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Materials Science in Additive Manufacturing SLA 3D printed triaxial nozzle

showing that the inlets can be used interchangeably. In to be 60 μL/min and 15 μL/min for the peptide solution
both configurations, a velocity magnitude in the range of and 5× PBS, respectively, for both IIZK and IIFK peptides.
0.0150 m/s was calculated in the outlet segment, compared The extruded hydrogel thread for the aforementioned
to a slightly lower magnitude in the range of 0.0125 m/s, flow rates displayed both continuity and stiffness, a prime
which represents the backflow. A slightly higher maximum indicator for printability. Lower flow rates resulted in less
velocity magnitude was calculated for the inlet where the viscous, softer gel, at times with notable PBS accumulation,
bend was placed lower (0.0350 m/s compared to 0.0327 m/s) whereas higher flow rates resulted in clog formation and
due to the sharper bend and the longer vertical part of the segmented hydrogel extrusion. Hence, the optimal flow
segment. Conversely, for the typical nozzle, the backflow was rates were set according to these observations to be used
significantly larger, with the velocity magnitude reaching for further printability assessments.
values in the range of 0.0180 m/s, considerably higher than
the 0.0110 m/s magnitude for the outlet. These results clearly 3.4. 3D Printing shape fidelity and resolution
indicate that the nozzle features are effective in minimizing Six-layer 15 × 10 × 1.2 mm rings were 3D-printed with
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backflow compared to a nozzle design without them. both peptide bioinks (Figure 3A). For the IIZK bioink, the
In the normal operation model, the velocity profiles construct exhibited excellent resolution and dimensional
were comparable for both configurations of the nozzle. The accuracy with a defined thin wall. No clumps or clogs
maximum velocity (0.0388 m/s) was observed at the outlet were observed during printing, attesting to the nozzle’s
segment, and the velocity magnitude for the peptide inlet effectiveness in controlling gelation. In addition, the hydrogel
was in the range of 0.0325 m/s for both configurations, deposition on each of the construct’s layers was seamless with
which further attests to the interchangeability of the nozzle no loss of continuity. For the IIFK bioink, the resolution was
inlets for 3D bioprinting. For the typical nozzle, a similar acceptable, but the ring wall was less defined. The gelation was
profile was observed, with the exception of the velocity sometimes inconsistent, yielding some clumps that resulted
magnitude for the peptide inlet being lower, in the range of in a less homogenous hydrogel. These observations should
0.0300 m/s. This difference is expected, given the absence not be collectively construed as deterrents to printing with
of the bends in the inlet segments. IIFK using the nozzle, as they are mostly attributed to the
properties of the bioink, which has previously been proven
3.3. Parameter optimization for 3D printing to be more challenging to achieve consistent gelation with .
[29]
Gelation time for the formation of a stable bioink thread was Fine grid squares of 20 × 20 mm were 3D-printed with
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found to be approximately 30 seconds for both peptides, both peptide bioinks. Figure 3B shows the formation of fine
significantly faster than previous nozzle designs . In terms threads formed in different layers. For IIZK, the resolution
[29]
of gelation continuity, the best flow rate profile was found of the grid was very good, with clear and continuous

A

B

C

Figure 3. 3D-Printed peptide acellular scaffolds using the 3D-printed nozzle. These scaffolds demonstrated varying levels of shape complexity, including a
hollow cylinder measuring 15 × 15 × 1.2 mm (A), a grid measuring 20 × 20 mm (B), and a tall hollow cylinder measuring 10 × 10 × 10 mm (C).
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Volume 2 Issue 3 (2023) 7 https://doi.org/10.36922/msam.1786