Inter-rod Spacing Research Articles

F-Doped Micropore/Nanorod Hierarchically Patterned Coatings for Improving Antibacterial and Osteogenic Activities of Bone Implants in Bacteria-Infected Cases.

Advanced titanium (Ti) based bone implants with antibacterial and osteogenic activities are extremely needed in clinics. Herein, biomimetic hierarchical micropore/nanorod patterned coatings (MNRs) on Ti were developed, in which the nanorods revealed a fixed interrod spacing of about 70 nm and consisted of fluorine (F) incorporated Ca9Sr1(PO4)6(OH)2 (Sr1-HA, strontium containing hydroxyapatite) with the fixed Sr but different F content. The incorporation of F was determined by XRD, FTTR, and TEM, revealing the substitution of OH- in Sr1-HA to F-. The topography, surface roughness, and hydrophilic nature of MNRs were not apparently affected by the incorporation of F. The antibacterial and osteogenic activities of MNRs were assessed in vitro and in a bacterial-infected rabbit model. Both the in vitro and in vivo results showed that F-free and ∼1 wt % F doped MNR significantly promoted osteogenic activity compared to that of Ti but showed a lack of antibacterial activity. The incorporation of a higher dose of F led to the significantly improved antibacterial and osteogenic activities, and the effects were related to the incorporated F dose. In total, compared to F-free, ∼1, ∼2, and ∼7 wt % F doped MNRs, ∼5 wt % F doped MNR significantly enhanced antibacterial and osteogenic activities, especially new bone formation and osseointegration in the bacteria-infected case, showing a high potential as the next generation of advanced bone implant.

The osteogenic capacity of biomimetic hierarchical micropore/nanorod-patterned Sr-HA coatings with different interrod spacings

Advanced titanium based bone implant with fast established, rigid and stable osseointegration is stringently needed in clinic. Here the hierarchical micropore/nanorod-patterned strontium doped hydroxyapatite (Ca9Sr1(PO4)6(OH)2, Sr1-HA) coatings (MNRs) with different interrod spacings varying from about 300 to 33nm were developed. MNRs showed dramatically differential biological performance closely related to the interrod spacing. Compared to micropore/nanogranule-patterned Sr1-HA coating (MNG), MNRs with an interrod spacing of larger than 137nm resulted in inhibited in vitro mesenchymal stem cell functions and in vivo osseointegration, while those of smaller than 96nm gave rise to dramatically enhanced the biological effect, especially those of mean 67nm displayed the best effect. The differential biological effect of MNRs was related to their modulation on the focal adhesion mediated mechanotransduction. These results suggest that MNRs with a mean interrod spacing of 67nm may give rise to an advanced implant of improved clinical performance.

Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies.

The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth. Sound maxillary first premolars of 15-50-year-old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter-rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM). In white tooth, the inter-rod spaces were observed at the width of about 0.1 μm, while in yellow tooth, the inter-rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter-rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter-rod spaces. The generation of particles in the tooth enamel inter-rod spaces was considered to be caused by the long-time progression of calcification. These results suggested that the change in fine structure, filling in inter-rod spaces of tooth enamel, was related to progression of calcification in the inter-rod spaces with advancing age and one of the factors of yellowness of human tooth.

Control of charge dynamics by blending ZnO nanoparticles with poly(3-hexylthiophene) for efficient hybrid ZnO nanorods/polymer solar cells

Photovoltaic performances of hybrid ZnO nanorods/polymer solar cells have been improved by controlling their charge dynamics through addition of ZnO nanoparticles into poly(3-hexylthiophene) (P3HT) photoactive layer. The inter-rod space of ZnO nanorod substrates is completely filled with the solution-processed ZnO nanoparticles/P3HT blends, forming homogeneous junction among the components. The optimum PCE of 1.020 % has been achieved from the device with 13 vol % ZnO nanoparticles loaded. The enhancement in external quantum efficiency has been also observed, indicating the improved excitons separation at the ZnO/P3HT interface. The information on charge dynamics in the system has been investigated by electrochemical impedance spectroscopy. It has been found that the additional space-charge layer formed at the ZnO nanoparticles–contact electrode interface is a reason behind the improvement of open-circuit voltage. Moreover, the formation of ZnO nanoparticles domain extending across the active layer and the percolation path for charge carriers promotes charge transport by reducing transit time of the carriers, extending charge carrier lifetime and enhancing the charge transfer at the ZnO/P3HT interface. Interestingly, it has been found that charge transport in the devices does not limit the device performances, even for the 400-nm-thick active layer.

Controlled growth of ZnO nanorod arrays via wet chemical route for NO2 gas sensor applications

Metal oxide gas sensors are promising devices that are widely used to detect various gases at moderate temperatures. In this study, nitrogen di-oxide (NO2) sensors were fabricated using zinc oxide (ZnO) nanorod arrays. ZnO nanorod arrays (ZNAs) with various rod lengths were deposited using a wet chemical route with zinc acetate as a precursor. The structural and surface morphological properties of the ZNAs were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD patterns showed ZNAs with wurtzite crystal structures that were preferentially oriented in the (002) direction. The intensity of the (002) plane was found to vary with the length of the nanorods. FESEM micrographs show that the ZNAs had a vertical alignment perpendicular to the substrate, and the diameter and length of the nanorods increased as the nanorod deposition time was increased. The gas sensing performance was studied as a function of the nanorod length, operating temperature, time and gas concentration. The length and inter-rod space was observed to play a crucial role in determining the gas sensing performance of the devices. ZNA gas sensors deposited for 9h and operating at a temperature of 175°C were able to detect NO2 at a concentration of 100ppm with a high sensitivity of 3100%.

Discontinuous reactions in melt-spun Cu–10 at. %Co alloys and their effect on magnetic anisotropy

The occurrence of discontinuous reactions under isothermal annealing of melt-spun Cu–10 at. % Co alloys, consisting of ribbons (20 µm thick) with columnar grains in the as-solidified state, has been investigated. The microstructure of the ribbons for different annealing temperatures (723–923 K) and annealing times (5–60 min) was determined by transmission electron microscopy, including analysis by energy-dispersive X-ray spectroscopy. Magnetic properties at room temperature were measured by means of hysteresis curve measurements in a vibrating sample magnetometer. Different types of microstructure were observed within grains and at grain boundaries. The spinodal decomposition microstructure was observed during the early stages of annealing for all annealing temperatures. Spherical precipitates grew from the modulated structure at a later stage, forming homogenous distributions throughout the grains. Heterogeneous distributions of incoherent precipitates formed at T > 873 K. As result of discontinuous precipitation, all grain boundaries exhibited arrays of rod-like Co precipitates with diameters and inter-rod spacing of few nanometers. The coarsening of discontinuous precipitates is attributed to a grain boundary-controlled phenomenon, called discontinuous coarsening (DC). The columnar morphology of the grains in the as-solidified alloy was connected with Co rods that were primarily oriented along the ribbon plane. This structure is connected with magnetic anisotropy, which is later weakened by DC. These results elucidate the unusual magnetic behavior of melt-spun Cu–Co alloys and provide a key to understanding their higher magnetoresistance in comparison with other heterogeneous systems.

Direct role of interrod spacing in mediating cell adhesion on Sr-HA nanorod-patterned coatings.

The process in which nanostructured surfaces mediate cell adhesion is not well understood, and may be indirect (via protein adsorption) or direct. We prepared Sr-doped hydroxyapatite (Sr1-HA) 3D nanorods (with interrod spacing of 67.3±3.8, 95.7±4.2, and 136.8±8.7 nm) and 2D nanogranulate patterned coatings on titanium. Employing the coatings under the same surface chemistry and roughness, we investigated the indirect/direct role of Sr1-HA nanotopographies in the regulation of osteoblast adhesion in both serum-free and serum-containing Dulbecco’s Modified Eagle/Ham’s Medium. The results reveal that the number of adherent cells, cell-secreted anchoring proteins (fibronectin, vitronectin, and collagen), vinculin and focal adhesion kinase (FAK) denoted focal adhesion (FA) contact, and gene expression of vinculin, FAK, and integrin subunits (α2, α5, αv, β1, and β3), undergo significant changes in the inter-nanorod spacing and dimensionality of Sr1-HA nanotopographies in the absence of serum; they are significantly enhanced on the <96 nm spaced nanorods and more pronounced with decreasing interrod spacing. However, they are inhibited on the >96 nm spaced nanorods compared to nanogranulated 2D topography. Although the adsorption of fibronectin and vitronectin from serum are higher on 136.8±8.7 nm spaced nanorod patterned topography than nanogranulated topography, cell adhesion is inhibited on the former compared to the latter in the presence of serum, further suggesting that reduced cell adhesion is independent of protein adsorption. It is clearly indicated that 3D nanotopography can directly modulate cell adhesion by regulating integrins, which subsequently mediate anchoring proteins’ secretion and FA formation rather than via protein adsorption.

Tuneable magneto-optical metamaterials based on photonic resonances in nickel nanorod arrays

We investigate the magneto-optical properties of a nanostructured metamaterial comprised of arrays of nickel nanorods embedded in an anodized aluminum oxide template. The rods are grown using a self-assembly bottom-up technique that provides a uniform, quasi-hexagonal array over a large area, quickly and at low cost. The tuneability of the magneto-optic response of the material is investigated by varying the nanorod dimensions: diameter, length and inter-rod spacing as well as the overall thickness of the template. It is demonstrated that the system acts as a sub-wavelength light trap with enhanced magneto-optical properties occurring at reflectivity minima corresponding to photonic resonances of the metamaterial. Changes in dimensions of the nickel rods on the order of tens of nanometers cause a spectral blue-shift in the peak magneto-optical response of 270 nm in the visible range. A plasmonic enhancement is also observed at lower wavelengths, which becomes increasingly damped with larger diameters and increased volume fraction of nickel inclusions. This type of structure has potential applications in high density magneto-optical data storage (up to 1011–12 rods per square inch), ultrafast magneto-plasmonic switching and optical components for telecommunications.

Mechanism of Gravity Effect on Solidification Microstructure of Eutectic Alloy

The influence of gravity on the solidification microstructure of Al–Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was always larger under microgravity (μg) than those under normal gravity (1g). Moreover, with increasing growth rate, the spacing difference between 1g samples and μg samples reduced progressively. Based on the experimental results and analysis, a physical model was proposed to describe the effect of gravity on the solidification process of eutectic alloy.

Regulation of Osteoblast Proliferation and Differentiation by Interrod Spacing of Sr-HA Nanorods on Microporous Titania Coatings

Strontium-doped hydroxyapatite (Ca9Sr1(PO4)6(OH)2, Sr1-HA) nanorods with different lateral spacing (e.g., interrod spacing) values (67.3 ± 3.8, 95.7 ± 4.2, and 136.8 ± 8.7 nm) and nanogranulates were grown on microarc-oxidized microporous TiO2, respectively, to form multilayer coatings. The coatings reveal two kinds of micro/nanoscaled hierarchical surfaces with a similar microscale roughness, e.g., nanogranulated 2D pattern and nanorod-shaped 3D pattern in nanotopography. When hFOB1.19 cells are employed, the proliferation and differentiation of osteoblasts on the coatings were evaluated by examining MTT assay, expressions of osteogenesis-related genes [alkaline phosphatase (ALP), runt-related transcription factor 2, osterix, osteopontin (OPN), osteocalcin (OCN), and collagen I (Col-I)], ALP activity, contents of intracellular Ca(2+), Col-I, OPN, and OCN, extracellular collagen secretion, and extracellular matrix mineralization. The results reveal that the proliferation and differentiation of osteoblasts can be directly regulated by the interrod spacing of the Sr1-HA nanorods, which are significantly enhanced on the nanorod-shaped 3D patterns with interrod spacing smaller than 96 nm and more pronounced with decreasing the interrod spacing but inhibited on the nanorods with spacing larger than 96 nm compared to the nanogranulated 2D pattern. The difference in the cellular activity is found to be related with the intracellular Ca(2+) concentrations, which are regulated by variation of the surface topology of Sr1-HA crystals. Our work provides insight to the surface structural design of a biomedical implant favoring osteointegration.

Tuning surface plasmons in nanorod arrays with ultrasmall spacing

In this work, we first investigate the optical properties of nanorod arrays with normal inter-rod spacing (&gt;100 nm) and realize the tuning of nanorod localized surface plasma resonance (LSPR) by changing array parameters (e.g., periodicity). Then we filter our individual colors in the visible range using nanorod arrays with ultrasmall inter-rod spacing and ultrahigh density fabricated by electron beam lithography (EBL) and ion etching. The functional nanorod arrays developed in this work are compatible with current digital light processing technique, enabling screen with ultrasmall pixels which can find extensive applications in display and imaging.

Highly Ordered Fe–Au Heterostructured Nanorod Arrays and Their Exceptional Near-Infrared Plasmonic Signature

The potential of highly ordered array nanostructures in sensing applications is well recognized, particularly with the ability to define the structural composition and arrangement of the individual nanorods accurately. The use of heterogeneous nanostructures generates an additional degree of freedom, which can be used to tailor the optical response of such arrays. In this article, we report on the fabrication and characterization of well-defined Fe-Au bisegmented nanorod arrays in a repeating hexagonal arrangement. Through an asymmetric etching method, free-standing Fe-Au nanorod arrays on a gold-coated substrate were produced with an inter-rod spacing of 26 nm. This separation distance renders the array capable of sustaining resonant electromagnetic wave coupling between individual rods. Owing to this coupling, the subwavelength arrangement, and the structural heterogeneity, the nanorod arrays exhibit unique plasmonic responses in the near-infrared (NIR) range. Enhanced sensitivity in this spectral region has not been identified for gold-only nanorods of equivalent dimensions. The NIR response offers confirmation of the potential of these highly ordered, high-density arrays for biomedical relevant applications, such as subcutaneous spectroscopy and biosensing.

Effect of growth rate on rod spacing and undercooling of Bridgman-grown Si–TaSi2 eutectic in situ composite

Directionally solidified Si–6wt.%TaSi2 eutectic alloy has been studied to characterize the variation of inter-rod spacing at different growth rates (V=6–200μm/s) with a constant temperature gradient (210K/cm). Statistical distributions of inter-rod spacings at each solidification rate are determined. It is confirmed that the relationship between inter-rod spacing and solidification rate obeys the Magnin–Kurz model, and the theoretical value of λa2V=5435.6μm3/s (λa is the average inter-rod spacing) approximately equals to the experimental value of λa2V1.06=5343.6μm3.06/s. For the Si–TaSi2 system, the operating parameter ϕ is a function of the solidification rate due to the transition of the TaSi2 phase from facet to nonfacet, and as the solidification rate increases the kinetic undercooling cannot be ignored.

Effect of Inter-Rod Coupling on 1-3 Piezocomposite High-Power Ultrasonic Transducers

Efficiency is a critical performance for a high-power ultrasonic transducer composed of 1-3 piezocomposites and geometric parameters of the composites can influence the efficiency of the transducer. The effect of inter-rod responses in the composite matrix on the efficiency was experimentally investigated in this study. For analyses, four PZT4-epoxy composite ultrasonic transducers with various volume fractions and inter-rod spacing were fabricated in-house. The experimental results demonstrated that the inter-rod coupling of the 0.1-mm spacing could significantly degrade the efficiency of the composite probe at about 1.0 MHz resonance since the 0.1-mm spacing between PZT4 rods was so small as to cause a high interference. At the same volume fraction, the transducer engineer should take the inter-rod coupling into account for the design of the high-power ultrasonic transducer.

Electrophoretic Deposition of Poly(3-decylthiophene) onto Gold-Mounted Cadmium Selenide Nanorods

Molecular mechanisms of electrophoretic deposition (EPD) of poly(3-decylthiophene) (P3DT) molecules onto vertically aligned cadmium selenide arrays have been studied using large-scale, nonequilibrium molecular dynamics (MD), in the absence and presence of static external electric fields. The field application and larger polymer charges accelerated EPD. Placement of multiple polymers at the same lateral displacement from the surface reduced average deposition times due to "crowding", giving monolayer coverage. These findings were used to develop and validate Brownian dynamics simulations of multilayer polymer EPD in scaled-up systems with larger inter-rod spacings, presenting a generalized picture in qualitative agreement with random sequential adsorption.

Wetting of nanostructured germanium electrodes by polyethylene oxide

One of the crucial factors that affects the performance of solid electrolyte – lithium-ion batteries is the electrode/electrolyte contact characteristics. Better contact implies greater ion transfer efficiency, leading to improved charge/discharge characteristics, and higher-power densities. In this study, the authors investigate the contact characteristics, viz. wettability, of germanium nanorod thin films initially by water, followed by polyethylene oxide (PEO)/water solution and PEO melt. The authors demonstrate that the electrode surface is hydrophilic, and considerably wettable, as evidenced by the contact angle for PEO/water solution and PEO melt, which are both below 25°. Electron microscopy was used to investigate the electrode/electrolyte contact area, and our results showed that PEO melt efficiently penetrates the inter-rod space, which is a further indication of considerable increase in the contact area.

CdSe Nanorods Dominate Photocurrent of Hybrid CdSe−P3HT Photovoltaic Cell

Photovoltaic devices based on organic semiconductors require charge-separating networks (bulk heterojunctions) for optimal performance. Here we report on the fabrication of organic-inorganic photovoltaic devices with tailored (n-type) CdSe nanorod arrays aligned perpendicularly to the substrate. The nanorod lengths varied from 58 ± 12 to 721 ± 15 nm, while the diameters and inter-rod spacings were kept constant at 89.5 ± 7.5 and 41.3 ± 9.9 nm, respectively. Short-circuit densities improved linearly with nanorod length, resulting in power conversion efficiencies of up to 1.38% for cells with nanorods 612 ± 46 nm long. Notably, the cell's efficiency was dominated by exciton generation in the CdSe nanorods.

Assembly of Nanorods into Designer Superstructures: The Role of Templating, Capillary Forces, Adhesion, and Polymer Hydration

The assembly mechanism by which hundreds of thousands of two-segment gold-polypyrrole nanorods are assembled into kinetically controlled shape-directed superstructures is examined to predict the range of nanoparticle sizes and materials that can be utilized in their formation. Four processes are responsible for assembly: templating, capillary force assembly, adhesion, and polymer hydration. It is shown that templating, where rods are prepositioned for assembly, is scale invariant and that the energy-minimized state after this step is highly disordered. In addition, we predict that superstructures can be made independently from patterns of rods separated by a distance as small as six times the inter-rod spacing. Both modeling and experiment show that adhesion and polymer dehydration, which induces curvature in the superstructures, are applicable to other materials. However, the high surface energy and low elastic modulus of polypyrrole are advantageous toward generating three-dimensional structures, inducing curvature at gold/polypyrrole length ratios as large as 7:1.

Analysis of the high growth-rate transition in Al–Si eutectic solidification

The local solidification conditions and mechanisms associated with the flake-to-fiber growth mode transition in Al–Si eutectic alloys are investigated here using Bridgman-type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections, showing three-dimensional microstructural features. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake-to-fiber transition, whereas traditional spacing parameters are not effective indicators of the transition. For a thermal gradient of 7–14 K/mm, the transition was found to occur in two stages, appearing over velocity regimes from 0.10 to 0.50 mm/s and from 0.50 to 0.95 mm/s. The initial stage is dominated by in-plane plate breakup and rod formation within the plane of the plate, whereas the second stage is characterized by the onset of out-of-plane silicon rod growth, leading to the formation of an irregular fibrous structure. The boundary between the two stages is marked by widespread fibrous growth and the disappearance of the remnant flake structure, indicating a transition in the structural feature that governs the relevant diffusion length, from inter-flake spacing to inter-rod spacing.

Effects of high magnetic fields on solidified structures of Mn-90.4 wt% Sb hypoeutectic alloy

Mn-90.4 wt% Sb alloy specimens were solidified under both uniform magnetic field and magnetic field gradient conditions. The solidification behavior was examined to elucidate the effects of high magnetic fields on the solidified structure evolution of this hypoeutectic alloy. The macrostructures on the longitudinal section of the alloys were investigated by optical microscopy and x-ray diffraction (XRD). The volume fraction of primary MnSb phases and the interrod spacing of the eutectic were measured by metallographic analysis. It was found that the segregation of the primary MnSb particles at the certain regions of the specimens occurred under the influence of high magnetic field gradients. The MnSb phases obtained under magnetic fields were oriented with their (h0 l) planes along the direction of the magnetic field. Both the volume fraction of primary MnSb phases and the interrod spacing of the eutectic were decreased upon the application of the high magnetic fields.