Fast and Fine Manipulation of RBCs in Artificial Capillary and Their Mysterious Behaviors

While the fluid flow in microfluidic channel is usually laminar and the flow pattern has been well understood, the cell behavior in microfluidic channel often shows unexplainable behavior under the coupling effect between cell and the boundary condition, such as under the contact of the wall of artificial capillary. We first introduce the Beyond Human Heart that can achieve fast and fine cell manipulation with the frequency of more 100 Hz and the resolution of 250 nm by using both a high-speed pump and an online high-speed vision. The Beyond Human Heart is the combination of macro actuator and the micro channel, for achieving the quick action. On the other hand, the cross-sectional area of the actuator is one million larger than that of microfluidic channel, which makes the system result in velocity increasing mechanism unless there is any alternative velocity decreasing mechanism in the system. By considering the elasticity in the PDMS microfluidic chip, we succeed in implementing the virtual reduction mechanism into the artificial capillary. This mechanism greatly contributes to achieving a fine manipulation of red blood cells (RBCs) as well. By using the developed system, we execute various tests on deformability of RBC, through which we found two interesting behaviors of RBCs in artificial capillary. One is “Cell Pinball” where a RBC moves with the velocity component perpendicular to the main flow and behaves as if it were an elastic ball. The other is the dramatic change of recovery behavior after loading. While these behaviors are interesting enough, there exist a couple of behaviors where we still cannot explain. We believe that raising such issues is also our important role, particularly for researchers working in biology.