Finite Element Analysis On The Effect Of Bioactives On The Mechanical Properties Of Bone Tissue

As the most important supporting part of the human body,bone have good stiffness and toughness because of biological evolution,which are due to its special bioactivity and highly ordered microstructure.The effects of the microstructure characteristics of bone tissue and the compositions of bioactive substances at different scales were studied on the biotribological behaviors and mechanical properties of bone tissue.This study can not only deepen the scientific understanding of bone tissue,but also has great significance in guiding the development of human bone repair and development and application of artificial bone materials.First,the effect of water on the biotribological behavior and the damage mechanism of bone tissue were studied in vitro.Then a multi-scale finite element model was established to simulate the effect of water on the stress distribution of bone tissue under practical conditions.Further,a three-dimensional finite element model of mineralized collagen microfibril at the nano scale and a RVE finite element model of a single bone plate at the micro scale were established separately.The effects of the volume fraction of the collagen phase and mineral phase as well as the number of cross-links on the mechanical properties of microfibril were investigated in detail.Moreover,the effects of the size,arrangement and interface mode of mineral crystal were researched on mechanical properties and failure strength of the bone plate.The main conclusion can be shown as follows:(1)Water has effect on the biotribological behaviors of bone.Fresh bone tissue has good plasticity,toughness and properties of friction and wear,which takes adhesive wear as the main wear mechanism.The decrease of water content resulted in elastic modulus and nano-hardness of bone tissue increased.Bone tissue becomes brittle and sensitive to the external loading and its tribological properties decreased significantly.(2)Multiscale finite element analysis shows that the Haversian canal,circumferential lamellas and the interstitial tissues appear stress concentration.With the increase of load,the stress concentration areas are gradually increasing.The drastic change of stress and the repeated deformation of the tissue easily result in the initiation and propagation of micro-crack and finally the peeling off and wear.In the meso-scale,the dehydration of boneplate medium has weaker function on absorption and interruption of stress,which is easy to induce the crack extension in pore and serious wear.In micro-scale,the high stress gradient around the lacunae and canaliculi are found.The dehydrated bone tissue has higher porosity,which will easily cause serious tissue damage and wear.(3)With the increasing of degree of mineralization,the microfibril model has obvious nonlinear behavior under tensile strain load.On the one hand,the introduction of collagen phase increases the overall toughness of microfibril and puts off the complete failure under relatively high load.Shrinkage behaviors of tropocollagen molecules directly affect the overall stiffnes and failure behavior.On the other hand,the number of cross-links can improved the mechanical properties of bone tissue but result in its brittle fracture.The numbers of cross-links have a greater influence on the overall mechanical properties of bone tissue with the decrease of volume fraction of collagen phase.When the number of cross-links is greater than 30,the overall mechanical properties of bone tissue are no longer sensitive to its number.(4)The size,the spatial orientation and arrangement mode of the mineral crystal have great influence on the mechanical properties of the whole bone plate.The stiffness and tensile yield strength of bone tissue increase with the increase of the crystal length.The different space orientations affect the mechanical properties of the bone plate in different directions.The gaps of adjacent crystal on length direction have small effect on the overall stiffness and the gaps on width direction have obvious effect on the stiffness.The study shows that the delamination and detachment of adjacent interfaces is mainly because of the different deformation between the mineral phase and collagen phase which have different stiffness.Different types of adjacent interfaces have great effect on the tensile yield strength and toughness of the compact bone plate,but a little effect on stiffness.