Enhanced stress transfer and thermal properties of polyimide composites with covalent functionalized reduced graphene oxide

This work prepares (3-aminopropyl) trimethoxysilane (APTMS)-functionalized reduced graphene oxide (APTMS-rGO)/polyimide (PI) composite (APTMS-rGO/PI) through in-situ polymerization. NH₂-functionalized rGO coupled by APTMS demonstrates the good reinforced efficiency in mechanical and thermal properties, which is ascribed to the covalent-functionalized PI matrix by APTMS-rGO sheets. The uniform dispersion of APTMS-rGO increases the glass transition temperature (Tg) and the thermal decomposition temperature (Td), exhibiting 21.7 °C and 44 °C improvements, respectively. The tensile strength of the composites with 0.3 wt% APTMS-rGO is 31% higher than that of neat PI, and Young’s modulus is 35% higher than that of neat PI. Raman spectroscopy show the obvious G band shift, and also clearly demonstrates the enhanced interfacial interaction between rGO nanofillers and PI matrix. The high mechanical property of the APTMS-rGO/PI composites is attributed to the covalent functionalized GO by NH₂ groups and its good dispersion in comparison with GO.     

Reduction-responsive drug delivery based on mesoporous silica nanoparticle core with crosslinked poly(acrylic acid) shell

A novel reduction-responsive drug delivery system was successfully constructed with mesoporous silica nanoparticle (MSN) core as a drug carrier and poly(acrylic acid) (PAA) shell crosslinked by disulfide linkages as a drug release switcher. To keep the pore structure of MSN intact, PAA was covalently attached to the exterior surface of MSN before removing structure-template via radical polymerization. After removing structure-template and loading doxorubicin (DOX), the PAA shell was crosslinked by cystamine dihydrochloride through amidation reaction. The loading content and the entrapment efficiency of DOX could reach up to 40.2% and 80.4%, respectively. Because that the dissociation of disulfide linkage is reduction-responsive, the release behavior of DOX could be controlled by varying the concentration of reductant, and the release rate was 49.4% after 24 h with the existence of 2 mM glutathione (simulated environment of cancer cells), about three times higher than that of without glutathione (corresponding to normal human cells), which was only 16.9%. The in vitro cell assays demonstrated that the disulfide linkages crosslinked MSN–PAA (MSN–PAA-crosslinked) was highly biocompatible and suitable to use as drug carrier, and the DOX loaded MSN–PAA-crosslinked showed remarkable cytotoxicity to HeLa cells (human cancer cells), and relatively lower cytotoxicity to 293 cells (human normal cells). These results imply that the MSN–PAA-crosslinked is a promising platform to construct reduction-responsive controlled drug delivery system for cancer therapy.     

Free-standing functional graphene reinforced carbon films with excellent mechanical properties and superhydrophobic characteristic

In this work, we reported a simple method to fabricate novel free-standing stiff carbon-based composite films with excellent mechanical properties and superhydrophobic behaviors. The free-standing stiff carbon composite films based on reduced graphene oxide/glassy carbon (rGO/GC) were prepared by the combination of in-situ polymerization and carbonization process. The obtained composite films exhibited excellent mechanical properties by the addition of rGO nanosheets. It was found that incorporating 0.5 wt.% of rGO sheets in GC precursors resulted in enhancements of 99% in strength (202.6 MPa) and 184% in modulus (33.8 GPa), respectively. More interestingly, carbon nanoarrays were uniformly grown on the surface of composite films by the incorporation of rGO sheets. Superhydrophobic surfaces of carbon films were subsequently formed through functionalizing carbon nanoarrays with Trichloro(1H, 1H, 2H, 2H-perfluorodecyl)silane. Contact angle (CA) analysis suggested that superhydrophobic surfaces with a CA as high as 155° could be formed through optimizing the fabrication process.     

Tensile properties of hot rolled Mg–3Sn–1Ca alloy sheets at elevated temperatures

Mechanical behavior of hot rolled Mg–3Sn–1Ca (TX31) magnesium alloy sheets were studied in the temperature range 25–350 °C. The microstructure of the alloy consisted of the eutectic structure of α-Mg + Mg₂Sn and a dispersion of needle-like CaMgSn. The highest room-temperature ductility of 18% was obtained by hot rolling of the cast slabs at 440 °C, followed by annealing at 420 °C. The high temperature tensile deformation of the material was characterized by a decrease in work hardening exponent (n) and an increase in strain rate sensitivity index (m). These variations resulted in respective drops of proof stress and tensile strength from 126.5 MPa and 220 MPa at room temperature to 23.5 MPa and 29 MPa at 350 °C. This was in contrast to the ductility of the alloy which increased from 18% at room temperature to 56% at 350 °C. The observed variations in strength and ductility were ascribed to the activity of non-basal slip systems and dynamic recovery at high temperatures. The TX31 alloy showed lower strength than AZ31 magnesium alloy at low temperatures, while it exhibited superior strength at temperatures higher than 200 °C, mainly due to the presence of thermally stable CaMgSn particles.     

Effect of reduced graphene oxide (rGO) on structural,optical, and dielectric properties of Mg(OH)2/rGO nanocomposites

In this paper, we report the synthesis of Mg(OH)₂ NPs and Mg(OH)₂–rGO nanocomposites (NCs) by microwave assisted co-precipitation method. The crystal phase, structural morphology and functional groups of the as-synthesized samples were analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Raman spectroscopy was used to study the defects in the samples. Raman spectroscopy and the SEM results validate the growth of Mg(OH)₂ NPs on the rGO nanosheets. The chemical composition of the prepared samples was analyzed by EDAX. Optical properties of the as-synthesized samples were studied by UV–visible spectroscopy and the energy band gap was calculated by Tauc relation which shows a decrease in band gap with an increase in the amount of Graphene Oxide (GO) in the NCs. The dielectric properties were studied as a function of frequency over a range of 50 Hz to 5 MHz at room temperature. The value of dielectric constant decreases with an increase in frequency, this could be due to the existence of a polarization process at the border of the rGO sheets and Mg(OH)₂ NPs. The value of dielectric loss shows a decreasing trend with an increase in frequency whereas the larger value of AC conductivity in Mg(OH)₂–rGO NCs as compared to Mg(OH)₂ NPs approves the restoration of sp² network in the graphene sheets.     

Effect of grain size on mechanical,surface and biological properties of microwave sintered hydroxyapatite

Hydroxyapatite (HA) compacts having average grain sizes of 168 ± 0.086 nm, 1.48 ± 0.627 μm and 5.01 ± 1.02 μm are processed from synthesized HA powder by microwave sintering at varying sintering temperature for different times. Superior mechanical and biological properties are shown by nano-grain HA compacts as compared to their micron grained counterparts. Compressive strength, indentation hardness, and indentation fracture toughness are increased with the decrease in HA grain size. The highest surface energy and maximum wettability are exhibited by nano-grain HA. HA compacts are assessed for cell–material interaction by SEM, MTT and immunochemistry assays using human osteoblast cell line for 1, 5 and 11 days. MTT assays showed higher number of living cells and faster proliferation on nano-grain HA surface. Osteoblast cells on nano-grain HA surface expressed significantly higher amount of vinculin and alkaline phosphatase (ALP) protein markers for cell adhesion and differentiation respectively. This study shows the effect of grain size on physical, mechanical and in vitro biological properties of microwave sintered HA compacts.     

Achieving a weak basal texture in a Mg–6Al–3Sn alloy by wave-shaped die rolling

An innovative rolling approach was proposed to achieve weak basal texture in rolled Mg alloy sheets, by laying a wave-shaped die during rolling. It was shown that, Mg–6Al–3Sn (AT63) alloy sheets processed by this wave-shaped die rolling (labeled as WDR) exhibited basal textures with low intensity and tilted basal peak. A substantial basal texture weakening was found to occur during WDR after a single pass. Moreover, the WDRed alloy sheets exhibited basal texture gradients through the center to the surface, reflecting the asymmetric deformation mode of the sheets during rolling. In addition, WDR was effective to refine the grain size of AT63 alloy, from ~ 35 μm to ~ 10.3–11.5 μm. Tensile tests revealed that, the WDRed AT63 sheets presented much enhanced strain hardening ability (n = 0.295) and high elongation to failure (ε_f = 22.5%), as compared with the equivalent AT63 sheet rolled without wave-shaped die.     

Highly transparent terbium gallium garnet crystal fabricated by the floating zone method for visible–infrared optical isolators

Highly transparent terbium gallium garnet (Tb₃Ga₅O₁₂; TGG) single crystal having a large Verdet constant based on the visible and near-infrared region (VIS–NIR) Faraday rotator was grown by Floating Zone (FZ) growth machine. We successfully grew TGG single-crystal rods of 8–10 mm in diameter, which was suitable for the use in optical devices. The crystal showed a full-width at half-maximum as little as 18 arcsec by the X-ray rocking curve measurement. The Faraday rotation (B = 0.55T) was investigated at wavelength of 532, 632.8, 1064 nm at room temperature. The lower weak absorption coefficient, higher Verdet constant, thermal conductivity and laser induced damage threshold (LIDT) compared to the commercial TGG gives the great potential of using this new method to meet the increasing demand of VIS–NIR Faraday rotators (FRs).     

Mechanical and physical properties of medium density fiberboard panels laminated with thermally compressed veneer

The objective of study was to evaluate some of the physical and mechanical properties of medium density fiberboard (MDF) panels laminated with veneer sheets compressed at different levels of pressure and temperature. Rotary peeled veneer samples of European beech (Fagus orientalis Lipsky) were compressed at temperatures of 150 °C, 180 °C, and 200 °C using 4 MPa and 6 MPa pressure for 8 min. Commercially produced MDF samples also were laminated with such compressed veneer sheets. Both modulus of elasticity (MOE) and modulus of rupture (MOR) of the specimens increased with increasing pressure and press temperature. Bending characteristics of the samples tested parallel to the grain orientation resulted in significantly higher values than that perpendicular to the grain orientation for each manufacturing parameter. Thickness swelling of the samples also was influenced by increased pressure but variation in press temperature did not result in any influence on dimensional stability. The findings of this work provide potential to produce sandwich type panels with improved properties. Initial results found in this study could be used to manufacture laminated panels with a fixed rate of adhesive while controlling press parameters as a function of the magnitude of pressure and temperature.     

Fabrication of Ag-doped MoO3 and its nanohybrid with a two-dimensional carbonaceous material to enhance photocatalytic activity

Recently, two-dimensional (2D) carbon-based materials and their nanocomposites have gained considerable fascination as a photocatalysts due to their remarkable contribution towards photocatalytic water splitting and remediation. Herein, a novel 2D reduced graphene oxide (rGO) based silver doped molybdenum trioxide (Ag/MoO₃) photocatalyst was synthesized successfully via hydrothermal and ultra-sonication methods. The surface structure, morphology, functional group characterization, and bandgap of the synthesized photocatalysts were analyzed using advanced physicochemical techniques. The photocatalytic performance of the prepared materials was scrutinized for Methylene blue (MB) dye degradation under solar light illumination. Because of its lower charge transfer resistance (19.54 Ω) and higher electrical conductivity (12.74 × 10² Sm^?1) the rGO/Ag/MoO₃ photocatalyst demonstrated significantly higher photocatalytic activity for dye removal than pure MoO₃ and Ag/MoO₃ photocatalysts. In particular, the rGO/Ag/MoO₃ photocatalyst illustrated about 98% dye degradation at a rate constant (0.0571 min^?1) greater than MoO₃ (0.0097 min^?1) and Ag/MoO₃ (0.0184 min^?1). Ag doping and the addition of rGO sheets led to enhanced optical absorbance and effectual separation of photo-induced electron-hole pairs, causing major progress in the photocatalytic behavior of MoO₃. Transient photocurrent results revealed longstanding photo-excited charge carriers in the graphene-based material.     

Ultrasonic spot welding of Al/Mg/Al tri-layered clad sheets

Solid-state ultrasonic spot welding (USW) was used to join Al/Mg/Al tri-layered clad sheets, aiming at exploring weldability and identifying failure mode in relation to the welding energy. It was observed that the application of a low welding energy of 100 J was able to achieve the optimal welding condition during USW at a very short welding time of 0.1 s for the tri-layered clad sheets. The optimal lap shear failure load obtained was equivalent to that of the as-received Al/Mg/Al tri-layered clad sheets. With increasing welding energy, the lap shear failure load initially increased and then decreased after reaching a maximum value. At a welding energy of 25 J, failure occurred in the mode of interfacial failure along the center Al/Al weld interface due to insufficient bonding. At a welding energy of 50 J, 75 J and 100 J, failure was also characterized by the interfacial failure mode, but it occurred along the Al/Mg clad interface rather than the center Al/Al weld interface, suggesting stronger bonding of the Al/Al weld interface than that of the Al/Mg clad interface. The overall weld strength of the Al/Mg/Al tri-layered clad sheets was thus governed by the Al/Mg clad interface strength. At a welding energy of 125 J and 150 J, thinning of weld nugget and extensive deformation at the edge of welding tip caused failure at the edge of nugget region, leading to a lower lap shear failure load.     

Influence of TiO2 dimension and graphene oxide content on the self-cleaning activity of methylene blue-stained photocatalytic films

In the present study, TiO₂ and graphene oxide (GO)/TiO₂ composite films were simply fabricated by hot-plate spray coating technique. The influences of TiO₂ dimension and GO content on the self-cleaning activity of methylene blue (MB)-stained films were investigated. The matrix of anatase TiO₂ quasi-cubic and octahedral particles in diameter of 6–9 nm (ST film) degraded 80% stained dye, much higher than those either in bigger size (30–50 nm) or in flower morphology due to the nano effect. Moreover, the photocatalytic performance of such nanostructured film was strongly enhanced by the combination with GO sheets. Increasing GO content led to significant enhancement in film transmittance and MB adsorptivity. In the aspect of the self-cleaning activity for MB, the addition of GO up to 1 wt.% showed higher efficiency but excess content led to similar performance in comparison with pure TiO₂ film.     

Encapsulation of Ellipticine in poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) based nanoparticles and its in vitro application

Biodegradable, biocompatible, renewable and non-toxic polyhydroxyalkanoates (PHAs) based nanoparticles are the novel nanotherapeutic tool which are used for the encapsulation of antineoplastic drugs for cancer therapy. In this study, poly-3-hydroxybutyrate-co-5 mol% 3-hydroxyvalerate (PHBV-S), poly-3-hydroxybutyrate-co-11 mol% 3-hydroxyvalerate (PHBV-11) and poly-3-hydroxybutyrate-co-15 mol% 3-hydroxyvalerate (PHBV-15) were used as a nanocarrier for encapsulation of Ellipticine (EPT). EPT is a model anticancer drug. Physicochemical characteristics such as particle size, its morphology and zeta potential of blank and EPT loaded PHBV-S, PHBV-11 and PHBV-15 nanoparticles were studied. In vitro cytotoxicity tests confirmed that the blank PHBV-S, PHBV-11 and PHBV-15 nanoparticles were demonstrating significant biocompatibility without affecting the survival of cancer cell line A549. The loading efficiency of EPT in PHBV nanoparticles was observed in the range of 39.32 to 45.65%. The % inhibition of cancer cell line A549 ranged from 64.28 to 67.77% in comparison to EPT alone in which % inhibition found to be ≤ 45.11%. The IC50 value for each of three different formulations of EPT loaded PHBV nanoparticles ranged from 1.00 to 1.31 μg/mL. The order of % inhibition of cancer cell line A549 for drug loaded nanoparticles was EPT-PHBV-15 > EPT-PHBV-S > EPT-PHBV-11. This system had demonstrated a great potential to increase the cytotoxic effect of EPT by increasing its bioavailability.     

Structural and mechanical behaviour of severe plastically deformed high purity aluminium sheets processed by constrained groove pressing technique

High purity aluminium sheets (∼99.9%) are subjected to intense plastic straining by constrained groove pressing method successfully up to 5 passes thereby imparting an effective plastic strain of 5.8. Transmission electron microscopy studies of constrained groove pressed sheets divulged significant grain refinement and the average grain sizes obtained after five pass is estimated to be ∼0.9 μm. In addition to that, microstructural evolution of constrained groove pressed sheets is characterized by X-ray diffraction peak profile analysis employing Williamson–Hall method and the results obtained fairly concur with electron microscopy findings. The tensile behaviour evolution with increased straining indicates substantial improvement of yield strength by ∼5.3 times from 17 MPa to 90 MPa during first pass corroborated to grain refinement observed. Marginal increase in strengths is noticed during second pass followed by minor drop in strengths attributed to predominance of dislocation recovery is noticed in subsequent passes. Quantitative assessment of degree of deformation homogeneity using microhardness profiles reveal relatively better strain homogeneity at higher number of passes.     

Silk fibroin immobilization on poly(ethylene terephthalate) films: Comparison of two surface modification methods and their effect on mesenchymal stem cells culture

Silk fibroin (SF) has played a curial role for the surface modification of conventional materials to improve the biocompatibility, and SF modified poly(ethylene terephthalate) (PET) materials have potential applications on tissue engineering such as artificial ligament, artificial vessel, artificial heart valve sewing cuffs dacron and surgical mesh engineering. In this work, SF was immobilized onto PET film via two different methods: 1) plasma pretreatment followed by SF dip coating (PET-SF) and 2) plasma-induce acrylic acid graft polymerization and subsequent covalent immobilization of SF on PET film (PET-PAA-SF). It could be found that plasma treatment provided higher surface roughness which was suitable for further SF dip coating, while grafted poly(acrylic acid) (PAA) promised the covalent bonding between SF and PAA. ATR-FTIR adsorption band at 3284 cm^? 1, 1623 cm^? 1 and 1520 cm^? 1 suggested the successful introduction of SF onto PET surface, while the amount of immobilized SF of PET-SF was higher than PET-PAA-SF according to XPS investigation (0.29 vs 0.23 for N/C ratio). Surface modified PET film was used as substrate for mesenchymal stem cells (MSCs) culture, the cells on PET-SF surface exhibited optimum density compared to PET-PAA-SF according to CCK-8 assays, which indicated that plasma pretreatment followed by SF dip coating was a simple and effective way to prepare biocompatible PET surface.     

Modification of porous calcium phosphate surfaces with different geometries of bioactive glass nanoparticles

In this study, the effects of bioactive glass nanoparticles' (nBGs) size and shape incorporated into hydroxyapatite/β-tricalcium phosphate (BCP) scaffolds were investigated. We prepared a highly porous (> 85%) BCP scaffold and coated its surface with a nanocomposite layer consisted of polycaprolactone (PCL) and rod (~ 153 nm in height and ~ 29 nm in width) or spherical (~ 33 nm and 64 nm in diameter) nBGs. Osteogenic gene expression by primary human osteoblast-like cells (HOB) was investigated using quantitative real time polymerase chain reaction (q-RT-PCR). We demonstrated for the first time that in vitro osteogenesis is dramatically affected by the shape of the nBGs, whereby rod shaped nBGs showed the most significant osteogenic induction, compared to spherical particles (regardless of their size). Importantly, the good biological effect observed for the rod shaped nBGs was coupled by a marked increase in the modulus (~ 48 MPa), compressive strength (~ 1 MPa) and failure strain (~ 6%), compared to those for the BCP scaffolds (~ 4 MPa, ~ 1 MPa and ~ 0.5% respectively). The findings of this study demonstrated that the shape of the nBGs is of significant importance when considering bone regeneration.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Fabrication of ZK60 magnesium alloy thin sheets with improved ductility by cold rolling and annealing treatment

Thin ZK60 magnesium alloy sheets with ultrafine-grain structure were successfully fabricated by continuous cold rolling with proper intermediate annealing treatments at 503–523 K for 30 min. Meanwhile, microstructure uniformity and planar texture anisotropy were strikingly improved by rolling deformation and static recrystallization, resulting in continuous improvement in the strength anisotropy. Excellent ductility more than 30% in fracture elongation was achieved after further annealing treatment at a lower temperature of 473 K. This was primarily attributed to the significant weakening of the {0 0 0 2} pole intensity and grain refinement during the process. It is shown that mechanical properties of the final sheets could be closely controlled by the present process.     

Rheological characterization and in-situ investigation of the time-dependent cholesteric based lyotropic liquid crystals

The impact of cell culture media on the rheology of liquid crystals is critical to developing liquid crystal (LC) based biosensors. The rheological properties of cholesteryl ester based lyotropic liquid crystals (LLC) were investigated in a rotational rheometer and using in-situ methods after incubation in cell culture media for periods of 24, 48 and 72 h. The results of the rheological experiments indicated that for incubation up to 48 h, LLC exhibited a linear viscoelastic behavior < 10% strain at low angular frequencies < 1 s^? 1 and an insignificant decrease in the complex viscosity. The in-situ experiments involved examining the response of the LLC to stresses generated by keratinocyte. It was found that cells induced deformations in the liquid crystal surfaces could be completely removed by disrupting the actin cytoskeletons of cells with cytochalasin-B after 48 h in culture media, but could only be partially removed after 48 h in culture media. In fixed stress experiments, it was found that LC deformation lengths remained constant over 72 h and exhibited a statistically insignificant decrease after 72 h in culture media. These later results indicate very little time related change of viscosity in the LLC. However, the in-situ rheological behaviors were in good agreement with the rheological results obtained from oscillatory tests for the LLC incubated up to 48 h. These results suggest that LLC coated substrates have viable physical properties within 48 h of incubation that can allow them to monitor cell-generated stresses in culture.     

Buckling,collapse and failure analysis of FRP sandwich panels

Rectangular orthotropic fiber-reinforced plastic (FRP) sandwich panels were tested for buckling in uni-axial compression. The panels, with 0.32 cm (0.125 in.) face sheets and a 1.27 cm (0.5 in.) core of either balsa or linear poly(vinyl chloride) (PVC) foam, were tested in two sizes: 154×77 cm² (72×36 in.²) and 102×77 cm² (48×36 in.²). The sandwich panels were fabricated using the vacuum-assisted resin transfer molding process. The two short edges of the sandwich panels were clamped, while the two long edges were simply supported for testing. The clamped panel ends were potted into a steel frame. The experimental elastic buckling loads were then measured using strain gauges fixed to both sides of the panels. A total of 12 panels were tested under uni-axial compression. Bifurcation in the load versus engineering strain curve was noted in all cases. For all six sandwich panels tested using balsa core, the type of failure was easily identified as face sheet delamination followed by core shear failure. For all six PVC foam core sandwich panels tested, the type of failure consisted of core shear failure with little or no face sheet delamination. In the failed balsa core panels there was little or no evidence of balsa remaining on the FRP face sheet, however, in the PVC foam core panels there were ample amounts of foam left on the FRP face sheet. It was concluded that although the buckling loads for the foam core panels were not as high as those for the balsa core panels, PVC foam core bonding to the FRP face sheets was superior to balsa core bonding.