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.