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。     

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。     

缺损关节软骨在循环压缩载荷下棘轮行为的实验研究

目的研究缺损软骨在循环压缩载荷下的棘轮应变行为,探索缺损关节软骨的损伤演化规律。方法取新鲜的成年猪股骨远端关节软骨,对不同缺损深度软骨试样进行不同参数的三角波循环加载。结合非接触式数字图像技术,获得软骨不同层区的棘轮应变。结果随循环加载圈数的增加,软骨各层棘轮应变均表现为先急剧增大,然后缓慢增加并趋于平稳,由浅层到深层棘轮应变逐渐减小。各层区对循环圈数响应不同,浅层在50圈内应变增加较快,中层在100圈内应变增加较快,深层在75圈内应变增加较快。除了中层区域响应有滞后性,浅层、深层的棘轮应变与应力幅值、缺损深度呈正相关,与加载速率呈负相关。结论软骨的棘轮行为受软骨的特殊结构的影响,缺损使软骨各层区的应变增大,易造成损伤加剧。实验结果为组织工程软骨的构建提供参考依据。     

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。     

组织工程软骨植入缺损后修复区力学特性分析

目的利用组织工程技术建立体外软骨缺损实验模型,研究修复区人工软骨和宿主软骨的力学特性。方法采用一种琼脂糖凝胶作为人工软骨,制作猪软骨深层缺损,在缺损处仿临床植入人工软骨,用生物胶黏接,建立组织工程修复膝关节软骨缺损的体外模型;在压缩载荷作用下,通过数字图像相关技术研究组织工程软骨植入缺损后修复区即刻力学行为。结果压缩过程中界面处没有出现开裂现象,压缩分别为软骨层厚度的3.5%、5.6%、7.04%和9.0%时获得了修复区中间层应变分布图和应变变化曲线。压缩量从3.5%增加到9%时,在垂直软骨面方向上宿主软骨最大压应变增加75.9%,人工软骨最大拉应变增加226.99%;在平行软骨表面方向,交界面处最大拉应变增加116.9%,增加量远高于宿主软骨区和人工软骨区;对于修复区剪应变,随着压缩量增加交界处剪应变方向发生相反的改变。结论软骨组织工程修复缺损效果有很大的不确定性,这与修复区的力学环境有关。组织工程软骨植入缺损后,修复区受到复杂应变状态,随着压缩量增加,界面处、宿主软骨、人工软骨都发生较大的应变变化,界面处垂直软骨面方向的应变由压应变可转化为拉应变,平行软骨表面方向的拉应变有显著增加,交界处剪应变方向甚至发生了相反的改变,而且剪应力数值迅速增加。这种复杂应变状态造成修复区细胞力学环境的较大变化,还可能引起界面的开裂,影响缺损修复过程,这些力学环境变化应受到临床治疗的重视。     

滚压载荷下成年和幼年软骨的棘轮行为

文题释义： 非接触数字相关技术：非接触式测量方法以前主要有光学式和气动式两种,实验采用光学式图像采集系统。图像测量技术作为一种新兴的非接触测量方法有着独特的优越性,它通过把被测对象的图像作为检测和传递信息的手段,从图像中提取有用信息进而获得待测参数,研究通过图像采集点的坐标变化从而计算出受载前后软骨的应变。 棘轮效应：材料受到拉伸或压缩时,如果力大于材料的屈服强度,那么材料就会发生塑性变形。在非对称应力控制循环加载下,材料反向变形大小就会小于初始变形,进而产生了残余应变,如此反复而产生的沿应力方向上塑性变形累积的现象,这种现象即称为棘轮效应。 背景：国内外学者对关节软骨在不同力学环境及循环压缩载荷下的受力情况做了不少研究,但均集中在循环压缩载荷对软骨的作用,有关软骨年龄因素对软骨力学特性影响的研究和软骨在复杂受力环境下的特性研究不深入。                                                      目的：研究不同滚压载荷条件对成年和幼年关节软骨棘轮行为的影响。 方法：以成年猪股骨软骨和幼年猪股骨软骨为实验对象,在不同实验条件下(压缩量：10%,20%,30%;滚压速率：1.66,3.44,6.68 mm/s;缺损宽度：1,2,4 mm)采用滚压加载装置施加载荷,同时使用非接触数字相关技术对加载过程中的试样进行图像采集,通过分析处理图像,研究循环滚压载荷作用下成年及幼年关节软骨的棘轮行为。 结果与结论：①在滚压载荷下,随着滚压循环载荷的进行,成年软骨和幼年软骨的棘轮应变都呈现先快速增加后缓慢增加的趋势;②随着压缩量的增加,成年软骨和幼年软骨的棘轮应变都增加;在相同压缩量下,幼年软骨的棘轮应变大于成年软骨,并且他们的棘轮应变沿着软骨深度从表层到深层逐渐降低;③随着滚压速率的增加,成年软骨和幼年软骨的棘轮应变减小;④1 mm微型缺损关节软骨的棘轮应变数值和趋势与完整无缺损软骨大致相同。在2,4 mm缺损状态下,缺损软骨的棘轮应变值均比同样条件下完整软骨的棘轮应变值要高。 ORCID: 0000-0003-3586-1073(李凯);0000-0002-7288-6686(高丽兰) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

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。     

不同弹性模量人工软骨对缺损软骨修复区细胞力学环境影响的研究

应用有限元软件COMSOL建立关节软骨固液双相模型和细胞微观模型,跨尺度研究在生理载荷作用下不同弹性模量的人工软骨修复缺损时,宿主软骨各层细胞的力学环境和液相流场。模拟结果表明,均一弹性模量的人工软骨对不同层区细胞微环境的影响规律不同。随着人工软骨弹性模量增大,浅表层、中间层细胞应力增大,深层细胞应力减小。人工软骨植入改变了中间层、底层软骨的流场方向和营养供给方式,可能会造成软骨细胞营养供应障碍。上述影响可造成修复结果不确定。通过对跨尺度软骨细胞有限元模型进行仿真分析,可定量地评价宿主软骨各层细胞的力学环境,有助于更准确地评估软骨缺损修复的临床效果。     

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。     

An ultrasonic measurement for in vitro depth-dependent equilibrium strains of articular cartilage in compression

The equilibrium depth-dependent biomechanical properties of articular cartilage were measured using an ultrasound-compression method. Ten cylindrical bovine patella cartilage-bone specimens were tested in compression followed by a period of force-relaxation. A 50 MHz focused ultrasound beam was transmitted into the cartilage specimen through a remaining bone layer and a small hole at the centre of a specimen platform. The ultrasound echoes reflected or scattered within the articularcartilage were collected using the same transducer. The displacements of the tissues at different depths of the articular cartilage were derived from the ultrasound echo signals recorded during the compression and the subsequent force-relaxation. For two steps of 0.1 mm compression, the average strain at the superficial 0.2 mm thick layer (0.35 +/- 0.09) was significantly (p < 0.05) larger than that at the subsequent 0.2 mm thick layer (0.05 +/- 0.07) and that at deeper layers (0.01 +/- 0.02). It was demonstrated that the compressive biomechanical properties of cartilage were highly depth-dependent. The results suggested that the ultrasound-compression method could be a useful tool for the study of the depth-dependent biomechanical properties of articular cartilage.     

Video microscopy to quantitate the inhomogeneous equilibrium strain within articular cartilage during confined compression

The objectives of this study were to develop a method to quantitate the displacement and strain fields within articular cartilage during equilibrium confined compression, and to use the method to determine the variation of the equilibrium confined compression modulus with depth from the articular surface in bovine cartilage. The method made use of fluorescently labeled chondrocyte nuclei as intrinsic fiducial markers. Articular cartilage was harvested from the patellofemoral groove of adult bovines and trimmed to rectangular blocks 5 mm long, 0.76 mm wide, and 500 μm deep with the articular surface intact. Test specimens were stained with the DNA binding dye Hoechst 33258, placed in a custom confined compression chamber, and viewed with an epifluorescence microscope equipped for video image acquisition. Image processing was used to localize fluorescing chondrocyte nuclei in uncompressed and compressed (∼ 17%) speciments, allowing determination of the intratissue displacement profile. Strain was determined as the slope of linear regression fits of the displacement data in four sequential 125-μm-thick layers. Equilibrium strains varied 6.1-fold from the articular surface through 500 μm of cartilage depth, with the greatest compressive strain in the superficial 125-μm layer and the least compressive strain in the two deepest 125-μm layers. Thus, the four successive 125-μm layers have moduli that are 0.44 (superficial), 1.07, 2.39, and 2.67 (deep), times the apparent modulus for a 500 μm thick cartilage sample assumed to be homogeneous.     

Influences of the depth-dependent material inhomogeneity of articular cartilage on the fluid pressurization in the human knee

The material properties of articular cartilage are depth-dependent, i.e. they differ in the superficial, middle and deep zones. The role of this depth-dependent material inhomogeneity in the poromechanical response of the knee joint has not been investigated with patient-specific joint modeling. In the present study, the depth-dependent and site-specific material properties were incorporated in an anatomically accurate knee model that consisted of the distal femur, femoral cartilage, menisci, tibial cartilage and proximal tibia. The collagen fibers, proteoglycan matrix and fluid in articular cartilage and menisci were considered as distinct constituents. The fluid pressurization in the knee was determined with finite element analysis. The results demonstrated the influences of the depth-dependent inhomogeneity on the fluid pressurization, compressive stress, first principal stress and strain along the tissue depth. The depth-dependent inhomogeneity enhanced the fluid support to loading in the superficial zone by raising the fluid pressure and lowering the compressive effective stress at the same time. The depth-dependence also reduced the tensile stress and strain at the cartilage–bone interface. The present 3D modeling revealed a complex fluid pressurization and 3D stresses that depended on the mechanical contact and relaxation time, which could not be predicted by existing 2D models from the literature. The greatest fluid pressure was observed in the medial condyle, regardless of the depth-dependent inhomogeneity. The results indicated the roles of the tissue inhomogeneity in reducing deep tissue fractures, protecting the superficial tissue from excessive compressive stress and improving the lubrication in the joint.     

Use of controlled mechanical stimulation in vivo to induce cartilage layer formation on the surface of osteotomized bone

A micromachine was used to study the response of mesenchymal tissue to mechanically controlled motion in vivo. The middle portion of the coccygeal vertebra of Fischer 344 rats was osteotomized, and continuous bending motion was applied for 4 weeks. The experimental groups were divided into two groups with higher sliding displacement applied at the osteotomized gap of group II. Hyaline cartilage tissue was generated at the osteotomized ends, and was predominantly formed on the side that extended during the bending motion. These newly formed tissues stained intensively with safranin O and toluidine blue, positively with immunostain for type II collagen, but negatively with immunostain for type I collagen. Articular cartilage-like tissues with a surface and a layer structure were obtained in group II, in which higher sliding motion was applied. Light and electron microscopy revealed morphological features similar to those of normal articular cartilage tissue in the superficial and middle zones of the tissues obtained in group II. Collagen fibrils in the superficial zone were found aligned parallel to the smooth surface. Although tidemark formation was not observed in the deep zone, the structure was much more natural than that of any other tissue-engineered cartilage reported to date. These results suggest that controlled sliding stimulation can elicit the generation of articular cartilage structure in vivo.     

关节软骨力学特征研究进展

骨关节炎(osteoarthritis OA)是一种以关节疼痛和僵硬为特征的慢性退行性关节疾患,好发于老年人群。OA发病缓慢,病程较长,早期临床表现和组织学改变均不明显,限制了疾病的早期诊断与治疗。关节软骨微观结构决定了软骨宏观力学特性。软骨微观结构具有区域差异性,导致软骨的力学性能也具有区域依赖性,从软骨浅表区到深区软骨抗负荷、抗形变能力逐渐增加。然而,在OA病程发展过程中,软骨微观构成改变导致OA软骨抗负荷、抗形变能力降低。通过检测关节软骨的微观构成可以推测软骨的力学特性,反之检测软骨的力学指标可以了解软骨早期的微观改变,从而有助于了解OA的病程发展,便于疾病的早期诊断。综述近年来关节软骨在正常和急慢性损伤状态下力学性能的相关研究文献,阐述软骨结构与力学性能之间的关系,为OA的病程发展、早期诊断与治疗提供进一步理论依据。     

Prediction of volumetric strain in the human temporomandibular joint cartilage during jaw movement

Human temporomandibular joint loading causes pressurization and flow of interstitial fluid in its cartilaginous structures. This largely determines its load-bearing and maintenance capacity. It was hypothesized that during cyclical jaw movements normal pressure distribution dynamics would enable fluid to reach all necessary cartilage regions. This was tested qualitatively by analysis of local volumetric strain dynamics during jaw open-close movements predicted by a dynamic model of the human masticatory system. Finite-element analysis was performed in separate regions of the articular cartilage layers and articular disc. Heterogeneous patterns of dilatation and compression were predicted. Compression was found to be more dominant during jaw closing than opening. The pressure gradient in the superior layer of the articular disc was more mediolaterally orientated than in its inferior layer. The findings suggest that, where necessary, regionally the cartilage can imbibe fluid to protect the subchondral bone from impact loads effectively. In the disc itself presumably all areas receive regular refreshment of interstitial fluid.