Search

Chondrocytic hypertrophy, a phenotype not observed in healthy hyaline cartilage, is often concomitant with the chondrogenesis of human mesenchymal stromal cells (hMSCs). This undesired feature represents one of the major obstacles in applying hMSCs for hyaline cartilage repair. Previously, we developed a method to induce hMSC chondrogenesis within self-generated extracellular matrix (mECM), which formed a cartilage tissue with a lower hypertrophy level than conventional hMSC pellets. In this study, we aimed to test the utility of hypoxia and insulin-like growth factor-1 (IGF1) on further reducing hypertrophy. MSC-mECM constructs were first subjected to chondrogenic culture in normoxic or hypoxic (5%) conditions. The results indicated that hMSC-derived cartilage formed in hypoxic culture displayed a significantly reduced hypertrophy level than normoxic culture. However, hMSC chondrogenesis was also suppressed under hypoxic culture, partially due to the reduced activity of the IGF1 pathway. IGF1 was then supplemented in the chondrogenic medium, which promoted remarkable hMSC chondrogenesis under hypoxic culture. Interestingly, the IGF1-enhanced hMSC chondrogenesis, under hypoxic culture, was not at the expense of promoting significantly increased hypertrophy. Lastly, the cartilage tissues created by hMSCs with different conditions were implanted into osteochondral defect in rats. The results indicated that the tissue formed under hypoxic condition and induced with IGF1-supplemented chondrogenic medium displayed the best reparative results with minimal hypertrophy level. Our results demonstrate a new method to generate hyaline cartilage-like tissue from hMSCs without using exogenous scaffolds, which further pave the road for the clinical application of hMSC-based cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: In this study, hyaline cartilage-like tissues were generated from human mesenchymal stromal cells (hMSCs), which displayed robust capacity in repairing the osteochondral defect in rats. In particular, the extracellular matrix created by hMSCs was used, so no exogenous scaffold was needed. Through a series of optimization, we defined that hypoxic culture and supplementation of insulin-like growth factor-1 (IGF-1) in chondrogenic medium resulted in robust cartilage formation with minimal hypertrophy. We also demonstrated that hypoxic culture suppressed chondrogenesis and hypertrophy through modulating the Wnt/β-catenin and IGF1 pathways, respectively. Our results demonstrate a new method to generate hyaline cartilage-like tissue from hMSCs without using exogenous scaffolds, which will further pave the road for the clinical application of hMSCs-based cartilage tissue engineering.

A room temperature halide exchange mediated cation exchange strategy leads to Ln3+ doping in perovskite NPs.

We have for the first time elucidated the microstructural evolution and deformation behaviors of a gradient textured AZ31B Mg alloy plate under the ultrahigh strain rate of ~106 s−1 that is generated by a two-stage light gas gun with the hypervelocities of 1.6−4.4 km s−1. The hypervelocity impact cratering behaviors indicate that the cratering deformation of AZ31B Mg alloy is mainly affected by the inertia and strength of the target material. The crater prediction equation of AZ31B Mg alloy target under impact velocity of 5 km s−1 is given. The 2017Al projectile completely melts in the Mg alloy target plate at the impact velocities of 3.8 km s−1 and 4.4 km s−1, and the microstructural evolution around the crater is: dynamic recrystallization zone, high-density twinning zone, low-density twinning zone, and Mg alloy matrix. It is found that the dynamic recrystallization, twinning and cracking are the main deformation behaviors for the AZ31B Mg alloy to absorb the shock wave energy and release the stress generated by the hypervelocity impact. The main plastic deformation mechanisms of the Mg alloy target during hypervelocity impact are twinning and dislocation slip. Microstructure analysis shows the interactions of twins-twins, dislocations-dislocations, and twins-dislocations determine the strain hardening during the hypervelocity impact process, which eventually contributes the dynamic mechanical properties. The evolution of microhardness around the crater further demonstrates the microstructural evolutions and their interactions under the hypervelocity impacts.

Grain boundary (GB) structural change is commonly observed during and after stress-driven GB migration in nanocrystalline materials, but its exact atomic scale transformation has not been explored experimentally. Here, using in situ high-resolution transmission electron microscopy combined with molecular dynamics simulations, we observed the dynamic GB structural transformation stemming from reversible facet transformation and GB dissociation during the shear-mediated migration of faceted GBs in gold nanocrystals. A reversible transformation was found to occur between (002)/(111) and Σ11(113) GB facets, accomplished by the coalescence and detachment of ( 1 ¯ 1 ¯ 1 ) / ( 002 ) -type GB steps or disconnections that mediated the GB migration. In comparison, the dissociation of (002)/(111) GB into Σ11(113) and Σ3(111) GBs occurred via the reaction of ( 111 ) / ( 11 1 ¯ ) -type steps that involved the emission of partial dislocations. Furthermore, these transformations were loading dependent and could be accommodated by GB junctions. This work provides atomistic insights into the dynamic structural transformation during GB migration.

Transmission Electron Microscopy (TEM) offers multiple advanced techniques such as imaging, diffraction, and spectroscopy to learn essential information about the physical, chemical, and structural properties of materials at the microscale to nanoscale to atomic scale. It is a critical tool for studies of sizes, shapes, defects, crystal and surface structures, compositions, and electronic states of nanometer-size areas of thin films, nanoparticles, and nanostructured systems. This article first gives a brief introduction to the TEM-based techniques. It then highlights recent application examples of TEM in the studies of nanostructured heat-assisted magnetic materials, electronics, and photovoltaics to illustrate the critical role of the TEM techniques in various research and development fields of nanoscience and nanotechnology.

This study aimed to characterize porcine Achilles tendon (PAT) in terms of its structural components, vascularity, and resident tendon cells. We found that PAT is composed of a paratenon sheath, a core of fascicles, and an endotenon/interfascicular matrix (IFM) that encases the fascicle bundles. We analyzed each of these three tendon components structurally using tissue sections, and by isolating cells from each component and analyzing in vitro. Many blood vessel-like tissues were present in the paratenon and IFM but not in fascicles, and the vessels in the paratenon and IFM appeared to be inter-connected. Cells isolated from the paratenon and IFM displayed characteristics of vascular stem/progenitor cells expressing the markers CD105, CD31, with α-smooth muscle actin (α-SMA) localized surrounding blood vessels. The isolated cells from paratenon and IFM also harbored abundant stem/progenitor cells as evidenced by their ability to form colonies, and express stem cell markers including CD73 and CD146. Furthermore, we demonstrate that both paratenon and IFM isolated cells are capable of undergoing multi-differentiation. In addition, both paratenon and IFM cells expressed elastin, osteocalcin, tubulin polymerization promoting protein (TPPP), and collagen IV, whereas fascicle cells expressed none of these markers, except collagen I. The neurotransmitter substance P (SP) was also found in the paratenon and IFM localized surrounding blood vessels. The findings of this study will help us to better understand the vascular and cellular mechanisms of tendon homeostasis, injury, healing, and regeneration.

This study presents a post-synthetic ligand modification strategy for the generation of chiroptically active, blue emitting CsPbBr3 nanoparticles (NPs) – an expansion to the library of 3D chiral perovskite nanomaterials. Addition of [R- and S-] 1-phenylethylamine, 1-(1-naphthyl)ethylamine, or 2-aminooctane to the synthesized CsPbBr3 NPs is shown to induce Cotton effects in the NP first exciton transition, suggestive of a successful electronic coupling between the chiral ligands and the NPs. The availability of these chiral CsPbBr3 NPs thrusts them into the forefront of perovskite nanomaterials for examining the implications of the chiral induced spin selectivity (CISS) effect and other applications in spintronics.

This study presents a halide exchange mediated cation exchange strategy for a room temperature doping of trivalent lanthanide cations (Ln

While bio-inspired synthesis offers great potential for controlling nucleation and growth of inorganic particles, precisely tuning biomolecule-particle interactions is a long-standing challenge. Herein, we used variations in peptoid sequence to manipulate peptoid-Au interactions, leading to the synthesis of concave five-fold twinned, five-pointed Au nanostars via a process of repeated particle attachment and facet stabilization. Ex situ and liquid-phase TEM observations show that a balance between particle attachment biased to occur near the star points, preferential growth along the [100] direction, and stabilization of (111) facets is critical to forming star-shaped particles. Molecular simulations predict that interaction strengths between peptoids and distinct Au facets differ significantly and thus can alter attachment kinetics and surface energies to form the stars. This work provides new insights into how sequence-defined ligands affect particle growth to regulate crystal morphology.

Our work reports on the fundamental details of the crystal structure and phase transformations in Ba(Fe0.7Ta0.3)O3-δ, the best known temperature-independent oxygen-sensing ceramic material for applications in extreme environments. Ba(Fe0.7Ta0.3)O3-δ ceramics were synthesized using conventional solid-state ceramic reaction under variable sintering temperatures (Ts = 1200–1350 °C). Combined X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements revealed the Ts-induced phase transformations and their origin in Ba(Fe0.7Ta0.3)O3-δ. Associated with phase transformations, pseudo-cubic (PC) reflections, such as {200}PC, {211}PC, and {220}PC, exhibited distinct anomalies with increasing Ts. At Ts = 1200 °C, Ba(Fe0.7Ta0.3)O3-δ stabilized in mixed orthorhombic + rhombohedral phases (Amm2 + R3m). With increasing Ts (≥1250 °C), Ba(Fe0.7Ta0.3)O3-δ ceramics stabilized in tetragonal/rhombohedral [P4mm + R3m] mixed phases, while variations in the quantity of the respective phases were observed. Because both structure and crystal chemistry play key roles in achieving enhanced performance in chemical sensing and catalytic converters, detailed understanding of the phase transformations and crystal structure of Ba(Fe0.7Ta0.3)O3-δ ceramics, as derived in this work, will be useful to develop chemical sensors with optimum performance for high-temperature and corrosive environments.

The ability of plasmonic metal nanostructures (PMNs), such as silver and gold nanoparticles, to manipulate and concentrate electromagnetic fields at the nanoscale is the foundation for wide range o...

Correction for ‘Self-cleaning, high transmission, near unity haze OTS/silica nanostructured glass’ by Sajad Haghanifar et al., J. Mater. Chem. C, 2018, 6, 9191–9199, https://doi.org/10.1039/C8TC02513D.

Identification, development, and engineering of high-performance, earth-abundant, and cost-effective precious group metal (PGM)-free electrocatalysts for catalyzing oxygen evolution reaction (OER) ...

This paper reports on the formation of moth-eye nanopillar structures on surfaces of alkali-aluminosilicate Gorilla glass substrates using a self-masking plasma etching method. Surface and cross-section chemical compositions studies were carried out to study the formation of the nanostructures. CF x induced polymers were shown to be the self-masking material during plasma etching. The nanostructures enhance transmission at wavelengths over 525 nm may be utilized for fluid-induced switchable haze. Additional functionalities associated with nanostructures may be realized such as self-cleaning, anti-fogging, and stain-resistance.

This study presents a post-synthetic ligand modification strategy for the generation of chiroptically active, blue emitting CsPbBr

We report for the first time on the parahydrophobicity and stick-slip wetting dynamics of vertically aligned carbon-nanotube (CNT) forests and compare it with previously observed droplet infiltration characteristics. CNT surfaces have generally been reported to be superhydrophobic, but unstable, as the water rapidly infiltrates the forest. In this paper, we demonstrate the first observation of parahydrophobicity of CNT forests, where the surface exhibits an apparent static water contact angle close to 150° but may be turned upside down without the droplet rolling off. Evaporation plays a critical role in the dynamic wetting behavior of these high-density samples as water droplets are stable in moisture-saturated environments. The wetting dynamics in the ambient is driven by evaporation as opposed to infiltration and characterized by contact line pinning from the strong adhesive forces in the CNTs. The pinning force at the contact line gradually increases as the droplet evaporates until a critical force is reached, where the contact line suddenly jumps radially inward with a concomitant deflection of CNTs inward. We observe that taller CNT forests have a higher critical force for deflection and coalesce into cellular patterns with larger cell size, which both suggest that taller CNTs have stronger mechanical interactions with each other.

The effect of titanium (Ti) doping on the crystal structure, phase, surface/interface chemistry, microstructure and optical band gap of gallium oxide (Ga2O3) (GTO) films is reported. The Ti content was varied from 0 to ~ 5 at% in co-sputtering, using Ga2O3 ceramic and Ti metal targets, deposited GTO films produced. The sputtering power to the Ti target was varied in the range of 0–100 W, while keeping the sputtering power to Ga2O3 constant at 100 W, to produce GTO films with 0–5 at% Ti. The Ti-incorporation-induced effects were significant for the crystal structure, phase, surface/interface chemistry and morphology, which in turn induce changes in the band gap. The high-resolution core-level X-ray photoelectron spectroscopy (XPS) analyses confirm that the Ga ions exist as Ga3+ in both intrinsic Ga oxide and GTO films. However, XPS data reveal the formation of Ga2O3–TiO2 films with the presence of Ti4+ ions with increasing Ti sputtering power, i.e., higher Ti contents in GTO. Evidence for the formation of nanocrystalline Ga2O3–TiO2 films was also found in the structural analyses performed using electron microscopy and grazing incidence X-ray diffraction. Significant band gap reduction (Eg ~ 0.9 eV) occurs in GTO films with increasing Ti dopant concentration from 0 to 5 at%. A correlation between the Ti dopant concentration, surface/interface chemistry, microstructure and band gap of GTO films is established.

While nitrogen doping greatly broadens graphene applications, relatively little is known about the influence of this heteroatom on the biological activity of graphene. A set of systematically modified nitrogen-doped graphene (NG) materials was synthesized using the hydrothermal method in which the degree of N-doping and N-bonding type is manipulated using two nitrogen precursors (urea and uric acid) and different thermal annealing temperatures. The bioactivity of the NG samples was evaluated using the oxidation of the intracellular antioxidant glutathione (GSH) and bacterial viability (of Escherichia coli K12), and oxidative stress was identified as the predominant antibacterial mechanism. Two key energy-relevant electrochemical reactions, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), were used to characterize the influence of different N-types on the electronic properties of the NG materials. Electron-donating graphitic-N and electron-withdrawing pyridinic-N were identified as effective promoters for ORR and OER, respectively. The similar mechanisms between the GSH oxidation (indicative of oxidative stress) and ORR mechanisms reveal the role of graphitic-N as the active site in oxidative stress related bioactivity, independent of other consequential properties (e.g., defect density, surface area). This work advances a growing rational design paradigm for graphene family materials using chemical composition and further provides valuable insight into the performance-hazard tradeoffs of NG applications in related fields.

Two-dimensional (2D) transition-metal dichalcogenide superconductors have unique and desirable properties for integration with conventional superconducting circuits. However, fully superconducting contact must be made between the 2D material and three-dimensional (3D) superconductors in order to employ the standard microwave drive and readout of qubits in such circuits. Here, we present a method for creating zero-resistance contacts between 2D NbSe$_2$ and 3D aluminum that behave as Josephson junctions (JJs) with large effective areas compared to 3D-3D JJs. We present a model for the supercurrent flow in a 2D-3D superconducting structure by numerical solution of the Ginzburg-Landau equations and find good agreement with experiment. These results demonstrate a crucial step towards a new generation of hybrid superconducting quantum circuits., Comment: 14 pages, 13 figures

Transient absorption captures dynamics of nanocubes, showing negative delay-time signals associated with perturbed free induction. This validates dielectric-resonance energy transfer between electromagnetic modes for light-harvesting applications.

High nickel content layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising cathode material with a high theoretical capacity of 200 mAh g−1 for use in high energy density lithium-ion batteries. However, its surface can easily get passivated by LiOH and Li2CO3 due to its surface residual Li2O being reacting with ambient moisture and CO2. Herein, NMC811 was treated in a 3.0 M solution of lithium bis(fluorosulfonyl)imide (LiFSI) in dimethyl carbonate (DMC) at 60 °C for 8 h, 16 h and 24 h, respectively, resulting in coating of the NMC811 surface with LiF due to the basic nature of those residual lithium salts that react with LiFSI. The facile treatment of NMC811 in LiFSI/DMC not only improves the cycling stability but also enhances the capacity of the Li/NMC811 cells, mainly because of the thinning of the Li2CO3 layer as suggested by cyclic voltammograms and impedance analyses. This method opens a new avenue for activation of passivated NMC811 particles for practical battery applications.

High haze, high transparency substrates can increase the power conversion and extraction efficiency of solar cells and light emitting diodes (LEDs), respectively. In this paper, we demonstrate a new octadecyltrichlorosilane (OTS)/silica nanostructured substrate that displays high transmission (91.5 ± 0.5% at 550 nm wavelength) and near unity haze (98.1 ± 0.5% at the same wavelength) with 143° scattering angle. The OTS/silica nanostructures are fabricated through a scalable and facile maskless reactive ion etching (MRIE) process followed by OTS coating. The OTS coating enhances the transmission of the structures by merging silica nanostructures together by capillary forces and effectively grading the index of refraction. The OTS/silica nanostructures display the highest combination of both transmission and haze in the literature as defined by Pareto optimality. The OTS/silica nanostructured glass exhibits lotus leaf-like wetting with a 159.7 ± 0.6° water contact angle (WCA) and 4.9 ± 0.6° contact angle hysteresis. We demonstrate the structures have self-cleaning functionality where about 100% of transparency can be easily recovered after graphite soiled substrates are rinsed with water. This self-cleaning functionality is maintained after 200 cycles of soiling and cleaning. The OTS/silica nanostructured glass may be an important substrate in optoelectronic applications where a combination of high transmission, high haze, and self cleaning function are important.

Due to the temperature gradients generated from the complex heating and cooling cycles during Laser Powder Bed Fusion, strong columnar texture is often observed in the as-built Inconel 718 alloys together with notable residual stress, which leads to anisotropic properties of manufactured alloy components. We found that, in contrast to the typical homogenization performed at 1065°C, a simple higher temperature homogenization step conducted at 1180°C can effectively remove the residual stress and reconstruct the microstructure by introducing recrystallization. More importantly, it can introduce isotropic microstructures and tensile properties, which are critical in engineering applications. Additionally, owing to the elimination of the residual stress, the precipitation of the strengthening phase γ″ becomes more isotropic (i.e., with three variants precipitating) during the subsequent aging process. This work is conducive to developing effective post-heat treatment of additively manufactured alloys for better performance.

Single crystalline (SC) cathode materials, which are less susceptible to micro/nano-cracks formation and offer better structure stability compared to the polycrystalline counterpart, have attained great attention. However, the parasitic side reactions at the cathode-electrolyte interface induces the loss of active species, which consequently leads to continual degradation of the electrochemical performances. Herein, a triple coupling of concentration-gradient Na+, F- co-doping and surface NaF coating are exploited for the first time on SC LiNi0.5Co0.2Mn0.3O2 cathode by the hydrolysis of NaPF6. This process regulates the external structure of materials by constructing a “sandwich” configuration from surface to bulk: rock salt - mixing zone - layered phase. The detailed interface transformation mechanism is revealed by Neutron powder diffraction (NPD), spherical aberration corrected high-resolution scanning transmission electron microscopy (HR-STEM), electron energy loss spectroscopy (EELS), and Ar+ sputtering assisted X-ray photoelectron spectroscopy (XPS). The synergistic effects endow the SC cathode with outstanding capacity retentions: 91.3% at 25 °C and 85% at 45 °C, after 500 cycles at 5 C between 3.0 and 4.5 V. In addition, a high full-cell reversible capacity of 168.9 mAh g−1 with a capacity retention of 92.4% is achieved after 300 cycles at 1 C. Multiple characterizations further indicate that these superior results are mainly ascribed to the overall structure integrity of SC material, the thin cathode electrolyte interface, high content of lithium fluoride, and the low solubility of transition metal ions. This work opens a new avenue to construct a benign interface towards high-performance lithium ion batteries.

Magnesium (Mg) and its alloys are promising candidates for use as resorbable materials for biomedical devices that can degrade in situ following healing of the defect, eliminating the need for a second surgery to remove the device. Hydrogen gas is the main product of magnesium corrosion, and one of the limitations for use of Mg devices in clinic is the formation of gas pockets around them. One potential solution to this problem is reducing the rate of corrosion to the levels at which H2 can diffuse through the body fluids. The study’s aim was to evaluate the potential of hybrid alkylsilane self-assembled multilayer coatings to reduce Mg corrosion and to modify physicochemical properties of the coatings using surface functionalization. The coating was made by copolymerization of n-Decyltriethoxysilane and Tetramethoxysilane followed by dip coating of metal discs. This resulted in a formation of homogeneous, micron thick, and defect free coating. The coated surface was more hydrophobic than bare Mg, however...

A new approach to measure the cross-plane thermal diffusivity of a microscale slab sample, which can be fabricated by the focused ion beam and attached to a substrate, is proposed. An intensity-modulated pump laser is applied to heat the front surface of the sample uniformly, and the thermoreflectance signal is observed at the rear surface to evaluate thermal wave transport in the material. The thermal diffusivity can be obtained by fitting the phase lags of the experimental data with a theoretical model. The model was developed for the sample with thin-film coatings and heat transfer to the substrate. Although the absorbed heat can cause a significant DC temperature increase in the microscale sample, a thin-film coating with high thermal conductivity can effectively reduce the DC temperature increase within low thermal conductivity samples. To validate the method, we conducted measurements of a fused silica sample of 2.16 µm thickness, coated with 95 nm Ti film on the front surface and 120 nm Au film on the rear surface. The measured thermal diffusivity is in good agreement with the literature value. The uncertainty analysis shows that the measurement uncertainty is within 6%. This proposed approach, designed for microscale samples, offers a unique option for thermal property measurements of special materials, such as irradiated nuclear fuel or other irradiated materials, to enable microscale property determination while minimizing sample radioactivity.

Recent research results discover that graphene nanoplatelets (GNPs) and graphene oxide nanoplatelets (GONPs) are capable of enhancing the smartness as well as improving the strength of cementitious materials by utilizing their unique mechanical, thermal and electrical properties. Although the graphene-reinforced concrete exhibits promising potentials in these studies, its application to construction practice demands for a deeper understanding of the effects of graphene nano-particles on the durability-related properties of concrete. To meet this need, this study is focused on the strength, corrosion resistance and freeze-and-thaw performance of graphene-reinforced cementitious materials. In this investigation, the mortar specimens reinforced by different types of GNPs and GONPs are tested and then compared with the benchmark samples. To capture the reinforcement mechanisms of graphene, nano-scale characterization is carried out with a focus on the microstructure of the cement paste around the graphene nano-particles. The observed microstructure morphology and modulus profile show that GNPs and GONPs can significantly reshape the microstructure of cement paste. Based on the micro-characterization, atomistic models of the graphene-reinforced C-S-H gels are constructed and the freeze-and-thaw process is simulated. It is found that in addition to the reshaped microstructure, the effects of graphene and graphene oxides on water migration in the nano-pores of cement paste play an important role in the frost resistance of graphene-reinforced concrete.

Hybrid superconductor-semiconductor structures attract increasing attention owing to a variety of potential applications in quantum computing devices. They can serve to the realization of topological superconducting systems, as well as gate-tunable superconducting quantum bits. Here we combine a SiGe/Ge/SiGe quantum-well heterostructure hosting high-mobility two-dimensional holes and aluminum superconducting leads to realize prototypical hybrid devices, such as Josephson field-effect transistors (JoFETs) and superconducting quantum interference devices (SQUIDs). We observe gate-controlled supercurrent transport with Ge channels as long as one micrometer and estimate the induced superconducting gap from tunnel spectroscopy measurements in superconducting point-contact devices. Transmission electron microscopy reveals the diffusion of Ge into the aluminum contacts, whereas no aluminum is detected in the Ge channel.

We report an experimental study on the fabrication and characterization of hierarchical graphene/metal grid structures for transparent conductors. The hierarchical structure allows for uniform and local current conductivity due to the graphene and exhibits low sheet resistance because the microscale silver grid serves as a conductive backbone. Our samples demonstrate 94% diffusive transmission with a sheet resistance of 0.6 Ω/sq and a direct current to optical conductivity ratio σdc/σop of 8900. The sheet resistance of the hierarchical structure may be improved by over 3 orders of magnitude and with little decrease in transmission compared with graphene. Furthermore, the graphene protects the silver grid from thermal oxidation and better maintains the sheet resistance of the structure at elevated temperature. The graphene also strengthens the adhesion of the metal grid with the substrate such that the structure is more resilient under repeated bending.