On-chip fabrication to add temperature control to a microfluidic solution exchange system

We present a concept for the post production modification of commercially available microfluidic devices to incorporate local temperature control, thus allowing for the exact alignment of heating structures with the existing features, e.g. wells, channels or valves, of a system. Specifically, we demonstrate the application of programmable local heating, controlled by computerized PI regulation, to a rapid solution exchanger. Characterisation of the system to show that both uniform temperature distributions and temperature gradients can be established, and to confirm that the solution exchange properties are undisturbed by heating, was achieved using in situ thermometry and amperometry. \ua9 The Royal Society of Chemistry

Lipid Self-Spreading on Solid Substrates

This chapter is dedicated to wetting and fracturing processes involving molecular phospholipid films and high-energy solid surfaces. In these systems, wetting of planar surfaces occurs in an aqueous environment by means of self-spreading of phospholipid membranes from artificially generated lipid sources, which range from manually deposited single sources (multilamellar liposomes) to liposome suspensions of different particle sizes, which are directly pipetted onto the substrate. The most prominent of the molecular lipid films is the phospholipid bilayer, which constitutes the fundamental structure of the biological cell membrane. Lipid membranes have peculiar characteristics, are highly dynamic, feature two-dimensional fluidity, and can accommodate functional molecules. Understanding the interactions of lipid films with solid interfaces is of high importance in areas like cell biology, biomedical engineering, and drug delivery

Formation of giant unilamellar vesicles from spin-coated lipid films by localized IR heating

We report a novel method for the generation of GUVs (generate unilamellar vesicles) from spin-coated lipid films by means of localized heating. This technique enables GUV formation from both charged and neutral lipid species, as well as from a complex lipid mixture, in various ionic strength conditions. Encapsulation was possible during and after GUV formation

Millimetre-wave dielectric spectroscopy for cell analysis

A millimeter-wave sensor based on a CPW line has been designed and fabricated as a first prototype for impedance spectroscopy to be combined with a multifunctional micropipette for cell and membrane analysis. The first mm-wave measurement results show the sensitivity of the layout by distinguishing the cells from the media and monitoring the attachment process of the cells to the sensor surface. Measurements were performed on umbilical cord stem cells and cartilage thumb cells

Cellular communication via directed protrusion growth: Critical length-scales and membrane morphology

AbstractWe investigated the growth of cell protrusions from adherent HEK 293 cells and their capability to bridge cytophobic Teflon®  AF microgaps, establishing a critical length scale, beyond which cells cannot probe free space. For this purpose, we employed a photolithography-based surface fabrication strategy for producing micropatterned substrates composed of glass and the amorphous polymer Teflon®  AF. Cell protrusions growing from HEK 293 cells on these substrates were confined to extend on 2 μm wide glass lanes, intersected by Teflon®  AF microgaps of various lengths between 2 and 16 μm. After 24 hours of incubation, the frequency of cell protrusions crossing the gap was found to be strongly dependent on the gap size. Gaps which are greater than 4 μm were found to be increasingly difficult to cross. Cell extensions crossing the microgaps either appeared as nanosized connections, in approximately 30% of all observed cases, or as microsized connections. Molecular transport in the established cell-to-cell connection across the microgap was investigated by activation of TRPM8 ion channels followed by supply of Ca2+ to one of the connected cells. The diffusion of the Ca2+ ions was visualized by means of a cell-permeant pre-fluorescent dye. We observed both open- and closed-ended intercellular connections in both nano- and microsized cell protrusions

Heat-induced formation of single giant unilamellar vesicles

Giant unilamellar vesicles (GUVs) are an excellent model system for the investigation of lipid membranes, the study of membrane proteins and ion channels in a biomimetic environment, and in the creation of artificial cells. Here, we describe a novel method for the preparation of GUVs from single multilamellar liposomes by means of directed infrared laser heating. Our method generates individual unilamellar vesicles at selected locations, not only from natural and artificial lipid mixtures containing negatively charged lipids, but also from preparations of single lipids, such as neutral phosphatidylethanolamine. The presented method provides a new efficient resource for giant vesicle research and offers an alternative to the electroformation and de/rehydration techniques

Millimeter-wave sensor based on a λ/2-line resonator for identification and dielectric characterization of non-ionic surfactants

Studies of biological and artificial membrane systems, such as niosomes, currently rely on the use of fluorescent tags, which can influence the system under investigation. For this reason, the development of label-free, non-invasive detection techniques is of great interest. We demonstrate an open volume label-free millimeter-wave sensing platform based on a coplanar waveguide, developed for identification and characterization of niosome constituents. A design based on a λ/2-line resonator was used and on-wafer measurements of transmission and reflection parameters were performed up to 110 GHz. Our sensor was able to clearly distinguish between common niosome constituents, non-ionic surfactants Tween 20 and Span 80, measuring a resonance shift of 3 GHz between them. The complex permittivities of the molecular compounds have been extracted. Our results indicate insignificant frequency dependence in the investigated frequency range (3 GHz – 110 GHz). Values of permittivity around 3.0 + 0.7i and 2.2 + 0.4i were obtained for Tween 20 and Span 80, respectively