Hu Jingrui, Zheng Keke, Sherlock Benjamin E, Zhong Jingxiao, Mansfield Jessica, Green Ellen, Toms Andrew D, Winlove C Peter, Chen Junning
Biomedical Engineering, Faculty of Environment, Science and Economy, University of Exeter, UK.
Institute for Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot Watt University, Edinburgh, UK.
Acta Biomater. 2025 Mar 15;195:104-116. doi: 10.1016/j.actbio.2025.01.047. Epub 2025 Jan 25.
The biomechanical properties of articular cartilage arise from a complex bioenvironment comprising hierarchically organised collagen networks within the extracellular matrix (ECM) that interact with the proteoglycan-rich interstitial fluid. This network features a depth-dependent fibril organisation across different zones. Understanding how collagen fibrils respond to external loading is key to elucidating the mechanisms behind lesion formation and managing degenerative conditions like osteoarthritis. This study employs polarisation-resolved second harmonic generation (pSHG) microscopy to quantify the ultrastructural organisation of collagen fibrils and their spatial gradient along the depth of bone-cartilage explants under a close-to-in vivo condition. By combining with in-situ loading, we examined the responses of collagen fibrils by quantifying changes in their principal orientation and degree of alignment. The spatial gradient and heterogeneity of collagen organisation were captured at high resolution (1 μm) along the longitudinal plane of explants (0.5 mm by 2 mm). Zone-specific ultrastructural characteristics were quantified to aid in defining zonal borders, revealing consistent zonal proportions with varying overall thicknesses. Under compression, the transitional zone exhibited the most significant re-organisation of collagen fibrils. It initially allowed large deformation through the re-orientation of fibrils, which then tightened fibril alignment to prevent excessive deformation, indicating a dynamic adaptation mechanism in response to increasing strain levels. Our results provide comprehensive, zone-specific baselines of cartilage ultrastructure and micromechanics, crucial for investigating the onset and progression of degenerative conditions, setting therapeutic intervention targets, and guiding cartilage repair and regeneration efforts. STATEMENT OF SIGNIFICANCE: Achieved unprecedented quantification of the spatial gradient and heterogeneity of collagen ultrastructural organisation at a high resolution (1 μm) along the full depth of the longitudinal plane of osteochondral explants (0.5 mm by 2 mm) under close-to-in vivo condition. Suggested new anatomical landmarks based on ultrastructural features for determining zonal borders and found consistent zonal proportions in explants with different overall thicknesses. Demonstrated that collagen fibrils initially respond by reorienting themselves at low strain levels, playing a significant role in cartilage deformation, particularly within the transitional zone. At higher strain levels, more collagen fibrils re-aligned, indicating a dynamic shift in the response mechanism at varying strain levels.
关节软骨的生物力学特性源于一个复杂的生物环境，该环境由细胞外基质（ECM）中分层组织的胶原网络组成，这些网络与富含蛋白聚糖的组织液相互作用。这个网络在不同区域具有深度依赖性的纤维组织。了解胶原纤维如何响应外部载荷是阐明损伤形成背后机制以及管理骨关节炎等退行性疾病的关键。本研究采用偏振分辨二次谐波产生（pSHG）显微镜来量化胶原纤维的超微结构组织及其在接近体内条件下沿骨 - 软骨外植体深度的空间梯度。通过结合原位加载，我们通过量化胶原纤维主方向和排列程度的变化来研究其响应。沿着外植体纵向平面（0.5毫米×2毫米）以高分辨率（1微米）捕获了胶原组织的空间梯度和异质性。对特定区域的超微结构特征进行了量化，以帮助定义区域边界，揭示不同总厚度下一致的区域比例。在压缩下，过渡区表现出胶原纤维最显著的重新组织。它最初通过纤维的重新定向允许大变形，然后收紧纤维排列以防止过度变形，表明存在一种响应应变水平增加的动态适应机制。我们的结果提供了软骨超微结构和微力学的全面、特定区域基线，这对于研究退行性疾病的发病和进展、设定治疗干预目标以及指导软骨修复和再生努力至关重要。意义声明：在接近体内条件下，沿骨软骨外植体纵向平面（0.5毫米×2毫米）的整个深度以高分辨率（1微米）实现了对胶原超微结构组织的空间梯度和异质性的前所未有的量化。基于超微结构特征提出了用于确定区域边界的新解剖学标志，并在不同总厚度的外植体中发现了一致的区域比例。证明了胶原纤维最初在低应变水平下通过重新定向做出响应，在软骨变形中起重要作用，特别是在过渡区内。在较高应变水平下，更多的胶原纤维重新排列，表明在不同应变水平下响应机制发生了动态转变。
