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Freiburg, Germany

Tropmann A.,Laboratory for MEMS Applications | Tanguy L.,Laboratory for MEMS Applications | Koltay P.,Laboratory for MEMS Applications | Koltay P.,BioFluidix GmbH | And 3 more authors.
Langmuir | Year: 2012

This study presents a straightforward two-step fabrication process of durable, completely superhydrophobic microchannels in PDMS. First, a composite material of PDMS/PTFE particles is prepared and used to replicate a master microstructure. Superhydrophobic surfaces are formed by subsequent plasma treatment, in which the PDMS is isotropically etched and PTFE particles are excavated. We compare the advancing and receding contact angles of intrinsic PDMS samples and composite PTFE/PDMS samples (1 wt %, 8 wt %, and 15 wt % PTFE particle concentration) and demonstrate that both the horizontal and vertical surfaces are indeed superhydrophobic. The best superhydrophobicity is observed for samples with a PTFE particle concentration of 15 wt %, which have advancing and receding contact angles of 159° ± 4° and 158° ± 3°, respectively. © 2012 American Chemical Society.


Tropmann A.,Albert Ludwigs University of Freiburg | Lass N.,Albert Ludwigs University of Freiburg | Paust N.,Albert Ludwigs University of Freiburg | Metz T.,Albert Ludwigs University of Freiburg | And 5 more authors.
Microfluidics and Nanofluidics | Year: 2012

This study presents a new, simple and robust, pneumatically actuated method for the generation of liquid metal micro droplets in the nano- to picoliter range. The so-called StarJet dispenser utilizes a star-shaped nozzle geometry that stabilizes liquid plugs in its center by means of capillary forces. Single droplets of the liquid metal can be pneumatically generated by the interaction of the sheathing gas flow in the outer grooves of the nozzle and the liquid metal. For experimental validation, a print head was build consisting of silicon chips with a star-shaped nozzle geometry and a heated actuator (up to 280°C). The silicon chips are fabricated by Deep Reactive Ion Etching (DRIE). Chip designs with different star-shaped geometries were able to generate droplets with diameters in the range of the corresponding nozzle diameters. The StarJet can be operated in two modes: Either continuous droplet dispensing mode or drop on demand (DoD) mode. The continuous droplet generation mode for a nozzle with 183 μm diameter shows tear-off frequencies between 25 and 120 Hz, while droplet diameters remain constant at 210 μm for each pressure level. Metal columns were printed with a thickness of 0.5-1.0 mm and 30 mm height (aspect ratio >30), to demonstrate the directional stability of droplet ejection and its potential as a suitable tool for direct prototyping of the metal microstructures. © 2011 Springer-Verlag.


Schoendube J.,Albert Ludwigs University of Freiburg | Wright D.,Zurich Instruments AG | Yusof A.,Albert Ludwigs University of Freiburg | Zengerle R.,Albert Ludwigs University of Freiburg | And 2 more authors.
Proceedings of the 16th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2012 | Year: 2012

The CellJet microfluidic dispenser chip prints single living cells encapsulated in free-flying droplets. Two sets of parallel facing electrodes in a 50 x 55 μm channel are applied to measure the presence and velocity of a single cell in real-time. Typically a 500 pl droplet is printed on demand, when a cell is at the nozzle. Feeding 20 μm polystyrene beads, a cell model, resulted in a peak-to-peak voltage of 70±16 μV and velocity of 7.5±0.8 mm/s. Single bead printing efficiency was 26% (N=124) with 64% void droplets. Moreover, viable HeLa cells and fibroblasts have been printed successfully.


Patent
BioFluidix GmbH | Date: 2015-03-26

A pressure sensor for measuring a fluid pressure of a fluid within a measurement chamber has the measurement chamber having a mechanical deformable wall, a shape of the measurement chamber varying depending on a pressure within the measurement chamber. The pressure sensor further has a measurement electrode, wherein the measurement chamber is arranged relative to the measurement electrode to be arranged within a region of an electrical field originating from the measurement electrode upon application of a potential to the measurement electrode, wherein an influence of a variation of the shape of the measurement chamber on the electrical field can be detected.


Kalkandjiev K.,Albert Ludwigs University of Freiburg | Riegger L.,BioFluidix GmbH | Kosse D.,Institute For Mikro Und Informationstechnik | Welsche M.,Albert Ludwigs University of Freiburg | And 4 more authors.
Journal of Micromechanics and Microengineering | Year: 2011

We investigate TMMF photopolymer as a cost-efficient alternative to glass for the leak-tight sealing of high-density silicon microchannels. TMMF enables low temperature sealing and access to structures underneath via lamination and standard UV-lithography instead of costly glass machining and anodic bonding. TMMF is highly transparent and has a low autofluorescence for wavelengths larger than 400 nm. As the photopolymer is too thin for implementing bulky world-to-chip interfaces, we propose adhesive bonding of cyclic olefin copolymer (COC) modules. All materials were tested according ISO 10993-5 and showed no cytotoxic effects on the proliferation of L929 cells. To quantify the cost efficiency of the proposed techniques, we used an established silicon/Pyrex nanoliter dispenser as a reference and replaced structured Pyrex wafers by TMMF laminates and COC modules. Thus, consumable costs, manpower and machine time related to sealing of the microchannels and implementing the world-to-chip interface could be significantly reduced. Leak tightness was proved by applying a pressure of 0.2 MPa for 5 h without delamination or crosstalk between neighboring microchannels located only 100 μm apart. In contrast to anodic bonding, the proposed techniques are tolerant to surface inhomogeneities. They enable manufacturing of silicon/polymer microfluidics at lower costs and without compromising the performance compared to corresponding silicon/glass devices. © 2011 IOP Publishing Ltd.

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