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International Journal of Bioprinting In situ thermal monitoring in bioprinting

Figure 9. Geometric reconstruction from tracking approach outcomes. Top row shows the nominal sagoma images of the first three layers of a construct
(highlighted in blue). Bottom row shows the respective reconstructed layers obtained from the application of our algorithm during the tracking process.
The capability to segment the bioink filament at each built with complicated components, and in the case of
moment in the 3D printing process provides a unique IR devices, their purchase prices are higher than those in
advantage: the reconstruction of the distinct profile of visible light. Optics and detection systems in the IR are
each individual layer, isolated from the layers beneath not as widely used as those in VR. These components are
or the substrate. This is especially crucial when dealing more expensive, thus increasing the initial cost. Moreover,
with transparent bioink. Traditional visible range images thermal images cannot be captured if certain materials,
encounter challenges in distinguishing between multiple such as water and glass, are used. Unlike VR, IR radiation
layers deposited on top of each other. This issue becomes cannot pass through water or glass, from which it is
particularly pronounced when transparent bioink is reflected as in a mirror, unless special arrangements are
employed, as the cumulative effect of all printed layers made, such as the use of special filters or windows made
results in an overall image that combines these layers. of materials that allow the radiation to be transmitted
Consequently, the visual representation becomes a without interference. In addition, the monitoring system
summation of all the printed layers, obscuring the details of can only be used in printing processes where the geometry
individual layers and compromising the ability to discern of the last printed layer (or the construct in general) can
their distinct characteristics. In contrast, the developed be captured by registration systems (not applicable in SLA
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method could isolate the bioink belonging to a layer printed bioprinting, for example, unless custom-made systems are
on top of a previous one, effectively separating it from the foreseen at the machine design stage).
rest of the printed construct. It is important to note that the Despite these limitations, this approach would also
proposed method considers the shape of the bioink at the open the opportunity to develop a process control system
moment of deposition and does not account for spreading or and to modify control inputs for correcting errors in
diffusion that may occur between material deposition and subsequent layers. It is recommended that the approach
image acquisition. This distinction is evident in VR images be followed both by the end-users of extrusion bioprinters
where certain pores may appear occluded while being open and the manufacturer of bioprinters, since the monitoring
in the thermal reconstruction of the equivalent layer. system like the one proposed can be implemented also
Upon reconstructing the profile of a layer, the developed in the machines already on the market without having to
method enabled the evaluation of its geometric accuracy. create new bioprinters integrated with this system.
The DSC was assessed by measuring the similarity between For future development, a better image processing
the reconstructed profile and the binarized image of the system capable of identifying more features and operating
corresponding nominal layer. Of course, this method is not in real-time should be developed. In situ monitoring
exempt from limitations. Monitoring devices in the IR field techniques incorporated with the feedback systems for
have a higher purchase price. They are advanced devices process control should also be implemented.

Volume 10 Issue 3 (2024) 404 doi: 10.36922/ijb.2021