It is generally recognized that nanoparticles possess unique physicochemical properties that are largely different from those of conventional materials, specifically the electromagnetic properties of magnetic nanoparticles (MNPs). These properties have attracted many researchers to launch investigations into their potential biomedical applications, which have been reviewed in this article. First, common types of MNPs were briefly introduced. Then, the biomedical applications of MNPs were reviewed in seven parts: magnetic resonance imaging (MRI), cancer therapy, the delivery of drugs and genes, bone and dental repair, tissue engineering, biosensors, and in other aspects, which indicated that MNPs possess great potentials for many kinds of biomedical applications due to their unique properties. Although lots of achievements have been obtained, there is still a lot of work to do. New synthesis techniques and methods are still needed to develop the MNPs with satisfactory biocompatibility. More effective methods need to be exploited to prepare MNPs-based composites with fine microstructures and high biomedical performances. Other promising research points include the development of more appropriate techniques of experiments both in vitro and in vivo to detect and analyze the biocompatibility and cytotoxicity of MNPs and understand the possible influencing mechanism of the two properties. More comprehensive investigations into the diagnostic and therapeutic applications of composites containing MNPs with "core-shell" structure and deeper understanding and further study into the properties of MNPs to reveal their new biomedical applications, are also described in the conclusion and perspectives part.

Current investigations into magnetic nanoparticles for biomedical applications.

Opportunities for new CT contrast agents to maximize the diagnostic potential of emerging spectral CT technologies.

The Diatoms: Applications for the Environmental and Earth Sciences

This study investigates the microstructural evolution and mechanical response of sputter-deposited amorphous silicon oxycarbide (SiOC)/crystalline Fe nanolaminates, a single layer SiOC film, and a single layer Fe film subjected to ion implantation at room temperature to obtain a maximum He concentration of 5 at. %. X-ray diffraction and transmission electron microscopy indicated no evidence of implantation-induced phase transformation or layer breakdown in the nanolaminates. Implantation resulted in the formation of He bubbles and an increase in the average size of the Fe grains in the individual Fe layers of the nanolaminates and the single layer Fe film, but the bubble density and grain size were found to be smaller in the former. By reducing the thicknesses of individual layers in the nanolaminates, bubble density and grain size were further decreased. No He bubbles were observed in the SiOC layers of the nanolaminates and the single layer SiOC film. Nanoindentation and scanning probe microscopy revealed an increase in the hardness of both single layer SiOC and Fe films after implantation. For the nanolaminates, changes in hardness were found to depend on the thicknesses of the individual layers, where reducing the layer thickness to 14 nm resulted in mitigation of implantation-induced hardening.

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Mechanical Response of He-Implanted Amorphous SiOC/Crystalline Fe Nanolaminates.

We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at terahertz frequencies. For SRRs on doped GaAs films, incident terahertz radiation with peak fields of ~20-160 kV/cm drives intervalley scattering. This reduces the carrier mobility and enhances the SRR LC response due to a conductivity decrease in the doped thin film. Above ~160 kV/cm, electric field enhancement within the SRR gaps leads to efficient impact ionization, increasing the carrier density and the conductivity which, in turn, suppresses the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude in the carrier density in the SRR gaps on semi-insulating GaAs. Furthermore, we show that the effective permittivity can be swept from negative to positive values with an increasing terahertz field strength in the impact ionization regime, enabling new possibilities for nonlinear metamaterials.

Nonlinear Terahertz Metamaterials via Field-Enhanced Carrier Dynamics in GaAs

This paper reports a novel method of fabricating iodinated hydrogel microparticles for use as contrast agents for X-ray computed tomography (CT) imaging. Compared with the most common clinically available CT contrast agents, typically in the form of water soluble organic iodine compounds, as well as recently developed CT contrast agents including gold or tantalum oxide nanoparticles, the top-down approach presented herein yields an engineering flexibility to the design of CT contrast agents with different shapes, sizes and composition. From the preliminary experimental results, the fabrication approach affords the flexibility to generate next-generation CT contrast agents with the potential for myriad clinical applications.

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Iodinated hydrogel microparticles as x-ray computed tomography contrast agents

This paper reports the characterization of reactively sputtered iron oxide thin films for their application in a novel class of top-down engineered contrast agent particles for multispectral magnetic resonance imaging (MRI). Tunable saturation magnetic polarizations (JS) of iron oxide thin films ranging from approximately 0.05 to 0.2 emu/mg were achieved by adjusting sputtering parameters. The iron oxide thin films were characterized using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and superconducting quantum interference (SQUID) magnetometry to study their chemical compositions, crystalline structures, and magnetic property, respectively. A novel MRI contrast agent was fabricated using the iron oxide deposition parameters to achieve a desired JS; these particles were subsequently validated using MRI.

Characterization of reactively sputtered iron oxide thin films for developing magnetic resonance imaging contrast agents

This paper reports the characterization of composite hydrogel particles by using a novel fabrication method, which produces the X-ray attenuating media with particle varying size and shape for computed tomography (CT) imaging. The rheological testing demonstrated tunable mechanical properties of composite hydrogel based on UV crosslinking time. The leakage testing verified longer stability time of gold nanoparticle-based X-ray attenuating media. In contradistinction to the currently clinically available iodinated CT contrast agents, as well as recently developed nanoparticulate CT contrast agents, the approach presented herein yields an engineering flexibility to the design of CT contrast agents for specific imaging and sensing applications.

Fabrication and characterization of composite hydrogel particles with x-ray attenuating media

This paper reports the fabrication and characterization of composite hydrogel particles composed of poly(ethylene glycol) diacrylate (PEG-DA)-based hydrogels and x-ray attenuating payloads. The top–down fabrication method employed herein is demonstrated to yield composite hydrogel particles of varying size and shape for use as computed tomography (CT) imaging contrast agents. Characterization of the materials properties of the PEG-DA hydrogels was undertaken, demonstrating tunable mechanical properties of composite hydrogels based on hydrogel composition and UV cross-linking time. Analyses of the leakage rates of a conventional iodine-based small molecular contrast agent as well as a nanoparticulate x-ray attenuating material from the PEG-DA hydrogels were undertaken. In contradistinction to clinically available iodinated CT contrast agents, as well as recently developed nanoparticulate CT contrast agents, the approach presented herein yields an engineering flexibility to the design of CT contrast agents ...

Fabrication and characterization of composite hydrogel particles with x-ray attenuating payloads

This paper proposed a novel MEMS-based fabrication process for biocompatible, hollow cylindrical ferromagnetic contrast agents for magnetic resonance imaging (MRI). Compared to previous works on Ni-based cylindrical-nanoshells and Fe-based double-disk particles, biocompatibility and yield issues were strongly considered in this development of a simplified MEMS fabrication process incorporating iron oxide thin films. The novel, simplified microfabrication process developed herein yields a robust, reproducible fabrication methodology for the further development of this new class of MRI contrast agents, which offers the potential for multiplexing as well as functional imaging capacity with the incorporation of environmentally sensitive materials to modulate the degree of central water diffusion.

Xiaoning Wang

Papers

Iodinated hydrogel microparticles as x-ray computed tomography contrast agents

Characterization of reactively sputtered iron oxide thin films for developing magnetic resonance imaging contrast agents

Fabrication and characterization of composite hydrogel particles with x-ray attenuating media

Fabrication and characterization of composite hydrogel particles with x-ray attenuating payloads

Biocompatible microfabricated magnetic cylinders as contrast agents for magnetic resonance imaging