Constitutive Modeling of Time-Dependent Response of Human Plantar Aponeurosis

P G Pavan,A N Natali,P Pachera,C Stecco

doi:10.1155/2014/530242

P G Pavan, A N Natali + Show 2 more

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https://doi.org/10.1155/2014/530242

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Abstract

The attention is focused on the viscoelastic behavior of human plantar aponeurosis tissue. At this purpose, stress relaxation tests were developed on samples taken from the plantar aponeurosis of frozen adult donors with age ranging from 67 to 78 years, imposing three levels of strain in the physiological range (4%, 6%, and 8%) and observing stress decay for 240 s. A viscohyperelastic fiber-reinforced constitutive model with transverse isotropy was assumed to describe the time-dependent behavior of the aponeurotic tissue. This model is consistent with the structural conformation of the tissue where collagen fibers are mainly aligned with the proximal-distal direction. Constitutive model fitting to experimental data was made by implementing a stochastic-deterministic procedure. The stress relaxation was found close to 40%, independently of the level of strain applied. The agreement between experimental data and numerical results confirms the suitability of the constitutive model to describe the viscoelastic behaviour of the plantar aponeurosis.

Highlights

The plantar aponeurosis is deeply involved in the biomechanical behavior of the foot, being a structural element that directly affects the deformation of the foot arch
The comparison of experimental data taken from stress relaxation tests and numerical results shows a good capability of the constitutive model to describe the stress relaxation phenomena of the plantar aponeurosis tissue in a strain range that can be referred to physiological conditions, according to the literature
The main purpose of defining this constitutive model for the plantar aponeurosis is the adoption of this model for investigating foot biomechanics using a numerical approach

Summary

Introduction

The plantar aponeurosis is deeply involved in the biomechanical behavior of the foot, being a structural element that directly affects the deformation of the foot arch. A deeper knowledge about the mechanical properties of constituent materials and about the structural response of the plantar aponeurosis could lead to a better understanding of the biomechanical behavior of the foot, both in physiological and pathological conditions. Wright and Rennels [5] investigated plantar aponeurosis elastic properties testing samples taken from adult donors. Gefen [6] estimated by in vivo tests a larger compliance of the plantar aponeurosis, attesting a lengthening up to 11-12% strain under a load of 900 N. This larger deformability is in agreement with the outcomes of other pieces of work appeared in the literature [7]. The nonlinear behavior found by Wright and Rennels [5] was experimentally confirmed by Kitaoka et al [8]

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