Page 278 - IJB-10-1

International Journal of Bioprinting Permeability of NiTi gyroid scaffolds

Table 5. Analysis of cell cultivating
Pore size [μm] Number of cells seeded Viability [%] Number of collected cells Doubling rate per day
[×10 per 1 mL] [×10 per 1 mL]
6
6
680 0.4 96 2.8 0.4011
940 0.4 96 2.7 0.3936
1190 0.4 98 2.4 0.3693
Control 0.4 97 3.0 0.4153

the specific surface area, which provides anchorage for the resulting in a 61%–87% porosity range. The influence of
MSCs during cultivation. Such observation is consistent design parameters on structures’ geometrical integrity,
with the in vitro biocompatibility assessment results by Lv morphology of the surface, mass-transport characteristics,
et al. for scaffolds with the same pore size range (640–1200 and biocompatibility were investigated. Regarding the
45
μm), although the structure used (instead of TPMS) was present results, the following conclusions can be made:
manufactured from Ti6Al4V by electron beam melting. (i) All samples exhibited negative deviation of the
9
Ma et al. also concluded cell attachment was positively measured pore size in comparison with the designed
dependent on the surface area for 316L gyroid structures. one, indicating lower porosity of NiTi gyroid
However, the study showed that, for the samples with almost structures. The relative discrepancies of the pore size
equal surface area, a maximal quantity of cells grew on the have a noticeable dependence on the unit cell size
sample with the largest pore size of 1.3 mm. Furthermore, due to an increase in the cumulative deviation per
Ti6Al4V gyroid scaffolds at varying pore sizes of 250–400 unit volume with an increase in specific surface area.
μm studied by Hameed et al. did not exhibit a significant
7
difference in cell viability. Thus, we can conclude that at the (ii) The surface of the struts was extensively covered with
initial stage of osteointegration, the increased surface area fused particles that highly increased surface roughness.
is a positive factor for cell adherence and proliferation in Due to sintered particles, the interconnections of
the scaffold, as pore size has no distinct influence on the struts are accumulating higher deviations from the
cytocompatibility of the scaffold. prescribed design on the downskin surfaces.

NiTi intermetallic phase is known as a biocompatible (iii) Conducted CFD analysis revealed the positive
material despite the presence of toxic nickel in its chemical correlation of permeability with the unit cell size
composition. Furthermore, Ni-rich alloys are commonly and an inverse relationship with the wall thickness.
used to achieve superelastic properties as Ni content has a The in-plane radial unsaturated technique was
major influence on the temperature of the martensitic phase successfully adopted for measurements of the
transformation. In this regard, Ni ion release is of concern permeability coefficient for ordered porous structures
for porous nitinol components due to augmented exposed manufactured via LPBF. The calculated permeability
surface area, which is in direct contact with tissues. For range was 7–27 ´ 10 m when experimentally
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2
example, Gu et al. observed no cell attachment after 2 days obtained was 3.5–11 ´ 10 m .
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46
2
of incubation on the sample obtained by self-propagating (iv) The results of experimental measurements have
high-temperature synthesis (SHS) of elemental powders due lower values as compared to CFD analysis. The
to the presence of elemental Ni. However, in the case of the difference between the simulation and experiment
binding of Ni and Ti in the intermetallic crystal lattice and was attributed to the following reasons: different
the formation of oxide film on the surface due to the high surface morphology and wetting properties for real
reactivity of titanium with oxygen, nitinol demonstrates high samples, the higher apparent density of real porous
biocompatibility. In this research, the biocompatibility of structures, and the dependence of samples’ absolute
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LPBF parts was observed through a comparative analysis geometry deviation on the unit cell size.
of the growth rate, division, and viability of MSCs obtained
from the human umbilical cord during the cultivation in the (v) It was shown that within the investigated range of design
presence of the NiTi porous scaffolds. parameters, manufactured NiTi scaffolds effectively
mimic the mass transport of real bones. Overall, this
4. Conclusion study shed light on the optimization possibility of
scaffold architecture for particular bone types.
In this study, nine configurations of NiTi gyroid scaffolds
were fabricated via LPBF. The design window consisted (vi) Biocompatibility of NiTi samples was proven with a cell
of three levels for wall thickness and unit cell size culture experiment. A weak dependence of the quantity

Volume 10 Issue 1 (2024) 270 https://doi.org/10.36922/ijb.0119