Propulsion of microspheres in fluids using rotating magnetic fields

Abstract

Magnetic microspheres dispersed in fluids can be moved using static field gradients or by applying oscillating or rotating magnetic fields. Such separation methods are useful for many applications within biotechnology and medical technology as a tool to separate or extract cells or molecules. Efficient magnetic separation using field gradients usually requires having a strength of the source of the field of order B = 1 T. However, by applying alternating, or rotating, weak magnetic fields with field strength of order B = 1 mT, micron sized composite magnetic beads can be controlled and separated. This will happen since the beads are normally much heavier than the surrounding fluid. As the beads due to gravity approach the bottom surface of the sample cell, they may be propelled in a rolling/slipping motion due to a torque from the rotating magnetic field.

A Magnetically and Electrically Powered Hybrid Micromotor in Conductive Solutions: Synergistic Propulsion Effects and Label‐Free Cargo Transport and Sensing

“…[20] Micromotor actuation in biological samples by application of a magnetic field has become attractive because of its applicability to biological medium, [21] ability to move in the bulk without relying on its interaction with boundaries, [22] no requirement for fuel or direct contact between the external magnet and tissues, [23] steering accuracy, [24] and the ability to operate in a wide range of temperatures and solution conductivities (even in vivo [25] ). Magnetic microparticles actuated in fluids, using either an external uniform rotating magnetic field [26] or magnetic field gradients (i.e., magnetophoresis, [21] ) have enabled applications, such as biological cargo carriers, [16,27,28] probes in biophysical studies, [29] imaging-guided therapy, [23] and microinjections for drug delivery. [30,31] Spherical magnetic particles were shown to propel under rotating uniform magnetic field due to their rolling over surfaces.…”

“…[ 30,31 ] Spherical magnetic particles were shown to propel under rotating uniform magnetic field due to their rolling over surfaces. [ 26 ] A peanut shaped micromotor [ 32 ] has been shown to move in both rolling and wobbling modes to enable climbing over steep slopes, while a rotating spiral micromotor [ 33 ] has been shown to have the potential to for in‐vivo non‐invasive Zygote transfer, and a rolling and tumbling magnetic biohybrid micromotors for drug delivery in the small intestine of a mouse. [ 34 ] Magnetic field actuation of micromotors is commonly combined with an additional mode of actuation to form hybrid micromotors, as in the case of combined magnetic and electric fields to assemble mobile micromachines, [ 35 ] magnetic steering of catalytically driven micromotors within sea water [ 36 ] as well as targeted drug delivery using sperm cells with a magnetic cap.…”

Physics inspired by living matter: dynamics, topology and functionality

“…Active matter and driven matter generally exhibit self-assembled or self-organized dynamic structures. Examples of these phenomena are given in the papers by Rasmussen et al [1], Doostmohammadi and Yeomans [2], Horowitz et al [3] and Helgesen [4] in this issue.…”