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International Journal of Bioprinting Oozing 3D-printed scaffolds for tissue engineering

demonstrated that NaOH solution erodes the surface of of fibers per volume in the Os and Oc scaffolds. The
the fibers. In addition, the hydrophilicity assay showed immunofluorescence results (Figure 10B) were consistent
statistically significant differences (* p < 0.05) between with the metabolic activity, showing that scaffold walls of
controls and NaOH-treated groups at each measuring point Gy and Gof were mostly covered by spread cells at day 7.
(day 0, day 1, day 2, and day 9), with a constant shift of ~9° Similarly, fibers of Os, Or, and Oc were also completely
to 15° observed between conditions. Similarly, statistically covered by spread cells.
significant differences in contact angle within time were
separately found in both conditions. Additionally, the 4. Discussion
contact angle in the controls was statistically significant Oozing or stringing effect has been generally described
¶
( p < 0.05) between day 0 and day 1, and between day 0 as a non-desirable drawback in FDM. 38,62 Despite these
and day 2. However, the NaOH-treated group showed considerations, some recent studies have developed
differences between day 0 and day 2, and between day 0 interesting approaches utilizing this effect to design
and day 9 (Figure 8). environments with fibers in the range of microns (from a
3.6 Compression study few tens up to hundreds). Various geometries have been
Our results from the determination of elastic modulus (E), studied by means of this technique, such as planar parallel
maximum stress (Max stress), and maximum elongation at arrangements, 44,63 3D parallel distributions, 51,59,64 and also
maximum force (Max dL at F ) for all scaffolds in both hybrid constructions, combining FDM with another
max
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experimental conditions (NaOH treatment and control) technique, such as airbrushing or electrospinning, in
demonstrated no statistically significant differences (p order to create a stack of alternate layers. Nevertheless, these
< 0.05) between conditions for any studied parameter, approaches still fail to produce an improved biomimetic
indicating that treatment does not affect mechanical 3D environment with randomly distributed fibers, as they
66-68
properties (Figure 9). Interestingly, Gy and Gof specimens’ all remain gridded.
data showed a higher E modulus in both conditions (NaOH Our study focused on developing a set of novel FDM-
treatment and control) compared to the oozing groups, printed constructs with random and gridded distributions
with Gof’s being three or four times higher than that of of microfibers that may better mimic those of the native
Gy. Maximum stress values showed similar behavior in ECM niche. In addition, we analyzed the potential of
both experimental conditions for all specimens, except for these constructs, which support cell culture growth, as
Oc and Os, which were found to be considerably lower. bone tissue-engineering strategies. This may represent an
Maximum elongation at maximum force showed similar important progress, as we introduced for the first time the
results in both conditions for all specimens with a lower potential of using the oozing or stringing phenomenon to
value in Oc and Os specimens (Figure 9C). enhance the 3D-printed scaffolds characteristics for better
promoting cell attachment and growth, as the created fiber
3.7. Cell culture studies dimensions better matched the ECM natural niche. 69,70
To assess how the morphology or accuracy of the
3D-printed structure could affect the cell response, SaOs- We demonstrated that design is a fundamental tool
2 cells were seeded and cultured within the scaffolds. to overcome FDM printing limitations when using
Metabolic activity was determined using a resazurin salt conventional printing machines. Our results showed that it
reduction assay, and cytoskeleton staining was observed is possible to surpass the constraints of an accessible FDM
with a confocal microscope (Figure 10A). Tissue culture ordinary printer by using AAD to improve the architecture
plastic (TCP) was used as a control for cell behavior while of the scaffolds, corroborating similar algorithm-based
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Gof, commonly used in tissue-engineering applications, methodology previously described in the literature.
was used as a control of the infill structure. As shown in Moreover, our scaffolds’ design algorithms were especially
Figure 10B, there was no difference in the initial adhesion designed to create random distributions of the fibers,
(day 1) of cells to the different scaffolds, except for Or, providing an innovative framework that enhances the
which displayed a significantly lower cell adhesion (p FDM printing application to an improved biomimetic-like
70-72
< 0.05). However, this lower metabolic activity was not approach in the tissue-engineering field.
statistically significant at days 3 and 7. Moreover, the Our results demonstrated the oozing effect is a
metabolic activity was gradually increased during the repeatable technique that can be controlled considering
culture time, being comparable to that of Gof and normal a certain degree of tolerance within fiber geometry. An
TCP, and was significantly higher for Os and Oc at day accurate setting of the printing parameters, such as feeding
7 (p < 0.05). These results correlated with higher density speed and printing speed, among others, and other intrinsic

Volume 10 Issue 2 (2024) 512 doi: 10.36922/ijb.2337