骨性关节炎动物模型内侧副韧带的应力松弛

背景：韧带和其他生物软组织一样,具有黏弹性特性,其应力松弛和蠕变黏弹性特性是为适应人的生理功能需要而存在的。研究说明骨性关节炎对韧带力学性能具有一定影响。 目的：比较正常和骨性关节炎动物模型内侧副韧带的应力松弛流变特性,确定骨性关节炎对内侧副韧带应力松弛特性的影响。 方法：以闭合关节刻痕法复制骨性关节炎动物模型,取正常和骨性关节炎动物模型大鼠膝关节内侧副韧带各10个试样,进行应力松弛实验。应力松弛实验的应变增加速度为5%/s。设定实验时间为7 200 s,采集100个数据,观察应力松弛数据和曲线、应力与时间的变化规律,以一元线性回归分析的方法处理实验数据。 结果与结论：正常组和病态组试样应力松弛最初600 s变化较快,之后应力缓慢下降,正常组7 200 s应力松弛量0.47 MPa,病态组7 200 s应力松弛量0.29 MPa。模型组7 200 s应力松弛量显著低于正常组(P < 0.05),且应力松弛曲线是以对数关系变化的。说明骨性关节炎时可以使膝关节对内侧副韧带应力松弛量降低,对膝关节应力松弛特性具有一定影响。     

Viscoelastic Relaxation and Recovery of Tendon

Tendons exhibit complex viscoelastic behaviors during relaxation and recovery. Recovery is critical to predicting behavior in subsequent loading, yet is not well studied. Our goal is to explore time-dependent recovery of these tendons after loading. As a prerequisite, their strain-dependent viscoelastic behaviors during relaxation were also characterized. The porcine digital flexor tendon was used as a model of tendon behavior. Strain-dependent relaxation was observed in tests at 1, 2, 3, 4, 5, and 6% strain. Recovery behavior of the tendon was examined by performing relaxation tests at 6%, then dropping to a low but nonzero strain level. Results show that the rate of relaxation in tendon is indeed a function of strain. Unlike previously reported tests on the medial collateral ligament (MCL), the relaxation rate of tendons increased with increased levels of strain. This strain-dependent relaxation contrasts with quasilinear viscoelasticity (QLV), which predicts equal time dependence across various strains. Also, the tendons did not recover to predicted levels by nonlinear superposition models or QLV, though they did recover partially. This recovery behavior and behavior during subsequent loadings will then become problematic for both quasilinear and nonlinear models to correctly predict.     

去卵巢骨质疏松模型大鼠L4脊椎骨的应力松弛与蠕变

背景：去卵巢大鼠脊椎骨会发生哪些应力松弛与蠕变及时间的变化规律？ 目的：观察去卵巢骨质疏松对雌性大鼠承重骨黏弹性特性的影响。 方法：Wistar雌性大鼠44只随机等分为对去卵巢骨质疏松动物模型组和对照组。模型组大鼠于0周摘除卵巢,14周后对大鼠L4椎骨进行应变增加速度为1%/s的应力松弛实验和应力增加速度为0.01 MPa/s的蠕变实验,在7 200 s采集100个数据。 结果与结论：大鼠L4椎骨对照组7 200 s应力松弛量和蠕变量大于模型组(P < 0.05);同时大鼠L4椎骨应力松弛曲线是以对数关系变化的,蠕变曲线是以指数关系变化的。提示去卵巢骨质疏松大鼠椎骨黏弹性力学特性发生了改变。     

An Evaluation of the Quasi-Linear Viscoelastic Properties of the Healing Medial Collateral Ligament in a Goat Model

The viscoelastic properties of the healing medial collateral ligament (MCL) at 12 weeks after isolated injury were investigated in a goat model. The stress-strain relationships, static and cyclic stress-relaxation behaviors of the healing MCL up to 5% strain were determined experimentally using a femur-MCL-tibia complex. These experimental data were used in combination with the quasi-linear viscoelastic (QLV) theory of Fung (1972) to characterize the reduced relaxation function, G(t) (described by constants C, tau1, and tau2) and the elastic response, sigmae(epsilon) (described by constants A and B) of this tissue. It was found that the percentage of stress relaxation for the healing MCLs was significantly greater than those for sham-operated controls (49.0 +/- 12.1% vs. 26.5 +/- 8.1%, respectively; p < 0.05). The product of constants A x B, i.e. the initial slope of the stress-strain curves, was found to be significantly lower for healing MCLs compared to those for sham-operated controls (32.9 +/- 15.8 MPa vs. 118.8 +/- 48.3 MPa; p < 0.05). The dimensionless constant C, i.e. the magnitude of the viscous response, was nearly three times greater for healing MCLs, while constant tau1 was found to be similar between the two groups (0.80 +/- 0.43 s vs. 0.89 +/- 0.52 s, respectively). Constant tau2 for the healing MCL was significantly less than the controls (1269 +/- 38 s vs. 1845 +/- 431 s; p < 0.05) indicating that the stress relaxation reached a plateau earlier. These constants of the QLV theory used to describe the healing MCL were validated for the strain level utilized in this experiment (approximately equal to 4.5%) by predicting the peak stresses during a cyclic stress-relaxation experiment. The theoretically determined values closely matched the experimentally measured values. Thus, this study demonstrates that the QLV theory could be successfully used to describe the viscoelastic behavior of the MCL during the early phases of healing.     

兔髌韧带压缩力学性能

目的 研究不同应变率下韧带的压缩应力-应变关系,并构建本构模型,为韧带的损伤预估及替代材料的研 发提供参考。 方法 通过万能拉伸试验机测试兔髌韧带在不同应变率(0. 001、0. 01、0. 1、1 s-1 )下的压缩力学性能 和压缩松弛响应,并构建相应的本构方程。 结果 单轴无侧限压缩实验表明,随着应变率增加,30% 、40% 应变下的 应力和切线模量均明显增大。 相比于 Gent 模型,Fung 和 Ogden 模型更适用于拟合韧带压缩曲线(R2 >0. 99);采用 4 项 Prony 级数更适用于拟合韧带的松弛曲线(R2>0. 99)。 结论 兔髌韧带的压缩力学性能有显著的黏弹性响应, Fung 和 Ogden 模型可用于拟合韧带的压缩响应,4 项 Prony 级数可用于拟合兔髌韧带的压缩松弛响应。     

Biaxial stress-relaxation in skin

Results of 58 biaxial and uniaxial stress-relaxation tests on flat specimens of abdominal rabbit skin are analyzed. It is shown that rabbit skin is a nonlinear viscoelastic material, i.e., the relaxation mode of each stress component depends on the strain (or alternatively on the initial stress). The dependence of the relaxation mode on the initial stress is investigated in terms of a modified power law with three parameters (Eq. (15)) which are functions of the initial stress. The differences and similarities between uniaxial and biaxial stress relaxation tests and the effect of the tissue “preconditioning” is discussed. On the basis of the results a theory is developed for the uniaxial viscoelastic behavior of rabbit skin tissue when small incremental strains are super-imposed on large constant deformation.     

兔眼角膜生物力学特性的年龄相关性

目的 利用兔眼角膜条的单轴拉伸实验数据,研究角膜生物力学特性与年龄的相关性。 方法 分别取3月龄和7~8月龄兔眼角膜条,实施单轴拉伸实验,获得实验数据;用指数模型和幂模型对应力 应变数据进行分析;用黏弹性力学模型对应力松弛数据进行分析。结果 兔眼角膜条呈现非线性黏弹性特征。在实验误差允许的范围内,不同月龄兔眼角膜条的非线性应力-应变关系差别不明显,7~8月龄兔眼角膜的切线模量略偏大,但其应力衰减得明显快。不同的拉伸速率对3月龄兔眼角膜条非线性应力-应变关系的影响不明显,但快速拉伸后的角膜条应力衰减明显变快。结论 兔眼角膜随月龄增加会轻微变硬,而角膜的松弛特性随月龄变化明显。     

Estimation of the viscous properties of skin and subcutaneous tissue in uniaxial stress relaxation tests

Knowledge of viscoelastic properties of soft tissues is essential for the finite element modelling of the stress/strain distributions in finger-pad during vibratory loading, which is important in exploring the mechanism of hand-arm vibration syndrome. In conventional procedures, skin and subcutaneous tissue have to be separated for testing the viscoelastic properties. In this study, a novel method has been proposed to simultaneously determine the viscoelastic properties of skin and subcutaneous tissue in uniaxial stress relaxation tests. A mathematical approach has been derived to obtain the creep and relaxation characteristics of skin and subcutaneous tissue using uniaxial stress relaxation data of skin/subcutaneous composite specimens. The micro-structures of collagen fiber networks in the soft tissue, which underline the tissue mechanical characteristics, will be intact in the proposed method. Therefore, the viscoelastic properties of soft tissues obtained using the proposed method would be more physiologically relevant than those obtained using the conventional method. The proposed approach has been utilized to measure the viscoelastic properties of soft tissues of pig. The relaxation curves of pig skin and subcutaneous tissue obtained in the current study agree well with those in literature. Using the proposed approach, reliable material properties of soft tissues can be obtained in a cost- and time-efficient manner, which simultaneously improves the physiological relevance.     

非线性模型在椎间盘黏弹性特性分析中的应用

目的 构建变参数非线性模型,研究人体椎间盘在循环应变状态下的应力松弛特性。方法 采用变参数非线性模型结合椎间盘应力松弛和蠕变反应的实验数据,研究循环应变状态下椎间盘的应力松弛特性,比较线性与非线性模型在循环状态下椎间盘黏弹性特性的差异。结果 采用变参数非线性模型得出的循环模量和松弛系数在0.01Hz循环状态下与实验模型非常接近,得出的循环模量在0.1和1 Hz下也与实验值相近,但是得出的松弛系数在0.1和1 Hz下失真严重。结论 在压缩应变作用下椎间盘经历的是一个非线性的应力行为,非线性变参数模型更符合研究在循环应变下椎间盘应力松弛反应的需要。     

A Nonlinear Constitutive Model for Stress Relaxation in Ligaments and Tendons

A novel constitutive model that describes stress relaxation in transversely isotropic soft collagenous tissues such as ligaments and tendons is presented. The model is formulated within the nonlinear integral representation framework proposed by Pipkin and Rogers (J. Mech. Phys. Solids. 16:59?C72, 1968). It represents a departure from existing models in biomechanics since it describes not only the strain dependent stress relaxation behavior of collagenous tissues but also their finite strains and transverse isotropy. Axial stress?Cstretch data and stress relaxation data at different axial stretches are collected on rat tail tendon fascicles in order to compute the model parameters. Toward this end, the rat tail tendon fascicles are assumed to be incompressible and undergo an isochoric axisymmetric deformation. A comparison with the experimental data proves that, unlike the quasi-linear viscoelastic model (Fung, Biomechanics: Mechanics of Living Tissues. Springer, New York, 1993) the constitutive law can capture the observed nonlinearities in the stress relaxation response of rat tail tendon fascicles.     

兔子宫壁组织力学特性的实验研究

目的 研究兔子宫壁组织的生物力学特性,并对分娩与未分娩组兔子宫壁力学特性进行比较.方法 以14只新西兰雌性大白兔为研究对象,取其子宫壁组织为拉伸试样,分娩与未分娩分组对照,用WDW4100微机控制电子万能实验机进行拉伸实验,测定其极限强度、应力应变关系;蠕变实验和应力松弛实验测定其黏弹性特征.结果 兔子宫壁组织表现出明显的黏弹性特征,应力应变呈指数关系;分娩组的平均极限应力为0.119MPa,未分娩组的平均极限应力为0.444MPa;分娩组的蠕变和松弛实验均明显比未分娩组低.结论 分娩与未分娩的兔子宫壁组织生物力学特性有明显的差别,对临床上研究人类子宫壁组织有一定的参考价值,有助于妇产科学的发展.     

Effects of Creep and Cyclic Loading on the Mechanical Properties and Failure of Human Achilles Tendons

The Achilles tendon is one of the most frequently injured tendons in humans, and yet the mechanisms underlying its injury are not well understood. This study examines the ex vivo mechanical behavior of excised human Achilles tendons to elucidate the relationships between mechanical loading and Achilles tendon injury. Eighteen tendons underwent creep testing at constant stresses from 35 to 75 MPa. Another 25 tendons underwent sinusoidal cyclic loading at 1 Hz between a minimum stress of 10 MPa and maximum stresses of 30–80 MPa. For the creep specimens, there was no significant relationship between applied stress and time to failure, but time to failure decreased exponentially with increasing initial strain (strain when target stress is first reached) and decreasing failure strain. For the cyclically loaded specimens, secant modulus decreased and cyclic energy dissipation increased over time. Time and cycles to failure decreased exponentially with increasing applied stress, increasing initial strain (peak strain from first loading cycle), and decreasing failure strain. For both creep and cyclic loading, initial strain was the best predictor of time or cycles to failure, supporting the hypothesis that strain is the primary mechanical parameter governing tendon damage accumulation and injury. The cyclically loaded specimens failed faster than would be expected if only time-dependent damage occurred, suggesting that repetitive loading also contributes to Achilles tendon injuries. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr     

Mechanical properties of stapedial annular ligament

Stapedial annular ligament (SAL) provides a sealed but mobile boundary between the stapes footplate and oval window bony wall. Mechanical properties of the SAL affect the transmission of ossicular movement into the cochlea in sound conduction. However, the mechanical properties of this tissue have never been investigated due to its complexity. In this paper, we report measurement of the viscoelastic properties of SAL on human cadaver temporal bones using a micro-material testing system with digital image correlation analysis. The measured load-deformation relations of SAL samples were converted into shear stress-shear strain relationship, stress relaxation function, and ultimate shear stress and shear strain of the SAL. The hyperelastic Ogden model was used to describe constitutive behavior of the SAL and a 3D finite element model of the experimental setup with SAL was created for assessing the effects of loading variation and measurement errors on results. The study demonstrates that the human SAL is a typical viscoelastic material with hysteresis, nonlinear stress-strain relationship and stress relaxation function. The shear modulus changes from 3.6 to 220 kPa when the shear stress increases from 2 to 140 kPa. These results provide useful information on quasi-static behavior of the SAL.     

膝关节前交叉韧带与内侧副韧带粘弹性实验研究

目的　研究了新鲜成人尸体膝关节前交叉韧带和内侧副韧带的粘弹性力学性质，为临床提供生物力学参数依据。方法　对前交叉韧带和内侧副韧带进行应力松弛，蠕变实验。结果　对实验数据进行归一化处理，得出了归一化应力松弛函数，蠕变函数，以回归分析的方法处理实验数据，得出了回归系数和拟合曲线。结论　内侧副韧带7200s应力松弛、蠕变量小于前交叉韧带。对实验结果进行分析讨论。     

髂股韧带与股骨头韧带黏弹性实验研究

目的 研究新鲜成人尸体髋关节髂股韧带和股骨头韧带的黏弹性力学性质,为临床提供生物力学参数.方法 取正常国人髂股韧带和股骨头韧带各10个试样进行应力松弛、蠕变实验.结果 得出了应力松弛、蠕变实验曲线,以回归分析的方法处理实验数据,得出了回归系数.结论 髂股韧带7200s应力松弛蠕变量显著大于股骨头韧带.     

The mechanical properties of the human cervical spinal cord<Emphasis Type="Italic">In Vitro</Emphasis>

The response of spinal cord tissue to mechanical loadings is not well understood. In this study, isolated fresh cervical spinal cord samples were obtained from cadavers at autopsy and tested in uniaxial tension at moderate strain rates. Stress relaxation experiments were performed with an applied strain rate and peak strain in the physiological range, similar to those seen in the spinal cord during voluntary motion. The spinal cord samples exhibited a nonlinear stress-strain response with increasing strain increasing the tangent modulus. In addition, significant relaxation was observed over 1 min. A quasilinear viscoelastic model was developed to describe the behavior of the spinal cord tissue and was found to describe the material behavior adequately. The data also were fitted to both hyperelastic and viscoelastic fluid models for comparison with other data in the literature.     

人脊柱腰椎松质骨归一化应力松弛蠕变函数

目的研究正常国人新鲜尸体腰椎L5椎体松质骨的粘弹性力学性质,为临床提供生物力学参数。方法在ShimadzuAUTOGRAPH电子万能试验机上对L5椎体松质骨试样进行压缩应力松弛、蠕变实验。结果得到了L5椎体应力松弛、蠕变数据和曲线,还得出了归一化应力松弛、归一化蠕变函数及曲线取得了回归系数a、b、c、d值。结论L5椎体7200s应力松弛量为0.261MPa、7200s蠕变量为0.217%。     

腰椎L4松质骨应力松弛蠕变方程

研究正常国人新鲜尸体腰椎L 4椎体松质骨的粘弹性力学性质,为临床提供生物力学参数。在Shimadzu AUTOGRAPH电子万能试验机上,对L4椎体松质骨试样进行应力松弛蠕变实验。得出了L4椎体应力松弛蠕变曲线,以三参数模型处理实验数据,得出应力松弛蠕变方程。结果表明:L4椎体7200s,应力松弛量为0.232MPa、蠕变量为0.271%。     

正常国人肾动脉粘弹性实验研究

目的　对正常国人新鲜尸体肾动脉进行应力松弛 ,蠕变实验研究 ,为临床提供生物力学参数。方法　对肾动脉进行拉伸应力松弛、蠕变粘弹性力学性质进行实验研究。结果　得出了肾动脉的应力松弛 ,蠕变数据和曲线。用回归分析的方法处理实验数据 ,得出了归一化应力松弛函数和归一化蠕变函数。结论　肾动脉 72 0 0s松弛量为0 .2 80MPa ,72 0 0s蠕变量为 13.98%。应力松弛和蠕变在最初 6 0 0s变化较大 ,72 0 0s时应力松弛、蠕变曲线基本达到平衡。肾动脉为生物粘弹性固体材料