Design,Fabrication And Surface Modification Of Ti6Al4V Porous Fusion Cage

Interbody fusion procedure is the main surgical method for the treatment of lumbar degeneration disease.The procedure can restore and maintain the intervertebral height by implanting fusion cage,and reduce the compression of intervertebral disc on nerve root.Ti6A14V(Ti)fusion cage has been widely used for many years and achieved good clinical performance due to its good corrosion resistance and biocompatibility.However,the high stiffness of Ti causes stress shielding effect,which hinders the fusion of bone graft with adjacent vertebrae.In addition,Ti cage increases the risk of cage subsidence.The biological inertia of Ti also has negative effects on the fusion effect.It is essential to reduce the stiffness of Ti fusion cage and improve its biological properties.Therefore,this study has carried out research on the numerical analysis about the biomechanical performance of fusion cage,the optimization and additive manufacturing of porous fusion cage,the post-treatment and biological performance improvement of the fabricated porous fusion cage.The contents and achievements are as follows:The intact finite element model(FEM)of human lumbar spine L1-L5 segment is constructed based on the CT data.After the verification by the comparisons of the range of motion and the internal pressure of the nucleus pulposus,the transforaminal lumbar interbody fusion(TLIF)model is constructed based on the model.The biomechanical effects of fusion cages with different stiffness in the TLIF are analyzed.No obvious difference of mechanical effects on the non-operative segment and pedicle fixation device is observed between fusion cages.However,the fusion cage with similar stiffness to bone endplate can not only reduce the peak stress on the fusion cage,but also improve the stress energy density of the bone graft and reduce the peak stress on the bone endplates.Thus,the risk of stress shielding effect and cage subsidence is reduced.From biomechanical point of view,the fusion cage with similar stiffness to bone endplate can reduce the stress shielding effect and the risk of cage subsidence.Then,a multi-scale topology optimization method is proposed to design porous Ti lumbar fusion cage.The purpose is to design and fabricate a porous Ti lumbar fusion cage with the similar stiffness as the adjacent bone endplates.The basic mechanical properties are obtained via the compression test of dense samples fabricated by SLM.Then,two kinds of unit cells with the same volume fraction but different topology are designed based on homogenization method and compression load method respectively.The unit cell optimized based on the compression load is selected to construct porous cage due to the better mechanical and permeability performance.The framework structure is designed by macroscale topology optimization and the final porous fusion cage is constructed.The TLIF model was constructed to analyze the biomechanical effect of the porous cage.The designed porous cage can reduce the stress shielding effect and the risk of cage subsidence.The topology features of the porous fusion cage fabricated using SLM is similar to the design,but Ti particles are on the surface,which affects the surface morphology of the porous cage.The compressive elastic properties of the porous structure are similar to but slightly higher than the design value.The composite compression test of the fusion cage and polyurethane proves that the SLMfabricated Ti porous fusion cage can reduce the risk of cage subsidence.In order to remove the Ti particles on the surface of SLM-fabricated porous Ti fusion cage,a new method of flowing acid etching for porous Ti implants is proposed.A platform for flowing acid etching of porous samples is setted up and the effect of etching time on the post-treatment effect of SLM-fabricated porous Ti samples is analyzed.Compared with the immersion acid etching,flowing acid etching for 75s removes the Ti particles on the surface of porous samples uniformly and quickly.Flowing acid etching for 90?105s adjusts the elastic mechanical properties of the SLM-fabricated porous samples more close to the design.In addition,the flowing acid etching reduces the weight of porous samples and improves the permeability of porous samples.Cell experiments and animal experiments show that the biological properties of porous samples surface after flowing acid etching are better than those with residual Ti particles.Then,flowing acid etching is used to remove the Ti particles on the surface of the porous fusion cage.To further improve the surface biological properties of porous fusion cage,anodic oxidation is used to construct uniform TiO2 nanotubes on the surface of Ti porous strucuture after flowing acid etching removes the residual Ti powders and forms micron structure.The method retains the original elastic mechanical properties and surface morphology of the porous structure.Cell experiments and animal experiments have shown that the micro-nano structure on the surface can further improve the biological properties of porous samples.This method is applied to the SLM-fabricated porous fusion cage.The micro-nano structure is successfully constructed on all surfaces of porous cage,while preserving the original mechanical properties.