| In recent years,the development of bone tissue engineering has emphasized the importance of appropriate scaffold design to facilitate the integration and integration of bone tissue.Three-dimensional porous scaffolds can effectively reduce the stiffness and elastic modulus of scaffolds,which can avoid stress shielding and provide space for bone ingrowth and osteointegration.This would prolong the life of scaffolds.It is found that the key parameters such as cell unit,pore size and porosity will determine the mechanical and biological properties of porous scaffolds.Therefore,exploring the mechanical and biological effects of various macropore structure on porous scaffolds is very important for the optimization of bone tissue engineering scaffolds.Traditional manufacturing processes,such as powder sintering,plasma spraying and foam manufacturing,cannot precisely control the pore parameters of the scaffolds.Fortunately,with the development of AM technology,laser selective melting(SLM),as one of the most widely used technologies,can produce porous scaffolds consistent with CAD model tomeet the high controllability of its pore parameters.In this study,Porous Ti scaffolds with different pore structures were designed and manufactured by CAD and SLM.Micro-CT and Mimics analysis showed that SLM was able to produce Ti scaffolds with different pore structures.The mechanical properties evaluated by three-dimensional finite element analysis and compression tests.Then,in vitro,we used3D-printed porous discs to culture human bone marrow mesenchymal stem cells(hBMMSCs),the main seed cells of bone tissue engineering to evaluate their biocompatibility.In vivo,we evaluated new bone ingrowth and integration in a rabbit bone defect model.Part I: Using CAD and SLM technology,four kinds of porous Ti scaffolds with different macropore structure were designed and fabricated:Ti-r(diamond lattice,regular distribution),Ti-ir(diamond lattice,random distribution),Ti-g(diamond lattice,gradient distribution(inner porosity is60%,outer porosity is 80%),Ti-tr(dodecahedron unit,regular distribution).Micro-CT images analyzed by Mimics software showed that the pore parameters were consistent with our design.The mechanical properties of four porous Ti scaffolds with different macropore structures were tested by finite element analysis and compression experiments.The results of finite element analysis show that under 100 N vertical force,the compressive strength of Ti-r group is the best,and the stress distribution is uniform.Secondly,the Ti-tr group suffers the middle equivalent force and displacement,and the stress concentration mainly distributes at the intersection of struts.The compressive strength of Ti-ir and Ti-g groups is poor,and there are more stress concentration areas than the first two groups.The results of compression experiment were consistent with and finite element analysis,and indicated that the elastic modulus of the four groups are between 4-6 GPa,which are compatible with the mechanical properties of bone tissue.Part II: hBMMSCs were cultured on porous Ti plates: SEM observed that hBMMSCs grew well on all scaffolds with high cell activity.There was no significant difference in cell adhesion and proliferation;in addition,after osteogenic induction,Ti-g group had a higher ALP at 7 days,but Alizarin red semi-quantitative analysis showed that four groups showed considerable mineralization ability at 21 day.RT-PCR results showed that there was no significant difference in the expression of osteogenesis-related genes Runx-2,OCN,and Osterix.These results suggested that all four groups of porous Ti scaffolds have a good biocompatibility and similar osteogenic ability.Part III: 12-week-old New Zealand bone defect rabbits were divided into 5groups and implanted with scaffolds(4 porous groups and a dense one as control).Sequence fluorescence labeling was performed at 2W,4W and8 W after operation.By hard tissue section staining,the depth,area of bone tissue growth and the percent of bone contact to the scaffolds surface were calculated.The results showed that new bone formed in the pore as early as2 weeks after implantation,and the depth and area of bone growth increased with time;In addition,the area of bone growth in Ti-r and Ti-i groups was more than the other two groups,showing a better osteogenesis ability;The contact rate between the scaffold surface and bone tissue showed that the four groups of porous Ti scaffolds could form good osseointegration at 8W.The dynamic bone formation process in porous scaffolds was observed by sequential fluorescence labeling.The results showed that most of the new bone grew from host bone to pore in the four groups,mainly showing a distance osteogenesis pattern.The push-out tests showed the push-out forces of all porous groups were significantly higher than that of dense implants at each time point,and there is no significant difference among porous groups.These results indicate that four Ti scaffolds with different pore structures can support bone regeneration and bone integration in repairing small bone defects.In conclusion,four porous Ti scaffolds in this study are all matched with the mechanical properties of bone tissue,but Ti-r group has the strongest compressive strength and uniform stress distribution.In vitro,the four groups of porous Ti scaffolds have a good biocompatibility andosteogenesis ability.In vivo,the four groups of porous Ti scaffolds are conducive to bone regeneration and bone integration in small bone defects.In conclusion,combined with mechanical and biological properties,we believe that Ti-r structure is more conducive to bone regeneration and bone integration. |
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