Microstructural characteristics and nanomechanical properties across the thickness of the wild-type zebrafish skeletal bone

In this study, both atomic force microscopy (AFM) and transmission electronic microscopy (TEM) were used to explore the microstructural characteristics across the thickness of the wild-type zebrafish skeletal bone wall. Evident variations of the microstructure were observed from the inner to outer side of the bone by AFM, indicating that the mineralized fibrils become thinner and more confusing across the thickness. Correspondingly, similar results could be concluded from the TEM investigations. Both of the AFM and TEM results imply that the degree of mineralization from near the center of the skeletal bone were greater than those from the outer layers, which was supported by the TEM electron diffraction results. Nanoindentation tests displayed that there is a decline in both nanohardness and elastic modulus from the center of the skeletal bone outward. These alterations of mechanical properties across the thickness can be visually reflected by the AFM topographies of the residual indent impressions. Also, the characteristics of biomineralization and microstructures of zebrafish skeletal bone are similar with those of human Haversian bone. Zebrafish skeletal bone could be viewed as a simple model to study mineralization characteristics of the human Haversian system and human bone diseases.