Nanoparticles engineered for biomedical applications are meant to be in contact with protein-rich physiological fluids. These proteins are usually adsorbed onto the nanoparticle's surface, forming a swaddling layer that has been described as a 'protein corona', the nature of which is expected to influence not only the physicochemical properties of the particles but also the internalization into a given cell type. We have investigated the process of protein adsorption onto different magnetic nanoparticles (MNPs) when immersed in cell culture medium, and how these changes affect the cellular uptake. The role of the MNPs surface charge has been assessed by synthesizing two colloids with the same hydrodynamic size and opposite surface charge: magnetite (Fe3O4) cores of 25-30 nm were in situ functionalized with (a) positive polyethyleneimine (PEI-MNPs) and (b) negative poly(acrylic acid) (PAA-MNPs). After few minutes of incubation in cell culture medium the wrapping of the MNPs by protein adsorption resulted in a 5-fold increase of the hydrodynamic size. After 24 h of incubation large MNP-protein aggregates with hydrodynamic sizes of ≈1500 nm (PAA-MNPs) and ≈3000 nm (PEI-MNPs) were observed, each one containing an estimated number of magnetic cores between 450 and 1000. These results are consistent with the formation of large protein-MNPs aggregate units having a 'plum pudding' structure of MNPs embedded into a protein network that results in a negative surface charge, irrespective of the MNP-core charge. In spite of the similar negative ζ-potential for both MNPs within cell culture, we demonstrated that PEI-MNPs are incorporated in much larger amounts than the PAA-MNPs units. Quantitative analysis showed that SH-SY5Y cells can incorporate 100% of the added PEI-MNPs up to ≈100 pg/cell, whereas for PAA-MNPs the uptake was less than 50%. The final cellular distribution showed also notable differences regarding partial attachment to the cell membrane. These results highlight the need to characterize the final properties of MNPs after protein adsorption in biological media, and demonstrate the impact of these properties on the internalization mechanisms in neural cells.

No abstract

This work aims to demonstrate the need for in silico design via numerical simulation to produce optimal Fe3O4-based magnetic nanoparticles (MNPs) for magnetic hyperthermia by minimizing the impact of intracellular environments on heating efficiency. By including the relevant magnetic parameters, such as magnetic anisotropy and dipolar interactions, into a numerical model, the heating efficiency of as prepared colloids was preserved in the intracellular environment, providing the largest in vitro specific power absorption (SPA) values yet reported. Dipolar interactions due to intracellular agglomeration, which are included in the simulated SPA, were found to be the main cause of changes in the magnetic relaxation dynamics of MNPs under in vitro conditions. These results pave the way for the magnetism-based design of MNPs that can retain their heating efficiency in vivo, thereby improving the outcome of clinical hyperthermia experiments.

No abstract

The Linear Response Theory (LRT) is a widely accepted framework to analyze the power absorption of magnetic nanoparticles for magnetic fluid hyperthermia. Its validity is restricted to low applied fields and/or to highly anisotropic magnetic nanoparticles. Here, we present a systematic experimental analysis and numerical calculations of the specific power absorption for highly anisotropic cobalt ferrite (CoFe 2 O 4 ) magnetic nanoparticles with different average sizes and in different viscous media. The predominance of Brownian relaxation as the origin of the magnetic losses in these particles is established, and the changes of the Specific Power Absorption (SPA) with the viscosity of the carrier liquid are consistent with the LRT approximation. The impact of viscosity on SPA is relevant for the design of MNPs to heat the intracellular medium during in vitro and in vivo experiments. The combined numerical and experimental analyses presented here shed light on the underlying mechanisms that make highly anisotropic MNPs unsuitable for magnetic hyperthermia.

Chitosan nanoparticles (CSNPs) ionically crosslinked with tripolyphosphate salts (TPP) were employed as nanocarriers in combined drug delivery and magnetic hyperthermia (MH) therapy. To that aim, three different ferrofluid concentrations and a constant 5-fluorouracil (5-FU) concentration were efficiently encapsulated to yield magnetic CSNPs with core-shell morphology. In vitro experiments using normal cells, fibroblasts (FHB) and cancer cells, human glioblastoma A-172, showed that CSNPs presented a dose-dependent cytotoxicity and that they were successfully uptaken into both cell lines. The application of a MH treatment in A-172 cells resulted in a cell viability of 67-75% whereas no significant reduction of cell viability was observed for FHB. However, the A-172 cells showed re-growth populations 4h after the application of the MH treatment when CSNPs were loaded only with ferrofluid. Finally, a combined effect of MH and 5-FU release was observed with the application of a second MH treatment for CSNPs exhibiting a lower amount of released 5-FU. This result demonstrates the potential of CSNPs for the improvement of MH therapies.

We report a one-step synthesis protocol for obtaining polymer-coated magnetic nanoparticles (MNPs) engineered for uploading neural cells. Polyethyleneimine-coated Fe3O4 nanoparticles (PEI-MNPs) with sizes of 25 ± 5 nm were prepared by oxidation of Fe(OH)2 by nitrate in basic aqueous media and adding PEI in situ during synthesis. The obtained PEI-MNP cores displayed a neat octahedral morphology and high crystallinity. The resulting nanoparticles were coated with a thin polymer layer of about 0.7-0.9 nm, and displayed a saturation magnetization value M S = 58 A m2 kg-1 at 250 K (64 A m2 kg-1 for T = 10 K). Cell uptake experiments on a neuroblastoma- derived SH-SY5Y cell line were undertaken over a wide time and MNP concentration range. The results showed a small decrease in cell viability for 24 h incubation (down to 70% viability for 100 μg ml-1), increasing the toxic effects with incubation time (30% cell survival at 100 μg ml -1 for 7 days of incubation). On the other hand, primary neuronal cells displayed higher sensitivity to PEI-MNPs, with a cell viability reduction of 44% of the control cells after 3 days of incubation with 50 μg ml -1. The amount of PEI-MNPs uploaded by SH-SY5Y cells was found to have a linear dependence on concentration. The intracellular distribution of the PEI-MNPs analyzed at the single-cell level by the dual-beam (FIB/SEM) technique revealed the coexistence of both fully incorporated PEI-MNPs and partially internalized PEI-MNP-clusters crossing the cell membrane. The resulting MNP-cluster distributions open the possibility of using these PEI-MNPs for magnetically driven axonal re-growth in neural cells

The integration of noble metal and magnetic nanoparticles with controlled structures that can couple various specific effects to the different nanocomposite in multifunctional nanosystems have been found interesting in the field of medicine. In this work, we show synthesis route to prepare small Au nanoparticles of sizes  = 3.9 ± 0.2 nm attached to Fe3O4 nanoparticle cores ( = 49.2 ± 3.5 nm) in aqueous medium for potential application as a nano-heater. Remarkably, the resulted Au decorated PEI-Fe3O4 (Au@PEI-Fe3O4) nanoparticles are able to retain bulk magnetic moment MS = 82–84 Am2/kgFe3O4, with the Verwey transition observed at TV = 98 K. In addition, the in vitro cytotoxicity analysis of the nanosystem microglial BV2 cells showed high viability (>97.5%) to concentrate up to 100 µg/mL in comparison to the control samples. In vitro heating experiments on microglial BV2 cells under an ac magnetic field (H0 = 23.87 kA/m; f = 571 kHz) yielded specific power absorption (SPA) values of SPA = 43 ± 3 and 49 ± 1 μW/cell for PEI-Fe3O4 and Au@PEI-Fe3O4 NPs, respectively. These similar intracellular SPA values imply that functionalization of the magnetic particles with Au did not change the heating efficiency, providing at the same time a more flexible platform for multifunctional functionalization.