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Coaxial nozzle-assisted electrohydrodynamic printing for microscale 3D cell-laden constructs

(A) (B) (C) after the first three layers were completed. However,
it was found that the electrohydrodynamic printing
process became unstable with discontinuous alginate
filaments when the stage moving speed was 30 mm/
s (Supplementary Movie 1). Continuous alginate
(D) (E) (F) filaments can be achieved when the stage moving speed
decreased to 15 mm/s (Supplementary Movie 2). This
was mainly caused by the flow of CaCl solution during
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the electrohydrodynamic printing process. Therefore, a
lower stage moving speed of 15 mm/s was used to print
(G) the 3D constructs.
The effect of CaCl feeding rate on the elec tro hy dro-
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dy nam ic printing of 3D constructs was investigated.
Figure 4A shows the microscopic images of the printed
constructs with a layer number of 13 when CaCl
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feeding rate is zero. It was obviously observed that the
printed alginate solution was not instantly crosslinked at
the top layer due to diffusion-based limitation of calcium
ions and was prone to form aggregates at the crossed
sites. When CaCl feeding rate increased from 100 μL/
2
h to 300 μL/h, more layers of alginate filaments could be
electrohydrodynamically printed as shown in Figure 4B–
Figure 2. Effect of high voltage on width of elec tro hy dro dy- D. The printing layer number was mainly determined
nam ically printed filament. (A–C) Morphology of the extruded
filaments as the core nozzle diameter changed from 160 μm to 410 by CaCl feeding rate. Figure 4E shows the relationship
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μm. (D–E) Morphology of the electrohydrodynamically printed between the maximum printing layer and CaCl feeding
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filaments with the voltage of 4.5 kV as the core nozzle diameter rate. Alginate hydrogel constructs with the maximum
changed from 160 μm to 410 μm. (G) Quantification of the width
of the printed filament. printing layer number of 73 can be fabricated when
CaCl feeding rate was fixed at 300 μL/h. In addition,
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stage moving speed changed from 10 mm/s to 30 mm/ calcium chloride solution could fill in the pore of the 3D
s in Figure 3B. When the moving speed was over 30 constructs as the layer number increased. Therefore, the
mm/s, the printing filaments became discontinuous. The printed cell-laden filaments were always immersed into
smallest filament (<100 μm) was achieved when the the liquid environment during the electrohydrodynamic
feeding rate of alginate and stage moving speed were printing process, which might reduce the side effect of
fixed at 400 μL/h and 30 mm/s, respectively. water evaporation on the cell viability.
To test the feasibility of using coaxial nozzle- 3D alginate hydrogel constructs with different layer
assisted electrohydrodynamic printing to fabricate number were electrohydrodynamically printed when
3D hydrogel constructs, multilayer structures were alginate feeding rate, stage moving speed and CaCl
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further printed with CaCl feeding rate of 300 μL/h feeding rate were fixed at 400 μL/h, 15 mm/s and 300
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(A) (B)

Figure 3. Effect of process parameters on the width of the electrohydrodynamically printed filaments. (A) Quantification of filament width
as alginate feeding rate changed from 200 μL/h to 1000 μL/h. (B) Quantification of filament width as stage moving speed changed from
15 mm/s to 35 mm/s.

4 International Journal of Bioprinting (2018)–Volume 4, Issue 1