On The Modeling Of Cancellous Bone Porous Structure Based On Topology Optimization Technology

Bone defect,comminuted fracture and other orthopedic diseases have seriously affected the normal life of patients,which are difficult to repair damage by the bone recovery mechanism.Therefore,it is necessary to replace the injury site by an external implant to help patients recover normal level.In order to solve the problems of traditional solid implants,it is common to design the implant to be a porous structure.The structure of real cancellous bone is very complex,with great randomness.It can be applied to the simulation analysis,but hard to process.The traditional CAD design method cannot control the property of porous structure,so how to reconstruct the cancellous model with specific property is of great significance.In this paper,topology optimization technology can give the objective function according to the design requirements artificially,and solve the reasonable model by setting the constraint condition.We took the pig femur as the research object,and set the mechanical properties of cancellous bone as the design goal to study the reconstruction problems of the model with porous structure based on topology optimization.The main contents include:(1)Based on the Wolff's law,the hypothesis that the volume fraction distribution of cancellous bone was related to its position in the femur was proposed.Image-based modeling method was used to reconstruct the cancellous bone model by Mimics 17.0 software.Then the volume fraction of each model was calculated and analyzed.The results showed that the volume fraction of cancellous bone varied with the position,the closer the pressure center,the greater the volume fraction.(2)The mechanical properties of the cancellous bone model were analyzed using the finite element method and representative volume element method by ANSYS software.The results showed that the mechanical properties of cancellous bone were anisotropic,and related to the volume fraction.In conclusion,the elastic modulus of the main pressure direction increased with the volume fraction.(3)Taking the volume fraction of cancellous bone as the constraint condition,the anisotropic mechanical properties of cancellous bone were set as the design goal,and the method of reconstructing cancellous bone model using topology optimization technique was proposed.Based on the variable density method,the interpolation function with the unit density as the design variable was introduced.The equivalent property of the model in the iterative process was solved by Homogenization method.Then the optimization results were displayed in ANSYS by threshold filtering method,and the 3D model of porous structure is reconstructed according to the optimization results.After numerical analysis,the model basically met the property requirements and the stress distribution is more uniform.The amount of data is greatly reduced,easy to process and post-process.The method of modeling the porous structure based on topology optimization technology not only solves the shortcomings of traditional modeling methods,but also combines the advantages of image modeling method,which is of great significance to the reconstruction of porous structure of anisotropic cancellous bone.It provides application research for bone implants on clinical bone disease treatment and rehabilitation.