Self-organized twinning of actuated particles for microfluidic pumping

Abstract

The motion of monodisperse particle ensembles in fluidic channels actuated by axial magnetic or gravitation forces is studied. Interactions between particles, fluid, and nearby walls induce unforeseen self-organization phenomena. Superparamagnetic microparticles aligned on a channel axis successively organize toward a stable polytwin system under constant force conditions. In the absence of repelling particle interactions, full contact twinning is observed for particles driven by gravity. The mechanisms of successive twinning and spacing regulation are explained by a one-dimensional model based on the axis flow profile. Related performance enhancements for particle based microfluidic pumping are discussed.

Multibody interactions of actuated magnetic particles used as fluid drivers in microchannels

“…In this axially aligned configuration, the dipolar magnetic interactions resulted in small repelling forces between the particles. Successively, the particles self organized in a spread polytwin configuration (Derks et al 2008). Panel (b) shows an ensemble of particles that experience a magnetic field of 25 mT (y = 2 mm, halfway the channel).…”

“…3a. At the top of the channel (y = 0 mm, B = 10 mT), the channel walls induce a focusing effect on the particles that leads to a poly-twin configuration (Derks et al 2008) (a). With a higher field amplitude and lower field gradient halfway the channel (y = 2 mm, B = 25 mT), particles reorganize in less ordered configurations (b).…”

“…A first order approximation of the hydrodynamic interaction forces between identical magnetic particles can be estimated with (Derks et al 2008)…”

“…The particle-to-particle interactions are not considered in detail, although these affect the dynamics of the particles and the particle loaded fluid. Especially the hydrodynamic momentum transfer from a particle to the fluid (and from there back to neighboring particles) is often neglected, but can be dominant over magnetic particle interactions (Derks et al 2008;. To understand the influence of local magnetic and hydrodynamic particle interactions, we first summarize particle dynamics effects in open fluid volumes.…”

Analysis of individual magnetic particle motion near a chip surface

“…In early applications, large ensembles of magnetic particles were used, for example, to extract biomaterial or as contrast agents in magnetic resonance imaging. 1 Presently, there is a trend to use magnetic particles in more refined ways, such as applying them as a means of transport in lab-on-a-chip devices, [2][3][4] as detection labels for target molecules, [5][6][7] or even as tools for functional biosensing in cell property research or binding force measurements. 8,9 To improve the functioning of magnetic particles in magnetic particle-based biosensors or lab-on-a-chip devices, we have investigated several techniques to quantify the magnetic properties of individual magnetic particles.…”