Crack Bridging and Deflection Toughening Mechanisms of Staggered Hydroxyapatite Lamellar Microstructure in Bone

The observation experiment results of the microstructure of tibial cortical bone show that the cortical bone is a layered bio-ceramic composite material composed of Hydroxyapatite (HAP) and collagen arranged alternately. HAP is a reinforcing phase and accounts for a large proportion in cortical bone. These hydroxyapatites have long and thin sheet-like structures parallel to the outer surface of the bone, forming a unique " staggered structure" with collagen. During the propagation of cracks in the cortical bone of the tibia, crack bridging will occur. Based on the microstructural characteristics of HAP sheets and crack bridging observed in cortical bone, the effect mechanism of staggered structural features and HAP volumetric proportion on tibial fracture toughness was studied. Under a specific variation range, elevated hydroxyapatite proportion and its sheet aspect ratio will lead to obvious growth in the crack deflection coefficient and the dissipated fracture energy. As the volumetric proportion of HAP sheets rises from 0.6 to 0.8, the overall fracture toughness of this staggered composite structure improves markedly. This investigation provides reliable theoretical support for the optimized preparation and structural design of high-strength biomimetic ceramic composites.