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The present work shows the development, optimization and application of biomicrofluidic chips. The developed microfluidic chips are used to (1) analyze the stem cell differentiation; (2) produce valuable substances via metabolic engineering and (3) the fabrication of polymeric films possessing a gradient of morphology. To build up the different microfluidic chips two elementary structures are used; namely, a cascade micromixer with subsequent straight channels as well as a hexagonal chamber. The micromixer has zigzag channels, two inlets and six cascades with a channel width of 400 µm. The chamber has an area of 322 µm2 and a channel height of either 500 µm or 680 µm. The size of all microstructured parts is normalized to the size of a microscope glass slide (26×76 mm2), allowing the use of conventional microscope equipment and ensuring the exchangeability of the microstructured parts. The microfluidic chip for stem cell differentiation and the microfluidic chip for metabolic engineering are fabricated using a biocompatible production process in polycarbonate. Polycarbonate is suitable for industrial mass production. Both chips are 3-stacked devices with two microstructured parts and a nanoperforated membrane in-between. The pores allow for mass transfer from one microstructured part to the other one. To analyze the stem cell differentiation cells should be contacted with a morphogen gradient. Therefore a cell chamber for cultivating the cells and a micromixer for generating the gradient are integrated in this microfluidic chip. The microfluidic chip for metabolic engineering also has a chamber for cultivating the cells in. As plant cells behave like sand, this chamber cannot be perfused after loading the cells without risking channel clogging. Therefore a second chamber, separated from the cells by the membrane, is used for perfusion with culture media and the extraction of the products of the cells. The microstructured parts are produced by hot embossing. A thermal bonding process is applied for liquid-tight sealing of the microfluidic chips. This work focuses on a production process enabling the fabrication of transparent microfluidic chips. The transparency allows for continuous observation of the cells in the microfluidic chip. Furthermore the stability of the microfluidic chips is optimized, enabling a proper use in biological applications. The microfluidic chip for fabricating polymer films with a gradient of morphology consists of only one microstructured part and is fabricated applying a PDMS process. The microstructured part consists of a micromixer, generating the gradient and a subsequent reaction chamber for supplying the gradient. The used production process is mass production enabling by using a coating technique with curing agent instead of the standard plasma bonding technique. Forming stable but reversible seals is the main aim throughout this work for the production of these microfluidic chips. To ensure the functionality of the different microfluidic chips the hydrodynamics of the integrated micromixer is characterized. Furthermore the mass transport through the membrane is analyzed in biological experiments.