Magnetic filaments

Magnetic filaments, when exposed to external field, show various shape deformations, types of motion, etc., which depend on the elastic and magnetic properties. These structures resemble cilia and flagella in biological systems and additionally can be controlled with the external magnetic field, allowing interesting manipulations.

Schematic representation of the filament formation.

We are interested in the modes of the filament movement, formation of microscopic swimmers in particular, as well as their properties. Experimentally we create these filaments from magnetic particles that are functionalized with streptavidin and are further cross-linked with biotinylated DNA fragments. Changing the concentrations, magnetic field strength and the length of DNA strands allows us to control the total length and elasticity of filaments. Filaments are then observed in our coil setup under the microscope. Additionally, the processes of interest are described theoretically and compared with experiment, using numerical simulations.

The simulation capability we have developed is quite extensive, enabling us to not only compare the dynamics of ferromagnetic and superparamagnetic filaments with experimental results, but also to explore the motion of novel prospective microswimmer configurations taking into account the effects of hydrodynamic interactions. Consequently, we have described a prospective microswimmer consisting of an elastic (non-magnetic) tail attached to a magnetic dipole, which appears to exhibit considerably higher velocities compared to previously known magnetic microswimmers. Furthermore, the comprehensive treatment of hydrodynamic interactions enables us to model the dynamics of filament ensembles as well.

A flexible filament of superparamagnetic beads becomes a magnetic swimmer

A filament of ferromagnetic particles and a polystyrene bead becomes a magnetic swimmer

Magnetic filament relaxation

Loop formed by a ferromagnetic filament in a constant field

Velocity field induced by the motion of two hydrodynamically interacting ferromagnetic filaments

Magnetic dipole with an elastic tail (2D projection in the plane of motion)

Motion of a magnetic dipole with an elastic tail in an AC magnetic field

• R.Livanovičs, A. Cēbers (2012). Magnetic dipole with a flexible tail as a self-propelling microdevice. Phys. Rev. E 85, 041502. link
• K. Ērglis, R. Livanovičs, A. Cēbers (2011). Three dimensional dynamics of ferromagnetic swimmer. Journal of Magnetism and Magnetic Materials, 323(10), 1278–1282. link
• A. Cēbers, R. Livanovičs (2011). Flexible ferromagnetic filaments as artificial cilia. International Journal of Modern Physics B 25, 935. link
• A. Cēbers, H. Kalis (2011). Dynamics of superparamagnetic filaments with finite magnetic relaxation time. The European Physical Journal E, 34(3), 1–5. link
• R. Livanovičs, K. Ērglis, A. Cēbers (2010). Three dimensional instability of the flexible ferromagnetic filament loop. Magnetohydrodynamics, 46(3), 245–256. link
• K. Ērglis, M. Belovs, A. Cēbers (2009). Flexible ferromagnetic filaments and the interface with biology. Journal of Magnetism and Magnetic Materials, 321(7), 650–654. link
• K. Ērglis, D. Zhulenkovs, A. Sharipo, A. Cēbers (2008). Elastic properties of DNA linked flexible magnetic filaments. Journal of Physics: Condensed matter 20(20), 204107. link