Magnetic actuation and deformation of a soft shuttle.

Here, we describe the magnetic actuation of soft shuttles for open-top microfluidic applications. The system is comprised of two immiscible liquids, including glycerol as the soft shuttle and a suspension of iron powder in sucrose solution as the magnetic drop. Permanent magnets assembled on 3D printed motorized actuators were used for the actuation of the magnetic drop, enabling the glycerol shuttle to be propelled along customized linear, circular, and sinusoidal paths. The dynamics of the hybrid shuttle-magnetic drop system was governed by the magnetic force, the friction at the interface of the shuttle and the substrate, and the surface tension at the interface of the shuttle and the magnetic drop. Increasing the magnetic force leads to the localized deformation of the shuttle and eventually the full extraction of the magnetic drop. The versatility of the system was demonstrated through the propelling of the shuttle across a rough surface patterned with microfabricated barriers as well as taking advantage of the optical properties of the shuttle for the magnification and translation of microscale characters patterned on a planar surface. The integration of the system with current electrowetting actuation mechanisms enables the highly controlled motion of the magnetic drop on the surface of a moving shuttle. The simplicity, versatility, and controllability of the system provide opportunities for various fluid manipulation, sample preparation, and analysis for a range of chemical, biochemical, and biological applications.

Droplet on Soft Shuttle: Electrowetting-on-Dielectric Actuation of Small Droplets.

Here, we introduce the novel concept of a "soft shuttle" for transportation, manipulation, and diffusion studies of small liquid droplets using electrowetting on the dielectric mechanism. This method enables manipulation of droplets several times smaller than the electrode size and, importantly, minimizes evaporation, contamination, and exposure of the sample to high voltages. We demonstrate various modes of droplet loading, transporting, and unloading. Using advanced imaging processing techniques, we obtained detailed information about the shuttle and droplet centroids. Furthermore, varying water concentration on the soft shuttle allows for modulation of the diffusion kinetics of samples into the shuttle, which also can be controlled with soft shuttle actuation velocity. We believe that this novel approach for the manipulation of droplets will advance the field of droplet-based open microfluidics and can be potentially useful for applications in biotechnology, diagnostics, or analytical chemistry.