Micro injection molding is presently on its way to become an established manufacturing process in commercialising Microsystem Technologies. Enhanced products from plastics for micro optical or medical applications are entering the market. New developments like the different kinds of injection molding for microstructured components from plastics, metals or ceramics will increase the material range available in microdimensions. This will open up opportunities for increasing economic ef®ciency, for new ®elds of applications as well as for innovative products in the future.

We describe a multi-purpose platform for the three-dimensional cultivation of tissues. The device is composed of polymer chips featuring a microstructured area of 1-2 cm(2). The chip is constructed either as a grid of micro-containers measuring 120-300 x 300 x 300 microm (h x l x w), or as an array of round recesses (300 microm diameter, 300 microm deep). The micro-containers may be separately equipped with addressable 3D-micro-electrodes, which allow for electrical stimulation of excitable cells and on-site measurements of electrochemically accessible parameters. The system is applicable for the cultivation of high cell densities of up to 8 x 10(6) cells and, because of the rectangular grid layout, allows the automated microscopical analysis of cultivated cells. More than 1000 micro-containers enable the parallel analysis of different parameters under superfusion/perfusion conditions. Using different polymer chips in combination with various types of bioreactors we demonstrated the principal suitability of the chip-based bioreactor for tissue culture applications. Primary and established cell lines have been successfully cultivated and analysed for functional properties. When cells were cultured in non-perfused chips, over time a considerable degree of apoptosis could be observed indicating the need for an active perfusion. The system presented here has also been applied for the differentiation analysis of pluripotent embryonic stem cells and may be suitable for the analysis of the stem cell niche.

We are gratefully acknowledged to the Stifterverband Metalle and the Deutsche Forschungsgemeinschaft for financial support. Additionally we wish to thank the BASF AG, Hu¨ls AG, Hoechst AG and Degussa AG for delivering materials and the Ciba Additive GmbH for the kind donation of the photoinitiators. We also wish to thank our colleagues, especially Mr. P. Holzer and the members of the galvanic team of the corrosion division of our institute (IMFIII/KOR) and microparts GmbH for the electroplating and helpful support.Abstract Injection molding technology and its different modifications represent established processes for manufacturing polymer products with high accuracy in large scale production. Enhanced machine and tool technologies like evacuation units and special temperization systems have already been adapted to the molding of microstructures with high aspect ratios. Cycle times are actually in the range of minutes and depend on the geometry of the microstructures and the materials used. Based on injection molding of lost plastic microforms new processes for the manufacturing of ceramic or metal microstructures are being developed.

Originally developed for the replication of high aspect ratio LIGA structures, micro injection molding is presently on its way to become an established manufacturing process. Enhanced technological products like micro optical devices are entering the market. New developments like the different kinds of injection molding with several components open up opportunities for increasing economic efficiency as well as for new fields of applications. Software tools for the simulation of the thermal household of the molding tool and/or the moldfilling process itself can provide useful but not wholly sufficient assistance for the optimization of micro injection molding.

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