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Wave propagation control in piezoelectric meta-materials has been extensively investigated in recent years due to its significant effects on elastic wave attenuation. In this work, a novel piezoelectric meta-material rod connected to three configurations of shunting circuits is proposed for broad band gaps. The numerical model is constructed to predict the band gap, attenuation constant, and vibration transmission. For larger attenuation within the band gaps, the shunting circuit parameters are optimized with a genetic algorithm. The result shows that the structure with the optimized parameters provides prominent vibration control ability. Both the attenuation constant and the width of the band gaps are enlarged.

The dynamic characteristics studies of piezoelectric structures usually focus on the single vibration modes such as the longitudinal or the flexural mode, and the losses that cause heat generation and energy waste are generally neglected, which leads to discrepancies compared with experiments. In the present paper, a beam-type piezoelectric structure with four kinds of losses under coupled longitudinal-flexural vibration mode is investigated. In this approach, first, impedance matrix of the structure is obtained based on the motion equation and the electrical-mechanical boundary conditions. Secondly, admittance curves of this piezoelectric structure under different boundary conditions are simulated by the equivalent circuit methods that contain four losses—piezoelectric and dielectric losses, as well as two elastic losses. The simulation results by equivalent circuit methods has good agreement with COMSOL results, which demonstrate the effectiveness of the proposed method.

Purpose The purpose of this paper is to obtain a more accurate fatigue life of structures by introducing the surface roughness into fatigue life prediction model. Design/methodology/approach Based on the fatigue life prediction model with surface roughness correction, the shock absorber cylinder is taken as an example to verify the feasibility of the improved method. Based on the load of the shock absorber cylinder during driving, fatigue experiments are performed under longitudinal and lateral forces, respectively. Then, the fatigue life predicted by the modified model is compared with that predicted by the traditional model. Findings By comparing with the test results, considering the influence of mean stress, the Manson method is more accurate in life prediction. Then, the modified Manson-Coffin and Manson method with surface roughness is more accurate in life prediction under longitudinal force and lateral forces, respectively. This verifies the feasibility of the improved method with the surface roughness. Originality/value The research on the influence of surface roughness on fatigue life can lay the technical foundation for the life prediction of products and have great significance to the quality evaluation of products.

In order to determine the effect of different loads on fatigue damage, a strength degradation model is proposed according to the law of residual strength degradation of metal materials. The model is verified with the strength degradation test data, and the results show that the model can describe the strength degradation process of general metal materials well. Combined with the strength degradation model, an improved equivalent damage model for different loading sequences is proposed. On this basis, a nonlinear fatigue cumulative damage model based on strength degradation is derived. The cumulative damage model is applied to the estimation of fatigue residual life under two-, three-, and four-stage loads to investigate the effects of different loading sequence on fatigue damage under various loading conditions. Combining with experimental data, it is verified that the cumulative damage model can accurately estimate the fatigue life under two-, three-, and four-stage loads.

Rapid and convenient wound healing is crucial for reducing potential post-traumatic wound complications. In this study, a temperature-sensitive polymer of poly-(HEMA-co-NIPAM) (PHN) was synthesized by free-radical polymerization, in which the solution quickly underwent a sol-gel transition above 29°C, thus responding to a typical body temperature and facilitating wound sealing. PHN solution incorporated with copper ions (PHN-Cu) not only exhibited excellent antibacterial properties, but also expedited wound closure and facilitated tissue angiogenesis. The in vivo and in vitro experiments showed that the PHN-Cu had a higher wound closure rate and demonstrated an ability to promote skin tissue angiogenesis. Such a versatile, convenient aqueous solution could enable nonprofessionals to promptly treat wounds in a short time after injury, thus providing suitable conditions for later treatment, and can be used as a convenient method to clean wounds.

Cyclic loads have a significant impact on the fatigue life of aircraft lugs. To evaluate fatigue life of aircraft lugs, an accurate calculation of fatigue life is essential. Therefore, thermal stre...

In fatigue test, the fatigue life of metal components is affected by many factors, such as test temperature, stress ratio and loading frequency. In order to study the influence of temperature on fatigue life of bolted joints, thermal stress and fast coefficient are introduced. A numerical method of fatigue crack initiation life is proposed based on Manson-Coffin strain fatigue formula. The crack initiation life of 2024 aluminum alloy at different temperatures can be obtained by this method, which provides a theoretical basis for the fatigue life prediction of metals. Then, the stress severity factor SSF is introduced to calculate fatigue life of plane bolted joints. The data obtained from the model show that the crack initiation life of aluminum alloy specimen decreases significantly with test temperature rises, the same as the fatigue life of bolted joints.

Microarc oxidation (MAO) coating was prepared on the surface of the biomedical Mg–3Zn–0.2Ca alloy in a phosphate electrolyte with varying concentrations of Na2SiO3. The morphology, cross section, chemical composition, and corrosion resistance of the coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical polarization tests (EI), and in vitro immersion experiments. The addition of Na2SiO3 is performed to increase the thickness and compactness of the coating. When the Si/P atomic ratio is approximately equal to 1 (1.5 g/L Na2SiO3), the best corrosion resistance is achieved, while excessive addition may lead to coating defects such as voids and microcracks, resulting in decreased corrosion resistance. The competitive relationship between PO43– and SiO32– anions in the silicon–phosphorus microarc oxidation-mixed electrolyte is discussed. In this study, it was first proposed that, when Mg2SiO4 and Mg3 (PO4)2 phase contents were approximately the same, the synergistic improvement effect on coating corrosion resistance was the most effective.

To solve the fatigue crack initiation problem, it is necessary to calculate the fatigue crack initiation size. According to the aspect of macroscopic crack development, the calculation method of crack initiation size is determined by the critical dimension of fatigue crack initiation. Simultaneously, the elastic–plastic fracture mechanics (EPFM) method is used to study short crack fatigue life by considering the cumulative damage rule of crack initiation life, and the calculation model of fatigue crack initiation size caused by symmetric cyclic torsional alternating stress is established under low strain. The crack initiation dimension of component is estimated, which lays a foundation for the study of fatigue life. Then the feasibility of this method is verified by comparing with the crack initiation size, which is determined by predicting the non-propagating crack size (NPCS).

Bacteroides forsythus is the least investigated species of the "red complex" of bacteria responsible for periodontitis. This is due, at least in part, to the difficulty in identifying these bacteria by classic techniques requiring in vitro cultures. Thus, the aim of the current study was to design a fast and robust technique for the detection of B. forsythus. For this purpose, DNA was isolated by magnetic microbeads from dental plaque and gingival crevical fluid, and the presence of the gene coding for 16S rRNA of B. forsythus was detected by conventional of quantitative real-time PCR. The study enrolled patients affected by periodontitis and healthy subjects, and both groups were comprised of heavy and mild smokers. The assays revealed that bot gingival fluid and dental plaque served well as the material for test samples. The periodontitis group had a markedly higher rate of infection by B. forsythus than healthy subjects. The infection rate was also higher in the group of smokers but did not depend on whether the patients were heavy or mild smokers. In conclusion, the novel methodology may become a powerful tool in the hands of clinicians, allowing them to obtain a faster and more accurate diagnosis of B. forsythus in periodontal infections.

Magnesium and its alloys are biodegradable materials with great potential for biomedical development; however, their high rate of degradation in biological environments limits the widespread application of these materials. In order to improve the corrosion resistance of magnesium alloy, a functional calcium phosphate coating was prepared on Mg-3Zn-0.5Zr-0.5Sr alloy by microarc oxidation (MAO) combined with chemical deposition of fluoridated hydroxyapatite (FHA). A dense calcium-phosphorus coating 6 μm thick composed of needle-shaped fluoridated hydroxyapatite formed on the surface of the MAO layer. The MAO-FHA coating exhibited good mineralization ability to induce hydroxyapatite deposition on its surface during degradation testing in simulated bodily fluids.

Aiming at a better compatibility with micro-electro-mechanical system technologies to extract ambient energy from vibrational systems using piezoelectric energy harvesters (PEH) for powering smart wireless sensor devices, this work presents an analytical model of the quasi-static behavior of the electromechanical piezoelectric unimorphs and bimorphs in series and parallel connections, where the distributed or uniform load is applied. And the proposed model concerns harvesting charge/voltage/energy density. Evaluation methods are developed based on the output capacity density. A brand new analytic expression is derived for the global response of PEH subjected to the distributed load excitations. The influence of material properties and geometric parameters on output charge/voltage/energy density is analyzed with the identical equivalent load. The results of the theoretical analysis show that the optimal substrate-to-PZT elastic modulus ratio is deduced and could be referenced in the selections of substrate materials. Good agreements are obtained between the simulation and analytical results. Bimorphs exhibit higher energy density compared with unimorph for lower manufacturing cost and better economy. For distributed-loaded PEH, arranging the maximum load point at a desirable location can increase output capacity density. Additionally, the output density can be enhanced by increasing the length or reducing the width of PEH within the range of allowance stress. Moreover, for unimorph, the critical points of harvesting charge/voltage/energy density are found. This work provides new insights into the load distributions, material selections and evaluation indexes that are crucial for the design and optimization of PEH in different loading and boundary conditions.

Liquid cooling system is of great significance for guaranteeing the performance of lithium-ion battery because of its good conductivity to keep battery working in a cool environment. In this paper, a liquid cooling system for lithium-ion battery with changing contact surface is designed. Contact surface is determined by the width of cooling plate. Mathematical derivation and numerical analysis are conducted to evaluate cooling performance and the consumption of pump power. The results show that increasing inlet mass flow can effectively limit the maximum temperature, but cannot improve temperature uniformity significantly. The temperature is proportional to the inlet temperature, but inversely proportional to the width of cooling plate. Considering the effect of temperature on thermal properties, the thermal properties will weaken the effect of width of cooling plate, inlet temperature and mass flow rate on temperature performance, specifically the maximum temperature and temperature difference, and cause temperature changes in a nonlinear manner. It is difficult to improve the overall performance of the battery by only optimizing a single factor. Three factors (mass flow rate, inlet temperature, the width of cooling plate) for the thermal performance of battery are optimized by using the single factor analysis and the orthogonal test. The best cooling performance can be obtained when inlet temperature is 18 °C, the width of cooling plate is 70 mm and the mass flow rate is 0.21 kg/s. With the use of the optimization method, the lower bound of temperature and the temperature uniformity of battery are achieved and the pump consumption can be reduced. The strategy adopted in this research can be widely applied to battery thermal management to reduce analysis time.

Micro-arc oxidation (MAO) as an environmentally friendly technology is used to produce ceramic film on metal surfaces to improve its corrosion properties, and the films quality is mainly affected by the electrolyte composition and electrochemical parameters, Here, to improve the corrosion property and wear-resisting of low carbon steel, a compact, corrosion resistant α-Al2O3 ceramic film was prepared on the surface of low carbon steel containing boron (10B21) by MAO. A Na2SiO3 and NaH2PO4 electrolyte system was designed with different content of Na2CO3 and Na2B4O7. The ceramic layer produced with Na2CO3 and Na2B4O7 showed improved corrosion resistance. The corrosion current density was 2.7 μA·cm−2 and the impedance value reached 1900 Ω·cm2. After 7 days of neutral salt spray corrosion, the corrosion rate of this sample coating reduced to 53 g·m−2·h−1. The influence mechanism is discussed. The cooperation of Na2CO3 and Na2B4O7 in the electrolyte is more effectively regulated the ionization and chemical reactions of the MAO process, catalyzing the formation of α-Al2O3. The coating had a uniform thickness of 100 ± 10 μm, no gap between the coating and the substrate was observed, which indicated that the bonding state was good. Thus, the MAO ceramic layer prepared on low carbon steel surface increases the service life of iron and steel components effectively, which can significantly expand its application in more fields.

Spinal cord injury (SCI) is a catastrophic disease that induces a complex cascade of cellular reactions at the local lesion area, including secondary cell death and inflammatory reactions. Accumulating evidence has showed pro- and anti-inflammatory roles of microRNAs (miRNAs), a class of small RNAs, in SCI. The present study is aimed at investigating the effects of two miRNAs, miRNA-146a and miRNA-202-3p, on inflammatory response after SCI. Initially, we found that the expression levels of miRNA-146a and miRNA-202-3p were increased in the plasma samples of 32 SCI patients at days 3 and 7 after admission and the rat spinal cord at days 3 and 7 after SCI modeling compared with healthy controls and sham-operated rats, respectively. The expression levels of TLR4, IRAK1, and TRAF6 were declined in the rat spinal cord at days 1, 3, and 7 after SCI modeling compared with sham-operated rats. Injection of miRNA-146a mimic or miRNA-202-3p mimic decreased TLR4, IRAK1, and TRAF6 expressions in the rat spinal cord at days 1, 3, and 7 after SCI modeling, while injection of miRNA-146a antagomir or miRNA-202-3p antagomir produced opposed results. Subsequent results showed that the expression levels of tumor necrosis factor-α (TNF-α), IL-1β, IL-6, and IL-8 were upregulated in the rat serum at days 1, 3, and 7 after SCI modeling compared with sham-operated rats. Injection of miRNA-146a mimic or miRNA-202-3p mimic decreased TNF-α, IL-1β, IL-6, and IL-8 expression levels in the rat serum at days 1, 3, and 7 after SCI modeling, while injection of miRNA-146a antagomir or miRNA-202-3p antagomir yielded opposed results. The expression levels of TNF-α, IL-1β, IL-6, and IL-8 were higher in the supernatants of PC12 cells transfected with anti-miRNA-146a or anti-miRNA-202-3p than in those transfected with si-TLR4, si-IRAK1, or si-TRAF6. These findings support the notion that miRNA-146a/miRNA-202-3p exerts anti-inflammatory functions after SCI.

To consider the effect of crack closure on the mechanical properties of metals, the fatigue life of metal specimens is predicted based on energy dissipation model. The main feature of the model consists in considering the relationship between the total failure energy and the energy density increment. The total failure energy model considers the fatigue crack size and stress amplitude. It is assumed the energy density increment gradually decreases and tends to be stable. The influence of crack closure effect is considered. According to the law of metal fatigue characteristics, a new mathematical model for predicting fatigue life is established.

SiO2/ZrO2 and SiO2/ZrO2/Al2O3 composite organic&ndash, inorganic coatings were prepared by the sol-gel technology. The structure of the coating was characterized by IR, particle size analyzer, SEM, and AFM, respectively. The results showed that ZrO2, SiO2 (inorganic component), and siloxane had undergone a hydrolytic condensation reaction, and the composite organic&ndash, inorganic coatings were formed with -O-M-O- (M is Si, Zr) as molecular skeleton network structure. Adding an appropriate ratio of ZrO2 sol, no agglomeration and phase separation occurred, which could significantly improve the refractive index, hardness, and light transmittance of the coatings. Al2O3 sol could greatly improve the friction resistance of the composite organic&ndash, inorganic coatings, and the Bayer ratio of the composite coatings could reach 7.86. By adjusting the proportioning of composite sol solution, the refractive index of the composite transparent coatings could be controlled from 1.52 to 1.65.

Skin injury is a kind of common tissue damage in daily life and war. Silk fibroin (SF) is becoming an engineered material for skin wound repair due to its superior unique physical and chemical properties. The present study aimed to illustrate mechanism of SF hydrogel promoting skin repair in the second degree burn mice. Heat shock models were established. In vitro, cells were culture for 50 min at 44 °C water bath; while in vivo, the skin of anesthetic mice were treat with soldering iron at 90 °C. Then, they divided into silk fibroin gel group, purilon gel group and control (blank) group. The cellular activity of proliferation and apoptosis was detected by Kit-8, flow cytometry and HE-staining, and the migration and adhesion were detected by scratch test. qRT-PCR and WB were employed to detected adhesion and migration related genes and proteins expression. TLN1 siRNA and overexpression technologies were also employed to illustrate the potential mechanism of SF effects. Compared with the purilon gel group and control group, SF hydrogel could enhance cell proliferation, migration and adhesion and increase the expression of adhesion and migration related proteins (P

Intelligent polymers with tough networks are of considerable significance for thedevelopment of highly proficient polymer science and technology. In this work, polymeric elastomers with integrated stretchable and self-healable characteristics were designed by cross-linking hyperbranched polymers with flexible segments. The hyperbranched polymer with multiple terminal groups provided various cross-linking points, so that mechanically robust networks could be achieved. Driven by the reversibility of imine and disulfide bonds employed, the elastomers exhibited good self-healing property and the healing efficiency reached up to 99% under ambient environments. Furthermore, the dynamic reversibility of the polymers was investigated at molecular level. The imine and disulfide bonds were incorporated into the networks to construct soluble and recyclable hyperbranched polymer with pH and redox responsiveness via A2+B3 approach and Schiff base polymerization. The polymers containing imine bonds could complete the polymerization–depolymerizationtransition and undergo reversible cycles for several times through changing pH. Moreover, in the presence of disulfide bonds, the polymers were provided with redox cleavage property triggered by dithiothreitol. This study may provide new opportunities for the design and application of intelligent polymers with tough networks through regulating topological structures.

In this work, the effect of modified graphene oxide and polytetrafluoroethylene (PTFE) on the tribological and anticorrosion properties of waterborne polyurethane (WPU) was studied. The modified graphene oxide (MGO) was obtained by the surface functionalization modification of graphene oxide (GO) with isophorone diisocyanate (IPDI), and MGO/WPU composite coating and MGO-PTFE/WPU composite coating with different mass fractions of MGO were prepared. The tribological and electrochemical experiment results demonstrated that the tribological properties of the coating and the corrosion resistance of the worn coating were effectively enhanced under the synergistic effect of MGO and PTFE. Finally, a mechanism was proposed to explain the improvement in anticorrosion performance of the worn coating.

In this work, a novel friction-based welding technology was developed to weld Al/Cu bimetallic tubes. The macrostructure, microstructure evolutions, and mechanical properties of the joint under different welding speeds were investigated. Void defects are observed on the joint interface, especially at the welding speed 60 mm/min. From the Al side to the Cu side, the reaction layer can be divided into five layers. In addition, welding speed has an important influence on the microstructure evolution of reaction layer. Compression-shear testing results show that the shear strength decreases with the increase of the welding speed. The failure of compression-shear samples is first generated at the junction of hypereutectic layer and intermetallic compound (IMC) layer, and then, the crack propagates along the interface of the hypereutectic layer and IMC layer or through the hypereutectic layer to the eutectic layer.

Carbon nanotubes (CNTs) show a tremendous promise on strain sensor applications, but the stretchable ability of CNT devices is low due to their poor ductility. Herein, novel aligned conductive networks of CNT film were designed and introduced onto polydimethylsiloxane (PDMS) substrate, which realized highly stretchable multi-dimensional strain sensitivity up to a strain of 260% and an excellent cyclical durability. The gauge factor (GF) along the CNT aligned direction, i. e. A direction, can reach 461 up to a strain of 260% while the resistance of the perpendicular direction (B direction) keeps almost the same with initial value, showing a multi-dimensional strain detection capability. The high GF along A direction of the CNT film is caused by the slippage, damage and rupture of CNT bundles with strain increasing, while the CNT entanglement between the adjacent CNTs stabilizes the resistance along B direction. This study rationalizes the aligned CNT network concept to realize the multi-dimensional strain sensors, which have a great potential to be applied in complex strain detection in practical applications.

Tissue engineering (TE) is an emerging and promising strategy to heal tissue failure by integrating science and technology of materials, cells and growth factors. With the increasing of aging population, restoring musculoskeletal tissue has become the focus of TE. Among various materials tested in TE, silk fibroin (SF) is increasingly being recognized as a promising material. SF, a natural protein polymer with excellent physiochemical characteristics, has established a good reputation in terms of musculoskeletal tissue engineering (MTE). The present article provides an overview of SF and introduces various approaches of fabricating SF-based biomaterial followed by their applications in MTE.

Lead-free perovskites have received remarkable attention because of their nontoxicity, low-cost fabrication, and spectacular properties including controlled bandgap, long diffusion length of charge carrier, large absorption coefficient, and high photoluminescence quantum yield. Compared with the widely investigated polycrystals, single crystals have advantages of lower trap densities, longer diffusion length of carrier, and extended absorption spectrum due to the lack of grain boundaries, which facilitates their potential in different fields including photodetectors, solar cells, X-ray detectors, light-emitting diodes, and so on. Therefore, numerous research focusing on the novel properties, preparation methods, and remarkable progress in applications of lead-free perovskite single crystals (LFPSCs) has been extensively studied. In this review, the current advancements of LFPSCs are briefly summarized, including the synthesis approaches, compositional and interfacial engineering, and stability of several representative systems of LFPSCs as well as the reported practical applications. Finally, the critical challenges which limit the performance of LFPSCs, and their inspiring prospects for further developments are also discussed.

Bone pain is the primary problem for patients with osteoporosis. Ketoprofen is clinically used to treat osteoporotic pain, while long-term oral administration of ketoprofen can cause some side effects. In addition, osteoporosis is also accompanied by bone mass loss and inflammation. In this study, we designed a multifunctional drug (Ket@Mg-MOF-74) adopted Mg-MOF-74 to load ketoprofen to treat osteoporotic pain, bone loss and inflammation comprehensively. Mg-MOF-74 was prepared, and the physicochemical characterization proved that it had excellent physical and chemical stability. Ket@Mg-MOF-74 was synthesized by post-synthetic modification method and a high loading rate of ketoprofen was confirmed. Drug release and ion release experiments indicated Ket@Mg-MOF-74 had a good controlled release of ketoprofen and Mg in solution. Cell experiments in vitro proved the compound drug could significantly reduce the expression of pain-related genes of cyclooxygenase 2 (COX2), obviously up-regulated the expression of osteogenic cytokines and remarkably down-regulated the secretion of pro-inflammatory factors. Therefore, Ket@Mg-MOF-74 is believed a promising painkiller for osteoporotic bone pain, with the function of anti-inflammatory and promoting bone formation.

In this study, a novel friction-based welding technology was proposed for fabricating Al/Cu bimetallic tubes. The frictional heat and radial pressure during the friction-based welding process are used to achieve the metallurgical bonding between Al and Cu tubes in a rapid and efficient way. Successful joints indicate that this technology has the potential for fabricating bimetallic tubes. Microstructure evolution, bonding mechanism and mechanical properties of Al/Cu bimetallic tubes were also analyzed. Results reveal that columnar α-Al, intermediate transition layer and intermetallic compounds (IMC) are identified at the rotational speed of 950 rpm. While the rotational speed is decreased to 95 rpm, only solid-state diffusion occurs at the interface which results in three IMC layers, Al2Cu, AlCu, and Al2Cu3. The thickness of the Al2Cu is more significantly affected by the rotational speed than that of AlCu and Al2Cu3. Maximum hardness is observed at the reaction layer due to the formation of IMC. The appearance of intermediate transition and thick Al2Cu layer weakens the bonding strength of bimetallic tubes. The joints are fractured at the reaction layers, and the fracture exhibits typical brittle characteristic. Three crack propagation paths are observed at the interface of Al/Cu bimetallic tubes. Keywords: Friction-based welding, Bimetallic tubes, Intermetallic compound, Bonding strength

The effects of changing solution pH in the range of 3.6-10.0 during a one-step silk microsphere preparation process, by mixing silk and polyethylene glycol (PEG), was assessed. The microspheres prepared at low pH (3.6) showed a more homogeneous size (1-3μm) and less porous texture than those prepared at neutral pH. High pH (10.0) inhibited microsphere formation, yielding small and inhomogeneous microspheres. Compared to neutral pH, low pH also increased the content of silk crystalline β-sheet structure from approx. 30% to above 40%. As a result, the microspheres produced at low pH were more thermally stable as well as resistant to chemical (8M urea) and enzymatic (protease XIV) degradation when compared to microspheres prepared at neutral pH. Doxorubicin hydrochloride (DOX) and curcumin (CUR) were successfully loaded in silk microspheres via control of solution pH. The loading efficiency of DOX was approx. 95% at pH7.0 and approx. 60% for CUR at pH3.6, attributed to charge-charge interactions and hydrophobic interactions between the silk and drug molecules, respectively. When PBS, pH7.4, was used as a medium for release studies, the pH3.6 microspheres released both drugs more slowly than the pH7.0 microspheres, likely due to the high content of crystalline β-sheet structure that enhanced drug-silk interactions as well as restricted drug molecule diffusion.

In this work, multilayer composites composed of ethylene-propylene-diene monomer (EPDM) foams and EPDM perforated plates were proposed to improve sound absorption properties at medium and low frequency. Models of composites with variable section cavities were designed and explored the influence of structural parameters on sound absorption coefficient. Numeral calculations results showed that the sound absorption curves of multilayer composites usually have two peaks in 300–1300 Hz. Compared with the other, the composite composed of one perforated board with variable section cavities and two foams (VFF) shows best sound absorption capacities in low frequency. Two optimization algorithms: artificial fish swarm algorithm (AFSA) and improved particle swarm optimization (I-PSO) were presented to optimize structural parameters of VFF. It is found that the optimization results of I-PSO are better that of AFSA for improving the absorption properties at low medium and frequency. This work provide a simple method and a new idea to improve sound absorption properties of multilayer composites.

A novel acoustic metamaterial structure, made up of both resonator and multiple channels, is proposed to insulate low-frequency broadband noises. Three bandgaps with a total width of 658 Hz can be obtained below 900 Hz when the structure appears as a single negative characteristic within specific frequency ranges. These bandgaps are caused by the standing-wave characteristics under the coupling action of the interior and exterior cavities and the multiple channels. By changing structural parameters and materials, the low-frequency broadband sound insulation performance of the structure can be improved. Experimental results further prove the sound insulation characteristics. The results obtained herein can be used as a guide toward achieving low-frequency broadband sound insulation using a lightweight structure.

Magnesium (Mg) is frequently used as a biocompatible implantable material in the human body, but real-time detection of its corrosion state is not well understood. Fortunately, previous studies of triboelectric nanogenerators (TENG) as self-driven sensors in many fields have proposed solutions for this problem. In this work, Mg-based TENG was prepared as a self-driven sensor to detect the corresponding corrosion state of Mg treated by micro-arc oxidation (MAO-Mg). Mg-based sheets and polydimethylsiloxane (PDMS) film were used as triboelectric materials. The output of TENG was optimal under 350 V–800 Hz micro-arc oxidation (MAO) treatment of Mg, and the Voc, Isc and Qsc were 48.5 V, 35.3 μA and 44.2 nC, which were respectively 2.42, 3.42 and 3.27 times that of the untreated devices. Moreover, a linear relationship was found in simulated body fluid (SBF) immersion tests, showing that the rates of decrease in Isc and Voc were respectively 3.48 and 2.74 times the weight reduction rates of MAO-Mg sheets, indicating that our sensors successfully detected the corrosion of MAO-Mg. This work will lay a preliminary foundation for real-time detection of Mg as an implant in the human body (as do other implantable materials), and demonstrates a potential new application for TENG in the biomedical field.

Strain hardening geopolymer composite (SHGC) is a tailored group of sustainable high-performance fibre reinforced geopolymer composites with strain hardening behaviour and ultra-high ductility. This paper experimentally investigates the effect of fine silica sand content (0–40% by weight of the geopolymer binder) on engineering properties of fly ash-slag based SHGC cured at ambient temperature, including workability, setting time, drying shrinkage, compressive strength, and flexural strength as well as deflection hardening behaviour that is particularly emphasised. The results indicate that all SHGC specimens exhibit deflection hardening characteristics along with large deflection and multiple microcracks distributed over the tensile side of the specimens. The widths of microcracks are within 300 μm and mostly smaller than 45 μm. The flowability, setting time, drying shrinkage and compressive strength of SHGC reduce with the increase of sand content at early ages up to 28 d. However, at 28 d, the incorporation of sand up to 20 wt% increases the flexural strength and toughness of SHGC, but the further increase of sand content up to 40 wt% results in a decrease in flexural strength and toughness.

In this paper, the authors proposed a class of hierarchical square honeycomb metamaterials (HSHMs) with low-frequency broad bandgaps (BGs) and flat energy band characteristics. The mechanical model of the square honeycomb structure and the in-plane mode lattice dynamics model of the HSHMs are presented. The formation mechanism of BGs and flat energy band characteristics are obtained by combining the band structure with transmission spectra, which was calculated using the finite-element method. The numerical results show that the HSHM structure has multiple BGs below 100 Hz, and the transmission spectra are in accordance with the band structure calculations. Additionally, the effects of the scatterer shape and the honeycomb parameters of the elastic element on the BGs are further analyzed and discussed. Based on the analysis, it was concluded that the BGs can be modulated in a wider and lower frequency range by changing the scale factor, the length-to-width ratio of the honeycomb side beam, and layer dislocation. These research results provide a novel structure for the design and application of acoustic metamaterials.

Given the fabulous potential of promoting bone regeneration, BMP-2 has been investigated widely in the bone tissue engineering field. A sophisticated biomaterial loaded with BMP-2, which could avoid the required supraphysiological dose leading to high medical costs and risks of complications, has been considered as a promising strategy to treat non-healing bone defects. In this study, we developed a simple approach to engineer a composited hydrogel consisting polymeric particles (PLA/PLGA) used as a BMP-2 delivery vehicle. Compared with other groups, the introduction of PLA into PEG-silk gels endowed the hydrogel new physicochemical characteristics especially hydrophobicity which inhibited the burst release of BMP-2 and enhanced gel's structural stability. Moreover, such composited gels could stabilize entrapped proteins and maintain their bioactivity fully in vitro. In vivo, the bio-degradability experiment demonstrated this system was biocompatible and the reinforced hydrophobicity significantly decreased degradation rate, and in rat critical-sized cranial defects model, the gel containing PLA promoted the most bone formation. These findings demonstrated the introduction of PLA changed physicochemical features of gels more suitable as a BMP-2 carrier indicated by inducing bone regeneration efficiently in large bone defects at low delivered dose and this system may own translational potential.

Highly conductive flexible paper-based patterns were drawn directly using a brush pen dipped in ink consisting of copper–silver core–shell with individual silver (CucoreAgshell&Ag) particles. Using a cost-effective and green method, the formation of these CucoreAgshell&Ag particles is first driven by a transmetalation reaction on the surface of copper nanoparticles between copper atoms and silver ions, and then excessive Ag ions were further reduced by the glucose to form individual Ag nanoparticles. Characterization of these particles by XRD, SEM and TGA confirm the CucoreAgshell&Ag structure and their stability towards oxidation. The conductivity of the bending pattern was experimentally tested with different bending angles, bending cycles and bending storage times. It was found that the silver shell with external excessive Ag NPs not only improves the packing density, but also enhancing the particle purity results in the high conductivity of the bending pattern. Sintered at a low temperature of 160 °C and after 3000 bending cycles and storage for 300 days, the linear resistivity of the pattern increased from ∼5 μΩ cm to ∼20 μΩ cm, 4 times higher than before the pattern was bent, which is acceptable for conductive patterns in practical applications. Thus, this approach represents a promising method for the formation of microelectrodes or electronic devices with good flexibility and conductivity.

The mechanical properties of frozen soils are closely related to the unfrozen water content. It has been generally recognized that the unfrozen water content varies with plasticity of soils, while the quantitative relationship between the plastic index and the unfrozen water content is yet to be further examined. This paper takes soil samples with different plasticity as study objects, which are prepared from two typical soil materials, i.e., the Chinese ISO standard sand and bentonite. Nuclear magnetic resonance (NMR) is used to measure the unfrozen water content of soil samples under different temperatures. Test results show that there are three stages in the soil-freezing characteristic curve (SFCC), i.e., the super-cooling stage, the rapid-drop stage and the stable stage. With the increase of the plasticity index, the super-cooling stage is less significant, while the curve in the rapid-drop stage becomes gentler. In the stable stage, the unfrozen water content is barely affected by plasticity. A piecewise function consisting of a linear formula and a power formula is then proposed to describe the SFCC, where the formula parameters are functions of the plastic index. It is found that the unfrozen water content calculated by the proposed formula agrees with the measured results.

Several studies have demonstrated that the design of square lattice is an efficient approach to obtain band gap characteristics. However, there are still some challenges in the design of phononic crystals capable to prohibit the propagation of low-frequency waves. In the present paper, aiming to broaden and manipulate the low frequency band gaps, an innovative structure with filling materials in a square lattice is proposed, where the spatial distribution of the materials has been optimized using an improved genetic algorithm. By analyzing the band structure and vibration modes of the designed structure, it becomes evident that the low-frequency band gaps are obtained due to the local resonance of the constituent materials. The transmission spectrum of the finite designed structure confirms an efficient wave attenuation performance in the low-frequency range. Furthermore, the effect of ligament thickness on band gaps was also investigated. The designed phononic porous plate, featuring prominent band gap properties, can be used as an example to guide the topological design of phononic crystal structures for a wide range of engineering implementations.

To resolve the problem of inhomogeneous color depth during photochromism, the photochromic coating on the surface of a pre-molded lens as well as the photocuring process are proposed. The host polyurethane acryl (PUA) material with adjustable flexibility was constructed from isophorone diisocyanate trimer (t-IPDI). The polycarbonatediol (PCDL) was used for chain extension and the hydroxyethyl methylacrylate (HEMA) was introduced to the lateral chain for the subsequent photo-crosslinking. Multiple experimental conditions were optimized, which included selection of the photoinitiator (PI), operating spectral window for photocuring and the equivalent ratio of HEMA to NCO group. The spectrokinetics behavior of photochromic coating was investigated by monitoring relative grayscales (Gy*) with irradiation and fading time. The glass-transition temperature (Tg) was measured by the differential scanning calorimetry (DSC) as well. An attempt of application of this photochromic coating on the surface of a commercial lens blank was made tentatively.

Viscoelastic materials can dissipate energy and hinder propagation for plane waves, which can adjust the band structures of phononic crystals (PCs). In this study, the wave propagation in a two-dimensional PC with a viscoelastic matrix is investigated. The Maxwell model is utilized to analyze the effect of material parameters on the frequency dependence of viscoelasticity. Material parameters include the relaxation time, the initial value and the final value of the shear modulus. Band structures of viscoelastic phononic crystals (VPCs) are solved by combining the plane wave expansion method and iterative algorithm based on Bloch theory. The effects of the viscoelasticity on the band structures are studied using the single-mode and multi-mode Maxwell models. Results reveal that the viscoelasticity of the materials not only extends the band gaps but also shifts the band gaps to lower frequencies. Furthermore, the viscoelasticity simulated by the multi-mode model can precisely adjust anyone of the band gaps of VPCs separately. Results provide insights into the design and applications of VPCs.

The compressibility of frozen soil must be taken into consideration when the deformation of highway and high-speed railway is strictly controlled in permafrost regions. In this study, the frozen saturated Chinese ISO standard sand was taken as the study object, and step load tests under different temperatures were carried out using a self-developed confined compression apparatus for frozen soils. Tests were conducted at the loads of 1, 2, 3, 5, 10 MPa and under temperatures of −0.5, −1.0, −2.0, −3.0, −5.0 °C. The coefficient of compressibility was obtained according to the e-σz curves for both unfrozen and frozen samples under different temperatures. The experimental results of temperatures ranging from room temperature to negative temperature were then obtained. The test results indicate that the compression curve of the frozen material are similar to that of the samples under room temperature; for warm frozen samples, the compressibility is considerable; the compressibility of frozen soil is closely related to temperature, i.e., the coefficient of compressibility increases with the increase of temperature in a form of exponential function.

Mechanical properties of warm frozen soils are similar to those of unfrozen soils. In recent years, the mechanical properties of warm frozen soils have attracted great attentions. However, there is no definition of warm frozen soil according to the mechanical behaviors of frozen soils so far. This paper attempts to define the temperature threshold for a warm saturated frozen sand in terms of mechanical properties. The Chinese ISO standard sand was taken as study object. Triaxial and confined compression tests were carried out on the saturated frozen samples. Mechanical properties such as cohesion, modulus and compression index were obtained and their changing tendency along with temperature were analyzed. It is found that the range of −1.0 °C to −0.5 °C seems to be the temperature when the mechanical properties change abruptly. Therefore, −1.0 °C can be defined as the temperature threshold for warm frozen soils with regard to the material tested in this program.

SiOCN ceramics are formed by the thermal decomposition of a polyvinylsilazane precursor in the presence of a dicumyl peroxide (DP) thermal initiator with different concentrations. The SiOCN ceramics pyrolyzed at 1000°C with different concentrations of DP are characterized with X-ray diffraction, transmission electron microscope, electron paramagnetic resonance, and UV-visible spectroscopy. We find that the structure and optical band gap of the SiOCN ceramics can be changed by altering the concentration of DP. There is a critical concentration, at which the structural and optical behavior varied in different ways as a function of the concentration of DP. The detailed mechanism is discussed.

Silk hydrogels for tissue repair are usually pre-formed via chemical or physical treatments from silk solutions. For many medical applications, it is desirable to utilize injectable silk hydrogels at high concentrations (>8%) to avoid surgical implantation and to achieve slow in vivo degradation of the gel. In the present study, injectable silk solutions that formed hydrogels in situ were generated by mixing silk with low-molecular-weight polyethylene glycol (PEG), especially PEG300 and 400 (molecular weight 300 and 400g mol(-1)). Gelation time was dependent on the concentration and molecular weight of PEG. When the concentration of PEG in the gel reached 40-45%, gelation time was less than 30min, as revealed by measurements of optical density and rheological studies, with kinetics of PEG400 faster than PEG300. Gelation was accompanied by structural changes in silk, leading to the conversion from random coil in solution to crystalline β-sheets in the gels, based on circular dichroism, attenuated total reflection Fourier transform infrared spectroscopy and X-ray diffraction. The modulus (127.5kPa) and yield strength (11.5kPa) determined were comparable to those of sonication-induced hydrogels at the same concentrations of silk. The time-dependent injectability of 15% PEG-silk hydrogel through 27G needles showed a gradual increase of compression forces from ∼10 to 50N within 60min. The growth of human mesenchymal stem cells on the PEG-silk hydrogels was hindered, likely due to the presence of PEG, which grew after a 5 day delay, presumably while the PEG solubilized away from the gel. When 5% PEG-silk hydrogel was subcutaneously injected in rats, significant degradation and tissue in-growth took place after 20 days, as revealed by ultrasound imaging and histological analysis. No significant inflammation around the gel was observed. The features of injectability, slow degradation and low initial cell attachment suggests that these PEG-silk hydrogels are of interest for many biomedical applications, such as anti-fouling and anti-adhesion.

The galvanic corrosion induced failures have been investigated for three cases in PCB, TFT touch screen and wire bonding industries using comprehensive physical and chemical characterization methods. Obvious evidences of anode oxidation and corrosive ions were found for all three cases. Characterization methodology should be tailored based on different situations.

In regenerative medicine, accumulating evidence demonstrates that the property of substrates monitors neural stem cells behavior. However, how stem cells sense and interpret biochemical and topographical cues remains elusive. This study aimed to explore the mechanism how nanofibrous scaffold modulated stem cells behavior. Spinal cord derived neural progenitor cells (NPCs) were cultured on electrospun aligned and randomly oriented collagen nanofibrous scaffolds. A 30% increase in proliferation and an elevation of BrdU incorporation were observed in NPCs on collagen nanofibers, compared to that on collagen-coated surface. In particular, NPCs expanded faster on aligned nanofibers in comparison with that on randomly oriented nanofibers. Moreover, an alteration in cell cycle progression with a reduced percentage of cells in G0/G1 phase and increased cell proliferation index (S phase plus G2/M phase) was also detected in NPCs cultured on collagen nanofibers. Incubating NPCs with anti-β1 integrin antibody or U1026 (an inhibitor of mitogen-activated protein kinase kinase, MEK) eliminated the altered cell cycle dynamics and BrdU incorporation induced by collagen nanofibers. In addition, cyclin D1 and cyclin dependent kinase 2 (CDK2), downstream genes of β1 integrin/mitogen-activated protein kinase (MAPK) pathway that control G1/S phase transition, were correspondingly regulated by nanofibers. Collectively, these data suggested that the property of substrate modulated NPCs proliferation by promoting cell cycle through β1 integrin/MAPK pathway. Our findings provide a better understanding of the interaction between NPCs and the substrate and therefore will pave way for regenerative medicine.

Current challenge in spinal cord tissue engineering which is used in the spinal cord injury is to produce an implantable scaffold capable of bridging the nerve gaps which will produce results similar to autograft without requiring autologous donor tissue. Blending heparan sulfate proteoglycan (HSPG) with collagen resulted in increased hydrophilicity, high porosity (89%), improved mechanical properties and suitable pore sizes were fabricated by optical chemical crosslinking method. The biocompatibility of HSPG/collagen scaffold was assessed for culturing neural stem cells which assisted in directing the growth of regenerating axons in nerve tissue engineering and proliferation by performing MTS assay in vitro. The results of MTS assay and Scanning Electron Microscopy study confirmed the parallel and porous HSPG/collagen scaffold are suitable substrates for spinal cord tissue engineering.

Electrospinning technique can be used to produce the three-dimensional nanofibrous scaffold similar to natural extracellular matrix, which satisfies particular requirements of tissue engineering scaffold. Randomly-oriented and aligned poly(lactic-co-glycolic acid) (PLGA) and PLGA/gelatin biocomposite scaffolds were successfully produced by electrospinning in the present study. The resulting nanofibrous scaffolds exhibited smooth surface and high porous structure. Blending PLGA with gelatin enhanced the hydrophilicity but decreased the average fiber diameter and the mechanical properties of the scaffolds under the same electrospinning condition. The cell culture results showed that the elongation of the osteoblast on the aligned nanofibrous scaffold was parallel to the fiber arrangement and the cell number was similar to that of randomly-oriented scaffold, indicating that the aligned nanofibrous scaffold provide a beneficial approach for the bone regeneration.

Ag (I)/gelatin microgels with different Ag (I) content have been prepared through self-assembly at various pH values. Silver cations are supposed to be partly trapped in the microgels core after interaction with the carboxyl groups on gelatin chains due to electrostatic attraction. The hydrophobility of gelatin chains enhances when the Ag (I) concentration increases, which results in the contraction of the complex and relatively compactable structure as well as ununiform distribution. The fluorescence experiments show that static quenching plays a main role in the complex formation and the calculated binding sites indicate that pH 7.0—8.0 are optimal for Ag (I)/gelatin self-assembly.