On-Line Compensation for Micromilling of High-Aspect-Ratio Straight Thin Walls.

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls.

Adventitial Progenitor Cells of Human Great Saphenous Vein Enhance the Resolution of Venous Thrombosis via Neovascularization.

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.

Effect of statins on the risk of recurrent venous thromboembolism: A systematic review and meta-analysis.

BACKGROUND: Recent studies have suggested that statins may be associated with a lower risk of recurrent venous thromboembolism (VTE). METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Characteristics and clinical indicators of concomitant venous thromboembolism in acute limb ischemia.

BACKGROUND: Venous thromboembolism (VTE) concomitant to acute limb ischemia (ALI) is rarely reported. The aim of the study was to investigate characteristics and identify clinical indicators of VTE in patients with ALI. METHODS: Electronic medical record was used to identify patients diagnosed with ALI from January 2013 to June 2019. Eligible patients were categorized as VTE or non-VTE based on the presence or absence of concomitant VTE. Univariate analysis and multivariate analysis for indicators of VTE were performed. RESULTS: A total of 153 patients with 161 ischemic limbs were enrolled. Venous duplex ultrasound (DUS) for 149 patients (157 ischemic limbs) revealed deep vein thrombosis (DVT) in 38 (24.2%) ischemic limbs of 37 (24.8%) patients. Five femoral DVTs were found intraoperatively. Six patients had pulmonary embolism (PE) and three of them died. In all, 43 (28.1%) ALI patients were diagnosed with VTE. They were treated with trans-arterial catheter-directed thrombolysis (N.=22), embolectomy (N.=9), primary amputation (N.=4) and anticoagulation alone (N.=8). The univariate analysis indicated that symptoms ≥ 2 days [odds ratio (OR): 3.42, 95%CI:1.54-7.62], Rutherford classification IIb-III (OR: 9.17, 95%CI: 2.10-40.12), leg swelling (OR: 4.44, 95%CI: 2.07-9.53), neutrophil ratio ≥0.80 (OR: 3.92, 95%CI: 1.72-8.93) and positive D-dimer (OR: 8.44, 95%CI: 3.65-19.53) were indicators of VTE concomitant to ALI. In the multivariate analysis, leg swelling and positive D-dimer appeared to be independent indicators. CONCLUSIONS: VTE commonly occurs to ALI. Venous DUS for DVT screening should be considered for ALI patients who present one or more of these indicators.

Model for Predicting the Micro-Grinding Force of K9 Glass Based on Material Removal Mechanisms.

K9 optical glass has superb material properties used for various industrial applications. However, the high hardness and low fracture toughness greatly fluctuate the cutting force generated during the grinding process, which are the main factors affecting machining accuracy and surface integrity. With a view to further understand the grinding mechanism of K9 glass and improve the machining quality, a new arithmetical force model and parameter optimization for grinding the K9 glass are introduced in this study. Originally, the grinding force components and the grinding path were analyzed according to the critical depth of plowing, rubbing, and brittle tear. Thereafter, the arithmetical model of grinding force was established based on the geometrical model of a single abrasive grain, taking into account the random distribution of grinding grains, and this fact was considered when establishing the number of active grains participating in cutting Nd-Tot. It should be noted that the tool diameter changed with machining, therefore this change was taking into account when building the arithmetical force model during processing as well as the variable value of the maximum chip thickness amax accordingly. Besides, the force analysis recommends how to control the processing parameters to achieve high surface and subsurface quality. Finally, the force model was evaluated by comparing theoretical results with experimental ones. The experimental values of surface grinding forces are in good conformity with the predicted results with changes in the grinding parameters, which proves that the mathematical model is reliable.

Improving Machining Localization and Surface Roughness in Wire Electrochemical Micromachining Using a Rotating Ultrasonic Helix Electrode.

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.

Superaerophilic Wedge-Shaped Channels with Precovered Air Film for Efficient Subaqueous Bubbles/Jet Transportation and Continuous Oxygen Supplementation.

Pumpless and directed gas transportation in aqueous environments has promising application prospects in various domains. So far, researches on gas transportation based on superaerophilic channels are limited to the transportation of fewer bubbles with low transportation velocity. How to enhance the transportation velocity and realize the transportation of a large quantity of bubbles (especially for gas jet) for practical applications remain unclear. Here, a half-open wedge-shaped channel with subaqueous superaerophilicity is fabricated, which demonstrates excellent bubble affinity and can realize the pumpless and directed bubble transportation. It is proposed that a Laplace force is the main driving force during the transportation and the magnitude of the force is influenced by both the wedge angle of the channel and geometric parameters of the bubble whereas the direction of the force is determined by the orientation of the channel. By applying a precovered air film on the subaqueous superaerophilic wedge-shaped channel, bubbles demonstrate a higher transportation velocity. Additionally, the prepared channel shows an outstanding affinity to oxygen jet at high flux, which can be utilized to transport oxygen for continuous subaqueous oxygen supplementation.

[An improved method for stem cell derivation from human great saphenous vein].

The objectiue was to explore how to improve stem cell derivation from human great saphenous vein. After the saphenous vein was cut into small pieces, the cells of the vessel wall were obtained by tissue adherent method and digestion with type Ⅱ collagenase. The morphological changes of blood vessel wall were observed under inverted microscope. The survival of vascular wall cells was assessed by trypan blue staining. Stem cells doubly positive for CD34 and CD117 were sorted out by immunofluorescent staining and flow cytometry. The cells obtained by tissue adherence method exhibited signs of fibrotic changes and aging at the third passage (P3), while the cells extracted by enzymatic digestion still showed colony-like growth. Survival rates of these two groups of cells were (91.7±1.2)% and (97.2±0.7)%, (P=0.005). The results of flow cytometry showed that the positive rates of CD34 and CD117 double positive cells in these two groups were (0.16± 0.05)% and (0.44±0.07)%, respectively, with statistical significance (P=0.005). Immunofluorescent staining showed that the positive rates of double positive stem cells in the two groups were (89.41±2.06)% and (94.03±1.83)%, P<0.05 one week after the sorted stem cells were cultured. The positive rates of CD31, VEGF2 and SMA in the stem cells determined by flow cytometry were (0.12±0.01)%, (0.19±0.02)% and (0.45±0.01)%, respectively, which were not statistically different from those of the control groups. This could rule out substantial inclusion of mature endothelial cells and smooth muscle cells. Tube forming experiment confirmed that these vascular stem cells had developmental plasticity. More viable and morphologically healthy vascular stem cells can be derived by enzymatic digestion. These cells can be widely used in clinical and basic research.