| The bone defect caused by disease,sports injury,accident,and the aging population has always been a difficult problem in clinical orthopedic treatment,especially in cases of tibial comminuted fracture,resection of bone tumor,and resection of bone infection.When facing the repair of large segmental tibia bone defects,the use of a traditional bone plate fixation system has the risk of postoperative fracture caused by the stress concentration of bone plate in the fracture region,and the large distance results in the failure of bone cells to migrate and adhere and thus cannot be conducive to bone repair.Therefore,for the repair of large segmental tibia bone defect,it is necessary to use gradient porous filled scaffolds with good mechanical suitability in combination with a bone plate fixation system,but the mechanical performance and bone tissue regeneration ability of porous filled scaffolds implanted in the tibial bearing area play an important role in the repair of bone defects.For this reason,in this thesis,the Gyroid porous titanium alloy scaffolds with uniform and gradient distribution on pore size were designed,and the effects of structural parameters of pore size,porosity,and pore size distribution on their compression behavior,in vitro operational behavior,cell response and bone regeneration behavior were systematically studied.In this thesis,the selective laser melting(SLM)3D printing forming ability and compression behaviors of multi-scale Gyroid porous scaffolds were studied by combining theoretical modeling,experimental research,and numerical simulation.Secondly,the finite element model and the experimental model of the bovine tibia in vitro operational were established to study the mechanical behavior of the porous filled scaffolds in vitro operational under the standing phase,lift-off phase,and landing phase of human gait.Finally,in vitro cell culture experiments and in vivo rabbit implantation experiments were conducted to systematically study the mapping relationship between the pore size,porosity,and pore size distribution of scaffolds,as well as the alkali-activated surface treatment of scaffolds and cell response and bone tissue regeneration ability.The main conclusions are as follows:The Gyroid porous titanium scaffolds with uniform and gradient distribution on pore size designed in this thesis had good SLM forming ability,no collapse and blockage defects,and the size error of scaffolds was controlled within 5%.Under the same porosity,as the Gyroid cell period decreased,the forming errors of pore size and beam thickness of scaffolds increased,and as the porosity increased,the pore size was slightly increased,and the forming errors of pore size and beam thickness of scaffolds did not differ much.The forming errors of gradient porous scaffolds were slightly higher than that of uniform porous scaffolds,while the forming errors of edge area were opposite.Moreover,compared with the pore size and the thickness of scaffolds,the porosity of porous scaffolds had the greatest effect on their compression performance.The compression properties of homogeneous porous scaffolds were weak,and the fracture forms were mainly plastic fractures and supplemented by brittle fractures.The homogeneous strengthened porous scaffolds had a higher yield strength,but there are postoperative stress shielding and fracture risk.Gradient porous scaffolds had uniform compressive mechanical conduction,high compressive toughness,and lower risk of postoperative stress shielding.The in vitro operation simulation results of porous filled scaffolds showed that the porous filled scaffolds with uniform pore size distribution had different degrees of yield failure under the three gaits,and the fatigue life was only less than 120,000 times,and the most serious in the off-ground gait.The gradient porous filled scaffolds and their fixed system can withstand1 million times in vitro operation fatigue under the three gaits,and the compression deformations were small,which had high operation mechanical performance.Moreover,the G-0.66-90 gradient porous filled scaffold showed excellent mechanical performance in vitro operation tests,which could withstand one million operation tests under 931 N and had no fracture failure,and the maximum service displacement of the bovine tibia assembly model in the off-ground phase was the largest.The static compression test of the G-0.66-90 gradient scaffold embodied high yield strength and compression toughness,with the yield strength of151 ± 1.5MPa and the yield deformation of 15 ± 0.58%.The nano-microstructure obtained by alkali activation treatment improved the hydrophilicity of the titanium alloy surface,which was beneficial to cell proliferation and cell antenna extension on the surface.And the cell activity improved with the increase of alkali treatment solution concentration.With the increase of culture time,the number of cells on homogeneous porous scaffolds with large pore size(1117 μm-1763 μm)and gradient porous scaffolds(912 μm-1647 μm)showed a decreasing trend.However,the cell number did not change significantly in homogeneous porous scaffolds(721 μm-885 μm)and gradient porous scaffolds(593 μm-880 μm).The cell growth condition of porous scaffolds with gradient pore size distribution(593 μm-1647 μm)was better than that of porous scaffolds with uniform pore size distribution(721 μm-1763 μm).Under the same porosity,the larger the pore size,the more unfavorable the cell proliferation and migration.Under the condition of little pore size difference,the porosity had no significant effect on cell growth.With the increase of culture time,the number of cells on the scaffolds did not change obviously.The length of the cell antennae and the area of cells on the surface of large ribs(723 μm)were larger,and the antennae of adjacent cells crossed each other and grew in a three-dimensional superposition.However,the number of cells on the surface of small ribs(170 μm)was smaller,and the cell antennae gradually shortened.The repair result of rabbit artificial bone defects in vivo showed that there were still big holes in the artificial bone defect area of the blank group after the operation,and the bone repair effect was poor.However,new bone tissue was found on the bone sections of different depths of the porous scaffolds,and the bone tissue grew from the surface of the hole wall to the center of the hole and was tightly wrapped on the surface of the porous material,and the effect of bone ingrowth was good,so the bone growth effect was good.Compared with the uniform porous scaffolds with a large aperture(1117 μm-1763 μm),the uniform porous scaffold with a small aperture(721 μm-885 μm)had continuous new bone-like substance and fewer holes.The ability of bone tissue regeneration of porous scaffolds with gradient pore size distribution(1140 μm-1560 μm)was better than that of uniform porous scaffolds with similar aperture(1117 μm-1763 μm),and the bone tissue in the edge area was more than that in the central area.Under the same porosity,the larger the pore size,the less the bone tissue grown on the surface of the scaffold,and the porosity had no significant effect on the growth of bone tissue under the condition of a small pore size difference.The ability of collagen-like bone and bone calcification on the surface of porous scaffold treated by alkali activation was greater than that of porous scaffold treated by non-alkali activation.The results not only provide theoretical guidance for the bionic design of gradient porous filled scaffolds for large segmental bone defects of tibia bearing parts,but also provide application basis for the repair of large segmental bone defects in clinical and provide certain help for promoting the localization of orthopedic implant products in China. |
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