glues and adhesives can be defined as any substance with characteristics that allow for polymerization [1]. This chemical polymerization must also hold tissues together. Glues and adhesives are materials whose attachment to a surface principally involves molecular attraction. Certain logical features are required of surgical glues. First of all, the chemical substance employed as the adhesive must remain present and preserve its chemical characteristics long enough for the tissues to bond well without any additional supports and for the necessary time. Evidently, a rapid degradation of the adhesive before the healing process is completed would be counterproductive. The degradation of the adhesive should always occur after that time. Some authors describe the mechanism of action of a good adhesive as a result of two different physical forces. The glue is usually spread on each of two objects; it is held to them by adhesion involving intermolecular forces between the two dissimilar materials. With an effective glue, adhesion and cohesion are about as strong as the internal cohesion of the objects to be joined. Finally, it must be safe. The agent should not create more problems than it solves. When first introduced, fibrin sealants were banned from use in the United States because of the risk of the transmission of infections. Not until blood products could be adequately screened for these pathogens were they approved. Safety is a critical issue. Like all biomaterials, adhesives should meet certain safety norms, which are regulated by different international organizations. Adhesives and glues must promote tissue healing without the risk of infection or viral transmission. To obtain these properties, the different manufacturers must test their products at least for acute, subacute, local, and systemic toxicity according to well-established protocols that recommend that the tests be carried out in each individual component, in the final product (if there are two or more components mixed together to obtain the final glue or adhesive) and in its degradation products. As these materials will act in living organisms, it is necessary to take into account that the human body is a very aggressive environment. It is a saline medium with a temperature of 37°C, so certain conditions-minimum tissue toxicity at the application sites, parallel sealing and biodegradability times to get a proper healing time, wettability; ease of utilization in the surgical theater, and of course, low cost-must be met. At the present time, tissue adhesives are being used in a number of surgical specialties, but all of them have to offer the same properties or qualities. They must be easy to use (as mentioned above), have fast action in bleeding systems, undergo no exothermic reaction during polymerization, have sufficient strength for each type of tissue to which they are applied and produce no inflammatory reactions. We review some of the general characteristics of these adhesives and describe our experience (in experimental models) in the mechanical behavior of biological glues that could potentially be utilized, alone or in combination with sutures, to join inert biological tissues that have been chemically treated. The biological tissue employedwas glutaraldehyde-fixed calf pericardium similar to that employed in the manufacture of the valve leaflets of cardiac bioprostheses.