1 Physics, College of Engineering Mathematics and Physical Sciences, University of Exeter , Stocker Road, Exeter EX4 4QL , UK.
2 Princess Elizabeth Orthopaedic Centre, Royal Devon and Exeter Hospital , Barrack Road, Exeter EX2 5DW , UK.
J R Soc Interface. 2019 Jan 31;16(150):20180611. doi: 10.1098/rsif.2018.0611.
Type II collagen fibril diameters in cartilage are beneath the diffraction limit of optical microscopy, which makes the assessment of collagen organization very challenging. In this work we use polarization sensitive second harmonic generation (P-SHG) imaging to map collagen organization in articular cartilage, addressing in particular its behaviour under strain and changes which occur in osteoarthritis. P-SHG yields two parameters, molecular order and orientation, which provide measures of the degree of organization both at the molecular scale (below the diffraction limit) and above a few hundred nanometres (at the image pixel size). P-SHG clearly demonstrates the zonal collagen architecture and reveals differences in the structure of the fibrils around chondrocytes. P-SHG also reveals sub-micron scale fibril re-organization in cartilage strips exposed to tensile loading, with an increase in local organization in the superficial zone which weakly correlates with tensile modulus. Finally, P-SHG is used to investigate osteoarthritic cartilage from total knee replacement surgery, and reveals widespread heterogeneity across samples both microscale fibril orientations and their sub-micron organization. By addressing collagen fibril structure on scales intermediate between conventional light and electron microscopy, this study provides new insights into collagen micromechanics and mechanisms of degradation.
关节软骨中的 II 型胶原纤维直径低于光学显微镜的衍射极限，这使得胶原组织的评估变得极具挑战性。在这项工作中，我们使用偏振敏感二次谐波产生（P-SHG）成像来绘制关节软骨中的胶原组织，特别是在应变下的行为和骨关节炎中发生的变化。P-SHG 产生两个参数，分子有序性和取向，它们提供了在分子尺度（低于衍射极限）和几百纳米以上（在图像像素尺寸）的组织程度的度量。P-SHG 清楚地显示了关节软骨的分层胶原结构，并揭示了围绕软骨细胞的纤维的结构差异。P-SHG 还揭示了在拉伸加载下暴露的软骨条中的亚微米级纤维重新组织，在浅层区的局部组织增加，与拉伸模量的相关性较弱。最后，P-SHG 用于研究全膝关节置换手术中的骨关节炎软骨，并揭示了样本之间广泛的异质性，包括微观纤维取向及其亚微米组织。通过在传统光镜和电子显微镜之间的中间尺度上解决胶原纤维结构问题，本研究为胶原微观力学和降解机制提供了新的见解。
