Polymer coated superparamagnetic beads walking on polymer coated surface

Abstract

Biology has provided us with many organisms that are able to propel themselves through a fluid using cilia or flagella. This provides inspiration to create controllable systems that cannot only propel an organism or device through a fluid but can also create a fluid flow. Research has focused on how to mimic the mechanisms of these organisms for the use in microfluidic devices or drug delivery. This work examines walkers that are created using superparamagnetic beads placed in a rotating external magnetic field. Dipoles align in the beads so they assemble into rotors. These rotors follow the rotating magnetic field and are able to translate across a surface. This work looks at the effect of coating the beads and the surface with a polymer, Polyethylene Glycol(PEG). PEG has been shown to undergo a transition from an expanded state to a collapsed state under certain salt concentrations and temperature ranges. By looking at this transition we can see if the use of a polymer could affect the velocity of the rotors and if PEG could be used to control the velocity of the rotors or to initiate a transition. This transition is only seen by recording the velocity of the rotors, future research using other experimental procedures might be helpful in finalizing the transition of PEG in NaCl. It was unclear from these experiments whether the velocity of the rotors is dependent on the state of the polymer.