# Mechanical Behavior of Ti6 Al4V Scaffolds Filled with CaSiO\({}_{3}\) for Implant Applications
## 4 Results and Discussion  
An in vitro simulation and experimental results are required before an in vivo assessment of any biomaterial. From the literature, the ultimate strength of Ti6 Al4V manufactured by SLM or electron beam melting (EBM) can be found between \(\approx\)1.0-1.2 GPa [34; 35], and this value is applied for simulations in the current research. The rectangular scaffold (Figure 3) exhibits a high compressive strength, and deformation mostly occurs in the top and/or bottom part of the sample. The final height of rectangular and honeycomb after the compression test are similar. Comparison between Figures 3 and 7 present the findings that due to interlayer horizontal sheets, embedded multi-tubes (inspired by multi-walled carbon nanotubes) and hexagonal pores, the honeycomb scaffold has less stress concentration values; it is wrinkled with an expansion in diameter. As expected, primitive, lattice and gyroid scaffolds (Figures 4-6) exhibited uniform deformation. For these three conditions, adding layers upon layers with a defined unit cell size (for example a lattice with intersecting cellular rods) produce desired structure shapes easily, but will be deformed relatively easily during compressive loading. It shows that cell type, size and alignment together play a pivotal role on their failure mechanism [36]. The experimental stress-strain curves from the compression test are shown in Figure 10. As seen from Figure 10, primitive, lattice and gyroid scaffolds show a more inferior deformation stress than in the case of rectangular scaffolds. In addition, the rectangular  
Figure 8: **(A)** Wollastonite (CaSiO\({}_{3}\)) powder, **(B)** selective laser melting (SLM)-produced Ti6 Al4V lattice structure with 1 mm cell size, and **(C)** Sintered sample (dimensions of lattice structure: 20 mm diameter and 15 mm height before spark plasma sintering (SPS) and 6 mm height after SPS and polishing). Figure 9: SEM micrographs of **(A)** wollastonite (CaSiO3) powder, **(B)** Sintered CaSiO\({}_{3}\) embedded in a Ti6 Al4V lattice after SPS, and **(C)** High magnification image of metal-ceramic boundary. scaffold shows uniform plastic deformation allowances, where the stresses were distributed uniformly and the local overloading is completely avoided. It is shown that rectangular (due to vertical channels and fluid permeability) and honeycomb (due to horizontal plates and hexagon pores) are structures can bear high compressive loads. As demonstrated in section views of Figure 11, rectangular scaffolds have vertical thin plates that are resistant against distortion and deformation, whereas, honeycomb is more suitable for alive cell growth due to horizontal plates and continuous open porosity. The applicability of the porous TPMS scaffolds can be extended to applications related to (1) oxygen transport and/or (2) scaffold permeability [37]. The porous TPMS scaffolds can also contribute to enhanced cell seeding, and at the same time can maintain nutrient transport throughout the whole scaffold during in vitro culturing [16]. Regarding the final height of the deformed samples, the experimental compressive results (Figure 12A-E) are compared with the FEA analytical outcomes (Figures 3B, 4B, 5B, 6B and 7B), which are in good agreement. Regarding the Von Mises stress distribution (Figures 3A, 4A, 5A, 6A and 7A), primitive, lattice and gyroid scaffolds are relatively flexible/deformable structures, while more deformation energy can be absorbed by rectangular and honeycomb structures. Hence, for the rectangular structure, stress concentration and distortion can appear in the upper part of sample, but honeycomb failure started from the bottom of structures. Adding metallic lattice structure (Ti6 Al4V) to ceramic reinforcement like wollastonite (CaSiO\({}_{3}\)) produces a composite with higher wear resistance, damage tolerance and mechanical properties resulting in a higher durability of bones [38; 39]. The strut diameter of the lattice is currently \(\approx\) 200 \(\upmu\)m, while it could be increased up to 1 mm (Figure 9C).