Constitutive equations for ligament and other soft tissue: evaluation by experiment

Duenwald, Sarah E.; Vanderby, Ray; Lakes, Roderic S.

doi:10.1007/s00707-009-0161-8

Cited by 28 publications

(16 citation statements)

References 13 publications

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“…It should be noted that there are of course many other custom non-linear viscoelastic models of soft tissues that could potentially be applied to the plantar tissue4,10,17,33,36,38,39 but were not considered for this study for simplicity and since our initial hope was to compare our work with previous characterizations. Hence, the QLV theory was chosen based on its previous use to successfully describe young, healthy plantar soft tissue whereby an indirect frequency-insensitive fit method was employed 28.…”

Section: Discussionmentioning

confidence: 99%

The Quasi-Linear Viscoelastic Properties of Diabetic and Non-Diabetic Plantar Soft Tissue

Pai

Ledoux

2011

Ann Biomed Eng

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The purpose of this study was to characterize the viscoelastic behavior of diabetic and nondiabetic plantar soft tissue at six ulcer-prone/load-bearing locations beneath the foot to determine any changes that may play a role in diabetic ulcer formation and subsequent amputation in this predisposed population. Four older diabetic and four control fresh frozen cadaveric feet were each dissected to isolate plantar tissue specimens from the hallux, first, third, and fifth metatarsals, lateral midfoot, and calcaneus. Stress relaxation experiments were used to quantify the viscoelastic tissue properties by fitting the data to the quasi-linear viscoelastic (QLV) theory using two methods, a traditional frequency-insensitive approach and an indirect frequency-sensitive approach, and by measuring several additional parameters from the raw data including the rate and amount of overall relaxation. The stress relaxation response of both diabetic and non-diabetic specimens was unexpectedly similar and accordingly few of the QLV parameters for either fit approach and none of raw data parameters differed. Likewise, no differences were found between plantar locations. The accuracy of both fit methods was comparable, however, neither approach predicted the ramp behavior. Further, fit coefficients varied considerably from one method to the other, making it hard to discern meaningful trends. Future testing using alternate loading modes and intact feet may provide more insight into the role that time-dependent properties play in diabetic foot ulceration.

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Section: Discussionmentioning

confidence: 99%

The Quasi-Linear Viscoelastic Properties of Diabetic and Non-Diabetic Plantar Soft Tissue

Pai

Ledoux

2011

Ann Biomed Eng

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“…Some studies have also assumed a linear ramp history, which is not necessarily indicative of the actual physiologic loading profile (Duenwald et al, 2009b; Lakes, 1999), while other groups have included the actual strain history but used formulae that may produce non-unique fitting parameters (Clarke et al, 2009). Recently, our group has developed and validated a finite ramp time correction method for stress relaxation experiments (comprehensive viscoelastic characterization, or CVC, method) that can accommodate various viscoelastic formulations, can incorporate an arbitrary strain ramp history, and results in a unique set of coefficients (Troyer and Puttlitz, 2011, 2012).…”

Section: Introductionmentioning

confidence: 99%

Nonlinear viscoelastic characterization of the porcine spinal cord

et al. 2014

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Although quasi-static and quasi-linear viscoelastic properties of the spinal cord have been reported previously, there are no published studies that have investigated the fully (strain-dependent) nonlinear viscoelastic properties of the spinal cord. In this study, stress relaxation experiments and dynamic cycling were performed on six fresh porcine lumbar cord specimens to examine their viscoelastic mechanical properties. The stress relaxation data were fitted to a modified superposition formulation and a novel finite ramp time correction technique was applied. The parameters obtained from this fitting methodology were used to predict the average dynamic cyclic viscoelastic behavior of the porcine cord. The data indicate that the porcine spinal cord exhibited fully nonlinear viscoelastic behavior. The average weighted RMSE for a Heaviside ramp fit was 2.8kPa, which was significantly greater (p < 0.001) than that of the nonlinear (comprehensive viscoelastic characterization (CVC) method) fit (0.365kPa). Further, the nonlinear mechanical parameters obtained were able to accurately predict the dynamic behavior, thus exemplifying the reliability of the obtained nonlinear parameters. These parameters will be important for future studies investigating various damage mechanisms of the spinal cord and studies developing high resolution finite elements models of the spine.

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“…There are a number of mathematical models that have been used to fit the relaxation curves [15][16][17][18]. If the relaxation behavior can be represented by a single straight line over the entire test interval incorporating a semi-log plot of the data, then a power law [Equation (1)] or a single-phase exponential decay law [Equation (2)] can be used to model the data [15,17]:…”

Section: Testingmentioning

confidence: 99%

Time-Dependent Properties of Human Umbilical Fascia

Kirilova

2011

Connective Tissue Research

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This investigation is devoted to the study of the viscoelastic behavior of human abdominal fascia from the umbilical region. Seventeen samples 10 mm wide and up to 70 mm long were cut along the primary fiber direction (group FL) or perpendicular to it (group FT) and subjected to relaxation tests. The viscoelastic response of the tissue at three different strain levels (4%, 5%, and 6%) was investigated. The relaxation curves were fitted using a two-stage decaying exponential form. The following parameters were determined: initial stress σ(0), relaxation times τ(1) and τ(2), stress reduction Δσ, initial relaxation modulus E and equilibrium relaxation modulus E(eq), as well as the ratio E/E(eq). Fiber orientation and strain levels were varied to determine their influence on the viscoelastic properties of fascia. The results highlight the inherent viscoelastic mechanical properties of umbilical fascia. The values of the viscoelastic parameters determined for the longitudinal and transverse directions varied markedly. Significant differences were found between the two groups FL and FT for the initial stress at 5% and 6% strain (p < 0.038) and for the initial and equilibrium moduli at the 6% strain level (p < 0.046). The stress reduction in samples from the FL group (45-55%) was less than that in samples from the FT group (37-54%), but this difference was not significant (p > 0.388). The influence of strain level on the parameter values was not statistically significant (p > 0.121). The nonlinear response of the tissue was demonstrated over the chosen strain range.

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Constitutive equations for ligament and other soft tissue: evaluation by experiment

Cited by 28 publications

References 13 publications

The Quasi-Linear Viscoelastic Properties of Diabetic and Non-Diabetic Plantar Soft Tissue

The Quasi-Linear Viscoelastic Properties of Diabetic and Non-Diabetic Plantar Soft Tissue

Nonlinear viscoelastic characterization of the porcine spinal cord

Time-Dependent Properties of Human Umbilical Fascia

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