Page 39 - IJB-9-2

International Journal of Bioprinting Scaffolds printed with light sheet stereolithography

The alignment system consists of the scan lens (CLS-SL, performance of the novel LS printer in terms of speed,
Thorlabs Inc.), the cylindrical lens located before the scan scale, and resolution. The material used in this work is a
lens, the tube lens TL (TTL200-A, Thorlabs Inc.), and the one-photon polymerization resin used in conventional
CMOS camera (Mako U-130, Allied Vision). and commercial SLA-DLP systems to fabricate pieces with
strong mechanical properties. As in any one absorption
2.2.2. Patterns generated with LS illumination polymerization material, the curing height (C ) and
p
Patterns were generated by scanning and changing the transversal resolution in a 3D-printed structure can be
angular orientation of the LS with respect to the building described in terms of radiant exposure (E) as predicted
[52]
platform. As mentioned earlier, scanning was performed in by the Beer-Lambert law . Those characteristics are
our system using a Galvano mirror that steers the LS along the estimated by the working curve of the resin, Equation 3,
FOV of the scan lens. This allows for printing structures along which we obtained by measuring the height of various
one direction and controlling the steps between successive polymerized solids printed under different exposure
linear voxels with high precision. A pattern can consist of conditions. We found that the resin exhibits a penetration
linear voxels with different orientations, as can be found in depth of D = 110.95 μm and a critical exposure of
p
a rectangular scaffold; therefore, changing the orientation of E = 1.9 mJ/cm².
c
the LS becomes important. In our system, we modified the C = D ln (E/E ) (3)
orientation of the LS by rotating the building platform or p p c
rotating the beam shaping optics. The scaffolds presented in 2.5. Printing protocol
this work were printed following the first strategy. The printing protocol we used during the experiments is
2.3. Scaffold fabrication highlighted in Figure 2C. First, the LS was aligned and the
start position of the build platform was set with respect to the
Many features of a scaffold geometry can be controlled by FEP film of the resin vat. Then, the radiant exposure E and
the position and orientation of the strut, including pore exposure time t (typically < 0.1 s) are defined accordingly
size, pore shape, pore volume fraction, and as demonstrated to the desired curing depth C , e.g., ≈150 μm, for which the
p
in other works, mechanical properties and functional irradiance I at the FEP film is adjusted properly with the
gradients of the scaffold . In this work, we used two expression E = I. These printing conditions combined with
[11]
patterns to demonstrate the capabilities of LS illumination the geometrical parameters of the scaffold, for example, the
t
in controlling these features. The first scaffold comprises number of struts and pore size, constitute the set of values
0/90° struts composed of a set of uniform and rectangular we introduced in our custom-build application developed
pores, as shown in Figure 2A. To fabricate such a scaffold in LabView (National Instruments). At this stage, we filled
with 3D LS printing, 0° struts were distributed periodically the resin vat with 5 mL of resin to guarantee the immersion
along the FOV of the scan lens with controlled spacing. of the build surface. In general, resins exhibit good
Then, the LS orientation was rotated 90° with respect to the adhesion to metallic surfaces, but they can vary between
previous pattern and the second pattern was printed at the formulation and materials, specifically when working with
same layer. Subsequently, a set of layers of the same 0/90 biopolymers. While working with high porous and thin
pattern might be printed on top of one another to build a 3D layers, we found aluminum plates and glass substrates
scaffold. Other types of pore shapes and interconnectivity good adherent materials for the polymerized structures.
were achieved by changing the orientation of the struts. These types of materials also guarantee the fabrication of
Figure 2B shows a scaffold with 0/45/90 orientation. In complete 3D scaffolds. However, fixation of fine structures
this configuration, we opted for printing each orientation is largely improved when functionalizing the glass
pattern at a different layer, which leads to higher porosity substrates with 3-(Trimethoxysilyl)propyl methacrylate.
ratios and more complex pore interconnectivity. While We followed the procedure described in Sigma-Aldrich
[53]
the control of the pore size, shape, distribution, and strut to attach the scaffolds to the glass substrates during the
resolution are demonstrated in this paper with the two printing process. After printing, the scaffold was rinsed
scaffold configurations in Figure 2, the capabilities of the and kept in isopropanol 99%.
3D LS printer can be extended to more complex patterns
following the same principles of scanning and rotating the LS. 2.6. Scaffold measurement and characterization
We characterized the scaffolds with respect to the strut
2.4. Resin material and pore size, the pore distribution, the overall size, and
We demonstrated the proof of concept of our prototype the pore interconnectivity. To obtain a complete physical
with the commercial low-shrinkage Elegoo resin (Elegoo, characterization of the scaffolds, we used a Keyence digital
Shenzhen, China), which allowed us to assess the microscope with ×200 (Keyence, Japan). The illumination

Volume 9 Issue 2 (2023) 31 https://doi.org/10.18063/ijb.v9i2.650