Additive Manufacturing of Ti Alloy Lattices and Their Characterization

In this thesis, a number of experimental lattice structures (following the characteristics of “pentamode” and “gyroid” structures) have been produced by SLM from Ti-6Al-4V, and these samples have been subjected to a variety of structural, mechanical (in compression) and biological characterisation methods to determine the properties of these materials, and explore their variation with density. These methods are reinforced with information from modelling the mechanical response and the fluid flow behaviour through the lattices. As a result of this work, assessment can be made of the general compatibility of these lattices for hard tissue implants, and therefore how they could be exploited in the design of implants for spinal fusion.Both gyroid and pentamode lattice types can achive modulus in the range of cortical bone, and this can be affected by the density as a design parameter.Further assessments were made of the flow behaviour by simulation. As expected, higher porosity leads to higher permeability, which would in general be a desirable behaviour for an implant, to allow nutrient transport. Another important property to verify was the biological response of the samples. Pentamode 80 and 90 lattices had higher cell viability in comparison with Pentamode 70, which is likely to be due to the larger pore size supporting improved cell migration and nutrient transfer inside the scaffold. However, the cell population was higher for Pentamode 70. Comparing the other two densities, Pentamode 90 has a higher population, which could be due to a rougher surface supporting cell attachment better. Further assesment with Alizarin Red assay showed that the Pentamode 70 has the highest bone mineralization, with only low levels found in Pentamode 80 and 90, and the Sirius Red assay indicated also the highest collagen deposition in Penamode 70. This produces a clear discrimination that the lower prorosity structure produces a better effect and would be preferred for biomaterial implants.This work has therefore demonstrated that, of the tested materials, the Pentamode 70 has the most suitable properties for use as a hard tissue implant. It has been shown that such structures can be produced by SLM, at least up to the dimensions of a 10mm cube, and that several of the key properties and behaviours are suitable. More complex designs and properties have not been assessed, and would be the essential next stage of the work.