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The heat-to-electricity conversion efficiency of concentrated solar power plants may be enhanced, for lower cost electricity generation, by using high-temperature (750 °C) supercritical CO2 as a working fluid to drive the turbines in these plants. Unfortunately, such operation has been inhibited by the reduction in thermomechanical performance at ≥550 °C of metal alloys used, or considered for use, in compact heat exchangers for heat transfer to supercritical CO2. Co-continuous, melt-infiltration-processed SiC/Si composites possess an attractive combination of high-temperature mechanical and thermal properties for use in such compact heat exchangers. However, the corrosion behavior of melt-infiltration-processed, equivolume SiC/Si composites in CO2 at 750 °C has not been reported. In this work, the oxidation kinetics of SiC/Si composites, fabricated by Si liquid infiltration into porous SiC preforms, have been examined in CO2 and in air at 750 °C for up to 700 h. Continuous, thin, slow-growing external amorphous SiO2 scales formed on the SiC/Si composites during oxidation in both gases, without detectable oxide formation at internal (subsurface) SiC/Si interfaces. Corrosion-induced SiC formation in CO2, and Si3N4 formation in air, were also not detected below the SiO2 scales. The weight gains were small, with a significantly lower rate of weight gain detected in CO2 than in air. SiO2 scales formed on SiC in both gases were thinner than the scales formed on Si. The SiO2 scales formed on Si in air were notably thicker than the scales formed on Si in CO2, whereas SiO2 scales formed on SiC in air and CO2 were of similar thickness.

Compact heat exchangers (HXs) have gained attention in recent years in various fields such as solar and nuclear power generation, oil and gas, and refrigeration due to their low cost, high power density, and robustness in high-pressure and/or high-temperature environments. However, the large difference between a compact HX's overall dimensions (∼m) and the much smaller scale of its channels (∼mm) makes it challenging to model the entire HX at once, due to computational limitations. In this work, we treat the channeled region of a compact HX as a porous medium (PM) to circumvent the need to model/mesh each individual channel. This allows us to simulate the entire HX, including both the header and channeled regions while maintaining the computational cost at a practical level. Although the porous medium approach has been used to model heat exchangers, its validity is still questionable because (1) the resistance coefficients are heavily data-based and thus difficult to be applied to new heat exchangers and (2) the validation has been focused on matching the overall pressure drop in the channel region, which does not address whether such model can predict detailed pressure and velocity field. For the first time, this work addresses under what circumstances and with what uncertainty does the PM approach work for hydrodynamics modeling in compact HXs. By answering these questions, we introduce the PM approach as a powerful tool for HX hydrodynamics modeling that can predict not only the overall pressure drop but also the detailed pressure and velocity distributions.

Complex-shaped, finely-featured, ultra-high-melting ZrC/W composite structures were produced by coupling, for the first time, three-dimensional (3D) ink-extrusion printing with shape/size-preserving reactive melt infiltration (the Displacive Compensation of Porosity, DCP, process). Inks containing sub-micron WC powders were printed at ambient temperature into either fine-scale structures (sub-millimeter filaments) or into a larger-scale, finely-featured 3D structure (a centimeter-scale nozzle with a sub-millimeter-thick wall). After organic binder removal, the printed structures were sintered at 1650 °C for 1 h to achieve a porosity of 50%. The porous, rigid WC structures then underwent ambient pressure infiltration and reaction with Zr-Cu liquid at up to 1350 °C for 2 h. The reaction of WC to yield more voluminous ZrC and W products filled prior pores (DCP process) to yield shape-preserved, dense ZrC/W structures after Cu dissolution from external surfaces. This new integrated approach opens the door to ultra-high-melting ceramic/metal composite structures with complex 3D shapes and fine (millimeter-scale) features.

A dramatic reduction in man-made CO2 emissions could be achieved if the cost of electricity generated from concentrated solar power (CSP) plants could become competitive with fossil-fuel-derived electricity. The solar heat-to-electricity conversion efficiency of CSP plants may be significantly increased (and the associated electricity cost decreased) by operating CSP turbines with inlet temperatures >750 C instead of 750 C to allow for rapidly dispatchable and/or continuous electricity production. Unfortunately, earth-abundant MgCl2-KCl-based liquids currently being considered as low-cost media for large-scale, high-temperature TES are susceptible to oxidation in air, with associated undesired changes in liquid composition and enhanced corrosion of metal alloys in pipes and tanks containing such liquids. In this paper, alternative high-temperature, earth-abundant molten chlorides that are stable in air are identified via thermodynamic calculations. The oxidation resistance, and corrosion-resistant containment, of such molten chlorides at 750 C are then demonstrated. Such chemically-robust, low-cost TES media and effective containment provide critical advances towards the higher-temperature operation of, and lower-cost electricity generation from, CSP plants., 27 pages, 5 figures

Cellular metabolic pathways are paradigms for the rapid and waste-free conversion of molecules into useful products through multiple enzyme-catalyzed steps (cascade reactions). Attempts to establish efficient cascade reactions for technological applications have focused on mimicking nature's high degree of organization by controlling the positioning of enzymes through immobilization in tailor-made compartments. The present work utilized peptide-mediated layer-by-layer mineralization as a facile and generic method for the compartmentalisation of multi-enzyme systems in nanoscale silica layers. It is demonstrated that, in a multilayer system, the overall rate of the reaction cascade was primarily affected by the placement of the enzyme catalyzing the first step, with the placement of the enzyme possessing the lowest catalytic efficiency also being an important factor. As the rate-limiting enzymes were positioned closer to the external silica surface, the overall rate of cascade reactions increased. Furthermore, distributing the enzymes into different adjacent silica compartments yielded higher overall cascade reaction rates compared to placement of the enzymes into the same silica layer. The synthetic methods and kinetic analyses presented here provide guidance for improving the performance of immobilized multi-enzyme systems for a wide range of technological applications.

One pathway for reducing the cost of concentrated solar power (CSP) is to increase the system efficiency by operating a heat engine with a higher hot side (inlet) temperature. If a turbine is used, then a system utilizing a combined cycle could potentially reach upwards of ∼60% efficiency, provided that the turbine could be operated with an inlet temperature >1300 °C. Such high temperatures place severe limits on heat transfer fluids; that is, such fluids would need to remain chemically stable, and be compatible with containment materials, at such extreme temperatures. One potential class of such fluids are liquid metals, such as molten tin. While possessing low melting and high boiling points (232 °C and 2600 °C, respectively) for a high operational range, molten tin also tends to be highly corrosive towards common structural metal alloys used as components for the containment and controlled flow of liquids (i.e., for pipes, tanks, valves, pumps, etc.). Thus, it would be useful to identify materials that are compatible with molten tin at ≥1300 °C. The purpose of this paper is to evaluate three candidate high-temperature materials, possessing a range of thermal conductivities, for the containment of molten tin: graphite (C), silicon carbide (SiC), and mullite (Al6Si2O13). The corrosion and penetration of these materials by molten Sn or doped Sn liquids at 1350 °C for 100 h were evaluated via local electron microscopic analyses and global weight change measurements. Under appropriate conditions, all three of these materials exhibited minimal to no reaction with tin-based liquids at 1350 °C and were not penetrated by these liquids at this temperature. This work indicates that graphite, silicon carbide, and/or mullite can serve as effective containment materials for the use of tin-based liquids as heat transfer fluids operating at 1350 °C in CSP plants.

Background Periodontitis is an infectious/inflammatory disease most often diagnosed by deepening of the gingival sulcus, which leads to periodontal pockets (PPs) conventional manual periodontal probing does not provide detailed information on the three-dimensional (3-D) nature of PPs. Objectives To determine whether accurate 3-D analyses of the depths and volumes of calibrated PP analogues (PPAs) can be obtained by conventional cone beam computed tomography (CBCT) coupled with novel radiopaque micro-particle fillers (described in the companion paper) injected into the PPAs. Methods Two PPA models were employed: (1) a human skull model with artificial gingiva applied to teeth with alveolar bone loss and calibrated PPAs, and (2) a pig jaw model with alveolar bone loss and surgically-induced PPAs The PPAs were filled with controlled amounts of radiopaque micro-particle filler using volumetric pipetting Inter-method and intra-method agreement tests were then used to compare the PPA depths and volumes obtained from CBCT images with values obtained by masked examiners using calibrated manual methods. Results Significant inter-method agreement (0.938–0.991) and intra-method agreement (0.94–0.99) were obtained when comparing analog manual data to digital CBCT measurements enabled by the radiopaque filler. Significance CBCT imaging with radiopaque micro-particle fillers is a plausible means of visualizing and digitally assessing the depths, volumes, and 3-D shapes of PPs This approach could transform the diagnosis and treatment planning of periodontal disease, with particular initial utility in complex cases Efforts to confirm the clinical practicality of these fillers are currently in progress.

Conformal compact Mg2Si films can be formed on Si substrates (for battery, photovoltaic, thermoelectric, or other applications) via the direct reaction of Mg films with such substrates at modest temperatures (≥280 °C). In this work, in situ high-temperature X-ray diffraction (HTXRD) analyses have been used to track the reactive conversion of Mg films on Si single crystal (wafer) substrates into Mg2Si at 280–400 °C in a flowing He atmosphere. Prior reported complications associated with the evaporation or oxidation of magnesium films during heating were avoided by applying a thin (15 nm) titanium capping layer on the 1 μm thick magnesium films. The reaction of Mg films with oriented and oriented Si single crystals proceeded at parabolic rates with time. Similar values were obtained for the parabolic rate constants and activation energies for Mg reaction with both Si substrate orientations. These observations were consistent with solid-state diffusion through the thickening Mg2Si product as the rate-limiting step. The activation energy values obtained for Mg2Si formation were consistent with a previously reported correlation between the activation energies and melting points of other M2Si-type silicides formed by solid-state-diffusion-limited reaction with Si substrates.

To increase the power cycle efficiency and lower the levelized cost of electricity (LCOE) of concentrated solar power (CSP) plants, printed circuit heat exchangers (PCHEs) capable of operating above 700 °C with molten chloride salt and a sCO2-based fluid are needed. In this paper, the design of a high-pressure, high-temperature, 2 MW PCHE comprised of a thermomechanically-robust, zirconium carbide/tungsten (ZrC/W) composite is conducted for CSP plants. The ZrC/W composite is a material with high thermal conductivity, high stiffness, and high failure strength at high temperatures, along with excellent resistance to thermal cycling and thermal shock. In this work, a thermomechanical design analysis was conducted to select appropriate material thicknesses of the ZrC/W plates, and to determine the geometrical dimensions and the thermal performance of the PCHE. The influences of the plate number and heat exchanger length on power density and pressure drop have also been systematically investigated. Economic analyses were conducted to compare the cost of ZrC/W-based PCHEs to those comprised of IN740H (a state-of-the-art, nickel-based superalloy) and 316 stainless steel (316SS). At a sufficiently high plate production rate, the manufacturing cost of ZrC/W-based PCHEs can be significantly lower, while achieving a much higher power density, compared with state-of-the-art, nickel alloy-based and stainless steel-based PCHEs.

Micro-to-nanoscale surface topographies of orthopaedic and dental implants can affect fluid wetting and biological response. Nanoscale features can be superimposed on microscale roughness of titanium (Ti) surfaces at high temperatures, resulting in increased osteoblast differentiation. However, high temperatures can compromise mechanical properties of the bulk material. Here, we have developed a novel low-temperature microwave hydrothermal (MWHT) oxidation process for nanomodification of microrough (SLA) Ti surfaces. Nanoscale protuberances (20 -100 nm average diameter) were generated on SLA surfaces via MWHT treatment at 200°C in H2 O, or in aqueous solutions of H2 O2 or NH4 OH, for times ranging from 1 to 40 h. The size, shape, and crystalline content of the nanoprotuberances varied with the solution used and treatment time. The hydrophilicity of all MWHT-modified surfaces was dramatically enhanced. MG63 and normal human osteoblasts (NHOsts) were cultured on MWHT-treated SLA surfaces. While most responses to MWHT-modified surfaces were comparable to those seen on SLA controls, the MWHT-generated nanotopography reduced osteocalcin production by NHOst cells, suggesting that specific nanotopographic characteristics differentially mediate osteoblast phenotypic expression. MWHT processing provides a scalable, low-temperature route for tailoring nanoscale topographies on microroughened titanium implant surfaces with significantly enhanced wetting by water, without degrading the microscale surface structure of such implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 782-796, 2018.

Heat is fundamental to power generation and many industrial processes, and is most useful at high temperatures because it can be converted more efficiently to other types of energy. However, efficient transportation, storage and conversion of heat at extreme temperatures (more than about 1,300 kelvin) is impractical for many applications. Liquid metals can be very effective media for transferring heat at high temperatures, but liquid-metal pumping has been limited by the corrosion of metal infrastructures. Here we demonstrate a ceramic, mechanical pump that can be used to continuously circulate liquid tin at temperatures of around 1,473-1,673 kelvin. Our approach to liquid-metal pumping is enabled by the use of ceramics for the mechanical and sealing components, but owing to the brittle nature of ceramics their use requires careful engineering. Our set-up enables effective heat transfer using a liquid at previously unattainable temperatures, and could be used for thermal storage and transport, electric power production, and chemical or materials processing.

Hot-pressed Al2O3/Cr and Ti2O3/Cr composites were exposed to synthetic air or CO2 at 750 °C. The Al2O3/Cr composites formed external Cr2O3 scales, and exhibited slow parabolic oxidation kinetics, in both gases. The Cr2O3 scales formed in CO2 possessed finer grains, and thickened at a faster rate, than Cr2O3 scales formed in air. The Ti2O3/Cr composites formed thick external TiO2 scales with internal oxidation zones that also contained Cr2O3 scales on subsurface Cr grains. After 20 h at 750 °C, the Ti2O3/Cr composites exhibited parabolic oxidation kinetics in both gases, although the oxidation rates were significantly higher than for the Al2O3/Cr composites.

Aluminum oxide coatings deposited on LiMn2O4/carbon fiber electrodes by atomic layer deposition (ALD) are shown to enhance cathode performance in lithium-ion batteries. With a thin Al2O3 coating derived from 10 ALD cycles, the electrodes exhibit 2.5 times greater capacity retention over 500 cycles at a rate of 1C as well as enhanced rate capability and decreased polarization resistance. Structural and surface studies of the electrodes before and after cycling reveal that a near-surface phenomenon is responsible for the improved electrochemical performance. The crystal structure and overall morphology of the LiMn2O4 electrode are found to be unaffected by electrochemical cycling, both for coated and uncoated samples. However, evidence of Mn diffusion into the ALD coatings is observed from both transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM-EDS) and X-ray Photoelectron Spectroscopy (XPS) after electrochemical cycling. Furthermore, XPS analysis of the Al 2p photoemission peak for the ALD coated electrodes reveal a significant shift in binding energy and peak shape, suggesting the presence of an Al–O–F compound formed by sequestering HF in the electrolyte. These observations provide new insight toward understanding the mechanism in which ultrathin coatings of amphoteric oxides can inhibit capacity loss for LiMn2O4 cathodes in lithium-ion batteries.

Previous models based on thermodynamic considerations have identified the properties desired for reactive oxides that can be used as oxygen storage materials in thermochemical cycles to produce fuel from sunlight. However, there are several important assumptions made in such models, such as the neglect of the energy required to preheat unreacted species and the assumption of constant vacuum pump efficiency. When these assumptions are relaxed, one comes to significantly different conclusions about the optimal reactor operating conditions. Furthermore, comparing two materials is not straightforward due to the high degree of coupling between material properties and reactor operating conditions. Herein, we describe a new framework for material comparison which employs a thermodynamic reactor model to predict the maximum possible efficiency of a given oxygen storage material. This model demonstrates how new materials can impact reactor performance and the limitations of such improvements.

A facile, environmentally-friendly, low-cost, and scalable deposition process has been developed and automated to apply polyelectrolyte multilayers (PEMs) on flexible Kapton HN substrates. Two weak polyelectrolytes, poly(acrylic acid) and polyethylenimine, were deposited in an alternating, layer-by-layer fashion under controlled pH and ionic strength. Compared to strong polyelectrolytes, weak electrolytes can control the properties of the PEMs more systmatically and simply. To our knowledge, this work on surface modification of Kapton is not only the first to use only weak polyelectrolytes, but is also the first to take advantage of the surface properties of calcium-bearing additive particles present in Kapton HN. The resulting surface-modified Kapton HN substrate allowed for the inkjet printing of water-based graphene oxide (GO) inks and organic solvent-based inks with good adhesion and with desired printability. While the deposition of a single PEM layer on a Kapton substrate significantly reduced the water contact angle and allowed for the inkjet-printing of GO inks, the deposition of additional PEM layers was required to maintain the adhesion during post-printing chemical treatments. As a conceptual demonstration of the general applicability of this PEM surface modification approach, a flexible, robust, single-layered gas sensor prototype was fully inkjet printed with both water- and ethanol-based inks and tested for its sensitivity to diethyl ethylphosphonate (DEEP), a simulant for G-series nerve agents. The electrical conductivity and morphology of the sensor were found to be insensitive to repeated bending around a 1 cm radius.

The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heat exchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1–3, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage4–6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin9. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heat exchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost. A robust ceramic/refractory metal (ZrC/W)-based composite for use in heat exchangers in concentrated solar power plants above 1,023 kelvin is described, having attractive high-temperature thermal, mechanical and chemical properties combined with cost-effective processing.

Cellulose nanocrystals (CNCs) can be attractive templates for the generation of functional inorganic/organic nanoparticles, given their fine sizes, aspect ratios, and sustainable worldwide availability in abundant quantities. Here, we present for the first time a scalable, surfactant-free, tailorable wet chemical process for converting commercially available CNCs into individual aspected gold nanoshell-bearing particles with tunable surface plasmon resonance bands. Using a rational cellulose functionalization approach, stable suspensions of positively charged CNCs have been generated. Continuous, conductive, nanocrystalline gold coatings were then applied to the individual, electrostatically stabilized CNCs via decoration with 1-3 nm diameter gold particles followed by electroless gold deposition. Optical analyses indicated that these core-shell nanoparticles exhibited two surface plasmon absorbance bands, with one located in the visible range (near 550 nm) and the other at near infrared (NIR) wavelengths. The NIR band possessed a peak maximum wavelength that could be tuned over a wide range (1000-1300 nm) by adjusting the gold coating thickness. The bandwidth and wavelength of the peak maximum of the NIR band were also sensitive to the particle size distribution and could be further refined by fractionation using viscosity gradient centrifugation.

We present a rapid, low-power testbed for the detection and imaging of fluorescent probes utilizing two-photon excitation fluorescence (2PEF). The 2PEF signal from fluorophores commonly used in biological imaging have been enhanced using plasmonic substrates that have been designed to have a high plasmonic resonance over a narrow band that matches the source. The samples were illuminated and imaged using a low-power, in-house multiphoton microscope. A green fluorescent protein (bfloGFPa1), chlorophyll, or rhodamine 6G were deposited onto the plasmonic substrates and their 2PEF signals were measured relative to planar samples. The fluorescence intensities from the green fluorescent protein, chlorophyll, and rhodamine were enhanced by factors of 50, 8, and 4, respectively, with the structured substrates (relative to the planar substrates).

The ability to synthesize large quantities of 3-D microparticles with tunable adhesion is critically important for a variety of mature and emerging technologies, such as for paints, inks, chemical/water purification, drug delivery, cell manipulation, and assembly of hierarchical structures. Nature provides impressive examples of sustainable, complex-shaped microparticles with chemistries and structures tailored for adhesion, among the most common of which are pollen grains. We have recently used a surface sol–gel (SSG) coating process to generate iron oxide replicas of sunflower pollen grains. While these replicas exhibited multimodal adhesion, the tailorability and predictability of such adhesion was not examined. In the present paper, the layer-by-layer SSG process has been used to carefully adjust the amount of iron oxide deposited onto the pollen grains. Controlled-atmosphere thermal treatments then yielded freestanding replicas with tailored hematite (α-Fe2O3) or magnetite (Fe3O4) contents. The 3-D morphology of the starting pollen was well-preserved in the all-oxide replicas, and the shrinkage upon firing could be controlled by increasing the number of Fe–O-bearing layers deposited on the pollen. While the short-range van der Waals (VDW) adhesion of the oxide replicas to a variety of surfaces was lower than for the larger starting pollen grains, this difference was not due to shrinkage of the replicas. Analyses with a simple Hamaker model indicated that VDW adhesion of the oxide replicas was governed by the contact of oxide nanocrystals located on the spine tips (as opposed to the curvature of the entire spine tip). The longer-range attraction to a magnetic substrate could be tailored independently of the short-range VDW attraction by controlling the magnetite content of the replicas, and a simple and effective model for describing such magnetic attraction was developed. This work demonstrates that sustainable pollen microparticles can be converted into high-fidelity 3-D oxide replicas with predictable and tailorable multimodal adhesion.

3D replicas of sunflower pollen microparticles, comprised of a multicomponent magnetic spinel ferrite (CoFe

Objectives Approximately 10 9 bacteria can be harbored within periodontal pockets (PP) along with inflammatory byproducts implicated in the pathophysiology of systemic diseases linked to periodontitis (PD). Calculation of this inflammatory burden has involved estimation of total pocket surface area using analog data from conventional periodontal probing which is unable to determine the three-dimensional (3-D) nature of PP. The goals of this study are to determine the radiopacity, biocompatibility, and antimicrobial activity of transient micro-particle fillers in vitro and demonstrate their capability for 3-D imaging of artificial PP (U.S. Patent publication number: 9814791 B2). Methods Relative radiopacity values of various metal oxide fillers were obtained from conventional radiography and micro-computed tomography (μCT) using in vitro models. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to measure the biocompatibility of calcium tungstate (CaWO 4 ) particles by determination of viable keratinocytes percentage (%) after exposure. After introducing an antibacterial compound (K21) to the radiopaque agent, antimicrobial tests were conducted using Porphyromonas gingivalis ( P. gingivalis ) and Streptococcus gordonii ( S. gordonii ) strains and blood agar plates. Results CaWO 4 micro-particle-bearing fillers exhibited an X-ray radiopacity distinct from tooth structures that enabled 3-D visualization of an artificial periodontal pocket created around a human tooth. MTT assays indicated that CaWO 4 micro-particles are highly biocompatible (increasing the viability of exposed keratinocytes). Radiopaque micro-particle fillers combined with K21 showed significant antimicrobial activity for P. gingivalis and S. gordonii . Significance The plausibility of visualizing PP with 3-D radiographic imaging using new radiopaque, biocompatible, transient fillers was demonstrated in vitro . Antibacterial (or other) agents added to this formula could provide beneficial therapeutic features along with the diagnostic utility.

Recent studies of new surface modifications that superimpose well-defined nanostructures on microrough implants, thereby mimicking the hierarchical complexity of native bone, report synergistically enhanced osteoblast maturation and local factor production at the protein level compared to growth on surfaces that are smooth, nanorough, or microrough. Whether the complex micro/nanorough surfaces enhance the osteogenic response by triggering similar patterns of integrin receptors and their associated signaling pathways as with well-established microrough surfaces, is not well understood. Human osteoblasts (hOBs) were cultured until confluent for gene expression studies on tissue culture polystyrene (TCPS) or on titanium alloy (Ti6Al4V) disks with different surface topographies: smooth, nanorough, microrough, and micro/nanorough surfaces. mRNA expression of osteogenesis-related markers such as osteocalcin (BGLAP) and bone sialoprotein (BSP), bone morphogenetic protein 2 (BMP2), BMP4, noggin (NOG) and gremlin 1 (GREM1) were all higher on microrough and micro/nanorough surfaces, with few differences between them, compared to smooth and nanorough groups. Interestingly, expression of integrins α1 and β2, which interact primarily with collagens and laminin and have been commonly associated with osteoblast differentiation on microrough Ti and Ti6Al4V, were expressed at lower levels on micro/nanorough surfaces compared to microrough ones. Conversely, the av subunit, which binds ligands such as vitronectin, osteopontin, and bone sialoprotein among others, had higher expression on micro/nanorough surfaces concomitantly with regulation of the β3 mRNA levels on nanomodified surfaces. These results suggest that the maturation of osteoblasts on micro/nanorough surfaces may be occurring through different integrin engagement than those established for microrough-only surfaces.

Surface microroughness plays an important role in determining osteoblast behavior on titanium. Previous studies have shown that osteoblast differentiation on microtextured titanium substrates is dependent on alpha-2 beta-1 (α2β1) integrin signaling. This study used focused ion beam (FIB) milling and scanning electron microscopy (SEM), combined with 3D image reconstruction, to investigate early interactions of individual cells with their substrate and the role of integrin α2β1 in determining cell shape. MG63 osteoblast-like cells on sand blasted/acid etched (SLA) Ti surfaces after 3 days of culturing indicated decreased cell number, increased cell differentiation, and increased expression of mRNA levels for α1, α2, αV and β1 integrin subunits compared to cells on smooth Ti (PT) surfaces. α2 or β1 silenced cells exhibited increased cell number and decreased differentiation on SLA compared to wild type cells. Wild type cells on SLA possessed an elongated morphology with reduced cell area, increased cell thickness, and more apparent contact points. Cells on PT exhibited greater spreading and were relatively flat. Silenced cells possessed a morphology and phenotype similar to wild type cells grown on PT. These observations indicate that surface microroughness affects cell response via α2β1 integrin signaling, resulting in a cell shape that promotes osteoblastic differentiation.

Polymers are usually considered thermal insulators, because the amorphous arrangement of the molecular chains reduces the mean free path of heat-conducting phonons. The most common method to increase thermal conductivity is to draw polymeric fibres, which increases chain alignment and crystallinity, but creates a material that currently has limited thermal applications. Here we show that pure polythiophene nanofibres can have a thermal conductivity up to ∼ 4.4 W m(-1) K(-1) (more than 20 times higher than the bulk polymer value) while remaining amorphous. This enhancement results from significant molecular chain orientation along the fibre axis that is obtained during electropolymerization using nanoscale templates. Thermal conductivity data suggest that, unlike in drawn crystalline fibres, in our fibres the dominant phonon-scattering process at room temperature is still related to structural disorder. Using vertically aligned arrays of nanofibres, we demonstrate effective heat transfer at critical contacts in electronic devices operating under high-power conditions at 200 °C over numerous cycles.

We report the first syntheses of three-dimensional (3D) nanocrystalline all-oxide replicas of pollen microparticles tailored for multimodal (bioenabled and synthetic) adhesion via use of a scalable, highly conformal surface sol–gel (SSG) coating process. High-fidelity replication allowed the pollen-shaped oxide microparticles to be utilized for adhesion via tailorable short-range (∼10 nm) van der Waals (VDW) attraction, with the magnitude of such VDW-based adhesion influenced by the nanoscale topography of surface features retained by the replicas. Conversion of the pollen into ferrimagnetic (Fe3O4) microparticle replicas allowed the use of magnetic attraction at short and long ranges (up to ∼1 mm). By selecting pollen particles with particular surface features and by SSG-enabled conversion of such pollen into 3D nanocrystalline replicas composed of an appropriate type and amount of magnetic oxide, adhesive microparticles with tunable short- and long-range attractive forces can be generated.

A scalable, low-cost process for fabricating copper-based microwave components on flexible, paper-based substrates is demonstrated. An inkjet printer is used to deposit a catalyst-bearing solution (tailored for such printing) in a desired pattern on commercially-available, recyclable, non-toxic (Teslin®) paper. The catalystbearing paper is then immersed in an aqueous copper-bearing solution to allow for electroless deposition of a compact and conformal layer of copper in the inkjet-derived pattern. Meander monopole antennas comprised of such electroless-deposited copper patterns on paper exhibited comparable performance as for antennas synthesized via inkjet printing of a commercially-available silver nanoparticle ink. However, the solution-based patterning and electroless copper deposition process avoids nozzle-clogging problems and costs associated with noble metal particle-based inks. This process yields compact conductive copper layers without appreciable oxidation and without the need for an elevated temperature, post-deposition thermal treatment commonly required for noble metal particle-based ink processes. This low-cost copper patterning process is readily scalable on virtually any substrate and may be used to generate a variety of copper-based microwave devices on flexible, paper-based substrates.

Hierarchically-porous, rigid inorganic structures have attracted appreciable interest in a wide range of applications, including catalysis, filtration, sensing, and energy storage/harvesting. Naturally-occurring, hierarchically-porous, rigid assemblies with a wide range of three-dimensional (3D) structures are generated by diatoms (photosynthetic aquatic microorganisms); that is, each of the tens of thousands of diatom species forms a macro-to-mesoporous, silica-bearing cell wall (frustule) with a particular, highly-reproducible 3D morphology. We have recently demonstrated that such intricate biosilica structures can be converted, without loss of 3D morphology, into high surface area (>1300 m2/g) macro-to-microporous carbon. Here we demonstrate, for the first time, how the chemical tailoring of such hierarchically-porous, carbon-converted, 3D biogenic structures can result in a high degree of enzyme loading for rapid flow-through catalysis. Two approaches have been developed for enriching such structures with carboxylic acid groups: i) dendritic amplification of partially-oxidized C replicas, and ii) electrochemical Au deposition followed by self-assembly of a carboxylic acid-bearing surface layer. The terminal carboxylic acid groups were then used for electrostatic attachment of a protamine (PA) modified derivative of the model enzyme, glucose oxidase (GOx-PA). In a flow-through system, the GOx-PA-loaded, diatom-derived microscale structures displayed a glucose consumption rate more than 80% faster than for GOx-PA-loaded C black and Au nanoparticles. The rapid flow-through catalysis of the carbon and gold-bearing frustule replicas was enabled by the open 3D morphology of the starting diatom silica templates, along with the enhanced surface area and high enzyme loading resulting from the chemical conversion and surface functionalization processes.

A reaction-based processing technique to synthesize intragranular-metal/carbide-matrix micro/nanocomposite particles via internal reduction of carbide solid solutions is introduced. The presented method is the first-demonstrated analogue of internal reduction in oxide solid solutions for non-oxide-based ceramic systems. Selected thermodynamic, kinetic, and crystallographic analyses are discussed.

A combined conformal coating and gas/solid reaction process has been used for the first time to convert porous anodic alumina templates into robust, freestanding, multi-wall titania nanotube (MWTNT) arrays that resist appreciable nanotube bundling upon drying. A sol–gel infiltration process was first used to apply a thin conformal titania coating to the alumina templates. After selective etching to generate a gap between the template and the titania coating, exposed alumina was converted into nanocrystalline titania via reaction with titanium tetrafluoride gas and then with humid oxygen. After selective dissolution of residual aluminum-bearing phases and drying, freestanding, non-agglomerated, well-aligned MWTNT arrays were generated (i.e., with coating-derived inner titania tubes resting inside reaction-derived outer titania tubes). When incorporated as aligned electrodes in dye-sensitized solar cells, the dye loading and power conversion efficiencies were higher by factors of 2.2 and 1.8, respectively, than for solar cells with single-wall titania nanotube array electrodes. By controlling the conditions used for alumina template formation, sol–gel coating, and gas/solid reaction, this hybrid process may be used to generate robust, uniformly aligned MWTNT arrays with dimensions and functional chemistries tailored for a variety of electrical, optical, chemical, or biochemical applications.

A selective liquid/solid displacement reaction has been used, for the first time, to convert non-oxide ceramic solid solutions into composites comprised of intragranular metal nanoparticles embedded within non-oxide ceramic microcrystals. The reaction of (ZrxW1−x)C microparticles with a Zr–Cu liquid at 1300°C resulted in the formation of W/ZrC microparticles with a core-shell morphology. The internal microparticle core was comprised of W nanoparticles embedded within a single crystal ZrC matrix, whereas the W-free shell was comprised of an epitaxial layer of ZrC. Such a selective liquid/solid reaction process may be used to generate a variety of intragranular metal/ceramic-matrix composites.

A scalable wet chemical process has been used to convert the intricate silica microshells (frustules) of diatoms into gold structures that retained the three-dimensional (3-D) frustule shapes and fine patterned features. Combined use of an amine-enriching surface functionalization protocol and electroless deposition yielded thin (

Atomic layer deposition is used to synthesize Al2O3:ZnO(1:x) nanolaminates with the number of deposition cycles, x, ranging from 5 to 30 for evaluation as optically transparent, electron-selective electrodes in polymer-based inverted solar cells. Al2O3:ZnO(1:20) nanolaminates are found to exhibit the highest values of electrical conductivity (1.2 × 103 S cm−1; more than six times higher than for neat ZnO films), while retaining a high optical transmittance (≥80% in the visible region) and a low work function (4.0 eV). Such attractive performance is attributed to the structure (ZnO crystal size and crystal alignment) and doping level of this intermediate Al2O3:ZnO film composition. Polymer-based inverted solar cells using poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) mixtures in the active layer and Al2O3:ZnO(1:20) nanolaminates as transparent electron-selective electrodes exhibit a power conversion efficiency of 3% under simulated AM 1.5 G, 100 mW cm−2 illumination.

A combined layer-by-layer (LbL) surface amine amplification and electroless deposition process has been developed to convert biologically replicable three-dimensional (3-D) nanostructured micro-assemblies (such as siliceous diatom frustules) into freestanding Cu-bearing or Ni-bearing structures that retain the starting biogenic microscale 3-D shapes and nanoscale patterns. After reacting the hydroxyl-bearing surfaces of these biotemplates with an aminosilane, a LbL polyacrylate/polyamine deposition process was used to dendritically amplify the surface amine concentration. Subsequent binding of metal chloride catalysts to these amine-enriched surfaces enabled the rapid electroless deposition of thin, conformal, continuous, and nanocrystalline or amorphous metallic coatings on the 3-D biotemplates. Selective removal of the underlying templates then yielded freestanding Cu-bearing or Ni-bearing structures. The conformality and continuity of the thin coatings, and the fidelity with which the biogenic shape and fine features were preserved in the freestanding structures, were significantly enhanced by the amplification of surface amines (and the associated enrichment of catalytic sites) resulting from the LbL polyacrylate/polyamine treatment. Monolithic and multicomponent structures (e.g., Cu, multilayer Au/Cu, CuO, and Ni–P alloy) with bio-derived morphologies have been synthesized utilizing this approach. This readily-scalable process may be used to convert self-assembled rigid templates (of biological or synthetic origin) into nanostructured transition metal-based micro-assemblies with a wide variety of selectable 3-D hierarchical morphologies for use in numerous functional and structural applications.

Recent insight into the molecular mechanisms of biological mineral formation (biomineralization) has enabled biomimetic approaches for the synthesis of functional organic-inorganic hybrid materials under mild reaction conditions. Here we describe a novel method for enzyme immobilization in thin (nanoscale) conformal mineral coatings using biomimetic layer-by-layer (LbL) mineralization. The method utilizes a multifunctional molecule comprised of a naturally-occurring peptide, protamine (PA), covalently bound to the redox enzyme Glucose oxidase (GOx). PA mimics the mineralizing properties of biomolecules involved in silica biomineralization in diatoms, and its covalent attachment to GOx does not interfere with the catalytic activity. Highly effi cient and stable incorporation of this modifi ed enzyme (GOx-PA) into nanoscale layers ( ∼ 5‐7 nm thickness) of Ti-O and Si-O is accomplished during protamine-enabled LbL mineralization on silica spheres. Depending on the layer location of the enzyme and the type of mineral (silica or titania) within which the enzyme is incorporated, the resulting multilayer biocatalytic hybrid materials exhibit between 20‐100% of the activity of the free enzyme in solution. Analyses of kinetic properties ( V max , K M ) of the immobilized enzyme, coupled with characterization of physical properties of the mineral-bearing layers (thickness, porosity, pore size distribution), indicates that the catalytic activities of the synthesized hybrid nanoscale coatings are largely determined by substrate diffusion rather than enzyme functionality. The GOx-PA immobilized in these nanoscale layers is substantially stabilized against heat-induced denaturation and largely protected from proteolytic attack. The method for enzyme immobilization described here enables, for the fi rst time, the high yield immobilization and stabilization of enzymes within continuous, conformal, and nanoscale coatings through biomimetic LbL mineralization. This approach will likely be applicable to a wide variety of surfaces and functional biomolecules. The ability to synthesize thin (nanoscale) conformal enzyme-loaded layers is of interest for numerous applications, including enzyme-based biofuel cells and biosensors.

Titanium (Ti) osseointegration is critical for the success of dental and orthopaedic implants. Previous studies have shown that surface roughness at the micro- and submicro-scales promotes osseointegration by enhancing osteoblast differentiation and local factor production. Only relatively recently have the effects of nanoscale roughness on cell response been considered. The aim of the present study was to develop a simple and scalable surface modification treatment that introduces nanoscale features to the surfaces of Ti substrates without greatly affecting other surface features, and to determine the effects of such superimposed nano-features on the differentiation and local factor production of osteoblasts. A simple oxidation treatment was developed for generating controlled nanoscale topographies on Ti surfaces, while retaining the starting micro-/submicro-scale roughness. Such nano-modified surfaces also possessed similar elemental compositions, and exhibited similar contact angles, as the original surfaces, but possessed a different surface crystal structure. MG63 cells were seeded on machined (PT), nano-modified PT (NMPT), sandblasted/acid-etched (SLA), and nano-modified SLA (NMSLA) Ti disks. The results suggested that the introduction of such nanoscale structures in combination with micro-/submicro-scale roughness improves osteoblast differentiation and local factor production, which, in turn, indicates the potential for improved implant osseointegration in vivo.

An aqueous, protein-enabled (biomimetic), layer-by-layer titania deposition process is developed, for the first time, to convert aligned-nanochannel templates into high-aspect-ratio, aligned nanotube arrays with thin (34 nm) walls composed of co-continuous networks of pores and titania nanocrystals (15 nm ave. size). Alumina templates with aligned open nanochannels are exposed in an alternating fashion to aqueous protamine-bearing and titania precursor-bearing (Ti(IV) bis-ammonium-lactato-dihydroxide, TiBALDH) solutions. The ability of protamine to bind to alumina and titania, and to induce the formation of a Ti–O-bearing coating upon exposure to the TiBALDH precursor, enables the layer-by-layer deposition of a conformal protamine/Ti–O-bearing coating on the nanochannel surfaces within the porous alumina template. Subsequent protamine pyrolysis yields coatings composed of co-continuous networks of pores and titania nanoparticles. Selective dissolution of the underlying alumina template through the porous coating then yields freestanding, aligned, porous-wall titania nanotube arrays. The interconnected pores within the nanotube walls allow enhanced loading of functional molecules (such as a Ru-based N719 dye), whereas the interconnected titania nanoparticles enable the high-aspect-ratio, aligned nanotube arrays to be used as electrodes (as demonstrated for dye-sensitized solar cells with power conversion efficiencies of 5.2 ± 0.4%).

ZrC/W-based composites with complex shapes have been fabricated by combining rapid prototyping methods for synthesizing porous WC preforms with the shape/dimension-preserving, reactive infiltration-based Displacive Compensation of Porosity (DCP) process. Two automated rapid prototyping methods were examined: (i) computer-numerical-controlled machining of porous WC powder compacts, and (ii) 3D printing of WC powder. After binder removal and partial sintering (to neck the WC particles), the shaped, porous, and rigid preforms were exposed to molten Zr 2 Cu at 1150–1300 °C and ambient pressure. Upon infiltration, the Zr in the melt underwent a displacement reaction with WC to yield more voluminous ZrC and W products that filled prior pores (reaction-induced densification). The resulting ZrC/W-based composites retained the shapes and dimensions (to within 1%) of the WC preforms. This work demonstrates, for the first time, that rapid preform prototyping can be integrated with the DCP process to generate dense, ultrahigh-melting carbide/refractory metal composites with tailorable near net-shapes and -dimensions.

The chemical, electrochemical, optical and electro-optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2possesses a simple cubic structure (space groupPm{\overline 3}m) at room temperature. Three-dimensional nanostructured assemblies of polycrystalline TiOF2have recently been synthesizedviachemical conversion of intricate SiO2structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2product formed by such reaction at 623 K. Unlike prior reports, this TiOF2product possessed a hexagonal structure (space groupR{\overline 3}c) at room temperature. Upon heating through 333–338 K, the hexagonal TiOF2polymorph converted into cubic (Pm{\overline 3}m) TiOF2. Differential scanning calorimetry and X-ray diffraction analyses have been used to evaluate this thermally induced phase transformation.

The scalable fabrication of nano-structured materials with complex morphologies and tailorable chemistries remains a significant challenge. One strategy for such synthesis consists of the generation of a solid structure with a desired morphology (a “preform”), followed by reactive conversion of the preform into a new chemistry. Several gas/solid and liquid/solid reaction processes that are capable of such chemical conversion into new micro-to-nano-structured materials, while preserving the macroscopic-to-microscopic preform morphologies, are described in this overview. Such shape-preserving chemical transformation of one material into another could be considered a modern type of materials “alchemy.”

Amorphous silica is (next to CaCO3) the second most abundant biologically produced inorganic material. A certain group of photosynthetic microalgae, called diatoms, forms complex 3D silica architectures (frustules) containing regularly arranged nanoscale features (pores, channels, protuberances). Recently, biomolecules involved in diatom silica formation have been characterized, and first insights into their structure-function correlations have been obtained. This has spurred the development of synthetic (bio)polymers capable of directing thein vitroformation of silica and other inorganic materials from aqueous precursor solutions under mild conditions. Here we present a summary of current insight into the mechanism of silica formation by diatom biomolecules and provide examples of synthetic (bio)polymers for the formation of silica and titania materials with complex structures.

A simple protein-mediated approach for preparing freestanding (silica free) microscale titania structures with morphologies inherited from complex-shaped, three-dimensional (3-D) biosilica templates (diatom frustules) is demonstrated. The silica diatom frustules were exposed in a repetitive alternating fashion to a silica-binding, titania-forming protein (protamine) and then to an aqueous titania precursor to build up a conformal titania-bearing coating. After organic pyrolysis at 500 °C, the conformal, continuous nature of the resulting crystalline anatase titania coating was confirmed by (i) demonstrating that a titania-coated frustule acted as a sensitive electrochemical hydrogen detector and (ii) selectively removing the silica templates to yield freestanding titania structures that retained the 3-D diatom frustule shape.

Here, a straightforward and general method for the rapid dendritic amplification of accessible surface functional groups on hydroxylated surfaces is described, with focus on its application to 3D biomineral surfaces. Reaction of hydroxyl-bearing silica surfaces with an aminosilane, followed by alternating exposure to a dipentaerythritol-derived polyacrylate solution and a polyamine solution, allows the rapid, layer-by-layer (LBL) build-up of hyperbranched polyamine/polyacrylate thin films. Characterization of such LBL-grown thin films by AFM, ellipsometry, XPS, and contact angle analyses reveals a stepwise and spatially homogeneous increase in film thickness with the number of applied layers. UV–Vis absorption analyses after fluorescein isothiocyanate labeling indicate that significant amine amplification is achieved after the deposition of only 2 layers with saturation achieved after 3–5 layers. Use of this thin-film surface amplification technique for hydroxyl-enrichment of biosilica templates facilitates the conformal surface sol–gel deposition of iron oxide that, upon controlled thermal treatment, is converted into a nanocrystalline (∼9.5 nm) magnetite (Fe3O4) coating. The specific adsorption of arsenic onto such magnetite-coated frustules from flowing, arsenic-bearing aqueous solutions is significantly higher than for commercial magnetite nanoparticles (≤50 nm in diameter).