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Monitoring the response of cells and organisms to different chemical cues using microfluidics

Ramanathan, Nirupama

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Microfluidic devices allow precise control to manipulate fluids within micrometer sized channel networks. In single phase microfluidic systems where miscible fluids are infused, laminar flow can be generated. This means liquid streams can flow parallel to each other without convective mixing. In two phase microfluidic systems where two immiscible fluids are infused, droplets are generated. Using this system, uniformly sized aqueous micro compartments can be generated in oil. This dissertation describes the development of novel microfluidic devices based on single phase and two phase systems to monitor responsiveness of cells and organisms to different chemical cues. Firstly, the possibility to apply a specifically designed single-phase microfluidic chip to study zooplankton ecology has been demonstrated. Zooplankton perceive their surrounding using chemical cues and rely on these cues for development and survival. However, with the current rapid global climatic changes affecting the ocean chemistry, it is unclear on how plankton, which form the base of the marine food chain, are coping. So far, measurements on zooplankton ecology have been hampered by technical impracticalities of exposing actively swimming plankton species to different chemical conditions simultaneously while monitoring their behavior on an individual level. Using the microfluidic device, first measurements on behavioral preferendum of zooplankton species to changes in pH and salinity could be made with a precision that additionally allowed estimating the “responsiveness”, which is the minimum change in concentration required for the plankton to elicit a response, to an environmental stimulus. Platynereis dumerilii, cosmopolitan model plankton were more sensitive to changes in pH than salinity. In addition, comparing different species lead to the observation that Euterpina acutifrons, a copepod species showed a narrower pH preferendum than P.dumerilii. These measurements allow making predications on sensitive and resilient species. Furthermore, the ability to study the interaction of zooplankton with their prey and predators and perform functional studies on identifying cell types responsible for a sensory response has been demonstrated. For cell-based screening assays however, the high-throughput offered by droplet-based systems outcompetes single-phase systems. But, generating chemical diversity in droplets that can allow screening entire chemical libraries while being able to track the sample identity remains to be demonstrated. Here a novel approach has been devised that allows generating sample barcoded combinatorial mixtures. In addition the approach has been optimized to suit for screening rare vi and sensitive cells like mouse embryonic stem (mES) cells. The ability to maintain viable mES cells in droplets for a period of 48 h has been demonstrated and in addition the possibility to differentiate them by encapsulating them together with 10-8 M retinoic acid (RA) has been shown. Lastly, a new microfluidic approach combining the advantages of single phase and two phase microfluidics has been described. This approach allows high-content cell-based screening with freely accessible cells allowing regular tissue culture handling and potentially, immunostaining experiments which are not possible when cells are encapsulated. To maximize the throughput per chip, chemicals were encapsulated in droplets and were allowed to locally diffuse through the chip material to the cells. The usability of this approach has been demonstrated by localized induction of GFP in tetracycline inducible HeLa-TRexTM cells. In conclusion, different microfluidic approaches have been described in this thesis and used for applications ranging from analyzing cells to organisms. The good spatial resolution, precise control over liquids, possibility of assays on the individual level and low cell number/reagent quantity requirement, enabled by microfluidics makes the devices an advantageous tool for biological applications.

Item Type: Dissertation
Supervisor: Merten, Dr. Christoph
Date of thesis defense: 17 July 2015
Date Deposited: 30 Jul 2015 07:47
Date: 2016
Faculties / Institutes: The Faculty of Bio Sciences > Dean's Office of the Faculty of Bio Sciences
Subjects: 500 Natural sciences and mathematics
570 Life sciences
Controlled Keywords: microfluidics, marine ecology, stem cell biology
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