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Multicomponent bioprinting based on microfluidic printheads
used a microfluidic device to fabricate multicomponent dissolving agarose and calcium chloride powders into
hydrogel constructs. It enabled different bioinks flow into distilled water at 100°C. After boiling, agarose solution
the microfluidic device and cross-link by ultraviolet . was poured in a Petri dish and cooled down to form a
[23]
Ghorbanian et al. developed a microfluidic direct writer flat agarose hydrogel with a thickness of 3 mm as the
who is capable of alternatively delivering two different collecting substrate. For cell printing, GFP expressing
alginate gel solutions during the fabrication three- human umbilical vein endothelial cells (GFP-HUVEC;
dimensional (3D) hydrogel constructs . Hardin et al. ATCC, Manassas, VA, USA) and red fluorescent protein
[24]
developed a microfluidic printhead for the printing of embryonic rat cardiomyocytes (H9C2, ATCC, Manassas,
multiple viscoelastic inks such as polydimethylsiloxane VA, USA) were added into 3% alginate solution with a
5
−1
(PDMS) and investigated the interface of two inks during density of 5 × 10 cells mL .
printing . However, the effect of laminar flow within the
[25]
printhead and proportion of flow rate are neglected, which 2.2 Design and Fabrication of Microfluidic
can change the morphology of the printed heterogeneous Printhead for Multicomponent Printing
filaments and further influence printing controllability. The microfluidic printhead was designed to have three
Here, we developed a multicomponent bioprinting inlets and an outlet as shown in Figure 1A. The width
system based on microfluidic printhead with three (w ) and height (h ) of the inlet channels are 200 µm.
1
1
inlets and one outlet, which enables simultaneous The width (w ) and the height (h ) of the outlet channel
2
2
multicomponent extrusion and printing of heterogeneous are 300 µm and 200 µm, respectively. The length of
constructs through only one printhead. During the different channels is l =5 mm and l =3 mm, respectively.
1
2
printing process, different inks were connected to To fabricate the microfluidic printhead, two PDMS
different inlets of the printhead and simultaneously components with semi-channels were created by casting
or alternatively extruded through the same outlet. We PDMS in the designed molds printed by stereolithography
mainly studied spatially controlled distribution of technique. During the cast process, the PDMS components
different inks when altering the proportion of volumetric were vacuum treated to remove any bubbles and cured
flow rate of different inlets in printing process. In at 65ºC for a minimum of 2 h. Then, they were bonded
this way, heterogeneous filaments and constructs can together after oxygen plasma treatment. Finally, the
be printed along which diverse materials could be capillary nozzle was inserted into the cylindrical channel
spatiotemporally coded. In addition, a rotating motor was (Figure S1, supporting information). The diameter (d )
1
added into printing system for printing heterogeneous and the length (l ) of the nozzle is 200 µm and 12 mm.
3
filament along different printing directions and a coaxial Figure 1B schematically illustrates components of the
printhead was developed to improve the cross-linking. microfluidic printhead and the fabricated microfluidic
It could be a possible way to create macro-microscopic printhead is shown in Figure 1C.
integrative multicomponent constructs mimicking native 2.3 Multicomponent Printing Platform Based on
tissues with multiple cells.
Microfluidic Printhead
2. Materials and Methods The microfluidic printhead was connected with a rotating
motor and then mounted on the z moving stage (Xiamen
2.1 Materials Heidelstar Co., China). Different alginate inks were
separately loaded into 1 mL syringes, respectively, and
Polydimethylsiloxane (PDMS, Sylgard 184) was obtained the flow rate was controlled by a syringe pump (TJ-
from Dow Corning (Midland, MI, USA). Alginate with 2A, Longer Pump, Baoding, China). Each syringe was
medium viscosity was purchased from Sigma Aldrich connected to different inlets of the printhead through
(St. Louis, MO, USA). Calcium chloride powder was PTEE soft tubes. Agarose hydrogel with calcium ions was
bought from Aladdin (Shanghai, China). Agarose powder placed on the x-y moving stage (Xiamen Heidelstar Co.,
with low melting temperature (87–89°C) was bought China) as the collecting substrate (Figure 1D and E). The
from Biowest (Spain). Green fluorescent particles with distance between the nozzle tip and the collecting substrate
a particle size of 10 µm and red fluorescent particles was fixed at 100 µm. During printing, different inks were
with particle size of 10 µm and 3.2 µm were purchased pushed into the separate inlets and then extruded out of
from Base Line (Tianjin, China). Red/green/blue/yellow the printhead through the same nozzle. The proportion
pigment was purchased from M and G (China). Alginate of different inks in printed filaments was adjusted by
solutions with different concentration of 1%, 2%, and 3% controlling the volumetric flow ratio when the total
(w/v) were prepared by dissolving alginate powder into volume flow rate of all inlets was fixed. A 3D structure
distilled water or culture medium. About 2% (w/v) agarose with different materials can be printed by precisely
solution with 2% (w/v) calcium chloride was prepared by stacking the filaments in a layer-by-layer manner.

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