A Study On The Laser 3D Printing Process And Biomechanical Properties Of Porous Tantalum For Orthopedic Implant

In orthopedic medical diagnosis and treatment,the demand for personalized and accurate treatment is increasingly strong.The development of 3DP technology and modern medical imaging technology provides an excellent solution.In this paper,aiming at the design and manufacturing requirements of personalized porous tantalum for laser3DP（SLM）,the optimization process of SLM printing tantalum was studied.Based on this,the functional relationship between relative density and elastic modulus of porous tantalum was established by using Euler-Bernoulli beam theory,and the function model is modified by the finite element method in ABAQUS.Based on the theory of equal stiffness,the conversion relationship of geometric parameters between variable section beam model and corresponding constant section beam model is studied.Typical pore structure design parameters were selected,a series of porous structure samples were printed,and their mechanical properties were tested.The internal relationship between the relative density and the elastic modulus of the sample was studied.Finally,according to the requirements of human biomechanics and clinical surgery,the design structure of implant prosthesis was optimized by finite element method.The lightweight structure is optimized on the premise of ensuring the structural safety of prosthesis.The design method of variable density prosthesis was proposed,which laid a research foundation for the clinical application of porous tantalum prosthesis.The main research work and achievements of this paper are as follows:（1）For tantalum powder with high temperature resistance（melting point is 2996℃）and high density（16.65g/cm³）,four key process parameters of SLM process,including laser power,scanning speed,powder layer thickness and scanning distance,were systematically studied and optimized.The internal relationship between laser power density and forming sample quality was explored.The results show that when the laser power is less than 300w,the probability of crack formation in the sample can be effectively reduced.The density of the sample increases with the increase of laser energy density,but too high laser energy density will also cause printing defects.When the laser power density is about 800J/mm³,the micro defects of the sample are less.The relative density of the compact tantalum sample printed by SLM can reach 98%,which can achieve the static mechanical properties of the industrial tantalum.The cylindrical structure with the designed diameter of more than 0.25mm can be printed.（2）In this paper,the geometric characteristics of the rhombic dodecahedron with variable section beam are studied,and the main structural design parameter is the ratio of length to diameter（β）,hole diameter（d）and diameter change ratio（τ）.In order to ensure the geometric characteristics of the designed porous structure,at the fusion node of the rhombic dodecahedron,the ratio（α）of the minimum height（g）of the cylinder to the nominal diameter（D₁）of the trabecula should be?2?2.The theoretical limit value of relative density of porous body is about 0.5984 whenβapproaches?2.According to the Euler-Bernoulli beam theory,the function model of elastic modulus of rhombic dodecahedral unit cell structure with variable section beam is obtained in two directions perpendicular to each other.The theoretical elastic modulus is directly related to theβandτ.The function model is modified by the finite element method in ABAQUS,and the correction coefficient of the theoretical equivalent elastic modulus of rhombic dodecahedral cell structure with variable section beam is 0.76.The elastic modulus of the multi-cell structure is not significantly reduced.When the properties of the matrix material（Ta,185.7Gpa）and theτis determined,the relationship between the relative density and the equivalent elastic modulus of porous body accords with exponential function.（3）Based on Euler-Bernoulli beam theory,the theoretical mechanical model of rhombic dodecahedron with circular constant section beam is derived.The results show that the elastic modulus of the constant section beam model is also directly related to the ratio of length to diameter of the hole structure.Based on the theoretical calculation,the conversion relationship of geometric parameters between variable section beam model and constant section beam model under the condition of equal stiffness is obtained.A series of porous tantalum samples were printed by SLM with typical pore structure design parameters.The measured elastic modulus is between 1.82Gpa-5.15Gpa,which is close to the mechanical properties of human bone.It is found that due to the limitation of SLM process,the surface morphology of porous sample is rough,and the sample deviates greatly from the theoretical design model.The measured value of the elastic modulus of the sample increases with the relative density of the sample,and shows a linear growth trend.（4）For complex cases of revision hip surgery,according to the requirements of human biomechanics,an optimized prosthesis design scheme is found by using the mechanical properties of porous body in this paper.According to the stress distribution of prosthesis,a"frame type"design scheme of variable density porous structure prosthesis is proposed.The finite element method is used to simulate the loading of equivalent variable density model.On the premise of ensuring the structural safety,the designed variable density prosthesis can reduce the mass by 25%theoretically,which lays a research foundation for the clinical application of porous tantalum prosthesis.