Research On Design And Optimization Of Porous Structures Of 3D Printed Orthopedic Implants

The repair and replacement of critical size bone defects caused by diseases,trauma and aging have be continually studied for centuries.However,no perfect solution has been found to treat the critical size bone defects so far.For modern orthopedic medicine,bone implants have become a common treatment to reconstruct the structure and function of missing bone.Recently,the development of 3D printing technology has brought revolutionary advances in the design and fabrication of orthopedic implants.Due to its controllable mechanical properties and excellent biological properties,the porous structure is increasingly used in the design of orthopedic implants.The triply periodic minimal surface(TPMS)modeling method is an emerging porous structure modeling method.Compared with the traditional computer aided design(CAD)software modeling method,due to its easy operation of pore characteristics,it has attracted the interest of researchers.However,an ideal orthopedic implant needs to have both high porosity and high strength to achieve balanced of mechanical and biological properties.By rationally design and structural optimization,the goals can be fulfilled.Therefore,the study of porous structure design and optimization methods is of great value for the construction of a next-generation of orthopedic implants.The main work of this article is listed:Firstly,this paper studies the design method of TPMS porous structure.It also discusses and analyzes the parameter to control the modeling of uniform porous structure,graded porous structure and hybrid porous structure,and a radially graded porous structure design method imitating structural of natural bone is proposed.Based on 3D printing technology,the porous structure of TPMS was fabricated and characterized.To study the mechanical properties of the TPMS structure,finite element simulations and mechanical experiments are conducted.In order to solve the problem that the TPMS model is difficult to be converted into the finite element model,this paper proposes a set of finite element modeling methods for the TPMS structure,and provide an effective analysis method for the simulation analysis of the porous TPMS structures.Meanwhile,the factors affecting the mechanical properties of the uniform porous structure are comparatively studied,and the superiority of the mechanical properties of the radial graded porous structure imitating natural bone is verified,which provides an important reference for the design of orthopedic implants constructed by porous TPMS structure.For the propose of studing the properties for tissue regeneration of porous structures,the permeabilities and pore characteristics of TPMS porous structures are studied.Based on the principle of computational fluid dynamics,the finite element simulations are applied to analysis the factors that affect the permeabilities of the TPMS porous structures.In the study of pore characteristics,the advantages of the TPMS structures compared to the traditional porous structures were analyzed,and the rationality of applying TPMS porous structure to build orthopedic implant was verified.Finally,this study proposes a novel structural optimization method for designing orthopedic implants based on porous structure-topology optimization.The optimization method is intended to solve the stress shielding,insufficient strength and difficulities for tissue regeneration caused by the lack of reasonable optimal design of current orthopedic porous implants.Then,a cervical fusion cage is optimized as an example to illustrate the optimization method and processes.The rationality of the proposed optimization method is verified through the finite element comparative analysis.At the same time,according to the optimized porosity model,a density mapping method is proposed to establish the TPMS porous structure,and the porous cervical fusion cage is constructed.Based on the TPMS model,systematic researches are carried out on the structural design,performances and structural optimization of porous structures for orthopedic applications.An effective procedure has been established to study the orthopedic applications,which provides new insights for the future research of porous orthopedic implants.