Elastic modulus mapping for bovine cortical bone from submillimeter- to submicron-scales using PeakForce Tapping atomic force microscopy

Bone is a composite material consisting of organic and inorganic components that are organized into hierarchical structures to provide load-bearing functions. This paper presents the results of PeakForce Tapping atomic force microscopy (AFM) scans on cut and polished bovine cortical bone specimens that were submerged in water. The elastic modulus map and surface morphology were obtained for various bone hierarchical structures from submillimeter- to submicron-scales. The elastic modulus of osteons (20.51 ± 6.85 GPa) was slightly lower than the interstitial bone (21.87 ± 5.48 GPa); they were both much greater than that of the cement lines (7.49 ± 4.23 GPa). The elastic modulus in the lamella structures varied periodically from higher values in thick sub-lamellae (21.49 ± 6.58 GPa) to the lower values in thin sub-lamellae (9.67 ± 2.69 GPa). The results also show relatively softer mineralized collagen fibril bundle arrays (12.94 ± 2.71 GPa) embedded in harder matrix materials (28.39 ± 5.75 GPa). The variations in the elastic modulus suggest different degrees of mineralization or different fibril orientations. The histograms of elastic modulus indicate the dominating compositions or dominating fibril orientations.