In Situ Bending Reveals Simultaneous Enhancements of Strength and Ductility of Cortical and Cancellous Layers Induced by the Cartilage Layer.

ABSTRACT

The energy absorption and toughening effect of cartilage could effectively protect bone from damage, and the enhancement mechanisms of cartilage on deformation resistance or strength need to be revealed. Using a self-developed in situ bending tester integrated with an optical microscope, in situ bending of the composite bone structure consisting of the cartilage layer and cortical and cancellous layers was carried out, accompanied by simultaneously obtained continuous morphological changes in diverse deformation layers. Although the bending resistance of pure cartilage layer was only 0.3 N, the significant enhancements of bone strength and ductility induced by the cartilage layer were experimentally revealed, as the peak loads and ultimate bending deflections of the composite structure increased by 1.49- to 2.14-fold and 1.43- to 2.12-fold, respectively. The scanning electron microscopy images of the composite bone structure at various locations with disparate stress conditions exhibited significant difference in crack sizes and degrees of tearing damage. The cartilage layer was verified to induce a layered tearing dimple feature to inhibit the crack propagation and further enhance the deformation resistance. The frequency shift comparison between the Raman spectroscopies of various microregions also indirectly verified the inhibition effect of the cartilage layer on the stress increment in the cortical layer.