Hargrave-Thomas E, van Sloun F, Dickinson M, Broom N, Thambyah A
Experimental Tissue Mechanics Laboratory, Department of Chemical and Materials Engineering, University of Auckland, New Zealand.
Nanomechanics Laboratory, Department of Chemical and Materials Engineering, University of Auckland, New Zealand.
Osteoarthritis Cartilage. 2015 Oct;23(10):1755-62. doi: 10.1016/j.joca.2015.05.012. Epub 2015 May 29.
The calcified cartilage layer is thought to be integral to force transmission between the compliant articular cartilage (AC) above and underlying stiff bone. This study aims to determine how such a stiffness gradient across the calcified cartilage and bone changes with joint degeneration and how different scalar levels of testing are correlated.
Using a bovine model of early osteoarthritis (OA), multiple samples of calcified cartilage on subchondral bone (SB) from sixteen bovine patellae, displaying a range of cartilage states from intact (healthy) to moderately degenerate, were tested using macroscopic three-point bending, microhardness indentation, and nanoindentation. Mechanical properties were correlated to cartilage health and microstructural morphometric measurements obtained from high resolution imaging using Differential Interference Contrast (DIC) Microscopy.
There was a significant decrease in the moduli obtained from tests done at increasing scalar levels. The macroscale average modulus obtained from three-point bending showed that the SB was 10 times stiffer than the calcified cartilage in healthy tissue, 5 times in tissue displaying mildly degenerate AC and 8 times with moderate degeneration. Microhardness testing of multiple points from the calcified cartilage to the SB revealed that there was a monotonic gradual increase in the mean modulus. The moduli obtained from nanoindentation testing indicated that the SB was about twice the stiffness of the calcified cartilage.
The mechanical transition from calcified cartilage to SB involves a graded continuum of increasing material stiffness. This stiffness gradient is altered in association with early degenerative change in the overlying AC, detectable only at the macro level.
钙化软骨层被认为是上方顺应性关节软骨（AC）与下方坚硬骨骼之间力传递不可或缺的部分。本研究旨在确定钙化软骨和骨骼之间这种刚度梯度如何随关节退变而变化，以及不同标量水平的测试如何相互关联。
使用早期骨关节炎（OA）的牛模型，从16个牛髌骨的软骨下骨（SB）上获取多个钙化软骨样本，这些样本呈现出从完整（健康）到中度退变的一系列软骨状态，采用宏观三点弯曲、显微硬度压痕和纳米压痕进行测试。力学性能与软骨健康状况以及使用微分干涉对比（DIC）显微镜从高分辨率成像获得的微观结构形态测量结果相关联。
在不断增加的标量水平下进行测试所获得的模量有显著下降。从三点弯曲获得的宏观平均模量表明，在健康组织中，SB的刚度比钙化软骨大10倍；在显示轻度退变AC的组织中，大5倍；在中度退变时，大8倍。对从钙化软骨到SB的多个点进行显微硬度测试发现，平均模量呈单调逐渐增加。从纳米压痕测试获得的模量表明，SB的刚度约为钙化软骨的两倍。
从钙化软骨到SB的力学转变涉及材料刚度逐渐增加的连续梯度变化。这种刚度梯度会随着上方AC的早期退变变化而改变，且仅在宏观层面可检测到。
