Figure 4. UCA channel test results, (A) Experimental and simulation results of particle movement due to the strike magnetic field, (B) Experimental and simulation result of particle movement due to the rotating magnetic field, (C) Cumulative number of particles that reached the outlet when the strike magnetic field was applied, and (D) Cumulative number of particles that reached the outlet when the rotating magnetic field was applied
A unilateral cilia array (UCA) channel was constructed and two types of magnetic fields (strike and rotating magnetic fields) were applied. We performed an experiment to confirm the difference in the fluid flow and a simulation to verify the experimental results (Figure. 4 and Movie S2 ). When the strike magnetic field was applied to the UCA channel, the experimental results showed that the fluid flow, including particles, advanced very slowly, reaching approximately 15.75 mm in 80 s. Similar results were also confirmed through the simulation, such that the particles in the fluid moved forward slightly away from the UCA (Figure. 4A). In addition, it was confirmed through the graph showing the cumulative number of particles that the particles reached the channel outlet as time passed (Figure. 4C). When a rotating magnetic field was applied to the UCA channel, the experimental results confirmed that the fluid flow, including particles, moved forward following the tip of the UCA and reached the end of the channel by moving 18 mm in 80 s. The simulation results showed a similar tendency, in that the particles in the fluid moved rapidly along the tip of the UCA (Figure. 4B). In addition, all the particles reached the channel outlet after approximately 100 s (Figure. 4D).
Consequently, it was confirmed that the fluid flow containing particles moved forward in two types of magnetic fields in the UCA channel. When a rotating magnetic field was applied, the fluid moved faster than when a magnetic field was applied, and the particle movement pattern differed depending on the applied magnetic field. This is expected to be closely related to the distinct MCW that appeared when the rotating magnetic field was applied to the RMS cilia array shown in the fundamental motions.
2.4. Fluid Tests using Bilateral Cilia Array Channels
We constructed a Bilateral Cilia Array (BCA) channel by attaching two RMS cilia arrays to the top and bottom sides of the channel, based on the cilia array distributed within a narrow tube in the human body (e.g., a fallopian tube). The BCA channel was composed of symmetric and asymmetric structures (Figure. 5A ), and the optimal combinations for pumping and mixing, which are important functions of the cilia, were determined by applying strike and rotating magnetic fields via the EMA system and verifying through simulation.
To optimize each magnetic field, the tendency of fluid flow according to the frequency was observed. When the strike magnetic field is applied in both channels, the particle velocity increased with increasing frequency, peaking at 3 Hz and decreasing from 4 Hz (Figure. 5B). Furthermore, it was confirmed that particles were transmitted the fastest at 3 Hz through the coefficient of variation (CV), which quantifies the distribution of particles (Figure. S2A, B ). When the rotating magnetic field was applied, the particle velocity increased as the frequency increased in both channels, continuously increasing up to 8 Hz and decreasing from 9 Hz (Figure. 5B). The CV values exhibited the same trend (Figure. S2C, D). In other words, the particles were most well dispersed at 8 Hz, and thus, the color intensity became uniform. Therefore, it was found that the performance was the best at 3 Hz for the strike magnetic field and 8 Hz for the rotating magnetic field.