A Method to Determine Shear Adhesive Strength of Fibrin Sealants David H. Sierra* and Dale S. Feldman zyxwvuts Department of Biomedical Engineering, School zyxwvut of Engineering, University of Alabama at Birmingham, Birmingham, Alabama Renato Saltzt Division of Plastic and Reconstructive Surgery, University of Alabama at Birmingham, Birmingham, Alabama Shu Huang Division of Pathology, Blood Bank Services, University of Alabama at Birmingham, Birmingham, Alabama The adhesive strength of fibrin sealants has not been rigorously evaluated to date. The adhe- sive strength of six different concentrations of cryoprecipitated fibrinogen as well as the com- mercially available fibrin tissue adhesive TissucolQD was tested under controlled conditions utilizing split-thickness skin grafts as the test adherand. This test configuration permitted the modeling of bonding strength for attachment of skin grafts as well as incorporate estab- lished engineering test standards for adhesives. An increase in fibrin concentration corre- sponded with an increase in shear adhesive strength. No significant increases in adhesive strength were attained after 5 min of bonding for all tested concentrations, except for the commercial adhesive, which attained the adhesive strength of an equivalent concentration of cryoprecipitated adhesive after 90 min. The adhesive strength, however, was an order of mag- nitude less than reported values of the tensile strength of fibrin material for similar concen- trations. Therefore, it is important that the surgeon use a sufficiently high fibrinogen concentration for the specific clinical indication. The method of fibrin sealant preparation and/or the compounding adjuncts appear to have an effect on the development of adhesive strength. INTRODUCTION Fibrin glue is a biologic tissue adhesive derived from blood and used as an adhesive adjunct in a wide variety of surgical procedures. Fibrin adhesives are based on the last step of the coagulation cascade, utilizing thrombin with ionic calcium to catalyze the polymerization of fibrinogen into fibrin polymer and activating Factor XI11 to covalently crosslink the resultant gel. Gelation occurs over a range of time from instantaneous to several minutes, depending on the thrombin concentration. The first reported use of fibrin as a tissue adhesive in humans was by Seddon and Medawar in 1942 for use in nerve grafting.' Plasma containing physiologic fibrinogen concentrations was used. Follow-up experience in the 1940s, however, resulted in frequent and premature fail- ure and rapid lysis due to low adhesive strength. In 1975, *Current address: Matrix Pharmaceutical, Inc., 1430 O'Brien Drive, 'Current address: Division of Plastic and Reconstructive Surgery, Medical Requests for reprints should be sent to David H. Sierra, Matrix Pharma- Menlo Park, CA 94025. College of Georgia, Augusta, GA 30912. ceutical, Inc., 1430 O'Brien Drive, Menlo Park, CA 94025. Journal of Applied Biomaterials, Vol. 3, 147-151 (1992) zyxwvutsrqp 0 1992 John Wiley & zyxwvutsrqpo Sons, Inc. CCC 1045-4861/92/020147-05$4.00 Kuderna and Matras used concentrated fibrinogen (cryo- precipitate) for nerve anastomosis with promising re- sults? This work led to the commercializationof a human pooled donor fibrin adhesive kit, marketed worldwide as TissucoP by Immuno AG. Despite almost 20 years of ex- perience with this product, concerns regarding the pos- sibility of blood-borne viral transmission have prevented its approval by the FDA for use in the United States. This regulatory situation, coupled with the clinical bene- fits of using the adhesive as reported by European inves- tigators has led to the development of single donor and patient autologous fibrin adhesive formulations. Fibrin adhesive has been demonstrated to be nontoxic, biocompatible and completely re~orbable.~ Degradation and resorption occur by the same proteolytic and phago- cytic pathways as for clots with physiologic fibrinogen concentration^.^ The tensile mechanical properties of the commercial adhesive material have been shown to increase with an increase in fibrinogen c~ncentration.~ The adhe- sive has been demonstrated to lead to equivalent wound strength, in a cutaneous incision, to a suture repair con- trol until zyxw 4 days6The actual adhesive strength of the glue itself, however, has yet to be fully characterized. There is a lack of published work in this area due to the diffi- culties of controlling the test conditions affecting adhe- sion. Although several reports describe zy in zyx vitro methods