关节软骨不同层区的率相关性能研究

目的 采用不同加载速率对关节软骨进行非围限压缩试验,探究其不同层区的率相关性能。方法 采用新鲜猪关节软骨作为研究对象,结合非接触式数字图像相关技术,测试不同加载率下软骨不同层区的力学性能。结果 在恒定加载率作用下,取相同压缩应力时,软骨浅表层的压缩应变最大,深层区压缩应变最小,中间层压缩应变鉴于表层与深层之间;沿软骨厚度方向,从浅表层到深层,软骨的泊松比逐渐增大;不同加载率作用下,软骨的压缩应力 应变曲线不重合,说明关节软骨的压缩力学性能具有率相关性;随着加载速率的增大,软骨的弹性模量呈增大的趋势;取相同压缩应力时,加载率越大,不同层区的压缩应变都减小。结论 关节软骨沿厚度方向,从浅表层到深层的压缩应变逐渐减小,泊松比逐渐增大,软骨不同层区的力学性能具有率相关性。实验研究可为临床软骨疾病预防、治疗提供理论依据,同时对人工软骨力学评价具有重要意义。     

关节软骨胶原纤维增强特性

目的在COMSOL关节软骨计算中引入胶原纤维增强特性,并分析引入前后模型结果的差异。方法以软骨中胶原纤维的走向为基础,对胶原纤维的应力单独建模,将胶原纤维的应力写入到原来软骨多孔弹性模型中。为避免应变2次项的出现采用了函数调用方式,同时提高求解器的迭代次数以更好收敛。结果胶原纤维增强模型表面的Y方向初始位移仅为15μm,是非增强模型的17.6%。增强模型的X方向正应变仅为非增强模型的10%,而近表面的X方向正应力超过非增强模型的10倍。结论在COMSOL关节软骨计算中实现了胶原纤维增强特性的引入,为软骨胶原纤维损伤提供了计算模型和理论分析。胶原纤维通过横向增强约束了竖直方向的应变,提高了软骨承载能力,改善了软骨的力学性能。     

牛膝关节软骨的力学承载特性及其有限元仿真分析

目的分析软骨的压缩变形行为和液相力学承载特性的关系。方法利用压痕实验测定牛膝关节软骨在不同压头直径、不同载荷下的压缩变形位移,建立有限元模型模拟关节软骨内部液相流动及承载特性。结果模拟压缩位移与实验结果最大相对误差为1.73%,在相同载荷作用下,随着压头直径的增大,软骨的弹性模量与渗透系数随之增大;在相同压头直径作用下,随着载荷的增大,软骨的弹性模量与渗透系数随之减小。载荷作用在软骨上,软骨内部液相主要在软骨内流动,随着载荷的持续,液相逐渐向软骨外流动。软骨表面的孔隙压力、轴向应力、径向应力由于液相的流动呈非线性变化。结论软骨表面的液相流动、孔隙压力及应力分布等影响软骨表面的承载特性;在不同压头、不同载荷下,软骨的承载特性有较大差异。     

人膝关节软骨与聚乙烯醇水凝胶人工软骨压缩实验比较研究

目的 比较人膝关节软骨和聚乙烯醇水凝胶（PVA-H）人工软骨的生物力学性能 方法 使用人膝关节软骨和PVA-H人工软骨进行轴向压缩试验,分别进行压缩应力应变、应力松弛和蠕变实验,得到关节软骨和PVA-H人工软骨的应力应变关系。结果 实验中人关节软骨和PVA-H的力学性能有差异,人关节软骨压缩模量大于PVA-H人工软骨,人关节软骨的压缩模量为（3.6492±0.6199）Mpa,PVA-H的压缩模量为（1.5951±0.1469）Mpa。结论 软骨和PVA-H人工软骨的生物力学性能具有一定差异,试验结果对人工软骨的进一步改进具有指导意义。     

含裂纹缺损关节软骨的单轴准静态拉伸性能

背景:关节软骨一旦出现裂纹缺损其力学性能会发生改变,而先前研究中针对受损关节软骨的探究多集中在压缩,对于拉伸性能的研究较少。目的:预先在软骨层试样上制造裂纹缺损,测试其单轴准静态拉伸性能。方法:选取新鲜成年猪膝关节的关节软骨,制备含裂纹缺损的软骨试样,在不同应力率下(0.001,0.01,和0.1 MPa/s)测试其拉伸性能,在不同恒定应力下(1,2,3 MPa)测试其蠕变性能。结果与结论:①不同应力速率下的拉伸实验中,随着应力速率的增加,达到相同应变所需的应力逐渐增大,且试件的杨氏模量随应力率的增加而增加;②不同应力速率下含裂纹缺损关节软骨的拉伸应力-应变曲线不重合,说明含裂纹缺损关节软骨的拉伸性能具有率相关性;③不同恒定拉应力水平下的蠕变实验中,蠕变应变随着拉应力水平的提高而增大,蠕变柔量随拉应力水平的提高而降低,并且随着蠕变时间的推移蠕变应变先快速增加后缓慢增加;④结果表明,不同应力率和不同恒定应力对含裂纹缺损关节软骨的拉伸力学性能影响较大,该实验结果可为缺损关节软骨的修复提供力学参考。     

矩形微缺损关节软骨在压缩载荷损伤演化的数值分析

目的 研究软骨在压缩载荷作用下的损伤扩展行为和演变机制。方法 采用有限元方法建立微缺损的纤维增强多孔弹性的软骨模型,对压缩载荷作用下损伤演化过程进行模拟和参数研究,获得不同损伤扩展阶段软骨基体和纤维的应力、应变分布规律。结果 软骨损伤表层和损伤前沿的应变随压缩量的增大而显著增大,两者呈明显的正相关性;在软骨演化过程中同时存在向深层和左右两侧扩展的趋势;软骨中的裂纹和损伤优先沿着纤维切线方向延伸,随着损伤的加剧,软骨横向扩展度明显快于纵向扩展速度。结论 软骨损伤演化过程与纤维的分布有着密切的关系,基质和纤维的损伤相互促进,骨演化速度和程度在不同层区和不同阶段存在变化。研究结果可为软骨创伤性退变的预测及修复提供定性的参考,为临床解释损伤退变病理现象和治疗提供理论依据。     

矩形微缺损关节软骨在压缩载荷下损伤演化的数值分析

目的研究软骨在压缩载荷作用下的损伤扩展行为和演变机制。方法采用有限元方法建立微缺损的纤维增强多孔弹性的软骨模型,对压缩载荷作用下损伤演化过程进行模拟和参数研究,获得不同损伤扩展阶段软骨基体和纤维的应力、应变分布规律。结果软骨损伤表层和损伤前沿的应变随压缩量的增大而显著增大,两者呈明显的正相关性;在软骨演化过程中同时存在向深层和左右两侧扩展的趋势;软骨中的裂纹和损伤优先沿着纤维切线方向延伸,随着损伤的加剧,软骨横向扩展度明显快于纵向扩展速度。结论软骨损伤演化过程与纤维的分布有着密切的关系,基质和纤维的损伤相互促进,骨演化速度和程度在不同层区和不同阶段存在变化。研究结果可为软骨创伤性退变的预测及修复提供定性的参考,为临床解释损伤退变病理现象和治疗提供理论依据。     

循环加载下关节软骨的棘轮应变及理论预测

目的获得不同加载条件下关节软骨的棘轮应变,建立预测棘轮应变的理论模型,并对软骨的棘轮应变进行预测。方法将猪股骨远端滑车部的新鲜关节软骨作为研究对象,采用非接触式数字图像技术,测试循环压缩载荷下关节软骨的棘轮应变;建立预测棘轮应变的理论模型,对不同应力幅值和加载率下软骨的棘轮应变进行预测,并比较预测结果与实验结果。结果随循环圈数的增加,软骨的棘轮应变先快速增长然后趋于稳定;定加载率下,软骨的棘轮应变随应力幅值的增大而增大;定应力幅值下,棘轮应变随加载率的增大而减小。实验结果与建立的理论模型预测结果吻合良好。结论关节软骨的棘轮应变与应力幅值成正比,与加载率成反比。建立的理论模型可以预测软骨的棘轮行为,同时为组织工程软骨的构造提供指导。     

胶原纤维束对软骨力学性能的影响

目的 研究胶原纤维束对软骨力学性能的影响,为临床医生指导早期软骨损伤患者的康复运动提供参考。方法 建立一种纤维增强的多孔黏弹性二维数值模型,考虑纤维分布、弹性模量、孔隙率和渗透率随软骨深度的变化关系。研究纤维束局部断裂和从表面渐进断裂以及纤维束尺寸对软骨力学性能的影响,获得软骨基质的最大主应变。结果 基质的最大主应变出现在软骨中层靠上某个位置,此位置不受纤维断裂模式和纤维束尺寸的影响。含较粗纤维束软骨的应变降低。结论 软骨中层易发生力学损伤,纤维束增粗可以降低基质的最大主应变,一旦纤维束发生断裂,较粗纤维束的软骨的基质最大主应变更大,使软骨更易发生损伤演化情况。     

髌股关节软骨固-液二相性特性的生物力学研究

髌股关节软骨为覆盖在髌股关节表面的一层光亮结缔组织,是一种由固相和液相组成的二胡性材料,骸股关节软骨疾病是骨科和运动创伤中的常见病,异常机械应力是造成滚股关节软骨损伤的直接原因。国内外许多学者对机械应力作用下骸股关节软骨内的应力及变形进行了数值计算及实验分析。但是,在前述的数值计算中,为简化计算,一股将关节软骨作为线弹性固体处理。而实际上关节软骨内的问质液占其总重量的60－80％,关节软骨是一种固一液二胡性材料,将关节软骨作为线弹性固体不符合其物理本质。正确地描述镇服关节软骨的生物力学特性、获得与实…     

Finite Element Simulation of Location- and Time-Dependent Mechanical Behavior of Chondrocytes in Unconfined Compression Tests

Experimental evidence suggests that cells are extremely sensitive to their mechanical environment and react directly to mechanical stimuli. At present, it is technically difficult to measure fluid pressure, stress, and strain in cells, and to determine the time-dependent deformation of chondrocytes. For this reason, there are no data in the published literature that show the dynamic behavior of chondrocytes in articular cartilage. Similarly, the dynamic chondrocyte mechanics have not been calculated using theoretical models that account for the influence of cell volumetric fraction on cartilage mechanical properties. In the present investigation, the location- and time-dependent stress-strain state and fluid pressure distribution in chondrocytes in unconfined compression tests were simulated numerically using a finite element method. The technique involved two basic steps: first, cartilage was approximated as a macroscopically homogenized material and the mechanical behavior of cartilage was obtained using the homogenized model; second, the solution of the time-dependent displacements and fluid pressure fields of the homogenized model was used as the time-dependent boundary conditions for a microscopic submodel to obtain average location- and time-dependent mechanical behavior of cells. Cells and extracellular matrix were assumed to be biphasic materials composed of a fluid phase and a hyperelastic solid phase. The hydraulic permeability was assumed to be deformation dependent and the analysis was performed using a finite deformation approach. Numerical tests were made using configurations similar to those of experiments described in the literature. Our simulations show that the mechanical response of chondrocytes to cartilage loading depends on time, fluid boundary conditions, and the locations of the cells within the specimen. The present results are the first to suggest that chondrocyte deformation in a stress-relaxation type test may exceed the imposed system deformation by a factor of 3–4, that chondrocyte deformations are highly dynamic and do not reach a steady state within about 20 min of steady compression (in an unconfined test), and that cell deformations are very much location dependent. © 2000 Biomedical Engineering Society. PAC00: 8719Rr, 8717Aa, 0270Dh     

Poroviscoelastic Modeling of Liver Biomechanical Response in Unconfined Compression

Mechanistic modeling approaches are important for understanding how fluid and solid components of the liver interact during impact trauma. This study uses poroviscoelasticity (PVE) theory to simulate liver biomechanical response in unconfined compression stress relaxation experiments, for variable ramp strain rates ranging from 0.001 to 0.1 s⁻¹. Specimens included 17 ex vivo porcine liver samples tested in a humidified temperature-controlled chamber. Liver response was modeled using ABAQUS, and best-fit parameters were determined using non-linear least-squares algorithms. The PVE model was able to capture the behavior of porcine liver in unconfined compression, with regression analyses for the ramp phase demonstrating high correlation between model and experiment (R ² > 0.993, slope > 0.833, p < 0.05). The advantage of PVE modeling over traditional viscoelastic modeling is the ability to examine interstitial fluid pressure as a contributor to tissue mechanical response. This strategy creates new opportunities for quantifying an injury mechanism (burst injury) that is common in blunt abdominal trauma, and will lead to advancement of high-fidelity virtual crash test dummies, and improved vehicle safety.     

The generalized consolidation of articular cartilage: an investigation of its near-physiological response to static load

This paper presents a study of the response of articular cartilage to compression whilst measuring simultaneously its strain and fluid excess pore pressure using a newly developed experimental apparatus for testing the tissue in its unconfined state. This has provided a comparison of the load-induced responses of the cartilage matrix under axial, radial and 3-D consolidation regimes. Our results demonstrate that the patterns of the hydrostatic excess pore pressure for axial and 3-D consolidation are similar, but differ significantly from that obtained under the more physiologically relevant condition in which the matrix exhibits radial consolidation when loaded either through a non-porous polished stainless steel indenter or an opposing cartilage disc. Based on the transient strain characteristics obtained under axial and unconfined compression we argue that consolidation is indeed the controlling mechanism of cartilage biomechanical function.     

Load partitioning influences the mechanical response of articular cartilage

The role of the fluid within articular cartilage as affected by the load-sharing mechanism and its potential, beneficial effects were assessed with the u-p finite element method. The mechanical behavior of cartilage as it covers the surface of a diarthrodial joint was evaluated when the partitioning of an applied stress to the solid and fluid phases of the tissue was varied. Comparisons were made in the response of the cartilage when 0%, 25%, 50%, or 75% of the applied stress was supported by the fluid at the surface. Substantial changes in the behavior of the tissue were observed for each load case. As the fluid sustained a larger portion of the applied stress, several parameters were affected; the fluid pressure within the cartilage layer remained at a higher value, the stress and strain generated in the solid matrix decreased while the compression of the cartilage layer decreased. These findings indicate that an increased loadpartitioning to the fluid phase in cartilage may perform the function of shielding the solid matrix from excessive stresses. This could also potentially alter the mechanical environment around the chondrocytes, influencing metabolic activity and homeostasis.     

皮质骨中骨单元应力集中效应的有限元分析

目的建立包含骨单元的皮质骨三维实体模型,通过有限元分析验证骨单元的应力集中效应,并对应力集中位置进行疲劳仿真和预测。方法利用Pro/E wildfire 5.0和ANSYS 12.0软件建立包含骨单元的皮质骨三维实体模型,在不同轴向压缩载荷条件下计算分析皮质骨中局部应力和应变分布情况;选取关键位置进行疲劳仿真,预测不同疲劳载荷强度下骨组织的疲劳状态。结果轴向压缩载荷作用下,骨单元附近会出现明显的应力集中效应,随着压缩载荷的增加,模型内部病理性局部应变的比例逐渐增大;关键位置的疲劳仿真结果证明了骨组织生理强度运动时的低疲劳风险,也预测了高强度运动或训练时骨组织疲劳骨折的高风险。结论成功建立了包含骨单元的皮质骨三维实体模型,验证了骨单元的应力集中效应,预测了高强度运动训练条件下骨组织的疲劳损伤位置和风险,实验结果可为部队新兵或中长跑运动员运动训练计划的制定以及运动疲劳损伤的预防提供参考。     

MR validation of soft tissue mimicing phantom deformation as modeled by nonlinear finite element analysis

A study of the applicability of nonlinear finite element analysis (FEA) to predict soft tissue deformation was validated with phase contrast magnetic resonance velocity imaging. A phantom of varying stiffness was placed in a special purpose, computer controlled MR compatible compression apparatus which provided precise, time varying compression with surface deformations on the order of 11%. The resulting motion was measured with MR velocity images acquired throughout the cycle of compression. The phantom geometry was modeled with a finite element mesh and the mechanical properties of the phantom material were measured and incorporated in the FEA model. The motion as calculated by the FEA model was compared to the motion measured with MRI and the results were found to vary with the material's Poisson's ratio and the coefficient of friction. A minimum difference was reached when the Poisson's ratio and coefficient of friction were set to 0.485 and 0.3, respectively. Under these conditions, the root mean square difference was found to be 14.4%.     

Finite element analysis for the evaluation of the structural behaviour,of a prosthesis for trans-tibial amputees

The finite element analysis (FEA) has been identified as a useful tool for the stress and strain behaviour determination in lower limb prosthetics. The residual limb and prosthetic socket interface was the main subject of interest in previous studies. This paper focuses on the finite element analysis for the evaluation of structural behaviour of the Sure-flex? prosthetic foot and other load-bearing components. A prosthetic socket was not included in the FEA. An approach for the finite element modelling including foot analysis, reverse engineering and material property testing was used. The foot analysis incorporated ground reaction forces measurement, motion analysis and strain gauge analysis. For the material model determination, non-destructive laboratory testing and its FE simulation was used. A new, realistic way of load application is presented along with a detailed investigation of stress distribution in the load-bearing components of the prosthesis. A novel approach for numerical and experimental agreement determination was introduced. This showed differences in the strain on the pylon between the experimental and the numerical model within 30% for the anteroposterior bending and up to 25% for the compression. The highest von Mises stresses were found on the foot–pylon connecting component at toe off. Peak stress of 216 MPa occurred on the posterior adjusting screw and maximum stress of 156 MPa was found at the neck of the male pyramid.     

不同降解周期下Ⅱ型胶原-丝素蛋白复合软骨支架的应力松弛行为

目的 利用有限元分析与理论模型相结合的方法，研究软骨支架在不同降解周期下的应力松弛行为。方法 基于已建立的降解本构模型计算不同降解周期下支架弹性模量；建立软骨支架有限元模型，并进行应力松弛仿真，分析支架松弛应力随时间的变化。建立应力松弛本构模型，对支架力学性能进行预测。结果 软骨支架降解14、28、42、56 d时，弹性模量分别为32.35、31.12、29.91、28.74 kPa。软骨支架各层的应力分布表现为上层受力最大；支架整体松弛应力随着时间增加先快速下降，然后趋于平稳；降解56 d时，支架能承受的应力仍在软骨的生理载荷范围内。应力松弛本构模型预测结果与有限元模拟结果吻合较好。结论 随降解时间的增加，支架弹性模量逐渐减小。降解时间越长，支架能承受的应力越小。相同降解时间下，施加的压缩应变越大，支架受力越大。有限元仿真和应力松弛本构模型可以有效预测支架降解时的应力变化。