UV Sterilization Effects and Osteoblast Proliferation on Amorphous Carbon Films Classified Based on Optical Constants.

Optical classification methods that distinguish amorphous carbon films into six types based on refractive index and extinction coefficient have garnered increasing attention. In this study, five types of amorphous carbon films were prepared on Si substrates using different plasma processes, including physical and chemical vapor deposition. The refractive index and extinction coefficient of the amorphous carbon films were measured using spectroscopic ellipsometry, and the samples were classified into five amorphous carbon types-amorphous, hydrogenated amorphous, tetrahedral amorphous, polymer-like, and graphite-like carbon-based on optical constants. Each amorphous carbon type was irradiated with 253.7 nm UV treatment; the structure and surface properties of each were investigated before and after UV treatment. No significant changes were observed in film structure nor surface oxidation after UV sterilization progressed at approximately the same level for all amorphous carbon types. Osteoblast proliferation associated with amorphous carbon types was evaluated in vitro. Graphite-like carbon, which has relatively high surface oxidation levels, was associated with higher osteoblast proliferation levels than the other carbon types. Our findings inform the selection of suitable amorphous carbon types based on optical constants for use in specific medical devices related to osteoblasts, such as artificial joints and dental implants.

Correlation of Cell Proliferation with Surface Properties of Polymer-like Carbon Films of Different Thicknesses Prepared by a Radio-Frequency Plasma CVD Process.

In this study, correlation of cell proliferation with surface properties of the polymer-like carbon (PLC) films of different thicknesses prepared by radio-frequency plasma CVD are investigated. Four PLC samples were prepared via radio frequency plasma chemical vapor deposition on Si substrates. Each PLC film was analyzed using spectroscopic ellipsometry to determine its thickness, refractive index (n), and extinction coefficient (k); the thickness ranged from 29.0 to 356.5 nm. Based on their n−k plots, all the samples were classified as PLC-type films. The biological response of the PLC films was evaluated in vitro using a cell culture. The samples with relatively thick PLC films (>300 nm) exhibited stronger cell proliferation properties than those with thinner films. Moreover, the results of the surface analysis showed no significant differences in the surface composition of those PLC samples, as analyzed using X-ray photoelectron spectroscopy, but that as the PLC films became thicker, their surfaces became rougher on the nanoscale and their wettability improved. Overall, this study showed that careful control of the film growth of PLC films, which affects their surface properties, is essential for their use in bio-interface applications.

Osteoblastic MC3T3-E1 cells on diamond-like carbon-coated silicon plates: Field emission scanning electron microscopy data.

Diamond-like carbon (DLC) is an amorphous form of carbon that contains aspects of both the diamond and graphite structures. It is composed of carbon and hydrogen, and owing to its texture, high mechanical hardness, chemical inertness, and optical transparency, DLC is widely used as a protective coating in the form of a thin film, which is applied to the surfaces of many materials. Recently, it has attracted attention as a biomedical material because of its high biocompatibility and stability [1,2]. DLC is particularly suitable to be embedded in the body owing to its low friction properties and selective cell surface attachment properties [3]. The material is currently being developed for the treatment of bone fractures [4]. However, unlike fibroblasts, the attachment of osteoblasts has not been extensively examined and no morphological data is available on how osteoblastic cells form contacts with the surface of biocompatible DLC-coated materials. Herein, such data were collected by coating DLC on the surface of silicon plates. The attachment of mouse cells to the DLC-coated plates was examined by colorimetric cell proliferation assay, and morphological observations were made using a field emission scanning electron microscope. Also, the flat cross section of the cell and plate was obtained by the ion milling method.

Properties and Classification of Diamond-Like Carbon Films.

Diamond-like carbon (DLC) films have been extensively applied in industries owing to their excellent characteristics such as high hardness. In particular, there is a growing demand for their use as protective films for mechanical parts owing to their excellent wear resistance and low friction coefficient. DLC films have been deposited by various methods and many deviate from the DLC regions present in the ternary diagrams proposed for sp3 covalent carbon, sp2 covalent carbon, and hydrogen. Consequently, redefining the DLC region on ternary diagrams using DLC coatings for mechanical and electrical components is urgently required. Therefore, we investigate the sp3 ratio, hydrogen content, and other properties of 74 types of amorphous carbon films and present the classification of amorphous carbon films, including DLC. We measured the sp3 ratios and hydrogen content using near-edge X-ray absorption fine structure and Rutherford backscattering-elastic recoil detection analysis under unified conditions. Amorphous carbon films were widely found with nonuniform distribution. The number of carbon atoms in the sp3 covalent carbon without bonding with hydrogen and the logarithm of the hydrogen content were inversely proportional. Further, we elucidated the DLC regions on the ternary diagram, classified the amorphous carbon films, and summarized the characteristics and applications of each type of DLC.

Surface Reformation of Medical Devices with DLC Coating.

We evaluated the adhesion, friction characteristics, durability against bodily acids, sterilization, cleaning, and anti-reflection performance of diamond-like carbon (DLC) coatings formed as a surface treatment of intracorporeal medical devices. The major coefficients of friction during intubation in a living body in all environments were lower with DLC coatings than with black chrome plating. DLC demonstrated an adhesion of approximately 24 N, which is eight times stronger than that of black chrome plating. DLC-coated samples also showed significant stability without being damaged during acid immersion and high-pressure steam sterilization, as suggested by the results of durability tests. In addition, the coatings remained unpeeled in a usage environment, and there was no change in the anti-reflection performance of the DLC coatings. In summary, DLC coatings are useful for improving intracorporeal device surfaces and extending the lives of medical devices.

Photovoltaic Performance of Inorganic-Organic Heterojunction Solar Cells Using Boron-Doped Silicon Nanoparticles with Controlled Conductance.

We fabricated p-type boron (B)-doped silicon nanoparticles (SiNPs) with a mean diameter of 3.4 nm by a complex chemical reaction of inexpensive pure Si and pure B powders using a combination of ultra-high-speed mixing and thermal annealing techniques. The hole concentration in the p-type SiNPs increased with increasing Si:B blend ratio because of the incorporation of electrically active B atoms into the SiNP core; thus, the conductance of the p-type SiNPs was also enhanced by increasing the mobile carrier concentration. Furthermore, we discuss the effect of the Si:B blend ratio on the photovoltaic performances of the heterojunction solar cells consisting of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS)/p-type SiNPs/n-type Si with a micro-pyramidal structure. The photovoltaic parameters decreased with increasing Si:B blend ratio because of the influence of the insufficient collection rate of the separated charge carriers resulting from reduction in the pn junction region and increase in the carrier recombination. This resulted in the highest power conversion efficiency of 2.57% at a low Si:B blend ratio. These findings are important for designing heterojunction solar cells using p-type SiNPs.

Effects of silica and titanium oxide particles on a human neural stem cell line: morphology, mitochondrial activity, and gene expression of differentiation markers.

Several in vivo studies suggest that nanoparticles (smaller than 100 nm) have the ability to reach the brain tissue. Moreover, some nanoparticles can penetrate into the brains of murine fetuses through the placenta by intravenous administration to pregnant mice. However, it is not clear whether the penetrated nanoparticles affect neurogenesis or brain function. To evaluate its effects on neural stem cells, we assayed a human neural stem cell (hNSCs) line exposed in vitro to three types of silica particles (30 nm, 70 nm, and <44 µm) and two types of titanium oxide particles (80 nm and < 44 µm). Our results show that hNSCs aggregated and exhibited abnormal morphology when exposed to the particles at concentrations = 0.1 mg/mL for 7 days. Moreover, all the particles affected the gene expression of Nestin (stem cell marker) and neurofilament heavy polypeptide (NF-H, neuron marker) at 0.1 mg/mL. In contrast, only 30-nm silica particles at 1.0 mg/mL significantly reduced mitochondrial activity. Notably, 30-nm silica particles exhibited acute membrane permeability at concentrations =62.5 µg/mL in 24 h. Although these concentrations are higher than the expected concentrations of nanoparticles in the brain from in vivo experiments in a short period, these thresholds may indicate the potential toxicity of accumulated particles for long-term usage or continuous exposure.

Size-tunable silicon/iron oxide hybrid nanoparticles with fluorescence, superparamagnetism, and biocompatibility.

Magnetic/fluorescent composite materials have become one of the most important tools in the imaging modality in vivo using magnetic resonance imaging (MRI) monitoring and fluorescence optical imaging. We report herein on a simplified procedure to synthesize hybrid nanoparticles (HNPs) that combine silicon and magnetic iron oxides consisting of magnetite (Fe(3)O(4)) and maghemite (γ-Fe(2)O(3)). Intriguingly, our unique synthetic approach can control magnetic and optical behaviors by reducing the particle size, demonstrating that the HNPs with the mean diameter of 3.0 nm exhibit superparamagnetic behavior and green fluorescence in an aqueous solution, ambient air, and a cellular environment, whereas the HNPs with the mean diameter more than 5.0 nm indicate ferromagnetic behavior without fluorescence. Additionally, both HNPs with different diameters possess excellent magnetic responsivity for external applied magnetic field and good biocompatibility due to the low cytotoxicity. Our biocompatible HNPs with the superparamagnetism can provide an attractive approach for diagnostic imaging system in vivo.

The synthesis and structural characterization of boron-doped silicon-nanocrystals with enhanced electroconductivity.

Boron (B)-doped silicon-nanocrystals (Si-NCs) with wavelength-tunable photoluminescence (PL) properties in the visible region are successfully prepared for the first time, leading to significant enhancement of electroconductivities. The B-doped Si-NCs are prepared on a p-type Si(100) substrate by co-deposition of p-type Si(100) chips/boron chips/silica disk targets. As the number of the B chips used as the target is increased, the amount of doped B content increases gradually. Here the amount of doped B content in the Si-NCs is controlled from 0 to 0.4, 0.7, 2.3 at.%. The B elemental states, compositional ratios, and surface condition of the obtained Si-NCs are fully characterized by high-resolution transmission electron microscopy (HRTEM) observations, micro-Raman scattering spectroscopic analysis, etc. Our B-doped Si-NCs possess both the continuous luminescence property in the visible region and enhanced electroconductivity. The red-shift of the PL peak is confirmed by the increase of the amount of doped B content. This paper should be very important from the viewpoint of application to optoelectronic devices and electroluminescent (EL) displays.

Controlled chemical etching for silicon nanocrystals with wavelength-tunable photoluminescence.

The size of silicon nanocrystals is finely tuned by applying a chemical etching process, leading to differently coloured visible luminescence.

Enhancement of electroluminescent properties in ethanol dispersible nanocrystalline silicon particles.

We have fabricated two kinds of electroluminescent (EL) devices of which the luminous layer differs in order to improve an amount of injected carriers into the nanocrystalline silicon (nc-Si) particles. These EL devices showed red luminescence by the injection of carriers into the nc-Si particles after applying the direct current voltage. A large amount of carriers could be injected in the EL device prepared by the adhesion of ethanol dispersible nc-Si particles onto the dimples of Si substrate. The increase in the amount of injected carriers led to the enhancement of luminescent intensity. These results were achieved by the reduction of oxide layer surrounding nc-Si particles and the use of nc-Si particles without the nonradiative recombination centers (Pb centers).

Luminescent passive-oxidized silicon quantum dots as biological staining labels and their cytotoxicity effects at high concentration.

Semiconductor quantum dots (QDs) hold some advantages over conventional organic fluorescent dyes. Due to these advantages, they are becoming increasingly popular in the field of bioimaging. However, recent work suggests that cadmium based QDs affect cellular activity. As a substitute for cadmium based QDs, we have developed photoluminescent stable silicon quantum dots (Si-QDs) with a passive-oxidation technique. Si-QDs (size: 6.5 ± 1.5 nm) emit green light, and they have been used as biological labels for living cell imaging. In order to determine the minimum concentration for cytotoxicity, we investigated the response of HeLa cells. We have shown that the toxicity of Si-QDs was not observed at 112 µg ml(-1) and that Si-QDs were less toxic than CdSe-QDs at high concentration in mitochondrial assays and with lactate dehydrogenase (LDH) assays. Especially under UV exposure, Si-QDs were more than ten times safer than CdSe-QDs. We suggest that one mechanism for the cytotoxicity is that Si-QDs can generate oxygen radicals and these radicals are associated with membrane damages. This work has demonstrated the suitability of Si-QDs for bioimaging in lower concentration, and their cytotoxicity and one toxicity mechanism at high concentration.

Dissolution effect and cytotoxicity of diamond-like carbon coatings on orthodontic archwires.

Nickel-titanium (NiTi) has been used for implants in orthodontics due to the unique properties such as shape memory effect and superelasticity. However, NiTi alloys are eroded in the oral cavity because they are immersed by saliva with enzymolysis. Their reactions lead corrosion and nickel release into the body. The higher concentrations of Ni release may generate harmful reactions. Ni release causes allergenic, toxic and carcinogenic reactions. It is well known that diamond-like carbon (DLC) films have excellent properties, such as extreme hardness, low friction coefficients, high wear resistance. In addition, DLC film has many other superior properties as a protective coating for biomedical applications such as biocompatibility and chemical inertness. Therefore, DLC film has received enormous attention as a biocompatible coating. In this study, DLC film coated NiTi orthodontic archwires to protect Ni release into the oral cavity. Each wire was immersed in physiological saline at the temperature 37 degrees C for 6 months. The release concentration of Ni ions was detected using microwave induced plasma mass spectrometry (MIP-MS) with the resolution of ppb level. The toxic effect of Ni release was studied the cell growth using squamous carcinoma cells. These cells were seeded in 24 well culture plates and materials were immersed in each well directly. The concentration of Ni ions in the solutions had been reduced one-sixth by DLC films when compared with non-coated wire. This study indicated that DLC films have the protective effect of the diffusion and the non-cytotoxicity in corrosive environment.

Influence of surface electrode on luminescent properties of nanocrystalline silicon electroluminescent device.

We describe the electrical and luminescence properties of nanocrystalline silicon (nc-Si) based red electroluminescent (EL) devices using an indium tin oxide (ITO) and/or gold (Au) films as a surface electrode, and the variation in the transmittance and resistivity of two electrodes with various film thicknesses. The increase in the film thickness from 50 to 200 nm of the ITO electrode led to the lowering of resistivity from 2.0 x 10(-3) to 9.1 x 10(-4) omega cm and almost the same value (83-92%) of transmittance in the red region. On the other hand, the Au electrode was lowered the resistivity from 1.8 x 10(-4) to 1.6 x 10(-5) omega cm and the transmittance in the red region from 42 to 1.8% with increasing the film thickness from 10 to 80 nm. Moreover, the red luminescence from the EL devices using the ITO and/or Au electrodes having thickness of 200 and 10 nm, respectively, obtained by applying the direct current forward voltage above 4.5 and 2.5 V and/or by flowing the forward current density above 53 and 38 mA/cm2, respectively. However, the luminescence intensity of EL device with the ITO electrode strengthened more than about one order of magnitude in comparison to that of the EL device with the Au electrode. This was due to the high value of transmittance in the red region of the ITO electrode. We suggest that the ITO electrode is an optimum surface electrode for the realization of nc-Si based EL device with the high brightness.

Enhancement of green electroluminescence from nanocrystalline silicon by wet and dry processes.

Correlation between defects and luminescence property from electroluminescent (EL) device composed of nanocrystalline silicon (nc-Si) prepared by wet and dry processes such as hydrofluoric (HF) acid solution treatment and annealing have investigated using electron spin resonance and EL measurements. The EL device using HF-treated nc-Si emitted strong red light, because of existence of only P'ce-centers (radiative recombination centers) on the surface vicinity. On the other hand, the EL device using annealed nc-Si above 400 degrees C exhibited green luminescence by the reduction of particle size due to surface oxidation. When the annealing temperature was risen from 400 degrees C up to 600 degrees C, the green luminescence strengthened with increasing the P'ce-centers. These results indicate that the formation of many radiative recombination centers onto the nc-Si surface vicinity lead to the enhancement of green luminescence from the nc-Si based EL device.

Influence of oxidized layer on operating voltage and luminance of nanocrystalline silicon electroluminescent device.

A direct current (DC) operating voltage and luminescence property of red electroluminescent (EL) devices with and/or without a silicon dioxide (SiO2) layer at interface between nanocrystalline Si (nc-Si) region and Si substrate has investigated. The removal of SiO2 layer in the EL device led to the lowering of DC operating voltage from 4.0 up to 2.0 V and the increase of luminescence intensity more than one order of magnitude. The external quantum efficiency of red luminescence from the EL device without the SiO2 layer at the DC operating voltage of 3.0 V was 0.5%. These were realized by the efficient and easy injection of carriers to the radiative recombination centers in the nc-Si region due to the removal of SiO2 layer. These results indicate that the removal of SiO2 layer is drastically improved the DC operating voltage and luminescence intensity for the nc-Si based EL device.

Significant improvement of luminance and stability of a red electroluminescent device using nanocrystalline silicon.

An electroluminescent (EL) device using nanocrystalline silicon (nc-Si) was fabricated by annealing after cosputtering of Si chips and silicon dioxide target and subsequent hydrofluoric acid solution treatment. The device emitted a red light with a peak at 670 nm by applying a low direct current (DC) operating voltage of 4.5 V. The external quantum efficiency (EQE) of red luminescence at 4.5 V was 0.35%. Moreover, the intensity of red luminescence was very stable for an operating time of 15000 min. These results are a strong indication that the HF-treated device can be adapted to future light-related devices.

Fabrication of highly efficient full-color electroluminescent device composed of nanocrystalline silicon.

We fabricated a highly-efficient full-color electroluminescent device composed of nanocrystalline silicon (nc-Si). High luminance red, green and blue luminescence from the device was achieved by using hydrofluoric acid solution and oxidation techniques, because these techniques lead to reduction of both nc-Si size and P(b)-center on the surface, which is related closely to luminescent color and luminance, respectively. Moreover, direct current (DC) operating voltage on red/green/blue light emission of the device was realized at a relative low value below 10.0 V by controlling the thickness of the oxidized layer on the nc-Si surface. These results are a strong indication that the device developed in this study can be adapted to future flat panel display and illumination fields.

Investigating the functionality of diamond-like carbon films on an artificial heart diaphragm.

In this study, the authors used diamond-like carbon film to coat the ellipsoidal diaphragm (polyurethane elastomer) of artificial hearts. The purpose of such coatings is to prevent the penetration of hydraulic silicone oil and blood through the diaphragm. To attach diamond-like carbon film uniformly on the diaphragm, the authors developed a special electrode. In estimating the uniformity of the diamond-like carbon film, the thickness was measured using a scanning electron microscope, and the characteristics of the diamond-like carbon film was investigated using infrared spectroscopy, Ar-laser Raman spectrophotometer, and x-ray photoelectron spectrometer. Also, to estimate the penetration of silicone oil through the diaphragm, in vitro testing was operated by alternating the pressure of silicone oil for 20 days. The authors were able to successfully attach uniform deposition of diamond-like carbon film on the ellipsoidal diaphragm. In this in vitro test, diamond-like carbon film was proven to have good stability. The amount of silicone oil penetration was improved by one-third using the diamond-like carbon film coating compared with an uncoated diaphragm. It is expected that through the use of the diamond-like carbon film, the dynamic compatibility of an artificial heart diaphragm will increase.