Inter-rod Spacing Research Articles

High-Resolution Characterization of Enamel Remineralization Using Time-of-Flight Secondary Ion Mass Spectrometry and Electron Microscopy

Introduction: The aim of this in vitro study was to assess the suitability of high-resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS) for visualizing cross-sectional changes in human enamel microstructure and chemical composition during treatment and remineralization cycling of artificially generated caries lesions underneath an artificial plaque. Methods: Treatments consisted of exposure to twice daily toothpaste/water slurries prepared from 0, 1,100, and 5,000 μg/g fluoride (F) NaF/silica toothpastes. In addition, treatments with slurries prepared from 1,100 μg/g F SnF2/silica toothpastes were done using 44Ca in the remineralization solution to allow for differentiation of newly formed mineral and exploration of incorporated metal dopants using ToF-SIMS. Complementary microhardness, scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM) investigations were performed on enamel cross sections. Results: HR-TEM was used for the first time to determine the change in crystallinity during remineralization revealing distinct microstructural zones within one lesion. Chemical mapping using ToF-SIMS demonstrated that the distribution of F, while observed primarily in the new mineral phase, was widespread throughout the lesion with 44Ca substantially limited to the remineralizing mineral. Both penetrated the inter-rod spaces of the sound enamel illustrating how acid damage propagates into the native mineral as the caries lesion deepens. HR-TEM examination revealed different regions within the lesion characterized by distinct micro- and ultrastructures. Importantly, HR-TEM revealed a return of crystallinity following remineralization. F dose-response observations verified the ability of these high-resolution techniques to differentiate remineralization efficacy. Conclusion: The collective results provided new insights such as the visualization of F or calcium penetration pathways, as well as new tools to study the caries process.

Pressure drag reduction via imposition of spanwise wall oscillations on a rough wall

The present study tests the efficacy of the well-known viscous drag reduction strategy of imposing spanwise wall oscillations to reduce pressure drag contributions in transitional and fully rough turbulent wall flow. This is achieved by conducting a series of direct numerical simulations of a turbulent flow over two-dimensional (spanwise-aligned) semi-cylindrical rods, placed periodically along the streamwise direction with varying streamwise spacing. Surface oscillations, imposed at fixed viscous-scaled actuation parameters optimum for smooth wall drag reduction, are found to yield substantial drag reduction ( $\gtrsim$ 25 %) for all the rough wall cases, maintained at matched roughness Reynolds numbers. While the total drag reduction is due to a drop in both viscous and pressure drag in the case of transitionally rough flow (i.e. with large inter-rod spacing), it is associated solely with pressure drag reduction for the fully rough cases (i.e. with small inter-rod spacing), with the latter being reported for the first time. The study finds that pressure drag reduction in all cases is caused by the attenuation of the vortex shedding activity in the roughness wake, in response to wall oscillation frequencies that are of the same order as the vortex shedding frequencies. Contrary to speculations in the literature, this study confirms that the mechanism behind pressure drag reduction, achieved via imposition of spanwise oscillations, is independent of the viscous drag reduction. This mechanism is responsible for weakening of the Reynolds stresses and increase in base pressure in the roughness wake, explaining the pressure drag reduction observed by past studies, across varying roughness heights and geometries.

HISTOLOGICAL AND MORPHOMETRIC STUDIES OF BONE TISSUE AUTOGRAFTS FROM INTRAORAL AND EXTRAORAL DONOR ZONES

Major research carried out in modern dentistry and maxillofacial surgery is commonly focused on long-term and stable results for implant rehabilitation of jaw defects and deformities in patients with bone and soft tissue losses at the site of planned implantation. Various osteoplastic materials, donor or the patient’s own bone, tissue-engineering and cellular products are common in clinical medicine, since guided regeneration can help not only recover the volume of bone tissue once lost, yet also ensure an outcome acceptable from both functional and aesthetic view. Guided bone regeneration employs methods of regenerative medicine and tissue engineering, with transplantation of native bone tissue and cell transplants, as well as various osteoplastic materials with osteoinductive and osteoconductive properties. In order to compare the structure of intact bone tissue obtained from intraoral and extraoral donor zones, histological and morphometric studies of bone autografts in 4 certified male cadavers with intact dentition were carried out. The results of histological studies in bone tissue autografts from intraoral and extraoral donor zones revealed that the highest density of bone rods could be observed in biopsies taken from the mandible outer oblique line area and chin symphysis. Whereas the lowest rate of the said factor we observed in the biopsies obtained from the iliac crest area. The highest rate of the inter-rod girder space was found in the area of the iliac crest, and the minimal – in biopsies from the parietal bone. The highest bone vascularization level was identified at the iliac crest and the parietal bone, while its lowest levels were seen in biopsies taken from the area of the mandible outer oblique line. The density of cellular elements was found to be highest at the iliac crest. The lowest density level was registered in biopsies from the area of the mandible outer oblique line. The high rates of cellular elements in autografts from the iliac crest area can be accounted for by the predominance of spongy substance over cortical, while in bone biopsies taken from the mandible outer oblique line, chin symphysis, maxillary tuberosity and parietal bone, the share of cellular elements failed to exceed 27% within the total data set. This points at the predominance of cortical rather than spongy substance. In reconstructive bone plastic surgery for augmentation of the maxillary alveolar process and the mandible alveolar part with significant atrophy, it is reasonable to use autogenous transplants taken from intraoral donor zones. The autogenous transplants have cortical morphology and embryological origin similar to the jaw bones. Bone blocks from the donor zones of the mandible outer oblique line, the chin symphysis and the maxillary tuberosity have the highest density of the bone cortical substance and the duly sufficient amount of spongy substance.

Droplet Size-Assisted Polysiloxane Architecting

(Super)antiwetting shielding around engineering materials and protecting them against harsh environmental conditions have been achieved via growing various geometry polysiloxane (or silicone) patterns around them by using a droplet-assisted growth method, where the polymerization takes place inside of the water droplets acting as reaction vessels. The size and distribution of these reaction vessels are the main factors in making different geometry silicone patterns; however, very little is known about the fate of these droplets throughout the polymerization. Here, we propose keeping the relative humidity (% RH) inside the reactor stable throughout the polymerization as a new coating parameter to force the size of the reaction vessel water droplets to be the same for building simply shaped silicone rods with controlled geometry and distribution. In this manner, we grew simple geometry cylindric microrods on surfaces and could tune their length, diameter, inter-rod spacing, and thus the (super)hydrophobicity. Here, we also demonstrate that with changes in the amplitude and stability of the % RH, it is possible to fabricate different (super)hydrophobic nanograsses, conical silicone microrods, and isotropic silicone nanofilaments. The proposed new way of tuning initial and in situ reaction vessel droplet size can be used as a single factor to formulate different geometry silicone patterns with tunable dimensions, leading to different roughness and hydrophobicity. To a certain extent, the droplet size-assisted silicone shaping in this work provides a new way to control the length, diameter, morphology, inter-rod spacing, and thus the (super)hydrophobicity of the silicone patterns, especially those in the shape of simple cylindrical microrods. This control over silicone architecting will help to prepare new (super)hydrophobic coatings with more controlled morphology and thus wettability; on the contrary, it will support surface scientists modeling the connection between surface geometry and (super)antiwetting of such irregular pillared surfaces that remain elusive.

Molecular mechanisms of interrod spacing-mediated osseointegration via modulating inflammatory response and osteogenic differentiation

Osseointegration is initiated by immune cell-derived inflammatory responses to the surfaces of implanted materials. However, the bio-molecular mechanisms by which nanotopographic features of implant surfaces immunomodulate osseointegration remain to be clarified. To this end, herein, three kinds of TiO2 nanorod-like arrays on Ti with the interrod spacing of ∼0, 45 and 85 nm, termed as S0, S45 and S85, respectively, were hydrothermally grown, and their actions on the polarization of macrophages (MΦs) and MΦs-mediated contact osteogenesis of bone marrow-derived mesenchymal stromal cells (BMSCs) were explored, especially the involved signaling pathways. Compared to pure Ti (namely P-Ti), the nanorods-arrayed Ti activated FG-integrin αMβ2-IKK-NF-κB signaling pathway in the adhered MΦs at initial 6 h while FN-integrin α5β1-PI3K-Akt1 pathway since 24 h, accelerating the transition of MΦs from pro-inflammatory (M1) to anti-inflammatory (M2) phenotype. With the cytokines secreted by M2 cells, the coatings activated the BMP2-TGFβ1-SMAD signaling pathway to enhance osteogenic differentiation of the recruited BMSCs in vitro. Also, the nanorods-coated Ti induced a proper immune microenvironment and accelerated bone apposition in rabbit tibia marrow cavities in vivo. Furthermore, owing to the favorable capacity of osteoimmunomodulation, the ∼85 nm spaced nanorods-arrayed coating exhibited satisfactorily in orchestrating osteogenic differentiation in vitro and in vivo. This work provides insights into nanotopographic features of implant surfaces immunomodulating contact osteogenesis.

Immunomodulation and osseointegration activities of Na2TiO3 nanorods-arrayed coatings doped with different Sr content

To endow Ti-based orthopedic implants immunomodulatory capability and thus enhanced osseointegration, different amounts of Sr are doped in Na2TiO3 nanorods in the arrays with identical nanotopographic parameters (rod diameter, length and inter-rod spacing) by substitution of Na+ using hydrothermal treatment. The obtained arrays are denoted as STSr2, STSr4, and STSr7, where the arabic numbers indicate the incorporating amounts of Sr in Na2TiO3. The modulation effects of the Sr-doped nanorods arrays on macrophage polarization and osteogenetic functions of osteoblasts are investigated, together with the array without Sr (ST). Moreover, osseointegration of these arrays are also assayed in rat femoral condyles. Sr-doped nanorods arrays accelerate M1 (pro-inflammatory phenotype)-to-M2 (anti-inflammatory phenotype) transformation of the adhered macrophages, enhancing secretion of pro-osteogenetic cytokines and growth factors (TGF-β1 and BMP2), moreover, the Sr doped arrays directly enhance osteogenetic functions of osteoblasts. The enhancement of paracrine of M2 macrophages and osteogenetic function of osteoblasts is promoted with the increase of Sr incorporating amounts. Consequently, Sr doped arrays show significantly enhanced osseointegration in vivo compared to ST, and STSr7 exhibits the best performance. Our work sheds a new light on the design of surface chemical components and structures for orthopedic implants to enhance their osseointegration.

Interrod spacing dependent angiogenesis and osseointegration of Na2TiO3 nanorods-patterned arrays via immunoregulation

Nanorods-arrayed coatings show topographical parameters-dependent immunomodulation that plays a key role in angiogenesis and consequent osseoinegration, while immunomodulation by interrod spacing, as a solely altered topographic parameter of an array, has not been clarified yet. In this context, four kinds of nanorods-arrayed coatings, appearing similar surface roughness and hydrophilia, were hydrothermally grown on Ti. The coatings comprise a bilayer structure with compact nanogranular Na2TiO3 as an inner layer and Na2TiO3 nanorods-patterned array as an outer layer. The nanorods in the coatings exhibit identical rod diameter and length but different interrod spacing values of ~ 45, 75, 140, and 245 nm, respectively. Compared to Ti, the arrayed coatings promote adhesion and filopodia formation of macrophages to accelarate their transformation from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype. Moreover, the accelaration is more pronounced by the coatings with nanoscale interrod spacing (especially ~ 75 nm) compared to those with submicro-scale spacing. The rapid phenotypic switch of macrophages on the arrayed coatings trigers the increase in their secretion of pro-angiogenic factors, including PDGF-BB, ANG1 and SDF-1, to enhance recruitment and angiogenesis of human umbilical vein endothelial cells (HUVECs) in co-culture condition, and the enhancment is the most pronounced for HUVECs in response to macrophages on ~ 75 nm spaced nanorods-arrayed coating. Owing to the favorable immune microenvironment induced by the coating and consequently enhanced angiogenesis, ~ 75 nm spaced nanorods-arrayed coating exhibits the best osseoinetegration in rat femoral condyles. Our work provides insights into the surface structural design of an orthopedic implant favoring osseointegration.

Ezh2 knockout in mesenchymal cells causes enamel hyper-mineralization

Enhancer of zeste homolog 2 (EZH2) is the catalytic core of polycomb repressive complex 2 (PRC2), which primarily methylates lysine 27 on histone H3 (H2K27me3), generating transcriptionally suppressed heterochromatin. Since EZH2 suppresses expression of genes involved in dentin formation, we examined the role of EZH2 in tooth development. Intriguingly, microCT analysis of teeth from mice with conditional Ezh2 knockout in uncommitted mesenchymal cells showed hyper-mineralization of enamel, which is produced by the epithelial-lineage cells, ameloblasts. Scanning electron microscopy analysis and nano-indentation of the incisor enamel from knockout mice revealed smaller inter-rod spaces and higher hardness compared to wild type enamel, respectively. Interestingly, expression of the calcium channel subunit gene, Orai2, was decreased compared to its competitor, Orai1, both in knockout mouse incisors and the ex vivo culture of ameloblasts with the surrounding tissues under EZH2 inhibition. Moreover, histological analysis of incisor from knockout mice showed decreased ameloblastin and expedited KLK4 expression in the ameloblasts. These observations suggest that EZH2 depletion in dental mesenchymal cells reduces enamel matrix formation and increases enamel protease activity from ameloblasts, resulting in enamel hyper-mineralization. This study demonstrates the significant role of the suppressive H3K27me3 mark for heterochromatin on enamel formation.

(Invited) Solution-Processed Reorganization of Semiconductor Nanocrystals in Thin Films

Colloidal nanocrystals (NCs) have been attracted because of their strongly size-dependent luminous characteristics and solution processability. As prepared colloidal NCs covered with some bulky and long-chain organic ligands such as oleic acid, oleylamine (OAm), trioctylphosphine oxide, and so on are mostly dispersed in some solvents such as hexane, toluene, and so on. After preparation of thin films from the dispersed solutions of NCs, reduced inter NC distance (viz. NCs coming closer) with highly ordered alignment will lead to enhanced electronic coupling between adjacent NCs resulting in better wave function overlap and charge transport of the conducting solid materials.In this context, remarkable improvement of the alignment of the particles through solution-processed reorganization of AgInS2 quantum dots (QDs) covered with OAm by cast method was confirmed by bright-field TEM observation [1,2]. The interplanar spacing of the QDs was 0.33 nm, which corresponds to (112) crystal planes of the tetragonal phase of AgInS2.On the other hand, it was found that PbS colloidal QDs can be packed densely and infiltrated efficiently into the interrod space of vertically aligned ZnO nanowire arrays through convective deposition method, which is one of the meniscus coating techniques [3] as compared with spin-coating process, which brings many cracks and voids in the obtained thin films. As a result, a record power conversion efficiency of 9.92% has been demonstrated for ordered bulk heterojunction structured solar cells that are compatible with low-temperature and scalable manufacturing processes.While comparisons of perovskite CsPbBr3 NCs grafted on the surface of silica nanohelices as templates in dispersed state in toluene and dried state on quartz glass substrate revealed that the interparticle distance becomes shorter after the dryness by cast method from the dispersed state and the closely and helically packed NCs [4]. Tuning the conditions of solution-processed reorganization of CsPbBr3 NCs is crucial for reducing the inter NC distance with highly ordered alignment in the cast films with large circular dichroism and circularly polarized luminescence signals.On the basis of the above findings, reorganization of NCs with highly controlled crystal orientation and inter NC distance in thin films has deep influence on specific spectral characteristics and photovoltaic performances.[1] Kaewprajak, A.; Kumnorkaew, P.; Sagawa, T. Silver-indium-sulfide quantum dots in titanium dioxide as electron transport layer for highly efficient and stable perovskite solar cells. J. Mater. Sci.: Mater. Electron., 2019, 30, 4041-4055.[2] Kaewprajak, A.; Kumnorkaew, P.; Sagawa, T. Improved photovoltaic performance and device stability of planar heterojunction perovskite solar cells using TiO2 and TiO2 mixed with AgInS2 quantum dots as dual electron transport layers. Org. Electron., 2019, 69, 26-33.[3] Shi, G.; Kaewprajak, A.; Ling, X.; Hayakawa, A.; Zhou, S.; Song, B.; Kang, Y.-w.; Hayashi, T.; Altun, M. E.; Nakaya, M.; Liu, Z.; Wang, H.; Sagawa, T.; Ma, W. Finely interpenetrating bulk heterojunction structure for lead sulfide colloidal quantum dot solar cells by convective deposition. ACS Energy Lett., 2019, 4, 960-967.[4] Liu, P.; Chen, W.; Okazaki, Y.; Battie, Y.; Brocard, L.; Decossas, M.; Pouget, E.; M.-Buschbaum, P.; Kauffmann, B.; Pathan, S.; Sagawa, T.; Oda, R. Optically active perovskite CsPbBr3 nanocrystals helically arranged on inorganic silica nanohelices. Nano Lett., 2020, 20, 8453-8460.

Age-related dental phenotypes and tooth characteristics of FAM83H-associated hypocalcified amelogenesis imperfecta.

Autosomal-dominant hypocalcified amelogenesis imperfecta (ADHCAI) shows phenotypic heterogeneity. Our aim was to characterise the ADHCAI phenotypes, tooth properties and genotypes. Three unrelated ADHCAI probands and seven additional affected members of the three families were recruited. Mutations were identified by exome and Sanger sequencing, and haplotypes by SNP array. Tooth colour, roughness, density, nanohardness, minerals and ultrastructure were investigated. Ten participants were heterozygous for the FAM83H mutation c.1387C>T (p.Gln463*). All shared a 3.43 Mbp region on chromosome 8q24.3 encompassing the FAM83H variant, indicating a common ancestry. The c.1387C>T was estimated to be 23.8 generations or 600years. The FAM83H enamel had higher roughness and lower lightness, density, nanohardness, and calcium and phosphorus levels than controls. Blunted enamel rods, wide interrod spaces and disorganised dentinoenamel junctions were observed. Evaluating the patients with the same mutation and reviewing others with different mutations in FAM83H revealed that the FAM83H heterogeneous phenotypes are age-influenced. Tooth colour and surface texture change with ageing. FAM83H enamel demonstrated decreased lightness, density, hardness, calcium, phosphorus and defective ultrastructure. We have identified that the phenotypic variation in FAM83H-associated ADHCAI is age-related. Awareness of the correlation between age and clinical features of FAM83H-ADHCAI can help dentists make an accurate diagnosis.

Structural and chemical enamel characteristics of hypomineralised second primary molars.

Although hypomineralised second primary molars (HSPM) are considered belonging in the same entity as molar incisor hypomineralisation (MIH), the structure and chemistry of their defected enamel have not been described. We aimed to study these in justifying any similarities with MIH. Nine HSPM and five first permanent molars with MIH were either fractured or sectioned longitudinally through their defective enamel and examined by scanning electron microscopy. Relative amounts of calcium (Ca), phosphorus (P), oxygen (O), carbon (C) and the Ca:P ratio were calculated in the primary molar samples by energy -dispersive spectrometry. Rod width was deficient in the defected enamel of HSPM resulting in wide interrod spaces and suggesting similarities to permanent enamel structure in MIH. In areas with breakdown, cracks and disrupted coherence between enamel rods were more marked. Differences in Ca, P, O, C and Ca:P ratio between hypomineralised and sound enamel in HSPM followed the same trend as in MIH without reaching statistical significance. Marked structural differences between sound and hypomineralised enamel of HSPM and similarity to MIH enamel were verified.

The Role of ALD-ZnO Seed Layers in the Growth of ZnO Nanorods for Hydrogen Sensing.

Hydrogen is one of the most important clean energy sources of the future. Because of its flammability, explosiveness, and flammability, it is important to develop a highly sensitive hydrogen sensor. Among many gas sensing materials, zinc oxide has excellent sensing properties and is therefore attracting attention. Effectively reducing the resistance of sensing materials and increasing the surface area of materials is an important issue to increase the sensitivity of gas sensing. Zinc oxide seed layers were prepared by atomic layer deposition (ALD) to facilitate the subsequent hydrothermal growth of ZnO nanorods. The nanorods are used as highly sensitive materials for sensing hydrogen due to their inherent properties as oxide semiconductors and their very high surface areas. The low resistance value of ALD-ZnO helps to transport electrons when sensing hydrogen gas and improves the sensitivity of hydrogen sensors. The large surface area of ZnO nanorods also provides lots of sites of gas adsorption which also increases the sensitivity of the hydrogen sensor. Our experimental results show that perfect crystallinity helped to reduce the electrical resistance of ALD-ZnO films. High areal nucleation density and sufficient inter-rod space were determining factors for efficient hydrogen sensing. The sensitivity increased with increasing hydrogen temperature, from 1.03 at 225 °C, to 1.32 at 380 °C after sensing 100 s in 10,000 ppm of hydrogen. We discuss in detail the properties of electrical conductivity, point defects, and crystal quality of ALD-ZnO films and their probable effects on the sensitivity of hydrogen sensing.

Microstructure and Solid/Liquid Interface Evolutions of Directionally Solidified Fe-Al-Ta Eutectic Alloy

A modified Bridgman directional solidification technique was used to prepare Fe-Al-Ta eutectic in situ composites at different growth rates ranging from 6 to 80 µm/s. The directionally solidified Fe-Al-Ta eutectic composites are composed of two phases: Fe(Al,Ta) matrix phase, and Fe2Ta(Al) Laves phase. Solidification microstructure is affected by solidification rate. Microstructure of the Fe-Al-Ta eutectic alloy grown at 6.0 µm/s is broken-lamellar eutectic. Eutectic colonies are formed with the increase of the solidification rate. Microstructures are mainly composed of the lamellar or fibrous eutectic at the center of the colony and coarse lamellar eutectic zone at the boundary. Meanwhile, the inter-lamellar spacing (or the inter-rod spacing) is decreased. The spacing adjustments are also observed in Fe-Al-Ta eutectic alloy. The solid/liquid interface evolves from planar interface to shallow cellular interface, then to deep cellular, and finally to shallow cellular planar with the increase of the solidification rate.

Fano resonances in symmetric gold nanorod trimers

A symmetrical gold nanorod trimer structure consisting of a short center nanorod and two long nanorods on both sides is proposed. The scattering spectra, electromagnetic field and current density vector distributions across the central cross section of the nanorod trimer are calculated by the finite difference time domain method, and the effects of structural parameters and dielectric environment on Fano resonance characteristics are theoretically investigated in detail. The results show that the Fano resonance can be generated mainly due to the interference between the bonding electric dipole mode in lower energy and the antibonding electric dipole mode or antiphase magnetic dipole mode in higher energy. The Fano dip is blue-shifted with the decrease in the short nanorod length, the size of whole trimer structure with constant displacement, or the refractive index of dielectric medium in the gaps between the central nanorod and two side nanorods; the resonance intensity on both sides of the Fano dip also changes. Meanwhile, the bonding mode on the red side of the Fano dip is gradually dominated by the electric dipole mode of two side nanorods, and the spectral intensity increases, while the antibonding mode on the blue side gradually evolves into the short nanorod-dominated antiphase magnetic dipole mode, and the spectral intensity becomes weaker. The increase in the inter-rod spacing also leads the Fano dip to be blue-shifted, and a similar change in the spectral intensity occurs on both sides of the Fano dip, due to the degeneration of bonding and antibonding modes caused by the decrease of near-field coupling between the short nanorod and two side nanorods, which finally degenerate into the electric dipole modes generated by the short nanorod or the two side nanorods, respectively. In addition, the Fano dip is insensitive to the change of the side nanorod length, but the relative resonance intensity on both sides of the Fano dip also changes. Furthermore, it is found that the spectral contrast ratio of the Fano resonance first increases and then decreases by varying the above-mentioned structural parameters or dielectric environment. These results are expected to be used for guiding the design of Fano controllable nanostructures and also for developing the applications of specific micro-nano photonics.

Enhanced Gas-Sensing Response of Zinc Oxide Nanorods Synthesized via Hydrothermal Route for Nitrogen Dioxide Gas

In recent years, advanced material processing techniques have allowed scientists to research and document the properties of nanostructured metal oxides. One such material system, zinc oxide (ZnO), has emerged as a favorable option for a multitude of applications. In this study, thin films of ZnO with nanorod-like architectures were hydrothermally formed on a glass substrate and their physical and chemical properties were thoroughly characterized. X-ray diffraction confirmed the wurtzite structure and a scanning electron microscope was used to verify the vertical alignment of the rods. Defects due to the high oxygen vacancy concentration were revealed through photoluminescence studies. The high surface area of the nanorods works in conjunction with these defects and an optimal inter-rod spacing creates conditions for effective gas adsorption and diffusion. With this in mind, the nanorods were used to fabricate a gas sensor which demonstrated excellent NO2 sensitivity and selectivity at a relatively low operating temperature.

Systematic Analysis of the Coupling Effects within Supported Plasmonic Nanorod Antenna Arrays

Vertically aligned gold nanorod arrays (of aspect ratios from 3.0 to 18.0) supported on metal substrates were fabricated by electrochemical deposition within porous anodic aluminum oxide templates. However, the coupling effects that occur within these supported arrays are complex, involving both particle–substrate and particle–particle coupling, and far from fully understood. We have performed a systematic investigation into these effects using finite element modeling and correlated these results to experiment. We demonstrate that within the strong coupling regime, the optical properties of the arrays are predominantly governed by inter-rod spacing. Additionally, by supporting the arrays on metal films, the absorption efficiency is significantly enhanced. We explain these coupling effects in terms of plasmon hybridization theory and image charges. We demonstrate that the longitudinal mode may be tuned throughout the visible region and present resonant wavelength contour plots as a function of inter-rod sp...

Osteoimmunomodulation, osseointegration, and in vivo mechanical integrity of pure Mg coated with HA nanorod/pore-sealed MgO bilayer.

Fast degradation of Mg-based implants results in the loss of mechanical integrity and poor osseointegration. Herein, a bilayer-structured coating (termed as HAT), comprising an outer layer of hydroxyapatite (HA) nanorods and an inner layer of pores-sealed MgO with HA/Mg(OH)2, was formed on Mg using plasma electrolytic oxidation and hydrothermal treatment. Osteoimmunomodulation, osseointegration, mechanical integrity, and bone-implant interfacial structure evolution of the HAT-coated Mg were investigated by implantation in rabbit femora, together with Mg coated with plasma electrolytic oxidized porous MgO (termed as PEO0) and bare Mg. As compared to PEO0-coated and bare Mg, HAT-coated Mg greatly downregulated pro-inflammatory TNF-α and IL-1β, upregulated anti-inflammatory IL-10, and suppressed osteoclastogenesis, modulating the surrounding microenvironment toward favoring the recruitment of osteogenetic cells. Moreover, HAT-coated Mg accelerated bone sialoprotein and osteopontin secretion of osteogenetic cells and their mineralization to form a cement line matrix. It also promoted the differentiation of osteogenetic cells, secretion of collagen overlying on the cement line matrix, inducing an earlier and more pronounced bone matrix formation. The cement line matrix wrapped the HA nanorods and filled the interrod spaces of the HAT coating, forming strong interdigitation at the bone-coating interface, and therefore, yielding enhanced osseointegration by means of contact osteogenesis. Due to the considerably reduced corrosion of Mg by the pores-sealed bilayer structure of HAT coating, HAT-coated Mg maintained the mechanical integrity for a longer duration than PEO0-coated and bare Mg. It is clarified that the degradation of MgO and HA, rather than delamination, was the vanishing mode of PEO0 and HAT coatings during long-term implantation, avoiding osteolysis induced by the delamination-generated particles.

Solid-State Dewetting of Gold Aggregates/Islands on TiO2 Nanorod Structures Grown by Oblique Angle Deposition.

A composite film made of a stable gold nanoparticle (NP) array with well-controlled separation and size atop a TiO2 nanorod film was fabricated via the oblique angle deposition (OAD) technique. The fabrication of the NP array is based on controlled, Rayleigh-instability-induced, solid-state dewetting of as-deposited gold aggregates on the TiO2 nanorods. It was found that the initial spacing between as-deposited gold aggregates along the vapor flux direction should be greater than the TiO2 interrod spacing created by 80° OAD to control dewetting and produce NP arrays. A numerical investigation of the process was conducted using a phase-field modeling approach. Simulation results showed that coalescence between neighboring gold aggregates is likely to have caused the uncontrolled dewetting in the 80° deposition, and this could be circumvented if the initial spacing between gold aggregates is larger than a critical value smin. We also found that TiO2 nanorod tips affect dewetting dynamics differently than planar TiO2. The topology of the tips can induce contact line pinning and an increase in the contact angle along the vapor flux direction to the supported gold aggregates. These two effects are beneficial for the fabrication of monodisperse NPs based on Rayleigh-instability-governed self-assembly of materials, as they help to circumvent the undesired coalescence and facilitate the instability growth on the supported material. The findings uncover the application potential of OAD as a new method to fabricate structured films as template substrates to mediate dewetting. The reported composite films would have uses in optical coatings and photocatalytic systems, taking advantage of their ability to combine plasmonic nanostructures within a nanostructured dielectric film.

Repulsion between oppositely charged rod-shaped macromolecules: Role of overcharging and ionic confinement.

The interaction between two oppositely charged rod-shaped macro-ions in a micro-ion solution is investigated via Monte Carlo simulations of the primitive model. The focus is on the asymmetry in rod and/or ion charge, i.e., conditions where oppositely charged objects can repel one another. For equally and oppositely charged rods with asymmetric z:1 micro-ions, repulsion may be induced by overcharging one of the rods with the z valent ions. For asymmetrically charged rods in a symmetric z:z micro-ion solution, a repulsive interaction-at separation of the order of one ion diameter-can arise via an unbalanced osmotic pressure contribution from the ionic atmosphere in the inter-rod space, and an attractive interaction-at a smaller separation-may occur due to a "squeezing out" of the micro-ions from the space between the rods (with a consequent gain in entropy). The thermodynamics of each mechanism is investigated in terms of rod charge and size and micro-ion valence, size, and concentration. Our findings contribute to the understanding of the complex role of charge asymmetry on the interaction of, for example, oppositely charged polyelectrolytes, functionalized nanotubes, and rod-like biomolecules, e.g., viruses.

Effects of composition and growth rate on the microstructure transformation of β-rods/lamellae/α-rods in directionally solidified Mg-Li alloy

Mg-Li alloy is a unique system with a narrow dual-phase region and superstructure transformation. These characteristics will have significant influence on the solidification behavior. Using Bridgman-type vacuum furnace with liquid metal cooling method, the directional solidification experiments were performed on alloys with different Li contents (6.3wt.%, 6.6wt.%, 6.9wt.%, 7.2wt.%, 7.5wt.%, 7.8wt.%) at varied growth rates (3μm/s, 5μm/s, 10μm/s, 15μm/s, maximum to 21μm/s). As the Li content increases, the microstructures transform from divorced eutectic structure to lamellar structure, then to lamellae/α-Mg rod mixed structure, and finally to α-Mg rod-like structure. Fully eutectic structure is produced at a wide range of off-eutectic compositions. The effect of growth rate on the α-Mg rod-like structure is mainly to diminish the inter-rod spacing as growth rate increases, while additionally to affect the morphology of lamellar structure. High growth rate is found to be beneficial for producing straight and uniform lamellar structure. The eutectic spacing of Mg-Li system is one or two orders of magnitude lager than most other alloy systems. Moreover, a controllable three-stage transformation of β-rods/lamellae/α-rods is achieved in one single alloy system. A structure selection map is also given to define the microstructure transformation of the Mg-Li alloys.