Reversible and irreversible aggregation of magnetic liposomes

Abstract

Understanding stabilization and aggregation in magnetic nanoparticle systems is crucial to optimizing the functionality of these systems in real physiological applications. Here we address this problem for a specific, yet representative, system. We present an experimental and analytical study on the aggregation of superparamagnetic liposomes in suspension in the presence of a controllable external magnetic field. We study the aggregation kinetics and report an intermediate time power law evolution and a long time stationary value for the average aggregate diffusion coefficient, both depending on the magnetic field intensity. We then show that the long time aggregate structure is fractal with a fractal dimension that decreases upon increasing the magnetic field intensity. By scaling arguments we also establish an analytical relation between the aggregate fractal dimension and the power law exponent controlling the aggregation kinetics. This relation is indeed independent on the magnetic field intensity. Despite the superparamagnetic character of our particles, we further prove the existence of a population of surviving aggregates able to maintain their integrity after switching off the external magnetic field. Finally, we suggest a schematic interaction scenario to rationalize the observed coexistence between reversible and irreversible aggregation.

Kinetics of Aggregation and Magnetic Separation of Multicore Iron Oxide Nanoparticles: Effect of the Grafted Layer Thickness

“…Realization of such magnetic circuits is done either by cumbersome and energy consuming electromagnets [ 15 ] or sophisticated and presumably high-cost permanent micro-magnets [ 16 ]. Nevertheless, despite Brownian motion, it is still possible to get a strong magnetic response of nanoparticles at magnetic flux densities as low as 5–10 mT if they undergo a field-induced phase transition, i.e., gather into elongated bulk micron sized aggregates extended along the direction of the applied magnetic field [ 17 , 18 ], or form fractal clusters under the combined action of colloidal and magnetic dipolar interactions, as inferred from the static light scattering experiments on magnetic liposomes [ 19 ]. In the presence of a magnetic field gradient, the aggregates migrate along the field gradient with a speed proportional to the aggregate volume.…”

<p>An in vitro Model System for Evaluating Remote Magnetic Nanoparticle Movement and Fibrinolysis</p>

“…Achieving an improved understanding of the factors that influence MNP agglomeration, stability, translational movement, cellular uptake, and drug binding and release will be crucial for making the jump from in vitro and animal studies, to human applications for magnetic drug targeting. [56][57][58][59][60] Electrolyte composition, protein content, and viscosity (among many other factors) are very different in the various bodily fluids that could act as MNP conduits: cerebrospinal fluid versus blood, for instance. 61 Yet to date, only a few studies have analyzed the effect of these factors on MNP movement, aggregation/agglomeration, and/or drug delivery.…”

Static magnetization of immobilized, weakly interacting, superparamagnetic nanoparticles

“…where Z 0 is the normalization constant. The next step is to identify the effects of interparticle correlations, represented by the second term in eqn (12). It contains factors of concentration ρ and U d /k B T ∼ λ, in addition to the dependence of g 2 (1, 2) on those variables.…”

“…is the Heaviside step-function, describing the impenetrability of two particles. Combining eqn (12) and 16gives…”

“…Embedding a large number of such particles into a matrix makes it possible to control the properties of a composite material using an external magnetic field, and it is this control which is exploited in modern technologies. So-called magnetic soft matter includes ferrofluids, 1 magnetorheological fluids, magnetic elastomers [2][3][4][5] and ferrogels, [6][7][8] ferronematic liquid crystals, [9][10][11] and various biocompatible magnetic suspensions, [12][13][14][15][16] which are applied in targeted drug delivery and magnetic hyperthermia. [17][18][19][20][21][22] In addition to technical and biomedical applications, magnetic nanoparticle ensembles are also useful in colloid technology, because of interesting self-assembly processes.…”