Element distributions and crystallographic properties of human bone at <140 nm resolution in 2D and 3D

Research output: Contribution to conferencePosterResearch

Biomineralized tissue such as bone or shells often have a complex hierarchical 3D structure ranging over several length scales. To understand their structure, a method for probing the nanoscale structure in 3D is needed. Bone is particularly challenging due to its' many layers of hierarchical structure in combination with the complex system of osteocyte cells interconnected by canaliculi. Recent developments in synchrotron x-ray focusing optics afford minute x-ray beams, which open opportunities for probing structures at length scales smaller than ever before. Herein, we present how we probe the elemental distribution and crystallographic properties of human bone in 2D and 3D using combined fluorescence and diffraction scattering computed tomography (F-CT and DSCT) [1] with a 50 nm pencil X-ray beam. PURPOSE: This study aims to develop nanoscale 3D multimodal X-ray imaging with the purpose of studying the local chemistry around the mineralization front where new bone is formed, and around canaliculi. METHODS: We conducted multimodal tomography using a nanofocused <50 nm diameter X-ray beam. A 2.6x3.1 µm2 cross section rod-shaped sample was FIB-cut from human iliac crest bone. The sample was cut from an area close to an osteocyte and thus presents several canaliculi. We recorded 2D diffraction patterns and fluorescence spectra at each point in a 50 nm raster scan grid pattern. This was repeated for each of 92 projection angles covering 0-182°. This allowed us to reconstruct tomographically both x-ray diffraction patterns and the elemental composition in a ~5x5x3 µm3 volume encompassing the sample. We determined an upper estimate of the achieved resolution by fitting sharp features within the specimen. Secondly, we measured several 2D scans with the same beam size on several-micron thick human bone encompassing the mineralization front to shed light on the biomineralization process. RESULTS: We show that tomographic reconstruction of x-ray diffraction and fluorescence information is possible with these minute X-ray beams. The resolution was <140 nm estimated from features in reconstructed images indicating that the true resolution is in the 50-140 nm range. With this resolution we were able to clearly distinguish between canaliculi and solid bone based both on calcium fluorescence and mineral diffraction signals. On the 2D sample, we could follow the mineralization process and the spatial distribution of oligoelements such as zinc in relation thereto. CONCLUSIONS: This work show that biomineral crystalline structure and elemental composition can be studied in 3D at length scales an order of magnitude smaller than hitherto available in sample volumes of biological relevance. This method will allow studying biominerals in more detail than ever before especially around distinct structural features like osteocytes. [1] M. E. Birkbak, H. Leemreize, S. Frolich, S. R. Stock, H. Birkedal, Nanoscale 2015, 7, 18402.eon
Original languageEnglish
Publication year21 Oct 2019
Publication statusPublished - 21 Oct 2019
EventInternational Conferences on the Chemistry and Biology of Mineralized Tissues - Fairmont Le Chateau Montebello, Montebello, Canada
Duration: 21 Oct 201925 Oct 2019
Conference number: 13


ConferenceInternational Conferences on the Chemistry and Biology of Mineralized Tissues
LocationFairmont Le Chateau Montebello
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