Surveying the Directional Transport of Water Droplets upon Impact on Metallic Topographic Gradients.

Drop impact phenomena on raw, polished, and topography-altered gradient surfaces are investigated and presented. The main aim of this study is to demonstrate that in using a one-step industrial patterning process, it is possible to obtain metal topographical wetting gradients that can produce various desired outcomes after droplet impact. The findings could be applied to improving wind or steam turbine blades.

Influence of rheology and micropatterns on spreading, retraction and fingering of an impacting drop.

Rheology and surface microstructure affect many drop impact processes, including in emerging printing and patterning applications. This study reports on experiments systematically addressing the influence of these parameters on drop impacts. The experiments involved drop impacts of water, glycerol, and shear-thinning carbopol solutions on ten different microstructured surfaces, captured using high-speed photography.

Ferrofluid drop impacts and Rosensweig peak formation in a non-uniform magnetic field.

Vertical drop impacts of ferrofluids onto glass slides in a non-uniform magnetic field have been studied using high-speed photography. Outcomes have been classified based on the motion of the fluid-surface contact lines, and formation of peaks (Rosensweig instabilities) which affect the height of the spreading drop. The largest peaks are nucleated at the edge of a spreading drop, similarly to crown-rim instabilities in drop impacts with conventional fluids, and remain there for an extended time.

Biomechanical responses of encysted zoospores of the oomycete Achlya bisexualis to hyperosmotic stress are consistent with an ability to turgor regulate.

Zoospores are motile, asexual reproductive propagules that enable oomycete pathogens to locate and infect new host tissue. While motile, they have no cell wall and maintain tonicity with their external media using water expulsion vacuoles. Once they locate host tissue, they encyst and form a cell wall, enabling the generation of turgor pressure that will provide the driving force for germination and invasion of the host.

Asymmetric assembly of Lennard-Jones Janus dimers.

Self-assembly of Janus (or "patchy") particles is dependent on the precise interaction between neighboring particles. Here, the orientations of two amphiphilic Janus spheres within a dimer in an explicit fluid are studied with high geometric resolution. Molecular dynamics simulations and semianalytical energy calculations are used with hard- and soft-sphere Lennard-Jones potentials, and temperature and hydrophobicity are varied.

Depletion of HP1α alters the mechanical properties of MCF7 nuclei.

Within the nucleus of the eukaryotic cell, DNA is partitioned into domains of highly condensed, transcriptionally silent heterochromatin and less condensed, transcriptionally active euchromatin. Heterochromatin protein 1α (HP1α) is an architectural protein that establishes and maintains heterochromatin, ensuring genome fidelity and nuclear integrity. Although the mechanical effects of changes in the relative amount of euchromatin and heterochromatin brought about by inhibiting chromatin-modifying enzymes have been studied previously, here we measure how the material properties of the nuclei are modified after the knockdown of HP1α.

Stability of amphiphilic Janus dimers in shear flow: a molecular dynamics study.

Amphiphilic Janus particles in a flow are thought to experience a torque due to the asymmetry in slip at their surfaces. This effect has the potential to destabilise self-assembled Janus structures in flows due to the forces and torques applied to individual Janus nanoparticles. In this work, we investigate the stability of amphiphilic Janus dimers and homogeneous hydrophobic dimers in shear flow using molecular dynamics, and study possible break-up mechanisms.

Inertial capillary uptake of drops.

Uptake of liquid drops into capillary tubes has been experimentally studied and quantitatively analyzed. In experiments, drops of water and aqueous glycerol (≤50 wt %) were drawn into cylindrical borosilicate glass and quartz tubes with an inner diameter of 0.50-0.

High Throughput Analysis of Liquid Droplet Impacts.

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters such as material properties, impact conditions, and experimental configurations. Compounding this, drop impacts are often studied using data-rich high-speed photography, so that it is difficult to analyze many experiments in a detailed and timely manner. The purpose of this method is to enable efficient study of droplet impacts with high-speed photography by using a systematic approach.

Use of microaspiration to study the mechanical properties of polymer gel microparticles.

The mechanical properties of polyacrylamide (PA) and polydimethylsiloxane (PDMS) microparticle populations have been measured using microaspiration, a recently developed experimental technique. Microaspiration is an augmented version of micropipette aspiration, in which optical microscopy data are obtained as individual soft particles pass through the tip of a micropipette. During microaspiration, the ion current passing through the pipette tip is also measured, and the synchronised optical and current data streams are used to study and quantify mechanical properties.

Molecular dynamics simulations of Janus nanoparticles in a fluid flow.

We study the forces and torques on individual Janus nanoparticles in a fluid flow using molecular dynamics simulations. In particular, we consider amphiphilic Janus nanospheres that have different slip boundary conditions on each hemisphere, and calculate the forces and torques experienced by them as a function of their orientation with respect to the flow direction. Furthermore, we examine nanoparticles that are deformed slightly from a spherical shape, and have no-slip boundary conditions.

Mechanical properties of bovine erythrocytes derived from ion current measurements using micropipettes.

Synchronized data from ion currents and optical microscopy have been used to measure the mechanical properties of individual soft microparticles. This new experimental method draws on the signals generated by each particle as it passes through the tip of a pipette. The technique represents an advance on micropipette aspiration (MA), which uses optical microscopy in isolation.

Preclinical studies evaluating the effect of semifluorinated alkanes on ocular surface and tear fluid dynamics.

Purpose: Dry eye disease (DED) is one of the most prevalent ocular surface disorders that presents clinically. Recently, the semifluorinated alkane (SFA) perfluorohexyloctane (NovaTears; EvoTears) entered the market for the management of evaporative DED, while perfluorobutylpentane has been used as a vehicle to enhance ocular drug delivery. This study evaluated the mechanisms by which SFAs might improve therapeutic outcomes in DED.

Tunable Resistive Pulse Sensing: Better Size and Charge Measurements for Submicrometer Colloids.

Tunable resistive pulse sensing (TRPS) uses the Coulter principle to detect, measure, and analyze particles at length scales ranging from tens of nanometers through to micrometers. The technology and its associated methods have advanced so that TRPS is regularly used as a characterization technique in peer-reviewed studies. This Perspective is concerned with opportunities to further develop TRPS, with a specific focus on improved measurement of size and charge for submicrometer particles.

Scanning ion conductance microscopy mapping of tunable nanopore membranes.

We report on the use of scanning ion conductance microscopy (SICM) for topographical mapping of single tunable nanopores, which are used for tunable resistive pulse sensing. A customised SICM system was used to map the elastomeric pore membranes repeatedly, using pipettes with tip opening diameters of approximately 50 nm and 1000 nm. The effect of variations on current threshold, scanning step size, and stretching has been studied.

Pulse Size Distributions in Tunable Resistive Pulse Sensing.

The use of resistive pulse sensors for submicron particle size measurements relies on a clear understanding of pulse size distributions. Here, broadening of such distributions has been studied and explained using conical pores and nominally monodisperse polystyrene particles 200-800 nm in diameter. The use of tunable resistive pulse sensing (TRPS) enabled continuous in situ control of the pore size during experiments.

Asymmetries in the spread of drops impacting on hydrophobic micropillar arrays.

Studies of water drop impacts on microstructured surfaces are important for understanding dynamic wetting on rough surfaces, and for developing related design principles. Here, high-speed imaging has been used to study asymmetries within the spreading phase following vertical water drop impacts at Weber numbers between 34 and 167. The eleven polydimethylsiloxane surfaces studied had micropillars arranged in square and rectangular arrays, with feature sizes ranging from ∼5 μm to ∼240 μm and various pillar cross-sections, in most cases supporting a static Cassie state.

Conductive and biphasic pulses in tunable resistive pulse sensing.

This experimental study concerns the occurrence of biphasic pulses generated during tunable resistive pulse sensing (TRPS) of 200 nm carboxylate polystyrene spheres. In TRPS, a short-lived pulse in ionic current is observed when an individual colloid passes through a pore which separates two fluid reservoirs. The pulse is conventionally resistive, but conductive pulses are observed under certain experimental conditions, as well as biphasic pulses which include both resistive and conductive components.

Applications of tunable resistive pulse sensing.

Tunable resistive pulse sensing (TRPS) is an experimental technique that has been used to study and characterise colloidal particles ranging from approximately 50 nm in diameter up to the size of cells. The primary aim of this Review is to provide a guide to the characteristics and roles of TRPS in recent applied research. Relevant studies reflect both the maturation of the technique and the growing importance of submicron colloids in fields such as nanomedicine and biotechnology.

Co-ordinated detection of microparticles using tunable resistive pulse sensing and fluorescence spectroscopy.

Tunable resistive pulse sensing (TRPS) has emerged as a useful tool for particle-by-particle detection and analysis of microparticles and nanoparticles as they pass through a pore in a thin stretchable membrane. We have adapted a TRPS device in order to conduct simultaneous optical measurements of particles passing through the pore. High-resolution fluorescence emission spectra have been recorded for individual 1.

Nanoparticle ζ-potential measurements using tunable resistive pulse sensing with variable pressure.

Modern resistive pulse sensing techniques can be used to measure nanoparticle electrophoretic mobility, and hence ζ-potential. In contrast to conventional light scattering methods, resistive pulse sensing produces particle-by-particle data. We have used tunable resistive pulse sensing (TRPS) to compare methods for measuring the ζ-potential of carboxylated polystyrene nanoparticles.

Small molecule detection in solution via the size contraction response of aptamer functionalized nanoparticles.

We demonstrate a simple new sensor design that exploits aptamer functionalized nanoparticles (NPs) to transduce the signal of aptamer receptors binding to target small molecules. An aptamer capable of binding to our target 17β-estradiol (E2) was isolated by SELEX with dissociation constant of 50 nM and tethered to the surface of carboxylated polystyrene NPs. Upon exposing the aptamer functionalized NPs to E2 in buffered water, we use dynamic light scattering (DLS) and resistive pulse sensing (TRPS) to observe a distinct reduction of the conjugated particle size and a less negative zeta potential, which can be correlated to the E2 concentration in the lower nanomolar range.

Magnetic microbead transport during resistive pulse sensing.

Tunable resistive pulse sensing (TRPS) experiments have been used to quantitatively study the motion of 1 μm superparamagnetic beads in a variable magnetic field. Closed-form theory has been developed to interpret the experiments, incorporating six particle transport mechanisms which depend on particle position in and near a conical pore. For our experiments, calculations indicate that pressure-driven flow dominates electrophoresis and magnetism by a factor of ∼100 in the narrowest part of the pore, but that magnetic force should dominate further than ∼1 mm from the membrane.

Tunable SERS using gold nanoaggregates on an elastomeric substrate.

We report on the self-assembly of colloidal gold nanoparticles on a stretchable, elastomeric membrane, and the use of this membrane as a base substrate for far-field confocal Raman measurements. Surface-enhanced Raman scattering (SERS) enhancement for such a substrate was estimated as 10(6) to 10(7). Atomic force microscopy has been used to study the changes in nanoparticle topography when the membrane is stretched.

Size and charge characterisation of a submicrometre oil-in-water emulsion using resistive pulse sensing with tunable pores.

Resistive pulse sensing (RPS) with tunable pores (TPs) has been used to investigate an oil-in-water emulsion stabilised with β-lactoglobulin (BLG). The mode of the droplet size distribution steadily increased over four months, from less than 150 nm to more than 200 nm. Results suggest that the dominant growth mechanism was migration of oil to relatively large droplets, as in Ostwald ripening.