Effects of direction and shape of osteocyte lacunae on resisting impact and micro-damage of osteon

Microcrack behavior in bone: Stress field analysis at osteon cement line tips

Bone microstructure governs microcrack propagation complexity. Current research, relying on linear elastic fracture mechanics, inadequately considers authentic multi-level structures, like cement lines and osteons, impacting stress intensity at cracks. This study, by constructing models encompassing single or multiple osteons, delves into the influence of factors like crack length, osteon radius, and modulus ratio on the stress intensity factor at the crack tip. Employing a fracture mechanics phase-field approach to simulate crack propagation paths, it particularly explores the role of cement lines as weak interfaces in crack extension. The aim is to comprehensively and systematically elucidate the critical factors of bone microstructure in the context of crack propagation.

The influence of different shaped osteocyte lacunae on microcrack initiation and propagation

BACKGROUND

The morphology of osteocyte lacunae varies in bones of different ages and bone pathologies. Osteocyte lacunae can cause stress concentration and initiate microcracks. However, the influence of changes in osteocyte lacunar shape on microcrack is unknown. Therefore, the aim of this study was to determine the effects of osteocyte lacunae with different shapes on microcrack initiation and propagation.

METHODS

Osteon models containing osteocyte lacunae with different shapes were established. The progressive damage analysis method, based on computer simulations, was used to study the evolution of microdamage within the osteon, including the processes of intralaminar and interlaminar microdamage.

FINDINGS

Models with larger DoE values can effectively delay or prevent the formation of linear microcracks, which ensures high fracture toughness of cortical bone. It is subjected to stronger mechanical stimulation, making it more sensitive to loads. Models with smaller DoE values increase the load threshold for microdamage generation and reduces its impact on bone mechanical performance, making it less susceptible to microdamage than models with larger DoE values.

INTERPRETATION

These findings enhance the limited knowledge of the influence of the lacunar shape on microdamage and contribute to a better understanding of bone biomechanics.

Research on biomimetic design and impact characteristics of periodic multilayer helical structures

Osteons are composed of concentric lamellar structure, the concentric lamellae are composed of periodic thin and thick sub-lamellae, and every 5 sub-lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four biomimetic models with different fiber helix angles were established and fabricated according to the micro-nano structure of osteon. The effects of the fiber periodic helical structure on impact characteristic and energy dissipation of multi-layer biomimetic composite were investigated. The calculation results indicated that the stress distribution, contact characteristics and fiber failur during impact, and energy dissipation of the composite are affected by the fiber helix angle. The stress concentration of composite materials under external impact can be effectively improved by adjusting the fiber helix angle when the material composition and material performance parameters are same. Compared with the sample30, the maximum stress of sample60 and sample90 increases by 38.1% and 69.8%, respectively. And the fiber failure analysis results shown that the model with a fiber helix angle of 30° has a better resist impact damage. The drop-weight test results shown that the impact damage area of the specimen with 30° helix angle is smallest among the four types of biomimetic specimens. The periodic helical structure of mineralized collagen fibers in osteon can effectively improve the impact resistance of cortical bone. The research results can provide useful guidance for the design and manufacture of high-performance, impact-resistant biomimetic composite materials.

Bionic design based on micro-nano structure of osteon and its low-velocity impact damage behavior

It is found that the osteon is composed of thin and thick lamellae which are periodic and approximately concentric, every 5 lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four bionic composite models with different fiber helix angles were established and fabricated according to the microstructure of mineralized collagen fibers in osteon. Based on the impact analysis of four kinds of bionic composite models, the effects of the fiber periodic spiral structure on the impact resistance and energy dissipation of multi-layer bionic composite were investigated. The analysis results show that the fiber helix angle affects the impact damage resistance and energy dissipation of multi-layer fiber reinforced composites. Among the 4 kinds of multi-layer composite models, the composite model with helix angle of 30° has better comprehensive ability to resist impact damage. The test results show that the impact damage area of the specimen with 30° helix angle is smallest among the 4 types of bionic specimens, which is consistent with the results of finite-element impact analysis. Furthermore, in the case of without impact damage, the smaller the fiber helix angle is, the more uniform the stress distribution is and more energy is dissipated in the impact process. The periodic spiral structure of mineralized collagen fibers in osteon are the result of natural selection of biological evolution. This structure can effectively improve the ability of cortical bone to resist external impact. The research results can provide useful guidance for the design and manufacture of high-performance and strong impact resistant bionic composites.

Finite element analysis on multi-toughening mechanism of microstructure of osteon

The toughening mechanism of cortical bone is closely related to its hierarchical microstructure. Osteon is the most important microstructure of cortical bone. Therefore, it is very important to study the toughening mechanism of the microstructure of osteon. There are three main kinds of cracks in cortical bone: external crack of osteon, internal radial cracks of osteon and microporous damage cracks. Numerical models for these three kinds of cracks are established by XFEM and the progressive damage approach, respectively. The multi-toughening mechanisms of microstructure of osteon are found. The cement line on the outside of osteon is its first toughening mechanism, which can make the crack deflection and improve the fracture resistance of osteon. The resistance of cement line to fracture increases with the decrease of the strength and the increase of the thickness. The second toughening mechanism is elliptical osteocyte lacunae, which can attract the crack into the elliptical lacunae and cause stress redistribution to prevent the crack propagation. The annularly elliptical lacuna structure is an optimized arrangement and shape of microstructure, which is the third toughening mechanism of osteon. This microstructure can determine the location of the crack initiation and make the microcracks propagate along the annular direction rather than penetrating into the haversian cannal to protect the integrity of the osteon. The study of these toughening mechanisms provides new ideas for the research and design of synthetic composite structures.