Melanin-like nanoparticles were synthesized with size control through neutralization of dopamine hydrochloride with NaOH, followed by spontaneous air oxidation of dopamine. Although the particle characteristic of natural melanins was understood to be significantly affected by the biological and structural environment, melanin-lke nanoparticles can be realized through the chemical reactions only. Melanin-like nanoparticles that are <100 nm showed excellent dispersion stability in water as well as biological media and good biocompatibility to HeLa cells after the appropriate surface modification with thiol-terminated methoxy-poly(ethylene glycol) (mPEG-SH). Furthermore, the demonstrated ability of melanin-like nanoparticles to reduce 2,2-diphenyl-1-picrylhydrazyl (DPPH) suggests free radical scavenging activity of the material.

In recent years, there has been a great deal of research interest in fabricating superhydrophobic surfaces, which have static contact angles of water droplets greater than 150°, because of their importance in fundamental research [1,2] as well as in practical applications of biomimetic systems such as preventing the adhesion of snow or rain to antennas and windows, [3] producing stain-resistant textiles, [4] and wettabilityswitching surfaces. [5][6][7] The superhydrophobic property is believed to be governed by both the chemical composition of the surface material and the cooperative effect of nanostructures within the micrometer-scale areas (the so-called hierarchical structure). For example, the leaves of the lotus and taro and the wings of the cicada have superhydrophobic surfaces, [8][9][10][11] and they can undergo self-cleaning by removal of dust and pollutants using rolling water drops; this is usually called the "lotus effect". [5,9,10] Many researchers have generated artificial superhydrophobic surfaces by controlling the chemical composition of molecules, [12] polymers, [13][14][15][16] and metals [2,17,18] or by fabricating novel structures using various techniques such as spin-coating, [15] polymer imprinting, [19][20][21] self-assembly, [22] sublimation of a small molecule during gelation, [23] and etching techniques.[24] Although current fabricating techniques can generate some superhydrophobic surfaces, it is not easy to precisely control the nanostructures and microstructures within the hierarchical structures. Therefore, it would be worthwhile to develop fabrication methods that enable us to precisely and independently control the nanostructures and microstructures, in order to understand better the superhydrophobic phenomenon and to generate optimized biomimetic surfaces.We have developed a simple, efficient, and highly reproducible method of producing well-defined large-area nanostructured polymeric and metallic surfaces having nanoembossing or nanofibers with controllable aspect ratios by employing anodic aluminum oxides (AAOs) or a textured Al surface as a replication master. [19,25] As an extension of generating various nanostructures on the polymer surface, we have employed both photolithography and Al etching techniques to produce well-controlled micrometer-sized concave patterns on Al surfaces on which various nanostructures can be produced. From these combined techniques, hierarchical structures of templates can be precisely controlled at the micrometer scale as well as at the nanometer scale. On the basis of the heat-and pressure-driven imprinting process with thermoplastic polymers such as high-density polyethylene (HDPE), hierarchical polymer surfaces could be duplicated many times. The contact angle measurement of the water droplets on these surfaces clearly showed interesting cooperative effects of micrometerand nanometer-sized structures within the hierarchical structures to mimic water-repellent plant leaf surfaces. The fabrication process of biomimetic hierarchical surfaces compr...

Magnetic nanoparticles (MNPs) have proven themselves to be useful in biomedical research; however, previous reports were insufficient to address the potential dangers of nanoparticles. Here, we investigated gene expression and metabolic changes based on the microarray and gas chromatographyÀmass spectrometry with human embryo kidney 293 cells treated with MNPs@SiO 2 (RITC), a silicacoated MNP containing Rhodamine B isothiocyanate (RITC). In addition, measurement of reactive oxygen species (ROS) and ATP analysis were performed to evaluate the effect of MNPs@SiO 2 (RITC) on mitochondrial function. Compared to the nontreated control, glutamic acid was increased by more than 2.0-fold, and expression of genes related to the glutamic acid metabolic pathway was also disturbed in 1.0 μg/μL of MNPs@SiO 2 (RITC)-treated cells. Furthermore, increases in ROS concentration and mitochondrial damage were observed in this MNPs@SiO 2 (RITC) concentration. The organic acids related to the Krebs cycle were also disturbed, and the capacity of ATP synthesis was decreased in cell treated with an overdose of MNPs@SiO 2 (RITC). Collectively, these results suggest that overdose (1.0 μg/μL) of MNPs caused transcriptomic and metabolic disturbance. In addition, we suggest that a combination of gene expression and metabolic profiles will provide more detailed and sensitive toxicological evaluation for nanoparticles.

We have developed a simple, efficient, and highly reproducible method to fabricate the large-area biomimetic superhydrophobic polymer surfaces having hierarchical structures of micrometer-sized irregular steps and nanometer-sized fibrils. Commercial Al plates (99.0%) were etched using Beck's dislocation etchant (mixture of HCl and HF) for different time periods in order to alter the structure of the etched Al surfaces from micrometer-sized to highly rough nanometer-sized irregular steps. These hierarchical structures could be easily replicated onto the surface of various thermoplastic polymer plates from the etched Al templates by applying heat and pressure; many polymer replicas without any significant deviations from each other could be duplicated from the same etched Al master templates. All of thermoplastic polymer replicas having hierarchical structures exhibited superhydrophobic properties with water contact angles of larger than 150 degrees. Especially, the surfaces of the high-density polyethylene (HDPE) replicas having nanometer-sized curled strands exhibited superhydrophobicity with a static water contact angle of approximately 160 degrees and a sliding angle of less than 2 degrees. These superhydrophobic HDPE replicas having nanometer-sized curled strands showed excellent stability after being exposed to various organic solvents and aqueous solutions of various pH.

ObjectiveTo determine the feasibility of labeling human mesenchymal stem cells (hMSCs) with bifunctional nanoparticles and assessing their potential as imaging probes in the monitoring of hMSC transplantation.Materials and MethodsThe T1 and T2 relaxivities of the nanoparticles (MNP@SiO2[RITC]-PEG) were measured at 1.5T and 3T magnetic resonance scanner. Using hMSCs and the nanoparticles, labeling efficiency, toxicity, and proliferation were assessed. Confocal laser scanning microscopy and transmission electron microscopy were used to specify the intracellular localization of the endocytosed iron nanoparticles. We also observed in vitro and in vivo visualization of the labeled hMSCs with a 3T MR scanner and optical imaging.ResultsMNP@SiO2(RITC)-PEG showed both superparamagnetic and fluorescent properties. The r1 and r2 relaxivity values of the MNP@SiO2(RITC)-PEG were 0.33 and 398 mM-1 s-1 at 1.5T, respectively, and 0.29 and 453 mM-1 s-1 at 3T, respectively. The effective internalization of MNP@SiO2(RITC)-PEG into hMSCs was observed by confocal laser scanning fluorescence microscopy. The transmission electron microscopy images showed that MNP@SiO2(RITC)-PEG was internalized into the cells and mainly resided in the cytoplasm. The viability and proliferation of MNP@SiO2(RITC)-PEG-labeled hMSCs were not significantly different from the control cells. MNP@SiO2(RITC)-PEG-labeled hMSCs were observed in vitro and in vivo with optical and MR imaging.ConclusionMNP@SiO2(RITC)-PEG can be a useful contrast agent for stem cell imaging, which is suitable for a bimodal detection by MRI and optical imaging.