Resistance and elasticity of the suture threads employed in cardiac bioprostheses.

The mechanoelastic features of five types of sutures were studied. The breaking stress for each was determined by means of tensile tests in which a constant strain rate was applied, and a tensile test with graduated stress and relaxation defined the elastic limit, i.e. the point beyond which deformation becomes irreversible. The study of the stress-strain curve during this elastic period enabled us to obtain the mathematical function that governs these reversible deformations, which shows excellence of fit (R2 > 0.98). The prime derivative at each point of the resulting functions is the elastic modulus, the best parameter for comparing the elasticities of the suture threads. Since breaking stress alone does not suitably define the mechanical quality of a suture, we propose the use of other parameters during the elastic period, such as percentage of elongation at a point 10 times lower than the elastic limit (safety coefficient of 10), and tensile stress and elastic modulus at the said point, which are more reliable in the assessment of the resistance and elasticity of these threads.