Structural Optimization Of Variable-Density Porous Bone Scaffolds

Large bone defects caused by fractures,trauma,tumor surgery and orthopedic surgery cannot rely on regeneration for self-repair.A suitable bone scaffold structure needs to be selected according to the location and size of the bone defect to repair the defect and promote bone regeneration.The porous form of structure that bone scaffolds have reduces the elastic modulus of the material and meets the mechanical environmental stimulus and material requirements for cell growth.The higher its permeability,the more adequate the diffusion of nutrients and waste materials,and the more favorable the growth and proliferation of cells.In this thesis,the bone implants with porous structure are studied as follows.(1)A parametric modeling method of functional gradient porous structure based on cubic is proposed for the problem of stress shieding arising from solid material bone implants,combined with bone itself having obvious density gradient distribution and other characteristics.(2)Poly Jet technology with the advantages of high precision and high fidelity is adopted as the manufacturing method for the gradient porous structure implants In this thesis.Combined with the physical experimental(including static compression and fluid experiments),the computational model of the elastic modulus of the porous structure was established based on ANSYS finite element simulation,and the computational model of its permeability was established based on Fluent simulation.(3)A dual-objective optimization algorithm was developed based on NSGA-II with the elastic modulus and permeability of the porous scaffold as the target.For the need of multiple calculations of elastic modulus and permeability in iterative optimization,a batch simulation processing method based on APDL,ICEM,and Fluent was developed to realize the coupled calculation between APDL,Fluent,and NSGA-II for optimizing the geometric characteristic parameters of the porous scaffold.(4)Taking the femoral bone defect as an example,the stress distribution of the bone at the defect is extracted,and the corresponding porous structure scaffold is generated based on the above parametric variable density structure design algorithm;based on this,multiobjective iterative calculations are performed to realize the porous structure design with the implant matching elastic modulus and the maximum permeability.In this thesis,the porous structure design of bone implants is improved by using multiobjective optimization algorithm based on the stress distribution calculated by finite elements from the mechanical environment of human bones.A functional gradient porous structure was constructed using parametric modeling based on cubic to match the stress constraint requirements at the defect.The permeability of the scaffold was maximized by adjusting its internal cubic density.Combined with the high degree of freedom advantage of 3D printing technology,the internal space of the bone implant is customized to meet the requirements of its mechanical and biological properties in the human bone environment.In this thesis,a method for geometric design and optimization of functional gradient porous structures based on mechanical-biological performance criteria is developed to address the limitations of uniform porous structures that cannot adapt to the stress distribution of bones and the gradient structural characteristics possessed by bones themselves.It has important theoretical significance and application value for the design and application of scaffolds for bone defects.