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Effect of l-Arginine on Nitric Oxide Levels in Intrauterine Growth Restriction and its Correlation with Fetal Outcome

Shalini Singh Archana Singh Deepika Sharma Abha Singh M. K. Narula Jayashree Bhattacharjee 《Indian journal of clinical biochemistry : IJCB》2015,30(3):298-304

The current management of intrauterine growth restriction (IUGR) being empirical and aimed at selecting a safe time for delivery. Acknowledging the beneficial effects of l-arginine on endothelial vasculature the present study was designed to evaluate efficacy of l-arginine on bioavailability of nitric oxide (NO) with respect to fetal outcome. With l-arginine supplementation, mean NO levels were significantly increased and a significant mild reduction in systolic/end-diastolic velocity ratio (S/D ratio) was observed on doppler blood flow study, also neonatal outcome improved and incidences of complications were lowered. A deficiency in NO may play an important role in the causation of asymmetric fetal growth restriction. l-Arginine can be used to increase maternal NO levels, enhancing birth weight and decreasing neonatal morbidity. The ideal candidate for arginine therapy according to our study would be IUGR cases with S/D ratio less than 4.96 ± 0.49 and NO levels below 33 μmol/L with minimum of 3 weeks duration of arginine supplementation. 相似文献

Determination of Biological Variance and Validation of a Fluorometric Assay for Measurement of α-l-Iduronidase Activity in Dried Blood Spots Samples: The First Experience in Iran

Mohammad Abdi Mohammad Said Hakhamaneshi Mohammad Reza Alaei Namam-Ali Azadi Rahim Vakili Daniel Zamanfar Mohammad Taghikhani Shohreh Khatami 《Indian journal of clinical biochemistry : IJCB》2015,30(3):318-322

Methods for assaying lysosomal diseases in dried blood samples are very useful today due to its several advantages related to the stability of samples, its transportation, handled and analysis, and its potential use for newborn screening compared to traditional methods in leucocytes samples. For this reason, it is important to validate these assays before being used in routine laboratory. Because of different in biological markers based on ethnicity, we aimed this study to validation a DBS-based fluorometric assay for measurement of α-l-Iduronidase activity for diagnosis of MPS I patients in Iran. DBS samples were collected from 15 MPS I patients and 60 healthy age matched subjects. Diagnostic value, biological variance and α-l-Iduronidase activity were determined. DBS α-l-Iduronidase activity was significantly higher in male subjects than in female group. Using a cut-off level of 1.08 µmol/spot 20 h, sensitivity and specificity were 100 and 98 %. The linearity of test was proved and we showed that within-run and between run precision were 5.6 and 14.66 %. Measurement of α-l-Iduronidase activity in DBS samples is an accurate test for diagnosis of MPS I and because of its rapid shipping and simplicity to keeping, DBS-based enzyme activity could be considered as a useful diagnostic tool in this disease. 相似文献

Administering the Optimum Dose of l-Arginine in Regional Tumor Therapy

Emad Y. Moawad 《Indian journal of clinical biochemistry : IJCB》2014,29(4):442-451

The purpose of this study is optimizing the l-arginine (l-Arg) doses on the basis of chemical structure in regional accessible tumor therapy to settle down a new protocol for the treatment of cancer. ³H-thymidine-based cell proliferation assay was performed in vitro on tumor cell lines of fibrosarcoma (FS), lymphosarcoma-ascitic and on normal cell line of NIH 3T3 after treatment with different concentrations of l-Arg in phosphate buffered saline (PBS). The cultures were harvested after 22 h and the incorporated radioactivity was counted to identify their histologic grades as described in earlier studies. In vivo therapy of murine tumors was conducted where FS cells injected subcutaneously at ventro-lateral position of mice. Various drug delivery schedules were injected into the centre of tumor base, once a day for 4 days. Tumor diameter and survivals were monitored where the day of sacrifice was considered for monitoring the survival period. By identifying the histologic grades of the treated cultures in vitro and in vivo by different concentrations of l-Arg, the corresponding energy of such concentrations were determined. An efficient model with a good fit (R² = 0.98) was established to describe the energy yield by l-Arg dose. The equivalence between the tumor histologic grade and energy of the l-Arg dose delivered in saline (PBS) environment is the optimum condition for regional tumor therapy achieves higher survival rate. The selective cytotoxicity to tumor cells with minimal damage to normal cells by l-Arg due to its chemical structure suggests to be considered the most promising drug for regional therapy of the accessible tumors like breast cancers of early stage with no distant metastasis. 相似文献

The thermal conductivity of the Earth's core and implications for its thermal and compositional evolution

Kenji Ohta Kei Hirose 《国家科学评论(英文版)》2021,8(4)

Determining the thermal conductivity of iron alloys at high pressures and temperatures are essential for understanding the thermal history and dynamics of the Earth''s metallic cores. The authors summarize relevant high-pressure experiments using a diamond-anvil cell and discuss implications of high core conductivity for its thermal and compositional evolution.

The thermal conductivity of iron alloys is a key to understanding the mechanism of convection in the Earth''s liquid core and its thermal history. The Earth''s magnetic field is formed by a dynamo action that requires convection in the liquid core. Present-day outer core convection can be driven by the buoyancy of light-element-enriched liquid that is released upon inner core solidification in addition to thermal buoyancy associated with secular cooling. In contrast, before the birth of the inner core, the core heat loss must be more than the heat conducted down the isentropic gradient in order to drive convection by thermal buoyancy alone, which can be a tight constraint upon the core thermal evolution.Recent mineral physics studies throw the traditional value of the Earth''s core thermal conductivity into doubt (Fig. (Fig.1).1). Conventionally the thermal conductivity of the outer core had been considered to be ∼30 W m⁻¹ K⁻¹, an estimate based on shock experiments and simple physical models including the Wiedemann-Franz law: κ_el = LTρ⁻¹, where κ_el, L, T and ρ are electronic thermal conductivity, Lorenz number, temperature and electrical resistivity, respectively [1]. Such relatively low core conductivity indicates that liquid core convection could have been driven thermally even with relatively slow cooling rate. However, in 2012–2013, our conventional view was challenged by both computational and experimental studies showing much higher core conductivity [2–4].Open in a separate window Figure 1.(a) Electrical resistivity and (b) thermal conductivity values at the top of the Earth''s core in the literature [1,2,4–7,9,16]. Filled symbols were calculated on the basis of the Wiedemann-Franz law with ideal Lorenz number (L₀ = 2.44 × 10⁻⁸ W Ω K⁻²). Gray bands indicate (a) the range of saturation resistivity [9] and (b) thermal conductivity computed from the saturation resistivity and the Wiedemann-Franz law.Since then, experimental determinations of the thermal conductivity of iron and alloys have been controversial (Fig. (Fig.1).1). Ohta et al. [5] measured the electrical resistivity of iron under core conditions in a laser-heated diamond-anvil cell (DAC). The results demonstrate relatively high thermal conductivity of ∼90 W m⁻¹ K⁻¹ for liquid Fe-Ni-Si alloy based on their measured resistivity for pure iron, Matthissen''s rule and Wiedemann-Franz law, which is compatible with ab initio simulations [2,4]. On the other hand, flash laser-heating and fast thermal radiation detection experiments demonstrated the low core conductivity of 20–35 W m⁻¹ K⁻¹ based on finite element method simulations [6,7], in accordance with the traditional estimate [1]. Since transport properties that describe non-equilibrium phenomena are difficult to measure, the fact that determinations of the iron conductivity under core conditions have become viable these days is a remarkable success in mineral physics. Nevertheless, the discrepancy in core conductivity makes a big difference in the expected age of the inner core, mechanism of liquid core convection and thermal history [3].Despite a number of subsequent studies based on a variety of different techniques, we still see a dichotomy of proposed core conductivity values (Fig. (Fig.1).1). The ‘saturation’ resistivity, which is derived from the fact that the mean free path of electron–phonon interaction cannot be longer than the interatomic distance, gives the lower bound for conductivity. Such saturation resistivity lies between two clusters of reported high and low resistivity values. While the resistivity saturation is important in highly resistive transition metals and their alloys [3,8] (Fig. (Fig.2),2), the conventional estimate [1] did not include the effect of saturation in their models, which resulted in much higher resistivity than the saturation value and hence low core conductivity. The core electrical resistivity measured by recent DAC experiments [3,5,9] shows resistivity saturation (Fig. (Fig.2),2), demonstrating the high core conductivity as far as the Wiedemann-Franz law holds with ideal Lorenz number (Fig. (Fig.1).1). Additionally, since temperature has a large effect on resistivity, temperature gradient in a laser-heated sample is an issue. An internally-resistance-heated DAC provides homogenous and stable sample heating and is thus a promising technique for conductivity measurements at high pressure and temperature (P–T) [9]. The validity of the Wiedemann-Franz law under extreme conditions has also been an issue. Simultaneous measurements of the electrical resistivity and the thermal conductivity of iron alloy under core high P–T conditions will provide decisive evidence for it.Open in a separate window Figure 2.Temperature response of the electrical resistivity of (a) fcc iron estimated at 1 bar [8] (blue curve) and (b) hcp iron at 115 GPa [5]. Red curve and black line with gray uncertainty band indicate the predicted resistivity based on the Bloch-Grüneisen model with and without the resistivity saturation, respectively.As introduced above, the most recent high P–T measurements for Fe containing 2, 4, 6.5 wt.% Si using an internally-resistance-heated DAC have demonstrated that the thermal conductivity of Fe-12.7 wt.% (22.5 at.%) Si is ∼88 W m⁻¹ K⁻¹ at core-mantle boundary (CMB) conditions when the effects of resistivity saturation, melting and crystallographic anisotropy at measurements are taken into account [9] (Fig. (Fig.1).1). Thermal conductivity of Fe-10 at.% Ni-22.5 at.% Si alloy, a possible outer core composition, could be ∼79 W m⁻¹ K⁻¹ considering the impurity effect of Ni [10]. Si exhibits the largest ‘impurity resistivity’, indicating that the 79 W m⁻¹ K⁻¹ is the lower bound for the thermal conductivity of the Earth''s liquid core. The core thermal evolution models by Labrosse [11] demonstrated that if liquid core convection has been driven by thermal buoyancy with the core thermal conductivity of 79 W m⁻¹ K⁻¹ at the CMB and no radiogenic heating in the core, the CMB temperature is calculated to be ∼5500 K at 3.2 Ga and ∼4800 K at 2.0 Ga. Such high CMB temperature suggests that the whole mantle was fully molten until 2.0–3.2 Ga. It is not consistent with geological records, calling for a different mechanism of core convection.Chemical buoyancy may be an alternate means of driving convection in the core from the early history of the Earth. It has been proposed that the compositional buoyancy in the core could arise from the exsolution of MgO, SiO₂ or both [12–14]. Recent core formation models based on the core-mantle distributions of siderophile elements suggest that core metals segregated from silicate at high temperatures, typically at 3000–4000 K and possibly higher [13,15], which enhances the incorporation of lithophile elements including Si and O, and possibly Mg into metals. It is suggested that the (Si, O)-rich liquid core may have become saturated with SiO₂ upon secular cooling [14]. Indeed, the original core compositions proposed in recent core formation models include Si and O beyond the saturation limit at CMB conditions [15], i.e. 136 GPa and 4000 K, leading to SiO₂ crystallization [13]. The rate of SiO₂ crystallization required to sustain geodynamo is as low as 1 wt.% per 10⁹ years, which corresponds to a cooling rate of 100–200 K Gyr⁻¹ [14]. The most recent model of the core compositional evolution by Helffrich et al. [13] showed that MgO saturation follows SiO₂ saturation only when >1.7 wt.% Mg in the core. If this is the case, in addition to solid SiO₂, (Mg, Fe)-silicate melts exsolve from the core and transfer core-hosted elements such as Mo, W and Pt to the mantle. The core-derived silicate melts may have evolved toward FeO-rich compositions and now represent the ultra-low velocity zones above the CMB. 相似文献

Microfluidic sterilization

Rui Zhang Jie Huang Fei Xie Baojun Wang Ming Chu Yuedan Wang Haichao Li Wei Wang Haixia Zhang Wengang Wu Zhihong Li 《Biomicrofluidics》2014,8(3)

Nowadays, microfluidics is attracting more and more attentions in the biological society and has provided powerful solutions for various applications. This paper reported a microfluidic strategy for aqueous sample sterilization. A well-designed small microchannel with a high hydrodynamic resistance was used to function as an in-chip pressure regulator. The pressure in the upstream microchannel was thereby elevated which made it possible to maintain a boiling-free high temperature environment for aqueous sample sterilization. A 120 °C temperature along with a pressure of 400 kPa was successfully achieved inside the chip to sterilize aqueous samples with E. coli and Staphylococcus aureus inside. This technique will find wide applications in portable cell culturing, microsurgery in wild fields, and other related micro total analysis systems.Microfluidics, which confines fluid flow at microscale, attracts more and more attentions in the biological society.^1–4 By scaling the flow domain down to microliter level, microfluidics shows attractive merits of low sample consumption, precise biological objective manipulation, and fast momentum/energy transportation. For example, various cell operations, such as culturing^5–7 and sorting,^8–10 have already been demonstrated with microfluidic approaches. In most biological applications, sterilization is a key sample pre-treatment step to avoid contamination. However, as far as the author knew, this important pre-treatment operation is generally achieved in an off-chip way, by using high temperature and high pressure autoclave. Actually, microfluidics has already been utilized to develop new solution for high pressure/temperature reactions. The required high pressure/temperature condition was generated either by combining off-chip back pressure regulator and hot-oil bath,^11,12 or by integrating pressure regulator, heater, and temperature sensor into a single chip.¹³ This work presented a microfluidic sterilization strategy by implementing the previously developed continuous flowing high pressure/temperature microfluidic reactor.Figure Figure11 shows the working principle of the present microfluidic sterilization chip. The chip consists of three zones: sample loading (a microchannel with length of 270 mm and width of 40 μm), sterilization (length of 216 mm and width of 100 μm), and pressure regulating (length of 42 mm and width of 5 μm). Three functional zones were separated by two thermal isolation trenches. The sample was injected into the chip by a syringe pump and experienced two-step filtrations (feature sizes of 20 μm and 5 μm, not shown in Figure Figure1)1) at the entrance to avoid the channel clog. All channels had the same depth of 40 μm. According to the Hagen–Poiseuille relationship,¹⁵ the pressure regulating channel had a large flow resistance (around 1.09 × 10¹⁷ Pa·s/m³, see supplementary S1 for details¹⁶) because of its small width, thereby generated a high working pressure in the upstream sterilization channel under a given flow rate. The boiling point of the solution will then be raised up by the elevated pressure in the sterilization zone followed by the Antoine equation.¹⁶ By integrating heater/temperature sensors in the pressurized zone, a high temperature environment with temperature higher than 100 °C can thereby be realized for aqueous sample sterilization. The sample was collected from the outlet and cultured at 37 °C for 12 h. Bacterial colony was counted to evaluate the sterilization performance.Open in a separate window FIG. 1.Working principle of the present microfluidic sterilization. Only microfluidic channel, heater, and temperature sensor were schematically shown. The varied colour of the microchannel represents the pressure and that of the halation stands for the temperature.Fabrication of this chip has been introduced elsewhere.¹⁴ The fabricated chip and the experimental system are shown in Figure Figure2.2. There were two inlets of the chip. While, in the experiment, only one inlet used and connected to the syringe pump. The backup one was blocked manually. The sample load zone was arranged in between of the sterilization zone and the pressure regulating zone based on thermal management consideration. A temperature control system (heater/temperature sensor, power source, and multi-meter) was setup to provide the required high temperature. The heater and the temperature sensor were microfabricated Pt resistors. The temperature coefficient of resistance (TCR) was measured as 0.00152 K⁻¹.Open in a separate window FIG. 2.The fabricated chip and the experimental system. (a) Two chips with a penny for comparison. The left chip was viewed from the heater/temperature sensor side, while the right one was observed from the microchannel side (through a glass substrate). (b) The experimental system.Thermal isolation performance of the present chip before packaging with inlet/outlet was shown in Figure Figure3,3, to show the thermal interference issue. The results indicated that when the sterilization zone was heated up to 140 °C, the pressure regulating zone was about 40 °C. At this temperature, the viscosity of water decreases to 0.653 mPa·s from 1.00 mPa·s (at 20 °C), which will make the pressure in the sterilization zone reduced from 539 kPa (calculated at 20 °C and flow rate of 4 nl/s) to 387 kPa. The boiling point will then decrease to 142.8 °C, which will guarantee a boiling-free sterilization. In the cases without the thermal isolation trenches, the temperature of the pressure regulating zone reached as high as 75 °C because of the thermal interference from the sterilization zone, as shown in Figure Figure3.3. The pressure in the sterilization zone was then reduced to 268 kPa (calculated at flow rate of 4 nl/s) and the boiling temperature was around 130 °C, which was lower than the set sterilization temperature. Detail calculation can be found in supplementary S2.¹⁶ Open in a separate window FIG. 3.The temperature distribution of the chips (before packaged) with and without thermal isolation trenches (powered at 1 W). The data were extracted from the central lines of infrared images, as shown as inserts.Bacterial sterilization performance of the present chip was tested and the experimental results were shown in Figure Figure4.4. E. coli with initial concentration of 10⁶/ml was pumped into and flew through the chip with the sterilization temperatures varied from 25 °C to 120 °C at flow rates of 2 nl/s and 4 nl/s. The outflow was collected and inoculated onto the SS agar plate evenly with inoculation loops. The population of bacteria in the outflow was counted based on the bacterial colonies after incubation at 37 °C for 12 h. Typical bacterial colonies were shown in Figure Figure4.4. The low flow rate case showed a better sterilization performance because of the longer staying period in the sterilization channel. The population of E. coli was around 1.25 × 10⁴/ml after a 432 s-long, 70 °C sterilization (at flow rate of 2 nl/s). While at the flow rate of 4 nl/s, the cultivation result indicated the population was around 3.8 × 10⁴/ml because the sterilization time was shorten to 216 s. A control case, where the solution flew through an un-heated chip at 2 nl/s, was conducted to investigate the effect of the shear stress on the sterilization performance (see the supplementary S3 for details¹⁶). As listed in Table TableI,I, the results indicated that the shear stress did not show any noticeable effect on the bacterial sterilization. When the chip was not heated, i.e., the case with the largest shear stress because of the highest viscosity of fluid, the bacterial cultivation was nearly the same as the off-chip results (no stress). The temperature has the most significant effect on the sterilization performance. No noticeable bacteria proliferation was observed in the cases with the sterilization temperature higher than 100 °C, as shown in Figure Figure44.

Table I.

The E. coli cultivation results under different flow rates and sterilization temperatures. ^a

	25 °C	70 °C	100 °C	120 °C	25 °C ^b
2 nl/s	1.89/+++	1.38/+	1.16/−	1.04/−	0/+++
4 nl/s	3.78/+++	2.76/+	2.32/−	2.08/−	0/+++

Open in a separate window^aData in the table are shear stress (Pa)/population of bacteria, where “+++” indicates a large proliferation, “+” means small but noticeable proliferation, “−” represents no proliferation.^bOff-chip control group.Open in a separate window FIG. 4.Sterilization performance of the present chip with E. coli and S. aureus as test bacteria. All the original population was 10⁶/ml. Inserted images showed the images of the culture disk after bacteria incubation.Sterilization of another commonly encountered bacterium, Staphylococcus aureus, with initial population of 10⁶/ml was also tested in the present chip, as shown in Figure Figure4.4. Similarly, no noticeable S. aureus proliferation was found when the sterilization temperature was higher than 100 °C.In short, we demonstrated a microfluidic sterilization strategy by utilizing a continuous flowing high temperature/pressure chip. The population of E. coli or S. aureus was reduced from 10⁶/ml to an undetectable level when the sterilization temperature of the chip was higher than 100 °C. The chip holds promising potential in developing portable microsystem for biological/clinical applications. 相似文献

Black silicon as a platform for bacterial detection

Jennifer S. Hartley M. Myintzu Hlaing Gediminas Seniutinas Saulius Juodkazis Paul R. Stoddart 《Biomicrofluidics》2015,9(6)

Surface-enhanced Raman scattering (SERS) shows promise for identifying single bacteria, but the short range nature of the effect makes it most sensitive to the cell membrane, which provides limited information for species-level identification. Here, we show that a substrate based on black silicon can be used to impale bacteria on nanoscale SERS-active spikes, thereby producing spectra that convey information about the internal composition of the bacterial capsule. This approach holds great potential for the development of microfluidic devices for the removal and identification of single bacteria in important clinical diagnostics and environmental monitoring applications.Plasma etching of silicon can be used to produce inexpensive, large surface area, nano-textured surfaces known as black silicon. Recently, it has been shown that black silicon nano-needles can impale bacteria¹ and that it can be used as a sensor in microfluidic devices.² When coated by a plasmonic metal, such as gold, the nano-textured surface of black silicon is ideal for use as a surface-enhanced Raman scattering (SERS) sensing platform.³ This work aims to investigate whether gold-coated black silicon nano-needles can be used to both impale bacteria and identify them by SERS. This combination of properties would promote the development of microfluidic devices for the removal and monitoring of bacteria in a wide range of medical, environmental, and industrial applications.⁴Black silicon was fabricated by a reactive ion etching technique,⁵ resulting in pyramidal-shaped spikes of height 185 ± 30 nm, full width at half height of 54 ± 10 nm, and 10 ± 2.4 nm radius of curvature at the tip. Samples were then magnetron sputter coated with 200 nm of gold, as this coating thickness was found to provide a suitable compromise between SERS enhancement and impalement efficiency. E. coli (ATCC 25922) from −80 °C stock was isolated on a nutrient agar plate (Difco nutrient broth, Becton Dickinson) for approximately 12 h. A single E. coli colony was then inoculated from the plate into 20 ml of nutrient broth media and incubated overnight at 37 °C with orbital shaking at 200 rpm. The total biomass of overnight culture was adjusted to an optical density of 0.3 at λ = 600 nm by adding fresh sterile nutrient broth (Cary 50 spectrophotometer, Agilent). The E. coli planktonic cells were washed three times by centrifugation at 12 000 rpm (Centrifuge 5804 R, Eppendorf) for 2 min. The washed cells were then re-suspended in a low strength minimum medium (Dulbecco A, phosphate buffered saline). A volume of 100 μl of solution was pipetted onto substrates and left to incubate for 1 h on the bench. Separate sets of samples were created for scanning electron microscope (SEM) imaging, live/dead staining, and SERS. Three sets were needed as each of these measurements altered the samples and left them unsuitable for further analysis.The first set of samples was washed three times with milliQ water after incubation, allowed to dry and then immediately sputter coated with gold using the Emitech K975x (operating current 35 mA, sputter time 32 s, stage rotation 138 rpm, and vacuum of 1 × 10⁻² mbar). SEM imaging was performed with a Zeiss Supra 40VP in high vacuum mode with a working distance of 5 mm and an accelerating voltage of 3 kV. Figure Figure11 shows an example of the different levels of impalement that occurred on the black silicon surface. All cells showed signs of damage, but in some cases, the damage was limited to the perimeter of the cell and the main body appeared whole. In other cases, the entire cell had collapsed onto the spikes.Open in a separate window FIG. 1.A typical SEM image showing E. coli cells with different levels of impalement on gold-coated black silicon.The second set of samples was used for live/dead staining (Invitrogen BacLight Bacterial Viability Kit L7012) with 3.34 mM SYTO 9 (green fluorescence) and 20 mM propidium iodide (red fluorescence). Equal volumes of both dyes were mixed thoroughly in a tube and added to the sample in a ratio of 3 μl of mixed dye to 1 ml of bacterial suspension. After mixing, a volume of 100 μl of the solution was pipetted onto the substrates, which were then incubated at room temperature in the dark for 15 min, before the staining solution was removed by pipetting. The substrates were then washed three times with milliQ water and mounted on a microscope slide for fluorescence imaging. The substrates were not allowed to dry and were stored in phosphate buffered saline at 4 °C when not in use. An epifluorescence microscope (Olympus IX71) with a mercury lamp source and a 60× water immersion objective was used to collect live/dead images from the substrates. Two filter blocks were used to collect the images: U-MNIBA2 blue excitation narrow band delivered green emission (live) and U-MWIG2 green excitation wide band provided red emission (dead).The live/dead image in Figure Figure22 shows a mix of both live and dead cells on the black silicon sample. The prevalence of live cells could be due to the incomplete impalement seen under SEM for some cells. It can also be explained by the sample still being wet during live/dead staining. The cells are dried prior to imaging in the SEM and this could weaken the cell wall and allow capillary forces to draw the cells onto the spikes for impalement. This hypothesis is supported by the large number of cells on the stained sample and the presence of cell groupings and cells imaged during mid-division. If the cells were immediately impaled, then such activity would not have been visible and a greater proportion of red cells would be expected.Open in a separate window FIG. 2.Epifluorescence image showing live (green) and dead (red) E. coli cells after incubation on gold-coated black silicon.The third set of samples was washed three times with milliQ water after incubation and allowed to dry prior to spectral analysis. SERS spectra were collected with a Renishaw inVia Raman spectrometer operating at 785 nm with a 1200 l/mm grating. Power at the sample was 150 mW focused with a 100 × /0.85 NA objective to obtain a diffraction limited laser spot. The resulting spot size (≤2 μm in diameter) is well matched to the size of the bacterial cells. Spectra were collected with three accumulations of 10 s. Data were background subtracted⁶ and normalised to unity for ease of plotting. A great deal of variability was observed in the resulting spectra, as shown in Figure Figure33.Open in a separate window FIG. 3.SERS spectra of E. coli after incubation on a gold-coated black silicon substrate. The spectrum numbers represent single cells at different locations and different levels of impalement.It should be noted that E. coli SERS is known to produce a high level of variability,^7–12 depending on the experimental setup.¹³ However, the variability seen in the SERS spectra of Fig. Fig.33 is unusual for measurements performed under consistent experimental conditions. This increased level of variability may be related to the different levels of impalement seen in Fig. Fig.1,1, which results in the probing of different internal components. SERS is a surface sensitive technique, with the signal primarily arising within 2 nm of the metal surface.¹⁴ Note that unlike apertureless nanoprobes¹⁵ or conical plasmonic nanotips,¹⁶ the SERS signal in black silicon arises primarily from “hot spots” between the spikes, where the plasmon resonance field is particularly strong.¹⁷ Therefore, depending on the depth and location of impalement, different biomolecules are expected to be excited by this novel substrate.Some peaks occur in the same position for multiple spectra (e.g., peak positions 420, 893, 1001, 1285, and 1307 cm⁻¹), but there are also a lot of unique peaks. The vertical lines in Fig. Fig.33 indicate peaks which have appeared in the literature for SERS of E. coli.^7–12 Spectrum 3 has a high proportion of peaks matching published values. This is also the case for spectrum 5, which shares a few peak positions with spectrum 3. Preliminary peak allocations have identified carbohydrates¹¹ (420 cm⁻¹), tyrosine¹¹ (650 cm⁻¹), adenine^10,11 (706 and 735 cm⁻¹), hypoxanthine⁷ (722 and1373 cm⁻¹), phenylalanine⁹ (1001 cm⁻¹), amide III (Ref. ¹⁰) (1285 cm⁻¹), CH₂ deformation¹² (1556 cm⁻¹), and C=C¹⁰ (1587 cm⁻¹).Given the varying levels of impalement observed in the SEM, it appears that the spike shape and Au coating should be further optimized to ensure that the entire cell is consistently pierced and the internal biomolecules are more comprehensively probed. In this way, it may be possible to obtain a more reproducible SERS spectrum of the internal biomolecular constituents of single bacterial cells, thereby providing rapid identification for medical and environmental diagnostic applications. Given that SERS is insensitive to water,⁴ future work should aim to achieve impalement in an aqueous environment, so that the full capability of microfluidics can be used to separate and concentrate suspended bacteria before presenting them to the substrate for rapid analysis.⁴ This suggests a broad range of potential applications in the detection, monitoring, and control of bacterial contamination. 相似文献

Artificial helical microswimmers with mastigoneme-inspired appendages

Soichiro Tottori Bradley J. Nelson 《Biomicrofluidics》2013,7(6)

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Genetic Predisposition to Diabetic Nephropathy: Evidence for a Role of ACE (I/D) Gene Polymorphism in Type 2 Diabetic Population from Kutch Region

Deepak N. Parchwani Kamlesh M. Palandurkar D. Hema Chandan Kumar Darshan J. Patel 《Indian journal of clinical biochemistry : IJCB》2015,30(1):43-54

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Development of vertical SU-8 microneedles for transdermal drug delivery by double drawing lithography technology

Zhuolin Xiang Hao Wang Aakanksha Pant Giorgia Pastorin Chengkuo Lee 《Biomicrofluidics》2013,7(6)

Polymer-based microneedles have drawn much attention in transdermal drug delivery resulting from their flexibility and biocompatibility. Traditional fabrication approaches are usually time-consuming and expensive. In this study, we developed a new double drawing lithography technology to make biocompatible SU-8 microneedles for transdermal drug delivery applications. These microneedles are strong enough to stand force from both vertical direction and planar direction during penetration. They can be used to penetrate into the skin easily and deliver drugs to the tissues under it. By controlling the delivery speed lower than 2 μl/min per single microneedle, the delivery rate can be as high as 71%.Microelectromechanical systems (MEMS) technology has enabled wide range of biomedical devices applications, such as micropatterning of substrates and cells,¹ microfluidics,² molecular biology on chips,³ cells on chips,⁴ tissue microengineering,⁵ and implantable microdevices.⁶ Transdermal drug delivery using MEMS based devices can delivery insoluble, unstable, or unavailable therapeutic compounds to reduce the amount of those compounds used and to localize the delivery of potent compounds.⁷ Microneedles for transdermal drug delivery are increasingly becoming popular due to their minimally invasive procedure,⁸ promising chance for self-administration,⁹ and low injury risks.¹⁰ Moreover, since pharmaceutical and therapeutic agents can be easily transported into the body through the skin by microneedles,¹¹^,¹² the microneedles are promising to replace traditional hypodermic needles in the future. Previously, various microneedles devices for transdermal drug delivery applications have been reported. They have been successfully fabricated by different materials, including silicon,¹³ stainless steel,¹⁴ titanium,¹⁵ tantalum,¹⁶ and nickel.¹⁷ Although microneedles with these kinds of materials can be easily fabricated into sharp shape and offer the required mechanical strength for penetration purpose, such microneedles are prone to be damaged¹⁸ and may not be biocompatible.¹⁹ As a result, polymer based microneedles, such as SU-8,²⁰^,²¹ polymethyl meth-acrylate (PMMA),²²^,²³ polycarbonates (PCs),²⁴^,²⁵ maltose,²⁶^,²⁷ and polylactic acid (PLA),²⁸^,²⁹ have caught more and more attentions in the past few years. However, in order to obtain ultra-sharp tips for penetrating the barrier layer of stratum corneum,³⁰ conventional fabrication technologies, for instances, PDMS (Polydimethylsiloxane) molding technology,³¹^,³² stainless steel molding technology,³³ reactive ion etching technology,³⁴ inclined UV (Ultraviolet) exposure technology,³⁵ and backside exposure with integrated lens technology³⁶ are time-consuming and expensive. In this paper, we report an innovative double drawing lithography technology for scalable, reproducible, and inexpensive microneedle devices. Drawing lithography technology³⁷ was first developed by Lee et al. They leveraged the polymers'' different viscosities under different temperatures to pattern 3D structures. However, it required that the drawing frames need to be regular cylinders, which is not proper for our devices. To solve the problem, the new double drawing lithography is developed to create sharp SU-8 tips on the top of four SU-8 pillars for penetration purpose. Drugs can flow through the sidewall gaps between the pillars and enter into the tissues under the skin surface. The experiment results indicate that the new device can have larger than 1N planar buckling force and be easily penetrated into skin for drugs delivery purpose. By delivering glucose solution inside the hydrogel, the delivering rate of the microneedles can be as high as 71% when the single microneedle delivery speed is lower than 2 μl/min.An array of 3 × 3 SU-8 supporting structures was patterned on a 140 μm thick, 6 mm × 6 mm SU-8 membrane (Fig. (Fig.1a).1a). Each SU-8 supporting structure included four SU-8 pillars and was 350 μm high. The four pillars were patterned into a tubelike shape on the membrane (Fig. (Fig.1b).1b). The inner diameter of the tube was 150 μm, while the outer diameter was 300 μm. SU-8 needles of 700 μm height were created on the top of SU-8 supporting structures to ensure the ability of transdermal penetration. Two PDMS layers were bonded with SU-8 membrane to form a sealed chamber for storing drugs from the connection tube. Once the microneedles entered into the tissue, drugs could be delivered into the body through the sidewall gaps between the pillars (Fig. (Fig.1c1c).Open in a separate window Figure 1Schematic illustration of the SU-8 microneedles. (a) Overview of the whole device; (b) SU-8 supporting structures made of 4 SU-8 pillars; and (c) enlarged view of a single SU-8 microneedle.The fabrication process of SU-8 microneedles is shown in Fig. Fig.2.2. SU-8 microneedles fabrication started from a layer of Polyethylene Terephthalate (PET, 3M, USA) film pasted on the Si substrate by sticking the edge area with kapton tape (Fig. (Fig.2a).2a). The PET film, a kind of transparent film with poor adhesion to SU-8, was used as a sacrificial layer to dry release the final device from Si substrate. A 140 μm thick SU-8 layer was deposited on the top of this PET film. To ensure a uniform surface of this thick SU-8 layer, the SU-8 deposition was conducted in two steps coating. After exposed under 450 mJ/cm² UV, the membrane pattern could be defined (Fig. (Fig.2b).2b). In order to ensure an even surface for following spinning process, another 350 μm SU-8 layer was directly deposited on this layer in two steps without development. With careful alignment, an exposure of 650 mJ/cm² UV energy was performed on this 350 μm SU-8 layer to define the SU-8 supporting structures (Fig. (Fig.2c).2c). The SU-8 structure could be easily released from the PET substrate by removing the kapton tape and slightly bending the PET film. Two PDMS layers were bonded with this SU-8 structure by a method reported by Zhang et al.³⁸ (Fig. (Fig.2d2d).Open in a separate window Figure 2Fabrication process for SU-8 microtubes. (a) Attaching a PET film on the Si substrate; (b) exposing the first layer of SU-8 membrane without development; (c) depositing and patterning two continuous SU-8 layers as sidewall pillars; (d) releasing the SU-8 structure from the substrate and bonding it with PDMS; (e) drawing hollowed microneedles on the top of supporting structures; (f) baking and melting the hollowed microneedles to allow the SU-8 flow in the gaps between pillars; and (g) drawing second time on the top of the melted SU-8 flat surface to get microneedles.In our previous work,³⁹ we used one time stepwise controlled drawing lithography technology for the sharp tips integration. However, since the frame used to conduct drawing process in present study is a four-pillars structure rather than a microtube, the conventional drawing process can only make a hollowed tip but not a solid tip structure (Fig. (Fig.3).3). This kind of tip was fragile and could not penetrate skin in the practical testing process. To solve the problem, we developed an innovative double drawing lithography process. After bonding released SU-8 structure with PDMS layers (Fig. (Fig.2d),2d), we used it to conduct first time stepwise controlled drawing lithography³⁷ and got hollowed tips (Fig. (Fig.2e).2e). Briefly, the SU-8 was spun on the Si substrate and kept at 95 °C until the water inside completely vaporized. Device of SU-8 supporting structures was fixed on a precision stage. Then, the SU-8 supporting structures were immersed into the SU-8 by adjusting the precision state. The SU-8 were coated on the pillars'' surface. Then, the SU-8 supporting structures were drawn away from the interface of the liquid maltose and air. After that, the temperature and drawing speed were increased. Since the SU-8 was less viscous at higher temperature, the connection between the SU-8 supporting structures and surface of the liquid SU-8 became individual SU-8 bridge, shrank, and then broke. The end of the shrunk SU-8 bridge forms a sharp tip on the top of each SU-8 supporting structure when the connection was separated. After the hollowed tips were formed in the first step drawing process, the whole device was baked on the hotplate to melt the hollowed SU-8 tips. Melted SU-8 reflowed into the gaps between four pillars and the tips became domes (Fig. (Fig.2f).2f). Then, a second drawing process was conducted on the top of melted SU-8 to form sharp and solid tips (Fig. (Fig.2g).2g). The final fabricated device is shown in Fig. Fig.44.Open in a separate window Figure 3A hollowed SU-8 microneedle fabricated by single drawing lithography technology (scale bar is 100 μm).Open in a separate window Figure 4Optical images for the finished SU-8 microneedles.During the double drawing process, as long as the heated time and temperature were controlled, the SU-8 flow-in speed of SU-8 inside the gaps could be precisely determined. The relationship between baking temperature and flow-in speed was studied. As shown in Fig. Fig.5,5, the flow-in speed is positive related to the baking temperature. The explanation for this phenomena is that the SU-8''s viscosity is different under different baking temperatures.⁴⁰ Generally, baked SU-8 has 3 status when temperature increases, solid, glass, and liquid. The corresponding viscosity will decrease and the SU-8 can also have higher fluidity. When the baking temperature is larger than 120 °C, the flow-in speed will increase sharply. But, if the baking temperature is higher, the SU-8 will reflow in the gaps too fast, which makes the flow-in depth hard to be controlled. There is a high chance that the whole gaps will be blocked, and no drugs can flow through these gaps any more. Considering that the total SU-8 supporting structure is only 350 μm high, we choose 125 °C as baking temperature for proper SU-8 flow-in speed and easier SU-8 flow-in depth control.Open in a separate window Figure 5The relationship between flow-in speed and baking temperature.To ensure the adequate stiffness of the SU-8 microneedles in vertical direction, Instron Microtester 5848 (Instron, USA) was deployed to press the microneedles with the similar method reported by Khoo et al.⁴¹ As shown in Fig. Fig.6a,6a, the vertical buckling force was as much as 8.1N, which was much larger than the reported minimal required penetration force.⁴² However, in the previous practical testing experiments, even though the microneedles were strong enough in vertical direction, the planar shear force induced by skin deformation might also break the interface between SU-8 pillars and top tips. In our new device with four pillars supporting structure, the SU-8 could flow inside the sidewall gaps between the pillars to form anchors. These anchors could enhance microneedles'' mechanical strength and overcome the planar shear force problems. Moreover, the anchors strength could be improved by controlling the SU-8 flow-in depth. Fig. Fig.77 shows that the flow-in depth increases when the baking time increases as the baking time increases at 125 °C. Fig. Fig.6b6b shows that the corresponding planar buckling force can be improved to be larger than 1 N by increasing flow-in depth. Some sidewall gaps at bottom are kept on purpose for drugs delivery; hence, the flow-in depth is chosen as 200 μm.Open in a separate window Figure 6(a) Measurement of the vertical buckling force. (b) The planar buckling force varies under different flow-in depth (I, II, III, and IV corresponding to the certain images in Fig. Fig.77).Open in a separate window Figure 7Different flow-in depth inside the gaps between SU-8 pillars. (a) 0 μm; (b) 100 μm; (c) 200 μm; and (d) 350 μm (scale bar is 100 μm).The penetration capability of the 3 × 3 SU-8 microneedles array is characterized by conducting the insertion experiment on the porcine cadaver skin. 10 microneedles devices were tested and all of them were strong enough to be inserted into the tissue without any breakage. Histology images of the skin at the site of one microneedle penetration were derived to prove that the sharp conical tip was not broken during the insertion process (Fig. (Fig.8).8). It also shows penetrated evidence because the hole shape is the same as the sharp conical tip.Open in a separate window Figure 8Histology image of individual microneedle penetration (scale bar is 100 μm).In order to verify that the drug solution can be delivered into tissue from the sidewall gaps of the microneedles, FITC (Fluorescein isothiocyanate) (Sigma Aldrich, Singapore) solution was delivered through the SU-8 microneedles after they were penetrated into the mouse cadaver skin. The representative results were then investigated via a confocal microscope (Fig. (Fig.9).9). The permeation pattern of the solution along the microchannel created by microneedles confirmed the solution delivery results. The black area was a control area without any diffused florescent solution. In contrast, the illuminated area in Fig. Fig.99 indicates the area where the solution has diffused to it. These images were taken consecutively from the skin surface down to 180 μm with 30 μm intervals. The diffusion area had a similar dimension with the inserted microneedles. It has proved that the device can be used to deliver drugs into the body.Open in a separate window Figure 9Images of confocal microscopy to show the florescent solution is successfully delivered into the tissue underneath the skin surface. (a) 30 μm; (b) 60 μm; (c) 90 μm; (d) 120 μm; (e) 150 μm; and (f) 180 μm (scale bar is 100 μm).Due to the uneven surface of deformed skin, there is always tiny gap happened between tips of some microneedles and local surface skin. The microneedles could not be entirely inserted into the tissue. Drugs might leak to the skin surface through the sidewall gaps under certain driven pressure. Hydrogel absorption experiment was conducted to quantify the delivery rate (i.e., the ratio of solution delivered into tissues in the total delivered volume) and to optimize the delivery speed. Using hydrogel as the tissue model for quantitative analysis of microneedle releasing process was reported by Tsioris et al.⁴³ The details are shown here. Gelatin hydrogel was prepared by boiling 70 ml DI (Deionized) water and mixing it with 7 g of Knox^TM original unflavored gelatin powder. The solution was poured into petri dish to 1 cm high. Then, the petri dish was put into a fridge for half an hour. Gelatin solution became collagen slabs. The collagen slabs were cut into 6 mm × 6 mm sections. A piece of fully stretched parafilm (Parafilm M, USA) was tightly mounted on the surface of the collagen slabs. This parafilm was used here to block the leaked solution further diffusing into the collagen slab in the delivery process. Then, the microneedles penetrated the parafilm and went into the collagen slab. Controlled by a syringe pump, 0.1 ml–0.5 mg/ml glucose solution was delivered into the collagen slab under different speeds. Methylene Blue (Sigma Aldrich, Singapore) was mixed into the solution for better inspection purpose (Fig. 10a). Then, the collagen slabs was digested in 1 mg/ml collagenase (Sigma Aldrich, Singapore) at room temperature (Fig. 10b). It took around 1 h that all the collagen slabs could be fully digested (Fig. 10d). The solution was collected to measure the glucose concentration with glucose detection kit (Abcam, Singapore). Briefly, both diluted glucose standard solution and the collected glucose solution were added into a series of wells in a well plate. Glucose assay buffer, glucose enzyme, and glucose substrate were mixed with these samples in the wells. After incubation for 30 min, their absorbance were examined by using a microplate reader at a wavelength of 450 nm. By comparing the readings with the measured concentration standard curve (Fig. 11a), the glucose concentration in the hydrogel, the glucose absorption rate in the hydrogel, and the solution delivery rate by microneedles could be measured and calculated. As shown in Fig. 11b, when the delivering speed of a single microneedle increased from 0.1 μl/min to 2 μl/min, the glucose absorption rate also increased. Most of the glucose solution from microneedles could go into the hydrogel. The delivered rate could be as high as 71%. The rest solution leaked from sidewall gaps and blocked by parafilm. However, when the delivered speed for a single microneedle was larger than 2 μl/min, the hydrogel absorption rate was saturated. More and more solution could not go into the hydrogel but leak from the sidewall gaps. Then, the delivered rate decreased. Therefore, 2 μl/min was chosen as the optimized delivery speed for the microneedle.Open in a separate window Figure 10Glucose solution could be delivered into the hydrogel, and the collagen stabs were dissolved by collagenase.Open in a separate window Figure 11(a) Standard curve for glucose detection; (b) glucose absorption rate and solution delivery rate in a single needle corresponding to different delivery speed.In conclusion, a drug delivery device of integrated vertical SU-8 microneedles array is fabricated based on a new double drawing lithography technology in this study. Compared with the previous biocompatible polymer-based microneedles fabrication technology, the proposed fabrication process is scalable, reproducible, and inexpensive. The fabricated microneedles are rather strong along both vertical and planar directions. It is proved that the microneedles were penetrated into the pig skin easily. The feasibility of drug delivery using SU-8 microneedles is confirmed by FITC fluorescent delivery experiment. In the hydrogel absorption experiment, by controlling the delivery speed under 2 μl/min per microneedle, the delivery rate provided the microneedle is as high as 71%. In the next step, the microneedles will be further integrated with microfluidics on a flexible substrate, forming a skin-patch like drug delivery device, which may potentially demonstrate a self-administration function. When patients need an injection treatment at home, they can easily use such a device just like using an adhesive bandage strip. 相似文献

10.

Value,Rent, and the Political Economy of Social Media

Jakob Rigi Robert Prey 《The Information Society》2013,29(5):392-406

Fuchs (2010 Fuchs, C. 2010. Labor in information capitalism and on the Internet. The Information Society 26:179–196.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 2012 Fuchs, C. 2012. With or without Marx? With or without capitalism?: A re-joinder to Adam Arvidsson and Eleanor Colleoni. tripleC 10 (2):633–45. [Google Scholar]) argues that users of social media produce value and surplus value in the Marxian sense. Arvidsson and Colleoni (2012 Arvidsson, A., and E. Colleoni. 2012. Value in information capitalism and on the Internet. The Information Society 28:135–50.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) critique this hypothesis, claiming that Marx's theory of value is irrelevant to the regime of value production on social media platforms in particular and in informational capitalism in general. They claim that the affective relations and financial speculations that generate value on social media are not dependent on labor time. This article critically engages Fuchs, and Arvidsson and Colleoni, by revisiting Marx's theory of value. Contra Fuchs, we argue that audiences do not produce value and surplus value—neither for social nor for mass media. Contra Arvidsson and Colleoni, we argue that so-called affective relations (philia) do not produce value either. Instead we demonstrate that social media generate revenue from four primary sources—by leasing advertisement space to generate advertisement rent, by selling information, by selling services to advertisers, and by generating profits from fictitious capital and speculative windfalls. All four, we argue, can be adequately explained by Marx's theory of value. 相似文献

11.

A case report of short-chain acyl-CoA dehydrogenase deficiency (SCADD)

Barbka Repic Lampret Simona Murko Marusa Debeljak Mojca Zerjav Tansek Petja Fister Tadej Battelino 《Biochemia medica : ?asopis Hrvatskoga dru?tva medicinskih biokemi?ara / HDMB》2015,25(2):279-284

Background

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is a rare inherited mitochondrial fatty acid oxidation disorder associated with variations in the ACADS (Acyl-CoA dehydrogenase, C-2 to C-3 short chain) gene. SCADD has highly variable biochemical, genetic and clinical characteristics. Phenotypes vary from fatal metabolic decompensation to asymptomatic individuals.

Subject and methods

A Romani boy presented at 3 days after birth with hypoglycaemia, hypotonia and respiratory pauses with brief generalized seizures. Afterwards the failure to thrive and developmental delay were present. Organic acids analysis with gas chromatography-mass spectrometry (GS/MS) in urine and acylcarnitines analysis with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in dried blood spot were measured. Deoxyribonucleic acid (DNA) was isolated from blood and polymerase chain reactions (PCRs) were performed for all exons. Sequence analysis of all exons and flanking intron sequences of ACADS gene was performed.

Results

Organic acids analysis revealed increased concentration of ethylmalonic acid. Acylcarnitines analysis showed increase of butyrylcarnitine, C4-carnitine. C4-carnitine was 3.5 times above the reference range (<0.68 µmol/L). Confirmation analysis for organic acids and acylcarnitine profile was performed on the second independent sample and showed the same pattern of increased metabolites. Sequence analysis revealed 3-bp deletion at position 310-312 in homozygous state (c.310_312delGAG). Mutation was previously described as pathogenic in heterozygous state, while it is in homozygous state in our patient.

Conclusions

In our case clinical features of a patient, biochemical parameters and genetic data were consistent and showed definitely SCAD deficiency.Key words: SCAD deficiency, short chain acyl-CoA dehydrogenase deficiency, screening, acylcarnitine, polymorphism, genetic 相似文献

12.

Bacteria under the physical constraints of periodic micro-nanofluidic junctions reveal morphological plasticity and dynamic shifting of Min patterns

Jie-Pan Shen Chia-Fu Chou 《Biomicrofluidics》2014,8(4)

Morphological plasticity is an important survival strategy for bacteria adapting to stressful environments in response to new physical constraints. Here, we demonstrate Escherichia coli morphological plasticity can be induced by switching stress levels through the physical constraints of periodic micro-nanofluidic junctions. Moreover, the generation of diverse morphological aberrancies requires the intact functions of the divisome- and elongasome-directed pathways. It is also intriguing that the altered morphologies are developed in bacteria undergoing morphological reversion as stresses are removed. Cell filamentation underlies the most dominant morphological phenotypes, in which transitions between the novel pattern formations by the spatial regulators of the divisome, i.e., the Min system, are observed, suggesting their potential linkage during morphological reversion.Most bacteria have evolved sophisticated systems to manage their characteristic morphology by orchestrating the spatiotemporal synthesis of the murein sacculus (peptidoglycan exoskeleton), which is known to be the stress-bearing component of cell wall and presides over de novo generation of cell shape.¹ Morphological plasticity is attributed to a bacterial survival strategy as responding to stressful environments such as innate immune effectors, antimicrobial therapy, quorum sensing, and protistan predation.² It comes of no surprise that stress-induced diversified morphology and mechanisms, ascribed to shape control and determination, have drawn great attention in both fundamental and clinical studies.^3–6 The molecular mechanism to form filamentous bacteria has been revealed that both β-lactam antibiotics³ and oxidative radicals produced by phagocytic cells⁵ trigger the SOS response, promoting cell elongation by inactivating cell division via the blockade of tubulin-like FtsZ, known as the divisome initiator. While apart from the scenario of length control by the divisome-directed filamentation, the elongasome assembled by proteins associated with actin-like MreB complex^1,7,8 helps the insertion of peptidoglycans into lateral cell wall, suggesting the role in the determination of cell diameter during cell elongation.Recently, additional mechanisms other than the divisome/elongasome-directed pathways of shape maintenance are discovered to regenerate normal morphology de novo from wall-less lysozyme-induced (LI) spheroplasts of E. coli via a plethora types of aberrant division intermediates.⁹ Similar morphological reversion from different aberrant bacterial shapes has been observed as squashed wild-type bacteria generated through sub-micron constrictions are released into connected microchambers.¹⁰ Previous work using the microfluidic approach focuses on the septation accuracy and robustness of constricted bacteria,¹¹ but the reversion process of stress-released bacteria is not well studied and analyzed. In particular, the aberrant bacterial shape is mainly branched-type with bent and curved variants in the reverting bacteria, analogous to the aberrant intermediate found in the morphological reversion of LI spheroplasts with PBP5-defective mutant.⁹ Since bacteria suffering from starvation¹² or confronting mechanical stresses exerted by phagocytosis and protistan grazing⁶ can induce morphological alterations, one could manipulate the stress levels of physical constraints by adopting repeated structures of sub-micron constricted channels (nanoslits) and microchambers,^10,11 to select and enrich bacteria converting to specified aberrant intermediates. The stress incurred by the nanoslit on bacteria is about the mechanical intervention over de novo synthesis of the cell wall, which is the major factor causing morphological aberrancy, while the second environmental stress comes from bacterial growth in the restricted space of microchamber as bacteria proliferate to full confluency, resulting in growth pressure of high population density, nutrient deficiency, and the size reduction of bacteria.Here, we report the selection of distinctive bacterial morphologies by size shrinkage in the outlet cross-section (W × H = 1.5 × 1.5 μm) of the terminal microchamber in the periodic structures of nanoslit-microchamber (Figs. 1(a) and 1(b)). The fluidic structures were micropatterned on fused silica wafers by photolithography, fabricated through reactive ion etching (RIE) and inductively coupled plasma (ICP) etching, and encapsulated by cover glasses coated with polydimethylsiloxane (PDMS) or polysilsesquioxane (PSQ) layer as described earlier.^13,14 Two days after the outgrowth of Escherichia coli (imp4213 [MC4100 ΔlamB106 imp4213]) loaded to the microfluidic device at 25 °C, bacteria started to penetrate into the nanoslit as they proliferated to full confluency in the first microchamber (Fig. 1(c)). It takes about 10 days for bacteria traversing 500 μm long (5 repeated nanoslit-microchamber units) via proliferations and being released from the outlet of the terminal microchamber. The narrowed outlet allows only bacteria with smaller diameters to be squeezed into the spacious and nutrient-rich region, thus it acts as a spatial filter to avoid the passage of branching bacteria with cross-sectional size larger than that of the outlet. The rationale of this design is to select aberrant bacteria prone to promote de novo shape regeneration other than the branched-type, which is the dominant morphology of reverting bacteria in the prior microfluidic constriction study.¹⁰ As anticipated, the stress-released bacteria through the narrowed outlet are therefore mostly filamentous (see statistical analysis for cell morphology in the supplementary material).¹⁵ However, it is noted that the aberrant morphology of lemon-like shape with tubular poles (Figs. 1(d-1), 1(d-3), and 1(d-11)) is developed about 3 h after the stress-released bacteria escaped through the outlet. Though the generation of the lemon-like aberrancy in bacteria has been reported in PBP5/7-defective E. coli mutant subjected to a high-level inhibition of both MreB and FtsZ, while the same mutant treated with low-level MreB inhibitor, together with antagonized-FtsZ, displays filamentous shape with varying diameters,¹⁶ these morphological aberrances can be observed in our system (Figs. 1(d-2) and 1(d-12)). Besides, a high-level inhibition of MreB in E. coli with an intact divisome function is known to cause round bacteria, resembling to the cell morphology of the bacteria shown in Fig. 1(d-4). Interestingly, parallel experiments using bacteria mutants carrying impaired regulatory functions in either the divisome (Min⁻) or the elongasome (MreB⁻) do not develop morphological plasticity (supplementary Fig. S1).¹⁵ Taken together, the filamentous and lemon-like variants selected from our microfluidic platform, while elaborating the morphological plasticity and reverting progression, require both the functional divisome/elongasome. Alternatively, the selection by the spatial filter does not fully exclude cells with aberrant shapes such as the branched-type with initial budding (Fig. 1(d-7)), cells with asymmetric cross-section perpendicular to the longitudinal axis (Figs. 1(d-2), 1(d-8), 1(d-9), 1(d-9′), and 1(d-10)), and those resembling to the morphological phenotypes of the division intermediates reported in the LI-spheroplasts carrying genetic defects on some non-cytoskeletal proteins (Figs. 1(d-5) and 1(d-6)). In particular, intracellular vesicles and cell autolysis are observed in some reverting bacteria (Figs. 1(d-5) and 1(d-6)), which are reminiscent to the phenomena reported in the division intermediates of the LI-spheroplasts lacking stress response system (Rcs) or some accessory proteins (PBP1B and LpoB). Unlike the bacteria grow with odd shapes under the stress of nanofluidic confinement only¹⁰ (Fig. 1(c)), all the morphological aberrancy reported here are developed in the reverting bacteria, which grow in the spacious and nutrition-rich environment and are free from physical constraints. Further investigations over the expression levels of the divisome/elongasome networks and the stress-response system in bacterial cells subjected to micro-nanofluidic junctions could be insightful in understanding their role in bacterial shape control.⁹ Open in a separate window FIG. 1.(a) Schematics of the microfluidic device used in this study with an H-shaped geometry (left upper panel), where repeated nanoslit (L×W×H = 50×10×0.4 μm)−microchamber (L×W×H = 50×50×1.5 μm) structures are bridged between two arms of the H-shaped microchannels (left lower panel and enlarged view in right panel). (b) Top-view layout of an individual channel in (a) with close view of the outlet in the terminal microchamber (orange: nanoslits; blue: microchambers). (c) Fluorescence micrograph of E. coli imp4213 penetrating a nanoslit (scale bar: 5 μm). (d) Bright-field micrographs for various cell morphology of the selected imp4213 released from the outlet (magenta arrows: cells with vesicles; scale bar: 5 μm). (e) Sequential bright-field micrographs of morphological reversion. T1–T3 indicate the time after bacteria escaping from the outlet. T1: 3 h; T2: 6 h; T3: 24 h. Scale bar: 10 μm.During the morphological reversion, the stress-released bacteria rapidly increase their size in the first 3 h after escaping from the terminal microchamber (T1 in Fig. 1(e)). Some filamentous bacteria even grow over 50 μm long, though such a morphological phenotype implicates the cessation of functional divisome. With active growth and proliferation, the progeny of stress-released bacteria increase their population but gradually reduce their size about 6 h after being released from the constriction stress (T2 in Fig. 1(e)). Fig. Fig.22 displays the marginal histograms for different shape factors, where Fig. 2(a) is the plot of the minimal Feret diameter (cell diameter) versus Feret diameter (cell length), i.e., the shortest versus the longest distance between any two points with parallel tangents along the cell peripheral, respectively, indicating that cell diameters are larger for reverting bacteria at T1 (mean ± S.E.M. = 1.89 ± 0.08 μm) with respect to T2 (1.51 ± 0.06 μm). Moreover, the histogram of Feret diameter depicts two major populations of the cell length for reverting bacteria at T1, which mostly resume to typical cell length at T2 (the median of Feret diameter = 3.33 μm; see statistical analysis for Fig. Fig.22 in the supplementary material).¹⁵ The shape factors of circularity (4π × [area]/[perimeter]²) and aspect ratio ([major axis]/[minor axis] for the cell geometry fitted to an ellipse) confirm the existence of dual populations for bacteria at T1 as well (Fig. 2(b)). About 24 h after escaping (T3 in Fig. 1(e)), almost all the progeny of stress-released bacteria regained the rod shape.Open in a separate window FIG. 2.Marginal histograms for shape factors measured from the reverting imp4213 at T1 and T2. (a) Minimal Feret diameter (cell diameter) versus Feret diameter (cell length). (b) Circularity versus aspect ratio. N = 366 for T1 and N = 494 for T2.The bacterial size reduction of filamentous and lemon-like shape variants, though involving negative control of the divisome positioning by the spatial regulators of MinCDE system,¹⁷ is not completely understood as to how they coordinate in aberrant geometries. Besides, the filamentation of stress-released bacteria during the period of T1 to T2 implicates the inhibition of functional divisome. With minimal perturbation of the divisome by leaky expression of GFP-MinD and MinE (imp4213/P_lac-gfpmut2::minD minE), the patterning dynamics of GFP-MinD in different bacterial morphology were time-lapse imaged during morphological reversion. Intriguingly, more than the standing-wave-like pattern of MinD denoted in filamentous E. coli,¹⁸ we discovered bidirectional drifting of two standing-wave-like patterns of MinD occur in most reverting bacteria filaments (supplementary Figs. S2(a) and S2(b)).¹⁵ The bidirectional drifting in the longitudinal direction of the cells may be emanating from the cell poles (the blue upper panel of Fig. 3(a) and supplementary Fig. S2(c)¹⁵) and the cylinder region (the blue lower panel of Fig. 3(a) and supplementary Fig. S2(d)¹⁵). Furthermore, the MinD pattern transitions from the standing to traveling waves are occasionally observed (the lower panel of Figs. 3(a) and supplementary Fig. S2(e)¹⁵). Notably, the standing-wave-like MinD patterns exhibit bidirectional drifting along the cell longitudinal direction and intermittently change directions, implying the competition between coexisting MinD patterns can be supported under filamentous geometry. Despite there have been observations of multiple wave-packet of traveling waves in filamentous cells,¹⁹ the mixture of distinct wave-like MinD patterns have never been experimentally reported. While most intriguingly, multiple drifting movements of wave-like MinD patterns potentiate the mitigation of periodic minima in time-averaged Min gradient in the reverting filamentous bacteria, suggesting the disability of proper divisome positioning for recovering the typical rod shape. Apart from the wave-like movements, amoeba-like motion of Min proteins has been shown in vitro upon synthetic minimal system, but never been verified in vivo.²⁰ Strikingly, here amoeba-like motion of MinD is the dominant mode in lemon-like bacteria and the transitions between wave-like patterns and amoeba-like motion are supported even under filamentous geometry (Figs. 3(b) and 3(c), Multimedia view).Open in a separate window FIG. 3.Kymographs for GFP-MinD dynamics in selected imp4213 cells during morphological reversion: (a) Mixture modes of standing wave packets and traveling wave. The left panel is the stacked fluorescence micrograph displaying cell shape (scale bar = 5 μm). The kymograph is derived from the filamentous cell indicated by the green arrow (scale bar: 120 s horizontal; 5 μm vertical), where the lower panel follows the upper panel in time. The yellow windows indicate bidirectional-drifting standing wave packets, while the green indicates traveling waves (see also supplementary Fig. S2).¹⁵ (b) Sequential fluorescence micrographs of GFP-MinD in lemon-shape imp4213 show amoeba-like motion, with the first left a bright-field image (scale bar: 10 μm). (c) Mixed modes of amoeba-like motion and waves in selected filamentous imp4213 cell indicated by the green arrow in the left panel (scale bar = 5 μm). The filamentous cells depicted in (a) and (c) locate at the top region while the lemon-shape cell in (b) at the central region of the movie (time stamp in min:s). (Multimedia view) [URL: http://dx.doi.org/10.1063/1.4892860.1]In summary, we have demonstrated that the development of bacterial morphological plasticity can be stress-induced by periodic physical constraints with intact functions of the divisome and elongasome-directed pathways. Through size exclusion, the constricted outlet structure designed in our microfluidic device is useful in selecting bacteria with plethora morphological aberrancies other than the branched type. Interestingly, disparate morphological changes, rather than those being directly induced under a stressful environment, can be generated in the stress-released bacteria experiencing morphological reversion. Further, the discovery of novel transitions between the Min patterns in most reverting bacteria implicates its regulatory effect of cell filamentation. However, by exploiting the micro-nanofluidic approach, further investigations of the mechanism underlying the development of morphological plasticity in bacteria adapting to physical constraints are expected in future studies to gain more insights into the molecular basis of shape generation. 相似文献

13.

Role of l-Arginine on Dyslipidemic Conditions of Acute Myocardial Infarction Patients

Pratima Tripathi M. K. Misra Shivani Pandey 《Indian journal of clinical biochemistry : IJCB》2012,27(3):296-299

Oxidative stress conditions associated with atherosclerosis leads to oxidative modification of low-density lipoprotein (LDL). The body’s capabilities to inhibit LDL oxidation and to remove or neutralize the atherogenic oxidized LDL (ox-LDL) are limited. When the LDL cholesterol level increases in the blood, it leads to dangerous consequences like atherosclerosis, leading to myocardial infarction. The major effect of an antioxidant in the LDL environment is to prevent the formation of ox-LDL (during atherogenesis. Strategies to reduce LDL oxidation and prevent atherogenesis can involve the enrichment of arterial cells with potent antioxidants that can prevent oxidative damage to the arterial wall. The objective of this study is to evaluate the effect of l-arginine on serum lipid and cholesterol levels in the patients of acute myocardial infarction (AMI). The study consisted of 70 AMI patients and 60 healthy individuals (serving as control) age 55–65 years. Serum levels of total cholesterol, high density lipoprotein (HDL), LDL and Triglycerides were determined on day 1 and day 15 of l-arginine administration (oral dose 3 g/day). The total cholesterol/HDL and the LDL/HDL ratio were calculated and compared. As per the observations, l-arginine administration was found to improve the lipid profile of the subjects. Hence it could be used as an adjuvant therapy for AMI and as a preventive measure for the onset of the disease in the healthy elderly also. 相似文献

14.

Modulating patterns of two-phase flow with electric fields

Dingsheng Liu Bejan Hakimi Michael Volny Joelle Rolfs Robbyn K. Anand Frantisek Turecek Daniel T. Chiu 《Biomicrofluidics》2014,8(4)

This paper describes the use of electro-hydrodynamic actuation to control the transition between three major flow patterns of an aqueous-oil Newtonian flow in a microchannel: droplets, beads-on-a-string (BOAS), and multi-stream laminar flow. We observed interesting transitional flow patterns between droplets and BOAS as the electric field was modulated. The ability to control flow patterns of a two-phase fluid in a microchannel adds to the microfluidic tool box and improves our understanding of this interesting fluid behavior.Microfluidic technologies have found use in a wide range of applications, from chemical synthesis to biological analysis to materials and energy technologies.^1,2 In recent years, there has been increasing interest in two-phase flow and droplet microfluidics, owing to their potential for providing a high-throughput platform for carrying out chemical and biological analysis and manipulations.^3–8 Although droplets may be generated in many different ways, such as with electric fields or extrusion through a small nozzle,^9–12 the most common microfluidic methods are based on the use of either T-junctions or flow-focusing geometries with which uniform droplets can be formed at high frequency in a steady-state fashion.^13,14 Various operations, such as cell encapsulation, droplet fusion, splitting, mixing, and sorting, have also been developed, and these systems have been demonstrated for a wide range of applications, including cell analysis, protein crystallization, and material synthesis.^1–17In addition to forming discrete droplets, where a disperse phase is completely surrounded by a continuous phase, it is also possible in certain situations to have different phases flow side-by-side. In fact, multi-stream laminar flow, either of the same phase or different phases, has been exploited for both biochemical analysis and microfabrication.^1,2,18–20 Beads-on-a-string (BOAS) is another potential flow pattern, which has been attracting attentions in microfluidics field. BOAS flow, owing to its special flow structures, may be particularly useful in some applications, such as optical-sensor fabrication.²¹ In BOAS flow, queues of droplets are connected by a series of liquid threads, which makes them look like a fluid necklace with regular periods.^21–25 The BOAS pattern is easily found in nature, such as silk beads and cellular protoplasm, and is often encountered in industrial processes as well, such as in electrospinning and anti-misting.^21,22 In general, it is thought that BOAS structure occurs mostly in viscoelastic fluids²² and is an unstable structure, which evolves continually and breaks eventually.^21–29Flow patterns determine the inter-relations of fluids in a microdevice and are an important parameter to control. Common methods for adjusting microfluidic flow patterns include varying the fluid flow rates, fluid properties, and channel geometries. Additionally, the application of an electric field can be a useful supplement for adjusting microfluidic flow patterns, although most work in this area has been focused on droplets and in some cases also on multi-stream laminar flows.^30–33 Here, in addition to forming droplets and two-phase laminar flow with electro-hydrodynamic actuation, we also observed a new stable flow pattern in a non-viscoelastic fluid, BOAS flow. Such flow patterns may find use in controlling the interactions between droplets, such as limited mixing by diffusion between neighboring droplets.To generate droplets, we used the flow-focusing geometry (Figure 1(a)), in which aqueous phase (water) was flown down the middle channel and droplets were pinched off by the oil phase (1-octanol) from the two side channels at the junction; Figure 1(b) shows the droplets formed after the junction. To apply electric field along the main channel where the droplets were formed, we patterned a pair of electrodes upstream and downstream of the junction (Figure 1(a); for experimental details, please see Ref. ³⁴ for supplementary material). The average electric field strength may be calculated from the voltages applied and the distance (1.7 mm) between the two electrodes. When a high voltage was applied along the channel between the two electrodes, the aqueous-oil interface at the flow-focusing junction became charged and behaved like a capacitor. As a result, more negative charges were drawn back upstream towards the positive electrode, and left behind more positive charges at the aqueous-oil interface, which then became encapsulated into the aqueous droplets dispersed in the oil phase.Open in a separate window FIG. 1.(a) Schematic of the setup. (b) Micrograph showing droplet generation in a flow-focusing junction. The scale bar represents 40 μm.The positively charged aqueous-oil interface was stretched under an applied electric field, and by adjusting the voltage and/or the two-phase flow-rate ratio, we found interestingly that various flow patterns emerged. We tested different combinations of applied voltages and flow-rate ratios and found that most of them resulted in similar flow patterns and transitions between flow patterns.Figure Figure22 illustrates the effects of varying the applied voltages on droplets at a fixed liquid flow rate. With increasing electric-field strength and force, we found it was easier for the aqueous phase to overcome interfacial tension and form droplets. For example, as the voltage increased from 0.0 kV to 0.8 kV (average field strength increased from 0 to 0.47 V/μm), droplet-generation frequencies became slightly higher, and the formed droplets were smaller in volume. Additionally, droplets gradually became more spherical in shape at higher voltages.Open in a separate window FIG. 2.Images showing the effects of applied voltage on droplet shape and flow pattern. Oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.2 μl/min. The scale bar represents 40 μm.As the voltage increased further (e.g., up to 1.0 kV in Figure Figure3),3), the distance between neighboring droplets became smaller, and the aqueous-oil interface at the junction was stretched further toward the downstream channel. At a threshold voltage (1 kV here with corresponding average field strength of 0.59 V/μm), the tip of the aqueous-oil interface would catch up with the droplet that just formed, and the tip of the interface of this newly captured droplet would in turn catch up with the interface of the droplet that formed before it. Consequently, a series of threads would connect all the droplets flowing between the two electrodes, thus resulting in a BOAS flow pattern.Open in a separate window FIG. 3.Series of images showing the reversibility and synchronicity of a transitional flow pattern between droplets and BOAS (bead-on-a-string). Voltage applied, 1.00 kV (corresponding field strength of 0.59 V/μm); oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.2 μl/min. The scale bar represents 40 μm.At voltages near the threshold value, the flow pattern was not stable, but oscillated between droplets flow and BOAS flow. Figure Figure33 is a series of images captured by a high-speed camera that show the flow in this transition region. In Figures 3(a) and 3(b), the string of BOAS became thinner over time, and then the BOAS broke into droplets (Figures 3(c) and 3(d)). The newly formed droplets, however, were not stable either. Thin liquid threads would appear and then connect neighboring droplets, and a new switching period between discrete droplets and BOAS would repeat (Figures 3(e)–3(h)). In addition to this oscillation and reversibility, the flow pattern had a synchronous behavior: all the droplets appeared connected simultaneously by liquid threads or were separated at the same time.When the voltage reached 1.3 kV, which corresponded to an average field strength of 0.76 V/μm, a stable BOAS flow was obtained (Figure 4(a)). BOAS structures are thought to be present mostly in viscoelastic fluids,²² because viscoelasticity is helpful in enhancing the growth of beads and in delaying breakup of the string; thus, the viscoelastic filament has much longer life time than its Newtonian counterpart. Here, with the help of electric field, regular BOAS structures are realized in a non-viscoelastic fluid (water) in microchannels.Open in a separate window FIG. 4.(a) Micrograph showing BOAS flow in a channel. (b) Profile of the top-half of the BOAS flow recorded continuously at a cross-section (shown in Figure 4(a)) of a channel. Voltage applied, 1.30 kV (corresponding field strength of 0.76 V/μm); oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.2 μl/min. The scale bar represents 40 μm.Microenvironment and electric fields alter the common evolution of BOAS structure observed in macroscopic or unbound environments. The BOAS structure formed in our experiments is not a stationary pattern, but a steady-state flowing one. Electric-field force prevents liquid strings from breaking between beads, and thus plays a similar role as elastic force in viscoelastic fluids. Figure 4(b) shows the dynamic BOAS profile, obtained at a fixed plane (shown in Figure 4(a)) perpendicularly across the channel as the BOAS structure passed through it. Droplets and liquid-thread diameters were nearly constant during the sampling time. The longer term experiments (over 3 min) showed there were slight variations of the two diameters in time, but the essential BOAS structure still remained qualitatively the same as a whole.When the voltage was further increased, the string diameter became larger and the droplet diameter became smaller. Because of the low flow-rate ratio (0.4) between the aqueous phase and oil phase used in the experiment depicted in Figure Figure4,4, the flow did not further develop into a multi-stream laminar flow, as would be expected at a higher voltage, and instead became unstable and irregular. When the flow-rate ratio was increased to 1.0 and the voltage was adjusted to 3.0 kV (corresponding field strength of 1.76 V/μm), we observed a stable multi-stream laminar flow (Figure (Figure5).5). The aqueous stream flowed in the channel center surrounded by the oil phase on the sides. This experiment showed that higher electric-field strengths alone would not give rise to another stable flow pattern (i.e., multi-stream laminar flow), but a suitable flow-rate ratio of aqueous phase to oil phase is required for the formation of stable two-phase laminar flow.Open in a separate window FIG. 5.Micrograph showing multi-stream two-phase laminar flow in the channel. Voltage applied, 3.00 kV (corresponding field strength of 1.76 V/μm); oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.5 μl/min. The scale bar represents 40 μm.The flow patterns we observed may be described by a phase diagram (Figure (Figure6),6), which depends on two dimensionless numbers: capillary number, Ca = μ_aU_a/σ, and electric Bond number, Bo_e = E²(εD/σ). Ca and Bo_e describe the ratio of viscous force to interfacial tension force and the ratio of electric-field force to interfacial tension force, respectively. Here, μ_a (1 mPa s), σ (8.5 mN/m), ε (7.1 × 10⁻¹⁰ F/m), E, U_a, and D are, respectively, the aqueous-phase viscosity, aqueous-oil interfacial tension, aqueous-phase permittivity, electric field strength, aqueous-phase velocity, and the hydraulic diameter of the channel at the junction. Figure Figure66 shows clearly that at higher Ca, flow pattern changes gradually from droplet to BOAS and to multi-stream laminar flow with increasing Bo_e, which indicates the increasing importance of the electric-field force compared with the interfacial tension force. At lower Ca, flow pattern and transition show similar trend with increasing Bo_e as in the higher Ca case, except that multi-stream laminar flow is not observed. The relatively higher viscous force at higher Ca may be necessary for transitioning to the multi-stream laminar flow regime. In addition, Figure Figure66 shows that the BOAS window at the lower Ca is smaller than that at the higher Ca.Open in a separate window FIG. 6.Phase diagram showing different flow patterns in the Ca and Bo_e space. Hollow symbols: oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.5 μl/min. Solid symbols: oil-phase flow rate, 0.5 μl/min; aqueous-phase flow rate, 0.2 μl/min.In summary, we showed the ability to use electric fields to generate and control different flow patterns in two-phase flow. With the aid of an applied field, we were able to generate BOAS flow patterns in a non-viscoelastic fluid, a pattern that typically requires a viscoelastic fluid. The BOAS structure was stable and remained as long as the applied electric field was on. We also report transitional flow patterns, those between droplets and BOAS exhibited both good reversibility as well as synchronicity. And with a suitable flow-rate ratio between the two phases, BOAS flow could be transitioned into a stable two-phase laminar flow by applying a sufficiently high field strength. Finally, a phase diagram was presented to describe quantitatively the flow-pattern regimes using capillary number and electric Bond number. The phenomena we report here on the properties of two-phase flow under an applied electric field may find use in developing a different approach to exert control over droplet based or multi-phase laminar-flow based operations and assays, and also aid in understanding the physics of multi-phase flow. 相似文献

15.

You cannot tell a book by looking at the cover: Cryptic complexity in bacterial evolution

Qiucen Zhang Julia Bos Grigory Tarnopolskiy James C. Sturm Hyunsung Kim Nader Pourmand Robert H. Austin 《Biomicrofluidics》2014,8(5)

相似文献

16.

Water transport to the core–mantle boundary

Michael J Walter 《国家科学评论(英文版)》2021,8(4)

Water is transported to Earth''s interior in lithospheric slabs at subduction zones. Shallow dehydration fuels hydrous island arc magmatism but some water is transported deeper in cool slab mantle. Further dehydration at ∼700 km may limit deeper transport but hydrated phases in slab crust have considerable capacity for transporting water to the core-mantle boundary. Quantifying how much remains the challenge.

Water can have remarkable effects when exposed to rocks at high pressures and temperatures. It can form new minerals with unique properties and often profoundly affects the physical, transport and rheological properties of nominally anhydrous mantle minerals. It has the ability to drastically reduce the melting point of mantle rocks to produce inviscid and reactive melts, often with extreme chemical flavors, and these melts can alter surrounding mantle with potential long-term geochemical consequences. At the base of the mantle, water can react with core iron to produce a super-oxidized and hydrated phase, FeO₂H_x, with the potential to profoundly alter the mantle and even the surface and atmosphere redox state, but only if enough water can reach such depths [1].Current estimates for bulk mantle water content based on the average H₂O/Ce ratio of oceanic basalts from melt inclusions and the most un-degassed basalts, coupled with mass balance constraints for Ce, indicate a fraction under one ocean mass [2], a robust estimate as long as the basalts sampled at the surface tap all mantle reservoirs. The mantle likely contains some primordial water but given that the post-accretion Earth was very hot, water has low solubility and readily degasses from magma at low pressures, and its solubility in crystallizing liquidus minerals is also very low, the mantle just after accretion may have been relatively dry. Thus, it is plausible that most or even all of the water in the current mantle is ‘recycled’, added primarily by subduction of hydrated lithospheric plates. If transport of water to the core–mantle boundary is an important geological process with planet-scale implications, then surface water incorporated into subducting slabs and transported to the core–mantle boundary may be a requirement.Water is added to the basaltic oceanic crust and peridotitic mantle in lithospheric plates (hereafter, slab crust and slab mantle, respectively) at mid-ocean ridges, at transform faults, and in bending faults formed at the outer rise prior to subduction [3]. Estimates vary but about 1 × 10¹² kg of water is currently subducted each year into the mantle [4], and at this rate roughly 2–3 ocean masses could have been added to the mantle since subduction began. However, much of this water is returned to the surface through hydrous magmatism at convergent margins, which itself is a response to slab dehydration in an initial, and large, release of water. Meta-basalt and meta-sediments comprising the slab crust lose their water very efficiently beneath the volcanic front because most slab crust geotherms cross mineral dehydration or melting reactions at depths of less than 150 km, and even if some water remains stored in minerals like lawsonite in cooler slabs, nearly complete dehydration is expected by ∼300 km [5].Peridotitic slab mantle may have much greater potential to deliver water deeper into the interior. As shown in Fig. 1a, an initial pulse of dehydration of slab mantle occurs at depths less than ∼200 km in warmer slabs, controlled primarily by breakdown of chlorite and antigorite when slab-therms cross a deep ‘trough’, sometimes referred to as a ‘choke point’, along the dehydration curve (Fig. 1a) [6]. But the slab mantle in cooler subduction zones can skirt beneath the dehydration reactions, and antigorite can transform directly to the hydrated alphabet silicate phases (Phases A, E, superhydrous B, D), delivering perhaps as much as 5 wt% water in locally hydrated regions (e.g. deep faults and fractures in the lithosphere) to transition zone depths [6]. Estimates based on mineral phase relations in the slab crust and the slab mantle coupled with subduction zone thermal models suggest that as much as 30% of subducted water may have been transported past the sub-volcanic dehydration front and into the deeper mantle [4], although this depends on the depth and extent of deep hydration of the slab mantle, which is poorly constrained. Coincidentally, this also amounts to about one ocean mass if water subduction rates have been roughly constant since subduction began, a figure tantalizingly close to the estimated mantle water content based on geochemical arguments [2]. But what is the likely fate of water in the slab mantle in the transition zone and beyond?Open in a separate window Figure 1.(a) Schematic phase relations in meta-peridotite modified after [6,10,12]. Slab geotherms are after those in [4]. Cold slabs may transport as much as 5 wt% water past ‘choke point 1’ in locally hydrated regions of the slab mantle, whereas slab mantle is dehydrated in warmer slabs. Colder slab mantle that can transport water into the transition zone will undergo dehydration at ‘choke point 2’. How much water can be transported deeper into the mantle and potentially to the core depends on the dynamics of fluid/melt segregation in this region. (b) Schematic showing dehydration in the slab mantle at choke point 2. Migration of fluids within slab mantle will result in water dissolving into bridgmanite and other nominally anhydrous phases with a bulk storage capacity of ∼0.1 wt%, potentially accommodating much or all of the released water. Migration of fluids out of the slab into ambient mantle would also hydrate bridgmanite and other phases and result in net fluid loss from the slab. Conversely, migration of hydrous fluids into the crust could result in extensive hydration of meta-basalt with water accommodated first in nominally anhydrous phases like bridgmanite, Ca-perovskite and NAL phase, but especially in dense SiO₂ phases (stishovite and CaCl₂-type) that can host at least 3 wt% water (∼0.6 wt% in bulk crust).Lithospheric slabs are expected to slow down and deform in the transition zone due to the interplay among the many factors affecting buoyancy and plate rheology, potentially trapping slabs before they descend into the lower mantle [7]. If colder, water-bearing slabs heat up by as little as a few hundred degrees in the transition zone, hydrous phases in the slab mantle will break down to wadsleyite or ringwoodite-bearing assemblages, and a hydrous fluid (Fig. 1a). Wadselyite and ringwoodite can themselves accommodate significant amounts of water and so hydrated portions of the slab mantle would retain ∼1 wt% water. A hydrous ringwoodite inclusion in a sublithospheric diamond with ∼1.5 wt% H₂O may provide direct evidence for this process [8].But no matter if slabs heat up or not in the transition zone, as they penetrate into the lower mantle phase D, superhydrous phase B or ringwoodite in the slab mantle will dehydrate at ∼700–800 km due to another deep trough, or second ‘choke point’, transforming into an assemblage of nominally anhydrous minerals dominated by bridgmanite (∼75 wt%) with, relatively, a much lower bulk water storage capacity (< ∼0.1 wt%) [9] (Fig. 1a). Water released from the slab mantle should lead to melting at the top of the lower mantle [10], and indeed, low shear-wave velocity anomalies at ∼700–800 km below North America may be capturing such dehydration melting in real time [11].The fate of the hydrous fluids/melts released from the slab in the deep transition zone and shallow lower mantle determines how much water slabs can carry deeper into the lower mantle. Presumably water is released from regions of the slab mantle where it was originally deposited, like the fractures and faults that formed in the slab near the surface [3]. If hydrous melts can migrate into surrounding water-undersaturated peridotite within the slab, then water should dissolve into bridgmanite and coexisting nominally anhydrous phases (Ca-perovskite and ferropericlase) until they are saturated (Fig. 1b). And because bridgmanite (water capacity ∼0.1 wt%) dominates the phase assemblage, the slab mantle can potentially accommodate much or all of the released water depending on details of how the hydrous fluids migrate, react and disperse. If released water is simply re-dissolved into the slab mantle in this way then it could be transported deeper into the mantle mainly in bridgmanite, possibly to the core–mantle boundary. Water solubility in bridgmanite throughout the mantle pressure-temperature range is not known, so whether water would partially exsolve as the slab moves deeper stabilizing a melt or another hydrous phase, or remains stable in bridgmanite as a dispersed, minor component, remains to be discovered.Another possibility is that the hydrous fluids/melts produced at the second choke point in the slab mantle at ∼700 km migrate out of the slab mantle, perhaps along the pre-existing fractures and faults where bridgmanite-rich mantle should already be saturated, and into either oceanic crust or ambient mantle (Fig. 1b). If the hydrous melts move into ambient mantle, water would be consumed by water-undersaturated bridgmanite, leading to net loss of water from the slab to the upper part of the lower mantle, perhaps severely diminishing the slab’s capacity to transport water to the deeper mantle and core. But what if the water released from slab mantle migrates into the subducting, previously dehydrated, slab crust?Although slab crust is expected to be largely dehydrated in the upper mantle, changes in its mineralogy at higher pressures gives it the potential to host and carry significant quantities of water to the core–mantle boundary. Studies have identified a number of hydrous phases with CaCl₂-type structures, including δ-AlOOH, ϵ-FeOOH and MgSiO₂(OH)₂ (phase H), that can potentially stabilize in the slab crust in the transition zone or lower mantle. Indeed, these phases likely form extensive solid solutions such that an iron-bearing, alumina-rich, δ-H solid solution should stabilize at ∼50 GPa in the slab crust [12], but only after the nominally anhydrous phases in the crust, (aluminous bridgmanite, stishovite, Ca-perovskite and NAL phase) saturate in water. Once formed, the δ-H solid solution in the slab crust may remain stable all the way to the core mantle boundary if the slab temperature remains well below the mantle geotherm otherwise a hydrous melt may form instead [12] (Fig. 1a). But phase δ-H solid solution and the other potential hydrated oxide phases, intriguing as they are as potential hosts for water, may not be the likely primary host for water in slab crust. Recent studies suggest a new potential host for water—stishovite and post-stishovite dense SiO₂ phases [13,14].SiO₂ minerals make up about a fifth of the slab crust by weight in the transition zone and lower mantle [15] and recent experiments indicate that the dense SiO₂ phases, stishovite (rutile structure—very similar to CaCl₂ structure) and CaCl₂-type SiO₂, structures that are akin to phase H and other hydrated oxides, can host at least 3 wt% water, which is much more than previously considered. More importantly, these dense SiO₂ phases apparently remain stable and hydrated even at temperatures as high as the lower mantle geotherm, unlike other hydrous phases [13,14]. And as a major mineral in the slab crust, SiO₂ phases would have to saturate with water first before other hydrous phases, like δ-H solid solution, would stabilize. If the hydrous melts released from the slab mantle in the transition zone or lower mantle migrate into slab crust the water would dissolve into the undersaturated dense SiO₂ phase (Fig. 1b). Thus, hydrated dense SiO₂ phases are possibly the best candidate hosts for water transport in slab crust all the way to the core mantle boundary due to their high water storage capacity, high modal abundance and high-pressure-temperature stability.Once a slab makes it to the core–mantle boundary region, water held in the slab crust or the slab mantle may be released due to the high geothermal gradient. Heating of slabs at the core–mantle boundary, where temperatures may exceed 3000°C, may ultimately dehydrate SiO₂ phases in the slab crust or bridgmanite (or δ-H) in the slab mantle, with released water initiating melting in the mantle and/or reaction with the core to form hydrated iron metal and super oxides, phases that may potentially explain ultra-low seismic velocities in this region [1,10]. How much water can be released in this region from subducted lithosphere remains a question that is hard to quantify and depends on dynamic processes of dehydration and rehydration in the shallower mantle, specifically at the two ‘choke points’ in the slab mantle, processes that are as yet poorly understood. What is clear is that subducting slabs have the capacity to carry surface water all the way to the core in a number of phases, and possibly in a phase that has previously seemed quite unlikely, dense SiO₂. 相似文献

17.

Analysis of Modification of Liver Proteome in Diabetic Rats by 2D Electrophoresis and MALDI-TOF-MS

Dhanaraj Karthik Soundherrajan Ilavenil Balasubramanian Kaleeswaran Sivanesan Ravikumar 《Indian journal of clinical biochemistry : IJCB》2012,27(3):221-230

The uncontrolled hyperglycemia can lead to disturbances in the cell structure and functions of organs. This study was performed to analyze the “differential proteome” change in rat liver associated with diabetes mellitus in relation to effects of an anti-diabetic herb, Cynodon dactylon leaf extracts. Rats were intraperitoneally injected with alloxan (150 mg/kg/bw) and treated with C. dactylon leaf extracts (450 mg/kg/bw/day/orally). The liver proteins were subjected to proteome analysis using the advanced technologies i.e., 2D electrophoresis (2-DE) and mass spectrometry. Comparison of 2-DE protein distribution profiles among the livers from normal, alloxan-induced diabetic rats and alloxan-induced diabetic rats treated with C. dactylon leaves identified three proteins that were up-regulated in alloxan-induced diabetic rats i.e., nucleophosmin, l-xylulose reductase and carbonic anhydrase III which are known to be mainly involved in ribosome biogenesis, centrosome duplication, cell proliferation, tumor suppression, glucose metabolism, osmo-regulation, water–CO₂ balance and acid–base balance. These results help us to understand the elucidation of molecular mechanism connected to liver function and insulin associated with diabetes mellitus. These identified proteins were primarily involved in cell proliferation and homoeostasis of liver tissues upon the treatment with C. dactylon leaf extracts. 相似文献

18.

Separation of DNA by length in rotational flow: Lattice-Boltzmann-based simulations

Faihan Alfahani Michael Antonelli Jennifer Kreft Pearce 《Biomicrofluidics》2015,9(4)

We use a lattice-Boltzmann based Brownian dynamics simulation to investigate the separation of different lengths of DNA through the combination of a trapping force and the microflow created by counter-rotating vortices. We can separate most long DNA molecules from shorter chains that have lengths differing by as little as 30%. The sensitivity of this technique is determined by the flow rate, size of the trapping region, and the trapping strength. We expect that this technique can be used in microfluidic devices to separate long DNA fragments that result from techniques such as restriction enzyme digests of genomic DNA.The development of novel methods for manipulating biopolymers such as DNA is required for the continued advancement of microfluidic devices. Techniques such as restriction enzyme digests for genomic sequencing rely on the detection of DNA that differ in length by sometimes thousands of base pairs.¹ Methods that separate DNA strands with resolutions on the order of kilobase pairs are required to analyze the products of this technique. To gain an insight into possible techniques to separate polymers, it can be helpful to review the methods to separate particles in microfluidic devices. Experimental work has shown how hydrodynamic mechanisms can lead to separation of particles based on size and deformability.² Eddies, microvortices, and hydrodynamic tweezers have been used to trap and sort particles. The mechanism of the trapping and sorting arises from the differences between interactions of the particles with the fluid.^2–8 In particular, counter-rotating vortices have been used to sort particles and manipulate biopolymers. They have been used to deposit DNA precisely across electrodes⁹ and trap DNA.^10,11 Vortex flow may therefore be a good basis for a technique for sorting DNA by length.Streaming flow has been used in experiments to separate colloids of different size.^3,4 Particles are passed through a channel with a flow field driven by oscillating bubbles and pressure. The flow field becomes a combination of closed and open streamlines. The vortex flow is controlled by the accoustic driving of the bubbles while pressure controls the net flow of the fluid. Larger particles are trapped in the closed vortex flow created by the bubbles, while smaller particles can escape the neighborhood of a bubble in the open streamlines. This leads to efficient separation of particles with size differences as small as 1 μm.Previous work on DNA has shown that counter-rotating vortices can be used to trap DNA dynamically. Long strands of DNA have been observed to stretch between the centers of two counter-rotating vortices. The polymer stays trapped in this state for significant amounts of time.¹² In a different experiment, the vortices were used to thermally cycle the polymer and allow replication via the polymerase chain reaction (PCR). The DNA is also trapped against one wall by a thermophoretic force in these experiments.¹⁰ The strength of the trap is controlled by the gradient in temperature created by a focused infrared laser beam.Trapping DNA at one wall by counter-rotating vortices has also been explored in simulation and found to depend on the Peclet number, Pe = u_maxL/D_m, where u_max is the maximum speed of the vortex, L is the box size, and D_m is the diffusion coefficient of one bead in the polymer chain.¹¹ The trapping rate of the DNA was shown to depend on the competition between the flow compressing the DNA into the trap region and the diffusion of the DNA out of the trap. For the work presented here, Pe ≅ 2000, similar to the previous work done with the same simulation.We extend the previous work to investigate if counter-rotating vortices can be used to separate DNA of different lengths. We use the same type of simulation outlined in Refs. ¹¹ and ^13–17, based on the lattice-Boltzmann method. The simulation method has successfully modeled systems as diverse as thermophoresis of DNA,¹⁴ migration of DNA in a microchannel,¹⁶ and translocation of DNA through a micropore.^17,18 Using this method, the fluid is broken into a lattice with size, ΔL, chosen to be 0.5 μm, and is coupled to a worm-like chain model with Brownian dynamics for the polymer.^19,20 The fluid velocity distribution function, n_i(r, t), describes the fraction of fluid particles with a discretized velocity, c_i, at each lattice site.^21–24 A discrete velocity scheme with nineteen different velocities in three dimensions is used. The velocity distributions will evolve according to

n_{i} (r + c_{i} Δ τ, t + Δ τ) = n_{i} (r, t) + L_{i j} [n_{j} (r, t) - n_{j}^{e q} (r, t)],

(1)where L is a collision operator such that the fluid relaxes to the equilibrium distribution,

n_{i}^{e q}

given by a second-order expansion of the Maxwell-Boltzmann distribution

n_{i}^{e q} = ρ a^{c_{i}} [1 + (c_{i} \cdot u) / c_{s}^{2} + u u : (c_{i} c_{i} - c_{s}^{2} I) / (2 c_{s}^{4})],

(2)where

c_{s} = \sqrt{1 / 3} Δ L Δ τ

is the speed of sound. Δτ is the time step for the fluid in the simulation, Δτ = 8.8 × 10⁻⁵. The coefficients a^c_i are determined by satisfying a local isotropy condition

\sum_{i} a^{c_{i}} c_{i α} c_{i β} c_{i γ} c_{i δ} = c_{s}^{4} (δ_{α β} δ_{γ δ} + δ_{α γ} δ_{b e t a γ} + δ_{α δ} δ_{β γ}) .

(3)To simplify computation, the velocity distributions are transformed into moment space. The density ρ, momentum density j, and momentum flux density Π are some of the hydrodynamic moments of n_i(r, t). The equilibrium conditions for these three moments are given by

ρ = \sum n_{i}^{e q},

(4)

j = \sum c_{i} \cdot n_{i}^{e q},

(5)

Π = \sum n_{i}^{e q} \cdot c_{i} c_{i} .

(6)L has eigenvalues

τ_{0}^{- 1}, τ_{1}^{- 1}, \dots, τ_{18}^{- 1}

, which are the characteristic relaxation times of the moments. The Bhatanagar-Gross-Krook model is used to determine L:²⁵ the non-conserved moments have a single relaxation time, τ_s = 1.0. The conserved moments are density and momentum; for these, τ⁻¹= 0. Fluctuations are added to the fluid stress as in the method of Ladd.²⁴ We have also compared simulations with lattice sizes of 1 μm and 0.25 μm and found no significant differences in the results.The DNA used in the simulation is represented by a worm-like chain model parameterized to capture the dynamics of YOYO-stained λ DNA in bulk solution at room temperature.^15,16,26 Long, flexible DNA is modeled since techniques to separate long DNA molecules with kilobase pair resolution are necessary to complete techniques such as genomic level sequencing using restriction enzyme digests.¹ In addition, such DNA is often used in experiment. Its properties are similar to unstained DNA or DNA stained by other methods.²⁷ Each molecule is represented by N_b beads and N_b − 1 springs. A chain composed of N_b − 1 springs will have a contour length of (N_b − 1) × 2.1 μm. The forces acting on each monomer include: an excluded volume force, a non-linear spring force, the viscous drag force, a random force that produces Brownian motion, a repulsive force from the container walls, and an attractive trapping force only at one wall as shown in Fig. Fig.11.¹³ The excluded volume interaction between beads i and j located at r_i and r_j is modeled using the following potential:

U_{i j}^{e v} = \frac{1}{2} k_{B} T ν N_{k s}^{2} (\frac{3}{4 π S_{s}^{2}}) exp (\frac{- 3 | r_{i} - r_{j} |^{2}}{4 S_{s}^{2}}),

(7)where

ν = σ_{k}^{3}

is the excluded volume parameter with σ_k = 0.105 μm, the length of one Kuhn segment, N_ks = 19.8 is the number of Kuhn segments per spring, and

S_{s}^{2} = N_{k s} / 6) σ_{k}^{2}

is the characteristic size of the bead. This excluded volume potential reproduces self avoiding walk statistics. The non-linear spring force is based on force-extension curves from experiments and is given by

f_{i j}^{S} = \frac{k_{B} T}{2 σ_{k}} [{(1 - \frac{| r_{j} - r_{i} |}{N_{k s} σ_{k}})}^{- 2} + 4 \frac{| r_{j} - r_{i} |}{n_{K} σ_{k}} - 1] \frac{r_{j} - r_{i}}{| r_{j} - r_{i} |},

(8)which applies when N_ks ≫ 1.Open in a separate window FIG. 1.Simulation set-up. Arrows indicate direction of fluid flow. The region where the trapping force is active is shaded, and its width (X_stick) is shown. The region used to determine the trapping rate is indicated by the area labeled trap region. Figure is not to scale, the trap region and X_stick are smaller than shown.The beads are modeled as freely draining but subject to a drag force given by F_f = ?6πηa(u_p ? u_f).(9)The beads are also subjected to a random forcing term that is drawn from a Gaussian distribution with zero mean and a variance σ_v = 2k_BTζΔt.(10)The random force reproduces Brownian motion. To conserve total momentum, the momentum change imparted to the beads through their interactions with the fluid is balanced by a momentum change in the fluid. The momentum change is distributed to the three closest fluid lattice sites using a linear interpolation scheme based on the proximity of the lattice site to the polymer beads. Through this momentum transfer, hydrodynamic interactions between the beads occur.The beads are repelled from the walls with a force of magnitude

F_{w a l l} = \frac{250 k_{B} T}{σ_{k}^{3} {(x_{b e a d} - x_{w a l l})}^{2}}, x_{b e a d} > (x_{w a l l} - 1),

(11)where the repulsion range is 1ΔL. Each monomer will also be attracted to the top wall by a force with magnitude

F_{s t i c k} = \frac{K_{s t i c k} k_{B} T}{σ_{k}^{3} {(x_{b e a d} - x_{w a l l} + 10)}^{2}}, x_{b e a d} > (x_{w a l l} - X_{s t i c k})

(12)and range X_stick (see Fig. Fig.1).1). The sticking force is turned off every one out of one hundred time steps of the polymer (1% of the simulation time steps). We vary both X_stick and K_stick to achieve separation of the polymers.In previous experiments, DNA has been trapped against one wall by using thermophoresis,¹⁰ dielectrophoresis,²⁸ and nanoplasmonic tweezers.²⁹ In the case of thermophoresis, the trap strength (K_stick) can be controlled by tuning the intensity of the temperature gradient and the trap extension (X_stick) can be controlled through the area over which the gradient extends. Both of these are set through focusing of the laser used to produce local heating. Similarly, the trap parameters can be controlled when using plasmonic tweezers by controlling the laser beam exciting the nanoplasmonic structures. In dielectrophoresis, the DNA is trapped by an AC electric field and can be controlled by tuning the frequency and amplitude of the field.In this work, the number of polymers, N_p, is 10 unless otherwise noted, and the container size is 25 ΔL × 50 ΔL × 2 ΔL. The time step for the fluid is Δτ = 8.8 × 10⁻⁵ s, and for the polymer is Δt = 3.7 × 10⁻⁶ s. The total simulation time is over 100 chain relaxation times, allowing sufficient independent samples to perform statistical analysis.Two counter-rotating vortices, shown in 1, are produced by introducing external forces to the fluid bound by walls in the x-direction and periodic in the y and z. Two forces of equal magnitude push on the fluid in the upper x region (12ΔL < x < 25ΔL): one in the +y-direction along y = 10ΔL, and one in the –y-direction along y = 40ΔL. Such counter-rotating vortices can be produced in microfluidic channels using acoustically driven bubbles,^3,4,30 local heating,¹⁰ or plasmonic nanostructures.⁵ The flow speed is controlled by very different external mechanisms in each case. We therefore choose a simple model to produce fluid flow that is not specific to one mechanism.The simulations are started using random initial conditions, and therefore, both lengths of polymer are dispersed throughout the channel. Within a few minutes, the steady state configurations pictured in Figs. Figs.22 and and33 are reached. We define the steady state as when the number of polymer chains in the trap changes by less than one chain (10 beads) per 1000 polymer time steps. Intermittently, some polymers may still escape and re-enter the trap even in the steady state. Three final configurations are possible: Both the lengths of DNA have become trapped, both lengths continue to rotate freely, or the shorter strand has become trapped while the longer rotates freely. Two of these states leave the polymers mixed; in the third, the strands have separated by size.Open in a separate window FIG. 2.Snapshots at t = 0Δt (left) and t = 2500Δt (right) showing the separation of 15-bead strands (grey) from 10-bead strands (black) of DNA. For these simulations, K_stick = 55 and Y_stick = 0.7ΔL.Open in a separate window FIG. 3.Snapshots at t = 0Δt and t = 2500Δt showing the separation of 13-bead strands (grey) from 10-bead strands (black) of DNA. For these simulations, K_stick = 55 and Y_stick = 0.7ΔL as in Fig. Fig.2.2. Note that one long polymer is trapped, as well as all of the shorter polymers.By tuning the attractive wall force parameters and fluid flow, the separated steady state can be realized. We first set the flow parameters that allow the larger chains to rotate freely at the center of the vortices while the shorter chains rotate closer to the wall. The trap strength, K_stick, and extension, X_stick, are changed until the shorter polymers do not leave the trap. The same parameters were used to separate 10-bead chains from 15-bead and 13-bead chains.As shown in Fig. Fig.2,2, we have been able to separate shorter 10-bead chains from longer 15-bead chains. In the steady state, 97% of the rotating polymers were long polymers averaged over twenty simulations initialized with different random starting conditions. For three simulations, one small polymer would intermittently leave the trap region. In two of these simulations, one long polymer became stably trapped in the steady state. In another simulation, one 15-bead chain was intermittently trapped. On average, the trapped polymers were 5% 15-bead chains and 95% 10-bead chains. Again, 97% of the rotating polymers were 15-bead chains.Simulations conducted with 10-bead and 13-bead chains also showed significant separation of the two sizes as can be seen in Fig. Fig.3.3. In the steady state, 30% of the trapped polymers are 13-bead chains and 70% are 10-bead chains, averaged over twenty different random initial starting conditions and 1000 polymer time steps. Only 14.8% of the shorter polymers were not trapped, leading to 85.2% of the freely rotating chains being 13-bead chains. This is therefore a viable test to detect the presence of these longer chains.We have also separated 20-bead chains from 10-bead chains with all of the shorter chains trapped and all of the longer chains freely rotating in the steady-state. These results do not change for twenty different random initial starting conditions and 1000 polymer time steps. None of the longer polymers intermittently enter the trap region nor do any of the shorter polymers intermittently escape.The separation is achieved by tuning the trapping force and flow rate. Strong flows will push all the DNA molecules into the trap. The final state is mixed, with both short and long strands trapped. For flows that are too weak, the short molecules are not sufficiently compressed by the flow and therefore do not enter the trap region. The end state is mixed, with all polymers freely rotating. Separation is achieved when the flow rate is tuned so that the short strands are compressed against the channel wall while the long polymers rotate near the center of the vortices. The trap strength must then be set sufficiently high enough to prevent the short strands from being pulled by the hydrodynamic drag force out of the trap.The mechanism of the separation depends on the differences in the steady state configurations of the polymers and chances of a polymer escaping the trap. As shown in Fig. Fig.4,4, both longer and shorter chains are pulled into the trap region by the flow. However, the longer chains have a larger chance of a bead escaping into a region of the flow where the fluid velocity is sufficient to pull the entire strand out of the trap. As shown in Ref. ¹¹, the trapping rate depends on diffusion in a polymer depleted region near the trap, in agreement with classical theory which neglects bead-wall interactions. In addition, the theory depends on the single bead diffusion rate and does not take into account the elastic force holding the beads together. Diffusion becomes as significant as convection in the polymer depleted region leading to dependence on the Peclet number. Since longer polymers have more beads; they have more chances of a single bead diffusing through this layer into the region where convection is again more important. Thus, they are pulled out of the trap at a faster rate than the shorter chains.Open in a separate window FIG. 4.N, number of beads in the trap region, versus time for 15-bead DNA strands (solid line) and 10-bead DNA strands (dashed line). Here, ΔT = 10000Δt. The simulation parameters are the same as in Fig. Fig.22.In addition, longer chains have a second trap resulting from the microflow. As shown in Ref. ¹², DNA in counter-rotating vortices can tumble at the center of one vortex or be stretched between the centers of the two vortices. We have observed both these conformations for the longer polymer strand. They are a stable trajectory for the longer polymer that remains outside of the trapping region. As seen in Fig. Fig.4,4, few monomers of the longer chains enter the trap region once the steady state has been reached. However, the shorter polymer rotates at a larger radius than the longer polymer as seen in Fig. Fig.5.5. The shorter polymers therefore are pushed back into the trap while the longer strands rotate stably outside the trapping region.Open in a separate window FIG. 5.Trajectories of 15-bead DNA (grey) and 10-bead DNA (black). The position of each monomer is plotted for 100 consecutive time steps. Note that the longer polymers rotate in the center of the channel while the shorter polymers rotate at the edges. Simulation parameters are the same as in Fig. Fig.22.This mechanism is similar to the one proposed for the separation of colloids by size in Refs. ³ and ⁴. In that experimental work, the smaller colloidal particles rotated at larger radii. This allowed the smaller beads to be pushed out of the vicinity of the vortices by the streaming flow, while the larger beads continued to circle. However, in our simulations, we have the additional mechanism of separation based on the increased chance of a longer polymer escaping the trap region. This mechanism is important for maintaining the separation. Long polymers initially in the trap region or which diffuse into the trap would not be able to escape without it.We expect that this technique could be used to detect the sizes of DNA fragments on the order of thousands of base pairs. It relies on the flexibility of the molecule and its interaction with the flow. Common lab procedures such as restriction enzyme digests for DNA fingerprinting can produce these long fragments. Current techniques such as gel electrophoresis require significant time to separate the long strands that move more slowly through the matrix. This effect could therefore be a good candidate for developing a microfluidic analysis that is significantly faster than traditional procedures. Our separation occurs in minutes rather than in hours as for gel electrophoresis.As pointed out in Ref. ², hydrodynamic effects have been shown to be important for microfluidic devices for separation. We have demonstrated, in simulation, a novel hydrodynamic mechanism for separating polymers by length. We hope that these promising calculations will inspire experiments to verify these results. 相似文献

19.

Exploring Social Theory as a Framework for Social and Cultural Measurements of the Information Society

Pille Pruulmann-Vengerfeldt 《The Information Society》2013,29(5):303-310

Using Layder's domain theory (1997) Layder, D. 1997. Modern social theory:Key debates and new directions, London: UCL Press. [Google Scholar] as an analytical framework, this article shows how the information society can be measured through various levels of society. Layder's notions of psychobiography, situated activity, social setting, and contextual resources help identify cultural and social indicators for understanding changes in the information society. With the help of empirical indicators for each domain, this article uses the case of Estonia to show that there is often more to the information society than what is captured by traditional measures. This article calls for a context-sensitive approach, which takes into consideration social and cultural indicators. Measurements from all four domains are necessary for understanding the complexity of information-society-related issues. 相似文献

20.

Croatian Society of Medical Biochemistry and Laboratory Medicine

《Biochemia medica : ?asopis Hrvatskoga dru?tva medicinskih biokemi?ara / HDMB》2013,23(2):A56-A61

Introduction:

Intensive exercising may significantly damage muscles which is reflected in pain, fatigue and the increase of muscle proteins concentrations in blood such are creatinin kinase (CK), lactic dehydrogenase (LD), myoglobin (MB) and other biochemical parameters including urea serum concentration (SU). Biochemical markers vary with age, sex, race, muscle mass, physical activity and climate conditions. They also assist us in determining the limit between the capacity for adaptation to given training process which results in supercomepensation and in condition of overtraining (OT), in the case of load that exceeds the physiologic potential of regeneration. Concerning the problem of diagnosis and explanation of the symptoms of overtraining, markers that can apply reliably and with sufficient sensitivity and simplicity of interpretation in the praxis are sought. It is critical to take into account difference among individuals and groups that could hamper the interpretation.

The most frequently used markers:

The most frequently used biomarkers that provide us with the information on physical activity and on the amount of load through exercise are CK, SU and LD. Level of serum retaining kinas has been measured and interpreted for years as part of different scientific and professional investigations and presents one of basic parameters for determining the level of muscle damage. It reaches maximal concentration of the fourth day of exercising which depends on the type of exercise and the nature of stress triggered by exercise but also on individual characteristics.The level of serum urea presents marker of nitric compounds metabolism and is the principle chemical substance in the urine of mammals. It is thus possible to draw a parallel between the increases of serum urea concentration on increased degradations of proteins. Significant fall of serum amino acid levels occurs after sixty to seventy minutes of exercising with the increase of urea and free tyrosine and these changes have high correlation with the duration and intensity of.LD changes are important index of well-trained sportsmen and their capability to withstand the pace and force during strain in the training process. The level of LD is a good index of exercise intensity and marker of metabolic exchange in tissues whose concentration in serum is dependent of cell damage.

Conclusion:

There is not a single, unique parameter that would provide enough valuable information for the estimation of the quality of exercising, amount of load and identification of overtraining. Delayed measurement of biomarkers is far from ideal, but it is obvious that the amount of stress/ load in training is the most important factor for the development of state of overtraining. Daily body weight control, diet, biochemical indices values and the input of water should be known and standardized before measurements. For the most of parameters determination of basal levels are needed in specific populations for more accurate interpretation and evaluation of results. The sampling process itself should be under the most strict conditions of standardization by repeating measurement at least every third day. Dependence of mentioned parameters (SU, CK, LD) on exercise intensity varies among individuals and without these additional measurements and subpopulation evaluations it is difficult to come to conclusions with certainty as well as to come to conclusions on causative correlations of training load and dynamic in biochemical parameters.

Biochem Med (Zagreb). 2013 Jun; 23(2): A56–A61.

Common sports injuries

Biochem Med (Zagreb) 2013 Jun; 23(2): A57–A58. Published online 2013 Jun 15. doi: 10.11613/BM.2013.027

Common sports injuries

Miljenko FranićAuthor information Copyright and License information DisclaimerDubrava University Hospital, ZagrebCorresponding author: rh.dbk@cinarfm©Copyright by Croatian Society of Medical Biochemistry and Laboratory MedicineThis is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Sports injuries are injuries that occur in athletic activities and can be broadly classified as either traumatic or overuse injuries. Traumatic injuries because of the dynamic and high collision are nature of some sports. Overuse injuries cause wear and tear on the body, particularly on joints subjected to repeated activity.At every age, competitive and recreational athletes sustain a wide variety of soft tissue, bone, ligament, tendon and nerve injuries, caused by direct trauma or repetitive stress. Different sports are associated with different patterns and types of injuries, whereas age, gender and type of activity influence the prevalence of injuries. Sports trauma commonly affects joints of the extremities or the spine.The hip, knee and ankle are at risk of developing osteoarthritis (OA) after injury or in the presence of malalignment, especially in association with high impact sport. Spine pathologies are associated more commonly with certain sports. Upper extremity syndromes caused by a single stress or by repetitive micro-trauma occur in a variety of sports.Random control trials expose some subjects, but not others, to an intervention. This is more clinical in nature and not typically appropriate for the study of injury patterns. Cohort studies monitor both injured and non-injured athletes, thereby providing results on the effects of participation. Case-control studies monitor only those athletes who suffered an injury. The Ideal study would be Cohort design conducted over several teams, with longitudinal prospective data collection and one recorder where possible, as well as uniformity of injury definition across sports so comparisons between studies can be made accurately.Physical injury is an inherent risk in sports participation and, to a certain extent, must be considered an inevitable cost of athletic training and competition. Injury may lead to incomplete recovery and residual symptoms, drop out from sports, and can cause joint degeneration in the long term.Advances in arthroscopic techniques allow operative management of most intraarticular post-traumatic pathologies in the lower and upper limb joints, but long-term outcomes are not available yet. It is important to balance the negative effects of sports injuries with the many benefits that a serious commitment to sport brings.

Biochem Med (Zagreb). 2013 Jun; 23(2): A56–A61.

Determination of sample size and number of study groups in sport studies

Biochem Med (Zagreb) 2013 Jun; 23(2): A58–A59. Published online 2013 Jun 15. doi: 10.11613/BM.2013.027

Determination of sample size and number of study groups in sport studies

Mladen PetrovečkiAuthor information Copyright and License information DisclaimerDepartment of Laboratory Diagnosis, Dubrava University Hospital, Zagreb, Croatia, and Department of Medical Informatics, Rijeka University School of Medicine, RijekaCorresponding author: rh.irdem@pnedalm;©Copyright by Croatian Society of Medical Biochemistry and Laboratory MedicineThis is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 相似文献