Microfluidics for Biological Studies - A Double Emulsion Platform for Cell Encapsulation and Analysis
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- Institutt for fysikk 
Encapsulation of biologicalmaterial in small, confined volumes has enabled the studyof individual cells, revealing valuable and detailed information on cellular processes andbehavior unavailable in traditional bulk studies. This work presents a double emulsionplatform for the encapsulation and analysis of biological material. Double emulsionswere synthesized in 3D microfluidic PDMS devices and immobilized on PDMS microarraysfor imaging purposes. The effect of flowrates on droplet sizes and amount of doubleemulsion cores was explored, however, no definite relationship was determined due tovariations in the system. The origin of these variations was probably device alignment,surface treatment, the tubing of the syringe pump system, or a combination thereof. Thefluorosurfactant provided by SMaL at EPFL rendered the double emulsions stable withregards to coalescence, temperature variations, and shear forces exerted by the carrierfluid. The greatest challenge in terms of stability appeared to be osmotic pressure differences between the double emulsion cores and the surrounding medium. However, it islikely that this obstacle can be overcome by a thoroughmeasurement of the osmolaritiesof the inner and outer phases and subsequent balancing of possible differences by theaddition of sucrose. Double emulsion cores containing 0.60%, high G-content alginate(Mw = 275 kDa) and chelated calcium ions were gelated for the synthesis of spherical,micron-sized hydrogels. Two different internal gelation methods were investigated; pHtriggeredgelation and a novel gelation method recently established at NTNU termed CLEX. Both successfully synthesized hydrogels, however, CLEX is favorable for biologicalsystems as it occurs at neutral pH-values. Additionally, a device with two inner phaseinlets was applied for gelation of alginate cores by CLEX. This device introduces the possibility of on-chip mixing of double emulsion cargo, which may be utilized for studiesof cellular processes such as bacterial conjugation. Pseudomonas Putida and Chlamydomonasreinhardtiiwere encapsulated on-chipwith high throughput, resulting in compartmentalizationof single or few cells in suitable microenvironments. Three different encapsulation media were tested for their compatibility with a droplet-based microfluidic system and living material; 20% PEG, 0.60% and 0.15% alginate. The latter provided a viable and healthy microenvironment for cell growth. Double emulsions with 0.15% alginate cores and the microarray thus represent a suitable platformfor microbiological studies if the osmotic instability issue is resolved.