Microfluidic rectifier based on poly(dimethylsiloxane) membrane and its application to a micropump

A microfluidic rectifier incorporating an obstructed microchannel and a PDMS membrane is proposed. During forward flow, the membrane deflects in the upward direction; thereby allowing the fluid to pass over the obstacle. Conversely, during reverse flow, the membrane seals against the obstacle, thereby closing the channel and preventing flow. It is shown that the proposed device can operate over a wide pressure range by increasing or decreasing the membrane thickness as required. A microfluidic pump is realized by integrating the rectifier with a simple stepper motor mechanism. The experimental results show that the pump can achieve a vertical left height of more than 2 m. Moreover, it is shown that a maximum flow rate of 6.3 ml/min can be obtained given a membrane thickness of 200 μm and a motor velocity of 80 rpm. In other words, the proposed microfluidic rectifier not only provides an effective means of preventing reverse flow but also permits the realization of a highly efficient microfluidic pump.     

Disposable parallel poly(dimethylsiloxane) microbioreactor with integrated readout grid for germination screening of Aspergillus ochraceus

In this work a disposable, parallel microbioreactor (MBR) suitable for screening in batch or continuous mode is presented. The reactor consists of five parallel microchambers made of poly(dimethylsiloxane) bonded to a glass substrate. A grid structure is engraved on each chamber, allowing subsequent morphology imaging. Measurements are recorded over the entire cultivation period with constant parameters, namely, position and focus in the z-axis. The microdevice may be used for either parallel, uni- or multiparametric screening, and overcomes the drawback of gridless microwell plates which require expensive equipment such as an inverted microscope with an automatic stage. To validate the scalability from laboratory scale to microscale, and thus the cultivation protocol in the MBR, the germination of fungal spores (A. ochraceus) is evaluated for two different key magnitudes (pH and temperature) and compared to the results obtained from conventional laboratory scale systems (flasks and agar plates). Information on germination capacity with regard to interspecies' variability allows for optimization of industrial processes as optimal pH and temperature matched to the mesoscopic cultivation systems. The germination conditions therefore remain unaffected inside the MBR, while providing the following advantages: (i) dramatic reduction of medium consumption, (ii) submerged cultivation with constant oxygen supply, (iii) assured low cost and disposability, and (iv) possibility of a continuous cultivation mode.     

Screening ion-channel ligand interactions with passive pumping in a microfluidic bilayer lipid membrane chip

We describe a scalable artificial bilayer lipid membrane platform for rapid electrophysiological screening of ion channels and transporters. A passive pumping method is used to flow microliter volumes of ligand solution across a suspended bilayer within a microfluidic chip. Bilayers are stable at flow rates up to ∼0.5 μl/min. Phospholipid bilayers are formed across a photolithographically defined aperture made in a dry film resist within the microfluidic chip. Bilayers are stable for many days and the low shunt capacitance of the thin film support gives low-noise high-quality single ion channel recording. Dose-dependent transient blocking of α-hemolysin with β-cyclodextrin (β-CD) and polyethylene glycol is demonstrated and dose-dependent blocking studies of the KcsA potassium channel with tetraethylammonium show the potential for determining IC₅₀ values. The assays are fast (30 min for a complete IC₅₀ curve) and simple and require very small amounts of compounds (100 μg in 15 μl). The technology can be scaled so that multiple bilayers can be addressed, providing a screening platform for ion channels, transporters, and nanopores.     

Scaffold fabrication in a perfusion culture microchamber array chip by O(2) plasma bonding of poly(dimethylsiloxane) protected by a physical mask

Extracellular matrix (ECM) proteins are required for cell culture. In this paper, we report the use of O(2) plasma bonding to fabricate a perfusion culture microchamber array chip with identical-size ECM spots in the isolated microchambers. The chip was fabricated by assembly of two poly(dimethylsiloxane) (PDMS) layers, a microfluidic network layer, and an ECM array layer, which were aligned and then bonded by O(2) plasma oxidation with protection of the ECM microarray with a physical mask made from PDMS. We successfully cultivated Chinese hamster ovary K1 cells in the microchambers with fibronectin. In the fibronectin microchambers, the cells adhered and extended after 12 h of static culture and then grew over the course of 1 d of perfusion culture.     

Polyelectrolyte multilayer surface functionalization of poly(dimethylsiloxane) (PDMS) for reduction of yeast cell adhesion in microfluidic devices

Polyelectrolyte multilayers (PEMs) based on the combinations poly(diallyldimethylammonium chloride)∕poly(acrylic acid) (PDADMAC∕PAA) and poly(allylamine hydrochloride)∕PAA (PAH∕PAA) were adsorbed on poly(dimethylsiloxane) (PDMS) and tested for nonspecific surface attachment of hydrophobic yeast cells using a parallel plate flow chamber. A custom-made graft copolymer containing poly(ethylene glycol) (PEG) side chains (PAA-g-PEG) was additionally adsorbed on the PEMs as a terminal layer. A suitable PEM modification effectively decreased the adhesion strength of Saccharomyces cerevisiae DSM 2155 to the channel walls. However, a further decrease in initial cell attachment and adhesion strength was observed after adsorption of PAA-g-PEG copolymer onto PEMs from aqueous solution. The results demonstrate that a facile layer-by-layer surface functionalization from aqueous solutions can be successfully applied to reduce cell adhesion strength of S. cerevisiae by at least two orders of magnitude compared to bare PDMS. Therefore, this method is potentially suitable to promote planktonic growth inside capped PDMS-based microfluidic devices if the PEM deposition is completed by a dynamic flow-through process.     

Stable chemical bonding of porous membranes and poly(dimethylsiloxane) devices for long-term cell culture

We have investigated the bonding stability of various silane treatments for the integration of track-etched membranes with poly(dimethylsiloxane) (PDMS) microfluidic devices. We compare various treatments using trialkoxysilanes or dipodal silanes to determine the effect of the organofunctional group, cross-link density, reaction solvent, and catalyst on the bond stability. We find that devices made using existing silane methods delaminated after one day when immersed in cell culture medium at 37 °C. In contrast, the dipodal silane, bis[3-(trimethoxysilyl)propyl]amine, is shown to yield stable and functional integration of membranes with PDMS that is suitable for long-term cell culture. To demonstrate application of the technique, we fabricated an open-surface device in which cells cultured on a track-etched membrane can be stimulated at their basal side via embedded microfluidic channels. C2C12 mouse myoblasts were differentiated into myotubes over the course of two weeks on these devices to demonstrate biocompatibility. Finally, devices were imaged during the basal-side delivery of a fluorescent stain to validate the membrane operation and long-term stability of the bonding technique.     

DNA capture-probe based separation of double-stranded polymerase chain reaction amplification products in poly(dimethylsiloxane) microfluidic channels

Herein, we describe the development of a novel primer system that allows for the capture of double-stranded polymerase chain reaction (PCR) amplification products onto a microfluidic channel without any preliminary purification stages. We show that specially designed PCR primers consisting of the main primer sequence and an additional “tag sequence” linked through a poly(ethylene glycol) molecule can be used to generate ds-PCR amplification products tailed with ss-oligonucleotides of two forensically relevant genes (amelogenin and human c-fms (macrophage colony-stimulating factor) proto-oncogene for the CSF-1 receptor (CSF1PO). Furthermore, with a view to enriching and eluting the ds-PCR products of amplification on a capillary electrophoretic-based microfluidic device we describe the capture of the target ds-PCR products onto poly(dimethylsiloxane) microchannels modified with ss-oligonucleotide capture probes.     

Serum lipoprotein (a) and lipid profile in young South Indian patients with myocardial infarction

Coronary artery disease is now a major health problem in India. In past few decades the battle to reduce the incidence of coronary artery disease has led the researchers to look for various clinical markers, which would help early diagnosis of the diseases. The present study was undertaken to assess the level of lipoprotein (a) [Lp(a)] and few other lipids in selected myocardial infarction (MI) patients below 45 years without having any traditional risk factors but with positive family history. Fasting blood samples were taken from 65 patients and their total cholesterol, LDL cholesterol, VLDL cholesterol, HDL cholesterol, triglycerides and serum Lp(a) were determined. The control group consisted of 50 age matched healthy individuals. The mean Lp(a) level was 58.6±3.20 mg/dl in patients and 19.70±0.18 mg/dl in controls. Thus Lp(a) levels were found significantly higher in patients with MI (p<0.05 for patients versus control) as compared to the controls. There was no significant difference in the levels of total cholesterol (TC), LDL, VLDL HDL, TGL as compared to controls but there was an increase in TC/HDL cholesterol ratio. The results of this study suggest that high level of Lp(a) and TC/HDL ratio has a distinctive association with MI, independent of other common coronary risk factors. Hence, Lp(a) level in serum emerges to be a promising marker for diagnosis of coronary artery diseases.     

Consumer use of mobile banking (M-Banking) in Saudi Arabia: Towards an integrated model

Mobile banking is one of the most promising technologies that has emerged in recent years and could prove to have considerable value to both banks and customers. Thus, this study recognises the need to test the main factors that could predict the use of mobile banking as well as how using such a system could contribute to both customer satisfaction and customer loyalty. The conceptual model of this study combines two models (i.e. UTAUT2 and the D&M IS Success Model). A questionnaire survey was conducted to collect the required data from convenience sampling of Saudi bank customers. The main factors – performance expectancy, price value, facilitating conditions, hedonic motivation, habit, system quality and service quality – were found to have a significant impact on actual use behaviour. This study was cross-sectional, therefore future studies should implement longitudinal studies in order to re-collect the findings. Further, this study adopted convenience sampling of Saudi M-Banking users. This may adversely impact the issue of generalisability to the whole population. The gap in the M-Banking literature in Saudi Arabia would be bridged by proposing a comprehensive conceptual model that scrupulously clarifies the use of M-Banking from the perspective of Saudi users. Furthermore, this study would consider the adoption of numeric data in order to inferentially analyse them using SEM. This in turn would assist in generalising the findings to the whole Saudi population.     

连续运行卫星定位服务综合系统(CORS)在河湖基本情况普查中的应用

RTK GPS测量系统已经在测量行业得到广泛应用,但在大范围快速高精度定位上仍力不从心。本文介绍了基于多基站网络RTK技术建立的连续运行卫星定位服务综合系统(Continuous Operational Reference System,缩写为CORS)的基本原理及系统组成,探讨了CORS测量技术在河湖基本情况普查中的应用。     

Investigation of the heat transfer of a non-Newtonian fluid flow in an axisymmetric channel with porous wall using Parameterized Perturbation Method (PPM)

In the present article Parameterized Perturbation Method (PPM) is used to obtain the solutions of momentum and heat transfer equations of non-Newtonian fluid flow in an axisymmetric channel with porous wall for turbine cooling applications. The validity of the results of PPM solution were verified by comparison with numerical results obtained using a fourth order Runge–Kutta method. These comparisons reveal that Parameterized Perturbation Method is a powerful approach for solving this problem. The analytical investigation is carried out for different governing parameters namely, Reynolds number, injection Reynolds number, Prandtl number and power law index. The results show that skin friction coefficient increases with increase of Reynolds number, especially at high Reynolds numbers. Also it can be found that Nusselt number has direct relationship with Reynolds number, Prandtl number and power law index.     

Effects of feeding Pyrus malus (Apple) on serum lipid profile with special reference to high and low density lipoprotein cholesterol levels in normal albino rabbits

The effects of regular feeding ofPyrus malus whole fruit and its juice on total serum cholesterol, HDL cholesterol, LDL cholesterol, triglycerides and phospholipids have been studied in normal albino rabbits. It was observed that the whole fruit as well as juice caused significant and progressive decrease in total serum cholesterol, LDL cholesterol and triglycerides within a period of 30 days. On the other hand, serum phospholipids and HDL cholesterol showed progressive and significant increase. Apparently, whole fruit appeared to bring about more per cent lowering in total cholesterol, LDL cholesterol and more increase in HDL cholesterol as compared to juice. Whole apple fruit also caused increase in body weight of rabbits on 30th day (p<0.05) while oral administration of juice showed insignificant change in body weight even on 30th day (p>0.05).     

Detection of Bone Metastases in Breast Cancer (BC) Patients by Serum Tartrate-Resistant Acid Phosphatase 5b (TRACP 5b), a Bone Resorption Marker and Serum Alkaline Phosphatase (ALP), a Bone Formation Marker,in Lieu of Whole Body Skeletal Scintigraphy with Technetium99m MDP

Bone metastases are a serious problem in patients with advanced cancer disease and their presence usually signifies serious morbidity prior to the patient’s death. In breast cancer patients the incidence of bone metastasis is observed to be very high at 70 %, as seen during post-mortem examination. Bone metastasis is difficult to diagnose, treat or follow clinically without radiological tools. This study was designed to evaluate the utility of a novel bone resorption marker–serum tartrate-resistant acid phosphatase 5b (TRACP5b) and the bone formation marker such as serum total alkaline phosphatase (ALP), in comparison with whole body skeletal scintigraphy with Technetium99m MDP for the diagnosis of bone metastases (BM) in breast cancer (BC) patients. This study is intended to help the clinician to diagnose bone metastasis without resorting to radiological tools, as they are not cost effective and carry the risk of radiation. Experimental design: Four groups of samples were analysed. 1st group consists 52 normal female (cancer free women), 2nd group consists 38 BC patients without bone metastasis, 3rd group consists 27 breast cancer patients with limited bone metastasis (3 or less than 3 skeletal lesions) and 4th group consists 35 breast cancer patients with extensive bone metastasis (4 or more than 4 skeletal lesions), conformed by whole body skeletal scintigraphy with Technetium99m MDP. One way ANOVA was used to compare serum TRACP5b and serum ALP among these groups. Both serum TRACP5b and serum ALP are not markedly elevated in limited bone metastasis but are strongly elevated in extensive bone metastasis (p < 0.0001). As seen in this study the biochemical bone resorption marker, serum TRACP5b, abnormally increased in extensive bone metastasis of breast cancer patients and can be used as a specific marker for bone metastasis in lieu of radiological tools.     

Serum Lp(a) in diabetics with and without evidence of clinical nephropathy—A preliminary study

Type 2 diabetes is associated with a marked increase in the risk of coronary artery disease. Dyslipidaemia is believed to be a major cause of this increased risk. Recently, elevated levels of lipoprotein (a), Lp(a), have been reported to be associated with an increased risk. However there is very little data regarding Lp(a) concentrations and type 2 diabetes from India. The objective of the study was to assess serum Lp(a) levels in type 2 diabetics with and with out evidence of clinical nephropathy. We estimated serum Lp(a) levels in 30 control subjects, 30 diabetics without evidence of clinical nephropathy and 30 diabetics with evidence of clinical nephropathy. Statistical analysis showed that Lp(a) levels were increased in diabetic patients with nephropathy (mean 46.3±17.6 mg/dl). The Lp(a) levels however did not differ significantly between control (mean 20.2±15.9 mg/dl) and diabetics without nephropathy (mean 22.6±13.1mg/dl). Thus diabetes per se seems to have little or no influence on serum Lp(a) levels, however elevated levels were seen in patients with nephropathy.     

Lipid abnormalities,lipoprotein (a) and apoprotein pattern in non-dialyzed patients with chronic kidney disease

The present study was carried out to explore the altered lipid, lipoprotein and apoprotein abnormalities along with lipoprotein (a) in chronic kidney disease patients with stage I to V which were further divided into group 1 (stage I and II), group 2 (stage III and IV) and group 3 (stage V). 50 chronic kidney disease patients with stage I to V and 20 healthy normal subjects as controls were recruited for this study. Among the various parameters tested triglyceride levels were high in group 1 and 2, whereas VLDL cholesterol, Lp (a) and apo B levels were significantly high in all the groups when compared to controls (P<0.05). However, LDL cholesterol level was significantly low in group 3 only as compared to control group (P<0.05). Apoprotein AI values also showed significant decrease in all groups as compared to controls (P<0.05). Though total cholesterol levels in group 1 and LDL levels in group 1 and 2 were higher than controls, but the values attained not statistically significant (P>0.05). In conclusion high levels of VLDL cholesterol, Lp (a), apo B and low levels of apoprotein AI as reported in this study are the major lipid disorders in the development of cardiovascular complications at all the stages in these patients.     

谐振磁场中自旋系统的演化和几何相因子

量子不变量理论是研究几何相因子问题的有效方法。利用Ｌｅｗｉｓ－Ｒｉｅｓｅｎｆｅｌｄ不变量理论研究了谐振磁场中的自旋系统,给出了两种不同循环演化周期的精确解,并进而分别计算了此系统两种不同的几何相因子。研究表明,不同循环演化周期的几何相因子与初始态的选择有关。     

Hesperetin on Cell Surface Glycoconjugates Abnormalities and Immunohistochemical Staining with Cytokeratin in 7,12 Dimethylbenz(a)anthracene Induced Hamster Buccal Pouch Carcinogenesis

Hesperetin, a naturally occurring citrus flavanone of the bioactive substance, possesses different pharmacological and biochemical activities including anti-cancer and anti-oxidants effect. The aim of the study to investigate that hesperetin on abnormalities of glycoconjugates (protein bound hexose, hexosamine, total sialic acid and fucose), histology (PAS staining) and immunoexpression of cytokeratin during 7,12-dimethylbenz(a)anthracene (DMBA) induced hamster buccal pouch (HBP) carcinogenesis. Oral tumors were developed in the buccal pouches of male golden Syrian hamsters by topical application of 0.5% DMBA thrice a week for 10 weeks and developed morphological alterations depicted as hyperplasia, dysplasia and well-differentiated squamous cell carcinoma formation with noticeable abnormalities of glycoconjugates and cytokeratin. The protective effect of hesperetin against DMBA was evaluated by assessing immunohistochemical expression, histological sections of buccal tissues and the levels of glycoconjugates in the buccal mucosa and plasma were analyzed. Hesperetin administrated orally at a dose of 20 mg/kg b.w. to hamsters treated with DMBA, significantly reduced the status of glycoconjugates and cytokeratin to the near normal range. Overall findings accomplished that hesperetin protects cell surface glycoconjugates abnormalities in DMBA induced HBP carcinogenesis.