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International Journal of Bioprinting Nozzle optimization for multi-ink bioprinting

Figure 7. Nozzle proposal for switching SA inks with higher switching efficiency. (A) Typical switching behavior inside a T-junction nozzle in the simulation.
(B) Switching behavior of the T-junction nozzle with corners cut in the simulation. (C) Corner-cut nozzle fabricated using a vat polymerization-based
printer; scale bar = 1 mm. (D) Comparison of transition length between coner-shaved and T-junction nozzles. Experimental data were obtained five times
for each sample. Data are expressed as mean ± S.D.; * p < 0.05.

necessary for tissue engineering applications. Therefore, expand under pressure when liquid flows through it,
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the development of multi-ink printing techniques with a resulting in a decreased flow rate and delay. In our
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micro-order resolution is essential for further advancement experiments, we utilized plastic syringes, silicon tubes, and
of 3D bioprinting. In addition, it is expected that the surface acrylic-based single nozzles. Implementing a more rigid
tension of the liquids considerably affects the switching structure could enhance the resolution of the single-nozzle
behavior inside small single nozzles. Thus, we believe that printing system.
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the single nozzle should be designed based on this effect Moreover, the printing speed is crucial for building
for multi-ink printing with micro-order resolution.
large structures. Cells contained in a bioink do not survive
In this study, a commercially available vat- without a suitable environment for culturing. Therefore,
polymerization-based 3D printer was employed to fabricate the 3D printing process should be fast such that the
single nozzles. While this method is economical and rapid, 3D-printed structure can be immediately kept in a cell
the resolution is restricted to a few hundred micrometers. culture environment after printing. We experimentally
Alternately, the milling process has been widely utilized to investigated the effect of flow rate on switching efficiency,
fabricate nozzles 19,20 ; however, this method is unsuitable for and the result showed that Se decreased as the flow rate
creating micro-scale structures. Advanced fine processing increased when flowing 0.5 wt% SA solution against
technologies, such as stereolithography, facilitate the 0.5 wt% SA solution in a T-junction nozzle (Figure S7,
construction of microchannels with dimensions on the Supporting Information). In future work, we aim to
order of several dozen micrometers. This advancement can investigate further design optimization when we consider
facilitate the creation of nozzles capable of printing multi- the fast printing process in single-nozzle bioprinting.
ink structures at the micro-scale. 29,47 Additionally, incorporating feedback technology could

Furthermore, precise control over small volumes further improve printing resolution. Typical bioprinting
of bioink is critical in nozzles designed for micro-scale systems lack a real-time feedback mechanism during the
operation. In such systems, minor pressure variations printing process, solely relying on initial printer settings.
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in the nozzle, syringe pumps, and connecting tubes can This reliance can lead to failures or the production
significantly influence the bioink flow rate, potentially of low-resolution structures if any issues arise during
reducing resolution. For instance, silicon tubing may printing. Therefore, a feedback system that monitors

Volume 10 Issue 5 (2024) 164 doi: 10.36922/ijb.4091