Research On Porous Metal Implants Based On Selective Melting Forming Technology

With the continuous development of medical technology,the application of metal implants in bone repair surgery has become more and more extensive.The density of metal implants manufactured by traditional methods is large,and the elastic modulus is much larger than that of human bones.After implantation in the human body,stress shielding will occur,causing looseness after implantation and leading to failure of the implantation operation.Therefore,it is necessary to smooth the mechanical difference between the implant and the bone,and through the porous structure parameterization method,make the mechanical performance close to that of the bone,thereby increasing the bonding rate.In this paper,the porous structure is designed and manufactured by CAD design method and laser selective melting forming(SLM)technology.Finite element analysis and compression experiments are used to study the influence of different parameters on the mechanical properties of the porous structure,and the designed porous structure is applied to the femoral stem.On the prosthesis,stress shielding is relieved and the service life of the implant is improved.The main research content and results of this article are as follows:1.The 316 L stainless steel material is formed into a tensile sample,and the mechanical performance parameters of the sample are measured by the tensile experiment.Among them,the modulus of elasticity is 68.5GPa,which is 1/3 of the cast 316 L stainless steel,and the yield strength is 325 MPa.The obtained mechanical performance parameters are transformed into the real stress-strain plastic parameters of the printed 316 L stainless steel and applied to the finite element simulation.The simulation results are in good agreement with the experimental test values.2.Four types of unit structures were designed through Solidworks software,namely,face-centered cubic unit(FCC),diagonal cubic close-packed unit(DCC),body-centered cubic unit(BCC)and octahedral cylindrical unit(ODC).),the porosities are in the range of 60%-80%,and the pillar diameters are in the range of 220-600?m.Comparing four kinds of porous structure finite element simulations,it is found that the ODC structure has higher elastic modulus and yield strength.At the same time,the structure with vertical pillars in the horizontal position of the unit structure exhibits better reinforcement effect than the staggered pillar structure;in other parameters under the same condition,the porous structure will reduce its mechanical properties as the unit size increases.3.SLM is used to form the porous structure,and the electronic balance and scanning electron microscope(SEM)are used for forming quality analysis and surface morphology observation.Through the combination of compression experiment and finite element simulation,the three parameters of the four porous structures are studied,and the mechanical properties of the porous structure are analyzed.It is found that the results of the experiment and simulation are consistent,and the elastic modes of the four porous structures are consistent.The amount is between 1.9-8.4GPa,which is within the range of human bone demand.Moreover,the characteristics of the mechanical properties of the porous structure mainly depend on the type of the unit body,and have little relationship with the porosity.4.The four porous structures studied were applied to femoral stem prostheses,and compact femoral stem prostheses and four porous femoral stem prostheses models were established.The finite element analysis of the femoral stem prosthesis model found that the porous femoral stem prosthesis reduced the stiffness of the prosthesis and relieved the stress shielding.Among them,the ODC porous femoral stem has the smallest stiffness value,the stress distribution is more uniform,and the stiffness value is 796.5N/mm.Compared with the compact femoral stem prosthesis structure,the stiffness is reduced the most,by 20.9%.