Mechanical behaviour of knit synthetic mesh used in hernia surgery

There is a discussion in literature concerning mechanical properties and modelling of surgical meshes. An important feature of elastic modulus dependency on load history is taken into account in this paper, as implants are subjected to variable loading during human activity. The example of DynaMesh®-IPOM surgical implant is studied.

The analysis is based on failure tension tests and cyclic loading and unloading tests performed for the material samples. Stiffness changes of the material samples within successive load cycles are noted. The values the elastic modulus of the material tend to during successive cycles determine the material stiffness in the preconditioned state. The analysis is performed for two axes of the mesh, as the material reveals orthotropic properties.

For the initial displacements state of the material bilinear stiffness functions are determined for the two considered material axes. The functions for the preconditioned state are specified basing in the observed stiffness changes in subsequent loading cycles in experiments with different load (and strain) ranges. The identified elastic modulus values for different strain levels in the preconditioned state are then a basis for the nonlinear stiffness function formulation.

The author concludes that two states of the considered mesh should be considered in calculations, initial and preconditioned ones. As the material stiffness in its preconditioned state is higher than in the initial one, omitting of the preconditioned state in calculation, e.g., considering fixation of the mesh, may lead to underestimation of necessary fixation strength.