An Anisotropic Multiphysics Model for Intervertebral Disk

Journal of Biomechanics

2017

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An anisotropic multiphysics damage model is developed to characterize the couplings among multiple physical fields within soft tissues and the tissue damage based on thermodynamic principles. This anisotropic multiphysics damage model integrates the continuum mixture theory and a continuum damage model, and the anisotropic damage is considered by evolution of internal damage variables governing the anisotropic mechanical behaviors of tissues. The energy dissipation associated with the transport of fluid and ions is generally related to tissue damage. The anisotropic multiphysics damage model is applied to simulate a case of annulus fibrosus (AF) damage in an isolated intervertebral disc under compression, to understand the damage initiation and propagation. It is found that, for this case (with 1000 N/s of compression rate and neglected ground matrix damage), the damage initiated in the outer and middle posterior regions of AF at about 700 N of disc compression. The region-dependent yield stretch ratio predicted by this model is consistent with experimental findings. A sensitive study on the damage parameters is also presented. This study provides an additional insight into AF damage in the isolated disc under mechanical compression.

Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An anisotropic multiphysics damage model with application to annulus fibrosus

Journal of Biomechanics

2017

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“…1). Finite element method was used to discretize the mathematical model following the approach in (Gao et al, 2016; Sun et al, 1999), and it was implemented in COMSOL 5.1. A mesh with 2560 quadratic hexahedral elements were used in the simulation (Fig.…”

Section: Numerical Examplesmentioning

confidence: 99%

Prediction of glycosaminoglycan synthesis in intervertebral disc under mechanical loading

Journal of Biomechanics

2016

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The loss of glycosaminoglycan (GAG) content is a major biochemical change during intervertebral disc (IVD) degeneration. Abnormal mechanical loading is one of the major factors causing disc degeneration. In this study, a multiscale mathematical model was developed to quantify the effect of mechanical loading on GAG synthesis. This model was based on a recently developed cell volume dependent GAG synthesis theory that predicts the variation of GAG synthesis rate of a cell under the influence of mechanical stimuli, and the biphasic theory that describes the deformation of IVD under mechanical loading. The GAG synthesis (at the cell level) was coupled with the mechanical loading (at the tissue level) via a cell-matrix unit approach which established a relationship between the variation of cell dilatation and the local tissue dilatation. This multiscale mathematical model was used to predict the effect of static load (creep load) on GAG synthesis in bovine tail discs. The predicted results are in the range of experimental results. This model was also used to investigate the effect of static (0.2 MPa) and diurnal loads (0.1/0.3 MPa and 0.15/0.25 MPa in 12/12 hours shift with an average of 0.2 MPa over a cycle) on GAG synthesis. It was found that static load and diurnal loads have different effects on GAG synthesis in a diurnal cycle, and the diurnal load effects depend on the amplitude of the load. The model is important to understand the effect of mechanical loading at the tissue level on GAG synthesis at the cellular level, as well as to optimize the mechanical loading in growing engineered tissue.

Simulation of water content distributions in degenerated human intervertebral discs

Journal Orthopaedic Research

Brown

et al. 2016

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The objective of this study was to investigate the spatial and temporal variations of water content in intervertebral discs during degeneration and repair processes. We hypothesized that the patterns of water content distribution in the discs are related to the intensity patterns observed in T2-weighted MRI images. Water content distributions in the mildly (e.g., 80% viable cells in the disc, 2.3% decrease in disc height) and moderately (e.g., 40% viable cells in the disc, 9.3% decrease in disc height) degenerated discs were predicted using a finite element model. The variation of water content in the degenerated discs treated with three biological therapies [i.e., increasing the cell density in the NP (Case I), increasing glycosaminoglycan synthesis rate in the nucleus pulposus (Case II), and decreasing glycosaminoglycan degradation rate in the nucleus pulposus (Case III)] were also predicted. It was found that two patterns of water content distributions, a horizontal region with lower water content at the mid-axial plane of nucleus pulposus and a spot with higher water content at the posterior region, were shown during the degeneration progress for the disc simulated in this study. These two patterns disappeared after treatment in Case I, but in Case II and Case III. The implication of these patterns for the horizontal gray band and high intensity zone in T2-weighted MRI images was discussed. This study provided new guidance to develop a novel method for diagnosing disc degeneration and assessing outcomes of biological therapies with MRI techniques.