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Daskalakis, et al.
A B A B

C D
C D

E F

E F

G H

Figure 8. Scanning electron microscopy images of cells attachment
and spreading on (A) polycaprolactone bone brick (case 1), (B) 10
wt%/10 wt% hydroxyapatite/β-tri-calcium phosphate (HA/TCP)
bone brick (case 2), (C) 20 wt% HA bone brick (case 2), (D) 20
Figure 7. Top and cross-section scanning electron microscopy wt% HA bone brick (case 3), (E) 20 wt% TCP bone brick (case 3),
images of cells spreading in bone bricks (case 3) with different and (F) 20 wt% TCP bone brick (case 4).
material compositions (A), (B) polycaprolactone, (C), (D) 10/10
wt% hydroxyapatite/β-tri-calcium phosphate (HA/TCP), (E), (F) content. Moreover, for the same configuration and level of
20 wt% HA, and (G), (H) 20 wt% TCP.
reinforcement, FW is higher (lower PS) in HA bone bricks
than in TCP bone bricks. The PS also decreases by increasing
Table 2. Optimal design architectures regarding mechanical and the number of double filaments (from 25 to 38) and a
biological performance (darker color corresponds to the optimal similar trend was observed for spiral filaments (increasing
case and less dark color to the worst configuration) from 6 to 14). For the same material composition, the PS
Architecture Mechanical Biological of bone bricks with the same number of double filaments
properties performance (AU) decreases by increasing the number of spiral filaments. A
(MPa) similar trend was observed for bone bricks with the same
Case 1 95.4±4.9 10262.8±41.6 number of spiral filaments. In addition, PCL bone bricks
Case 2 165.8±1.7 10929±1718.6 showed micropore structures on the surface of the filaments
Case 3 207.8±3.6 11216±127 (Figure 4A), while PCL/HA, PCL/TCP, and PCL/HA/TCP
Case 4 344.9±2.7 9531±139 bone bricks show less micropores on the filaments surface
(Figure 4C, E, G). This can be explained by the effect of
and material composition differences, up to 24.5% can be the ceramic nanoparticles on the size of the polymer crystals
observed. These differences can be attributed to the fact and the recrystallization process inducing a smooth surface
[28]
that processing conditions were kept constant for all bone of the printed filaments .
bricks topologies and material compositions and can be 3.2. Mechanical analysis
solved in the future by adjusting the processing conditions
aiming to obtain similar values of FW. Results show that PS As shown in Figure 5, the mechanical behavior of
decreases and FW increases by increasing the bioceramic the bone bricks strongly depends on the architecture

International Journal of Bioprinting (2021)–Volume 7, Issue 2 49