Shear mechanical properties of human lumbar annulus fibrosus
Shear mechanical properties of human lumbar annulus fibrosus
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DOI：
10.1002/jor.1100170517
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发表时间：
1999-09-01
影响因子：
2.8
通讯作者：
Mow, VC
中科院分区：
文献类型：
--
作者：
Iatridis, JC;Kumar, S;Mow, VC
椎间盘的功能、失效和重塑都与组织中的应力和应变场有关，并且可以通过具有精确的材料特性、真实的几何形状和适当的边界条件的有限元模型来计算。文献中没有对纤维环的剪切材料特性进行全面的研究。这项研究获得了纤维环的剪切材料特性，并测试了以下假设：这些特性受到剪切幅度和频率、施加的压应力以及组织退行性状态的影响。在动态和静态条件下对来自七个非退化圆盘和六个退化圆盘的轴向圆柱形样本进行了扭转剪切测试。在三种不同的轴向压应力（17.5、25 和 35 kPa）下，以 0.05 rad 的剪切应变幅度在生理频率范围（0.1-100 rad/sec）上进行频率扫描实验。在最大压应力下，进行剪应变扫描实验（应变幅度范围：0.005-0.15 rad，频率为5 rad/sec）和瞬态应力松弛测试（剪应变范围：0.02-0.15 rad）。纤维环材料在较大的剪切应变幅度下刚性较小且耗散较多，在较高振荡频率下刚性较大，并且在较大轴向压应力下刚性较大且耗散较小。动态剪切模量 \ G*\ 的值范围为 100 至 400 kPa，具体取决于实验条件和退化水平。剪切行为也主要是弹性的，相角正切 (tan δ) 的值范围为 0.1 至 0.7。随着等级退化，环空材料也变得更硬、更耗散；然而，这在统计上并不显着。结果表明，非线性、压缩/剪切耦合、固有粘弹性以及较小程度的退化都会影响纤维环的纯粹材料行为，对椎间盘中的负载承载机制具有重要意义。在为有限元模型选择材料常数时，应考虑这些材料的复杂性。
Function, failure, and remodeling of the intervertebral disc are all related to the stress and strain fields in the tissue and may be calculated by finite element models with accurate material properties, realistic geometry, and appropriate boundary conditions. There is no comprehensive study in the literature investigating the shear material properties of the annulus fibrosus. This study obtained shear material properties of the annulus fibrosus and tested the hypothesis that these properties are affected by the amplitude and frequency of shearing, applied compressive stress, and degenerative state of the tissue. Cylindrical specimens with an axial orientation from seven nondegenerated and six degenerated discs were tested in torsional shear under dynamic and static conditions. Frequency sweep experiments over a physiological range of frequencies (0.1-100 rad/sec) at a shear strain amplitude of 0.05 rad were performed under three different axial compressive stresses (17.5, 25, and 35 kPa). At the largest compressive stress, shear strain sweep experiments (strain amplitude range: 0.005-0.15 rad at a frequency of 5 rad/sec) and transient stress-relaxation tests (shear strain range: 0.02-0.15 rad) were performed. The annulus fibrosus material was less stiff and more dissipative at larger shear strain amplitudes, stiffer at higher frequencies of oscillation, and stiffer and less dissipative at larger axial compressive stresses. The dynamic shear modulus, \ G*\, had values ranging from 100 to 400 kPa, depending on the experimental condition and degenerative level. The shear behavior was also predominantly elastic, with values for the tangent of the phase angle (tan delta) ranging from 0.1 to 0.7. The annulus material also became stiffer and more dissipative with degenerative grade; however, this was not statistically significant. The results indicated that nonlinearities, compression/shear coupling, intrinsic viscoelasticity, and, to a lesser degree, degeneration all affect the sheer material behavior of the annulus fibrosus, with important implications for load-carriage mechanisms in the intervertebral disc. These material complexities should be considered when choosing material constants for finite element models.