RESUMO
We studied the mechanical behavior in response to tensile stress of samples of ostrich pericardium bonded with a cyanoacrylate glue or sewn with a rectangular, overlapping suture that was subsequently sealed with the same bioadhesive. Seventy-two trials were performed in three series of 24 samples each: series AG, glued with an overlap of 1 cm2; series ASG, sewn with a rectangular, overlapping suture and sealed; and series AC, control samples that were left intact. The mean stress at rupture in series AG (glued) was 0.1 MPa, much lower than the working stress of a human valve leaflet, which is approximately 0.25 MPa. In the control series, this stress was 26.28 MPa. At rupture in series ASG (sutured/glued), the suture material was being subjected to a stress of 64.91 MPa, thus confirming the existence of an interaction between the suture and the shear stress exerted by the suture on the samples of pericardium. In series ASG, the mean value for the resistance to rupture when measured in machine kg was 8.83 kg, lower than but similar to that recorded in the control series AC (10.26 kg). The percentages of reversible deformation, or elongation, once the samples were torn were similar in series AC (19.15%) and ASG (21.93%). This phenomenon can only be explained by the damage to the collagen fibers in the area around the rupture, while other more distant regions work at a lower load within the elastic limit. We conclude that cyanocrylate adhesives alone are not suitable as bonding materials in cardiac bioprostheses. The results with the rectangular, overlapping suture, when subsequently sealed with an adhesive, can be considered good because, although this approach does not impede shear stress, it does maintain an excellent degree of resistance to rupture of the samples thus joined. We stress the need to take into account the concentration of the load in the design of bioprostheses.
