Droplet Microfluidic Optimisation Using Micropipette Characterisation of Bio-Instructive Polymeric Surfactants

Droplet microfluidics can produce highly tailored microparticles whilst retaining monodispersity. However, these systems often require lengthy optimisation, commonly based on a trial-and-error approach, particularly when using bio-instructive, polymeric surfactants. Here, micropipette manipulation methods were used to optimise the concentration of bespoke polymeric surfactants to produce biodegradable (poly(d,l-lactic acid) (PDLLA)) microparticles with unique, bio-instructive surface chemistries. The effect of these three-dimensional surfactants on the interfacial tension of the system was analysed. It was determined that to provide adequate stabilisation, a low level (0.1% (w/v)) of poly(vinyl acetate-co-alcohol) (PVA) was required. Optimisation of the PVA concentration was informed by micropipette manipulation. As a result, successful, monodisperse particles were produced that maintained the desired bio-instructive surface chemistry.

Handling technology for 0.075-square mm powder IC chip

We have developed a packaging technology for powder IC chip of 0.075-square mm × 5 μm thickness. The chip, which can be embedded into papers, is expected to be a key device in pioneering new markets, where it can cheaply and easily manage a number of articles and identify papers such as securities. Manipulating a fine chip in a dry environment has been difficult due to adhesion of the other chips and scattering from the influence of electrostatic phenomena. However, using the micro-bead and cell trapping technology, it is possible to put the chips on a substrate one by one. The technique uses a double-surface-electrode chip, and a novel water-based chip handling technique composed of a micropipette manipulation and a self-aligned positioning. The double-surface-electrode structure that has two individual surface electrodes is advantageous in that when mounting the powder chip on a substrate, the chips are placed on the substrate without the need for highly accurate positioning, including the chip orientation control (upside-down, rotation). As for the micropipette manipulation, the chips are kept dispersed by stirring liquid with addition of a 0.5% surfactant to prevent chips from sticking together, and a flat-end glass micropipette successfully manipulated a single chip with high chip-capturing ratio. The self-aligned positioning of the chip uses micro liquid droplet shrinkage during evaporation process. The chip was able to move together with the droplet edge, and was positioned in the predefined hydrophilic domain. The liquid cushioning pick-up and placing action enables stress-free handling.

Characterization of the Effect of Geometry on Single Cell Adhesion Strength Using a Microfluidic Device

Cell adhesion plays a crucial role in a number of fundamental physiological processes and is important in the development of implantable biomaterials. Cell adhesion strength has previously been measured using a range of techniques, including population assays (e.g., centrifugation [1], hydrodynamic flow [2]) and single-cell methods (e.g., AFM [3], micropipette manipulation [4]). Population studies are unable to provide detailed information about individual cell behavior, while the single-cell methods are often time-consuming and difficult to perform. Microfluidic channels present a way to generate well-defined stress fields on cells [5]. The small dimensions of these channels result in low Reynolds numbers that allow for the generation of sufficiently large stresses to detach well-spread cells under laminar flow conditions. In the present work, a microfluidic channel was used to controllably load adhered single-cells to detachment and measure the adhesion strength. Using this assay, the effect of cell geometry on adhesion strength was investigated.