Lithography

A model system helps to simplify complex physical circumstances, thus an integral part of daily science. Lithographic manufactured microchannels are an illustrative example for suchlike model systems. Diverse properties of fluids can be investigated as well as influences of channel geometry on these properties.

Our interest is focused on the flow behavior of fluids (laminar or turbulent), transport of objects (e.g. red blood cells) in this flow as well as occurring shear forces. For this purpose we use simple channel geometries as artificial vessels (see .bio). Furthermore we create more complex artificial labyrinth structures and investigate the behavior of bacteria in search of nutrition (see .bio). Microchannels are also applied for picking objects out of or into flows to manipulate them in a specific way (stopping, sorting, separating) and investigating their behavior and properties.

For all these applications a flexible manufacturing is needed, in which a spatial light modulator is utilized to create microchannels with certain geometries. The SLM modulates the amplitude of the light field. Hereby arbitrary two dimensional structures can be created by illuminating a SU8 layer. The exclusively in the illuminated areas activated acids leads to a hardening process during a thermal treatment. The topographically information included in the negative are transferred by a modelling process into the actual material, which is polydimethylsiloxane (PDMS). PDMS is a transparent, biocompatible and inexpensive material. Since the PDMS is able to represent all features from the SU8-negative, structures with a size of 8 µm are possible.