Model for hyperthermia with arrays of magnetic nanoparticles: spatial and time temperature distributions in tumor

Relating surface roughness and magnetic domain structure to giant magneto-impedance of Co-rich melt-extracted microwires

Understanding the relationship between the surface conditions and giant magneto-impedance (GMI) in Co-rich melt-extracted microwires is key to optimizing their magnetic responses for magnetic sensor applications. The surface magnetic domain structure (SMDS) parameters of ~45 μm diameter Co_69.25Fe_4.25Si₁₃B_13.5-xZr_x (x = 0, 1, 2, 3) microwires, including the magnetic domain period (d) and surface roughness (R_q) as extracted from the magnetic force microscopy (MFM) images, have been correlated with GMI in the range 1–1000 MHz. It was found that substitution of B with 1 at. % Zr increased d of the base alloy from 729 to 740 nm while retaining R_q from ~1 nm to ~3 nm. A tremendous impact on the GMI ratio was found, increasing the ratio from ~360% to ~490% at an operating frequency of 40 MHz. Further substitution with Zr decreased the high frequency GMI ratio, which can be understood by the significant increase in surface roughness evident by force microscopy. This study demonstrates the application of the domain period and surface roughness found by force microscopy to the interpretation of the GMI in Co-rich microwires.

Modeling receptor-mediated endocytosis of polymer-functionalized iron oxide nanoparticles by human macrophages

Although systemically applied nanoparticles are quickly taken up by phagocytic cells, mainly macrophages, the interactions between engineered nanoparticles and macrophages are still not well defined. We therefore analyzed the uptake of diagnostically used carboxydextran-coated superparamagnetic iron oxide nanoparticles of 60 nm (SPIO) and 20 nm (USPIO) by human macrophages. By pharmacological and in vitro knockdown approaches, the principal uptake mechanism for both particles was identified as clathrin-mediated, scavenger receptor A-dependent endocytosis. We developed a mathematical model of the uptake process that allows determination of key parameters of endocytosis, including the rate of uptake, the number of nanoparticles per cell in saturation, the mean uptake time, and the correlation between the number of internalized nanoparticles and their extracellular concentration. The calculated parameters correlate well with experimental data obtained by confocal microscopy. Moreover, the model predicts the individual and collective wrapping times of different nanoparticles, describes the relation between cytoskeletal forces, membrane elasticity and the uptake time. We also introduced a new physical parameter 'a' governing the collective uptake process, a reflecting minimal linear spacing between simultaneously acting neighboring endocytotic pits.