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Materials Science in Additive Manufacturing 3D-printed nozzle for 3D bioprinting

A B

C

Figure 3. Gelation continuity tests of DNC. (A) Continuous extrusion of peptide bioink thread showing gelation and stiffness. (B) Extrusion of continuous
five-segment line at different flow rates to optimize bioink formation. (C) Six-layer cubical constructs showing printability and layer deposition, top view,
and side view.
DNC: Disposable nozzle connectors.
In terms of gelation continuity, the best flow rate profile A B
was found to be 55 µL/min, 20 µL/min, and 20 µL/min
for the peptide hydrogel, ×7 PBS, and ×1 PBS inlets,
respectively. Different flow profiles were tested by printing
a continuous 5-segment line, which visibly indicated the
period of flow before clumps were formed from over-
gelation. A visible thread of gel was also extruded and
displayed gel continuity and stiffness, a prime indicator for
printability (Figure 3A). Gelation time for the formation
of a stable bioink thread was found to be approximately
81 s, which was relatively faster than homemade nozzles.
Hence, the optimal flow rates were set according to these
observations to be used for further printability assessments
(Figure 3B). It was observed that lower flow rates resulted
in insufficient flow, which was expected given the mixing
region ratio. The gelation therein needed to be accelerated
by increasing the overall flow to 95 µL/min.
A six-layer semi-filled cube of dimensions
10 × 10 × 2 mm was 3D-printed using the DNC. Based Figure 4. 3D printing of peptide-based acellular constructs with DNC.
on the gelation continuity test, the optimized flow rates Different levels of shape complexity were selected: Hollow cylinder
were set to 55 µL/min, 20 µL/min, and 20 µL/min for the 10 × 10 × 13 mm (A), and fine grid 20 mm (B).
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three inlets of peptide, ×7 PBS, and ×1 PBS, respectively. 3D: Three-dimensional; DNC: Disposable nozzle connectors.
The cubical shape was found to be well maintained with
defined lines (Figure 3C, Cube). No clumps or clogs 3.3. 3D printing shape fidelity and resolution
were observed during printing – A key marker of the To test the DNC, several acellular constructs with different
nozzle performance through consistent formation of levels of complexity were printed. In addition, automated
bioink thread. In addition, the construct layers piled square wave flow profiles were programmed for the
up smoothly without any sagging, which also indicated microfluidic pumps to enable smoother flow for longer
continuous layer deposition. For further verification, the periods. This was found to ease printing considerably,
peptide flow rate was increased to 60 µL/min for another allowing for 20-min prints without flow interruptions
construct, but results showed lower printing resolution or the need for user intervention to manually alter flow
due to several clumps, most likely due to the slightly rates. First, a hollow cylinder of 10 × 10 × 13 mm was
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accelerated gelation. printed (Figure 4A). This highlighted the layer-by-layer

Volume 2 Issue 1 (2023) 6 https://doi.org/10.36922/msam.52