Synthesis and controlled morphology of Ni@Ag core shell nanowires with excellent catalytic efficiency and recyclability.

Ni@Ag core shell nanowires (NWs) were prepared by in situ chemical reduction of Ag+ around NiNWs as the inner core. Different Ni@Ag NWs with controllable morphologies were achieved through the layer-plus-island growth mode and this mechanism was confirmed by scanning electron microscopy, X-ray fluorescence, and X-ray photoelectron spectroscopy analyses. When used as a catalyst, the synthesized Ni@Ag NWs exhibited high reduction efficiency by showing a high reaction rate constant k of 0.408 s-1 in reducing 4-nitrophenol at room temperature. Besides, combining the magnetic property, including high saturation magnetization and low coercivity, the magnetic NiNW core contributes to excellent recyclability and long-term stability with only a 2.2% performance loss after 10 recycles by magnets. The Ni@Ag NWs proposed here show unprecedentedly high potential in applications requiring high efficiency and a recyclable catalyst.

Excellent absorption properties of BaFe12-xNbxO19 controlled by multi-resonance permeability, enhanced permittivity, and the order of matching thickness.

For the sol-gel-derived BaFe12-xNbxO19 (x = 0-0.6), coercivity (Hc) and saturation magnetization (Ms) vary from 3.53-0.85 kOe and 70.3-53.8 emu g-1 to 1.02-0.22 kOe and 69.6-59.5 emu g-1, respectively, with an increase in sintering temperature from 1250 °C to 1350 °C. Moreover, ε' and ε'' increase from 4.13-4.04 and 0.0049-0.0045 to 7.64-6.93 and 1.50-0.97 over 26.5-40 GHz, and the multi-resonance peaks in permeability shift from ∼40+ GHz to ∼27 GHz. The bandwidth (BW) and reflection loss peak intensity (RLp) are broadened and enhanced from 0.8 GHz and -10.3 dB of the sample with x = 0.2 sintered at 1250 °C under 0.92 mm to 11.9+ GHz and -54 dB, respectively, of the sample with x = 0.6 sintered at 1350 °C under 0.86 mm around a millimeter-wave atmospheric window of 35 GHz. The effects of Nb5+ content (x) and sintering temperature on grain size, phase compositions, formations of Fe2+ and oxygen vacancy, and thus on static magnetism and EM parameters are investigated. The correlations of multi-resonance permeability, enhanced permittivity, and the order of matching thickness with absorption properties are also discussed in detail.

Mineralized collagen coatings formed by electrochemical deposition.

Understanding and controlling the process of electrochemical deposition (ECD) of a mineralized collagen coating on metallic orthopedic implants is important for engineering highly bioactive coatings. In this work, the influence of different ECD parameters was investigated. The results showed that the mineralization degree of the coatings increased with deposition time, voltage potential and H2O2 addition, while chitosan addition led to weakening of mineralization, heavy mineralization resulted in a porous coating morphology. Furthermore, two typical coatings, dense and porous, were analyzed to investigate their microstructure and evaluated for their cytocompatibility; the dense coating showed better osteoblast adhesion and proliferation. Based on our understanding of how the different coating parameters influenced the coating, we proposed an ECD process in which the pH gradient near the cathode and the collagen isoelectric point were suggested to play crucial roles in controlling the mineralization and morphology of the coatings. The proposed ECD process may offer a guide for controlled deposition of a desired bioactive coating.

Exchange coupling controlled ferrite with dual magnetic resonance and broad frequency bandwidth in microwave absorption.

Ti-doped barium ferrite powders BaFe12-x Ti x O19 (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by the sol-gel method. The phase structure and morphology were analyzed by x-ray diffraction (XRD) and scanning electron microscopy, respectively. The powders were also studied for their magnetic properties and microwave absorption. Results show that the Ti-doped barium ferrites (BFTO) exist in single phase and exhibit hexagonal plate-like structure. The anisotropy field Ha of the BFTO decreases almost linearly with the increase in Ti concentration, which leads to a shift of the natural resonance peak toward low frequency. Two natural resonance peaks appear, which can be assigned to the double values of the Landé factor g that are found to be ∼2.0 and ∼2.3 in the system and can be essentially attributed to the existence of Fe3+ ions and the exchange coupling effect between Fe3+ and Fe2+ ions, respectively. Such a dual resonance effect contributes a broad magnetic loss peak and thus a high attenuation constant, and leads to a dual reflection loss (RL) peak over the frequency range between 26.5 and 40 GHz. The high attenuation constants are between 350 and 500 at peak position. The optimal RL reaches around -45 dB and the practicable frequency bandwidth is beyond 11 GHz. This suggests that the BFTO powders could be used as microwave absorbing materials with extraordinary properties.

Preparation and antibiotic drug release of mineralized collagen coatings on titanium.

In this study, a mineralized collagen coating was electrolytically deposited onto titanium. The results showed that the mineralized collagen coatings with dense or porous morphology could be obtained. The mineral phase was mainly hydroxyapatite. In vitro evaluation showed the mineralized collagen coatings were stable in Kokubo's simulated body fluid, and displayed a good cytocompatibility in the cell multiplication test. The mineralized collagen coatings loaded with vancomycin hydrochloride showed an inhibitory effect on the growth of S. aureus. The present mineralized collagen coating demonstrates good suitability for surface modification of orthopedic metal implants.

Formation of calcium carbonate nanoparticles through the assembling effect of glucose and the influence on the properties of PDMS.

In order to prepare calcium carbonate nanoparticles in a green and environmentally friendly way, the concept of bio-mineralization has been proposed. Glucose, as a common small molecular organic substance found in organisms, participates in the mineralization process in cells. By adding glucose as a chemical additive, long chains of calcium carbonate form at the initial stage and then break granularly via over-carbonation. The average size of the calcium carbonate nanoparticles is about 40 nm based on the statistical analyses of three hundred particles. The growth mechanism of calcium carbonate under the influence of glucose is obtained. After the calcium carbonate nanoparticles are modified by sodium stearate, they are introduced to the PDMS matrix to achieve the composite material. Compared with pure PDMS, the composite with additional 3% calcium carbonate has its elongation at break and tensile strength increased by 23.96% and 48.15%, respectively.

Influence of substrates on the formation of the TiSi nanowire by atmosphere pressure chemical vapor deposition.

TiSi nanowires were deposited on both Si(111) and glass substrates by using SiH4, TiCl4 and N2 as the Si, Ti precursors and diluted gas respectively through atmosphere pressure chemical vapor deposition (APCVD) method. Effects of the substrates on formation of the nanowires were investigated. The results show that the nanowires can be formed on both Si(111) and glass substrates at ratio of SiH4/TiCl4 of 4. However, the quantities of the TiSi nanowires that formed with glass substrate are less than that with Si(111) substrate. The nanowires formed with glass substrate has length of 2-3 microm and diameters of 15-25 nm while that is 4-5 microm and 25-35 nm respectively with Si(111) substrate. Great quantities of the titanium silicide nanowires with relative higher contents of the C54 TiSi2 crystalline phase underneath can be obtained through improving the deposition conditions.

In Situ and Intraoperative Detection of the Ureter Injury Using a Highly Sensitive Piezoresistive Sensor with a Tunable Porous Structure.

Iatrogenic ureteral injury, as a commonly encountered problem in gynecologic, colorectal, and pelvic surgeries, is known to be difficult to detect in situ and in real-time. Consequently, this injury may be left untreated, thereby leading to serious complications such as infections, renal failure, or even death. Here, high-performance tubular porous pressure sensors were proposed to identify the ureter in situ intraoperatively. The electrical conductivity, mechanical compressibility, and sensor sensitivity can be tuned by changing the pore structure of porous conductive composites. A low percolation threshold of 0.33 vol % was achieved due to the segregated conductive network by pores. Pores also lead to a low effective Young's modulus and high compressibility of the composites and thus result in a high sensitivity of 448.2 kPa-1 of sensors, which is consistent with the results of COMSOL simulation. Self-mounted on the tip of forceps, the sensors can monitor tube pressures with different frequencies and amplitudes, as demonstrated using an artificial pump system. The sensors can also differentiate ureter pulses from aorta pulses of a Bama minipig in situ and in real-time. This work provides a facile, cost-effective, and nondestructive method to identify the ureter intraoperatively, which cannot be effectively achieved by traditional methods.

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.

Size- and density-controlled synthesis of TiO2 nanodots on a substrate by phase-separation-induced self-assembly.

This work presents a facile way, i.e. phase-separation-induced self-assembly, to prepare TiO(2) nanodots on a substrate. This method induces convective flow in a spin-coated titanium tetrabutoxide (TBOT)/polyvinyl pyrrolidone (PVP)/ethanol liquid film through the Marangoni effect and turns TBOT into crystalline TiO(2) nanodots on a substrate after calcination. The size and density of the TiO(2) nanodots can be finely tailored by controlling the concentrations of TBOT and PVP in the precursor sol. The TiO(2) nanodot-deposited surface showed a hydrophilic characteristic and the wettability was obviously improved by increasing nanodot size.

Anisotropy of Percolation Threshold of BaTiO3-Ni0.5Zn0.5Fe2O4 Composite Films.

A systematic study on the magnetic and electrical percolation phenomena of BaTiO3 (BTO)-NiZnF2O4 (NZFO) composite films is presented in this work with the purpose of simplifying the preparation process of high-performance 1-3-type multiferroic composite films. Results show that the percolation threshold of the composite films depends on the macroscopic dimension of the material. The low-dimensional nature of the composite films results in different percolation thresholds with topological transition in vertical and horizontal directions. BTO-NZFO composite films with a grain size of 15 nm and a thickness of 100 nm exhibited a percolation threshold of 0.18 in the normal direction and a percolation threshold of 0.48 in the horizontal direction. In light of this intriguing feature, a novel multiferroic composite film with 1-3 structure and strong magnetoelectric coupling was easily prepared by a 0-3 process via controlling the NZFO content in the region between two percolation thresholds.

Magnetoelectric coupling tailored by the orientation of the nanocrystals in only one component in percolative multiferroic composites.

Novel 1-3 type multiferroic composite thin films were prepared via a simple 0-3 composite fabrication process. The orientation of the Ni0.5Zn0.5Fe2O4 (NZFO) nanocrystals in the BaTiO3-Ni0.5Zn0.5Fe2O4 (BTO-NZFO) composite thin films was controlled by magnetron sputtering, and the controlling effect of such orientation on magnetoelectric coupling was investigated in detail. The NZFO lattice in the BTO-NZFO composite thin films grew with (100) orientation under the induction of the (111) plane of Si. The transfer of substrate stress between the closely contacted grains also contributes to the orientation of the NZFO nanocrystals. The 0.6BTO-0.4(100)NZFO multiferroic composite thin film exhibited a magnetization strength of 9.2% at the Curie point of the BTO phase, showing extremely strong magnetoelectric coupling characteristics. This work provides an effective strategy for the development of high-performance multiferroic composites, and brings about new conception of realizing strong magnetoelectric coupling effect from the perspective of physical chemistry.

A tri-phase percolative ceramic composite with high initial permeability and composition-independent giant permittivity.

The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO3 (BTO)/Ni0.5Zn0.5Fe2O4 (NZFO)/BaFe12O19 (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process of sol-gel and self-combustion methods. The content of the BFO phase could be tuned conveniently by controlling the preparation conditions. The as-prepared BTO/NZFO/BFO tri-phase composite exhibited unprecedented stable dielectric properties that were distinct from those of conventional percolative composites above the percolation threshold due to the existence of a third phase. When the volume fraction of the NZFO phase exceeds 55%, the electrical conductivity and effective permittivity of the composite remain at a stable value of about 10-5 S cm-1 and 10 000, respectively, which is almost independent of the composition. Such behavior is the result of the synergistic control effect of the percolation effect and specific phase composition in the system. It is evident that the stability of the dielectric properties of the composite is chiefly contributed by the introduction of the BFO phase. Meanwhile, the composite exhibited a relatively high permeability of ∼17 with 90% NZFO loading, and its saturated magnetization is larger than 73 emu g-1, approximately 95% of the pure NZFO phase. The finding of our BTO/NZFO/BFO tri-phase ceramic composite with stable giant permittivity and extremely high permeability paves a new way to solve the difficulty of property instability above the percolation threshold in the utilization of percolative materials.

Multimode Signal Processor Unit Based on the Ambipolar WSe2-Cr Schottky Junction.

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe2-Cr Schottky junction with an asymmetric Schottky contact area of the source and drain. A significant rectification ratio over 105 and multiple rectifying states (e.g., full pass, forward pass, off, and backward pass) were achieved in the single Schottky junction tuned by gate voltage. Furthermore, switching characteristic, rectification characteristic, and amplitude of a sin wave can be effectively modulated by the electrical field or light illumination in a signal process circuit based on the WSe2-Cr Schottky junction. The highly tunable Schottky junction working as a multimode signal processor unit has great potential in future optoelectronic-integrated chips.

Magnetic-Assisted Transparent and Flexible Percolative Composite for Highly Sensitive Piezoresistive Sensor via Hot Embossing Technology.

A highly transparent and flexible percolative composite with magnetic reduced graphene oxide@nickel nanowire (mGN) fillers in EcoFlex matrix is proposed as a sensing layer to fabricate high-performance flexible piezoresistive sensors. Large excluded volume and alignment of mGN fillers contribute to low percolation threshold (0.27 vol %) of mGN-EcoFlex composites, leading to high electrical conductivity of 0.003 S m-1, optical transmittance of 71.8%, and low Young's modulus of 122.8 kPa. Large-scale microdome templates for sensors are prepared by hot embossing technology cost-effectively and COMSOL Multiphysics is utilized to optimize the sensor performances. Piezoresistive sensors fabricated experimentally show superior average sensitivity of 1302.1 kPa-1 with a low device-to-device variation of 3.74%, which provides a new way to achieve transparent, highly sensitive, and large-scale electronic skin.

Fabrication and evaluation of Zn containing fluoridated hydroxyapatite layer with Zn release ability.

A biphasic layer with a Zn-containing beta-tricalcium phosphate (ZnTCP) phase and a fluoridated hydroxyapatite (FHA) phase on titanium alloy substrate was prepared by the sol-gel technique. Scanning electron microscopy and energy-dispersive X-ray analysis results showed the ZnTCP/FHA layer to have a heterogeneous surface with microscaled gibbous structures originating from ZnTCP particle agglomeration. This layer had a slow and sustained Zn release behavior. The scratch test result of the ZnTCP/FHA layer was 489+/-4mN, indicating good interface bonding between the layer and substrate. The ZnTCP/FHA layer supported cell growth, and showed a statistically significant increase in cell viability in comparison with another biphasic layer (TCP/FHA) without Zn. This work demonstrates that the present biphasic ZnTCP/FHA layer has the potential to play a significant role in enhancing bone growth when used as the outermost part of bioactive coatings on metallic implants.

A ferroelectric relaxor polymer-enhanced p-type WSe2 transistor.

WSe2 has attracted extensive attention for p-FETs due to its air stability and high mobility. However, the Fermi level of WSe2 is close to the middle of the band gap, which will induce a high contact resistance with metals and thus limit the field effect mobility. In this case, a high work voltage is always required to achieve a large ON/OFF ratio. Herein, a stable WSe2 p-doping technique of coating using a ferroelectric relaxor polymer P(VDF-TrFE-CFE) is proposed. Unlike other doping methods, P(VDF-TrFE-CFE) not only can modify the Fermi level of WSe2 but can also act as a high-k gate dielectric in an FET. Dramatic enhancement of the field effect hole mobility from 27 to 170 cm2 V-1 s-1 on a six-layer WSe2 FET has been achieved. Moreover, an FET device based on bilayer WSe2 with P(VDF-TrFE-CFE) as the top gate dielectric is fabricated, which exhibits high p-type performance over a low top gate voltage range. Furthermore, low-temperature experiments reveal the influence of the phase transition of P(VDF-TrFE-CFE) on the channel carrier density and mobility. With a decrease in temperature, field effect hole mobility increases and approaches up to 900 cm2 V-1 s-1 at 200 K. The combination of the p-doping and gating with P(VDF-TrFE-CFE) provides a promising solution for obtaining high-performance p-FET with 2D semiconductors.

A novel route to fabricate the biomedical material: structure strategy and the biologically active ions controllable release.

The multiple biologically active trace element delivery remains a problem in regeneration medicine and tissue engineering. A novel approach to fabricate the biologically active trace elements assembly in a core-shell system for cooperative controlled-release has been proposed. Firstly, using a pH-dependent electrostatic interaction, zinc and strontium ions were incorporated into the silica gel nanospheres. Subsequently a porous octacalcium phosphate (OCP) shell was coated on the nanospheres tailored by poly(acrylate sodium) molecules. In vitro test shows that this hierarchical multilayered nanostructure can achieve a shell-/pH-dependent controlled-release of silicon, strontium and zinc ions. The wet-chemical route to selective synthesis of the core-shell Silica@OCP system may provide a general model to develop cooperative encapsulation of biologically active ions in a silica-based system by using layer-by-layer assembly technique for controlled-release in biomedical areas.

Preparation, characterization and cytocompatibility of porous ACP/PLLA composites.

The purpose of this work was to incorporate amorphous calcium phosphate (ACP) into porous poly(L-lactic acid) (PLLA), because ACP is capable of fast phase transformation and morphological change in body fluid, such, a desired pore wall surface within bone tissue engineering scaffolds can be created. A highly porous ACP/PLLA composite was prepared by a thermally induced phase separation technique. The results showed that the composite had an interconnected pore structure with 100 mum macropores and 10 mum micropores, and 91% porosity; 40 nm primary particles of ACP were agglomerated to 3 mum aggregates, and the aggregates were homogeneously distributed in pore walls; These aggregates showed to be in situ transformed into bone-like apatite after 1 h soaking in phosphate buffered saline solution. Human osteoblast-like cell culture showed that the ACP/PLLA composite had better cell adhesion and alkaline phosphotase activity than pure PLLA. This study demonstrates that the ACP/PLLA composite can enhance cytocompatibility and could act as a promising scaffold for bone tissue engineering.

Preparation and characterization of porous beta-tricalcium phosphate/collagen composites with an integrated structure.

Porous beta-tricalcium phosphate (TCP)/collagen composites with different beta-TCP/collagen weight ratio were prepared. The influences of the preparation conditions on the microstructure of porous composite and the joint status of beta-TCP particles with collagen fibrils were characterized by X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The results showed: (1) an acid treatment could effectively disassemble collagen fibrils; (2) in the resulting porous composites, beta-TCP particles homogenously existed on the skeleton of the collagen fibril network and bonded tightly to both the fibrils and themselves. The tight bonding formation could be due to the reaction between Ca ions in the particles and carboxyl groups in collagen polypeptide chains and due to the reprecipitation of partially dissolved beta-TCP during synthesis. The tight bonding between beta-TCP particles and collagen fibrils in the composites demonstrated an integrated structure, which was reproducible when beta-TCP/collagen ratio ranged from 2 to 4. Such integrated structure would make significant contributions in reliably tailoring properties of the porous composites by varying beta-TCP content. In addition, the porous composites had large porosity (approximately 95%) and appropriate pore size (approximately 100 microm), showed no negative impact in cytotoxicity assay and complete bone tissue regeneration after 12 weeks in animal test.