Page 388 - IJB-10-4

International Journal of Bioprinting 3D cartilage induction and monitoring

a decrease in amplitude from day 1 to day 3 was observed seeded scaffolds to determine the capacity to record
in both cases, only cell-loaded scaffolds exhibited an different growth patterns. In contrast, Figure 6H displays
appreciable increase in amplitude. Notably, there was a the speed of sound of both cell-seeded and blank scaffolds.
significant difference in amplitude on all days (p < 0.001) Average values of the speed of sound are represented due to
(Figure 6A–C). The same difference was evident for the much lesser variation (standard deviation <1%) compared
computed ToF signal (Figure 6D), where blank scaffold to density. The figure demonstrated a significant difference
signals were slower than cell-loaded ones (p < 0.001). In between blank and cell-seeded scaffolds (p < 0.001), with
summary, results observed in Figure 6C and D imply that cells-loaded scaffolds exhibiting a higher c . Notably, c
SD
TPU
ultrasound signals induced considerable differences in = 1740 m·s and c = 1480 m·s from literature are
−1
−1
H2O
cells seeded in the scaffolds. relatively identical to those obtained in our experiments
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Raw recorded data do not comprehensively predict and model. For example, the porous ratio of printed
−1
the ECM synthesis rate. As explained, computational scaffolds was 0.3, which corresponds to a c of 1558 m·s .
SD
models were developed to describe the fluid dynamics These findings highlight the accuracy of our model and
and P-wave propagation, such as predicting the effect of suggest that a higher speed of sound corresponds to less
the fluid on cells if the scaffold fibers thicken over time. water content in the scaffold domain.
The result is expressed in Figure 6E, where three different
fiber diameters are proposed: an initial fiber diameter of 4. Discussion
200 µm, an intermediate of 250 µm, and a final estimated Osteoarthritis (OA) is a gradual and degenerative
diameter of 300 µm (i.e., obtained from the SEM images). It condition characterized by the loss of functionality
is inferred that shear stress increases directly proportional in cartilage tissue, which has a limited ability for
to the fiber diameter: regeneration. Therefore, the great potential of RM
products will be advantageous to the long-term treatment
∂u of OA. For RM development, the applied biomaterial
8
τ = µ (XVII)
∂y properties are significant. For instance, the stiffness of 3D
bioengineered scaffolds is essential for forming AC tissue
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where µ denotes the dynamic fluid viscosity and u due to cyclic mechanical pressures from bodily activity.
denotes the velocity of component X. Notably, the shear Hence, prior characteristics of scaffolds are significantly
stress changed from an initial range of 4–7 mPa to a final influenced by scaffold fiber geometry and PS. 54,55 Every
range of 8–10 mPa. More importantly, high shear stress joint in the musculoskeletal system relies on connective
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in the orthogonal direction of fluid flow becomes evident tissues (such as cartilage); AC experiences baseline
once the fiber diameter exceeds 250 µm. amounts of mechanical strain within their constituent
fibers due to growth and swelling. These strains impart
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Figure 6F features the BR output flow speed, where the biophysical signals to local cells, influencing cellular
boundary probe recorded data as instant flow speed (at phenotype and function. Drawing inspiration from
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the axial origin point) and output flow velocity (similar cartilage ECM and 3D TE principles, we developed an
to Figure 6E). Previous magnitudes were compared to alternative to previous therapeutic strategies. 59
an estimated increase in scaffold fiber diameters. Both
magnitudes are connected and exhibit distinct patterns. Previous works have studied the benefits of perfusion
The output velocity decreased linearly for a fiber diameter flows over MSCs and chondrocytes. 60,61 However,
of 360 µm, but the instantaneous speed increased from 200 there is still a lack of defined standard conditions for
to 320 µm. For fiber diameter >320 µm, the output flow such mechanical cues. Despite this, those studies
speed began to decline slightly, but at fiber diameter = have reported perfusion flows with the primary cilia
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360 µm, there was a sharp decrease, followed by increase stimulation and the intra-flagellar transport (IFT) of
38
in the output flow speed. This observation implies that chondrocytes, involving the TRPV4 channels. This
fiber diameters exceeding 340 µm would decrease the transport regulates the gene expression of collagen types
permeability of the scaffold and redirect the fluid channel II and IV, G proteins, Indian hedgehog homolog (Ihh),
2+
around the scaffold walls. Ca channels, connexins, purine, cAMP, and the PKA
pathway, among others. 63,64
Figure 6G and H presents the C and ρ . Figure 6G
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SD
provides two key observations: (i) no significant density Most of the previous literature only expresses the
variation was observed in blank scaffolds; (ii) an increase quantities of flow rates; in contrast, this article reports
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in the scaffold domain densities over time in cells-seeded the magnitude and exerted shear stress using FEM. Our
scaffolds. The non-average curve was computed in cell- estimated magnitudes are in concordance with previous
Volume 10 Issue 4 (2024) 380 doi: 10.36922/ijb.3389