IBMS BoneKEy | BoneKEy Watch

New insights into human lamellar bone organization



DOI:10.1038/bonekey.2015.4

Although the majority of the human skeleton comprises lamellar bone, its microstructure is not completely understood. In this study, Reznikov et al. use a dual-beam electron microscope and the Serial Surface View (SSV) method.

The sample preparation involves identifying an area of interest, demineralizing, conductive staining, freeze substituting and embedding in Epon. The SSV consisted in protecting the sample with a thin patch of platinum and then exposing the underlying structure of the lamellar bone surface within a U-shaped trench. The exposed surface is then sequentially milled with a focused ion beam and then examined with an electron beam at high magnification.

The images reveal an ordered layer of mineralized collagen fibrils that lie in two directions in the lamellar bone. One is perpendicular to the longitudinal axis of the bone while the other lies at an angle of 10-20o to that long axis. This layer also contains fanned arrays of ordered fibrils of collagen containing 2-3 μm diameter rods lying parallel to the lamellar boundaries. A disordered component fills the spaces between the rods and envelops them. Staining revealed the presence of an organic substance in addition to collagen, as yet unidentified.

Editor’s comment: The application of the recently developed SSV methodology to the lamellar bone of three human femora provides a breakthrough in our understanding of lamellar bone organization. The fascinating videos of the 3D reconstructions, which have a resolution of approximately 10nm, reveal the presence of two phases of collagen organization that reconcile the rotated plywood model with the alternative observation of alternating collagen rich and poor layers.


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