Magnetic Iron Nanoparticles: Synthesis, Surface Enhancements, and Biological Challenges

This review focuses on the role of magnetic nanoparticles (MNPs), their physicochemical properties, their potential applications, and their association with the consequent toxicological effects in complex biologic systems. These MNPs have generated an accelerated development and research movement in the last two decades. They are solving a large portion of problems in several industries, including cosmetics, pharmaceuticals, diagnostics, water remediation, photoelectronics, and information storage, to name a few. As a result, more MNPs are put into contact with biological organisms, including humans, via interacting with their cellular structures. This situation will require a deeper understanding of these particles’ full impact in interacting with complex biological systems, and even though extensive studies have been carried out on different biological systems discussing toxicology aspects of MNP systems used in biomedical applications, they give mixed and inconclusive results. Chemical agencies, such as the Registration, Evaluation, Authorization, and Restriction of Chemical substances (REACH) legislation for registration, evaluation, and authorization of substances and materials from the European Chemical Agency (ECHA), have held meetings to discuss the issue. However, nanomaterials (NMs) are being categorized by composition alone, ignoring the physicochemical properties and possible risks that their size, stability, crystallinity, and morphology could bring to health. Although several initiatives are being discussed around the world for the correct management and disposal of these materials, thanks to the extensive work of researchers everywhere addressing the issue of related biological impacts and concerns, and a new nanoethics and nanosafety branch to help clarify and bring together information about the impact of nanoparticles, more questions than answers have arisen regarding the behavior of MNPs with a wide range of effects in the same tissue. The generation of a consolidative framework of these biological behaviors is necessary to allow future applications to be manageable.

Raman spectroscopy to unravel the magnetic properties of iron oxide nanocrystals for bio-related applications

Iron oxide nanocrystals have become a versatile tool in biomedicine because of their low cytotoxicity while offering a wide range of tuneable magnetic properties that may be implemented in magnetic separation, drug and heat delivery and bioimaging. These capabilities rely on the unique magnetic features obtained when combining different iron oxide phases, so that an important portfolio of magnetic properties can be attained by the rational design of multicomponent nanocrystals. In this context, Raman spectroscopy is an invaluable and fast-performance tool to gain insight into the different phases forming part of the nanocrystals to be used, allowing correlation of the magnetic properties with the envisaged bio-related applications.

Tailoring of physicochemical properties of nanocarriers for effective anti-cancer applications

Nanotechnology has emerged strongly as a viable option to overcome the challenge of early diagnosis and effective drug delivery, for cancer treatment. Emerging research articles have expounded the advantages of using a specific type of nanomaterial-based system called as "nanocarriers," for anti-cancer therapy. The nanocarrier system is used as a transport unit for targeted drug delivery of the therapeutic drug moiety. In order for the nanocarriers to be effective for anticancer therapy, their physicochemical parameter needs to be tuned so that bio-functionalisation can be achieved to (1) allow drugs being attached to the substrate and for their controlled release, (2) ensure the stability of the nanocarrier up to the point of delivery, and (3) clearance of the nanocarrier after the delivery. It is therefore envisaged that tailoring of the physicochemical properties of nanocarriers can greatly influence their reactivity and interaction in the biological milieu, and this is becoming an important parameter for increasing the efficacy of cancer therapy. This review emphasizes the importance of physicochemical properties of nanocarriers, and how they influence its usage as chemotherapeutic drug carriers. The goal of this review is to present a correlation between the physicochemical properties of the nanocarriers and its intended action, and how their design based on these properties can enhance their cancer combating abilities while minimizing damage to the healthy tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2906-2928, 2017.

Magnetic Core-Shell Silica Nanoparticles with Large Radial Mesopores for siRNA Delivery

A novel type of magnetic core-shell silica nanoparticles is developed for small interfering RNA (siRNA) delivery. These nanoparticles are fabricated by coating super-paramagnetic magnetite nanocrystal clusters with radial large-pore mesoporous silica. The amine functionalized nanoparticles have small particle sizes around 150 nm, large radial mesopores of 12 nm, large surface area of 411 m(2) g(-1) , high pore volume of 1.13 cm(3) g(-1) and magnetization of 25 emu g(-1) . Thus, these nanoparticles possess both high loading capacity of siRNA (2 wt%) and strong magnetic response under an external magnetic field. An acid-liable coating composed of tannic acid can further protect the siRNA loaded in these nanoparticles. The coating also increases the dispersion stability of the siRNA-loaded carrier and can serve as a pH-responsive releasing switch. Using the magnetic silica nanoparticles with tannic acid coating as carriers, functional siRNA has been successfully delivered into the cytoplasm of human osteosarcoma cancer cells in vitro. The delivery is significantly enhanced with the aid of the external magnetic field.

Nano-objects for addressing the control of nanoparticle arrangement and performance in magnetic hyperthermia

One current challenge of magnetic hyperthermia is achieving therapeutic effects with a minimal amount of nanoparticles, for which improved heating abilities are continuously pursued. However, it is demonstrated here that the performance of magnetite nanocubes in a colloidal solution is reduced by 84% when they are densely packed in three-dimensional arrangements similar to those found in cell vesicles after nanoparticle internalization. This result highlights the essential role played by the nanoparticle arrangement in heating performance, uncontrolled in applications. A strategy based on the elaboration of nano-objects able to confine nanocubes in a fixed arrangement is thus considered here to improve the level of control. The obtained specific absorption rate results show that nanoworms and nanospheres with fixed one- and two-dimensional nanocube arrangements, respectively, succeed in reducing the loss of heating power upon agglomeration, suggesting a change in the kind of nano-object to be used in magnetic hyperthermia.

Magnetic, long persistent luminescent and mesoporous nanoparticles as trackable transport drug carriers

In this paper, Gd₂O₃@mSiO₂@CaTiO₃:Pr nanoparticles with a novel core/shell structure featured by mesoporous, magnetic and long persistent luminescent properties have been synthesized via a facile template method. The as-prepared nanoparticles show ordered mesoporous characteristics, monodisperse spherical morphology and narrow size distribution, so they are expected to be suitable as a drug carrier. These nanoparticles exhibit bright red phosphorescence at 614 nm after UV irradiation and the persistent luminescence can persist for more than one hour. Moreover, they possess a prominent longitudinal relaxivity (r₁) value of 6.43 mM^-1 s^-1, which suggests that these nanoparticles can be used as MR imaging agents. The combination of long persistent luminescent and magnetic properties reveals the high imaging sensitivity, which suggests that these nanoparticles can be used for imaging in vivo with a high signal to noise ratio. Drug release results indicate that the nanoparticles hold excellent drug sustained properties. The cumulative released amount of drugs can also be easily monitored by the change of luminescence intensity. After modification with polyethylene glycol, the resulting nanoparticles demonstrate good biocompatibility and low toxicity. Furthermore, we can realize in vivo imaging for over 20 min using these nanoparticles. These results indicate the promising use of these nanoparticles as multifunctional traceable drug carriers in vivo.