3.1 Flow characterization of the MO–MPS
The flow rate in the organ parts increased with increasing rotation
speed of the stirrer-based micropump (Fig. 2A). The flow ratio was
stabilized, and physiological blood flow ratio of 3.3 was achieved at
more than 1,900 rpm (Fig. 2B).
The increase in flow rate is due to an increase in the amount of liquid
pushed out in the similar direction as the flow as caused by increasing
rotational speed of the stirrer-based micropump. The physiological flow
ratio could not be replicated when the stirrer-based micropump
rotational speed was less than 1,600 rpm, and the dispersion of the flow
ratio was slightly large when the speed was less than 1,900 rpm. These
results suggest that the flow in the MO–MPS would be stable when the
rotational speed of the stirrer-based micropump is above 1,900 rpm. A
previous study reported that the flow is unsteady when the stirrer-based
micropump rotational speed is below 500 rpm, whereas the flow rate
increases linearly when the rotation speed is at least 500 rpm.(Kimura
et al., (2008)) Our obtained flow rate was lower, whereas the rotational
speeds we needed to stabilize the flow rate were higher than those of
previous study. The flow from the stirrer-based micropump depends on the
flow resistance of a microchannel. The channel’s resistance was higher
than that of the previous device; therefore, the amount of the liquid
pushed out by stirrer was smaller. The range of flow rate is limited by
the channel resistance, although the stirrer-based micropump is suitable
for evaluating organ–organ interactions because the culture medium
volume can be reduced, and continuous stable perfusion is possible.
Therefore, the rotational speed of the stirrer-based micropump was set
at 2,800 rpm in consideration of the flow ratio and flow stability in
our experiments.