Magnetic actuation principles using superparamagnetic beads suspended in a fluid are studied in this paper. An experimental setup containing a submicroliter fluid volume surrounded by four miniaturized electromagnets was designed and fabricated. On the basis of optical velocity measurements, the induced behavior of single beads and ordered chains was analyzed and compared to a theoretical model. This research can be used to develop new techniques for accelerated transportation in lab-on-a-chip bio-assays.

The forced motion of superparamagnetic particles and their multibody interactions are studied in view of the application as integrated fluid drivers in microchannel systems. Previous studies on particle manipulation in open fluid volumes serve as our starting point for the analysis of particle dynamics and interplay effects in confined fluid volumes. An experimental setup is designed that offers a constant force field on all individual particles dispersed in a microchannel. Distinguishable multi-particle configurations are observed and analyzed on the basis of magnetic and hydrodynamic particle interaction mechanisms. The fluid driving performance and the efficiency of the particles are evaluated on system level by means of numerical simulation models.

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.