The Ultrastructure of Bone and Its Relevance to Mechanical Properties

Abstract

Bone is a biologically generated composite material comprised of two major structural components: crystals of apatite and collagen fibrils. Computational analysis of the mechanical properties of bone must make assumptions about the geometric and topological relationships between these components. Recent transmission electron microscope (TEM) studies of samples of bone prepared using ion milling methods have revealed important previously unrecognized features in the ultrastructure of bone. These studies show that most of the mineral in bone lies outside the fibrils and is organized into elongated plates 5 nanometers (nm) thick, ∼80 nm wide and hundreds of nm long. These so-called mineral lamellae (MLs) are mosaics of single 5 nm-thick, 20-50 nm wide crystals bonded at their edges. MLs occur either stacked around the 50 nm-diameter collagen fibrils, or in parallel stacks of 5 or more MLs situated between fibrils. About 20% of mineral is in gap zones within the fibrils. MLs are apparently glued together into mechanically coherent stacks which break across the stack rather than delaminating. ML stacks should behave as cohesive units during bone deformation. Finite element computations of mechanical properties of bone show that the model including such features generates greater stiffness and strength than are obtained using conventional models in which most of the mineral, in the form of isolated crystals, is situated inside collagen fibrils.

Investigation of strontium transport and strontium quantification in cortical rat bone by time-of-flight secondary ion mass spectrometry

“…In both healthy and osteoporotic cortical bone, we obtain three-dimensional mass data which show nearly homogeneous Ca 2þ distribution, while for Sr 2þ , a concentration gradient with several fast diffusion paths can be observed (figure 1). These fast diffusion paths in cortical bone are possibly Haversian canals or osteocyte networks and need to be further investigated [42,43].…”

Collagen Hybrid Formulations for the 3D Printing of Nanostructured Bone Scaffolds: An Optimized Genipin-Crosslinking Strategy

“…The particle suspension was subsequently added to the collagen solution, obtained after dissolving type I collagen powders derived from bovine Achilles tendon (Blafar Ltd., Dublin, Ireland) in the same solvent, as schematically represented in Figure 1 . The relative amount of collagen powders and nanoMBG_Sr4% was calculated based on the ratio and volume percentages of the organic and inorganic constituents of bone, where collagen and hydroxyapatite count for 53 vol.% and 47 vol.%, respectively [ 40 ]. The resulting suspension of collagen and nanoMBG_Sr4% reached a final collagen concentration of 1.5 wt.% after pH neutralization, using 1 M NaOH.…”

Bone Ultrastructure as Composite of Aligned Mineralized Collagen Fibrils Embedded Into a Porous Polycrystalline Matrix: Confirmation by Computational Electrodynamics

“…ρ e,gap = 396 e/nm 3 , ρ e,OV = 412 e/nm 3 ; results in a diffraction pattern loosing any significant peak characteristics, see red line in Figure 7A. Putting all the mineral into the fibrils, leads to already better results, characterized by a Root-Mean-Square error of RMS = 0.23, see Figure 7B-however, this assumption is untenable from a micromechanical viewpoint, as the tissue anisotropy would be heavily overestimated; see e.g., Hellmich and Ulm [96] and Schwarz et al [97]. The best result is obtained for the extracollageneous mineral concentration being the same inside and outside the fibrils, characterized by a Root-Mean-Square error of RMS = 0.181, see Figure 7C-and this mineral distribution also proved essential for the performance of various micromechanical models [37,39,40,65].…”