Carden A, Rajachar R M, Morris M D, Kohn D H
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1078, USA.
Calcif Tissue Int. 2003 Feb;72(2):166-75. doi: 10.1007/s00223-002-1039-0. Epub 2002 Dec 10.
Raman spectroscopy and imaging are known to be valuable tools for the analysis of bone, the determination of protein secondary structure, and the study of the composition of crystalline materials. We have utilized all of these attributes to examine how mechanical loading and the resulting deformation affects bone ultrastructure, addressing the hypothesis that bone spectra are altered, in both the organic and inorganic regions, in response to mechanical loading/deformation. Using a cylindrical indenter, we have permanently deformed bovine cortical bone specimens and investigated the ultrastructure in and around the deformed areas using hyperspectral Raman imaging coupled with multivariate analysis techniques. Indent morphology was further examined using scanning electron microscopy. Raman images taken at the edge of the indents show increases in the low-frequency component of the amide III band and high-frequency component of the amide I band. These changes are indicative of the rupture of collagen crosslinks due to shear forces exerted by the indenter passing through the bone. However, within the indent itself no evidence was seen of crosslink rupture, indicating that only compression of the organic matrix takes place in this region. We also present evidence of what is possibly a pressure-induced structural transformation occurring in the bone mineral within the indents, as indicated by the appearance of additional mineral factors in Raman image data from indented areas. These results give new insight into the mechanisms and causes of bone failure at the ultrastructural level.
拉曼光谱和成像技术是分析骨骼、确定蛋白质二级结构以及研究晶体材料成分的重要工具。我们利用这些特性来研究机械加载及其导致的变形如何影响骨超微结构，验证了这样一个假设：响应机械加载/变形，骨骼光谱在有机和无机区域都会发生改变。我们使用圆柱形压头使牛皮质骨标本发生永久性变形，并结合多变量分析技术，利用高光谱拉曼成像研究变形区域及其周围的超微结构。使用扫描电子显微镜进一步检查压痕形态。在压痕边缘拍摄的拉曼图像显示，酰胺III带的低频成分和酰胺I带的高频成分增加。这些变化表明，由于压头穿过骨骼时施加的剪切力，胶原蛋白交联键发生断裂。然而，在压痕内部未发现交联键断裂的迹象，这表明该区域仅发生了有机基质的压缩。我们还提供了证据，表明压痕内的骨矿物质可能发生了压力诱导的结构转变，压痕区域的拉曼图像数据中出现的其他矿物质因素表明了这一点。这些结果为超微结构水平上骨骼破坏的机制和原因提供了新的见解。
