Mihyun Park

Mesoporous Silica-Coated Hollow Manganese Oxide Nanoparticles as Positive T1 Contrast Agents for Labeling and MRI Tracking of Adipose-Derived Mesenchymal Stem Cells

Mesoporous silica-coated hollow manganese oxide (HMnO@mSiO2) nanoparticles were developed as a novel T1 magnetic resonance imaging (MRI) contrast agent. We hypothesized that the mesoporous structure of the nanoparticle shell enables optimal access of water molecules to the magnetic core, and consequently, an effective longitudinal (R1) relaxation enhancement of water protons, which value was measured to be 0.99 (mM−1s−1) at 11.7 T. Adipose-derived mesenchymal stem cells (MSCs) were efficiently labeled using electroporation, with much shorter T1 values as compared to direct incubation without electroporation, which was also evidenced by signal enhancement on T1-weighted MR images in vitro. Intracranial grafting of HMnO@mSiO2-labeled MSCs enabled serial MR monitoring of cell transplants over 14 days. These novel nanoparticles may extend the arsenal of currently available nanoparticle MR contrast agents by providing positive contrast on T1-weighted images at high magnetic field strengths.

Synthesis of Uniform Ferrimagnetic Magnetite Nanocubes

We synthesized uniform ferrimagnetic magnetite nanocubes in the size range from 20 to 160 nm. The magnetic property of the nanocubes was characterized, and magnetic separation of the histidine-tagged protein was demonstrated.

Chitosan Oligosaccharide-Stabilized Ferrimagnetic Iron Oxide Nanocubes for Magnetically Modulated Cancer Hyperthermia

Magnetic nanoparticles have gained significant attention as a therapeutic agent for cancer treatment. Herein, we developed chitosan oligosaccharide-stabilized ferrimagnetic iron oxide nanocubes (Chito-FIONs) as an effective heat nanomediator for cancer hyperthermia. Dynamic light scattering and transmission electron microscopic analyses revealed that Chito-FIONs were composed of multiple 30-nm-sized FIONs encapsulated by a chitosan polymer shell. Multiple FIONs in an interior increased the total magnetic moments, which leads to localized accumulation under an applied magnetic field. Chito-FIONs also exhibited superior magnetic heating ability with a high specific loss power value (2614 W/g) compared with commercial superparamagnetic Feridex nanoparticles (83 W/g). The magnetically guided Chito-FIONs successfully eradicated target cancer cells through caspase-mediated apoptosis. Furthermore, Chito-FIONs showed excellent antitumor efficacy on an animal tumor model without any severe toxicity.

Direct synthesis of self-assembled ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes.

Extensive applications of rechargeable lithium-ion batteries (LIBs) to various portable electronic devices and hybrid electric vehicles result in the increasing demand for the development of electrode materials with improved electrochemical performance including high energy, power density, and excellent cyclability, while maintaining low production cost. Here, we present a direct synthesis of ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes. Uniform-sized ferrite nanocrystals and carbon materials were synthesized simultaneously through a single heating procedure using metal-oleate complex as the precursors for both ferrite and carbon. 2-D nanostructures were obtained by using sodium sulfate salt powder as a sacrificial template. The 2-D ferrite/carbon nanocomposites exhibited excellent cycling stability and rate performance derived from 2-D nanostructural characteristics. The synthetic procedure is simple, inexpensive, and scalable for mass production, and the highly ordered 2-D structure of these nanocomposites has great potential for many future applications.

Water-Dispersible Ferrimagnetic Iron Oxide Nanocubes with Extremely High r2 Relaxivity for Highly Sensitive in Vivo MRI of Tumors

The theoretically predicted maximum r(2) relaxivity of iron oxide nanoparticles was achieved by optimizing the overall size of ferrimagnetic iron oxide nanocubes. Uniform-sized iron oxide nanocubes with an edge length of 22 nm, encapsulated with PEG-phospholipids (WFION), exhibited high colloidal stability in aqueous media. In addition, WFIONs are biocompatible and did not affect cell viability at concentrations up to 0.75 mg Fe/ml. Owing to the enhanced colloidal stability and the high r(2) relaxivity (761 mM(-1) s(-1)), it was possible to successfully perform in vivo MR imaging of tumors by intravenous injection of 22-nm-sized WFIONs, using a clinical 3-T MR scanner.

Synthesis of Uniform Hollow Oxide Nanoparticles through Nanoscale Acid Etching

We synthesized various hollow oxide nanoparticles from as-prepared MnO and iron oxide nanocrystals. Heating metal oxide nanocrystals dispersed in technical grade trioctylphosphine oxide (TOPO) at 300 degrees C for hours yielded hollow nanoparticles retaining the size and shape uniformity of the original nanocrystals. The method was highly reproducible and could be generalized to synthesize hollow oxide nanoparticles of various sizes, shapes, and compositions. Control experiments revealed that the impurities in technical grade TOPO, especially alkylphosphonic acid, were responsible for the etching of metal oxide nanocrystals to the hollow structures. Elemental mapping analysis revealed that the inward diffusion of phosphorus and the outward diffusion of metal took place in the intermediate stages during the etching process. The elemental analysis using XPS, EELS, and EDX showed that the hollow nanoparticles were amorphous metal oxides containing significant amount of phosphorus. The hollow nanoparticles synthesized from MnO and iron oxide nanocrystals were paramagnetic at room temperature and when dispersed in water showed spin relaxation enhancement effect for magnetic resonance imaging (MRI). Because of their morphology and magnetic property, the hollow nanoparticles would be utilized for multifunctional biomedical applications such as the drug delivery vehicles and the MRI contrast agents.

Magnetosome-like ferrimagnetic iron oxide nanocubes for highly sensitive MRI of single cells and transplanted pancreatic islets

For ultrasensitive magnetic resonance imaging (MRI), magnetic nanoparticles with extremely high r2 relaxivity are strongly desired. Magnetosome-like nanoparticles were prepared by coating polyethylene glycol-phospholipid (PEG-phospholipid) onto ferrimagnetic iron oxide nanocubes (FIONs). FIONs exhibited a very high relaxivity (r2) of 324 mM-1 s-1, allowing efficient labeling of various kinds of cells. The magnetic resonance (MR) imaging of single cells labeled with FIONs is demonstrated not only in vitro but also in vivo. Pancreatic islet grafts and their rejection could be imaged using FIONs on a 1.5 T clinical MRI scanner. The strong contrast effect of FIONs enabled MR imaging of transplanted islets in small rodents as well as in large animals. Therefore, we expect that MR imaging of pancreatic islet grafts using FIONs has the potentials for clinical applications. Furthermore, FIONs will enable highly sensitive noninvasive assessment after cell transplantation.

Simple and Generalized Synthesis of Oxide−Metal Heterostructured Nanoparticles and their Applications in Multimodal Biomedical Probes

Heterostructured nanoparticles composed of metals and Fe3O4 or MnO were synthesized by thermal decomposition of mixtures of metal-oleate complexes (for the oxide component) and metal-oleylamine complexes (for the metal component). The products included flowerlike-shaped nanoparticles of Pt-Fe3O4 and Ni-Fe3O4 and snowmanlike-shaped nanoparticles of Ag-MnO and Au-MnO. Powder X-ray diffraction patterns showed that these nanoparticles were composed of face-centered cubic (fcc)-structured Fe3O4 or MnO and fcc-structured metals. The relaxivity values of the Au-MnO and Au-Fe3O4 nanoparticles were similar to those of the MnO and Fe3O4 nanoparticles, respectively. Au-Fe3O4 heterostructured nanoparticles conjugated with two kinds of 12-base oligonucleotide sequences were able to sense a complementary 24-mer sequence, causing nanoparticle aggregation. This hybridization-mediated aggregation was detected by the overall size increase indicated by dynamic light scattering data, the red shift of the surface plasmon band of the Au component, and the enhancement of the signal intensity of the Fe3O4 component in T2-weighted magnetic resonance imaging.

Hybrid Cellular Nanosheets for High-Performance Lithium-Ion Battery Anodes

We report a simple synthetic method of carbon-based hybrid cellular nanosheets that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The nanosheets consist of close-packed cubic cavity cells partitioned by carbon walls, resembling plant leaf tissue. We loaded carbon cellular nanosheets with SnO2 nanoparticles by vapor deposition method and tested the performance of the resulting SnO2-carbon nanosheets as anode materials. The specific capacity is 914 mAh g(-1) on average with a retention of 97.0% during 300 cycles, and the reversible capacity is decreased by only 20% as the current density is increased from 200 to 3000 mA g(-1). In order to explain the excellent electrochemical performance, the hybrid cellular nanosheets were analyzed with cyclic voltammetry, in situ X-ray absorption spectroscopy, and transmission electron microscopy. We found that the high packing density, large interior surface area, and rigid carbon wall network are responsible for the high specific capacity, lithiation/delithiation reversibility, and cycling stability. Furthermore, the nanosheet structure leads to the high rate capability due to fast Li-ion diffusion in the thickness direction.

Spatio-temporal expression patterns of Runx2 isoforms in early skeletogenesis

Skeletogenesis occurs through either intramembranous or endochondral ossification. In addition, some parts of the skeletal components maintain their cartilaginous characteristics throughout life without mineralization. Runx2 is known to be a pivotal transcription factor for all skeletogenic processes. In this study, we examined the expression patterns of two major isoforms of Runx2 in early skeletogenesis. During intramembranous bone formation, Runx2-type I (Runx2-I) was widely expressed in osteoprogenitor cells and active osteoblasts, while Runx2-type II (Runx2-II) expression was stringently restricted to cells lining mineralized bones. Cells in permanent cartilage expressed collagen type II (Col-II) but never expressed Runx2 or Col-X. These permanent cartilages were well circumscribed by Runx2-I positive cells, in which Runx2-II was negative. In endochondral bone formation, Runx2 expression temporarily disappeared in Col-II-positive proliferating chondrocytes, but a secondary surge of Runx2-I expression occurred in the prehypertrophic zone before the mineralization of cartilage. Collectively, both Runx2 isoforms showed very similar expression patterns in active bone forming areas; however, Runx2-I has an exclusive role in the early commitment stage of intramembranous or endochondral bone forming processes or in cells surrounding permanent cartilage.