Identification of mechanical properties of heterogeneous soft bodies using gravity loading

Abstract

This study investigates the use of multiple gravity‐loaded configurations of a soft heterogeneous body for the identification of its mechanical properties. It is largely motivated by the need for in vivo, non‐invasive determination of the mechanical properties of biological tissue, such as the breast, for the purposes of tracking and predicting tumor locations. In order to validate this approach, experiments were performed on a heterogeneous two‐layered silicone gel cantilever beam, laser scanned in eight different orientations under gravity loading. A finite element model of the beam was constructed and analyzed using non‐linear finite elasticity and a neo‐Hookean stress–strain relationship. The constitutive parameters representing the stiffness of each layer were estimated, using non‐linear optimization techniques, to best fit the laser‐scanned data. Different subsets of the experiments were used for training (parameter fitting), with the remaining experiments being used for validation. In both experimental sets, a cross‐validation study was performed in order to compare and assess the predictive power of the identified parameters. Several determinability criteria were used to assess the objective function in the neighborhood of the identified minimum. We found that individual experiments were not sufficient for reliable parameter identification of heterogeneous soft bodies under gravity loading, but that a small number of gravity‐loaded configurations were sufficient to reliably estimate the parameters within the scale of experimental errors. We also discuss the practical and numerical issues related to both single and multi‐experiment parameter estimation. Copyright © 2011 John Wiley & Sons, Ltd.

Surface deformation tracking of a silicone gel skin phantom in response to normal indentation

“…As silicone phantoms have successfully been used to mimic soft tissues [15][16][17], we hope that there will be little difficulty applying this deformation measurement technique to human skin. However, the multiple layered nature of skin will provide different deformation patterns to that seen in an isotropic, homogeneous gel.…”

“…Silicone gels have proved useful in simulated soft tissue experiments and validations of mechanical models, as they have well-defined material properties [15][16][17] . A 40 mm x 40 mm soft tissue phantom was constructed using Sylgard ® dielectric 527 silicone gel (Dow Corning, USA).…”

Relative identifiability of anisotropic properties from magnetic resonance elastography

“…Three criteria were evaluated in order to assess the determinability of the material parameters from the Hessian matrix, H , computed at the minimum of the objective function. () D‐optimality criterion. This is related to the volume of the indifference region, defined by the p ‐dimensional hyperellipsoid with size determined by the eigenvalues of the Hessian matrix.…”

Subject-specific finite element analysis to characterize the influence of geometry and material properties in Achilles tendon rupture

“…The lsqnonlin algorithm used has been previously detailed (Babarenda Gamage et al, 2011). For each specimen, 5 different randomly generated initial parameter guesses were tested to ensure global minimums were found, which was the case.…”