Two-dimensional Image Analysis And Property Investigations Of Cancellous Bone Microstructure

Cancellous bone matrix has been extensively used as the stenting material of tissue-engineering bone due to its excellent osteogenic property. Recently, promoted by the scientific and clinical problems such as age-related fracture, relaxation of artificial limb and bone remodelling, the experimental researches and numerical analysis on the mechanical property of cancellous bone have become more and more important. It has been proposed that cancellous bone is able to serve as solid-liquid coupling, biphasoc porous media, while the viscoelastic behavior and energy dissipation property in cancellous bone were cause to a great extent by the pore liquid flow and diffusion; Additionally, the change of microstructure of cancellous bone significantly affects its mechanical property. The microstructure property of cancellous bone has hence aroused more concerns in order to simulate the micro-dynamic environment of cancellous bone under in vivo physiological conditions.As the matter of fact, porosity and permeability are the most important indicators to describe the microstructure of cancellous bone. However, to date, only few literatures have reported the measurement methodology on the porosity and permeability of the microstructure of cancellous bone, and the effect of the microstructure change of cancellous bone on its mechanical properties has been still uncertain.Three aspects of cancellous bone microstructure researches were carried out in this paper. Firstly, a two-dimensional image analysis method was developed to determine the distribution characteristics of cancellous bone (fresh pig tibia cancellous bone) porosity. Secondly, cancellous bone was typically obtained as a fluid-solid coupled porous media and Darcy's Law was introduced to design the measurement device of cancellous bone permeability, where a penetrating fluid was driven by lower-pressure gas. Finally, the effects of microstructure changes caused by microstructure form, anatomic site, and age on its mechanical properties were analyzed according to the published literature data.The main results and conclusions are as follows:â‘ The cancellous bone porosity is gradually decreased along the axial direction of tibiae and approaching to the compact bone,but almost constant along the transversal direction.Correspondingly, cancellous bone is modeled as a transversely isotropic,1iquid saturated porous solid.Besides, the two-dimensional image analysis method stated in this paper can be used to relatively accurately determine the distribution characteristics of the cancellous bone porosity from different directions if the number of cancellous bone sections is sufficient.â‘¡The average Darcy permeability of all twenty-four cancellous bone specimens is (1.88±0.21)×10^-10·m²Â·Pa^-1·s^-1. Under four different driving pressures (50, 100, 150, 200 kPa), there were not significant changes in the Darcy permeability of cancellous bone among all specimen groups. It indicates no obvious correlation between Darcy permeate rate of cancellous bone specimens and driving pressure of penetrating fluid. These data are in accordance with Darcy's Law. It was implied from the stated experimental data that this experimental set-up could be used to determine the Darcy permeability of cancellous bone and provide a simple and practical experimental approach suitable for the cancellous bone permeability research.â‘¢The microstructure changes of cancellous bone can significantly affect the mechanical properties: a) The elastic modulus is related to the hole circumference of the model of rod-rod structure; that is, greater hole circumference corresponds to smaller elastic modulus; b) In children, the strength and elastic modulus of the epiphysial and distal lamellar bones are greater than those of the cancellous bone in epiphysial proximal lamellar sites; and c) The six indicators (such as elastic modulus, energy absorption, yield strength, ultimate strength and ultimate strain) of the tested thigh bone cancellous bone of the youth are all significantly greater than the corresponding ones in the older group.â‘£The method established in this paper, as well as the obtained results are conducive for full understanding of the complicated properties of the cancellous bone, and can help us to realistically simulate the micro-dynamic environment of cancellous bone under in vivo physiological conditions. The methods and results of this paper can also contribute to promoting the technology development of age-related fractures, prosthetic relaxation, as well as bone reconstruction and other bone tissue engineering.