Parallel single cell analysis on an integrated microfluidic platform for cell trapping, lysis and analysis

We report here a novel and easily scalable microfluidic platform for the parallel analysis of hundreds of individual cells, with controlled single cell trapping, followed by their lysis and subsequent retrieval of the cellular content for on-chip analysis. The device consists of a main channel and an array of shallow side channels connected to the main channel via trapping structures. Cells are individually captured in dam structures by application of a negative pressure from an outlet reservoir, lyzed on site and the cellular content controllably extracted and transported in the individual side channels for on-chip analysis.\u

Dynamics of Colloids Confined in Microcylinders

We studied both global and local effects of cylindrical confinement on the diffusive behavior of hard sphere (HS) colloids. Using confocal scanning laser microscopy (CSLM) and particle tracking, we measured the mean squared displacement (MSD) of 1 micron sized silica particles in water–glycerol. This combination of fluid and setup allowed us to measure MSDs in a 4-dimensional parameter space, defined by the HS volume fraction (Φ: 0.05–0.39), cylinder radius (R: 2.5–20 micron), distance to the wall (z) and lagtime (τ: 0.03–60 s). MSDs for the entire cylinder confirm earlier findings that both narrowing the cylinder and populating it cause a slower dynamics. Additionally a decrease in R was found to cause a stronger ordering of the fluid. The effect of confinement on dynamics was further examined as a function of (z) location. For the largest cylinder (with minor curvature), we found that the strong decrease in MSD near the wall, becomes much less pronounced for higher Φ. Analyzing the radial (r) and azimuthal (θ) components, we found pronounced differences in the z-dependence that were ‘hidden’ in the total MSD. Near the wall, the r-MSD shows a much steeper z-dependence while at larger z, it shows a remarkable anti-correlation with the (peaked) density n(z). Also the dependence of the r-MSD on lagtime correlates with n(z): diffusive in between layers, but subdiffusive inside layers. These observations bring earlier findings together, while also shedding new light on the diffusive dynamics of concentrated colloids in narrow capillaries

The effect of interfacial forces on 2-phase microfluidics

We present the influence of both the solid-liquid interfacial force (surface wettability) and liquid-liquid interfacial force (added surfactants) on water-oil two-phase flow in microfluidic devices. Experimental results show that, in contrast to macroscale experiments, the surface wettability crucially determines the emulsion type created in the microchannels: O/W in hydrophilic channel and W/O in hydrophobic channel. Surfactants, however, determines the flow pattern, changing from droplet-based to stratified flow by decreasing wo

Electrode‑assisted trapping and of droplets on hydrophilic in a hydrophobic microchannel

In two-phase flow microfluidics, there is an increasing interest in technologies which enable the encapsulation of biological cells into aqueous drops and the subsequent study of their molecular (excretion or lysis) products. One not yet available but very promising analysis method is the use of biospecific surface patches embedded in the wall of microfluidic channels. In this paper, we tackle some technological challenges encountered in the development of such applications. In the detection protocol, each drop must be enabled to wet the designated patch, be held in contact long enough for biomolecular detection and subsequently be released. This is engineered via a combination of well-defined chemical sites in the walls of the flow channel and insulated microelectrodes. The tunability of the local electric field allows to modify the competition between chemical (pinning) forces which tend to immobilize the drop and hydrodynamic forces which oppose this process. We developed a prototype microfluidic device which offers this functionality. A channel structure is sandwiched between an actuation surface with electrowetting (EW) electrodes on one side and a detector surface with a hydrophilic patch amidst a hydrophobic environment on the other. Two pairs of carefully aligned EW electrodes are used: one for drop adherence and another one for the subsequent release. We demonstrate these operations and discuss the required voltage signals in terms of the forces on the drop. Finally, we discuss possible steps for further improvement in the device

Influence of electrochemical cycling on the rheo-impedance of anolytes for Li-based Semi Solid Flow Batteries

The recently launched concept of Semi-Solid Flow Batteries (SSFBs) shows a strong potential for flexible energy storage, but the liquid-dispersed state of the electrode materials introduces several aspects of which a scientific understanding is lacking. We studied the effect of electrochemical cycling on the rheological and electrical properties of a SSFB anolyte containing Li4Ti5O12 (LTO) and Ketjen Black (KB) particles in EC:DMC solvent with 1 M LiPF6, using an adapted rheometer that allows in situ electrochemical cycling and electrical impedance spectroscopy. Charging (lithiation) caused a reduction in the electronic conductivity, yield stress and high shear viscosity of the fluid electrode. For mildly reducing voltages (1.4 V), these changes were partially reversed on discharging. For more reducing voltages these changes were stronger and persistent. The finding of comparable trends for a fluid electrode without the LTO, lends support to a simplistic interpretation, in which all trends are ascribed to the formation of a surface layer around the conductive KB nanoparticles. This Solid Electrolyte Interphase (SEI) insulates particles and reduces the van der Waals attractions between them. SEI layers formed at less reducing voltages, partially dissolve during the subsequent discharge. Those formed at more reducing voltages, are thicker and permanent. As these layers increase the electronic resistance of the fluid electrode by (more than) an order of magnitude, our findings highlight significant challenges due to SEI formation that still need to be overcome to realize SSFBs

Microfabrication of shaped MM-scale tissues to study vascular development using modular bottom-up approach

Recapitulating developmental mechanisms in vitro necessitate models of intermediate complexity, between simple 2D culture and complex in vivo models, which integrate both physical and molecular cues. Here, we describe a cheap and simple bottom-up microfabrication method to build 3D millimeter-scale tissues with geometric shapes. These tissues are suitable for long-term culture in tissue-based assays and as implants for clinical applications. In a case study, we recapitulate some mechanisms of vasculogenesis, the assembly of capillary blood vessels