| Objective:Porous titanium implant can effectively increase osseointegration area,improve the biomechanical compatibility of implant,promote osseointegration and enhance its strength at the same time.In this study,porous titanium alloy specimens with different pore types and pore sizes were prepared by 3D printing,then their printing precision and mechanical properties were analyzed to provide theoretical basis and technical support for the preparation of personalized porous titanium alloy implant.Method:The compression and three-point bending models of three pore types,named Cube(C),Octahedron(O)and Spider web cross-section(S),were established.Each pore type contained three kinds of pore sizes: 400,500 and 600 μm.Each pore size was divided into full-pore group and gradient group with a dense core(C).Among them,the porosity of the 400,500 and 600 μm full-pore groups was 60,65 and 70% respectively,while that of the gradient group was 50,55 and 60% respectively.We selected 500 μm full-hole groups for Selective Laser Melting(SLM)from horizontal and vertical directions,then the printing precision was compared to determine printing direction according to the surface morphology observation and mismatch ratio.Then all compression and three-point bending specimens were printed after printing direction selected,the surface morphology and chemical composition were analyzed by SEM and EDS.Compression and three-point bending tests were used to calculate compressive strength,compressive elastic modulus,bending strength and bending elastic modulus to evaluate mechanical properties.Graphpad 8.3 was used for statistical analysis.Results:1.In all of the 500 μm full-hole groups,the printing precision was evaluated by mismatch rate of pore size and strut thickness: the trend among horizontal and vertical printing directions were S > O > C and O > S > C,respectively,with the former printing direction better than the latter.All of the bending specimens and compression specimens except the horizontal C and O-type could be cut completely.2.When the pore type is determined,the printing precision of specimens decreased with the increasing of pore size.3.In the compression test,compressive elastic modulus of all the other groups were the within the range of the cancellous bone,except the O-type full-hole group(600 μm).For three-point bending test,bending elastic modulus of the O-type full-hole(600 μm),the S-type gradient(400 and 500 μm)and the other groups were lower than that of the cancellous bone,reached the compact bone and within the range of the cancellous bone,respectively.4.With the same pore type and graded design,compressive strength,compressive elastic modulus,bending strength and bending elastic modulus decreased with the increasing of pore size and the change trend of compression elastic modulus and bending elastic modulus were consistent with that of the compressive strength and bending strength,respectively.Under the same pore size and graded design,S-type could enhance the four kinds of mechanical properties significantly,compared with that of the O-type.With the same pore size and pore type,graded group could enhance the four mechanical properties significantly,compared with full-hole group.Conclusions:1.SLM can print personalized porous titanium alloy specimens.2.Printing precision of the horizontal direction was superior to that of the vertical direction.The trend of printing precision in the horizontal print direction is S > O > C.3.Compressive strength,elastic modulus,bending strength and elastic modulus all decrease with the increasing of pore size,with the change trend of compression and bending elastic modulus consistent with that of the compressive and bending strength,respectively.The S-type and dense core can significantly enhance all four kinds of mechanic properties.By changing the above-mentioned porous design parameters,the elastic modulus of porous titanium alloy can be adjusted within the range of natural bone so as to increase its biomechanical compatibility with natural bone. |
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