The Nonlinear Material Properties of Liver Tissue Determined From No-Slip Uniaxial Compression Experiments

Abstract

The mechanical response of soft tissue is commonly characterized from unconfined uniaxial compression experiments on cylindrical samples. However, friction between the sample and the compression platens is inevitable and hard to quantify. One alternative is to adhere the sample to the platens, which leads to a known no-slip boundary condition, but the resulting nonuniform state of stress in the sample makes it difficult to determine its material parameters. This paper presents an approach to extract the nonlinear material properties of soft tissue (such as liver) directly from no-slip experiments using a set of computationally determined correction factors. We assume that liver tissue is an isotropic, incompressible hyperelastic material characterized by the exponential form of strain energy function. The proposed approach is applied to data from experiments on bovine liver tissue. Results show that the apparent material properties, i.e., those determined from no-slip experiments ignoring the no-slip conditions, can differ from the true material properties by as much as 50% for the exponential material model. The proposed correction approach allows one to determine the true material parameters directly from no-slip experiments and can be easily extended to other forms of hyperelastic material models.

Strain rate-dependent viscohyperelastic constitutive modeling of bovine liver tissue

“…2, where there is a clear increase in the nominal stress levels with increasing strain rates, as has been reported by other researchers. The low scatter in the data is consistent with our earlier results, where the use of the correction factor approach accounts for the different diameter-to-height ratios of the specimens automatically [28]. These corrected data were used to obtain the material constants associated with our viscohyperelastic material model.…”

“…The numerical correction factor approach outlined in [28] was applied to stress-stretch data obtained from no-slip uniaxial compression of bovine liver tissue at four different strain rates. The resulting corrected stress-stretch responses are shown in Fig.…”

“…In our previous study [28], we developed a method to account for the problem of friction in uniaxial compression by enforcing a no-slip boundary condition so that there is no uncertainty in the experiment. A computationally determined correction factor is then used to correct the observed mechanical response.…”

Mechanical Characterization of Brain Tissue in High-Rate Extension

“…Ignoring this fact may lead to some overestimation of tissue stiffness [25] . In practice, however, the effect of no-slip condition is not easily measurable although Miller [26] derived an analytical description of the tissue deformation in uniaxial extension.…”

Sample, testing and analysis variables affecting liver mechanical properties: A review

“…The first studies on the mechanical behaviour of animal and human livers were principally focused on the investigation of static material properties [13,30,35,50]. Dynamic (e.g.…”