| Ti-15Mo alloy has excellent mechanical properties and biocompatibility,and is a new alloy with potential applications in the field of biomedical materials.Selective laser melting(SLM)is an excellent method for manufacturing porous metal bone scaffolds with excellent mechanical properties,high surface quality and dimensional accuracy.And it’s highly advantageous in the preparation of porous alloy bone scaffolds.This thesis investigates the mechanical and permeability properties of porous scaffolds,which need to meet various mechanical and biological requirements.The main innovation is to explore porous bone scaffolds with different structures and different direction of gradient,to verify their mechanical properties and to reveal the effect of their permeability on cell growth.The flow of fluid in porous bone scaffolds is investigated using computational fluid dynamics(CFD),and the manufacturability,mechanical properties and permeability of different porous structures are assessed.The main research and conclusions of this thesis are as follows.(1)A total of five structures based on the strut system of body-centred cubic(BCC)and decahedral(Kelvin)as well as Primitive,Diamond and Gyroid based on triply periodic minimal surfaces(TPMS)were designed,and porous structures with uniform and different direction of gradient were prepared using selective laser melting technology to assess their moulding quality.The porous structures with a large number of inclined struts had relatively poor moulding quality and the density gradient direction had little effect on the moulding quality of the gradient porous structures.All the gradient porous structures have no dimensional abruptness at the junction of different density gradient layers,and the transition is smooth and the overall moulding quality is good.(2)Compression experiments show that the vertical gradient porous structure is deformed layer by layer from high porosity to low porosity,while the transverse gradient porous structure is deformed in a way similar to uniform porosity,firstly the whole is uniformly deformed,then with the increase of strain there is a significant local deformation,and it expands towards the uniform deformation area layer by layer.The location of significant local deformation is related to the strength and actual stress distribution of the different types of transverse gradient porous structures,which are relatively more uniformly distributed and therefore have a higher strength than rod structures.The stress-strain curves for all porous structures show no significant stress fluctuations and exhibit excellent ductility.The TPMS porous structure has a densification strain of 60%,which is much higher than that of the rod porous structure,showing better ductility and energy absorption.Among the above porous structures,the Diamond porous structure has the best mechanical properties and energy absorption,with the elastic modulus,yield strength and plateau stress of its gradient structure ranging from 3.761 to 4.088 GPa,104.8 to 134.5 MPa and 165.2 to 175.4 MPa,respectively.the elastic modulus of the Diamond gradient porous structure is between cancellous and cortical bone(0.1～30GPa),but its strength can be comparable to that of cortical bone,which has good prospects for application in bone implantation.(3)The distribution of wall shear stress(WSS)generated by different structural fluids was investigated,with the maximum WSS ranging between 1.618 mPa for BCC and 60.23 mPa for Primitive,and the maximum mean WSS of 6.61 mPa for Primitive,while the mean WSS for induced osteogenic differentiation of mesenchymal stem cells(MSC)ranged from 0.1 to 10 mPa.Analysis of the wall shear stress distribution statistics revealed that the Gyroid structure had a more homogeneous WSS.(4)The permeability simulation results were ranged from 2.1 x 10-9 to 13.5 x 10-9m2 and the results were consistent with the range of permeability of human bone trabeculae.Structure has a significant effect on permeability,with the best permeability being the Primitive structure and the worst being the Diamond structure,and there is up to a 3-fold difference in permeability for the same porosity,with permeability increasing with increasing porosity.The analysis of the flow behaviour inside the porous structure shows that although the Primitive structure has the best permeability,it has a large number of straight up and down flow channels,which weakens the contact between the fluid and the wall and is not conducive to cell attachment and proliferation.The Gyroid structure,on the other hand,combines high permeability with more tortuous flow channels,making it a more desirable choice for orthopaedic implants.The permeability prediction model for porous structures was improved based on the Hagen-Poiseuille equation with an error of around 5%compared to the calculated value,and this idea can be extended to other TPMS structures for permeability prediction. |
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