Microparticle Manipulation Performed on a Swirl-Based Microfluidic Chip Featured by Dual-Stagnation Points.

Stagnation-based microfluidics technology is promising for microparticle control due to its noncontact and low cost. However, the current research is still hindered by insufficient pose regulating ability and soft control. Based on our previous work on controlling single particles by generating a swirling flow region (SFR) with a stagnation point in the designed flow field, a new 3-microchannel structure is herein proposed for simultaneous control of two microparticles. It is addressed as the dual-stagnation model because there are two SFRs generated for particle capturing and manipulation. Simulation study is conducted to optimize the fluid field structure and explore the regulation of the two SFRs by adjusting velocities of microchannel inlets. Experiments are carried out on a 3D-printed microfluidic chip to validate the feasibility of the dual-stagnation model and the predicting capacity of the simulations. It is demonstrated that two SFRs with stagnation points are successfully formed in specific locations, indicating that two microparticles can be concurrently captured and controlled. Significantly, the results of simulation and experimental studies agree well with each other referring to flow streamlines and stagnation point regulation. During experiments, it is confirmed that microparticles with different shapes and varied sizes can be captured. Besides, the deviation between the positions of microparticles and the generated stagnation points is characterized to reveal the trapping stability of this microfluidic chip. This work contributes to an advanced flow field structure for swirl-based microfluidic chips and provides insights into soft contact and flexible manipulation of multiple microparticles for revealing the interaction between two bio-/chemical microparticles.