Hofmann Tobias, Heyroth Frank, Meinhard Holger, Fränzel Wolfgang, Raum Kay
Q-BAM Group, Department of Orthopedics, Martin Luther University of Halle-Wittenberg, 06097 Halle, Germany.
J Biomech. 2006;39(12):2282-94. doi: 10.1016/j.jbiomech.2005.07.009. Epub 2005 Sep 6.
Measurement of the elastic properties of single osteon lamellae is still one of the most demanding tasks in bone mechanics to be solved. By means of site-matched Raman microspectroscopy, acoustic microscopy and nanoindentation the structure, chemical composition and anisotropic elasticity of individual lamellae in secondary osteons were investigated. Acoustic impedance images (911-MHz) and two-dimensional Raman spectra were acquired in sections of human femoral bone. The samples were prepared with orientations at various observation angles theta relative to the femoral long axis. Nanoindentations provided local estimations of the elastic modulus and landmarks necessary for spatial fusion of the acoustic and spectral Raman images. Phosphate nu(1) (961 cm(-1)) and amide I (1665 cm(-1)) band images representing spatial distributions of mineral and collagen were fused with the acoustic images. Acoustic impedance was correlated with the indentation elastic modulus E(IT) (R(2)=0.61). Both parameters are sensitive to elastic tissue anisotropy. The lowest values were obtained in the direction perpendicular to the femoral long axis. Acoustic images exhibit a characteristic bimodal lamellar pattern of alternating high and low impedance values. Since this undulation was not associated with a variation of the phosphate nu(1)-band intensity in the Raman images, it was attributed to variations of the lamellar orientation. After threshold segmentation and conversion to elastic modulus the orientation and transverse isotropic elastic constants were derived for individual ensembles of apparent thin and thick lamellae. Our results suggest that this model represents the effective anisotropic properties of an asymmetric twisted plywood structure made of transverse isotropic fibrils. This is the first report that proves experimentally the ability of acoustic microscopy to map tissue elasticity in two dimensions with micrometer resolution. The combination with Raman microspectroscopy provides a unique way to study bone and mineral metabolism and the relation with mechanical function at the ultrastructural tissue level.
测量单个骨单位薄片的弹性特性仍然是骨力学中最具挑战性的待解决任务之一。借助位点匹配拉曼显微光谱、声学显微镜和纳米压痕技术，对次生骨单位中单个薄片的结构、化学成分和各向异性弹性进行了研究。在人股骨切片中获取了声阻抗图像（911兆赫兹）和二维拉曼光谱。制备的样本具有相对于股骨长轴的不同观察角度θ的取向。纳米压痕提供了弹性模量的局部估计以及声学和光谱拉曼图像空间融合所需的标记。代表矿物质和胶原蛋白空间分布的磷酸盐ν₁（961厘米⁻¹）和酰胺I（1665厘米⁻¹）带图像与声学图像进行了融合。声阻抗与压痕弹性模量E(IT)相关（R² = 0.61）。这两个参数对弹性组织各向异性都很敏感。在垂直于股骨长轴的方向上获得了最低值。声学图像呈现出高低阻抗值交替的特征双峰层状模式。由于这种起伏与拉曼图像中磷酸盐ν₁带强度的变化无关，因此归因于层状取向的变化。经过阈值分割并转换为弹性模量后，得出了明显薄和厚薄片的各个集合的取向和横向各向同性弹性常数。我们的结果表明，该模型代表了由横向各向同性原纤维制成的不对称扭曲胶合板结构的有效各向异性特性。这是第一份通过实验证明声学显微镜能够以微米分辨率在二维中绘制组织弹性的报告。与拉曼显微光谱的结合提供了一种独特的方法来研究骨和矿物质代谢以及在超微结构组织水平上与机械功能的关系。
