Abstract
Human bone is a complex hierarchical material. Understanding bone structure and its corresponding composition at the nanometer scale is critical for elucidating mechanisms of biomineralization under healthy and pathological states. However, the three-dimensional structure and chemical nature of bone remains largely unexplored at the nanometer scale due to the challenges associated with characterizing both the structural and chemical integrity of bone simultaneously. Here, we use correlative transmission electron microscopy and atom probe tomography for the first time, to our knowledge, to reveal structures in human bone at the atomic level. This approach provides an overlaying chemical map of the organic and inorganic constituents of bone on its structure. This first use of atom probe tomography on human bone reveals local gradients, trace element detection of Mg, and the co-localization of Na with the inorganic-organic interface of bone mineral and collagen fibrils, suggesting the important role of Na-rich organics in the structural connection between mineral and collagen. Our findings provide the first insights into the hierarchical organization and chemical heterogeneity in human bone in three-dimensions at its smallest length scale – the atomic level. We demonstrate that atom probe tomography shows potential for new insights in biomineralization research on bone.
Highlights
Human bone is a complex hierarchical material
Focused ion beam (FIB) serial sectioning has surfaced as another potential 3D imaging modality for bone structure, present studies[2,6] report demineralized bone tissue and this modality is restricted to the resolution limits of scanning electron microscopy (SEM)
atom probe tomography (APT) unveiled the chemical distributions at the near sub-nanometer level, which could be correlated with the electron microscopic images
Summary
Human bone is a complex hierarchical material. Understanding bone structure and its corresponding composition at the nanometer scale is critical for elucidating mechanisms of biomineralization under healthy and pathological states. The characterization of the nanoscale structural and chemical architecture of bone embodies a number of challenges, in three-dimensions Established techniques, such as nano-computed tomography (nano-CT), can probe the 3D structure of bone on the order of 100 nm yet the constituents of bone, collagen fibrils and carbonated hydroxyapatite crystals, are orders of magnitude smaller[9]. The inherent energy and spatial resolution limits of analytical spectroscopic techniques, such as energy dispersive x-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) on beam-sensitive bone, have prevented the possibility for combined TEM and chemical analysis in 3D at the nanometer level To circumvent these challenges, we demonstrate that correlative compositional contrast imaging in the TEM with atom probe tomography (APT) provides a both a structural and chemical nanotomography of human bone. This technique has enabled us to perform the first APT on human bone to identify chemical heterogeneities and localization of trace elements
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