Lab-on-a-chip technologies for manipulation and imaging of C. elegans worms and embryos

The nematode Caenorhabditis elegans is an attractive model organism, owing notably to its short life cycle, genetic tractability, and optical transparency facilitating microscopic observation. This thesis deals with the realization of technological tools for the manipulation of worms and for studying thereby biologically relevant questions. The novel microfluidic devices that were developed are: #1 A microfluidic approach for size-dependent sorting of C. elegans nematodes on-chip. We take advantage of the external pressure-deformable profile of polydimethylsiloxane (PDMS) transfer channels that connect two on-chip worm chambers. The pressure-controlled effective cross-section of these channels creates adjustable filter structures that can be easily tuned for a specific worm sorting experiment, without changing the design parameters of the device itself. Considering that our sorting device is merely based on geometrical parameters and operated by simple fluidic and pressure control, we believe that it has strong potential for further use in advanced, automated, microfluidic C. elegans-based assay platforms. #2 A microfluidic device for studying signaling via diffusive secreted compounds between two specific C. elegans populations over prolonged durations. In particular, we designed a microfluidic assay to investigate the biological process of male-induced demise, i.e. lifespan shortening, in C. elegans hermaphrodites in the presence of a physically separated male population. For this purpose, male and hermaphrodite worm populations were confined in adjacent microchambers on the chip, whereas molecules secreted by males could be exchanged between both populations by periodically activating controlled fluidic transfer of ÎŒl-volume aliquots of male-conditioned medium. For male-conditioned hermaphrodites, we observe a reduction in mean lifespan of 4 days compared to non-conditioned on-chip culture. #3 Development of two reversible C. elegans immobilization methods for imaging applications. The first immobilization method takes advantage of a biocompatible and temperature-responsive hydrogel-microbead matrix. Our gel-based immobilization technique does not require a specific chip design and enables fast and reversible immobilization, thereby allowing successive imaging of the same single worm or of small worm populations at all development stages for several days. The second immobilization method takes advantage of the elastic properties of PDMS. We present two distinct microdevices, namely a micropillar array and a serpentine microchannel, for on-chip feeding and high-resolution imaging studies, respectively. Both devices consist of size-tunable PDMS structures that allow the same chips to be used for immobilization of worms at all development stages. Our microfluidic approach provides appropriate physiological conditions for long-term studies and enables worm recovery after the experiment. #4 A fully integrated microfluidic approach for the exploration of C. elegans early embryogenesis including the possibility of testing small-molecule inhibitors with increased throughput and versatility. Here, up to 100 embryos can be immobilized in parallel for simultaneous high-resolution time-lapse imaging of embryonic development from the 1-cell stage to hatching. We demonstrate time-controlled and reversible drug delivery to on-chip immobilized embryos, which is of relevance for biochemical and pharmacological assays.