| The hierarchical structure, nanomechanical properties and their response during demineralization of mature human dental enamel and wild type zebrafish (Danio rerio) skeletal bone, two representative systems of the apatite-based hard tissues formed under different mineralization mechanisms, were studied in this work. Then from the point of hierarchical assembly, the microstructural characteristics of the apatite-based mineralized biomaterials, as well as their fine-tuning to the nanomechanical properties were discussed in detail.Human dental enamel is mostly built up of hydroxyapatite crystals in well controlled assembly manners. Based on the investigations to its microstructure from nano-scale to micron-scale, we for the first time proposed a novel model of 7 levels hierarchical structure of enamel and described its organization with a scheme representing a complete spectrum that covers a wide scale from nanometer to millimeter. Hydroxyapatite nano-fibrils are the fundamental hierarchical structure level, which then assemble into fibrils and fibers level by level. With the different orientations and densities of the crystal nano-fibrils, the prism/interprism/sheath continuums are imposed that are differently arranged across the whole enamel layer. More than that, we for the first time reported the significant alternations of the nanohardness and elastic modulus between prisms and sheaths, which can strongly support the close relationship between the microstructure and nanomechanical properties of enamel in terms of hierarchy.The zebrafish skeleton is another model with hierarchical structure. Explorations to the mineralization of the collagen fibrils, the hierarchical assembly structure and the nanomechanical properties across the whole thickness of the bone wall provide an efficient way to understand the formation and remodeling of the hierarchical structure of bone. The new formed bone near the periosteum mainly contains the mineralized... |
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