Comparative study of the viscoelastic behaviour of hernia meshes

The time-dependent mechanical behaviour of hernia meshes may have an influence on the quality of hernia repairs. Viscoelastic behaviour of commonly used meshes in surgical practice in Bulgaria was investigated. The nine meshes (standard and lightweight meshes), differing from each other with respect to composition and weight, were put to the ex vivo relaxation tests at applied nominal strains of 5 %. The stress relaxation phenomena were monitored for 1800 s. The experimental results clearly demonstrate the orthotropy of the all hernia meshes. The changes in the stress reduction were 19-100 % after half an hour. Mean value of the reduction of the stress during relaxation ΔT for standard meshes is 66.84 ± 23.98 %, while Δ T for lightweight meshes is 51.48 ± 34.55 %. There are four meshes for which the tension falls to 0 MPa. All parameters of lightweight meshes change in broader intervals than those of standard meshes and have higher values. For lightweight meshes stress reduction decreases when density increases, while for standard meshes an opposite trend was observed. The parameters of polypropylene meshes change in broader intervals than the parameter of composite and polyethylene terephthalate meshes. Our results about the level of stress reduction can be used as a reference for im-provement of hernia meshes.