Matrix mechanical properties of transversalis fascia in inguinal herniation as a model for tissue expansion

Inguinal herniation represents a common condition requiring surgical intervention. Despite being regarded as a connective tissue disorder of uncertain cause, research has focused predominantly on biochemical changes in the key tissue layer, the transversalis fascia (TF) with little direct analysis of functional tissue mechanics. Connective tissue tensile properties are dominated by collagen fibril density and architecture. This study has correlated mechanical properties of herniated TF (HTF) and non-herniated TF (NHTF) with fibrillar properties at the ultrastructural level by quasi-static tensile mechanical analysis and image analysis of collagen electron micrographs. No significant difference was found between any of the key mechanical properties (break stress, strain or modulus) for HTF and NHTF. In addition, no significant differences were found in average collagen fibril diameter, density or fibre bundle spacing. However, both groups displayed anisotropy with greater break stress (p=0.001) on average in the transverse anatomical plane compared to the longitudinal plane in a mean ratio of 2:1 (anisotropy ratio), though there was no evidence of a difference in this ratio for HTF and NHTF for both break stress and modulus. It was noted that this anisotropy ratio corresponds closely with the expected force distribution on a model cylindrical structure loaded axially. The absence of other functional differences does not support the idea of a failing (injured) tissue but is consistent with it being a tissue undergoing chronic growth/expansion under multi-vectored mechanical loading. These findings provide new clues to collagen tissue herniation for mathematical modelling and model tissue engineering.