Figure
7 Cell viability and morphology in liver-on-a-chip. (A) Schematic of
cell encapsulation and seeding. (B-D) Representative images showing
living cells (green: Calcein AM) and dead cells (red: PI) at Day 4.
Scale bar=200 µm. (E) Cell viability at Day 0 to Day 4. (F) Comparison
of burst pressure of the chips made by layer-by-layer adhesion and
sacrificial template. (G) Maximum shear stress that the chips were able
to endure.
In previous study, poly-L-lysine has been used as an electrostatic glue
to seal the hydrogel-based chips 32. However, this
method provided weak adhesion with fluid leakage occurring at applied
pressures higher than 3 kPa, providing an extremely low shear stress of
approximately 0.1 dyne/cm2. To compare the perfusion
tolerance of chips constructed by different methods, liver-on-a-chip
with the same channel morphology was constructed by Gel-MA hydrogel and
alginate sacrificial template. As shown in Figure 7F, the chip made by
layer-by-layer adhesion showed the high burst pressure of
>40 kPa during the culture, due to the strong support
provided by the tough F127-DA layer 33. In contrast,
the Gel-MA chip made by sacrificial template was brittle and weak, and
was easily broken by an extremely low pressure of 3 kPa. Consistently,
the assembled chip shown in Figure 7A was able to withstand flow-induced
shear stress of >45 dyne/cm2, which is in
the range of physiological values of 1-50 dyne/cm2 in
human blood vessels 34. However, the Gel-MA chip made
by sacrificial template could only tolerate a very low shear stress of
0.1-0.2 dyne/cm2, thus limiting its applications in
perfusing culture. As the accurate mimicking of mechanical
microenvironments is essential in construction of organs-on-chips35, layer-by-layer adhesion performs better than the
use of sacrificial templates.