CREB knockdown inhibits growth and induces apoptosis in human pre-B acute lymphoblastic leukemia cells through inhibition of prosurvival signals

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Rima Manafi Shabestari, Majid Safa, Fatemeh Alikarami, Mehdi Banan, Ahmad Kazemi
A majority of acute lymphoblastic leukemia patients overexpress CREB in the bone marrow. However, the functional significance of this up-regulation and the detailed molecular mechanism behind the regulatory effect of CREB on the growth of B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells has not been elucidated. We demonstrated here that CREB knockdown induced apoptosis and impaired growth of BCP-ALL NALM-6 cells which was associated with caspase activation. The gene expression levels of prosurvival signals Bcl-2, Mcl-1, Bcl-xL, survivin and XIAP were down-regulated upon CREB suppression. These findings indicate a critical role for CREB in proliferation, survival, and apoptosis of BCP-ALL cells. The data also suggest that CREB could possibly serve as potential therapeutic target in BCP-ALL.



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Spectral characterisation, antiviral activities, in silico ADMET and molecular docking of the compounds isolated from Tectona grandis to chikungunya virus

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Sangeetha K., Indu Purushothaman, Rajarajan S.
Chikungunya infection is treated symptomatically with antipyretics and anti-inflammatory drugs without any specific antiviral drug till date. The lack of an approved antiviral drug and the emergence of virulent strains after 2006 epidemics emphasize the need for the development of potential antiviral drugs to Chikungunya virus. Hence, we studied the antiviral activity of the extracts and compounds isolated from Tectona grandis leaves to both the Asian and East central South African strains of Chikungunya virus. Five compounds were isolated from the ethanolic extract of Tectona grandis by bioactivity guided fractionation followed by Spectral Characterisation through GC–MS and NMR spectroscopy and investigated for the antiviral activity. Also in silico ADMET and Molecular Docking of the characterised compounds against the structural and non structural proteins of Chikungunya virus were performed. The characterised compound Benzene-1-carboxylic acid hexadeconate was effective at IC 50 3.036μg/ml (7.5μM) and 76.46μg/ml (189.02μM) to Asian and ECSA strain of CHIKV respectively. The compound showed desirable pharmacokinetic properties and significant molecular interactions with the E1 protein of Chikungunya virus by in silico analysis. Thus Benzene-1-carboxylic acid-2-hexadeconate isolated from Tectona grandis was found to be a promising drug candidate to both the Asian and ECSA strains of Chikungunya virus with high selectivity indices in comparison to the reference RNA antiviral drug Ribavirin.

Graphical abstract

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Effect of the Egyptian propolis on the hepatic antioxidant defense and pro-apoptotic p53 and anti-apoptotic bcl2 expressions in aflatoxin B1 treated male mice

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Abeer A. Alm-Eldeen, Mohammed A. Basyony, Nabil K. Elfiky, Mohamed M. Ghalwash
Aflatoxins are potent hepatotoxic due to their role in producing reactive oxygen species and consequently peroxidative damage. Propolis is a honey bee product known for its antioxidant capacity. The aim of this study was to verify the antioxidant effect of the Egyptian propolis extract (EPE) against aflatoxin B1 (AFB1)-induced hepatotoxicity in mice. Forty eight male mice were divided: first, second and third groups were used as control receiving saline, olive oil and EPE respectively, fourth was AFB1 group, fifth and sixth received EPE post or pre AFB1 treatment, respectively. EPE was given as (0.2mg/kg) 3 times a week. AFB1 was given as a single dose (0.25μg/kg). After 2 weeks, the mice were scarified and biochemical, histopathological and immunohistochemical investigations were assessed. EPE has a high content of total phenolics and alkaloids. The inhibitory concentration 50 (IC50) value for DPPH radical scavenging was 1353.8μg/mL. Pretreatment with EPE improved AFB1-induced hepatotoxicity represented in lowering alanine transaminase, aspartate aminotransferase, alkaline phosphatase, cholesterol, triglycerides, lipid peroxidation and pro-apoptotic p53 expression to 33.48±1.98 IU/ml, 53.00±2.37 IU/ml, 123.50±2.02 IU/ml, 76.50±2.66mg/dl, 54.00±3.03mg/dl, 2.22±0.14 nmol/g and 4.31±2.1 cells/field and raising the reduced glutathione, catalase, superoxide dismutase and anti-apoptotic bcl2 expression to 3.37±1.65 nmol/g, 4.92±0.25 nmol/g, 57±0.91UI/g and 39.7±5.9 cells/field which all had non-significant differences with the control, respectively. In conclusion, EPE can attenuate aflatoxin B1-induced hepatotoxicity in mice.



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The impact of different extracellular matrices on melatonin effect in proliferation and stemness properties of ovarian cancer cells

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Maryam Akbarzadeh, Reza Rahbarghazi, Elahe Nabat, Ali Akbar Movassaghpour, Daruish Shanehbandi, Behnaz Faramarzian Azimi Maragheh, Danial Matluobi, Balal Barazvan, Masoume Kazemi, Nasser Samadi, Mohammad Nouri
AimEndogenous melatonin has numerous physiological roles on modulating the function of different organs. Recent studies revealed oncostatic and protective effects of this molecule on tumor development. In this study, we examined the impact of melatonin and key underlying mechanisms on stemness, morphology, invasiveness and viability of SKOV3 ovarian cancer cells in different types of extracellular matrix.MethodsCell viability was evaluated by MTT Assay. Colony-forming assay was performed by seeding 4×10³ cells on different matrices in six well-plate. The percentage of cancer stem like cells was determined by flow cytometric assay after applying antibodies against stemness markers, CD133 and CD44. Different types of extracellular matrix including fibronectin, gelatin, collagen and matrigel were applied to incubate the cells in the presence of melatonin. Downstream gene expressions including VEGF and E-cadherin were determined by Real-time PCR.ResultsMelatonin (0.1mM) decreased the percentage of viable cells up to 61.79±8.2% (p<0.05). Colony formation assay revealed the significant impact of melatonin in inhibition of colony formation in these cells. The maximum effect was shown in the cells incubated with melatonin on gelatin (p<0.05). Identification of stemness markers showed that applying matrigel caused significant increase in the percentage of cancer stem like cells compared to other types of extracellular matrix (p<0.05). However melatonin slightly diminished the number of stem cell like cells in all incubated matrices. Our results from gene expression assays revealed that melatonin induced a marked increase in E-cadherin along with decrease in VEGF expression levels (p<0.05).ConclusionOur results suggest that interaction between ovarian cancer cells and neighboring matrices determines the subsequent anti invasive activities of melatonin.



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Contemporary imaging of incidentally discovered adrenal masses

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Daniel J. Wale, Ka Kit Wong, Benjamin L. Viglianti, Domenico Rubello, Milton D. Gross
Adrenal lesions are routinely encountered incidentally in clinical practice. Although most of these lesions are benign, malignancy needs to be excluded. Therefore, the initial clinical workup is to exclude aggressive characteristics suggesting malignancy and to identify characteristics predictive of the most common benign lesion, an adrenal adenoma. Predicting a benign adenoma using a variety of imaging modalities has been widely studied using unenhanced computed tomography (CT), contrast enhanced CT, and magnetic resonance (MR) imaging. This review article describes the currently used imaging protocols and clinical interpretation criteria of common adrenal lesions. An adenoma can be predicted if a homogenous soft tissue adrenal mass demonstrates low attenuation (upper threshold value of 10 Hounsfield Units) on unenhanced CT, demonstrates an absolute enhancement washout of ≥ 60% and/or relative enhancement washout of ≥ 40% on adrenal washout contrast enhanced CT, or demonstrates signal loss in opposed-phased MR imaging. If an adrenal adenoma cannot be predicted based upon these criteria, the lesion should be evaluated for other imaging characteristics that suggest a specific pathology, such as an adrenal cyst or myelolipoma. Although nonspecific and with limitations, 18F-fluorodeoxyglucose (FDG) PET/CT has a potential role for differentiating benign from malignant lesions based upon the amount of radiopharmaceutical uptake with malignant lesions generally having greater uptake. If clinical and/or hormonal screening suggests a pheochromocytoma, consideration can be given to 18F-dihydroxyphenylalanine (DOPA) or 123I-metaiodobenzylguanidine (MIBG) in addition to CT and MR. Finally, this review proposes a diagnostic work-up strategy for routine use in clinical practice.



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Synthesis and in vitro photodynamic therapy of chlorin derivative 131-ortho-trifluoromethyl-phenylhydrazone modified pyropheophorbide-a

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Jianjun Cheng, Wenting Li, Guanghui Tan, Zhiqiang Wang, Shuying Li, Yingxue Jin
Photodynamic therapy (PDT) is entering the mainstream of the cancer treatments recently. Pyropheophorbide-a (Pa), as a degradation product of chlorophyll-a, has been shown to be a potent photosensitizer in photodynamic therapy. In this paper, we investigated the in vitro photodynamic therapy of 13¹-ortho-trifluoromethyl-phenylhydrazone modified pyropheophorbide-a (PHPa) against human HeLa cervical cancer cell line, together with ultraviolet-visible spectra, fluorescence emission spectra, stability in various solvents, and single oxygen quantum yield. The results indicated that PHPa not only showed a greater molar extinction coefficient reached 4.55×10⁴ Lmol⁻¹cm⁻¹, the long absorption wavelength (681nm) as we expected that makes it potential in deep tumor treatment, but also showed better stability in near neutral phosphate buffers (pH 7.4) and culture medium, as well as higher single oxygen quantum yield (ФD=40.5%) in DMF solutions. Moreover, cell experiments suggested that PHPa could be uptaken by HeLa cells successfully, and has low dark toxicity without irradiation, but remarkable photo-cytotoxicity (IC50, 1.92±0.59μM) that the inhibition rate of HeLa cells could increase up 91.4% at 30μM of PHPa after irradiation. In addition, morphological changes of HeLa cells further demonstrated that PHPa can induce damage and apoptotic cell death. Furthermore, the mechanism of photochemical processes was investigated by using specific quenching agent sodium azide (SA) and D-mannitol (DM), respectively, which showed the formation of singlet oxygen (Type II reaction mechanism) may play a predominant role, Type I and Type II photodynamic reactions could occur simultaneously in this PHPa mediated PDT process.

Graphical abstract

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Tinospora cordifolia extract attenuates cadmium-induced biochemical and histological alterations in the heart of male Wistar rats

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Lohanathan Bharathi Priya, Rathinasamy Baskaran, Pitchai Elangovan, Velumani Dhivya, Chih-Yang Huang, Viswanadha Vijaya Padma
Persistence of cadmium (Cd) in the environment causes serious ecological problems. Tinospora cordifolia is a medicinal herb used in Ayurveda for treating various metabolic disorders and toxic conditions. The present study investigates the protective effect of T. cordifolia stem methanolic extract (TCME) on a heavy metal, Cd-induced cardiotoxicity in male Wistar rats. Male albino Wistar rats were divided into four groups (n=6). The animals after treatment for 28days with Cd and TCME were analysed for biochemical and histological changes in the serum and heart tissues. Cd induced lipid peroxidation and protein carbonylation was significantly reduced by TCME. TCME also reduced the histological alterations induced by Cd treatment in the heart tissues with diminished loss of myocardial fibers. Administration of TCME effectively prevented the altered levels of serum marker enzymes (creatine kinase and lactate dehydrogenase), antioxidants, such as superoxide dismutase, catalase, glutathione, glutathione peroxidase and glutathione-S-transferase, and glycoproteins contents such as hexose, hexoseamine, fucose, and sialic acid by Cd intoxication. TCME also offered protection against the change in levels of Na⁺K⁺ATPase, Mg²⁺ATPase and Ca²⁺ATPase activities against Cd toxicity. The study suggests TCME as a potent cardioprotective agent against Cd induced toxicity.



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The properties of red seaweed (Kappaphycus alvarezii) and its effect on mammary carcinogenesis

Publication date: March 2017
Source:Biomedicine & Pharmacotherapy, Volume 87
Author(s): Vi-Sion Chang, Patrick N. Okechukwu, Swee-Sen Teo
The edible red seaweed (Kappaphycus alvarezii) is one of the algae species which was found to be rich in nutrients and nutraceutical. Hence, K. alvarezii may have the ability to suppress cancer through its antiproliferative properties. The aim of this study was to investigate the potential compounds of K. alvarezii, cytotoxicity properties of K. alvarezii extract on breast cancer cell line (MCF-7), investigated toxicity effect of high dosage K. alvarezii extract in rats and determined the effect of K. alvarezii on 7, 12-dimethylbenz[a]anthracene (DMBA) mammary carcinogenesis in rats. The method of LCMS/MS and MTT assay were used. For animal study, sub-chronic toxicity method was used, the rats were supplemented with 2000mg/kg body weight daily of K. alvarezii crude extracts by oral gavage. For the anticancer effect of K. alvarezii crude extracts, this study consisted of three groups of the experimental, untreated and normal group of rats. The experimental and untreated groups of rats were induced with mammary tumour with DMBA. The experimental group of rats was given with K. alvarezii crude extracts orally. The results were being used to compare with the untreated group of rats and normal group of rats. All the rats were fed with standard diet and water ad libitum. Mortality, behavior changes and tumour sizes were observed specifically. The differences between the three groups of rats were evaluated by using the ANOVA test. By using LCMS/MS method, six unknown compounds were analysed. K. alvarezii crude extract reduced the cell viability of MCF-7 from 84.91% to 0.81% and the IC50 value is 4.1±0.69mg/mL. For sub-chronic and heavy metal toxicity studies, no significant difference was found in haematological and biochemical values of the control group and experimental group. The growth rate of tumours in the untreated group of rats was found significantly higher than the experimental group of rats. Besides that, the white blood cells level in untreated group was found significantly higher than the experimental group and the normal group. In conclusion, K. alvarezii extract might able to slow down the growth rate of the tumour cells, therefore, identification of an active compound of inhibition growth rate of the tumour cells can be positively carried out in the future.



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Dimorphic placental stress: A repercussion of interaction between endocrine disrupting chemicals (EDCs) and fetal sex

Publication date: Available online 4 January 2017
Source:Medical Hypotheses
Author(s): Surbhi Sood, Sudhanshu Shekhar, Winkins Santosh
Placental homeostasis is critical for fetal development as it determines the health of mother and fetus during pregnancy and in later life. Interestingly even the fetus, in a sexually dimorphic manner, influences the pedantic growth and development of placenta. Although placenta is thought to act as a protective barrier against chemical exposures, certain endocrine disrupting chemicals (EDCs) that are circulating in mother's blood tend to cross placenta. These EDCs have been reported to cause changes in expression levels of certain genes, immunogenic factors and non-coding RNAs such as micro RNA (miRNA) and long non-coding RNA (lncRNA) leading to placental stress. We hypothesize that these changes in placenta occur in a sexually dimorphic manner as a result of interaction between EDC exposure and fetal sex. Therefore, we propose that the ability of placenta to respond and buffer EDC exposure depends on fetal sex and, hence the EDC associated disease susceptibility of one sex differs from the other.



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Breaking from tradition: establishing more realistic sediment quality guidelines

Abstract

Sediment quality guidelines vary wildly across nations. The approaches to derive these guidelines range from crude percentile rankings of total concentrations of single chemicals to theoretical approaches that are driven by biological available effect levels. This results in a range of orders of magnitude for "safe" or threshold levels by chemical. Even the more scientifically advanced approaches using theoretical approaches are problematic in that they do not consider chemical mixtures, alternate routes of exposure, and other ligands that limit bioavailability. In the end, all that matters is that desirable resident biota are protected and with no significant ecological impacts. Complicating this determination is the role of habitat, flow, sedimentation, and nutrients—all of which are common in human-dominated waterways. A possible effective way forward is to consider the common, relevant stressors that may influence biotic communities associated with sediments. This approach would consider relevant sensitive species in terms of their ecological context and dominant exposure pathway (considering habitat, overlying water, sediment, periphyton, and hyporheos). In addition, the sum of water column (and pore water) and sediment probable effect concentration vs probable no effect concentrations ratios would be summed and considered for mixtures. Since this non-scientific mixture effect assessment may be overly conservative, in situ caged toxicity tests with benthic and water column organisms exposed to sediments, pore waters, and overlying water would be conducted for field validations along with comparisons of indigenous biota to BioCriteria.

http://ift.tt/2hUoZ89

Trend of childhood blood lead levels in cities of China in recent 10 years

Abstract

The adverse effects of lead on human especially childhood have been well established. Largely due to the phase out of lead in gasoline, blood lead levels (BLLs) had declined substantially all over the world including China. In 2004, 2007, 2010, and 2013, we conducted a continuous project including 47,346 children aged 0–6 years old from 11 cities all over China to show how the decline happened and to explore what to do next to improve the BLLs of children of China. Our data shown the BLLs of Chinese children decreased from 46.38, 43.58, 38.95 to 37.17 μg/L, but the decline was not enough. These decline was mainly because of the number decrease of children with high BLLs. Integrated strategy should be used to promote the BLLs of Chinese children, like striving to improve the environment, setting new cutoff for high BLLs, and establishing routine blood lead screening.

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Catalytic reduction of 2-nitroaniline: a review

Abstract

2-nitroaniline (2-NA) is highly toxic and environmental contaminant. It is reduced to less toxic and environmental benign product o-phenylenediamine by using different reducing agents like sodium borohydride, potassium borohydride, or hydrazine hydrate in the presence of various catalytic systems. These catalytic systems have various advantages and drawbacks. Silica-supported gold nanoparticles are frequently reported catalyst for the reduction of 2-nitroaniline in aqueous medium. In this review article, different catalytic systems reported for reduction of o-nitroaniline under various reaction conditions have been discussed. The critical review of the recent research progress for development of novel catalysts used for the reduction of 2-nitroaniline has been provided here.

http://ift.tt/2hSq0dw

Racial/ethnic differences in electronic cigarette knowledge, social norms, and risk perceptions among current and former smokers

Publication date: April 2017
Source:Addictive Behaviors, Volume 67
Author(s): Monica Webb Hooper, Stephanie K. Kolar
Psychosocial factors that may affect electronic cigarette (e-cigarette) initiation or maintenance among racial/ethnic minorities are not well-understood. This study examined racial/ethnic differences in e-cigarette knowledge, risk perceptions, and social norms among current and former smokers. Individuals with a tobacco smoking history and an awareness of e-cigarettes (N=285) were recruited from the community from June to August 2014. Telephone-administered surveys assessed demographics, smoking status, and e-cigarette knowledge, risk perceptions, and normative beliefs. Analyses of covariance and multinomial logistic regression tested associations by race/ethnicity. Controlling for sociodemographics and smoking status, White participants scored significantly higher on e-cigarette knowledge, compared to both Hispanics and African Americans/Blacks. Knowledge was lower among African Americans/Blacks compared to Hispanics. Compared to both Whites and Hispanics, African American/Black participants held lower perceptions regarding e-cigarette health risks and were less likely to view e-cigarettes as addictive. Normative beliefs did not differ by race/ethnicity. In conclusion, e-cigarette knowledge, health risk perceptions, and perceived addictiveness differed by race/ethnicity. The variation in e-cigarette knowledge and beliefs among smokers and former smokers has implications for use, and potentially, dual use. Understanding these relationships in unrepresented populations can inform future research and practice.



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Assessment of pain in adolescents: Influence of gender, smoking status and tobacco abstinence

Publication date: April 2017
Source:Addictive Behaviors, Volume 67
Author(s): Kara S. Bagot, Ran Wu, Dana Cavallo, Suchitra Krishnan-Sarin
PurposeWe examined sex differences between smokers and nonsmokers in pain threshold, tolerance, and intensity and the effect of pain on cardiovascular measures, withdrawal, and craving during acute smoking abstinence.MethodsNinety-six (53 smokers, 43 nonsmokers) adolescents completed the Cold Pressor Task (CPT) to assess pain responses after minimal (1h) and 42-hour smoking deprivation. Vital signs and craving were assessed before and after CPT completion.ResultsSmokers, compared to nonsmokers, had significantly lower pain tolerance (p<0.01) and pain threshold (p<0.001). Female smokers had significantly lower pain tolerance prior to, and following, 42-hour deprivation compared to male smokers (p's<0.01), male nonsmokers (p's<0.01), and female nonsmokers (p's<0.001), while male smokers demonstrated significantly decreased pain tolerance following 42-hour deprivation (p<0.05). Additionally, during minimal deprivation, at time of hand removal, female smokers had higher pain intensity compared to female nonsmokers (p<0.05) and male smokers (p<0.01). Withdrawal was not significantly correlated with any CPT measures or subjective pain during or following minimal deprivation or acute abstinence. Craving was associated with pain 15s after hand submersion (p=0.007) at 42-hour deprivation.ConclusionsSmokers had a lower pain threshold than non-smokers, with female smokers demonstrating lower pain tolerance during minimal deprivation than all comparison groups, and, continuing to have diminished pain tolerance compared to female nonsmokers following 42h of abstinence. Male smokers demonstrated tobacco-deprivation-induced reductions in pain tolerance. Further study of pain-related factors that may contribute to relapse and maintenance of smoking behaviors, and mechanisms of these relationships among adolescent smokers is warranted.



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On the investigation of self-healing behavior of bitumen and its influencing factors

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): Quan Lv, Weidong Huang, Xingyi Zhu, Feipeng Xiao
Bitumen, which combines individual aggregate particles, is crucial in the self-healing of asphalt materials. However, the underlying mechanism and influencing factors of self-healing remain ambiguous. In this study, the effects of different factors were investigated using a multi-failure-healing cycle test based on the Binder Bond Strength (BBS) test. Then, Computed Tomography scan (CT-scan) test was performed to visually confirm the results of the BBS test. Results indicate that bond strength recovery displays various patterns over time under different conditions. What is unexpected is that the water exerts multiple effects on the healing potential of bitumen, although it negatively influences the healing capability of this material over time. In addition, the healing capability of bitumen continuously increases with healing temperature. The result of CT-scan test further confirms this phenomenon and indicates that healing temperature is more important than healing time. As for the aging process, it elicits different effects on the base bitumen and modified binder. Both the BBS test and CT-scan test show the negative effect of Styrene–Butadiene–Styrene (SBS) modifier on the healing potential of the base bitumen. Moreover, CT-scanned images reveal that three healing stages can be suggested to interpret the healing behavior: gathering, moving, and rounding.

Graphical abstract

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Design and modeling of auxetic and hybrid honeycomb structures for in-plane property enhancement

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): Aniket Ingrole, Ayou Hao, Richard Liang
Honeycomb structures have been used extensively in lightweight sandwich structure and impact energy absorption applications. Recently the research has been carried out on auxetic honeycombs that have negative Poisson's ratio (NPR). Auxetic structures are attractive for various engineering applications because of their unique mechanical properties, volume change control and excellent impact energy absorption performance. In this study, novel design and performance improvement of new auxetic-strut structures were presented. A comparative study of in-plane uniaxial compression loading behavior of regular honeycomb, re-entrant auxetic honeycomb, locally reinforced auxetic-strut structure and a hybrid structure of combining regular honeycomb and auxetic-strut structure was conducted on 3D printed samples. The deformation and failure modes of the different cells were studied and their performance was also discussed. The new auxetic-strut structure showed better mechanical properties than the honeycomb and auxetic structure. For example, the compressive strength of the auxetic-strut design is ~300% more than that of honeycomb structure and ~65% more than that of auxetic structure. With lower values of the Poisson's ratio, the new design can absorb more energy when compared to the other structures. Hybrid structure of auxetic-strut and honeycomb cells allows us tailor the deformation paths to provide desired failure modes.

Graphical abstract

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Multi-objective optimization of tungsten CMP slurry for advanced semiconductor manufacturing using a response surface methodology

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): Jihoon Seo, Joo Hyun Kim, Myoungjae Lee, Keungtae You, Jinok Moon, Dong-Hee Lee, Ungyu Paik
In this study, a response surface methodology (RSM) coupled with a face center cube design (FCD) was used to optimize the three principal components (i.e., Fe(NO3)3, H2O2, and SiO2 abrasives) in polishing slurries for a W barrier chemical mechanical planarization (CMP) process. The experimental ranges of the three components were 10–50ppm of Fe(NO3)3, 0.3–0.9wt% of H2O2, and 1–5wt% of SiO2 abrasives. Based on the experimental data from the FCD, the second-order models for the material removal rate (MRR) of the W and Oxide films were fitted; these were determined to be statistically valid and reliable. We have achieved the optimal conditions for the three components where the MRR is maximized and the selectivity between the W and Oxide MRRs is ~1. The predicted MRR and selectivity at the optimal conditions were well correlated with the results of a confirmation run, which was conducted by using the W barrier CMP process with W-patterned wafers. In addition, we employed a particular RSM called dual-response optimization in order to investigate the tradeoff between the MRR and selectivity. Based on the tradeoff information, process engineers can conduct the optimization of the three components more flexibly.

Graphical abstract

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Hybrid-fiber reinforced engineered cementitious composite under tensile and impact loading

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): M.A.E.M. Ali, A.M. Soliman, M.L. Nehdi
The behavior under impact loading of an innovative hybrid fiber-reinforced engineered cementitious composite incorporating short randomly dispersed shape memory alloy (HECC-SMAF) and PVA fibers was explored using a drop weight impact test. Test specimens were also heat-treated to investigate possible pre-stressing effects of SMA fibers on the impact resistance of the ECC. Uniaxial tensile testing on ECC coupon specimens was also conducted. A two-parameter Weibull distribution was used to analyze variations in experimental results in terms of reliability function. Results indicate that SMA fibers significantly enhanced the tensile and impact performance of the ECC. Adding fibers beyond a certain dosage led to fiber clustering, thus, no further gain in tensile and impact performance was measured. The impact resistance of HECC-SMAF specimens was further improved after exposure to heat treatment. This highlights the significant contribution imparted by the local pre-stressing effect of SMA fibers to the impact resistance of the composite. The Weibull distribution was adequate to predict the impact failure strength of ECC, allowing to avert additional costly experiments. This research underscores the potential to engineer new cementitious composites with superior tensile properties and impact resistance for the protection of critical infrastructure in the event of explosive or impact loading.

Graphical abstract

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Overall improvement in dielectric and mechanical properties of porous graphene fluoroxide/polyimide nanocomposite films via bubble-stretching approach

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): Zhigeng Chen, Shumei Liu, Shijing Yan, Xia Shu, Yanchao Yuan, Haohao Huang, Jianqing Zhao
Low dielectric constant is desired for polyimide to be used in microelectronic industry. In the present study, a series of porous graphene fluoroxide/polyimide (GFO/pPI) nanocomposite films with improved dielectric and mechanical properties were fabricated. Polyethylene glycol (PEG) was introduced into the system to play the roles of an intercalator in exfoliation of graphite fluoroxide and a blowing agent in preparation of porous structure. The in-situ bubble-stretching, resulting from PEG decomposition during the thermal imidization, not only hindered the agglomeration of GFO nanosheets, but also generated micro-pores in PI matrix. Both the porous structure and the GFO nanosheets significantly decreased the dielectric constant of composite films, and the load transfer between GFO and PI matrix efficiently improved the mechanical properties of composite films. A very low dielectric constant of 2.29 as well as high tensile modulus of 4.43GPa and tensile strength of 159MPa was obtained for the composite film with the GFO loading of only 0.30wt%. In addition, the glass transition temperature of GFO/pPI films was increased from 355°C to 388°C, and the coefficient of linear thermal expansion of GFO/pPI films was decreased from 48.7ppm/K to 24.9ppm/K.

Graphical abstract

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Numerical and physical simulation of rapid microstructural evolution of gas atomised Ni superalloy powders

Publication date: 5 March 2017
Source:Materials & Design, Volume 117
Author(s): Liang Zheng, T.L. Lee, Na Liu, Zhou Li, Guoqing Zhang, J. Mi, P.S. Grant
The rapid microstructural evolution of gas atomised Ni superalloy powder compacts over timescales of a few seconds was studied using a Gleeble 3500 thermomechanical simulator, finite element based numerical model and electron microscopy. The study found that the microstructural changes were governed by the characteristic temperatures of the alloy. At a temperature below the γ' solvus, the powders maintained dendritic structures. Above the γ' solvus temperature but in the solid-state, rapid grain spheroidisation and coarsening occurred, although the fine-scale microstructures were largely retained. Once the incipient melting temperature of the alloy was exceeded, microstructural change was rapid, and when the temperature was increased into the solid+liquid state, the powder compact partially melted and then re-solidified with no trace of the original structures, despite the fast timescales. The study reveals the relationship between short, severe thermal excursions and microstructural evolution in powder processed components, and gives guidance on the upper limit of temperature and time for powder-based processes if desirable fine-scale features of powders are to be preserved.

Graphical abstract

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