(I-343) A Microfluidic Tweezer for Simultaneous Confinement of a Pair of Cells and Particles

Introduction:: Recent advancements in science and engineering have allowed for trapping and manipulation of individual particles and macromolecules within an aqueous medium using a flow-based confinement method. In this work, we demonstrate the feasibility of trapping and manipulating two particles using coupled planar extensional flows¹. Using Brownian dynamics simulations and a proportional feedback control algorithm, we show that two micro/nanoscale particles can be simultaneously confined and manipulated at the stagnation points of a pair of interconnected planar extensional flows.

Materials and Methods:: Our simulations are based on the Langevin equation with the extensional flow term solved using Brownian dynamics². The combined advective and diffusive motion of the particles are calculated using Brownian dynamics. We specifically studied the effect of strain rate, particle size, and feedback control parameters on particle confinement. The time step/interval for the simulation is taken as 1 ms, which is typical for trapping micro/nanoscale particles using fluid flow. We also assumed that the channel width is W=100 µm and the distance between the center points of the two junctions is three times the channel width, Z=300 µm. In addition, we set the feedback control parameters to K_p= -1.5 and Td= 150 ms, except specified otherwise. We ran each simulation for a minimum of 2²⁰ time intervals which was determined by considering the number of intervals needed to yield nearly ideal Gaussian particle position histograms, and consistent values for mean particle position and particle displacement (standard deviation) from the trap center.

Results, Conclusions, and Discussions:: We found out that particle confinement improved with larger particle size, higher strain rate and tighter/faster feedback control parameters. Particle displacement from the trap center was within 0.2-14.08µm for particle sizes, strain rates, proportional gain constants, control delays ranging between 10-10,000 nm, ε₁=0.52-10.5 s^-1 and ε₂=0.02-5 s^-1, -2< K_p< -1.1, 2ms< T_d< 500 ms, respectively. Due to flow coupling between the two traps, modifying the parameters listed above in the “upstream” trap (in Junction 2) impacts particle confinement in the “downstream” trap (in Junction 1), but not vice versa. We also demonstrated that the microfluidic tweezer allows for precise control of the distance between the two trapped particles through: i) modulation of the strain rates in either junction, ii) the manipulation of the particle position along the outlets in the “upstream” junction (Junction 2).

We described a microfluidic tweezer capable of simultaneous and precise confinement of two micro/nanoscale particles using coupled stagnation point flows. Current flow-based particle trapping and manipulation methods executed in a single microfluidic junction rely on sophisticated control algorithms and generate highly complex flow fields. Further, scaling up is not trivial; increasing the number of particles makes the design and implementation gradually arduous. Contrarily, this microfluidic tweezer uses a simple linear feedback control algorithm and generates well-defined, planar extensional flow fields around confined particles. Its linear design allows for easy extension to multi-particle trapping by adding junctions to the design. We anticipate that our microfluidic tweezer will help stimulate the development of novel applications in studying real-time interaction of a pair or an array of biomolecules, vesicles, or cells.



Acknowledgements (Optional): :

References (Optional): : [1] Boyd et al., under review (2023). [2] Tanyeri et al., Nano Letters (2013) 13 (6), 2357.