Uniaxial and biaxial mechanical properties of porcine linea alba.

Incisional hernia is a severe complication post-laparoscopic/laparotomy surgery that is commonly associated with the linea alba. However, the few studies on the mechanical properties of the linea alba in the literature appear contradictory, possible due to challenges with the physical dimensions of samples and variations in protocol. This study focuses on the tensile mechanical characterisation of the porcine linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods. Results show that the linea alba demonstrated a non-linear elastic, anisotropic behaviour which is often observed in biological soft tissues. The transverse direction (parallel to fibres) was found to be approximately eight times stiffer than the longitudinal (cross-fibre) direction under both uniaxial and equi-load biaxial loading. The equi-load biaxial tensile tests revealed that contraction could occur in the transverse direction despite increasing load, probably due to the anisotropy of the tissue. Optical surface marker tracking and digital image correlation methods were found to greatly improve the accuracy of stretch measurement, resulting in a 75% change in the apparent stiffness compared to using strain derived from machine cross-head displacement. Additionally, a finite element model of the experiments using a combination of an Ogden and fibre exponential power law model for the linea alba was implemented to quantify the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the results. The preliminary model results were used to apply a correction factor to the uniaxial experimental data prior to inverse optimisation to derive best fit material parameters for the fibre reinforced Ogden model. Application of the model to the equi-load biaxial case showed some differences compared to the experimental data, suggesting a more complex anisotropic model may be necessary to capture biaxial behaviour. These results provide an improved assessment of the mechanical properties of the porcine linea alba for wound closure and other studies.

Cooney GM ，Moerman KM ，Takaza M ，Winter DC ，Simms CK ... -  《-》

Uniaxial and biaxial tensile stress-stretch response of human linea alba.

There are few studies on the stress-stretch behaviour of human linea alba, yet understanding the mechanics of this tissue is important for developing better methods of abdominal wound closure. Published data focuses mainly on porcine linea alba and for human tissue there are conflicting results and no bi-axial data available. This variability is likely due to challenges with the physical dimensions of the tissue and differences in experimental methodology. This study focussed on the tensile mechanical characterisation of the human linea alba using uniaxial and equi-load biaxial testing performed using image-based strain measurement methods. Thirteen freshly frozen human cadaveric abdominal walls were obtained and used to prepare 7 samples in both the transverse and longitudinal directions for uniaxial testing, and 13 square samples for bi-axial testing. The results showed significant anisotropy and for the equi-load biaxial tests the deformation was heavily biased in the longitudinal direction. In comparison with similar tests on porcine tissue from a previous study, it was found that the response of porcine linea alba to uniaxial loading is similar to that of human linea alba, with no statistically significant differences observed. Under biaxial loading human and porcine linea showed no statistical significance in the difference between their means in the transverse direction. However, a significant difference was observed in the longitudinal direction, and further study of the respective tissue structures is needed to better understand this result. These results provide the first data on the biaxial tensile properties of human linea alba and can aid in an improved assessment of wound closure mechanics.

Cooney GM ，Lake SP ，Thompson DM ，Castile RM ，Winter DC ，Simms CK ... -  《-》

Mechanical characterisation of porcine rectus sheath under uniaxial and biaxial tension.

Incisional hernia development is a significant complication after laparoscopic abdominal surgery. Intra-abdominal pressure (IAP) is known to initiate the extrusion of intestines through the abdominal wall, but there is limited data on the mechanics of IAP generation and the structural properties of rectus sheath. This paper presents an explanation of the mechanics of IAP development, a study of the uniaxial and biaxial tensile properties of porcine rectus sheath, and a simple computational investigation of the tissue. Analysis using Laplace׳s law showed a circumferential stress in the abdominal wall of approx. 1.1MPa due to an IAP of 11kPa, commonly seen during coughing. Uniaxial and biaxial tensile tests were conducted on samples of porcine rectus sheath to characterise the stress-stretch responses of the tissue. Under uniaxial tension, fibre direction samples failed on average at a stress of 4.5MPa at a stretch of 1.07 while cross-fibre samples failed at a stress of 1.6MPa under a stretch of 1.29. Under equi-biaxial tension, failure occurred at 1.6MPa with the fibre direction stretching to only 1.02 while the cross-fibre direction stretched to 1.13. Uniaxial and biaxial stress-stretch plots are presented allowing detailed modelling of the tissue either in silico or in a surrogate material. An FeBio computational model of the tissue is presented using a combination of an Ogden and an exponential power law model to represent the matrix and fibres respectively. The structural properties of porcine rectus sheath have been characterised and add to the small set of human data in the literature with which it may be possible to develop methods to reduce the incidence of incisional hernia development.

Lyons M ，Winter DC ，Simms CK 《-》

Material model calibration from planar tension tests on porcine linea alba.

The purpose of this study was to determine biomechanical properties of linea alba subjected to transverse planar tension and to compare its behavior at different locations of the abdominal wall. Samples of linea alba from five different porcine abdominal walls were tested in planar tension. During these tests, strain maps were measured for the first time ever using the stereo-digital image correlation (S-DIC) technique. The strain maps were used to derive the properties of different hyperelastic material models. It was shown that the Ogden model and the Holzapfel-Gasser-Ogden model are appropriate to reproduce the response in planar tension. The linea alba located above the umbilicus was significantly more compliant than below the umbilicus. This difference which is reported for the first time here is consistent with the tissue microstructure and it is discussed within the perspective of clinically-relevant numerical simulations.

Acosta Santamaría V ，Siret O ，Badel P ，Guerin G ，Novacek V ，Turquier F ，Avril S ... -  《-》

The suture pullout characteristics of human and porcine linea alba.

There is a substantial prevalence of post-operative incisional hernia for both laparoscopic and laparotomy procedures, but there have been few attempts at quantifying abdominal wound closure methodology in the literature. One method to ascertain a more robust method of wound closure is the identification of the influence of suture placement parameters on suture pullout force. Current surgical practice involves a recommended bite depth and bite separation of 10mm, but the evidence base for this is not clear. In this paper, the suture pullout characteristics of both porcine and human linea alba were investigated to ascertain a suture placement protocol for surgical wound closure. Uniaxial suture pullout force testing on fresh frozen porcine and human linea alba samples was performed using standard materials testing machines. The influence of the number of suture loops, the bite depth and the bite separation of the sutures and the orientation of the sutures with respect to the principal fibre direction in the linea alba were assessed. Results showed a clearly identifiable relationship between pullout force of the suture, bite separation and bite depth, with low suture separation and high suture depth as optimal parameters for increasing pullout force. Resistance to pullout could be improved by as much as 290% when optimizing test conditions. Both human and porcine tissue were observed to exhibit very similar pullout force characteristics, corroborating the use of a porcine model for investigations into wound closure methodology. Orientation of suture application was also found to significantly affect the magnitude of suture pullout, with suturing applied longitudinally across a transverse defect resulting in higher pullout forces for small suture bite separations. Although further assessment in an environment more representative of in vivo conditions is required, these findings indicate that increasing the bite depth and reducing the bite separation with respect to the current surgical recommendations may reduce the risk of post-operative incisional hernia.

Cooney GM ，Lake SP ，Thompson DM ，Castile RM ，Winter DC ，Simms CK ... -  《-》