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 2.12fold, 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.

Full Regional Creep Displacement Map of Articular Cartilage Based on Nanoindentation Array

“…13,14 In order to further analyze the differences in the structure, composition, and mechanical characteristics of AC, we have previously conducted studies on the mechanical properties of the whole cartilage surface and the in situ three-point bending test of the composite structure in cartilage. 15,16 The purpose of this experiment was to study the creep properties and morphological characteristics of the entire knee joint cartilage, and to record the surface morphology changes and internal composition structure. To this end, we recently used nanoindentation experiments to compare the creep properties of four regions in normal porcine knee cartilage, and determined the global creep properties of AC using five-point sampling.…”

“…Athanasiou et al found that the posterior cartilage of the medial femoral condyle was harder than the posterior cartilage of the lateral femoral condyle. , Appleyard′s study discovered that the AC under the meniscus of the sheep knee joint was 200% to 500% harder than the uncovered area . The ability of AC to perform its functions depends on its main components, unique structural and biomechanical properties. , In order to further analyze the differences in the structure, composition, and mechanical characteristics of AC, we have previously conducted studies on the mechanical properties of the whole cartilage surface and the in situ three-point bending test of the composite structure in cartilage. , The purpose of this experiment was to study the creep properties and morphological characteristics of the entire knee joint cartilage, and to record the surface morphology changes and internal composition structure. To this end, we recently used nanoindentation experiments to compare the creep properties of four regions in normal porcine knee cartilage, and determined the global creep properties of AC using five-point sampling.…”