连续网状结构Ti_(2)AlN/TiAl复合材料的制备及力学性能

采用高温气体渗氮法将氮引入TiAl预合金粉末中,然后采用放电等离子烧结法制备具有连续网络增强相结构的Ti_(2)AlN/TiAl复合材料。结果表明,复合材料的硬度明显高于TiAl合金的硬度,并随着氮化时间的增加而增加。该强化效果是粉末渗氮引起的固溶体强化、具有高硬度和弹性模量的连续网状Ti_(2)AlN相以及位错密度增加协同作用的结果。同时,与TiAl合金相比,Ti_(2)AlN/TiAl复合材料的抗压强度降低,这与氮化后直接形成的一部分Ti_(2)AlN颗粒和过多的增强相含量有关。

Meta-analysis of radiofrequency ablation in combination with transarterial chemoembolization for hepatocellular carcinoma

AIM: To compare radiofrequency ablation (RFA) and transcatheter arterial chemoembolization (TACE) with RFA monotherapy in hepatocellular carcinoma (HCC). METHODS: We searched PubMed, Medline, Embase and Chinese databases (CBMdisc and Wanfang data) for randomized controlled trails comparing RFA plus TACE and RFA alone for treatment of HCC from January 2000 to December 2012. The overall survival rate, re-currence-free survival rate, tumor progression rate, and safety were analyzed and compared. The analysis was conducted on dichotomous outcomes and the standard meta-analytical techniques were used. Pooled odds ratios (ORs) with 95%CIs were calculated using either the fixed-effects or random-effects model. For each meta-analysis, the χ2 and I2 tests were first calculated to assess the heterogeneity of the included trials. For P<0.05 and I 2>50%, the assumption of homogeneity was deemed invalid, and the random-effects model wasused; otherwise, data were assessed using the fixed-effects model. All statistical analysis was conducted us-ing Review manager (version 4.2.2.) from the Cochrane collaboration. RESULTS: Eight randomized controlled trials were identified as eligible for inclusion in this analysis and included 598 patients with 306 treated with RFA plus TACE and 292 with RFA alone. Our data analysis indicated that RFA plus TACE was associated a sig-nificantly higher overall survival rate (OR 1-year=2.96, 95%CI: 1.84-7.74, P<0.001; OR 2-year=3.72, 95%CI: 1.24-11.16, P=0.02; OR 3-year=2.65, 95%CI: 1.81-3.86, P<0.001) and recurrence-free survival rate (OR 3-year=3.00, 95%CI: 1.75-5.13, P<0.001; OR 5-year=2.26, 95%CI: 1.43-3.57, P=0.0004) vs that of RFA alone. The tumor progression rate in patients treated with RFA alone was higher than that of RFA plus TACE (OR=0.60, 95%CI: 0.42-0.88, P=0.008) and there was no significant difference on major complications between two different kinds of treatment (OR=1.20, 95%CI: 0.31-4.62, P=0.79). Additionally, the meta-analysis data of subgroups revealed that the survival rate was significantly higher in patients with intermediate-and large-size HCC underwent RFA plus TACE than in those underwent RFA monotherapy; however, there was no significant difference between RFA plus TACE and RFA on survival rate for small HCC. CONCLUSION: The combination of RFA with TACE has advantages in improving overall survival rate, and pro-vides better prognosis for patients with intermediate-and large-size HCC.

Effects of hypoxia-inducible factor-1α silencing on the proliferation of CBRH-7919 hepatoma cells

AIM:To study the effects of hypoxia-inducible factor1α(HIF-1α) silencing on the proliferation of hypoxic CBRH-7919 rat hepatoma cells.METHODS:The CBRH-7919 rat hepatoma cell line was used in this study and the hypoxic model was constructed using CoCl2.The HIF-1α-specific RNAi sequences were designed according to the gene coding sequence of rat HIF-1α obtained from GeneBank.The secondary structure of the HIF-1α gene sequence was analyzed using RNA draw software.The small interfering RNA(siRNA) transfection mixture was produced by mixing the siRNA and Lipofectamine2000TM,and transfected into the hypoxic hepatoma cells.Real time reverse transcription-polymerase chain reaction(RTPCR) and Western blotting assay were used to detect the expression levels of mRNA and protein.HIF-1α and vascular endothelial growth factor(VEGF) mRNA was determined using real time RT-PCR;the protein expression levels of AKT,p-AKT,p21 and cyclinD1 were determined using Western blotting.The proliferation of hepatoma cells was observed using the methyl thiazolyl tetrazolium(MTT) assay and the bromodeoxyuridine(BrdU) incorporation cell proliferation assay.RESULTS:Under induced hypoxia,the viability of the hepatoma cells reached a minimum at 800 μmol/L CoCl2;the viability of the cells was relatively high at CoCl2 concentrations between 100 μmol/L and 200 μmol/L.Under hypoxia,the mRNA and protein expression levels of HIF-1α and VEGF were significantly higher than that of hepatoma cells that were cultured in normaxia.HIF-1α-specific RNAi sequences were successfully transfected into hepatoma cells.The transfection of specific siRNAs significantly inhibited the mRNA and protein expression levels of HIF-1α and VEGF,along with the protein expression levels of p-AKT and cyclinD1;the protein expression of p21 was significantly increased,and there was no significant difference in the expression of AKT.The MTT assay showed that the amount of hepatoma cells in S phase in the siRNA transfection group was obviously smaller than that in the control group;in the siRNA transfection group,the amount of hepatoma cells in G1 phase was more than that in the control group.The BrdU incorporation assay showed that the number of BrdU positive hepatoma cells in the siRNA transfection group was less than that in the control group.The data of the MTT assay and BrdU incorporation assay suggested that HIF-1α silencing using siRNAs significantly inhibited the proliferation of hepatoma cells.CONCLUSION:Hypoxia increases the expression of HIF-1α,and HIF-1α silencing significantly inhibits the proliferation of hypoxic CBRH-7919 rat hepatoma cells.

Prognostic factors for survival after transarterial chemoembolization combined with microwave ablation for hepatocellular carcinoma

AIM: To analyze prognostic factors for survival after transarterial chemoembolization (TACE) combined with microwave ablation (MWA) for hepatocellular carcinoma (HCC).

Conventional transarterial chemoembolization vs microsphere embolization in hepatocellular carcinoma:A meta-analysis

AIM: To compare conventional transarterial chemoembolization (c-TACE) with microsphere embolization in hepatocellular carcinoma (HCC).

Interventional digital subtraction angiography for small bowel gastrointestinal stromal tumors with bleeding

AIM: To retrospectively evaluate the diagnostic efficacy of interventional digital subtraction angiography (DSA) for bleeding small bowel gastrointestinal stromal tumors (GISTs).

Vascular endothelial growth factor-165b protects the blood-retinal barrier from damage after acute high intraocular pressure in rats

AIM:To elucidate the role of vascular endothelial growth factor-165b(VEGF-165b)in blood-retinal barrier(BRB)injury in the rat acute glaucoma model.METHODS:In this study,the rat acute high intraocular pressure(HIOP)model was established before and after intravitreous injection of anti-VEGF-165b antibody.The expression of VEGF-165b and zonula occludens-1(ZO-1)in rat retina was detected by double immunofluorescence staining and Western blotting,and the breakdown of BRB was detected by Evans blue(EB)dye.RESULTS:The intact retina of rats expressed VEGF-165b and ZO-1 protein,which were mainly located in the retinal ganglion cell layer and the inner nuclear layer and were both co-expressed with vascular endothelial cell markers CD31.After acute HIOP,the expression of VEGF-165b was up-regulated;the expression of ZO-1 was down-regulated at 12h and then recovered at 3d;EB leakage increased,peaking at 12h.After intravitreous injection of anti-VEGF-165b antibody,the expression of VEGF-165b protein was no significantly changed;and the down-regulation of the expression of ZO-1 was more obvious;EB leakage became more serious,peaking at 3d.EB analysis also showed that EB leakage in the peripheral retina was greater than that in the central retina.CONCLUSION:The endogenous VEGF-165b protein may protect the BRB from acute HIOP by regulating the expression of ZO-1.The differential destruction of BRB after acute HIOP may be related to the selective loss of retinal ganglion cells.

Microstructure and fatigue properties of TiAl-based alloy with different tungsten contents

Microstructure and fatigue properties of TiAlbased alloys with different W contents were investigated.The results indicate that the grain size and lamellar spacing can be significantly refined,and the optimal W content on both the microstructure and fatigue property is about1.00 at%.The amount of B2（ω） phase gradually increases with the increase in W content,and excessive B2（ω） phase located in the boundary of lamellar colony trends to be the weak region with low resistance against crack propagation.Another result is that with the increase in W content,the region of peritectic reaction is also enlarged.The interdendritic Al-rich region is another weak region against crack propagation.Both of these effects are responsible for the worse fatigue property of Ti-45.1Al-5Nb-1.40W-1.4B W alloy compared with that of Ti-45.7Al-5Nb-0.75W-1.4B alloy.Instability of fatigue property still exists,but it slightly reduces with the decrease in grain size and lamellar spacing.

Electrochemical Properties of Tungsten-Alloying-Modified AISI 430 Stainless Steel as Bipolar Plates for PEMFCs used in Marine Environment

To improve the corrosion resistance and surface electrical conductivity of AISI 430 stainless steel （430 SS） as bipolar plates for proton exchange membrane fuel cells （PEMFCs） used in marine environment, a tungsten alloying layer has been successfully prepared on 430 SS substrate via the plasma surface diffusion alloying technique. The tungsten- modified （W-modified） 430 SS displays a 7-8 Ixm tungsten alloying layer with a body-centered-cubic structure. The W-modified surface also shows a better hydrophobicity with contact angle of 93.5~ and a lower interfacial contact resistance compared with the untreated 430 SS. The potentiodynamic and potentiostatic polarization and electrochemical impedance spectroscopy measurements show that the corrosion resistance of 430 SS is obviously improved in simulated PEMFC environment （0.05 M H2SO4 ＋ 2 ppm HF ＋ 0.01 M NaC1 solution at 70℃）, after the plasma surface diffusion alloying process.

Fatigue properties of a medium-strength γ-TiAl alloy with different surface conditions

Effects of surface condition on fatigue properties of a medium-strength γ-TiAl alloy Ti-45Al-5Nb-lW（at%） were investigated.It is found that the maximum stresses of fatigue samples are lower than the yield stresses of the medium-strength γ-TiAl alloy.Meanwhile,the local plastic deformation is unconspicuous to occur at the crack tip.In this case,the fatigue strength is mainly decided by surface conditions of maximum-stressed surface,but compressive stress and deformation especially resulted from shot peening play an important role in the improvement of the condition fatigue strength.The affecting depth of shot peening is about 250 μm.As a result,the relatively weak microstructures and phases become the preferential initiation sites and propagation routes.They are observed to be equiaxed γ grains,B2 ＋ ω grains,and α_2-γ lamellar interface in soft orientations.The existence of V-notch can significantly reduce the fatigue properties of the samples.

Microstructure evolution and diffusion mechanism of Nb/TiAl alloy diffusion-bonded joints

The interdiffusion behavior in Nb/TiAl alloy diffusion couples was studied.The process was carried out in the temperature range of 950-1400℃for 8 h in the vacuum hot-pressure sintering furnace.The microstructural evolution was observed by optical microscopy(OM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD)technique and transmission electron microscopy(TEM).The element concentration distribution at the bonded interface was obtained by scanning electron microscopy with an energy-dispersive X-ray spectroscopy(EDS)apparatus.The thickness of reaction interface increases with bonding temperature increasing.The formed phases in diffusion interface are found to be O-Ti_(2)AlNb,σ-Nb_(2)Al,δ-Nb_(3)Al and Nb solid solution(Nbss)at 1350℃.The average interdiffusion coefficient of the interface elements was calculated by the theory of Dayananda.The results indicate that Al diffuses faster than Nb and Nb diffuses faster than Ti in the Ti-Al-Nb system.Meanwhile,it is found that Ti promotes the diffusion of Al and Nb and Nb inhibits the diffusion of Ti and Al in the process of diffusion.