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Gear involute artifact (GIA) is an indispensable tool in the detection of high-precision gears. In this paper, a new method of horizontal electrode wire electrochemical contour evolution machining (HE-WECEM) was proposed to machine GIA. Compared with traditional circular interpolation for machining involute, HE-WECEM simulates the evolving process of involute to greatly improve the machining accuracy. Firstly, the machining mechanism of GIA by HE-WECEM was studied through mathematical models and electric field simulations. Secondly, reciprocating feed and two-way flushing fluid system was used, and its effectiveness in updating the electrolyte in the machining slit was analyzed through a flow-field simulation. And then, comparative experiment was designed to further validate the effectiveness of the flushing fluid system. The results indicate that the flushing system can effectively improve the stability of HE-WECEM. Finally, single-factor experiments were designed to investigate the effects of electrical parameters on machining. Based on the single-factor experiments, the Box–Behnken experiment was conducted on the electrical parameters. The response surface methodology (RSM) was used to analyze the composite effects of electrical parameters and obtain the optimal combination of machining parameters. A GIA blank with base circle radius of 50 mm was fabricated on an 8-mm-thick GCr15 workpiece, and the maximum deviation of tooth profile can reach 17.18 μm. The average surface roughness Sa reaches 1.435 μm. It is proved that HE-WECEM is a reliable method for machining GIA blank. [ABSTRACT FROM AUTHOR]

Background. Vascular adventitia contains progenitor cells and is shown to participate in vascular remolding. Progenitor cells are recruited into the venous thrombi in mice to promote neovascularization. We hypothesized that the adventitial progenitor cells of human great saphenous vein (HGSV-AdPC) enhance the resolution of venous thrombosis via neovascularization. Methods. Human great saphenous vein (HGSV) was harvested from the patients with great saphenous vein varicose and sectioned for immunohistochemistry, or minced for progenitor cell primary culture, or placed in sodium dodecyl sulfate solution for decellularization. Human venous thrombi were collected from patients with great saphenous vein varicose and superficial thrombophlebitis. Infrarenal abdominal aorta of New Zealand white rabbits was replaced with interposing decellularized vessel, and the patency of the grafts was confirmed by ultrasonic examination. Animal venous thrombi in the left infrarenal vena cava of mice were produced with Prolene suture ligation and ophthalmic force clipping of this portion. After HGSVs were digested by collagenase, the CD34+CD117+ HGSV-AdPC were isolated on FACS system, labelled with CM-Dil, and transplanted into the adventitia of infrarenal vena cava of nude mice. The percentage of thrombus organization area to the thrombus area was calculated as the organization rate. The thrombus cell, endothelial cells, and macrophages in the thrombi were counted in sections. Cell smears and frozen sections of human saphenous veins and venous thrombi were labeled with Sca1, CD34, CD117, Flk1, CD31, and F4/80 antibodies. The CD34+CD117+ HGSV-AdPC were cultured in endothelial growth medium with vascular endothelial growth factor (VEGF) to induce endothelial cell differentiation and analyzed with real time-PCR, Western blotting, and tube formation assays. Results. Immunohistochemical staining showed that the CD34+CD117+ cells were located within the adventitia of HGSVs, and many CD34+ and CD117+ cells have emerged in the human venous thrombi. The number of progenitor cells within the marginal area of 7 days mice thrombi was shown to be Sca1+ ≈21%, CD34+ ≈12%, CD117+ ≈9%, and Flk1+ ≈5%. Many CD34+adventitial progenitor cells have migrated into the decellularized vessels. FACS showed that the number of CD34+CD117+ HGSV-AdPC in primary cultured cells as 1.2 ± 0.07 %. After CD34+CD117+HGSV-AdPC were transplanted into the adventitia of nude mice vena cava with venous thrombi, the organization rate, nucleate cell count, endothelial cells, and macrophage cells of thrombi were shown to be significantly increased. The transplanted CD34+CD117+ HGSV-AdPC at the adventitia have crossed the vein wall, entered the venous thrombi, and differentiated into endothelial cells. The CD34+CD117+ HGSV-AdPC in the culture medium in the presence of VEGF-promoted gene and protein expression of endothelial cell markers in vitro and induced tube formation. Conclusions. HGSV-AdPC could cross the vein wall and migrate from the adventitia into the venous thrombi. Increased HGSV-AdPC in the adventitia has enhanced the resolution of venous thrombi via differentiating into endothelial cells of neovascularization. [ABSTRACT FROM AUTHOR]

Surface textures, such as micro pillar arrays, greatly promote the developments of many advanced fields. As many methods have been applied to fabricate the micro pillar arrays on silicon and polymer substrates, it is a still challenge to fabricate micro pillar arrays on metals. In this paper, through-mask electrochemical micromachining (TMEMM) was employed to fabricate micro pillar arrays on aluminum (Al) substrate. The effects of the direct and pulsed currents on surface morphology of the micro pillar arrays were investigated, and the ordered micro pillar arrays with different top diameters were obtained at the pulsed currents. Then, the influences of the current densities on the morphology of the micro pillar arrays were studied, and the largest etching anisotropy factor (EF) was obtained at a current density of 1 A/cm2. Finally, the wettability of the as-prepared micro pillar arrays with low surface energy modification was investigated. When the top diameters were 50– 90 μm and the heights were larger than 35 μm, all the micro pillar arrays obtained at different current densities showed superhydrophobicity with water contact angle larger than 150°. Unlabelled Image • Micro pillar arrays were fabricated by through-mask electrochemical micromachining. • Duty cycles and frequencies of etching currents affect pillar morphology seriously. • The larger etching anisotropy factor is obtained at low current densities. • Superhydrophobicity is obtained with suitable parameters. [ABSTRACT FROM AUTHOR]

In order to further reduce the machining errors of microstraight thin walls caused by the elastic deformation in micromilling process, the deformation mechanism has been studied, and a compensation method is proposed to reduce the machining errors. Firstly, conventional micromilling experiments have been conducted. It shows that large dimensional errors exist in finished thin walls. Second, a mathematical model is established to calculate the thin wall deformation based on Rayleigh–Ritz theory. The deformation values are determined by calculating the selected discrete measurement points. Based on the deformation of measurement points, the thin wall deformation of any position can be calculated by numerical method. Finally, the thin wall dimensional errors are reduced by compensating the deformation according to the analysis based on the introduced mathematical model. The high machining quality of the thin wall is realized. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the deformation compensation. The average relative dimensional errors have been reduced from 6.86 to 1.11 ~ 2.69%. Also, the fabricated thin walls keep good shape accuracy. The experimental results show that the introduced device and the compensation method can effectively improve micromilling quality of thin walls. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is proposed to improve the machining performance of WECMM. Firstly, a flow-field simulation in the machining gap was carried out; the results showed that the ultrasonic vibration of electrode can remarkably enhance the mass transport in the machining gap and improve the machining condition. Secondly, experiments were performed to confirm the effect of ultrasonic vibration, which illustrated that the vibration with proper amplitude can reduce the slit width and improve the morphology of machined surface. Moreover, the influence of other machining parameters were also discussed. Finally, a T-type micro connector with good surface roughness (Ra 0.286 μm) was fabricated on a 300-μm-thick 304 stainless steel workpiece and a micro gear (diameter: 3.362 mm; Ra: 0.271 μm) with an aspect ratio of 7 was fabricated on a 2-mm-thick workpiece. It is proved that the proposed ultrasonic-assisted wire electrochemical micromachining method has considerable potential and broad application prospects. [ABSTRACT FROM AUTHOR]

In order to satisfy the increasing fabrication quality requirements of micro curved thin wall structures, deformation, burrs height and dimensional errors in micro-milling processes of curved thin walls are studied. At first, the finite element analysis of curved thin wall deformation is carried out, it shows that complex elastic-plastic deformation and recutting occur in each micro-milling layer. Appropriate radial depth of cut, smaller spindle speed and axial depth of cut are beneficial to reduce deformation. Then, the influence of key process parameters in micro-milling as the speed of spindle n , feed engagement f z , radial depth of cut a e and axial depth of cut a p on milling force (F n), burrs height (H) and dimensional errors (△ w) are analyzed using the response surface method (RSM). To facilitate the quantitative analyses, mathematical models of burrs height and dimensional errors are established considering the interactions and quadratic effects of key parameters. It shows that the interactions among key parameters cannot be ignored. Therefore, cutting parameters should be delicately selected. The multi-objective particle swarm optimization (MOPSO) experiments are carried out based on the established prediction model. The results show that the combination of the optimized parameters identified by this method can effectively reduce the burr height and the dimensional error. Finally, under the guidance of this method, high-quality curved thin wall parts are fabricated. • The method to solve the deformation in curved thin wall micro-milling. • An optimal micro-milling parameter identification method for curved thin walls. • Multi-objective optimization for reducing dimensional errors and burr height. • The interactions and quadratic effects of key parameters are considered. • The method proposed provides a guidance for curved thin wall fabrications. [ABSTRACT FROM AUTHOR]

In order to further improve the dimensional accuracy of micromilled thin walls with high aspect ratios, the machining process should be actively controlled. A device for active cutting force measurement and cutting parameter compensation is developed to realize the real-time measurement of radial cutting forces and compensation of radial cutting parameters in thin wall cutting process. Firstly, a mathematical model is established to calculate the deformation and cutting force of thin walls based on the cantilever beam deformation theory. The thin wall deformation in the cutting process is estimated by measuring the cutting force. Then, the obtained incremental thin wall deformation is to be compared with the compensation threshold, which is set at 0.5 μm. If the value of the incremental deformation is less than 0.5 μm, compensation will not be processed. Otherwise, the incremental deformation is used as the compensation value for iterative compensation, until the incremental deformation of the thin wall is less than 0.5 μm. At last, a contrast experiment is carried out. The experimental results show that the introduced device and compensation method are feasible. Machining quality of the thin wall has been obviously improved in dimension precision after the cutting parameter compensations. [ABSTRACT FROM AUTHOR]

Concrete is often used in building, bridges, dams, roads and other infrastructures. However, the porosities and natural hydrophilicity of concrete often induce the damage of the concrete architecture or other disasters. Endowing the concrete with superhydrophobicity can effectively improve the antifreeze–thaw, anti-corrosion and anti-icing properties and expand the application prospect of concrete in the modern construction industry. Despite all this, the compressive strength of superhydrophobic concrete is not high enough, limiting its application. Here, we maintained superhydrophobic concrete for 28 days and improved the compressive strength for 3.5 times from 10 MPa to 34.48 MPa. The main mechanism is that calcium silicate hydrate structures grow with the increase in maintenance time and make the inside microstructures connected more closely. In addition, XPS spectra were also collected to investigate the chemical compositions of the superhydrophobic concrete. A series of tests were carried out on superhydrophobic concrete and indicated that the superhydrophobic concrete after maintenance had high surface robustness, anti-corrosion property and high anti-icing and deicing capacity, showing the application value. [ABSTRACT FROM AUTHOR]

Self‐propelled autonomous devices have huge application prospects in the field of environmental protection and energy. Nonetheless, the requirement of special chemicals or external electric and thermal energy limits their practical application. Here, a green self‐propelling method based on Laplace pressure originated from water droplets is reported. First, a triangle‐shaped miniboat composed of a superhydrophobic plate with an inclined superhydrophilic pore is fabricated. Water droplets put on superhydrophilic pore pass through the pore and form a jellyfish‐like jet, which further propels the miniboat to move spontaneously and directionally. The propelling distance, propelling time, and instantaneous propelling velocity of the miniboat is greatly affected by the pore size and the initial water droplet volume. Then, two types of devices are designed and installed on the miniboat to successively provide small water droplets from the reservoir or rain to realize the continuous and long‐distance self‐propelled motion. Moreover, a spindle‐shaped miniboat with two or four symmetrical and inclined pores is designed. Under propelling by the torque, the spontaneous and continuous rotation motion is also achieved. This finding will open a new avenue for a wide range of applications ranging from a detecting minirobot on the water surface to a power generation device from rain. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of statins on risk of recurrent venous thromboembolism (VTE) was systematically analyzed. • Statins were associated with lower risks of recurrent VTE and its two forms, i.e. DVT and PE. • Statins were associated with a lower risk of mortality among patients with VTE. • Randomized clinical trials are warranted to corroborated these findings. Recent studies have suggested that statins may be associated with a lower risk of recurrent venous thromboembolism (VTE). We systematically searched PubMed, Web of Science and Cochrane Library from inception until May 2020 to identify any eligible studies that reported the association between statin use and the risk of recurrent VTE, and conducted a comprehensive systematic review and meta-analysis (PROSPERO registration number: CRD42020190169) on this matter. A total of 14 observational studies were included for qualitative review and 12 of them qualified for meta-analyses. The main meta-analysis found that statin use was associated with a lower risk of disease recurrence among patients with VTE (pooled adjusted HR: 0.76, 95% CI: 0.69−0.83), which was robust in sensitivity analyses and free of significant publication bias. Additionally, such association was present when restricting to periods after anticoagulation withdrawal (pooled adjusted HR: 0.78, 95% CI: 0.70−0.88) and when separately analyzing recurrent deep vein thrombosis (pooled adjusted HR: 0.71, 95% CI: 0.62−0.81) and recurrent pulmonary embolism (pooled adjusted HR: 0.80, 95% CI: 0.66−0.97; P = 0.027). Furthermore, statin use in patients with VTE was also found to be associated with a lower risk of all-cause mortality (adjusted HR: 0.65, 95% CI: 0.56−0.77), and possibly an even lower risk of bleeding (adjusted HR: 0.88, 95% CI: 0.73–1.07), albeit not statistically significant. Statins have the potential to reduce recurrent events among patient with VTE. Randomized clinical trials to better explore the effect of statins in secondary prevention of VTE are warranted. [ABSTRACT FROM AUTHOR]

• A colorful superhydrophobic concrete (CSC) coating was developed. • The coating had good robustness due to high mechanical strength and self-similarity. • The coating possessed anti-icing, anti-corrosion and self-cleaning abilities. • The coating can be high-efficient and large-area fabricated. Concrete is widely used in architecture because of its advantages such as high strength, low cost, good durability and plasticity. However, due to its hydrophilicity and porous structures, the concrete suffers from damages caused by oxidative corrosion, freezing environment, acid rain, etc. Superhydrophobic coating with excellent water-repellent property has great potential to solve this problem. However, a colorful and robust superhydrophobic coating which meets both performance and aesthetic requirements is still not reported. Here, we develop a colorful and robust superhydrophobic concrete (CSC) coating with a water contact angle of 158 ± 0.5° and a sliding angle of 5 ± 0.8° and composing of cement, sand, water-based stone protector, and dyes for concrete coloring. Four kinds of colors including red, yellow, blue, and green can be obtained by adding red, yellow, blue, and green iron oxide dyes, respectively. The high robustness is originated from the high adhesive force between the coating and the substrate, the inherent high hardness of concrete itself, and self-similarity of inside micro-structures. The CSC coating also exhibit excellent chemical durability and weather resistance. Thus, this kind of CSC coating has promising application prospects in the outside wall of concrete architecture to improve decorative and waterproof effects and keep clean. [ABSTRACT FROM AUTHOR]