The effects of age and sex on the elastic mechanical properties of human abdominal fascia.

BACKGROUND: The abdominal hernias become more prevalent with age, that can adversely affect life quality. The mechanical properties of abdominal wall layers are supposed to play a significant role in developing of an abdominal hernia.The objective of this study was to determine the mechanical properties of the human abdominal layer - fascia and the effects of age and sex on it for choosing the proper brand of hernia mesh. METHODS: 78 samples harvested from 19 fresh cadavers were subjected to uniaxial tension tests and divided into four groups according to age. Group A corresponds to age up to 60 years, Group B to age 61-70 years, Group C to age 71-80 years and Group D to 81-90 years. Median stress-stretch ratio curves with respect to age, sex and direction of loading were obtained. Median values of the maximum tensile stress, stretch at maximum stress and elastic modulus calculated at 5% strain were determined. FINDINGS: The abdominal fascia showed large variations between specimens depending on age and sex. The stiffness of the fascia increased with age. There is statistically significant differences between the median curves of male samples (P = 0.008) and female samples (P = 0.019) according to age in the L direction. Statistically significant differences between the values of maximum stress (P = 0.01) and elastic modulus (P = 0.003) from Group C in the L direction and maximum stress (P = 0.03) from Group D in the T direction was established. INTERPRETATION: The female samples are stiffer than male samples especially after 80 years.

Age-related changes in mechanical properties of human abdominal fascia.

The purpose of this study is to assess and model age-related changes in the mechanical properties of human fascia. The samples were divided into three age groups: group A-up to 60 years (mean age 52.5 ± 6 years), group B-61-80 years (mean age 70.4 ± 5.2 years), and group C-81-90 years (mean age 83.2 ± 2 years). A uniaxial tensile test was applied to fascia specimens cut perpendicular and parallel to fibers. The secant modulus at 5% strain, the maximum stress, and the stretch at maximum stress were calculated from the stress-stretch ratio curves. The results indicated an increase in the secant modulus with the increased age. The trend is clearer in the longitudinal direction. Considering the strain energy function which accounts the isotropic and non-isotropic response of the fascia where isotropic and anisotropic parts are split, we evaluated which material model is the most suitable to present isotropic mechanical behavior of the tissue. The experimental stress-stretch ratio curves were approximated using Mooney-Rivlin, Yeoh, and neo-Hookean strain energy functions and a good match between theoretical and experimental results was obtained. On the basis of objective function values and normalized mean square root error, we recommend using the Yeoh model to describe the isotropic mechanical behavior of human abdominal fascia. Graphical abstract .

Investigation of mechanical compatibility of hernia meshes and human abdominal fascia.

OBJECTIVE: Understanding the biomechanical properties of hernia meshes is essential in facilitating their selection. The aim of this study was to evaluate the mechanical compatibility of hernia meshes and human abdominal fascia and assess their applicability in hernia repair. METHODS: Uniaxial tensile tests were performed. A total of eight hernia meshes were tested - three standard meshes (Surgimesh®, Surgipro™, TecnoMesh®) and five light-weight meshes (Optilene®, TiO2Mesh™, Parietex™, Vypro™ II, Ultrapro™). RESULTS: The secant modulus at 5% strain and the level of orthotropy (the ratio between tensile stress in the longitudinal and the transversal direction) at 5% strain were calculated from the stress-stretch ratio curves. The impact of pore size and thickness on the elastic properties of these meshes was determined. The relationships between density and elasticity as well as between elasticity and the strain developed at 16 N/cm load were presented. The resulting mechanical properties of meshes were compared to the elasticity, orthotropy and deformability of human abdominal fascia. CONCLUSIONS: Vypro™ II and Parietex™ brands display properties similar to those of fascia in both directions. The TiO2Mesh™ and Ultrapro™ display deformability close to the deformability at 16 N/cm of the fascia transversalis. Only the Vypro™ II brand's orthotropy is similar to that of fascia.

The effects of strain amplitude and localization on viscoelastic mechanical behaviour of human abdominal fascia.

PURPOSE: The purpose of the paper is to examine and compare the viscoelastic mechanical properties of human transversalis and umbilical fasciae according to chosen strain levels. METHODS: A sequence of relaxation tests of finite deformation ranging from 4 to 6% strain with increment 0.3% was performed at strain rate 1.26 mm/s. Initial and equilibrium stresses T0, Teq, initial modulus E and equilibrium modulus Eeq, reduction of the stress during relaxation process ΔT, as well as the ratio (1 - Eeq /E) were calculated. RESULTS: The range in which parameters change their values are (0.184-1.74 MPa) for initial stress, (0.098-0.95 MPa) for equilibrium stress, (43.5-4.6 MPa) for initial modulus E. For Eeq this interval is (23.75-2.45 MPa). There are no statistically significant differences between the values of these parameters according to localization. The differences in viscoelastic properties of both fasciae are demonstrated by reduction of the stress during relaxation process and ratio (1 - Eeq /E). The values of ΔT and (1 - Eeq /E) ratio for umbilical fascia are significantly greater than that of fascia transversalis. An increase of 2% in strain leads to change of the normalized relaxation ratio of fasciae between 28%-66%. There is a weak contribution of viscous elements in fascia transversalis samples during relaxation, while in umbilical fascia the contribution of viscous component increases with strain level to 0.66 at 5.3% strain. CONCLUSIONS: This study adds new data for the material properties of human abdominal fascia. The results demonstrate that in chosen range of strain there is an influence of localization on visco-elastic tissue properties.

Experimental study of the mechanical properties of human abdominal fascia.

The aim of the study is to characterise mechanical properties of human abdominal fascia according to its direction of loading and localization. The one-dimensional tensile behaviour of human abdominal fascia and its orthotropy has been studied experimentally using human umbilical (UF) and transversalis fascia (FT). The specimens have been cut and stretched parallel and orthogonal to the main fibre bundles. 90 specimens 10 mm wide and up to 70 mm long have been tested. The following mechanical parameters, characterising tensile properties of human abdominal fascia, have been calculated from the obtained stress-stretch ratio curves: maximal stress T(L)(max), stretch ratio at maximal stress λ(T(max)), maximal stretch ratio at failure λ(max), and a secant modulus E(i). The tissue strips obtained from defined areas reveal break stress between 0.63 and 1.99 MPa for FT and 0.93-1.61 MPa for UF. The parameter estimation has shown that in the physiological strain range specimens from both type of fascia can be considered orthotropic material according to their secant module, maximum stress T(L)(max) and stretch at maximum stress. Anisotropy factor AF (ratio of the stress in longitudinal and transverse directions) has been used to establish the level of the orthotropy of material and its variations with the stretch ratio. The maximum AF is 4.3 for FT at 20% deformation and 3.3 for UF at 5% deformation. The differences between the mechanical properties of FT and UF according to localization are not statistically significant thus the mechanical properties of human abdominal fascia are not affected by the localization.