Intrafibrillar damage accumulation & the contribution of extrafibrillar mineral to bone elastic modulus

Bone quality deterioration due to age-related causes are manifested in reduced toughness of bone. Microdamage accumulation (Micro crack, diffuse Damage) is involved in the post yield deformation of bone, which makes it important to understand the mechanism of microdamage progression in bone to elucidate the causes of age-related bone fractures. In this study a 2D finite element model of nanostructure of bone were built in ABAQUS to represent the ultra-structural behavior of bone.

The first objective of this study was to understand the effect of interfacial bonding between the mineral and collagen phase on the microdamage accumulation in the mineralized collagen fibril of bone. The main purpose of this study is to understand how different types of interface can influence the damage progression in bone. Three types of mineral- collagen interaction (Ionic interaction, Hydrogen/van der Waals bonds and van der Waals/viscous shear in opening and sliding mode respectively) were simulated in this study using cohesive zone modeling techniques. The outcome of this study will help understand the mineral-collagen interaction during the post yield deformation of bone at ultrastructural levels, which may give rise to insightful information on the underlying mechanism of bone fragility fractures. The results of this study indicated that the interface between mineral and collagen may play an important role in microdamage accumulation in mineralized collagen fibrils.

The second objective of this study was to find the influence of extrafibrillar mineral to the elastic modulus of bone. Also, a 2D finite element of lamellae with staggered mineralized collagen fibrils was developed to address this issue. The results indicate that the extrafibrillar mineral considerably reinforces the stiffness of lamellar structure. In addition, the elastic modulus of bone is dependent on the volumetric ratio between the intra and extrafibrillar mineral crystals. It was observed that the estimated elastic modulus of the model is similar to that of human bone samples when the volume fraction of the extrafibrillar crystals is 45-62.5 vol% of the total mineral phase.