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Stem cell research is today an active and promising field of research. To learn more about the biology of stem cells, technical improvements are needed such as tools to study stem cells in order to characterize them further and to gain insights to the molecular regulations of their maintenance, differentiation and identification. Common procedure when studying stem cells is to coat the surface where the stem cells are to be cultured with organic materials like matri-gel, poly-L-lysine and fibronectin. The resulting coating is usually relatively fragile and it is difficult to know if the coating is evenly distributed. In addition, these forms of coatings cannot be sterilized and re-used, but must be added as an initial, time-consuming step in the daily protocol. A microwell chip with hundreds of 500 nl wells has recently been shown to be a useful tool for stem cell culturing. This platform is here modified to facilitate and improve the coating conditions for adherent cell culture. A robust and highly porous film of TiO2 is deposited in the wells prior cell seeding. TiO2 is known to be biocompatible and provides a surface that is even and well characterized, simple to produce and re-usable. Furthermore it enables the microwell chips to be stored pre-coated for longer periods of time before use. We investigated the growth of rat mesenchymal stem cells on nanoporous titania films and found that they proliferated much faster than on conventional coatings. The combination of the robust TiO2 coating of the microwell chip enables thousands of individually separated single, or clones of, stem cells to be studied simultaneously and opens up the possibility for more user-friendly cell culturing.

Cell heterogeneity in genetically identical cell populations is becoming a well-known and important phenomenon in cell biology. Current methods commonly utilise population-based analysis founded on averaged result. Hence there is a need for high-throughput cell assays on the single-cell level. By using miniaturised devices it is possible to enhance spatial and temporal control of the individual cells, increase the potential throughput and minimise the needed sample and reagent volume while enabling a wide range of biological applications.This thesis is based on the results generated with a miniaturised microwell slide for cell assays. The microwell slide’s high-throughput compartmentalised configuration enables several hundred isolated experiments to be run simultaneously. The bottom of the wells is made out of a thin glass slide, which supports high-resolution imaging. The slide has a standardised format and its’ compatibility with conventional instruments is used extensively throughout the thesis. The presented papers all contribute to the development of the microwell slide by adding technical value or increasing the number of potential applications. For example, the slide was success-fully implemented as a chip-to-world output format for single microfluidic droplets in Paper I, by interfacing two miniaturised systems with fluorescence-activated cell sorting. In Paper II and III, microfluidic channels were integrated to increase spatial and temporal control of the added samples and reagents. In Paper II an automated stepwise concentration gradient generator was developed delivering a drug gradient to adherent mammalian cells in designated wells. In Paper III fluidic-imposed shear stress on endothelial cells was studied. In Paper IV, the slide was functionalised by coating the surfaces of the wells with several antibiotics at a defined concentration range. The coated slide was used for multiplex antibiotic susceptibility testing of bacterial pathogens, using an algorithm-based identification of the point defining lag to exponential phase transition. It successfully determined the pathogens susceptibility profile in 3-5 hours. Finally, in Paper V, a method to retrieve bacteria colonies with a desired phenotype from the wells for downstream genetic analysis was developed. In summary, the presented work has furthered the development of miniaturised high-throughput tools for various cell heterogeneity assays.