基于数字光刻投影系统的快速微加工技术

设计一种经济有效的微流体芯片加工方法,可以快速地在聚二甲基硅氧烷（PDMS）表面加工出不同尺寸的微流路。 利用商用数字投影仪的成像原理,对其进行简单的改装,得到成缩小像的数字光刻投影系统（DLPS）,并利用该系统在PDMS表面加工微流路;同时通过荷叶效应和毛细吸附效应两组实验,对DLPS的加工性能进行了验证和应用。 该DLPS可在PDMS表面加工微结构,最小稳定加工精度可达40 m,通过模仿荷叶效应获得的材料表面,其疏水角增加到1233。 该DLPS系统可用于快速加工微流体芯片,当流路尺寸要求不是很严格时,低成本和高效率等优点使该系统完全适合在普通实验室开展微流体技术的研究。     

Influence of Fluid Flow Distribution in Micro-Channel Arrays to Phase Transition Processes

Microstructured heat exchangers are well suited for such phase transition processes as evaporation of liquids due to their heat transfer capabilities, being two to three orders of magnitude higher than those of conventional heat transfer devices. Controlling liquid evaporation inside micro-channels to provide full evaporation in a stable way is not trivial. In most cases, such instabilities as slug flow, bubbly flow, or vapor clogging occur, based on cross-talk possibilities between the individual micro-channels of a channel array, normally caused by open void inlet structures. Therefore, fluid inlet distribution is inhomogeneous, which results, in the best case, in a parabolic shape of a stable evaporation frontline. The parabolic shape occurs due to the residence time distribution of the fluid, generated by shorter path length in the array center and longer ones in the outer areas of the micro-channel array. Computational fluid dynamics simulation approves this result. Such a frontline can be kept stable when the process parameters are well controlled. Small deviations of the inlet parameters may lead to strong disturbances of the evaporation process, destabilizing it. When changing the inlet fluid distribution system to provide the most equal flow distribution possible, the span of the parabolic shape of the evaporation frontline can be reduced drastically. Finally, a stable evaporation frontline perpendicular to flow direction can be obtained. This status is no longer very sensitive to process deviations.

This article presents an optimized micro-channel device for the optical investigation of phase transition phenomena. The device allows the exchange of integrated micro-channel arrays to investigate different designs for their suitability. It is separated into three independent sections, which can be heated or cooled individually. Therefore, very strict and rapid temperature jumps can be obtained within relatively short distances. The micro-channel array foils used for the experiments have been manufactured by mechanical micro-machining. Thus, the cross-sections of the micro-channels are always rectangular. Hydraulic diameter and length of the micro-channels, as well as the shape of the inlet and outlet voids, can be varied. Using a simple triangular or rectangular open inlet void, a stable evaporation line was generated, showing a parabolic shape. Depending on the mass flow and the size and shape of the inlet void, the span of the parabolic arc was influenceable.     

Iron oxide nanoparticles for use as an MRI contrast agent: pharmacokinetics and metabolism

The pharmacokinetics and metabolism of a new preparation of superparamagnetic iron oxide nanoparticles were evaluated by 59Fe radiotracer studies and histologic examination of mice liver and spleen tissues (light and transmission electron microscopy). In the first 30 min following IV injection of the product half of the dose injected remains in the blood, the other part being sequestered mainly by the mononuclear phagocyte system (MPS). In the first five days following IV administration of the nanoparticles, early metabolization of the iron oxide cores occurs, revealed by modification of their aspect in the lysosomes of Kupffer cells and macrophages of the splenic red pulp. The incorporation of 59Fe is then observed in RBC of the mice. These results are discussed in relation with the physicochemical properties of this new preparation of nanoparticles, and compared with current pharmacokinetic data concerning injectable particle systems.     

大功率光导开关硅微通道散热器设计与测试

 因焦耳加热导致光导开关芯片温度升高并形成局部热点,影响了光导开关功率容量、重复频率和寿命的提高,因此需对光导开关进行主动冷却。设计了一种矩形微槽硅微通道散热器,其由散热器本体和盖板两部分组成,散热器本体上设有分流槽、矩形微槽阵列、汇流槽,盖板通过半导体刻蚀工艺形成通孔,两部分通过硅-硅键合工艺连接以形成闭合通道。以水为工质,实验测试了不同冷却工质流量、进口温度时微通道散热器的换热性能、温度均匀性和流体阻力,证明该微通道散热器在适中的冷却工质流量下具有较高的换热性能、较低的流体阻力和较好的温度均匀性,满足重复频率大功率光导开关的散热冷却需求。     

NMR-based metabonomic analysis of MnO-embedded iron oxide nanoparticles as potential dual-modal contrast agents

MnO-embedded iron oxide nanoparticles (MnIO-NPs) can be treated as potential dual-modal contrast agents. However, their overall bio-effects and potential toxicity remain unknown. In this study, the metabolic effects of MnIO-NPs (dosed at 1 and 5 mg Fe/kg) on Sprague–Dawley rats were investigated using metabonomic analysis, histopathological examination, and conventional biochemical analysis. The histological changes included a focal inflammation in the liver at high-dose and a slightly enlarged area of splenic white pulp after 48 h post-dose. Blood biochemical analysis showed that albumin, globulins, aspartate aminotransferase, lactate dehydrogenase, blood urea nitrogen, and glucose changed distinctly compared to the control. The metabonomic analysis of body fluids (serum and urine) and tissues (liver, kidney, and spleen) indicated that MnIO-NPs induced metabolic perturbation in rats including energy, nucleotides, amino acids and phospholipid metabolisms. Besides, the variations of supportive nutrients: valine, leucine, isoleucine, nicotinamide adenine dinucleotide (phosphate), and nicotinamide, and the conjugation substrates: glycine, taurine, glutamine, glutathione, and methyl donors (formate, sarcosine, dimethylglycine, choline, and betaine) were involved in detoxification reaction of MnIO-NPs. The obtained information would provide identifiable ground for the candidate selection and optimization.

     

毛细微模塑实现单链微球的有序排列

以微米级的聚苯乙烯微球当作真实大分子链的结构单元,用软刻蚀的毛细微模塑法在玻璃基片上把它们组装成单链形状的微球串,加热使微球相互连接,从而为“亚观”尺度上模拟“大分子”链(刚性链)提供简单又直观的“模型”．并把基片上的模型链剥离下来,处于自由态．     

复杂微通道内非混相驱替过程的格子Boltzmann方法

本文采用改进的基于伪势模型的格子Boltzmann方法研究复杂微通道内的非混相驱替问题.这种方法克服了原始伪势模型中计算结果对网格步长的依赖.首先用Laplace定律验证模型的正确性,然后用该方法研究壁面润湿性、粗糙结构、黏性比以及距离对非混相驱替过程的影响.模拟结果表明:与壁面粗糙结构和黏性比相比,壁面润湿性的影响是决定性的因素.随着接触角的增加,驱替效率增加,当接触角大于某一值后,驱替效率不再变化;随着黏性比的增加,驱替效率增加;而壁面粗糙性对驱替过程的影响较复杂,只有凸起半圆的半径在一定范围内增加时,驱替效率增加;距离较小时将促进驱替过程.     

Two-phase flow boiling heat transfer of FC-72 in parallel micro-channels

Experimental research is performed on two-phase flow boiling heat transfer in micro-channels. FC-72 is used as the working fluid. In order to analyze the heat transfer mechanism during two-phase flow boiling, the dimensionless parameters, e.g., boiling number and convection number, are used, and the effect of these parameters on the heat transfer can be confirmed during flow boiling in the micro-channel. In addition, the transition criterion from bubbly/slug flow to annular flow is proposed from the modified Weber number. Based on the boiling heat transfer mechanism obtained from the experiments, a new correlation is proposed to predict the heat transfer coefficient. The new correlation predicts well the experimental results within a mean absolute error of 5.2%.     

Numerical model for light propagation and light intensity distribution inside coated fused silica capillaries

Numerical simulations of light propagation through capillaries have been reported to a limited extent in the literature for uses such as flow-cell design. These have been restricted to prediction of light path for very specific cases to date. In this paper, a new numerical model of light propagation through multi-walled cylindrical systems, to represent coated and uncoated capillaries is presented. This model allows for light ray paths and light intensity distribution within the capillary to be predicted. Macro-scale (using PMMA and PC cylinders) and micro-scale (using PTFE coated fused silica capillaries) experiments were conducted to validate the model's accuracy. These experimental validations have shown encouragingly good agreement between theoretical predictions and measured results, which could allow for optimisation of associated regions for monolith synthesis and use in fluidic chromatography, optical detection systems and flow cells for capillary electrophoresis and flow injection analysis.     

Signalling crosstalk in FGF2-mediated protection of endothelial cells from HIV-gp120

Background  

The blood brain barrier (BBB) is the first line of defence of the central nervous system (CNS) against circulating pathogens, such as HIV. The cytotoxic HIV protein, gp120, damages endothelial cells of the BBB, thereby compromising its integrity, which may lead to migration of HIV-infected cells into the brain. Fibroblast growth factor 2 (FGF2), produced primarily by astrocytes, promotes endothelial cell fitness and angiogenesis. We hypothesized that treatment of human umbilical vein endothelial cells (HUVEC) with FGF2 would protect the cells from gp120-mediated toxicity via endothelial cell survival signalling.     

Plasticity of human dental pulp stromal cells with bioengineering platforms: A versatile tool for regenerative medicine

In recent years, human dental pulp stromal cells (DPSCs) have received growing attention due to their characteristics in common with other mesenchymal stem cells, in addition to the ease with which they can be harvested. In this study, we demonstrated that the isolation of DPSCs from third molar teeth of healthy individuals allowed the recovery of dental mesenchymal stem cells that showed self-renewal and multipotent differentiation capability. DPSCs resulted positive for CD73, CD90, CD105, STRO-1, negative for CD34, CD45, CD14 and were able to differentiate into osteogenic and chondrogenic cells. We also assayed the angiogenic potential of DPSCs, their capillary tube-like formation was assessed using an in vitro angiogenesis assay and the uptake of acetylated low-density lipoprotein was measured as a marker of endothelial function. Based on these results, DPSCs were capable of differentiating into cells with phenotypic and functional features of endothelial cells. Furthermore, this study investigated the growth and differentiation of human DPSCs under a variety of bioengineering platforms, such as low frequency ultrasounds, tissue engineering and nanomaterials. DPSCs showed an enhanced chondrogenic differentiation under ultrasound application. Moreover, DPSCs were tested on different scaffolds, poly(vinyl alcohol)/gelatin (PVA/G) sponges and human plasma clots. We showed that both PVA/G and human plasma clot are suitable scaffolds for adhesion, growth and differentiation of DPSCs toward osteoblastic lineages. Finally, we evaluated the interactions of DPSCs with a novel class of nanomaterials, namely boron nitride nanotubes (BNNTs). From our investigation, DPSCs have appeared as a highly versatile cellular tool to be employed in regenerative medicine.     

Using NMR displacement imaging to characterize electroosmotic flow in porous media.

Pulsed field gradient nuclear magnetic resonance (PFG-NMR) and NMR imaging were used to study temporal and spatial domains of an electrokinetically-driven mobile phase through open and packed segments of capillaries. Characteristics like velocity distribution and an asymptotic dispersion are contrasted to viscous flow behavior. We show that electroosmotic flow in microchannel geometries can offer a significant performance advantage over the pressure-driven flows at comparable Peclét numbers, indicating that velocity extremes in the pore space of open tubes and packed beds are drastically reduced. An inherent problem of capillary electrochromatography that we finally address is the existence of wall effects when in the general case the surface zeta-potentials of the capillary inner wall and the adsorbent particles are different. Using dynamic NMR microscopy we were able resolve this systematic velocity inequality of the flow pattern which strongly influences axial dispersion and may be responsible for long time-tails of velocity distribution in the mobile phase.     

Simultaneous iso-electric focusing of proteins in a micro-fabricated capillary coated with hydrophobic and hydrophilic plasma polymerized films

The ability to modify and reduce the electroosmotic flow (EOF) is one of the most influential parameters which affects iso-electric focusing (IEF) of proteins. Therefore capillaries are usually coated with polymers or gels to prevent non-specific adsorption and suppress the EOF in capillary iso-electric focusing (cIEF) of proteins. In this research hexamethyldisiloxane (HMDS) and 2,3-epoxy-1-propanol (glycidol) plasma polymerized films were deposited onto both surfaces of the capillary separation channel. Cathode solution pH 3, anode solution pH 10 and a carrier ampholyte, pharmalyte provided the necessary stable pH gradient. Simultaneous IEF of proteins in capillaries coated with hydrophobic and hydrophilic plasma polymerized films occurred within minutes. The electroosmotic force of uncoated glass capillaries was suppressed by 50% after deposition of 200 nm 2,3-epoxy-1-propanol compared with a 30% reduction of EOF when the capillary was coated with 200 nm HMDS. The hydrophilic 2,3-epoxy-1-propanol plasma polymerized film was more resistant with a stronger attachment to the glass surface than previously prepared acetonitrile plasma polymerized films.     

The variations of heat transfer and slip velocity of FMWNT-water nano-fluid along the micro-channel in the lack and presence of a magnetic field

Simulation of forced convection of FMWNT-water (functionalized multi-walled carbon nano-tubes) nano-fluid in a micro-channel under a magnetic field in slip flow regime is performed. The micro-channel wall is divided into two portions. The micro-channel entrance is insulated while the rest of length of the micro-channel has constant temperature (T_C). Moreover, the micro-channel domain is exposed to a magnetic field with constant strength of B₀. High temperature nano-fluid (T_H) enters the micro-channel and exposed to its cold walls. Slip velocity boundary condition along the walls of the micro-channel is considered. Governing equations are numerically solved using FORTRAN computer code based on the SIMPLE algorithm. Results are presented as the velocity, temperature, and Nusselt number profiles. Greater Reynolds number, Hartmann number, and volume fraction related to more heat transfer rate; however, the effects of Ha and ϕ are more noteworthy at higher Re.     

Cyclodextrin modified gold nanoparticles-based open-tubular capillary electrochromatographic separations of polyaromatic hydrocarbons

In this study, spherical gold nanoparticles (GNPs) of 14.7 nm diameter, prepared by citrate reduction of a gold(III) salt and characterized by UV–Vis absorption spectrometry and transmission electron microscopy, were modified by a covalent attachment of 6^I-O-(3-mercaptopropyl)β-cyclodextrin (β-CD-SH) or per-6-deoxy-per-6-mercapto-β-cyclodextrin (β-CD-SH7). Subsequently, via three alternative approaches, β-CD-modified GNPs were immobilized onto the inner wall of the fused-silica (FS) capillaries and applied as special stationary phases for open-tubular capillary electrochromatography (OT-CEC). The first immobilization procedure was based on pre-derivatization of a FS capillary with (3-mercaptopropyl)trimethoxysilane (MPTMS) followed by subsequent reactions with GNPs and β-CD-SH or β-CD-SH7. The other two preparation protocols took advantage of sol–gel approach gaining a significant increase in the interaction surface for solutes. In both instances, the sol–gel created 3D structure was further covalently modified with GNPs. Serving that purpose, either β-CD-SH7 modified GNPs were used for the immobilization into the sol–gel matrix (“one-step sol–gel technique”) or native GNPs were immobilized first into the sol–gel matrix and subsequently modified with β-CD-SH7 (“two-step sol–gel technique”). The separation performance of CD-GNPs modified FS capillaries was tested by OT-CEC in reversed-phase mode applied to separation of a model mixture of five polyaromatic hydrocarbons. The highest separation efficiencies were obtained with the capillaries prepared by two-step sol–gel technique. However, with respect to the relatively low reproducibility of this method, the first of the above preparation procedures, i.e., a simple pre-derivatization of the FS capillary with MPTMS ensued with β-CD-SH7-GNPs immobilization seems to be more feasible approach providing decent separation efficiency.     

Inner capillary diameter of hypothalamic paraventricular nucleus of female rat increases during lactation

Background

The role of the endothelial cell (EC) in blood flow regulation within the central nervous system has been little studied. Here, we explored EC participation in morphological changes of the anterior hypothalamic paraventricular nucleus (PVN) microvasculature of female rats at two reproductive stages with different metabolic demand (virginity and lactation). We measured the inner capillary diameter (ICD) of 800 capillaries from either the magnocellular or parvocellular regions. The space occupied by neural (somas, dendrites and axons) and glial, but excluding vascular elements of the neurovascular compartment was also measured in 100-μm² sample fields of both PVN subdivisions.

Results

The PVN of both groups of animals showed ICDs that ranged from 3 to 10 microns. The virgin group presented mostly capillaries with small ICD, whereas the lactating females exhibited a significant increment in the percentage of capillaries with larger ICD. The space occupied by the neural and glial elements of the neurovascular compartment did not show changes with lactation.

Conclusions

Our findings suggest that during lactation the microvasculature of the PVN of female rats undergoes dynamic, transitory changes in blood flow as represented by an increment in the ICD through a self-cytoplasmic volume modification reflected by EC changes. A model of this process is proposed.     

Nucleation time of nanoscale water bridges

Water capillaries bind together grains of sand. They also can bind an atomic force microscope tip to a substrate. The kinetics of capillary condensation at the nanoscale is studied here using friction force microscopy. At 40% relative humidity we find that the meniscus nucleation times increase from 0.7 to 4.2 ms when the temperature decreases from 332 to 299 K. The nucleation times grow exponentially with the inverse temperature 1/T obeying an Arrhenius law. We obtain a nucleation energy barrier of 7.8 x 10(-20) J and an attempt frequency ranging between 4 and 250 GHz, in excellent agreement with theoretical predictions. These results provide direct experimental evidence that capillary condensation is a thermally activated phenomenon.     

The influence of spatial patterns of capillary networks on transverse relaxation

Tissue-inherent relaxation parameters offer valuable information about the arrangement of capillaries: in an external field, capillaries act as magnetic perturbers to generate local inhomogeneous fields due to the susceptibility difference of deoxygenated blood and the surrounding tissue. These field inhomogeneities influence the free induction decay in a characteristic way, and, conversely, the above tissue parameters can be recovered by multi-parametric fits of adequate theoretical models to experimentally sampled free induction decays. In this work we study the influence of different spatial patterns of capillary positions on the free induction decay. Starting from the standard single capillary approximation (Krogh cylinder) for a symmetric array of capillaries, the free induction decay is analyzed for increasingly random capillary positions, using a previously described Gibbs point field model. The effects of diffusion are implemented with a flexible and fast random walk simulation. We find that the asymmetric form of the obtained frequency distribution is more robust against variations of capillary radii than against shifts of capillary positions, and further that, for an inclusion of diffusion effects, the single capillary approximation models the uniform alignment of capillaries in the hexagonal lattice to great accuracy. An increase in randomization of capillary positions then leads to a significant change in relaxation times. This effect, however, is found less pronounced than that of changes in the off-resonance field strengths which are controlled by the oxygen extraction fraction, thus indicating that observed changes in BOLD imaging are more likely to be attributed to changes in oxygenation than to capillary alignment.     

毛细管阵列电泳检测过程中的杂散光分析

建立了激光诱导荧光检测系统.采用光学仿真方法,建立与实际光学系统相同的模型.模拟表明:聚焦光束扫描毛细管阵列,轴上光束入射到毛细管内径中心时产生的杂散光最大,在两边逐渐减小.由毛细管产生的杂散光的平均光强是无毛细管时的2.725倍,说明由它产生的杂散光比较严重.对不同大小的内径产生的杂散光影响进行了分析比较,增大毛细管的内径,杂散光增大,但毛细管内径减小会使进样量少,检测困难,同时还会加大清洗与灌胶的难度.综合考虑,选取内径为50 μm的毛细管较为合适.利用自行设计的激光诱导荧光检测系统扫描毛细管阵列,进行了杂散光检测实验,光电倍增管记录所收集到的信号,作出了激光束扫描毛细管的不同位置时的杂散光信号强度分布图,实验与模拟结果相一致.