Page 279 - IJB-10-2

International Journal of Bioprinting Microfluidic spinning for neural models

In addition, we examined the effects of the core 3.3. Preparation and characterization of multi-
solution material selection, concentration, and flow rate hollow composite microfibers
on the preparation of composite hollow microfibers. Based on the above results, we further prepared multi-
The core solution, as the occupancy fluid of hollow hollow CaA/GelMA composite microfibers by adjusting
microfibers, is generally selected as a substance with high the perfusion fluid strategy. While keeping the sheath
viscosity that does not react with the sample solution; flow and sample flow unchanged, the core flow was
polyvinyl alcohol and PF-127 are commonly used. In changed from M to M and the number of core flows was
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this study, for biocompatibility and stability reasons, increased from one to two to facilitate the preparation of
we chose chitosan and PF-127 as the core solutions, double-lumen hollow CaA/GelMA composite microfibers,
which can stabilize the CaA gel so that it does not easily as shown in Figure 3A and Video S1 (Supplementary File).
dissolve and degrade; of note, PF-127 is suitable for In addition, by adding different types of fluorescent PS
spinning systems by virtue of good biocompatibility microspheres, such as blue fluorescent PS microspheres and
and adjustable viscosity. We added fluorescent PS green fluorescent PS microspheres, to the sample solution
microspheres to the sample solution in order to perform of M and M , two types of double-lumen hollow CaA/
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fluorescence photography of the confocal microscope, GelMA composite microfibers with different inclusions
and the structure of the microfibers is shown in Figure were obtained, as shown in Figure 3B and Video S2
2D. When the core flow was 1% chitosan solution, no (Supplementary File). This type of microfiber with different
hollow structure was formed inside the microfiber; when contents holds application potential for 3D co-culture, 3D
the core flow was 10% PF-127, the hollow pores were biomanufacturing, and multi-tissue simulation in complex
generated inside the microfiber, but the homogeneity systems. Furthermore, by applying core flow to both
was poor and the hollow pores were discontinuous; channels M and M and further increasing the number
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when 20% PF-127 solution was used as the core solution, of core flows, three more complex three-lumen hollow
the hollow pores were obvious and the hollow structure CaA/GelMA composite microfibers could be prepared, as
of the microfiber was stable. Therefore, 20% PF-127 shown in Figure 3C and Video S3 (Supplementary File). In
solution was selected as the core solution. Subsequently, theory, one can continue to increase the number of fluid
when the sample flow (80 μL/min) and sheath flow (160 channels and set up more complex fluid infusion strategies
μL/min) rates were kept constant, the core flow rate was to prepare more complex multi-lumen hollow microfibers.
changed to prepare hollow microfibers. When the core However, increasing the number and type of fluids would
flow rate was increased from 10 to 60 L/min, the hollow further complicate the microfluidic spinning chip and
pores of the composite microfibers gradually became encumber the peripheral fluid-driven devices, adversely
obvious (Figure 2E). Among them, the flow rate of 20 affecting the preparation of the microfluidic spinning
μL/min promoted the formation of microfiber hollow microchip and the stability of the fluid perfusion system.
structure with a regular circular cavity. When the flow 3.4. Hollow composite microfibers for the 3D culture
rate was less than 10 μL/min, the cavities were small and of HUVECs
irregular. In contrast, when the flow rate was between 40 In the above-mentioned experiment, PS microspheres
and 60 μL/min, the cavity structure flattened, becoming were added to the sample solution to assist with microfiber
elliptical and larger but remaining incomplete. This loading. These microspheres had a diameter of 5 µm
may be due to the fact that the core flow rate was too each, similar to the cell diameter (~10 µm). Since it is not
high for the whole system, which squeezed the sheath difficult to prepare cell-loaded hollow microfibers using
and sample flows, pushing them closer to the wall of the hollow microfiber preparation method mentioned
the microchannel. This leads to thinner liquid flows, above, we loaded HUVECs into the CaA/GelMA hollow
causing the deformation of the hollow microfibers and composite microfibers to explore the feasibility of using
the formation of incomplete lumen. A core flow rate them as cell scaffolds to achieve microvascularization. The
of 20 μL/min was chosen for subsequent experiments HUVECs were stained with Cell Tracker Green CMFDA
to ensure the stable formation of hollow composite for microfluidic spinning. The resulting hollow microfibers
microfibers and the integrity of the lumen. Under these are shown in Figure 4A. After HUVECs-loaded hollow
optimized conditions, the flow was stable throughout microfiber was incubated in the culture medium for 7
the continuous spinning process, and the prepared days, propidium iodide staining was performed to assess
hollow microfibers had a distinct and complete lumen cell viability. The cell viability rate of HUVECs-loaded
structure, thereby confirming the controllability and hollow microfiber, measuring approximately 90%, was
stability of the microfluidic spinning strategy used in significantly higher than that of the HUVEC-loaded
these experiments. CaA microfibers (Figure 4A). This was because the

Volume 10 Issue 2 (2024) 271 doi: 10.36922/ijb.1797