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Lopez de Armentia, et al.
4.7. Thermal conductivity information about layers adhesion, which could be related

Thermal conductivity measurements were completed to printability. and R+GoxNP slightly increased
R+GO
to evaluate, together with viscosity, the nanofiller
dispersion. Thermal conductivity decreases with free hydrophilicity of the resin. There were minor decreases
volume; therefore, it is possible to have information about in contact angle: 4% for R+GO and 6.2% for R+GoxNP.
However, R+G showed a subtle increase in contact
it through thermal conductivity measurements. angle, which means that its hydrophilicity was lower.
Figure 11 shows the results obtained for different
nanofillers. The addition of GoxNP slightly increased However, with the deviations that these values presented,
differences were not significant.
thermal conductivity, whilst G reduced this parameter. In
the case of GO, thermal conductivity was not affected by 4.9. Roughness
this nanoparticle. However, differences found between
the nanocomposites and R were not significant (P > 0.05). The R parameters of roughness of the different samples
a
are shown in Table 9.
4.8. Wettability Roughness results showed that the addition of
Water contact angle on the different investigated surfaces nanofillers may affect the roughness of 3D printed
is presented in Table 8. These measurements could give samples. These differences of surface roughness are due
to the surface finish; the higher the roughness, the worse
A B the surface finish. Therefore, these measurements were
used as an indicator of the printing quality. Although
there were no major differences, it could be observed that
the addition of GoxNP did not affect roughness compared
to R, GO addition slightly increased roughness (17%) and
G showed the highest increase in roughness (34%).

5. Discussion
This study demonstrated the effect of different GBN on
the polymerization reaction and the printability of an
C acrylic photocurable resin. It was found that G affected
polymerization degree due to its high light absorption
and therefore, it also affected printability. Conversely,
GoxNP did affect polymerization degree slightly, but
it allowed printing process. Finally, GO did not affect
polymerization reaction nor printability of the resin.
Although the differences on UV polymerization and
wettability between G and GoxNP are subtle, their impact
on the printing performance is highly notable due to the
differences in light absorbance. R+G showed the highest
Figure 10. GBN dispersion of R+G (A), R+GO (B) and R+GoxNP light absorbance (Table 5). Therefore, G absorbs more
(C). Red circles show graphene-based nanomaterials agglomerates light (1.43 a.u.) than GoxNP (1.10 a.u.). and curing depth
of different size. could be reduced, leading to lower adhesion between
layers and worse printability.
Polymerization reaction was studied using DSC,
FTIR and hardness measurements. First, thermal
polymerization was studied to investigate the effect of

Table 8. Contact angle (°) of water on sample surface
R R+G R+GO R+GoxNP
72.9 ± 1.6 74.0 ± 3.7 70.0 ± 2.7 68.4 ± 3.6

Table 9. Roughness (Ra) of printed samples (µm)
R R+G R+GO R+GoxNP
Figure 11. Thermal conductivity of R, R+G, R+GO, R+GoxNP. 1.90 ± 0.24 2.56 ± 1.20 2.23 ± 0.53 1.87 ± 0.48

International Journal of Bioprinting (2022)–Volume 8, Issue 1 191