Upton Maureen L, Gilchrist Christopher L, Guilak Farshid, Setton Lori A
Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA.
Biophys J. 2008 Aug;95(4):2116-24. doi: 10.1529/biophysj.107.126938. Epub 2008 May 16.
Cells within fibrocartilaginous tissues, including chondrocytes and fibroblasts of the meniscus, ligament, and tendon, regulate cell biosynthesis in response to local mechanical stimuli. The processes by which an applied mechanical load is transferred through the extracellular matrix to the environment of a cell are not fully understood. To better understand the role of mechanics in controlling cell phenotype and biosynthetic activity, this study was conducted to measure strain at different length scales in tissue of the fibrocartilaginous meniscus of the knee joint, and to define a quantitative parameter that describes the strain transferred from the far-field tissue to a microenvironment surrounding a cell. Experiments were performed to apply a controlled uniaxial tensile deformation to explants of porcine meniscus containing live cells. Using texture correlation analyses of confocal microscopy images, two-dimensional Lagrangian and principal strains were measured at length scales representative of the tissue (macroscale) and microenvironment in the region of a cell (microscale) to yield a strain transfer ratio as a measure of median microscale to macroscale strain. The data demonstrate that principal strains at the microscale are coupled to and amplified from macroscale principal strains for a majority of cell microenvironments located across diverse microstructural regions, with average strain transfer ratios of 1.6 and 2.9 for the maximum and minimum principal strains, respectively. Lagrangian strain components calculated along the experimental axes of applied deformations exhibited considerable spatial heterogeneity and intersample variability, and suggest the existence of both strain amplification and attenuation. This feature is consistent with an in-plane rotation of the principal strain axes relative to the experimental axes at the microscale that may result from fiber sliding, fiber twisting, and fiber-matrix interactions that are believed to be important for regulating deformation in other fibrocartilaginous tissues. The findings for consistent amplification of macroscale to microscale principal strains suggest a coordinated pattern of strain transfer from applied deformation to the microscale environment of a cell that is largely independent of these microstructural features in the fibrocartilaginous meniscus.
纤维软骨组织中的细胞，包括半月板、韧带和肌腱中的软骨细胞和成纤维细胞，会响应局部机械刺激来调节细胞生物合成。施加的机械负荷通过细胞外基质传递到细胞环境的具体过程尚未完全明确。为了更好地理解力学在控制细胞表型和生物合成活性中的作用，本研究旨在测量膝关节纤维软骨半月板组织中不同长度尺度下的应变，并定义一个定量参数来描述从远场组织传递到细胞周围微环境的应变。实验对含有活细胞的猪半月板外植体施加可控的单轴拉伸变形。通过共聚焦显微镜图像的纹理相关性分析，在代表组织（宏观尺度）和细胞区域微环境（微观尺度）的长度尺度上测量二维拉格朗日应变和主应变，以得出应变传递比，作为微观尺度与宏观尺度应变中值的度量。数据表明，对于位于不同微观结构区域的大多数细胞微环境，微观尺度的主应变与宏观尺度的主应变相关联并被放大，最大和最小主应变的平均应变传递比分别为1.6和2.9。沿施加变形的实验轴计算的拉格朗日应变分量表现出相当大的空间异质性和样本间变异性，并表明存在应变放大和衰减现象。这一特征与微观尺度上主应变轴相对于实验轴的面内旋转一致，这种旋转可能是由纤维滑动、纤维扭转以及纤维 - 基质相互作用引起的，而这些作用被认为对调节其他纤维软骨组织的变形很重要。宏观尺度到微观尺度主应变一致放大的研究结果表明，从施加变形到细胞微观环境的应变传递存在一种协调模式，这种模式在很大程度上独立于纤维软骨半月板中的这些微观结构特征。
