Hydrodynamic Confinement Research Articles

The Influence of Gradient Patterned Design on Nanoshapes Deposition

Experimental exploration of surface modifications for nanoparticle patterning on hydrophilic set of stripes reveals unique patterns on gradient patterned designs. Combining theory with empirical data offers insights into droplet-induced assembly dynamics for gold nanorods and nanospheres mixture. The unique patterns and assembled arrays of nanospheres and nanorods has been evaluated and mapped with theoretical analytics. Gradient patterned surfaces demonstrate controlled particle deposition via precise manipulation of surface properties and complex energy interplay. Confinement effects induced by the surface design through engineered hydrophobic stripes that induce hydrodynamic flow play a critical role in guiding nanorods towards the center of the hydrophilic stripes, impacting wetting behavior and droplet dynamics. Such interplay of forces in suspension facilitates precise control over hydrodynamic confinement and capillary alignment. Study of theoretical models in this regard can play critical role in nanoparticle deposition, alignment, and shape separation effect.

Additive Manufacturing of Multi‐Metal Microstructures by Localized Electrochemical Deposition Under Hydrodynamic Confinement

AbstractThis study presents a device and method for multi‐metal printing of microscale structures. The method is based on combining hydrodynamic confinement of electrolytes with localized electrochemical deposition (HLECD), allowing rapid switching of the deposited metal. The device used in HLECD integrates a micro‐anode on a vertical microfluidic chip containing two open‐ended channels that control the flow of electrolytes surrounding the anode. When placed on top of a conducting surface, a localized electrochemical reaction is initiated, wherein the deposited metal composition is dictated by the electrolyte in the confinement. A range of electrolytes, which are used to deposit copper, tin, silver, and nickel, are used to fabricate multiple structures involving more than 60 material changes within a single printing process. The structures are analyzed using electron microscopy, showing the ability to achieve sharp transitions between pure metals. The constant replenishment of electrolytes also eliminates the problem of ion depletion commonly occurring in localized electrochemical deposition, and enables printing rates that are nearly an order of magnitude greater.

Hydrodynamic synchronization in strong confinement.

Cellular appendages conferring motility, such as flagella and cilia, are known to synchronise their periodic beats. The origin of synchronization is a combination of long-range hydrodynamic interactions with physical mechanisms allowing the phases of these biological oscillators to evolve. Two of such mechanisms have been identified by previous work, the elastic compliance of the periodic orbit or oscillations driven by phase-dependent biological forcing, both of which can lead generically to stable phase locking. In order to help uncover the physical mechanism for hydrodynamic synchronization most essential overall in biology, we theoretically investigate in this paper the effect of strong confinement on the effectiveness of hydrodynamic synchronization. Following past work, we use minimal models of cilia where appendages are modeled as rigid spheres forced to move along circular trajectories near a rigid surface. Strong confinement is modeled by adding a second nearby surface, parallel to the first one, where the distance between the surfaces is much smaller than the typical distance between the cilia, which results in a qualitative change in the nature of hydrodynamic interactions. We calculate separately the impact of hydrodynamic confinement on the synchronization dynamics of the elastic compliance and the force modulation mechanisms and compare our results to the usual case with a single surface. Applying our results to the biologically relevant situation of nodal cilia, we show that force modulation is a mechanism that leads to phase-locked states under strong confinement that are very similar to those without confinement as a difference with the elastic compliance mechanism. Our results point therefore to the robustness of force modulation for synchronization, an important feature for biological dynamics that therefore suggests it could be the most essential physical mechanism overall in arrays of nodal cilia. We further examine the distinct biologically relevant situation of primary cilia and show in that case that the difference in robustness of the mechanisms is not as pronounced but still favors the force modulation.

Assessment of hindered diffusion in arbitrary geometries using a multiphase DNS framework

The hydrodynamics around a Brownian particle has a noticeable impact on its hindered diffusion in arbitrary geometries (such as channels/pores) due to reduced mobility close to walls. These effects are difficult to describe at sub-pore scales, wherein a complete analytical solution of the underlying hydrodynamics is challenging to obtain. Here, we propose a coupled Langevin-multiphase direct numerical simulation (DNS) framework, that fully resolves the hydrodynamics in such systems and consequently provides an on-the-fly capability to probe local instantaneous particle diffusivities.We validate and establish the capabilities of this framework in square micro-channels (under varying degrees of hydrodynamic confinement) and in an arbitrary pore. Our results show that directional variations in mean-squared displacements, velocity auto-correlation functions and diffusivities of the Brownian particle, due to inherent asymmetries in the geometry are adequately captured. Further, a local anisotropy in the hydrodynamic resistances along the co-axial direction of the channel is also noted.

Deposition and patterning of gold nanostructures on various wettable and nonwettable patterned surfaces

Suspensions comprises of gold nanostructures deposited on a number of alternating wettable silicon dioxide (SiO2) and nonwettable perfluorodecyltrichlorosilane (PFDTS) patterned surfaces via droplet evaporation technique. On such surfaces during evaporation of aqueous phase, three-phased contact line of a droplet deposit nanoparticles preferentially on the wettable set of stripes and consequently leads to nanoparticles patterning over the substrate. The presence of the nonwettable stripes on both sides of the wettable stripe on such patterned substrates will push the liquid towards the wettable stripe. Such liquid drive will induce hydrodynamic confinement effect. This hydrodynamic confinement will produce nanoparticle patterns that will merely decorate wettable stripes with gold nanorod deposits. Aligned arrays of gold nanorods are observed near the interfacial boundaries. Ribbon-like arrays of face-to-face aligned nanorods are observed in some locations within the deposits. In case of citrate-stabilized gold nanospheres (diameter∼10 nm), bonding sites for nanospheres on the wettable stripes are provided by the self-assembled monolayers of 3-triethoxysilylpropylamine (APTES). The presence of APTES will facilitate gold nanoparticles deposition (monolayer) on the wettable stripes whereas nonwettable stripes demonstrated agglomerated and mobilized bunches of nanoparticles. As such nanoparticle clusters are unstable on the PFDTS surface, hence can be removed by air blowing mechanism. The air rushing across the substrate removes nearly all nanoparticles settled over the nonwettable stripes whereas nanoparticle arrangement on the wettable region remains unaltered.

Onset of thin film meniscus along a fibre

The dynamics of spreading of a macroscopic liquid droplet over a wetting surface is often described by a power-law relaxation, namely, the droplet radius increases as $t^{m}$ for time $t$, which is known as Tanner’s law. Here we show, by both experiments and theory, that when the liquid spreading takes place between a thin soap film and a glass fibre penetrating the film, the spreading is significantly slowed down. When the film thickness $\ell$ becomes smaller than the fibre diameter $d$, the strong hydrodynamic confinement effect of the soap film gives rise to a logarithmic relaxation with fibre creeping time $t$. Such a slow dynamics of spreading is observed for hours both in the measured time-dependent height of capillary rise $h(t)$ on the fibre surface and viscous friction coefficient $\unicode[STIX]{x1D709}_{s}(t)$ felt by the glass fibre in contact with the soap film. A new theoretical approach based on the Onsager variational principle is developed to describe the dynamics of thin film spreading along a fibre. The newly derived equations of motion provide the analytical solutions of $h(t)$ and contact angle $\unicode[STIX]{x1D703}(t)$, which are found to be in good agreement with the experimental results. Our work thus provides a common framework for understanding the confinement effect of thin soap films on the dynamics of spreading along a fibre.

Microfluidic technology for investigation of protein function in single adherent cells.

Instrumental techniques and associated methods for single cell analysis, designed to investigate and measure a broad range of cellular parameters in search of unique features, address key limitations of conventional cell-based assays with their ensemble average response. While many different single cell techniques exist for suspension cultures, which can process and characterize large numbers of individual cells in rapid succession, the access to surface-immobilized cells in typical 2D and 3D culture environments remains challenging. Open space microfluidics has created new possibilities in this area, allowing for exclusive access to single cells in adherent cultures, even at high confluency. In this chapter, we briefly review new microtechnologies for the investigation of protein function in single adherent cells, and present an overview over related recent applications of the multifunctional pipette (Biopen), a microfluidic multi-solution dispensing system that uses hydrodynamic confinement in open volume environments in order to establish a superfusion zone over selected single cells in adherent cultures.

Hydrodynamic Models and Confinement Effects by Horizontal Boundaries

Confinement effects by rigid boundaries in the dynamics of ideal fluids are considered from the perspective of long-wave models and their parent Euler systems, with the focus on the consequences of establishing contacts of material surfaces with the confining boundaries. When contact happens, we show that the model evolution can lead to the dependent variables developing singularities in finite time. The conditions and the nature of these singularities are illustrated in several cases, progressing from a single layer homogeneous fluid with a constant pressure free surface and flat bottom, to the case of a two-fluid system contained between two horizontal rigid plates, and finally, through numerical simulations, to the full Euler stratified system. These demonstrate the qualitative and quantitative predictions of the models within a set of examples chosen to illustrate the theoretical results.

Deep-Reaching Hydrodynamic Flow Confinement: Micrometer-Scale Liquid Localization for Open Substrates With Topographical Variations.

We present a method for nonintrusive localization and reagent delivery on immersed biological samples with topographical variation on the order of hundreds of micrometers. Our technique, which we refer to as the deep-reaching hydrodynamic flow confinement (DR-HFC), is simple and passive: it relies on a deep-reaching hydrodynamic confinement delivered through a simple microfluidic probe design to perform localized microscale alterations on substrates as deep as 600 μm. Designed to scan centimeter-scale areas of biological substrates, our method passively prevents sample intrusion by maintaining a large gap between the probe and the substrate. The gap prevents collision of the probe and the substrate and reduces the shear stress experienced by the sample. We present two probe designs: linear and annular DR-HFC. Both designs comprise a reagent-injection aperture and aspiration apertures that serve to confine the reagent. We identify the design parameters affecting reagent localization and depth by DR-HFC and study their individual influence on the operation of DR-HFC numerically. Using DR-HFC, we demonstrate localized binding of antihuman immunoglobulin G (IgG) onto an activated substrate at various depths from 50 to 600 μm. DR-HFC provides a readily implementable approach for noninvasive processing of biological samples applicable to the next generation of diagnostic and bioanalytical devices.

Trapping It Softly: Ultrasoft Zirconium Metallogels for Macromolecule Entrapment and Reconfiguration.

Trapping nanosized drugs in ultrasoft, shear-thinning hydrogels with large pores is of particular interest, yet a persistent challenge in nanomedicine due to the lack of hydrodynamic confinement. Engineering molecular interactions between a macromolecule and a supramolecular gel may address this shortcoming, providing a key route to develop advanced drug carriers without compromising matrix elasticity. Here, we show that ultrasoft zirconium-based metallogels are able to trap and reconfigure model nanodrugs (e.g., dextran) through complexation and hydrogen bonding. The diffusion coefficients of dextran molecules (Mw ∼ 10-2000 kDa, a ∼ 2-20 nm) in zirconium carbonate (ZC) metallogels (G' < 30 Pa) were measured by pulsed field gradient nuclear magnetic resonance (PFGNMR), which revealed the coexistence of hindered and enhanced collective diffusion regimes for the first time. This work may pave the way toward designing next generation ultrasoft drug carriers and functional templates to control biomacromolecular processes, such as protein folding.

Ion current density profiles in negative corona gaps versus EHD confinements

This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode.

Hydrodynamic thermal confinement: creating thermo-chemical microenvironments on surfaces.

We present a new, general concept termed Hydrodynamic Thermal Confinement (HTC), and its implementation for the creation of microscale dynamic thermo-chemical microenvironments on biological surfaces. HTC is based on a scanning probe and operates under physiological conditions. The temperature can be regulated between 30° and 80 °C with ±0.2 °C precision and temperature ramps of 5 °C s-1 over a footprint of ∼50 μm × 80 μm in a volume of ∼50 × 80 × 15 μm3 (∼50 pl).

Hydrodynamic confinement and capillary alignment of gold nanorods

Controlling the alignment and orientation of nanorods on various surfaces poses major challenges. In this work, we investigate hydrodynamic confinement and capillary alignment of gold nanorod assembly on chemically stripe-patterned substrates. The surface patterns consist of alternating hydrophilic and hydrophobic micrometer wide stripes; a macroscopic wettability gradient enables controlling the dynamics of deposited suspension droplets. We show that drying of residual liquid on the hydrophilic stripes gives rise to spatially localized deposition and alignment of the nanorods. Moreover, a universal relation between the extent of order within the single layers of nanoparticles and the lateral dimension of the deposits is presented and discussed.

Two-Aperture Microfluidic Probes as Flow Dipole: Theory and Applications.

A microfluidic probe (MFP) is a mobile channel-less microfluidic system under which a fluid is injected from an aperture into an open space, hydrodynamically confined by a surrounding fluid, and entirely re-aspirated into a second aperture. Various MFPs have been developed, and have been used for applications ranging from surface patterning of photoresists to local perfusion of organotypic tissue slices. However, the hydrodynamic and mass transfer properties of the flow under the MFP have not been analyzed, and the flow parameters are adjusted empirically. Here, we present an analytical model describing the key transport properties in MFP operation, including the dimensions of the hydrodynamic flow confinement (HFC) area, diffusion broadening, and shear stress as a function of: (i) probe geometry (ii) aspiration-to-injection flow rate ratio (iii) gap between MFP and substrate and (iv) reagent diffusivity. Analytical results and scaling laws were validated against numerical simulations and experimental results from published data. These results will be useful to guide future MFP design and operation, notably to control the MFP “brush stroke” while preserving shear-sensitive cells and tissues.

Passive removal of immiscible spacers from segmented flows in a microfluidic probe

Microfluidic probes (MFPs) are a class of non-contact, scanning microfluidic devices that hydrodynamically confine nanoliter volumes of a processing liquid on a surface immersed in another liquid. So far only chemical processes using a single processing liquid have been implemented using MFPs. In this letter, we present the design and implementation of a probe head that allows segmented two-phase flows to be used, which will enable different chemical species to be sequentially delivered to a surface in defined volumes and concentrations. Central to this probe head is a spacer-removal module comprising blocking pillars in the injection channel, a bypass and an orifice leading to the aspiration channel. We present a capillarity-based analytical model that provides insight into the functionality of the module based on geometrical parameters. In addition, we study the difference between two- and three-channel modules and predict a 30% reduction in fluctuation of the footprint of the confined liquid for the three-channel module. We show that such a module with a 15 μm pillar spacing, a 30 μm orifice width, and an oblique angle of 30° can remove immiscible spacers (Fluorinert FC-40) from an aqueous flow at a rate of up to 15 spacers per second while maintaining hydrodynamic confinement of processing liquid.

Spatial characterization of a multifunctional pipette for drug delivery in hippocampal brain slices.

Among the various fluidic control technologies, microfluidic devices are becoming powerful tools for pharmacological studies using brain slices, since these devices overcome traditional limitations of conventional submerged slice chambers, leading to better spatiotemporal control over delivery of drugs to specific regions in the slices. However, microfluidic devices are not yet fully optimized for such studies. We have recently developed a multifunctional pipette (MFP), a free standing hydrodynamically confined microfluidic device, which provides improved spatiotemporal control over drug delivery to biological tissues. We demonstrate herein the ability of the MFP to selectively perfuse one dendritic layer in the CA1 region of hippocampus with CNQX, an AMPA receptor antagonist, while not affecting the other layers in this region. Our experiments also illustrate the essential role of hydrodynamic confinement in sharpening the spatial selectivity in brain slice experiments. Concentration-response measurements revealed that the ability of the MFP to control local drug concentration is comparable with that of whole slice perfusion, while in comparison the required amounts of active compounds can be reduced by several orders of magnitude. The multifunctional pipette is applied with an angle, which, compared to other hydrodynamically confined microfluidic devices, provides more accessible space for other probing and imaging techniques. Using the MFP it will be possible to study selected regions of brain slices, integrated with various imaging and probing techniques, without affecting the other parts of the slices.

Separation behavior of short single‐ and double‐stranded DNA in 1 micron and 100 nm glass channels

Micro- and nanofluidic lab-on-chip technology offers the unique capability of high-resolution separation, identification, and manipulation of biomolecules with broad applications in chemistry, biology, and medicine. In this work, we probe the effects of ionic strength on separation of ss- and dsDNA within 1 micron and 100 nm-deep glass channels. Separation behavior of DNA is influenced by a number of parameters, including ionic strength, melting temperature, strand length, strand conformation, and channel size. Specifically, we find a shift in the observed mobility of 10-bp (base pair) dsDNA for different ionic strengths due to changes in kinetic parameters, underlying the importance of these considerations when working with short DNA. For 50-base DNA, the electrophoretic mobility difference between ss- and dsDNA increases as the ionic strength increases due to changes in conformation of the ssDNA. Finally, we find that decreasing channel size decreases the absolute electrophoretic mobility of 10- and 20-bp ss- and dsDNA, due to both hydrodyamic confinement and electric double layer (EDL) interactions. We hypothesize that about 4% mobility reduction is due to hydrodynamic confinement, which is observed at all ionic strengths, and further reduction is due to EDL interactions between the DNA and the channel walls, only observed at low ionic strengths.

An optofluidic temperature probe.

We report the application of a microfluidic device for semi-contact temperature measurement in picoliter volumes of aqueous media. Our device, a freely positionable multifunctional pipette, operates by a hydrodynamic confinement principle, i.e., by creating a virtual flow cell of micrometer dimensions within a greater aqueous volume. We utilized two fluorescent rhodamines, which exhibit different fluorescent responses with temperature, and made ratiometric intensity measurements. The temperature dependence of the intensity ratio was calibrated and used in a model study of the thermal activation of TRPV1 ion channels expressed in Chinese hamster ovary cells. Our approach represents a practical and robust solution to the specific problem of measuring temperature in biological experiments in vitro, involving highly localized heat generation, for example with an IR-B laser.

Comparison of Calculated and Measured Critical Flow Rates for Dragging Linear Polymer Chains through a Small Cylindrical Tube

Using recently developed analytical Green’s function/numerical inverse Laplace transform methods, we calculate the hydrodynamic drag and confinement forces on a linear Gaussian chain inside an interacting and impenetrable cylindrical tube in the free draining limit. Equating the two forces leads to an estimation of the critical (minimum) flow rate (qc) to drag the chain through the tube. The estimated qc is compared with our measured qc in theta solutions as well as with our previous scaling argument for a variety of experimental conditions (solvent quality and tube radius, R). Satisfactory agreement between the calculated and observed critical flow rates reveals that the previous description by de Gennes of a linear chain confined in a tube as a series of hard spheres (blobs) significantly underestimates the hydrodynamic drag force, such that the predicted qc for the hard sphere model is 102–103 times higher than observed. The calculations also confirm our previous scaling argument that qc decreases with increasing R, thus departing from the hard-sphere blob prediction that qc is independent of R. More importantly, the calculation describes how interactions with the tube walls affect chain confinement.

Isotropically etched radial micropore for cell concentration, immobilization, and picodroplet generation

To enable several on-chip cell handling operations in a fused-silica substrate, small shallow micropores are radially embedded in larger deeper microchannels using an adaptation of single-level isotropic wet etching. By varying the distance between features on the photolithographic mask (mask distance), we can precisely control the overlap between two etch fronts and create a zero-thickness semi-elliptical micropore (e.g. 20 microm wide, 6 microm deep). Geometrical models derived from a hemispherical etch front show that micropore width and depth can be expressed as a function of mask distance and etch depth. These models are experimentally validated at different etch depths (25.03 and 29.78 microm) and for different configurations (point-to-point and point-to-edge). Good reproducibility confirms the validity of this approach to fabricate micropores with a desired size. To illustrate the wide range of cell handling operations enabled by micropores, we present three on-chip functionalities: continuous-flow particle concentration, immobilization of single cells, and picoliter droplet generation. (1) Using pressure differentials, particles are concentrated by removing the carrier fluid successively through a series of 44 shunts terminated by 31 microm wide, 5 microm deep micropores. Theoretical values for the concentration factor determined by a flow circuit model in conjunction with finite volume modeling are experimentally validated. (2) Flowing macrophages are individually trapped in 20 microm wide, 6 microm deep micropores by hydrodynamic confinement. The translocation of transcription factor NF-kappaB into the nucleus upon lipopolysaccharide stimulation is imaged by fluorescence microscopy. (3) Picoliter-sized droplets are generated at a 20 microm wide, 7 microm deep micropore T-junction in an oil stream for the encapsulation of individual E. coli bacteria cells.