Magnetorelaxometry in the Presence of a DC Bias Field of Ferromagnetic Nanoparticles Bearing a Viscoelastic Corona

Abstract

With allowance for orientational Brownian motion, the magnetorelaxometry (MRX) signal, i.e., the decay of magnetization generated by an ensemble of ferromagnet nanoparticles, each of which bears a macromolecular corona (a loose layer of polymer gel) is studied. The rheology of corona is modelled by the Jeffreys scheme. The latter, although comprising only three phenomenological parameters, enables one to describe a wide spectrum of viscoelastic media: from linearly viscous liquids to weakly-fluent gels. The “transverse” configuration of MRX is considered where the system is subjected to a DC (constant bias) field, whereas the probing field is applied perpendicularly to the bias one. The analysis shows that the rate of magnetization decay strongly depends on the state of corona and slows down with enhancement of the corona elasticity. In addition, for the case of “transverse” MRX, we consider the integral time, i.e., the characteristic that is applicable to relaxation processes with an arbitrary number of decay modes. Expressions for the dependence of the integral time on the corona elasticity parameter and temperature are derived.

Effects of Constant Magnetic Field to the Proliferation Rate of Human Fibroblasts Grown onto Different Substrates: Tissue Culture Polystyrene, Polyacrylamide Hydrogel and Ferrogels γ-Fe2O3 Magnetic Nanoparticles

“…According to finite-element computer modeling (Figure 3b), the distribution of magnetic field in the magnetic system had similar shape as in the experiment. Magnetic field strength was 550 and 660 Oe, root-mean-square deviation was 140 and 60 Oe, respectively for zone and zone (8)(9)(10)(11)(14)(15)(16)(17). The evaluation of the root-mean-square deviation of magnetic field strength in the model was higher than in the experiment.…”

“…The average magnetic field strength formed by 1-24 magnets is 380 Oe, root-mean-square deviation is 70 Oe. In the area formed by magnets (8)(9)(10)(11)(14)(15)(16)(17), the magnetic field strength increased to 430 Oe, root-mean-square deviation decreased to 30 Oe.…”

“…The advantage of the use of ferrogel-based scaffolds for cellular technologies is an ability to operate and control the cells adhesion, proliferation and differentiation by the application of constant external magnetic field. The fundamental principles of the effect of applied magnetic field of controlled strength on living cells are not yet fully understood [14][15][16]. At the same time, they certainly should be taken into account and analyzed as complex processes involving such parameters as external magnetic field strength, magnetic field gradient and superposition of magnetic susceptibility of cell contribution and nearby environment properties.…”

Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles

“…The remanent magnetization can be exploited in MRX imaging [ 60 ]. In this respect it is worth noting that in unshielded experiments, the Earth’s field (or any other bias field) contributes non-neglectably to the remanent magnetization and to the relaxation behavior of the MNP [ 64 , 65 ].…”

OPM magnetorelaxometry in the presence of a DC bias field

“…Transverse MRX of MNP wearing a viscoelastic corona, with an applied background magnetic field perpendicular to the excitation field has been modeled and investigated mathematically. It was shown in simulations that in transverse MRX, background magnetic fields alter the shape of the relaxation and decrease the relaxation time constant [22]. The dynamics of MNP's magnetic moments can be described by two concurrent processes: rotation of the whole particle is named Brownian motion, whereas the flipping of the single MNP's magnetic moments along their easy axis is described by so-called Néel relaxation [23].…”