Hydrophobic Walls Research Articles

Heterogeneous bubble nucleation dynamics

Abstract

Properties of Cavities in Biological Structures-A Survey of the Protein Data Bank.

We performed a PDB-wide survey of proteins to assess their cavity content, using the SPACEBALL algorithm to calculate the cavity volumes. In addition, we determined the hydropathy character of the cavities. We demonstrate that the cavities of most proteins are hydrophilic, but smaller proteins tend to have cavities with hydrophobic walls. We propose criteria for distinguishing between cavities and pockets, and single out proteins with the largest cavities.

Application of lattice Boltzmann method to simulate a pressure-affected electroosmotic pump with hydrophobic thermally-jumped walls and temperature-sensitive operating fluid

The present work attempts to show the accuracy of lattice Boltzmann method (LBM) to study a liquid flow with volumetric forces of electroosmotic and pressure gradient over hydrophobic surfaces. Navier boundary condition, slip velocity and temperature jump are taken into account. The flow has temperature-dependent physical properties and is assumed to be laminar, steady and viscous. Joule heating effects and velocity distribution within channel are studied and verified by comparing the numerically computed slip length with the coefficient of velocity derivative at the wall. The results show that unlike no-slip condition, velocity and temperature magnitude in the middle and near wall regions have approximately the same significant growth. Slip amplifies the effect of fluid properties changes on the wall heat transfer rate; because it increases the temperature derivative at the channel wall.

Non-Tuberculous Mycobacteria: Molecular and Physiological Bases of Virulence and Adaptation to Ecological Niches.

Non-tuberculous mycobacteria (NTM) are paradigmatic colonizers of the total environment, circulating at the interfaces of the atmosphere, lithosphere, hydrosphere, biosphere, and anthroposphere. Their striking adaptive ecology on the interconnection of multiple spheres results from the combination of several biological features related to their exclusive hydrophobic and lipid-rich impermeable cell wall, transcriptional regulation signatures, biofilm phenotype, and symbiosis with protozoa. This unique blend of traits is reviewed in this work, with highlights to the prodigious plasticity and persistence hallmarks of NTM in a wide diversity of environments, from extreme natural milieus to microniches in the human body. Knowledge on the taxonomy, evolution, and functional diversity of NTM is updated, as well as the molecular and physiological bases for environmental adaptation, tolerance to xenobiotics, and infection biology in the human and non-human host. The complex interplay between individual, species-specific and ecological niche traits contributing to NTM resilience across ecosystems are also explored. This work hinges current understandings of NTM, approaching their biology and heterogeneity from several angles and reinforcing the complexity of these microorganisms often associated with a multiplicity of diseases, including pulmonary, soft-tissue, or milliary. In addition to emphasizing the cornerstones of knowledge involving these bacteria, we identify research gaps that need to be addressed, stressing out the need for decision-makers to recognize NTM infection as a public health issue that has to be tackled, especially when considering an increasingly susceptible elderly and immunocompromised population in developed countries, as well as in low- or middle-income countries, where NTM infections are still highly misdiagnosed and neglected.

Effect of surface coating on droplet generation in flow-focusing microchannels

Different stages of droplet generation are reported in this paper with two immiscible liquids, silicone oil and deionized water, inside a flow-focusing device for hydrophobic and hydrophilic channel walls. Hydrophobic and hydrophilic channels of identical geometry are compared. In this first set of experiments, the efficacy of the hydrophobic channel is compared with a square cross junction for a continuous oil phase with low viscosity. In the hydrophobic case, the flow-focusing design with a diverging outlet delays jetting and allows for the use of higher flow rate ratios in the squeezing regime. For the hydrophilic case, stable and well-structured droplet and slug generation can be achieved using oil and water, resulting in an inverse emulsion. However, the morphology of the fluid interface displays an unusual behavior compared to that of a hydrophobic microchannel. The droplet generation in the hydrophilic channel occurs following the formation of single and double T-junctions, a phenomenon hitherto unreported in the literature. The results demonstrate that the uncoated hydrophobic channels generate monodisperse droplets at a higher capillary number when compared to the hydrophilic channels.

Effects of wall hydrophobicity on the thermohydraulic performance of the microchannels with nanofluids

Three-dimensional heat transfer of nanofluids in microchannels with hydrophilic, hydrophobic and, superhydrophobic surfaces were studied using numerical simulation. For this purpose, Navier Stokes and energy equations were solved using the finite volume method. The flow Reynolds numbers were in the range of 40–500. Water/Al2O3 and Water/TiO2 were considered as coolant fluids. By applying hydrophobic surfaces, the flow pressure drop decreased, especially for the case of superhydrophobic walls. Microchannel with hydrophobic walls required 12% less pumping power than those with hydrophilic walls. The superhydrophobic wall caused a 66% reduction in the required pumping power. The use of nanofluids as a coolant improved the thermal performance. The results showed that the simultaneous use of the hydrophobic surface and the addition of nanoparticles could increase the performance evaluation criterion to 1.75 at Re = 400 and caused the lowest substrate temperatures. In addition, for the flows with Re > 150, applying the superhydrophobic walls was more effective than the usage of nanofluids as coolants with conventional walls.

Identification and Investigation of Chalcone Derivatives as Calcium Channel Blockers: Pharmacophore Modeling, Docking Studies, In vitro Screening, and 3D-QSAR Analysis.

The chalcones were reported to have many biological activities by showing affinity towards many enzymatic targets. The effect of nitric oxide (NO) on calcium channel was extensively studied in different animals; the study was also carried out for NO donor drug and its effect on calcium channel. Till date, the inhibition of calcium channel is of prime importance in the medicinal chemistry to discover newer vascular smooth muscle relaxant drugs. The main objective of this work is to carry out in silico and in vitro evaluation of NO donor chalcones for calcium channel blocking potency. The present work includes in silico evaluation of chalcone derivatives for calcium channel blocking potency. The promising scaffolds were identified after pharmacophore modeling and docking study. The in vitro screening of 21 lead molecules for calcium channel blocking potency was carried out on pulmonary veins of adult goat, IC50 values were determined and 3D QSAR was performed. The pharmacophore modeling revealed that hydrogen bond donor, hydrogen bond acceptor, and hydrophobic groups are important features for calcium channel blocking activity. The docking study revealed the existence of hydrophobic, hydrogen bond and Vander wall's interactions between amino acid residues and ligands. The in vitro screening showed that the compounds AI6, Ca2, and D8 were potent, produced 4.756, 3.608 and 5.211 μM of IC50 respectively, whereas the standard Nifedipine showed the potency of 1.304 μM of IC50. The 3D QSAR study explained the importance of different steric and electrostatic parameters and their correlation for L type calcium channel blocking activity. This study showed that the chalcone scaffold with NO donor capacity is promising for designing novel calcium channel blockers to treat vascular disorders.

Local Molecular Field Theory for Nonequilibrium Systems.

We provide a framework for extending equilibrium local molecular field (LMF) theory to a statistical ensemble evolving under a time-dependent applied field. In this context, the self-consistency of the original LMF equation is achieved dynamically, which provides an efficient method for computing the equilibrium LMF potential, in addition to providing the nonequilibrium generalization. As a concrete example, we investigate water confined between hydrophobic or charged walls, systems that are very sensitive to the treatment of long-ranged electrostatics. We then analyze confined water in the presence of a time-dependent applied electric field, generated by a sinusoidal or abrupt variation of the magnitudes of uniform charge densities on each wall. Very accurate results are found from the time-dependent LMF formalism even for strong static fields and for time-dependent systems that are driven far from equilibrium where linear response methods fail.

Slowing DNA translocation through a solid-state nanopore by applying hydrophobic microchannel-guided walls

Here, the authors present a novel solid-state nanopore device, fabricated by a transfer of a nanopore device to a dielectric polydimethylsiloxane (PDMS) microchannel-guided structure, and investigate the characteristics of DNA translocation through the nanopore. Apart from the extremely low noise level exhibited by this device on a highly insulating and low dielectric PDMS microchannel, this device also shows a slow translocation speed of 48 kbp Lambda DNA (λ-DNA), with a reduction of more than one order of magnitude than that in previously reported results on SiNx nanopores. The authors propose that the electrostatic interaction between the PDMS microchannel and DNA, resulting from the hydrophobicity of both PDMS and DNA, provides an additional attraction force that slows down DNA translocation. Such advanced solid-state nanopore devices can be utilized in various fields, including DNA or protein sequencing, drug screening, and microRNA detection.

Near-wall hydrodynamic slip triggers swimming state transition of micro-organisms

The interaction of motile micro-organisms with a nearby solid substrate is a well-studied phenomenon. However, the effects of hydrodynamic slippage on the substrate have received little attention. In the present study, within the framework of the squirmer model, we impose a tangential velocity at the swimmer surface as a representation of the ciliary propulsion, and subsequently obtain an exact solution of the Stokes equation based on a combined analytical–numerical approach. We illustrate how the near-wall swimming velocities are non-trivially altered by the interaction of wall slip and hydrodynamic forces. We report a characteristic transition of swimming trajectories for both puller- and pusher-type microswimmers by hydrodynamic slippage if the wall slip length crosses a critical value. In the case of puller microswimmers that are propelled by a breaststroke-like action of their swimming apparatus ahead of their cell body, the wall slip can cause wall-bound trapping swimming states, as either periodic or damped periodic oscillations, which would otherwise escape from a no-slip wall. The associated critical slip length has a non-monotonic dependence on the initial orientation of the swimmer, which is represented by novel phase diagrams. Pushers, which get their propulsive thrust from posterior flagellar action, also show similar swimming state transitions, but in this case the wall-slip-mediated reorientation dynamics and the swimming modes compete in a different fashion from that of the pullers. Although neutral swimmers lack a sufficient reorientation torque to exhibit any wall-bound trajectory, their detention time near the substrate can be significantly increased by tailoring the extent of hydrodynamic slippage at the nearby wall. The present results pave the way for understanding the motion characteristic of biological microswimmers near confinements with hydrophobic walls or strategize the design of microfluidic devices used for sorting and motion rectification of artificial swimmers by tailoring their surface wettability.

Free energy profile of permeation of Entecavir through Hepatitis B virus capsid studied by molecular dynamics calculation

Abstract Entecavir, triphosphorylated in liver cells, is an antiviral reagent against Hepatitis B virus (HBV). The reagent inhibits reverse transcription of RNA inside the virus capsid. In the present study, free energy profile of an Entecavir triphosphate (ETVTP) molecule has been calculated when it passes through pores of the capsid along two- and three-fold rotational symmetry axes in order to investigate permeation pathway of the reagent to the inside of the capsid. The calculations have been done based on thermodynamic integration (TI) method combined with all-atomistic molecular dynamic (MD) calculations. A free energy minimum of −19 kJ/mol was found at the entrance of the pore from the outside along the three-fold symmetry axis. This stabilization is from the interaction of negatively charged ETVTP with positively charged capsid methionine residues. This excess free energy concentrates of the reagent at the entrance of the pore by a factor of about 2000. A free energy barrier of approximately 13 kJ/mol was also found near the exit of the pore to the inside of the capsid due to narrow space of the pore surrounded by hydrophobic wall made by proline residues and negatively charged wall by aspartic acid residues. There, ETVTP is partially dehydrated in order to pass through the narrow space, which causes the great free energy loss. Further, the negatively charged residues produce repulsive forces on the ETVTP molecule. In contrast, in the case of the pore along the two-fold symmetry axis, the calculated free energy profile showed shallower free energy minimum, −4 kJ/mol at the entrance in spite of the similarly high barrier, 7 kJ/mol, near the exit of the pore.

Structure regulation for synergistically improving the permeation properties of the reverse osmosis membrane based on an amphiphilic hyperbranched polymer

The aromatic polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membrane has been widely used in the desalination processes to settle the global water crisis. To further decrease the desalination cost, in this work, an amphiphilic hyperbranched polymer of HBPO-star-PEO-COCl with abundant end groups of acyl chloride and core-shell hydrophilic/hydrophobic phase separation structure was synthesized and used as the functional nanomaterial to modify the conventional polyamide TFC RO membrane through interfacial crosslinking reaction. The modified RO membrane with 0.005% HBPO-star-PEO-COCl presents the optimal structure and permeation properties. Its PA layer becomes thinner and denser, and its water flux reaches 69.8LMH nearly double that of the original membrane (33.27LMH), at the same time, its NaCl rejection rate reaches 99.22% higher than that of the original membrane. It can attribute to the unique amphiphilic core-shell structure of HBPO-star-PEO-COCl. On the one hand, the PEO shell of HBPO-star-PEO-COCl is highly hydrophilic while the internal HBPO is highly hydrophobic and collapses easily in water to form a three-dimensional quasi-spherical structure, which leads to the formation of the core-shell two-phase interface, thereby facilitating the water molecules to rapidly pass through the PA layer along the hydrophobic wall surface. On the other hand, the end acly chloride groups of HBPO-star-PEO-COCl take part in the crosslinking reaction, which makes the PA layer have higher crosslinking degree and become denser, thereby enhancing the salt retention. Therefore, this study provides an effective way to fabricate a new reverse osmosis composite membrane with favorable comprehensive separation performance based on amphiphilic hyperbranched polymer.

Multiscale Characteristic in Symmetric/Asymmetric Solar-Driven Nanofluid Droplet Evaporation.

Driven by nanoparticle plasmonic heating, sessile droplet evaporation presents challenges on the coupling mechanisms between time-spatial heat source distribution and flow/temperature fields in a droplet. Here, symmetric/asymmetric solar-driven droplet evaporation is investigated. An infrared camera captures droplet surface temperatures in the micrometer scale after correction. An optical three-dimensional profiler quantifies nanoparticle deposition in the nanoscale. We show that droplet surface temperatures do display a nonmonotonic variation trend. Based on measurements, we are able to decouple the droplet into a contact line region (CLR) and a bulk volume region (BVR). The CLR volume is two to three magnitudes smaller than the droplet volume. The temperature gradient is significant in CLR, but flat temperature exists in BVR. Radial flow in BVR transports nanoparticles from the droplet body to the contact line, while Marangoni flow in CLR stabilizes nanoparticles there. Light energy is also decoupled based on its wavelength band. It is found that CLR dominates the visible energy absorption, but BVR has a weak contribution. Top light heating causes symmetry temperatures and a coffee-ring profile along the circumference. However, side heating yields higher temperatures and more nanoparticles deposition on the sunny side than on the night side. The above findings are valid when the initial droplet volume and incident irradiation flux are changed on the hydrophilic wall. The hydrophilic wall and hydrophobic wall maintain the evaporation modes of constant contact diameter and "stick-slip", respectively. The present paper enhances the understanding of light-induced droplet evaporation from the multiscale point of view.

Experiment characterization of the influence of wall wettability and inclination angle on bubble rising process using PIV

Bubble behavior is an important branch of the research field of gas–liquid two-phase flow, and the wall has a significant impact on the rising process of a bubble. In this paper, a visual bubble observation platform with an adjustable wall was built to observe the effect of the wall with different inclination angles and different wettability on bubble rising behavior. During this experiment, particle image velocimetry (PIV) was used to obtain the velocity vector field of water around the rising bubble. Through experiments, the instantaneous and average rising velocity of the bubble as well as the flow field around the bubble under different conditions was obtained, and the morphological change of the bubble during its rising process was found. The experimental results showed that the rising velocity of the bubble under the influence of the hydrophobic wall was obviously faster than that under the influence of the hydrophilic wall. Even when the bubble rose near the hydrophobic wall, it was 34.53% faster than that in the free case. When the bubble contacted the hydrophobic wall, it deformed and adhered to the wall to slip up, but when the bubble contacted the hydrophilic wall, it was bounced off the wall. In addition, when the wall was vertical, the bubble rising close to the hydrophilic wall formed a larger range of wake flow. However, the wake formed by the bubble rising near the hydrophobic wall had a smaller wake range and a weaker wake strength. That is, the hydrophilic wall combined with the rising of bubble would bring better mixing effect to the flow field.

Poly-thiourea formaldehyde based anticorrosion marine coatings on type 304 stainless steel

In the present study, hexamethylene diisocyanate (HMDI) encapsulated poly-thiourea formaldehyde (PTF) (10wt%) coating was developed in an epoxy-polyamine matrix and their anticorrosion studies on Type SS304 stainless steel substrate have been conducted using electrochemistry techniques. The compact and hydrophobic shell wall of PTF proved to be a potent shell wall material for HMDI encapsulation. The effect of temperature and pH values was found to be decisive factor in the synthesis of microcapsules. The PTF microcapsules were synthesized in acidic condition with a pH value of 3. Over 90% of the core fraction is retained in water after 21 days immersion. However, core content decreased with increasing temperature. The capsules were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Electrochemical Impedance spectroscopy (EIS). Scanning electron microscopic analysis depicts the uniform morphology of coating with a particle size in the range of 1.08μm–22.06μm. The vibrational band at 2271cm−1 attributed to NCO signal further endorses the successful encapsulation of HMDI into the PTF capsules. Electrochemical testing on steel specifies the appreciable anticorrosion performance of the synthesized poly thiourea formaldehyde (PTF) coating against artificial sea water.

Mycobacterium abscessus-Bronchial Epithelial Cells Cross-Talk Through Type I Interferon Signaling.

Introduction: Mycobacteria are aerobic non-motile organisms with lipid rich, hydrophobic cell walls that render them resistant to antibiotics. While there are over 150 different species of NTM, Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MAB) are two of the most common culprits of pulmonary infection. MAB has been found to be most common in southeastern United States (Florida to Texas) and the third most rapidly growing NTM infection. It is responsible for chronic lung infections. Mycobacterial cell wall components initiate the interaction between bacteria and host. The reaction between bronchial epithelia and components in the envelope of mycobacterial cell wall is poorly understood.Methods: A lung-on-membrane model was developed with normal human bronchial epithelial (NHBE) cells re-differentiated at the air-liquid interface (ALI) and human endothelial cells on a transwell® polyester membrane. Microparticles from MAB cell walls were developed by an inhouse protocol and added to the ALI side of lung model. NHBE cells were harvested at day 3. RNA was isolated and analyzed with RNASeq. NHBE cells were lysed and protein assay was performed with western blot. We tested whether lung INF-alpha expression would increase in mice treated with intratracheal MAB cell wall particles. A paired t-test is used to compare two population means using GraphPad Prism 7 software.Results: RNAseq analysis identified 1759 differentially expressed genes between NHBE cells challenged with and without MAB microparticles with FDR < 0.5. 410 genes had a 2.5-fold change (FC) or greater. NHBE cells exposure to MAB microparticles significantly enriched the IFN I signaling pathway. Protein overexpression of IFN I family (2′-5′-Oligoadenylate Synthetase 1, Interferon-induced GTP-binding protein Mx1, Interferon-stimulated gene 15) was found in bronchial epithelial cells following exposure to MAB cell wall microparticles. IFN-α protein and gene expressions were significantly increased in mice lung challenged with microparticles in comparison with controls.Conclusion: These data strongly support the role of Type I IFN in cross-talk between NHBE cells and MAB. They also suggest that initiating immune response by NHBE cells may play a central role in innate immunity. Furthermore, this study underscores the importance of mycobacterial cell wall in initiating innate immune response.

Strong Electroosmotic Coupling Dominates Ion Conductance of 1.5 nm Diameter Carbon Nanotube Porins.

Extreme confinement in nanometer-sized channels can alter fluid and ion transport in significant ways, leading to significant water flow enhancement and unusual ion correlation effects. These effects are especially pronounced in carbon nanotube porins (CNTPs) that combine strong confinement in the inner lumen of carbon nanotubes with the high slip flow enhancement due to smooth hydrophobic pore walls. We have studied ion transport and ion selectivity in 1.5 nm diameter CNTPs embedded in lipid membranes using a single nanopore measurement setup. Our data show that CNTPs are weakly cation selective at pH 7.5 and become nonselective at pH 3.0. Ion conductance of CNTPs exhibits an unusual 2/3 power law scaling with the ion concentration at both neutral and acidic pH values. Coupled Navier-Stokes and Poisson-Nernst-Planck simulations and atomistic molecular dynamics simulations reveal that this scaling originates from strong coupling between water and ion transport in these channels. These effects could result in development of a next generation of biomimetic membranes and carbon nanotube-based electroosmotic pumps.

Encapsulated HKUST-1 nanocrystal with enhanced vapor stability and its CO2 adsorption at low partial pressure in unitary and binary systems

To improve vapor stability of metal organic framework (MOF) HKUST-1 required in practical application of CO2 gas adsorption, a simple strategy for synthesizing nanocomposite HKUST-1@OMC, HKUST-1 nanocrystal encapsulated in an ordered mesoporous carbon (OMC), is demonstrated for the first time by “in-situ” converting the HKUST-1 precursor physically dispersed in OMC’s mesochannel with the assistance of mixed vapor. Enhanced onset decomposition temperature of HKUST-1 nanocrystal in mesopores of the activated OMC indicates that the nanocomposite HKUST-1@OMC is compounded at the nanoscale. Benefiting from the shielding effect of hydrophobic pore wall of OMC, the nanocomposite shows good vapor stability even at 110 °C. Fast CO2 saturation adsorption is achieved in a binary system because of the speedy diffusion in mesopores and short path in nanocrystal which are distinguishingly different from the long and simplex micropores in large HKUST-1 crystal. It also shows selective adsorption of low content CO2 over N2 in the binary system and its CO2 adsorption capacity basically stabilizes at 1.05 mmol/g after ten cyclic adsorption. The good cyclic performance may depend on its easy regeneration with a low energy consumption related to suitable interaction between CO2 molecule and the nanocomposite. The strategy of shielding HKUST-1 nanocrystal with hydrophobic carbon is efficient on improving its stability against the vapor in flue gas and diminishing the mass transfer resistance in adsorption process. Excellent cyclic performance makes it a promising candidate for scalable fabrication of robust MOF-based composites towards CO2 capture in humid surroundings.

Spectrophotometric and visual determination of zoledronic acid by using a bacterial cell-derived nanopaper doped with curcumin.

A nanopaper-based analytical device (NAD) is described for a colorimetric metal-complexing indicator-displacement assay (M-IDA) for zoledronic acid (ZA). Bacterial cellulose nanopaper was doped with curcumin to obtain a chemosensor on which hydrophilic test zones were patterned via laser printing of hydrophobic walls. The color intensity of the test zones decreases in the presence of Fe(III) due to the formation of Fe(III)-curcumin complex. However, upon addition of ZA, Fe(III) ions preferably binds ZA. Subsequently, the color of the zone changes from light yellow to dark yellow. The changes in the absorption (measured at 427nm) and of the color of the test stripe can be monitored visually, by using a digital camera, or by a spectrophotometer. Under optimal conditions, the analytical signals increase linearly in the 0.01-100μM ZA concentration range, and the detection limits are 8.8 and 8.0nM for smartphone and spectrophotometer-based methods, respectively. The method was employed to the determination of ZA in (spiked) urine, serum, saliva, and in pharmaceutical samples. Graphical abstract Schematic representation of a nanopaper-based analytical device based on curcumin-doped BC nanopaper (CDBC) integrated with smartphone for metal-complexing indicator-displacement assay of zoledronic acid (ZA). High affinity of ZA to Fe(III) on the NAD/CDBC leads to color change.

Structural analysis of human sterol transfer protein STARD4

The steroidogenic acute regulatory protein (StAR)-related lipid transfer domain-4 (STARD4) is a sterol-binding protein that is involved in cholesterol homeostasis by intracellular sterol transport. In this work, we determined the crystal structures of human STARD4 and its Ω1-loop mutant in apo forms at 1.95 and 1.7 Å resolutions, respectively. The structure of human STARD4 displays a conserved α-helix/β-grip fold containing a deep hydrophobic pocket. The Ω1-loop which serves as a lid for the hydrophobic pocket has a closed conformation. The shape of the sterol-binding cavity in the closed form is not complementary to accommodate cholesterol, suggesting that a conformational change of the Ω1-loop is essential for sterol binding. The human STARD4 displayed sterol transfer activity between liposomes, and the mutations in the Ω1-loop and the hydrophobic wall abolished the transfer activity. This study confirms the structural conservation of the STARD4 subfamily proteins and the flexibility of the Ω1-loop and helix α4 required for sterol transport.