Magnetic microrollers as a platform for active transport

Transport and mixing at the microscale are difficult due to the absence of inertia and strong wall friction in confined systems, and a wide range of solutions have been proposed to address this challenge. Many existing techniques for micro fluidic transport focus on leveraging the dominance of boundary effects over bulk effects, for instance using capillary or electro-osmotic flows. Pressure driven flows use mechanical pressure gradients along a channel to generate a parabolic channel flow. However, the magnitude of this flow is strongly channel size-dependant, limiting applications in micro fluidic systems. Electro-osmotic flows over a key advantage: they are not limited by wall friction and they can be controlled locally with patterned surfaces of electrodes. However, they lack exibility due to the requirement of a fabricated channel, and their high electric �fields can cause damage when transporting living organisms. Furthermore, they are compatible with a limited class of fluids, and are extremely sensitive to surface conditions. Another approach to cargo transport uses bio-inspired microrobots, mimicking the behavior of microorganisms or cilia. Many of the microrobots designed for cargo transportation use ingenious but complex strategies to achieve the non-reciprocal actuation needed to self-propel at low Reynolds number. However, confinement dramatically hinders their motion due to wall friction. Other kinds of active matter systems, such as chemically or thermally driven colloids, are a simpler tool for creating compact structures, and have recently been shown to useful for cargo transport applications. These active systems allow for rapid structure formation, and can be externally driven, for example using light fi�elds. However, many, if not all, of these systems consume chemical fuel, making them undesirable for applications where biological compatibility is required. We propose a new way to achieve active transport, which will be ideal in situations where recon�figurability and suitability for a variety of environments are the main design concerns. We will focus on the development of an active transport system which uses the strong advective flows generated by rotating microrollers. Our approach takes advantage of the boundaries that are always present in real-world cofined geometries.