Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, the University of Hong Kong, Hong Kong.
Osteoarthritis Cartilage. 2012 Aug;20(8):916-22. doi: 10.1016/j.joca.2012.04.018. Epub 2012 Apr 28.
This study aimed to characterize the in-situ mechanical property and morphology of individual collagen fibril in osteoarthritic cartilage using indentation-type atomic force microscopy (IT-AFM).
The specimens with intact articular cartilage (AC), mild to severe degenerated cartilage from osteoarthritis (OA) were collected with informed consent from the postmenopausal women who underwent hip or knee arthroplasty. The fresh specimens were cryo-sectioned by layers with 50μm thick for each from the articular surface to calcified cartilage, and then processed for AFM imaging and nanoindentation test. For each layer, a total of 20 collagen fibrils were randomly selected for testing. AFM tips with the nominal radius less than 10nm were employed for probing the individual collagen fibril, and the obtained cantilever deflection signal and displacement were recorded for calculating its elastic modulus.
An intact AC exhibited a gradation in elastic modulus of collagen fibrils from articular surface (2.65 ± 0.31 GPa) to the cartilage-bone interface (3.70 ± 0.44 GPa). It was noted in mildly degenerated OA cartilage that the coefficient of variation for mechanical properties of collagen fibers, ranging from 25% to 48%, significantly increased as compared with intact one (12%). The stiffened collagen fibrils occurred at either articular surface (3.11 ± 0.91 GPa) or the cartilage-bone interface (5.64 ± 1.10 GPa), accompanied by loosely organized meshwork with advancement of OA cartilage degeneration. It was echoed by histological findings of OA cartilage, including fibrotic changes of surface region and tidemark irregularities.
The stiffened collagen fibrils in AC occurred with OA onset and progression, not only at articular surface but also the cartilage-bone interface.
本研究旨在通过压痕原子力显微镜（IT-AFM）对骨关节炎软骨中的单个胶原纤维的原位力学性质和形态进行特征描述。
本研究从接受髋关节或膝关节置换术的绝经后妇女处获得具有完整关节软骨（AC）、轻度至重度退行性骨关节炎（OA）软骨的标本。新鲜标本从关节表面到钙化软骨以 50μm 厚的层进行冷冻切片，并进行 AFM 成像和纳米压痕测试。对于每一层，总共随机选择 20 个胶原纤维进行测试。使用名义半径小于 10nm 的 AFM 探针探测单个胶原纤维，并记录获得的悬臂挠度信号和位移，以计算其弹性模量。
完整的 AC 表现出从关节表面（2.65±0.31GPa）到软骨-骨界面（3.70±0.44GPa）的胶原纤维弹性模量逐渐增加。在轻度退行性 OA 软骨中，胶原纤维力学性能的变异系数从 25%到 48%，明显高于完整的 AC（12%）。在 OA 软骨退行性变的进展过程中，无论是在关节表面（3.11±0.91GPa）还是软骨-骨界面（5.64±1.10GPa），均会出现胶原纤维变硬的现象，并且胶原纤维的网络变得松散。这与 OA 软骨的组织学发现相呼应，包括表面区域的纤维化变化和嵴线不规则。
在 OA 发生和进展时，AC 中的胶原纤维变硬不仅发生在关节表面，而且还发生在软骨-骨界面。
