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Mao, et al.
petri dish filled with 2% (w/v) agarose hydrogel was be further printed by precisely stacking the core-sheath
placed on the grounded stage as the collecting substrate filaments in a layer-by-layer manner.
to avoid the high electric current during the EHD printing We then studied the effect of process parameters
process. The alginate and collagen/CaCl solution were (feeding rate of alginate and collagen, moving speed of the
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respectively controlled by two high-precision syringe printing stage) on the size of core and sheath within EHD
pumps and loaded into the outer layer and inner layer of printed filaments. Alginate solution and collagen/CaCl2/
the coaxial nozzle. When the high voltage was applied, green fluorescent particles solution were loaded into the
alginate solution and collagen/CaCl solution would be outer and inner layers of the coaxial nozzle, respectively.
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pulled out of the coaxial nozzle simultaneously and the The size of the core line was characterized as the width
alginate solution would be instantly cross-linked by the of the bands with green fluorescent particles through the
calcium ions, resulting in core-sheath filaments deposited fluorescent images, while the size of the sheath line, defined
onto the collecting substrate under the control of the as the external width of the filament, was measured in the
user-specific design. Multiple layers of constructs could same region through the bright-field images. Figure 2A-E

Figure 1. Schematic of EHD bioprinting strategy of core-sheath hydrogel filaments for generating cell-laden constructs.

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C D H I M N

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Figure 2. The effect of process parameters on the width of the EHD-bioprinted filaments. (A-E) The morphology and width of the core and
sheath lines in the filaments as alginate feeding rate changed from 1500 μL/h to 3000 μL/h. (D-G) The morphology and width of the core
and sheath lines in the filaments as collagen solution changed from 400 μL/h to 700 μL/h. (K-O) The morphology and width of the core and
sheath lines in the filaments as moving speed changed from 2 mm/s to 8 mm/s.
International Journal of Bioprinting (2021)–Volume 7, Issue 3 89