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Feng F, et al.
3.3 Rotating Microfluidic Printhead bioengineering research, such as controlling of cell

As shown in Figure 6A, multicomponent filaments with distribution and study of the interaction among different
types of cells.
half-green and half-yellow color can be obtained along
the printing direction using microfluidic printhead. 3.4 Printing of Multicellular Constructs Using
However, when the printing direction was changed Coaxial Microfluidic Printheads
with 90° to print the next layer of the grid structure, the
filaments changed from the left-right multicolor into the To cross-link the printed hydrogel filament during the
top-bottom multicolor. To address this issue, a rotating printing process, a coaxial microfluidic printhead was
motor was introduced to this printing system, which designed and added into the printing system, as shown in
enabled the printhead to rotate with the designed angles Figure 7A and B. The inner and outer channels were used
during the printing process for creating heterogeneous to deliver the hydrogel ink solution and cross-linking
filaments along different directions. Figure 6B shows solution independently. The gelation of the inks took
a grid structure consisting of the filaments with place at the tip of the inner nozzle, where these two kinds
left-right multicolor along the different directions, of solution met. Here, alginate hydrogel solution was
which is achieved by rotating printhead with 90° as printed, which underwent instantaneous gelation when
designed during the printing process. Furthermore, exposed to calcium ions solution. Figure 7C shows the
a triangular pattern with heterogeneous filaments 25-layer heterogeneous hydrogel constructs successfully
along three directions and a grid structure coded with printed by coaxial printhead.
three compositions within the filaments was printed To improve efficiency of printing multicomponent
through rotating printhead (Figure 6C and D). It could concentric ring, a rotary substrate was introduced here
provide a way to create a heterogeneous constructs for (Figure 7D). During the printing process, the printhead

A B

C D

Figure 6. Printing of multicomponent grid structure using rotating microfluidic printhead. (A) Schematic and photograph illustrating printed
grid structure without the rotating printhead. (B) Schematic and photograph illustrating printed grid structure with the rotating printhead.
(C) Printed triangular pattern with the rotating printhead. (D) Grid structure consists of heterogeneous filaments (red, blue, and purple).

International Journal of Bioprinting (2019)–Volume 5, Issue 2 45