Finite Element Simulation Of The Poroelastic Behavior Of Osteon

In the daily physiological activities(such as walking, running, jumping,etc.), bone tissue will bear different forms of cyclic loading. The microstructure of bone tissue called osteon will feel the external loading directly or indirectly with flowing of bone fluid to change the macroscopic property to withstand the loads. Variationsof bone fluid’s pressure and velocity have a major influence on the exchange and transport of nutrients and metabolic waste, the flow shear stress of bone fluid, the flow potential of bone fluid etc. Under the cyclic loading of daily activities will induce a certain amount of fatigue microcracks in osteon,which is considered to be an important stimulus in the bone remodeling.However, this “feel” and “adapt” mechanism has not been well known for us.For this reason, this paper establishes osteon’s analysis model and varieties of finite element model and focus on the comparison of the bone fluid pressure and velocity to explore the mechanism.The more detailed task list and the main conclusion are as follows:㈠, We respectively proposed a hollow and Haversian fluid(pressure)contained osteon model to examine its intraosseous pressure characteristics and fluid flowing behavior under the external loading environments. The relationship among the external loads(axial and cyclic), intraosseous pressure,and fluid velocity was established. Some conclusions are obtained below: ⑴The fluid pressure amplitude in the Haversian fluid(pressure) considered osteon model is much higher than that in hollow osteon model. With the increasing ofthe amplitude of pulse pressure in Haverian canal the fluid pressure amplitude increases linearly. The frequency change of pulse pressure in Haverian canal the fluid pressure amplitude has a little influence, moreover, the fluid pressure amplitude decrease with the increasing of the frequency of pulse pressure in Haverian canal; ⑵The bone fluid velocity is no difference when compare the Haversian fluid pressure model with the hollow osteon model. Moreover, the amplitude and frequency of pulse pressure in Haverian canal have little effect on the bone fluid velocity too.㈡,In order to evaluate the poroelastic responses with different load types’ osteon three kinds of finite element models with different loading(axial compression、bend loading、compressive bending) are established. The results show :⑴ The pressure and velocity amplitudes produced in axial compression loading present an axial symmetrical distribution, while in compressive bending is axial centrosymmetric distribution. In the bend loading case, the pressure amplitude presents an antisymmetrical distribution, but the velocity amplitude is axially symmetrical distributed. ⑵ under the same loading amplitude the pressure and velocity amplitudes produced in axial compression loading case are the largest, followed by compressive bending loading, and the smallest is bending.㈢, In order to evaluate the poroelastic responses with microcracks’ osteon,varieties finite element models with different shape, size and direction’s microcrack are established. The results show :⑴equalarea microcrack with ellipsoid-like shape produced a larger fluid pressure and velocity fields in the osteon than that of rectangular shaped. ⑵in the elliptic microcracks, the longer of the length(major semi-axis) induce a smaller fluid pressure and velocity amplitudes, whereas the width(minor axis) has little effect.(3)The direction of the microcracks(major axial direction) with the same size has a limited influence area around about 1/15 of the osteon cross-sectional area.