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Materials Science in Additive Manufacturing SLA 3D printed triaxial nozzle

backflow happens when the molten material can flow back up nozzles to evaluate gelation continuity, printability,
the annular zone between the filament and the liquefier wall, biocompatibility, and shape fidelity. This section focuses
escape the heated area, and cool below its solid/fluid transition on the methods applied to design, fabricate, and evaluate
temperature. It is certain that these issues are a result of the the 3D-printed nozzle for cellular 3D bioprinting with
interaction between the soft material/biomaterial’s rheological peptide bioinks.
qualities and the extrusion process parameters .
[27]
2.1. Designing of the nozzle
To prevent ink from one channel from flowing upstream
into a nearby channel that houses a different ink, pressure- The nozzles were designed using Siemens NX CAD
driven extrusion necessitates careful adjustment of the software with millimeter measurements. Initially, the
ink rheology, nozzle geometry, and printing pressure. In channels were designed, followed by the outer case of the
the event of backflow, the incorrect voxel composition is nozzle. The channel design consists of three inlets and one
outlet, as shown in Figure 1. The peptide and phosphate-
extruded right away after switching. Even the potential of buffered saline (PBS) channels incorporate features to
a good biomaterial for 3D printing is compromised by this prevent backflow, as illustrated in Figure 1. This design
phenomenon. Therefore, additional fundamental studies aims to delay any backflow that may occur at the mixing
are required for further comprehension of the underlying region where the two liquids (peptide and PBS) meet. The
mechanisms and formulation of the best strategies to stop length of the mixing region, which met the requirements
them, particularly backflow prevention. Skylar-Scott et al. of our peptide hydrogels for 3D bioprinting, was derived
made Y-junction nozzles and examined the ink flows in from previous studies . After mixing, the design focuses
[29]
real-time . With a symmetric single nozzle that alternates on maintaining a 90° angle for smooth flow. The inlet for
[28]
between two materials, the researchers essentially printed cells was designed to extrude cells after the peptide and the
a two-material design. However, there has not been much PBS had mixed but before the materials had been extruded
progress made in terms of nozzle innovation and printing out of the nozzle outlet. Finally, the outer case of the nozzle
settings to prevent backflow, which underscores the was designed around the channels with a Luer-Lok design
importance of our work . to ensure compatibility [20,21,30] .
[28]
The nozzle design and fabrication method proposed
are the key components of the novelty of this work. 2.2. 3D Printing nozzle using vat
Conventionally, there is a distinction between the inlets, photopolymerization
outlets, and their assembly separately from the nozzle The nozzles were 3D-printed using FormLabs 3B 3D
setup, whereas in our work, the three inlets and outlets are printer in the recommended settings of the white and
integrated within the nozzle, eliminating the necessity of clear polymer resin. It is important to note that the nozzle
manual assembly using the connectors. This would otherwise during the slicing must be placed vertically for the print
result in the connectors being fragile, thus increasing the plate to ensure the printability of the inner channels, as
occurrence of issues including leaking, which compromise illustrated in Figure S1. Post-printing, the 3D-printed
the printing capability. In addition, we modified the interior nozzles were washed with isopropanol for 30 min and then
design of the inlet with backflow prevention features to cured at 40°C for 65 min using the FormLabs Washer and
remedy potential clogging problems. The nozzle design Cure post-processing devices.
also incorporates an additional cell inlet, which enables
cell extrusion right before the hydrogel extrusion from the 2.3. Finite element analysis of fluid flow in nozzle
nozzle outlet. This ensures better cell distribution within A finite element analysis for the fluid flow in the nozzle
the extruded material. All of which ultimately improve the was performed using the COMSOL Multiphysics software.
utilization and overall experience of 3D bioprinting in terms A 2D DXF domain, defined as the intersection of the 3D
of user-friendliness, practicality, accessibility, and versatility model with the frontal symmetry plane, was created from
in accommodating a wide range of materials. the nozzle 3D CAD model and divided into three different
2. Materials and methods segments, one for each fluid (Figure S2A). The cells inlet
was not included in the model, as the cells were extruded
Using CAD design and SLA 3D printing, we designed just before the outlet and after gelation had occurred, and
and 3D-printed multiple nozzles that meet our bioink the cell flow did not affect backflow or gel formation in any
requirements. The newly designed nozzle was compatible way. The first segment has the peptide solution properties
with Luer-Lok, making it easy to print using our microfluidic (ρ = 1000 kg/m , μ = 0.1 Pa∙s), the second segment has the
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syringe pump-based extrusion system with peptide and live PBS properties (ρ = 1000 kg/m , μ = 0.001 Pa∙s), and the
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cells. We conducted 3D bioprinting using the 3D-printed third segment has the hydrogel properties (ρ = 1000 kg/m ,
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Volume 2 Issue 3 (2023) 3 https://doi.org/10.36922/msam.1786