Increasing flow rates in polydimethylsiloxane-based deterministic lateral displacement devices for sub-micrometer particle separation

Advanced Materials Interfaces

Nanostructured materials that mimic structural coloration in nature can be synthetically created by colloidal self‐assembly. To maximize optical effects, the natural world integrates melanin as a broadband absorber to remove incoherently scattered light. Polydopamine (PDA) is used as a synthetic analog of natural melanin to systematically investigate the influence of absorber quantity and distribution on color saturation in colloidal photonic crystals. The absorbing PDA is integrated into two distinct ways: homogenous colloidal crystals are produced from core–shell particles with incrementally increasing polydopamine shells, and heterogeneous colloidal crystals are formed by co‐assembly of varying ratios of polystyrene (PS) and absorbing PS@PDA particles. The chromaticity is quantified by converting the measured spectra to reconstructed colors in the L*a*b* color sphere to identify structures with optimal color …

Langmuir

Unraveling the two-dimensional (2D) structural ordering of colloidal particles assembled at a flat surface is essential for understanding and optimizing their physical properties. So far, grazing-incidence small-angle X-ray scattering (GISAXS) has been widely used to determine crystallographic information on 2D self-assembled structures of nanosize objects. However, solving the structure of 2D lattices consisting of micrometer (μm)-sized objects still remains a challenge using scattering methods. Here, a model 2D SCALMS (supported catalytically active liquid metal solution) template is fabricated from μm-sized polystyrene (PS) spheres that form a monolayer on top of the flat solid support. GISAXS patterns of the sample were collected for rotation angles around its surface normal in steps of 3°. For every rotation angle, different Bragg-type interference maxima along the out-of-plane (qz) direction were observed. On …

Microfluidics and Nanofluidics

In this study, we show the design and manufacturing of microfluidic deterministic lateral displacement (DLD) devices for sub-micrometer particle separation. For that purpose, devices with pillar gaps of 4 µm and a periodicity of 50 were designed. After photolithographic manufacturing of SU-8 masters with different heights (15 and 30 µm) and vertical sidewalls for soft-lithographic replication with polydimethylsiloxane (PDMS) the influence of flow rate on the separation efficiency of 0.45 and 0.97 µm particles was investigated. The 15 µm devices were operated at 0.125 and 0.5 µl/min sample flow rate and the 30 µm devices at 0.5 and 2.0 µl/min, respectively. Excellent separation efficiencies were observed for both device heights at the lower sample flow rates, while separation efficiencies decreased at the respective higher sample flow rates. The decrease in separation efficiency was attributed to deformation of the soft …

Advanced Materials

Continuous gradients in self-assembled materials can provide functionality exceeding that of the homogenous case. In article number 2208745, Markus Retsch and co-workers present a synthesis method that provides gradient size distributions via a controlled extraction emulsion process (CrEEP). The high degree of control allows the fabrication of a continuous-gradient photonic glass with enhanced broadband reflectance.

ACS photonics

Molecular chirality plays fundamental roles in biology. The chiral response of a molecule occurs at a specific spectral position, determined by its molecular structure. This fingerprint can be transferred to other spectral regions via the interaction with localized surface plasmon resonances of gold nanoparticles. Here, we demonstrate that molecular chirality transfer occurs also for plasmonic lattice modes, providing a very effective and tunable means to control chirality. We use colloidal self-assembly to fabricate non-close packed, periodic arrays of achiral gold nanoparticles, which are embedded in a polymer film containing chiral molecules. In the presence of the chiral molecules, the surface lattice resonances (SLRs) become optically active, i.e., showing handedness-dependent excitation. Numerical simulations with varying lattice parameters show circular dichroism peaks shifting along with the spectral positions of …

Advanced Engineering Materials

A novel strategy for manufacturing of the main insulation of high‐voltage rotating machines is presented. The developed process is based on established electrostatic powder coating equipment. Using complete automation enables the precise and reproducible application of homogeneous powder coating layers. Individual layers can be stacked by process repetitions to achieve a desired layer thickness. This coating strategy alters the particle deposition process by introducing additional capillary bridges that significantly increase powder adhesion. A systematic parameter study is performed to provide process–structure relations connecting various process parameters with the resultant coating thickness and homogeneity. The parameters of the developed coating process are iteratively improved to maximize coating homogeneity and minimize defect density, the most critical parameters in high‐voltage insulation …

Macromolecular Materials and Engineering

Liquid‐infused surfaces exhibit remarkable repellency properties toward water, oils, and complex fluids and are widely applied to maintain clean, operational, and high‐performing surfaces in various fields, from the biomedical sector to marine infrastructure. Polydopamine (PDA) forms an ideal base layer for the development of such coatings as it adheres to virtually any substrate and can be chemically modified via amino‐containing molecules to adjust the surface properties. Here, strategies are explored to increase the mechanical stability of such coatings by i) incorporating imidazole during film formation to increase crosslinking, and ii) formation of a composite consisting of the organic PDA and an inorganic siliceous porous coating by infiltration of a preformed porous silica layer with PDA. Both strategies exhibit improved resistance to tangential shear assessed by a sandpaper abrasion test and to dynamic …

Advanced Materials

2D colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long‐range order of such crystals is essential to ensure functionality, but difficult to achieve in self‐assembling systems. Here, a simple loudspeaker setup for the acoustic crystallization of 2D colloidal crystals (ACDC) of polystyrene, microgels, and core–shell particles at liquid interfaces is introduced. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. The order is characterized via the structural color of the colloidal crystal, the acoustic annealing process is optimized via the frequency and the amplitude of the applied sound wave, and its efficiency is rationalized via the surface coverage‐dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple …

Advanced Materials

Colloidal crystals and glasses manipulate light propagation depending on their chemical composition, particle morphology, and mesoscopic structure. This light–matter interaction has been intensely investigated, but a knowledge gap remains for mesostructures comprising a continuous property gradient of the constituting particles. Here, a general synthetic approach to bottom‐up fabrication of continuous size gradient colloidal ensembles is introduced. First, the technique synthesizes a dispersion with a specifically designed gradual particle size distribution. Second, self‐assembly of this dispersion yields a photonic colloidal glass with a continuous size gradient from top to bottom. Local and bulk characterization methods are used to highlight the significant potential of this mesostructure, resulting in vivid structural colors along, and in superior light scattering across the gradient. The process describes a general …

Langmuir

Colloidal lithography utilizes self-assembled particle monolayers as lithographic masks to fabricate arrays of nanostructures by combination of directed evaporation and etching steps. This process provides complex nanostructures over macroscopic areas in a simple, convenient, and parallel fashion without requiring clean-room infrastructure and specialized equipment. The appeal of the method comes at the price of imperfections impairing the optical quality, especially for arrayed nanostructures relying on well-ordered lattices. Imperfections are often generically mentioned to rationalize the discrepancy between experimental and simulated resonances. Yet, little attention is given to detailed structure–property relationships connecting typical defects directly with the optical properties. Here, we use a correlative approach to connect nano- and microscopic defects occurring from the colloidal lithography process with …

Nature communications

Bifurcations in kinetic pathways decide the evolution of a system. An example is crystallization, in which the thermodynamically stable polymorph may not form due to kinetic hindrance. Here, we use confined self-assembly to investigate the interplay of thermodynamics and kinetics in the crystallization pathways of finite clusters. We report the observation of decahedral clusters from colloidal particles in emulsion droplets and show that these decahedral clusters can be thermodynamically stable, just like icosahedral clusters. Our hard sphere simulations reveal how the development of the early nucleus shape passes through a bifurcation that decides the cluster symmetry. A geometric argument explains why decahedral clusters are kinetically hindered and why icosahedral clusters can be dominant even if they are not in the thermodynamic ground state.

Communications Physics

The narrow escape theory (NET) predicts the escape time distribution of Brownian particles confined to a domain with reflecting borders except for one small window. Applications include molecular activation events in cell biology and biophysics. Specifically, the mean first passage time can be analytically calculated from the size of the domain, the escape window, and the diffusion coefficient of the particles. In this study, we systematically tested the NET in a disc by variation of the escape opening. Our model system consisted of micro-patterned lipid bilayers. For the measurement of , we imaged diffusing fluorescently-labeled lipids using single-molecule fluorescence microscopy. We overcame the lifetime limitation of fluorescent probes by re-scaling the measured time with the fraction of escaped particles. Experiments were complemented by matching stochastic numerical simulations. To conclude, we confirmed the …

Journal of Rheology

Interfacial rheology is important for understanding properties such as Pickering emulsion or foam stability. Currently, the response is measured using a probe directly attached to the interface. This can both disturb the interface and is coupled to flow in the bulk phase, limiting its sensitivity. We have developed a contactless interfacial method to perform interfacial shear rheology on liquid/liquid interfaces with no tool attached directly to the interface. This is achieved by shearing one of the liquid phases and measuring the interfacial response via confocal microscopy. Using this method, we have measured steady shear material parameters such as interfacial elastic moduli for interfaces with solidlike behavior and interfacial viscosities for fluidlike interfaces. The accuracy of this method has been verified relative to a double-wall ring geometry. Moreover, using our contactless method, we are able to measure lower …

Catalysis Science & Technology

Supported catalytically active liquid metal solution (SCALMS) materials represent a recently developed class of heterogeneous catalysts, where the catalytic reaction takes place at the highly dynamic interface of supported liquid alloys. Ga nuggets were dispersed into nano-droplets in propan-2-ol using ultrasonication followed by the addition of Pt in a galvanic displacement reaction – either directly into the Ga/propan-2-ol dispersion (in situ) or consecutively onto the supported Ga droplets (ex situ). The in situ galvanic displacement reaction between Ga and Pt was studied in three different reaction media, namely propan-2-ol, water, and 20 vol% water containing propan-2-ol. TEM investigations reveal that the Ga–Pt reaction in propan-2-ol resulted in the formation of Pt aggregates on top of Ga nano-droplets. In the water/propan-2-ol mixture, the desired incorporation of Pt into the Ga matrix was achieved. The ex situ …

Langmuir

Colloidal crystals are excellent model systems to study self-assembly and structural coloration because their periodicities coincide with the wavelength range of visible light. Different assembly methods inherently introduce characteristic defects and irregularities, even with nearly monodisperse colloidal particles. Here, we investigate how these imperfections influence the structural coloration by comparing two techniques to obtain colloidal crystals. 3D colloidal crystals produced by convective assembly are well-ordered and periodically arranged but show microscopic cracks. (2+1)D colloidal crystals fabricated by stacking individual monolayers show a decreased hexagonal order and limited crystal registration between single monolayers in the z-direction. We investigate the optical properties of both systems by comparing identical numbers of layers using correlative microspectroscopy. These measurements show …

The present invention relates to a process for producing a particle dispersion comprising the steps of: a) providing a dispersion consisting of a solvent and solid core particles, b) providing a solution of a soluble, interfacially-active polymer having a molecular weight of more than 5 kDa, c) mixing said dispersion of solid core particles with said polymer solution, d) removing free polymer from the obtained mixture; wherein in step a) the solvent is selected from an organic solvent, a mixture of at least two organic solvents or a mixture of at least one organic solvent with water; wherein in step c), the amount of the soluble, interfacially-active polymer mixed with said dispersion of solid core particles exceeds the amount of polymer required to coat the surface of each of the solid core particles with a monolayer of the polymer; wherein step d) is repeated until the requirement described by the following formula is fulfilled:

Microfluidics and Nanofluidics

Polydimethylsiloxane (PDMS) is a popular material to rapidly manufacture microfluidic deterministic lateral displacement (DLD) devices for particle separation. However, manufacturing and operation challenges are encountered with decreasing device dimensions required to separate submicron particles. The smaller dimensions, notably, cause high hydraulic resistance, resulting in significant pressure even at relatively low throughputs. This high pressure can lead to PDMS deformation, which, in turn, influences the device performance. These effects may often be overlooked in the design and operation of devices but provide a systematic source of error and inaccuracies. This study focuses in detail on these effects and investigates pillar deformation in detail. Subsequently, we discuss a potential solution to this deformation using thermal annealing to stiffen the PDMS. We evaluate the influence of stiffness on the …

Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self …

Materials Horizons

Nanostructuration is a promising tool for enhancing the performance of sensors based on electrochemical transduction. Nanostructured materials allow for increasing the surface area of the electrode and improving the limit of detection (LOD). In this regard, inverse opals possess ideal features to be used as substrates for developing sensors, thanks to their homogeneous, interconnected pore structure and the possibility to functionalize their surface. However, overcoming the insulating nature of conventional silica inverse opals fabricated via sol–gel processes is a key challenge for their application as electrode materials. In this work, colloidal assembly, atomic layer deposition and selective surface functionalization are combined to design conductive inverse opals as an electrode material for novel glucose sensing platforms. An insulating inverse opal scaffold is coated with uniform layers of conducting aluminum …

Microfluidics and Nanofluidics

In rarefied gas dynamics scattering kernels deserve special attention since they contain all the essential information about the effects of physical and chemical properties of the gas–solid surface interface on the gas scattering process. However, to study the impact of the gas–surface interactions on the large-scale behavior of fluid flows, these scattering kernels need to be integrated in larger-scale models like Direct Simulation Monte Carlo (DSMC). In this work, the Gaussian mixture (GM) model, an unsupervised machine learning approach, is utilized to establish a scattering kernel for monoatomic (Ar) and diatomic () gases directly from Molecular Dynamics (MD) simulations data. The GM scattering kernel is coupled to a pure DSMC solver to study isothermal and non-isothermal rarefied gas flows in a system with two parallel walls. To fully examine the coupling mechanism between the GM scattering kernel and the DSMC approach, a one-to-one correspondence between MD and DSMC particles is considered here. Benchmarked by MD results, the performance of the GM-DSMC is assessed against the Cercignani–Lampis–Lord (CLL) kernel incorporated into DSMC simulation (CLL-DSMC). The comparison of various physical and stochastic parameters shows the better performance of the GM-DSMC approach. Especially for the diatomic system, the GM-DSMC outperforms the CLL-DSMC approach. The fundamental superiority of the GM-DSMC approach confirms its potential as a multi-scale simulation approach for accurately measuring flow field properties in systems with highly nonequilibrium conditions.

Microfluidics and Nanofluidics

Kinetic equations are crucial for modeling non-equilibrium phenomena, but their computational complexity is a challenge. This paper presents a data-driven approach using reduced order models (ROM) to efficiently model non-equilibrium flows in kinetic equations by comparing two ROM approaches: proper orthogonal decomposition (POD) and autoencoder neural networks (AE). While AE initially demonstrate higher accuracy, POD’s precision improves as more modes are considered. Notably, our work recognizes that the classical POD model order reduction approach, although capable of accurately representing the non-linear solution manifold of the kinetic equation, may not provide a parsimonious model of the data due to the inherently non-linear nature of the data manifold. We demonstrate how AEs are used in finding the intrinsic dimension of a system and to allow correlating the intrinsic quantities with …

Microfluidics and Nanofluidics

The electro-osmotic flow (EOF) in a neutral system consisting of an aqueous NaCl solution confined in a nanochannel with two parallel Molybdenum disulfide () walls and in the presence of an external electric field parallel to the channel walls, is investigated for the first time. The results indicate that the thickness of the Stern layer grows as the negative electric surface charge density on the nanochannel walls increases. The Stern layer becomes thinner as the salt concentration is increased. Moreover, the EOF occurs under the no-slip condition on the walls. In addition, by increasing the surface charge density the average of the flow velocity across the nanochannel initially grows (Debye--Hckel regime) and reaches its maximum value. Then, by further increasing the surface charge density the water flow rate decreases (intermediate regime), and gets the zero value and becomes negative (reverse flow regime) at even larger values of the surface charge densities. Comparing the results of the previous work wherein the channels are composed of the black phosphorene walls with those of the present study for a channel composed of surfaces, show that for the latter case the reverse flow occurs at a lower surface charge density and with a greater value of the peak velocity with respect to the change in the surface charge density for the former case.

Microfluidics and Nanofluidics

This study introduces an innovative method aimed at achieving exceptional stability in emulsions. The primary focus is on re-emulsifying precisely controlled and uniform initial single emulsions, generated by microfluidic devices, to produce single-core double emulsions and core–shell microparticles. Departing from traditional approaches, our method employs a unique combination of advanced Two-level fractional factorial design and numerical simulation. These tools are utilized to discern and optimize critical parameters necessary for the formation of highly monodispersed stable single emulsions and their subsequent transformation into double emulsions. Correlations are established to estimate the size and stability of the primary single emulsion based on immiscible phase flow rate ratio and surfactant concentration. These correlations provide a comprehensive understanding that facilitates the intentional …

Microfluidics and Nanofluidics

Despite several decades of development, microfluidics lacks a sealing material that can be readily fabricated, leak-tight under high liquid water pressure, stable over a long time, and vacuum compatible. In this paper, we report the performances of a micro-scale processable sealing material for nanofluidic/microfluidics chip fabrication, which enables us to achieve all these requirements. We observed that micrometric walls made of SU-8 photoresist, whose thickness range from 35 to 135 µm, are at least leak-tight to 1.5 bars and up to 5.5 bars, exhibit no water porosity even after 2 months of aging, and are able to sustain under mbar vacuum. This sealing material is therefore reliable and versatile for building microchips, part of which must be isolated from liquid water under pressure or vacuum. Moreover, the fabrication process we propose does not require the use of either aggressive chemicals or high …

Microfluidics and Nanofluidics

This paper reports a fabrication method that can make microstructures such as microfluidic channels and nanostructures to generate surface plasmon resonance (SPR) signals in one-step using hot embossing. We first made a micro/nanostructural mold on a silicon substrate through sequential e-beam lithography, reactive ion etching (RIE), photolithography, and inductively coupled plasma RIE. The fabricated mold and cyclo-olefin polymer (COP) film were pressed between two flat, heated metal bases under optimal conditions, and the micro/nanostructures were complementarily transferred to the COP film. After depositing a thin aluminum film onto the nanostructure, the device was completed by patterning Nafion that crossed two channels and a nearby nanostructure, and by bonding the COP film to a flat polydimethylsiloxane (PDMS) substrate with holes punched for the inlets and outlets. SPR signals of the …

Microfluidics and Nanofluidics

This study introduces a practical approach utilizing microfluidic trap and mixer modules fabricated with polydimethylsiloxane (PDMS) microfluidic devices. These modules were employed to capture and fluorescently label various randomly shaped microplastics (MPs) like polyethylene (PE), polypropylene (PP), and polystyrene (PS). Within the MPs trap module, grooves were incorporated into a straight-lined channel using SU-8 photolithography. This design induced turbulence effectively trapping and gathering the MPs within aqueous phases at 15 groove spaces, which achieved a trapping efficiency of up to 69% for PS MPs sized at a flow rate of 2 mL/min. Additionally, a mixer module featuring two flow inlets was designed to create a serpentine microfluidic channel, whose design significantly reduced sample and reagent (Nile Red) consumption during MP fluorescence staining at 80 °C. Furthermore, 2 nm gold …

Microfluidics and Nanofluidics

Curvilinear microchannels have enabled high throughput sized-based separation and manipulation of microparticles. Real life applications usually deal with fluid’s non-Newtonian behavior, where particles dynamics are altered compared to Newtonian mediums. Despite multiple reports on particle manipulation in shear-thinning fluids, no fundamental experimental investigation has been reported on microparticle focusing behavior inside shear-thickening fluids such as metallic oxide nanofluids in water (e.g., SiO2-water). These nanofluids pose unique thermal characteristics and exhibit a drastic increase in viscosity as the shear rate rises in the microchannel. Here, we investigate the particle focusing behavior of co-flows of SiO2 nanofluids inside curved microchannels with various channel widths and radii of curvature. We also report on the effect of nanofluid concentration, fluid axial velocity, and the particle size on …

Microfluidics and Nanofluidics

This study introduces an innovative method aimed at achieving exceptional stability in emulsions. The primary focus is on re-emulsifying precisely controlled and uniform initial single emulsions, generated by microfluidic devices, to produce single-core double emulsions and core–shell microparticles. Departing from traditional approaches, our method employs a unique combination of advanced Two-level fractional factorial design and numerical simulation. These tools are utilized to discern and optimize critical parameters necessary for the formation of highly monodispersed stable single emulsions and their subsequent transformation into double emulsions. Correlations are established to estimate the size and stability of the primary single emulsion based on immiscible phase flow rate ratio and surfactant concentration. These correlations provide a comprehensive understanding that facilitates the intentional …

Microfluidics and Nanofluidics

Mathematical and computational models linking cell mechanical properties with deformation are crucial for understanding cellular behavior. While various techniques measure the stiffness and viscosity of cells, recent experiments suggest that cells exhibit poroelastic behavior, characterized by solid mesh networks immersed in cytosol liquid (Moeendarbary et al. in Nat Mater 12:253–261, 2013. https://doi.org/10.1038/nmat3517). Despite this, a mathematical model relating poroelastic cell deformation and Young's modulus of solid networks has not been reported. This study presents the first poroelasticity-based mathematical model for relating cell deformation with Young’s modulus of solid mesh networks. The model is validated by utilizing the experimental data of the cell’s squeezing behavior through a constriction microchannel. The predicted Young’s modulus for HeLa, MCF-10A, and MDA MB-231 cell lines are …

Microfluidics and Nanofluidics

Snap-off events are one of the most common and essential phenomena in two-phase flow in porous media. This paper uses the scanning results of a siltstone slice to construct a two-dimensional heterogeneous pore network structure to visualise microscopic snap-off phenomena and displacement processes accurately. The relationship between snap-off events and the non-wetting phase saturation was studied using two-phase flow displacement experiments. Results show that although the non-wetting phase snap-off events benefit freeing the trapped non-wetting phase in the microchannels, high-frequency snap-off events are the main reason for trapping the non-wetting phase during the displacement process, eventually leading to residuals. The frequency of non-wetting phase snap-off events in the pore network structure can be reduced to lower the non-wetting phase saturation and reduce the non-wetting …

Microfluidics and Nanofluidics

Snap-off events are one of the most common and essential phenomena in two-phase flow in porous media. This paper uses the scanning results of a siltstone slice to construct a two-dimensional heterogeneous pore network structure to visualise microscopic snap-off phenomena and displacement processes accurately. The relationship between snap-off events and the non-wetting phase saturation was studied using two-phase flow displacement experiments. Results show that although the non-wetting phase snap-off events benefit freeing the trapped non-wetting phase in the microchannels, high-frequency snap-off events are the main reason for trapping the non-wetting phase during the displacement process, eventually leading to residuals. The frequency of non-wetting phase snap-off events in the pore network structure can be reduced to lower the non-wetting phase saturation and reduce the non-wetting …

Microfluidics and Nanofluidics

In rarefied gas dynamics scattering kernels deserve special attention since they contain all the essential information about the effects of physical and chemical properties of the gas–solid surface interface on the gas scattering process. However, to study the impact of the gas–surface interactions on the large-scale behavior of fluid flows, these scattering kernels need to be integrated in larger-scale models like Direct Simulation Monte Carlo (DSMC). In this work, the Gaussian mixture (GM) model, an unsupervised machine learning approach, is utilized to establish a scattering kernel for monoatomic (Ar) and diatomic () gases directly from Molecular Dynamics (MD) simulations data. The GM scattering kernel is coupled to a pure DSMC solver to study isothermal and non-isothermal rarefied gas flows in a system with two parallel walls. To fully examine the coupling mechanism between the GM scattering kernel and the DSMC approach, a one-to-one correspondence between MD and DSMC particles is considered here. Benchmarked by MD results, the performance of the GM-DSMC is assessed against the Cercignani–Lampis–Lord (CLL) kernel incorporated into DSMC simulation (CLL-DSMC). The comparison of various physical and stochastic parameters shows the better performance of the GM-DSMC approach. Especially for the diatomic system, the GM-DSMC outperforms the CLL-DSMC approach. The fundamental superiority of the GM-DSMC approach confirms its potential as a multi-scale simulation approach for accurately measuring flow field properties in systems with highly nonequilibrium conditions.

Microfluidics and Nanofluidics

Mathematical and computational models linking cell mechanical properties with deformation are crucial for understanding cellular behavior. While various techniques measure the stiffness and viscosity of cells, recent experiments suggest that cells exhibit poroelastic behavior, characterized by solid mesh networks immersed in cytosol liquid (Moeendarbary et al. in Nat Mater 12:253–261, 2013. https://doi.org/10.1038/nmat3517). Despite this, a mathematical model relating poroelastic cell deformation and Young's modulus of solid networks has not been reported. This study presents the first poroelasticity-based mathematical model for relating cell deformation with Young’s modulus of solid mesh networks. The model is validated by utilizing the experimental data of the cell’s squeezing behavior through a constriction microchannel. The predicted Young’s modulus for HeLa, MCF-10A, and MDA MB-231 cell lines are …

Microfluidics and Nanofluidics

Sharp edge structures have been demonstrated as an efficient way of generating acoustic streaming in microfluidic devices, which finds numerous applications in fluid mixing, pumping, particle actuation, and cell lysis. A sharp tip capillary is widely available means of generating sharp structures without the need of microfabrication, which has been used for studying enzyme kinetics, droplet digital PCR, and mass spectrometry analysis. In this work, we studied the influence of liquid inside the vibrating glass capillary on its efficiency of generating acoustic streaming. Using fluorescence microscopy and fluorescent particles, we observed that adding liquid to the inside of the vibrating glass capillary changed the streaming patterns as well as led to increased streaming velocity. Based on the observed streaming patterns, we hypothesized the liquid present in the capillary changed vibration mode of the capillary, which is …

Microfluidics and Nanofluidics

In this work, merged and alternating droplets generated in a microfluidic double T-junction are investigated using experiments and numerical simulations. The double T-junction is constructed by symmetrically inserting two capillaries into a microfluidic chip at specific positions. We explore the effects of the two-phase flow rate fraction, capillary tip distance (30 μm, 60 μm, and 200 μm), and fluid properties on droplet formation phenomena. Detailed observations reveal four distinct regimes during the dynamic evolution of the two-phase interface morphology: merged state, stable alternating droplets, droplet pairs, and jetting. Two phase diagrams are obtained to demonstrate that interfacial tension and dispersed phase viscosity significantly influence these regimes. Moreover, we find that as the flow rate fraction increases from 0.054 to 0.286, the length of generated droplets increases from 156 to 789 μm; we provide a …

Microfluidics and Nanofluidics

Some anticancer treatments may cause Multidrug Resistance (MDR). In these cases, cells pump the drug out of the intracellular environment, thereby preventing drug effects. Several strategies have been used to avoid MDR, including using two or more drugs at low concentrations to increase the sensitivity of cells to treatment. We present an effective, cheap, fast microfluidic alternative to test two drugs simultaneously using a reversible sealing and reusable device to determine the optimal concentration. We used the rugs doxorubicin (DOX) and paclitaxel (PXT) as proof of concept. The microdevice allows the testing of two drugs in real time. Furthermore, running two experiments in sextuplicates and control in the same microchip is possible. We used two combinations of drugs, varying the drug concentration (C1 = 0.010 mg.mL− 1 DOX and 0.002.mL− 1 mg PXT, C2 = 0.010 mg.mL− 1 DOX and 0.004 mg.mL …

Microfluidics and Nanofluidics

The migration of sperm cells in a female reproductive tract is responsible for the successful fertilization of the female egg. In this research work, the effect of the surrounding fluids on the motion of sperm cells has been studied using a microfluidic channel. To analyze the motility of sperm, primary motility parameters such as velocity, beat frequency, amplitude, and derived parameters such as linearity, straightness, and wobble have been measured. The results indicate that sperms possess higher progressive motility in non-Newtonian fluids compared to Newtonian fluids in the same viscosity range. The motion of the sperm shows an inverse relationship between the amplitude of the head trajectory and the beat frequency of the flagella. Numerical studies were performed to measure the drag force on these sperm. The trajectories of the flagella, forces acting on sperm, power generated, pulling power, and efficiency of …

Microfluidics and Nanofluidics

Mathematical and computational models linking cell mechanical properties with deformation are crucial for understanding cellular behavior. While various techniques measure the stiffness and viscosity of cells, recent experiments suggest that cells exhibit poroelastic behavior, characterized by solid mesh networks immersed in cytosol liquid (Moeendarbary et al. in Nat Mater 12:253–261, 2013. https://doi.org/10.1038/nmat3517). Despite this, a mathematical model relating poroelastic cell deformation and Young's modulus of solid networks has not been reported. This study presents the first poroelasticity-based mathematical model for relating cell deformation with Young’s modulus of solid mesh networks. The model is validated by utilizing the experimental data of the cell’s squeezing behavior through a constriction microchannel. The predicted Young’s modulus for HeLa, MCF-10A, and MDA MB-231 cell lines are …

Microfluidics and Nanofluidics

Snap-off events are one of the most common and essential phenomena in two-phase flow in porous media. This paper uses the scanning results of a siltstone slice to construct a two-dimensional heterogeneous pore network structure to visualise microscopic snap-off phenomena and displacement processes accurately. The relationship between snap-off events and the non-wetting phase saturation was studied using two-phase flow displacement experiments. Results show that although the non-wetting phase snap-off events benefit freeing the trapped non-wetting phase in the microchannels, high-frequency snap-off events are the main reason for trapping the non-wetting phase during the displacement process, eventually leading to residuals. The frequency of non-wetting phase snap-off events in the pore network structure can be reduced to lower the non-wetting phase saturation and reduce the non-wetting …