MICROFLUIDIC FORMATION OF CELL-LADEN HYDROGEL MODULES FOR TISSUE ENGINEERING - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 186

FIGURE 8.1 (a) Schematic illustration of the formation monodisperse droplets using the T-
junction microchannel and images of droplet formation at the T-junction taken by a high-speed
video camera. (b) Size distribution of the alginate gel beads produced by the T-junction device.
The alginate gel beads show monodispersity (CV ¼ 2.8%). 13 (c) Monodisperse alginate gel
beads encapsulating Jurkat cells. The beads are also of a narrow size distribution. 13 (d)
Schematic view of the 2D flow-focusing device and images of droplet formation in a flow-
focusing device. In the 2D flow-focusing device, the droplets produced come into contact with
the top and bottom of the channel walls. Therefore, the wetting problem occurs. (e) Schematic
diagram of an AFFD used to produce monodisperse droplets. AFFDs can prevent droplets
from adhering to the surface of the channels because the droplets are always surrounded by the
outer fluid. 18 (f) Plot of the sizes of the alginate gel beads in the oil versus the flow rate ratio
(outer flow rate/inner flow rate). CVs of every point are less than 5%, indicating all beads
produced by the AFFD are monodisperse. 18 (g) Image of alginate gel beads in oil correspond-
ing to (g) in figure (f). 18 (h-i) Formation of monodisperse agarose gel beads. The graph and
images are in the same sequence as the alginate gel beads. 18 (e-i) Copyright (2009) Springer.
droplets are formed at the orifice or the downstream channel (Fig. 8.1e). The inner
fluid and the produced droplets are always surrounded by an outer fluid, allowing the
monodisperse droplets not to contact the channel walls, thus eliminating the wetting
problem. The AFFD can control the size of droplets by adjusting flow rates and the
orifice dimensions because droplet formation in an AFFD is controlled by the
Plateau-Rayleigh instability (Fig. 8.1f-i). 17 Moreover, similar to 2D microfluidic
devices, an AFFD can produce sol droplets with high uniformity and high through-
put. After gelation of these monodisperse sol droplets produced by the microfluidic
devices, monodisperse hydrogel microbeads are obtained.
Alternatively, monodisperse hydrogel microbeads are obtained using microjet-
ting. 21 Using an inkjet printing technology, monodisperse sol droplets are produced
in air, and the droplets are gelated to hydrogel microbeads by submerging them in an
initiator of gelation. Also, the inkjet printing technology can organize hydrogel