Biomedical subjects

Ralf Seemann

Publications and source records attributed to Ralf Seemann.

5 recordsLinked to original sources

PubMed2005

Electroactuation of fluid using topographical wetting transitions.

The complex morphologies of liquids on topographically structured substrates are exploited for liquid actuation in open microchannels. The liquid is either confined in prefabricated grooves, thus forming elongated filaments, or gathers in macroscopic drops without invading the grooves, depending on conditions. Using the electrowetting effect, we can reversibly switch between these two states. The length of the filaments is sensitive to the ionic content of the liquid and can be described quantitatively with an electrical model considering the voltage drop along the groove.

Journal Article↗

PubMed2005

Wetting morphologies at microstructured surfaces.

The wetting of microstructured surfaces is studied both experimentally and theoretically. Even relatively simple surface topographies such as grooves with rectangular cross section exhibit a large variety of different wetting morphologies as observed by atomic force microscopy. This polymorphism arises from liquid wedge formation along the groove corners and from contact line pinning along the groove edges. A global morphology diagram is derived that depends only on two system parameters: (i) the aspect ratio of the groove geometry and (ii) The contact angle of the underlying substrate material. For microfluidics, the most interesting shape regimes involve extended liquid filaments, which can grow and shrink in length while their cross section stays essentially constant. Thus, any method by which one can vary the contact angle can be used to switch the length of the filament, as is demonstrated in the context of electrowetting.

Humans↗

PubMed2003

Trends in microfluidics with complex fluids.

The rapid developments in biotechnology create a great demand for fluid handling systems on the nano- and picoliter scale. The characterization of minute quantities of DNA or protein samples requires highly integrated, automated, and miniaturized "total analysis systems" (mu-TAS). The small scales necessitate new concepts for devices both from a technological and from a fundamental physical point of view. Here, we describe recent trends in both areas. New technologies include soft lithography, chemical, and topographical structuring of surfaces in order to define pathways for liquids, as well as electro-wetting for manipulation purposes. Fundamentally, the interplay between geometric confinement and the size of biological macromolecules gives rise to complex dynamic behavior. The combination of both fluorescence imaging and scattering techniques allows for detailed insight into the dynamics of individual molecules and into their self-assembly into supramolecular aggregates.

Biotechnology↗

PubMed2003

Complex dewetting scenarios captured by thin-film models.

In the course of miniaturization of electronic and microfluidic devices, reliable predictions of the stability of ultrathin films have a strategic role for design purposes. Consequently, efficient computational techniques that allow for a direct comparison with experiment become increasingly important. Here we demonstrate, for the first time, that the full complex spatial and temporal evolution of the rupture of ultrathin films can be modelled in quantitative agreement with experiment. We accomplish this by combining highly controlled experiments on different film-rupture patterns with computer simulations using novel numerical schemes for thin-film equations. For the quantitative comparison of the pattern evolution in both experiment and simulation we introduce a novel pattern analysis method based on Minkowski measures. Our results are fundamental for the development of efficient tools capable of describing essential aspects of thin-film flow in technical systems.

Biomedical Engineering↗

PubMed2002

Generic morphologies of viscoelastic dewetting fronts.

A simple model is put forward which accounts for the occurrence of certain generic dewetting morphologies in thin liquid coatings. It demonstrates that, by taking into account the elastic properties of the coating, a morphological phase diagram may be derived which describes the observed structures of dewetting fronts. It is demonstrated that dewetting morphologies may also serve to determine nanoscale rheological properties of liquids.

Journal Article↗