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International Journal of Bioprinting 3D cartilage induction and monitoring

model, the estimated velocity of the wave corresponds to the scaffold stimulation increased cell presence and AC
empirically recorded ToF. In conclusion, the methodology ECM. These findings not only corroborate our previous
using ultrasonic waves enables non-destructive evaluation research but also indicate a notable enhancement over it.
of the scaffold, providing valuable insights into its In previous work, the effectivity of functionalized bTPUe
mechanical properties and validating the model. scaffolds for cartilage-like grafts was demonstrated within
Results from the BR assays demonstrated that the perfusion flow BRs, i.e., enabling strong cell adhesion over
signal amplitude of the cell-loaded scaffolds was higher time, inducing direct forces onto the cells without the risk
than the blank scaffolds, implying that the stiffness of the of cell detachment, and facilitating the early differentiation
cell-seeded scaffolds was higher. A shared characteristic of MSCs. If another biomaterial is used, the properties of
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between cell-loaded and blank scaffold samples is the BR should be adjusted in terms of ultrasonic conditioning.
decrease of amplitude from day 1 to day 3, indicating an This implies the BR is dependent on the topography and
external factor such as plastic deformation of the materials mechanical properties of the biomaterial. Nevertheless,
exerting contact tension on the transducers. ToF is an the combination of biomaterial properties and BR design
inadequate parameter for tissue expansion prediction induces a massive increase of ECM compounds in a
because its variations are much lower than the rates of cell relatively short time, allowing the development of a useful
proliferation and ECM synthesis. Notably, the absence of cartilage-like graft for cartilage TE. To confirm that our AC
considerable near rebounds in study samples compared grafts display a similar conformation to naive AC tissue,
with blank scaffolds implies a smaller PS. Our empirical long-term evaluation, in vivo experiments, and histological
signals distinguish between measuring the scaffold with assays should be conducted in future research. Additionally,
cells attached to their fiber surface and without cells using FEM to analyze the current fluid dynamics reveals
attached (blank). Thus, employing FEM alongside big the necessity to regulate the initial flow rate and modify it
data analysis tools, such as signal cross-correlation, proves over time to accommodate tissue growth.
to be an accurate tool for enhancing the information We have developed a system capable of independently
derived from extracted results. In this case, it facilitates tracking the rise in tissue graft density over time and
the transformation of a qualitative approximation into a determining the graft speed of sound using inverse problem
quantitative one. characterization through FEM. Given the close association
of both metrics with increased material stiffness and
Moreover, an apparent increase in the scaffold domain
density was observed over time in the BR, and this collagen content, our method effectively monitors tissue
growth over time. In summary, we have developed a BR
phenomenon was not attributed to any degradation in to induce chondrogenesis in cell-loaded scaffolds and
bTPUe after 14 days, it can be inferred that this result is measure tissue growth in real-time. While further studies
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attributable to ECM synthesis and cellular proliferation. are warranted, our results suggest the great potential of our
Consequently, our system demonstrated the capability BR as a medical device in AC-bioengineered therapeutic
to monitor tissue development in real time. In addition, strategies.
the notable increase in the speed of sound in cellular
scaffolds suggests that the K component of the speed of Acknowledgments
sound equation increased more than the density, implying
a higher elastic modulus (E) or lower viscosities (v). The authors thank Ana Santos, Mohamed Tassi, Fátima
Particularly intriguing is the asymptotic value of 1300 Linares, Isabel Sánchez, and Gustavo Ortiz from the
kg·m obtained in cell-loaded scaffolds, possibly due to Centre for Scientific Instrumentation (CIC) (University of
−3
reduced nutrient support associated with higher shear Granada) for the excellent technical assistance. In addition,
stress. Interestingly, this value resembles literature findings we want to thank Juan de Vicente for letting us use their
for collagen (1.3 g·cm ), suggesting that the final density server with COMSOL.
−3 81
is mainly composed of collagen.
Funding
5. Conclusion This research was supported by the Ministerio de Economía,
In this work, we have developed a unique BR that, when Industria y Competitividad (ERDF funds; project no.:
compared to static cultures, improves chondrogenesis RTC-2016-5451-1), Fundación Mutua Madrileña (FMM-
through fluid with low shear stress. Our BR boosts the AP17196-2019), Consejería de Economía, Conocimiento,
growth of IPFP-MSCs seeded in bTPUe-PBA scaffolds Empresas y Universidad de la Junta de Andalucía (ERDF
and facilitates ECM production with high collagen type funds; project nos.: B-CTS-230-UGR18, PY18-2470,
II levels. SEM and confocal imaging validated that BR SOMM17-6109, and P18-FR-2465), Junta de Andalucía

Volume 10 Issue 4 (2024) 382 doi: 10.36922/ijb.3389