Stock S R, Barss J, Dahl T, Veis A, Almer J D
Institute for Bioengineering and Nanoscience in Advanced Medicine, Northwestern University, Chicago, IL 60611-3008, USA.
J Struct Biol. 2002 Jul;139(1):1-12. doi: 10.1016/s1047-8477(02)00500-2.
Two noninvasive X-ray techniques, laboratory X-ray absorption microtomography (microCT) and X-ray diffraction mapping, were used to study teeth of the sea urchin Lytechinus variegatus. MicroCT revealed low attenuation regions at near the tooth's stone part and along the carinar process-central prism boundary; this latter observation appears to be novel. The expected variation of Mg fraction x in the mineral phase (calcite, Ca(1-x)Mg(x)CO(3)) cannot account for all of the linear attenuation coefficient decrease in the two zones: this suggested that soft tissue is localized there. Transmission diffraction mapping (synchrotron X-radiation, 80.8 keV, 0.1 x 0.1mm(2) beam area, 0.1mm translation grid, image plate area detector) simultaneously probed variations in 3-D and showed that the crystal elements of the "T"-shaped tooth were very highly aligned. Diffraction patterns from the keel (adaxial web) and from the abaxial flange (containing primary plates and the stone part) differed markedly. The flange contained two populations of identically oriented crystal elements with lattice parameters corresponding to x=0.13 and x=0.32. The keel produced one set of diffraction spots corresponding to the lower x. The compositions were more or less equivalent to those determined by others for camarodont teeth, and the high Mg phase is expected to be disks of secondary mineral epitaxially related to the underlying primary mineral element. Lattice parameter gradients were not noted in the keel or flange. Taken together, the microCT and diffraction results indicated that there was a band of relatively high protein content, of up to approximately 0.25 volume fraction, in the central part of the flange and paralleling its adaxial and abaxial faces. X-ray microCT and microdiffraction data used in conjunction with protein distribution data will be crucial for understanding the properties of various biocomposites and their mechanical functions.
两种非侵入性X射线技术，即实验室X射线吸收显微断层扫描（显微CT）和X射线衍射图谱分析，被用于研究海胆Lytechinus variegatus的牙齿。显微CT显示在牙齿的石质部分附近以及沿着嵴突 - 中央棱柱边界存在低衰减区域；后一观察结果似乎是新发现。矿物相（方解石，Ca(1 - x)Mg(x)CO₃）中镁分数x的预期变化无法解释这两个区域中线性衰减系数的所有降低：这表明软组织位于此处。透射衍射图谱分析（同步辐射X射线，80.8 keV，0.1×0.1mm²束斑面积，0.1mm平移网格，成像板面积探测器）同时探测了三维变化，并表明“T”形牙齿的晶体元素排列非常整齐。来自龙骨（近轴腹板）和远轴凸缘（包含初级板和石质部分）的衍射图案明显不同。凸缘包含两组取向相同的晶体元素，其晶格参数对应于x = 0.13和x = 0.32。龙骨产生一组对应较低x值的衍射斑点。其组成与其他学者对楔齿类牙齿所确定的组成大致相当，并且高镁相预计是与下面的初级矿物元素外延相关的次生矿物盘。在龙骨或凸缘中未发现晶格参数梯度。综合来看，显微CT和衍射结果表明，在凸缘的中央部分存在一条蛋白质含量相对较高的带，其体积分数高达约0.25，且与凸缘的近轴面和远轴面平行。结合蛋白质分布数据使用的X射线显微CT和微衍射数据对于理解各种生物复合材料的性质及其机械功能至关重要。
