A Comparison of Uniaxial and Biaxial Mechanical Properties of the Annulus Fibrosus: A Porcine Model

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Diane E. Gregory ◽  
Jack P. Callaghan
Keyword(s):  
Mechanical Properties ◽  
Annulus Fibrosus ◽  
Axial Direction ◽  
Stretch Ratio ◽  
Intervertebral Disk ◽  
Circumferential Direction ◽  
Biaxial Tests ◽  
Maximal Stress ◽  
Biaxial Mechanical Properties

The annulus fibrosus of the intervertebral disk experiences multidirectional tension in vivo, yet the majority of mechanical property testing has been uniaxial. Therefore, our understanding of how this complex multilayered tissue responds to loading may be deficient. This study aimed to determine the mechanical properties of porcine annular samples under uniaxial and biaxial tensile loading. Two-layer annulus samples were isolated from porcine disks from four locations: anterior superficial, anterior deep, posterior superficial, and posterior deep. These tissues were then subjected to three deformation conditions each to a maximal stretch ratio of 1.23: uniaxial, constrained uniaxial, and biaxial. Uniaxial deformation was applied in the circumferential direction, while biaxial deformation was applied simultaneously in the circumferential and compressive directions. Constrained uniaxial consisted of a stretch ratio of 1.23 in the circumferential direction while holding the tissue stationary in the axial direction. The maximal stress and stress-stretch ratio (S-S) moduli determined from the biaxial tests were significantly higher than those observed during both the uniaxial tests (maximal stress, 97.1% higher during biaxial; p=0.002; S-S moduli, 117.9% higher during biaxial; p=0.0004) and the constrained uniaxial tests (maximal stress, 46.8% higher during biaxial; S-S moduli, 82.9% higher during biaxial). These findings suggest that the annulus is subjected to higher stresses in vivo when under multidirectional tension.

An Examination of the Influence of Strain Rate on Subfailure Mechanical Properties of the Annulus Fibrosus

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Diane E. Gregory ◽  
Jack P. Callaghan
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Nucleus Pulposus ◽  
Annulus Fibrosus ◽  
Maximum Stress ◽  
Axial Direction ◽  
Applied Strain ◽  
Circumferential Direction ◽  
Disk Herniation ◽  
Mechanical Responses

Disk herniation is often considered a cumulative injury in that repetitive stress on the posterior annulus can result in the nucleus pulposus penetrating the annulus fibrosus and eventually extruding posteriorly. Further, it has been documented that the nucleus pulposus works its way through the annulus through clefts, which form as a result of repetitive tensile strain. The annulus fibrosus is viscoelastic in nature and therefore could express different mechanical responses to applied strain at varying rates. Other viscoelastic tissues, including tendons and ligaments, have shown altered mechanical responses to different rates of applied strain, but the response of the annulus to varying rates of strain is largely unknown. The present study examined the mechanical properties of 20 two-layered samples of porcine annulus fibrosus tissue at three distinct rates of applied 20% biaxial strain (20% strain over 20 s (slow), over 10 s (medium), and over 5 s (fast)); these three rates are considered applicable to nontraumatic loading. No differences in the stiffness or maximum stress in each of the two directions of applied strain were observed between the three strain rates. Specifically, the average (standard deviation) moduli calculated at the fast, medium, and slow rates, respectively, in the axial direction were 7.42 MPa (6.06), 7.77 MPa (6.61), and 7.63 MPa (6.67) and 8.22 MPa (8.4), 8.63 MPa (9.00), and 8.49 MPa (8.69) in the circumferential direction. The maximum stress values reached during the fast, medium, and slow rates, respectively, in the axial direction were 0.40 (0.36) MPa, 0.40 (0.36) MPa, and 0.39 (0.35) MPa and 0.45 (0.47) MPa, 0.44 (0.46) MPa, and 0.43 (0.46) MPa in the circumferential direction. At submaximal strain magnitudes over a range of nontraumatic rates likely to result in clefts in the annulus and potentially leading to disk herniation, any strain rate dependence is not significant.

Magnetic Resonance Elastography for the Measurement of Annulus Fibrosus Material Properties

2011 ◽  
Author(s):  
Daniel H. Cortes ◽  
Lachlan J. Smith ◽  
Sung M. Moon ◽  
Jeremy F. Magland ◽  
Alexander C. Wright ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Magnetic Resonance ◽  
Shear Modulus ◽  
Disc Degeneration ◽  
Annulus Fibrosus ◽  
Pulse Sequence ◽  
Imaging Techniques ◽  
Mechanical Vibration ◽  
Magnetic Resonance Elastography

Intervertebral disc degeneration is characterized by a progressive cascade of structural, biochemical and biomechanical changes affecting the annulus fibrosus (AF), nucleus pulposus (NP) and end plates (EP). These changes are considered to contribute to the onset of back pain. It has been shown that mechanical properties of the AF and NP change significantly with degeneration [1,2]. Therefore, mechanical properties have the potential to serve as a biomarker for diagnosis of disc degeneration. Currently, disc degeneration is diagnosed based on the detection of structural and compositional changes using MRI, X-ray, discography and other imaging techniques. These methods, however, do not measure directly the mechanical properties of the extracellular matrix of the disc. Magnetic Resonance Elastography (MRE) is a technique that has been used to measure in vivo mechanical properties of soft tissue by applying a mechanical vibration and measuring displacements with a motion-sensitized MRI pulse sequence [3]. The mechanical properties (e.g., the shear modulus) are calculated from the displacement field using an inverse method. Since the applied displacements are in the order of few microns, fibers may not be stretched enough to remove crimping. Therefore, it is unknown if the anisotropy of the AF due to the contribution of the fibers is detectable using MRE. The objective of this study is twofold: to measure shear properties of AF in different orientations to determine the degree of AF anisotropy observable by MRE, and to identify the contribution of different AF constituents to the measured shear modulus by applying different biochemical treatments.

Mapping of Intervertebral Disk Annulus Fibrosus Compressive Properties Is Sensitive to Specimen Boundary Conditions

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Sarah E. Duclos ◽  
Arthur J. Michalek
Keyword(s):  
Residual Strain ◽  
Annulus Fibrosus ◽  
Intervertebral Disk ◽  
Transverse Plane ◽  
The State ◽  
Compressive Properties ◽  
Spatial Homogeneity ◽  
Matrix Deposition ◽  
Residual Strains

Predicting the mechanical behavior of the intervertebral disk (IVD) in health and in disease requires accurate spatial mapping of its compressive mechanical properties. Previous studies confirmed that residual strains in the annulus fibrosus (AF) of the IVD, which result from nonuniform extracellular matrix deposition in response to in vivo loads, vary by anatomical regions (anterior, posterior, and lateral) and zones (inner, middle, and outer). We hypothesized that as the AF is composed of a nonlinear, anisotropic, viscoelastic material, the state of residual strain in the transverse plane would influence the apparent values of axial compressive properties. To test this hypothesis, axial creep indentation tests were performed, using a 1.6 mm spherical probe, at nine different anatomical locations on bovine caudal AFs in both the intact (residual strain present) and strain relieved states. The results showed a shift toward increased spatial homogeneity in all measured parameters, particularly instantaneous strain. This shift was not observed in control AFs, which were tested twice in the intact state. Our results confirm that time-dependent axial compressive properties of the AF are sensitive to the state of residual strain in the transverse plane, to a degree that is likely to affect whole disk behavior.

Effect of Cold Storage on Mechanical Properties of Aorta

2015 ◽  
Author(s):  
Shijia Zhao ◽  
John Lof ◽  
Shelby Kutty ◽  
Linxia Gu
Keyword(s):  
Mechanical Properties ◽  
Uniaxial Tension ◽  
Cold Storage ◽  
Elastic Moduli ◽  
Heart Diseases ◽  
Axial Direction ◽  
Circumferential Direction ◽  
Control Group ◽  
Aortic Tissue ◽  
Tension Tests

Aortic allografts have been widely used in treatments of congenital heart diseases with satisfactory clinical outcomes. They were usually cryopreserved and stored for surgical use. The objective of this work was to investigate the effect of cold storage on mechanical properties of aorta, since the compliance mismatch was one important factor associated with the complication after graft surgery. The segments of porcine descending aorta were divided into two groups: the fresh samples which were tested within 24 hours after harvesting served as control group, and frozen samples which were stored in −20°C for 7 days and then thawed. The uniaxial tension tests along circumferential direction and indentation tests were conducted. The average incremental elastic moduli within each stretch range were obtained from the experimental data obtained during tension tests, and the elastic moduli were also calculated by fitting the force-indentation depth data to Hertz model when the tissue was stretched at 1.0, 1.2, 1.4 and 1.6. In addition, the average incremental elastic moduli of both fresh and frozen aortic tissue along axial direction were also obtained by using uniaxial tension tests. The comparison showed that cold storage definitely increased the average incremental elastic modulus of the aortic tissue along circumferential direction; however, the difference is not significant for the elastic moduli along axial direction.

scholarly journals Passive biaxial mechanical properties and in vivo axial pre-stretch of the diseased human femoropopliteal and tibial arteries

2014 ◽  
Vol 10 (3) ◽  
pp. 1301-1313 ◽  
Author(s):  
Alexey V. Kamenskiy ◽  
Iraklis I. Pipinos ◽  
Yuris A. Dzenis ◽  
Carol S. Lomneth ◽  
Syed A. Jaffar Kazmi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tibial Arteries ◽  
Biaxial Mechanical Properties

Biaxial incremental homeostatic elastic moduli of coronary artery: two-layer model

2004 ◽  
Vol 287 (4) ◽  
pp. H1663-H1669 ◽  
Author(s):  
Xiao Lu ◽  
Aditya Pandit ◽  
Ghassan S. Kassab
Keyword(s):  
Coronary Artery ◽  
Axial Direction ◽  
Circumferential Direction ◽  
Small Perturbations ◽  
Porcine Coronary Artery ◽  
Physiological Relevance ◽  
Health And Disease ◽  
The Media

The detailed mechanical properties of various layers of the coronary artery are important for understanding the function of the vessel. The present article is focused on the determination of the incremental modulus in different layers and directions in the neighborhood of the in vivo state. The incremental modulus can be defined for any material subjected to a large deformation if small perturbations in strain lead to small perturbations of stresses in a linear fashion. This analysis was applied to the porcine coronary artery, which was treated as a two-layered structure consisting of an inner intima-media layer and an outer adventitia layer. We adopted a theory based on small-perturbation experiments at homeostatic conditions for determination of incremental moduli in circumferential, axial, and cross directions in the two layers. The experiments were based on inflation and axial stretch. We demonstrate that under homeostatic conditions the incremental moduli are layer- and direction dependent. The incremental modulus is highest in the circumferential direction. Furthermore, in the circumferential direction, the media is stiffer than the whole wall, which is stiffer than the adventitia. In the axial direction, the adventitia is stiffer than the intact wall, which is stiffer than the media. Hence, the coronary artery must be treated as a composite, nonisotropic body. The data acquire physiological relevance in relation to coronary artery health and disease.

Active Biaxial Mechanical Properties of Bladder Wall Tissue

2003 ◽  
Author(s):  
Jiro Nagatomi ◽  
Michael B. Chancellor ◽  
Michael S. Sacks
Keyword(s):  
Mechanical Properties ◽  
Smooth Muscle ◽  
Urinary Bladder ◽  
Muscle Tone ◽  
Bladder Wall ◽  
Upper Urinary Tract ◽  
Biaxial Stress ◽  
Bladder Tissue ◽  
Biaxial Mechanical Properties

The urinary bladder is a smooth muscle organ whose main functions are to store and to void urine. Since the most important aspect of the storage function of the bladder is to maintain low intravesical pressure in order to protect the upper urinary tract from backflow of urine, the compliance of the bladder wall is one of the key functional paramters to assess the health of this organ. Previously, our laboratory reported, for the first time, the biaxial mechanical properties of bladder wall tissue in the inactive state (in the absence of calcium in the testing bath solution and thus smooth muscle contraction was abolished) (Gloeckner et al. 2002). The bladder in vivo, however, normaly exhibits passive smooth muscle tone during filling and active contraction during voiding. Therefore, in order to completely characterize the bladder tissue mechanical behaviors, it is necessary to examine the load-deformation relationship of the bladder under the passive and active states. In the present study, a novel experimental model was designed to allow collection of biaxial stress-strain data from urinary bladder wall tissue under passive, active and inactive states.

scholarly journals A Novel Method for Repeatable Failure Testing of Annulus Fibrosus

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Benjamin Werbner ◽  
Minhao Zhou ◽  
Grace O'Connell
Keyword(s):  
Mechanical Properties ◽  
Annulus Fibrosus ◽  
Mechanical Test ◽  
Local Strain ◽  
Intervertebral Disk ◽  
Failure Behavior ◽  
Fiber Reinforced ◽  
Failure Mechanics ◽  
Dog Bone ◽  
Failure Properties

Tears in the annulus fibrosus (AF) of the intervertebral disk can result in disk herniation and progressive degeneration. Understanding AF failure mechanics is important as research moves toward developing biological repair strategies for herniated disks. Unfortunately, failure mechanics of fiber-reinforced tissues, particularly tissues with fibers oriented off-axis from the applied load, is not well understood, partly due to the high variability in reported mechanical properties and a lack of standard techniques ensuring repeatable failure behavior. Therefore, the objective of this study was to investigate the effectiveness of midlength (ML) notch geometries in producing repeatable and consistent tissue failure within the gauge region of AF mechanical test specimens. Finite element models (FEMs) representing several notch geometries were created to predict the location of bulk tissue failure using a local strain-based criterion. FEM results were validated by experimentally testing a subset of the modeled specimen geometries. Mechanical testing data agreed with model predictions (∼90% agreement), validating the model's predictive power. Two of the modified dog-bone geometries (“half” and “quarter”) effectively ensured tissue failure at the ML for specimens oriented along the circumferential-radial and circumferential-axial directions. The variance of measured mechanical properties was significantly lower for notched samples that failed at the ML, suggesting that ML notch geometries result in more consistent and reliable data. In addition, the approach developed in this study provides a framework for evaluating failure properties of other fiber-reinforced tissues, such as tendons and meniscus.

scholarly journals Effect of Deformation Rate on the Mechanical Properties of Rectangular and Cruciform Arterial Samples: Uniaxial and Biaxial Testing

2007 ◽  
Author(s):  
Jorge O. Virues Delgadillo ◽  
Sebastien Delorme ◽  
Robert DiRaddo ◽  
Savvas G. Hatzikiriakos
Keyword(s):  
Mechanical Properties ◽  
Material Properties ◽  
Deformation Rate ◽  
Arterial Wall ◽  
Large Deformations ◽  
Elastic Behavior ◽  
Anisotropic Behavior ◽  
Biaxial Testing ◽  
Biaxial Tests

The elastic behavior of arteries is nonlinear when subjected to large deformations. In order to measure their anisotropic behavior, planar biaxial tests are often used. Uniaxial tests are also commonly used due to simplicity of data analysis, but their capability to fully describe the in vivo behavior of a tissue remains to be proven. Mechanical behaviour of arteries submitted to uniaxial or biaxial testing has been done previously [1–4]. Each one of these works was performed only at one deformation rate: 1 %/s [1, 3], 10 %/s [2], 1 Hz [4]; but those works do not show the behaviour of the arterial wall when it is submitted to different deformation rates. Thus, in this study we present the effect of deformation rate in the material properties (i.e. loading forces) of uniaxial and biaxial tests.

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