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International Journal of Bioprinting Droplets prepared by air-focused bioprinting

Air-focused microfluidic 3D droplet printing system liquid flow rate, and polymer concentration, as shown in
was developed by mounting the microfluidic device on the Figure 1d–f, respectively. The droplet diameter decreased
printer head of a modified extrusion-based 3D printer. The as the air flow rate and thus the viscous force increased,
inner channel of the microfluidic device was connected as shown in Figure 1g. In contrast, the droplet diameter
to a syringe pump controlled by the 3D printer, while the increased with the liquid flow rate, since more liquid could
outer channel was connected to an air pump with a glass enter the flow tip before it broke up into droplets, as shown
rotameter. To print a pattern consisting of droplets, a pre- in Figure 1h. When the polymer concentration, e.g., PEG
designed picture was first sliced into a droplet pattern or alginate, increased, the droplet diameter decreased, as
using a slicing software, as shown in Figure 1b, and then shown in Figure 1i and j.
discrete droplets were printed at each specific site by the To systematically investigate the performances of
AFMDP system, which precisely controlled the position microfluidic devices, three different structures were
of the printer head and the infusion of the liquid via designed and tested, including inward contraction, parallel
programmable codes, as shown in Figure 1c.
alignment, and outward extension of the inner capillary
Under a constant air flow, uniform droplets with a with respect to the outer capillary, as shown in Figure 2a–c,
small size distribution could be printed in the dripping respectively. For all three different structures, monodisperse
regime, and their size could be tuned by air flow rate, droplets could be achieved, and the experimental results

Figure 2. Influence of microfluidic device structure on printed droplet. Schematics showing microfluidic device structures with (a) inward contraction,
(b) parallel alignment, and (c) outward extension of the inner capillary with respect to the outer capillary and optical images of droplets prepared by these
microfluidic devices under different air flow rates. The inner capillary diameter was kept constant at 150 μm, while the outer capillary diameter was kept
constant at 600 μm. Cross denoted no uniform droplet formation. (d) Dependence of droplet diameter on air flow rate when prepared by using different
microfluidic devices. (e) Dependence of droplet diameter on air flow rate when prepared by using inner capillaries of different diameters. The outer
capillary diameter was kept constant at 600 μm. If not specified, the microfluidic device structure is inward contraction, and the inner capillary diameter
was 150 μm.

Volume 10 Issue 1 (2024) 400 https://doi.org/10.36922/ijb.1102