Page 191 - v11i4

International Journal of Bioprinting Design of SLM-Ta artificial vertebral body

The topological thin-walled TTS-3 consisted of vertical the fixation system and reduce the stress shielding effect.
struts that significantly enhanced the elastic modulus Therefore, AVB-2 has a lower risk of subsidence than
and yield strength of AVB-3. However, owing to TTS- conventional Ti mesh in clinical applications.
3’s insufficient constraint on the expansion deformation The deformation behavior of AVBs was closely related
of the lattice structure during compression, the vertical to their mechanical properties. The sidewall curvatures of
struts buckled, and the thin-walled structure exhibited −1
premature yielding (Figure 17). This resulted in the lowest the LS-1 and LS-2 specimens were 0.027 and 0.014 mm ,
yield-strength-to-elastic-modulus ratio of AVB-3. Because respectively, resulting in a reduced number of intact unit
the sidewall curvature of the topologically thin wall in cells in the central region compared with the upper and
AVB-1 was larger than that in AVB-2, the interaction force lower sections of the specimens. This explains why the unit
between the topologically thin wall and the lattice structure cells in the middle of specimens LS-1 and LS-2 deformed
in AVB-1 was greater than that in AVB-2. This interaction first during compression, as depicted in Figures 9 and 10.
force exerted a more pronounced enhancement on the The reason for the appearance of the shear band in the
elastic modulus than on the yield strength. Therefore, as YOZ plane of the LS-3 specimen (Figure 11) was that the
shown in Figure 8, the yield-strength-to-elastic-modulus maximum shear stress formed at an angle of 45° to the
ratios of AVB-2 were higher than those of AVB-1. AVB- axial compression direction. The unit cells in this shear
2, with a sidewall curvature of 0.014 mm , has potential band deformed first. The asymmetry of the ISS unit cell
−1
for clinical application because it can meet the daily load- prevented the formation of a shear band in the XOZ plane
bearing requirements of the human cervical spine while of the LS-3 specimen.
reducing the risk of stress shielding. In the Ta AVB specimen, the material density
Ti mesh is widely used in the clinical treatment of distribution of the topologically thin wall significantly
spinal tumors owing to its simple structure. Although Ti influenced its deformation behavior. During the load
mesh is effective for spinal reconstruction, it is poorly transfer process, the area with the highest material
adapted to vertebral bone in terms of size, shape, and density in the topological thin wall exhibited the highest
mechanical properties, which seriously affects the load-carrying capacity and lowest deformation tendency.
therapeutic effect. Surgeons need to cut the Ti mesh In contrast, areas with lower material density showed
size on-site according to the patient’s intervertebral diminished load-carrying capacity and a tendency to yield
height during the surgery, resulting in an increase in prematurely. As shown in Figures 12 and 13, along the
surgical time and difficulty. The shape of the end face z-axis direction of the specimens, the material densities in
of the Ti mesh cannot match the curvature of the end regions ① and ② of the topologically thin walls in AVB-1
plate, leading to stress concentration at the contact and AVB-2 varied. The material density in the upper part
surface between the Ti mesh and the end plate, thereby of these regions was greater than that in the lower part.
increasing the risk of subsidence. Moreover, the Ti mesh Consequently, plastic hinges formed first in these regions,
has an insufficient load-bearing capacity, and most of the resulting in bending deformation.
load is carried by the fixation system, which produces
stress shielding of the contacted vertebrae, resulting The topologically thin walls of the AVB-3 specimen
in bone resorption and stress collapse. According to experienced failure as a result of plastic deformation
clinical reports, there are still a large number of cases of in regions ① and ②, as displayed in Figure 14. The
poor osseointegration, inadequate immediate and long- topologically thin wall of AVB-3 comprised vertical struts
term stability, and short in vivo survival cycles after Ti and exhibited no variation in material density in regions
mesh implantation. 21,61,62 ① and ②. Under compressive loading, the internal lattice
expanded outward, acting as a perturbation source for
In this study, the Ta artificial vertebra was custom- vertical strut buckling and accelerating the instability of
designed based on the shape and anatomical dimensions the topologically thin wall (Figure 17).
of the vertebrae of a specific patient. The height of the AVB
remained the same as the intervertebral height, avoiding As exhibited in Figure 16, the finite element results
on-site adjustment and reducing the difficulty of surgery. indicated that the stress concentrations were localized
The upper and lower end faces of the customized artificial in areas with alternating material densities within the
vertebrae can be accurately fitted to the endplate, thereby topologically thin walls of AVB-1 and AVB-2 (regions
reducing stress concentration at the contact interface ① and ②). AVB-3 displayed pronounced stress
and lowering the risk of subsidence. Meanwhile, AVB-2 concentrations at locations where the vertical struts
exhibited the highest yield-strength-to-elastic-modulus buckled. This stress accumulation initially caused the
ratio, which could prevent excessive load transfer along structure in these areas to deform.

Volume 11 Issue 4 (2025) 183 doi: 10.36922/IJB025150133