Date

2021-9-13

Author

Hatiboğlu, Anıl

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Modeling cell membrane permeability in different solutions is a critical requirement in controlling the response of cells during preconcentration processes in biotechnological applications, such as drug delivery, fluorescence imaging, and cryopreservation . Current multi-step methods employed in loading cells with high concentrations of cryoprotectant agents (CPAs) prior to cryopreservation for long term storage affect cell viability as a result of extended exposure times associated with these methods. One of the objectives of this research to observe the response of different types of cells in a continous microfluidic system allowing for reduced exposure times to the CPAs and to model the transport of CPA through the cell membrane. In this study, a micro thermo-fluidic device designed for faster and continuous preconcentration of cells with CPAs is used to study cell membrane permeability. Cells are encapsulated in uniform aqueous droplets with a low CPA concentration, The concentration of the CPA in the droplet is increased along the microchannel by controlling the temperature, and thus the water solubility of the oil phase. Selective diffusion of water out of the droplet causes the droplet to shrink and get concentrated vi in CPAs. The response of the cell to the changes in the extracellular concentration is observed and analysed. The dynamic extracellular CPA concentration data is integrated in a permeability model to calculate the dynamic permeability of the cell membrane to a specific CPA. Two-phase flow conditions for droplet generation are optimized to determine the flow rate to achieve the desired droplet size. A linear relationship is found between flow rates and the size of the droplets, regardless of the size and geometry of the microfluidic device. The performance of encapsulation of cells in the droplets based on the flow rate is assessed. The undesired phenomena, such as the encapsulation of cells in multiples and the sedimentation inside the microchannels, are found to be associated with the low flow rates. Employing a continuous two-phase microfluidic system has proved valuable in observing the response of the cell to increasing CPA concentrations. Encapsulation in smaller droplets has yielded a higher increase in the intracellular CPA concentration. A conventional mathematical model for the permeability of the cell membrane is modified by using the dynamic extracellular concentrations obtained from the microfluidic system. Membrane permeability parameters are determined for MDA-MB231 cells using glycerol as the CPA, where concentration is increased from 1 M to 2.05 M in the aqueous droplets with heating to 40°C in the microfluidic channels.

Subject Keywords

Droplet Microfluidics, Cell Encapsulation, Cell Membrane, Membrane Permeability, Cryoprotectant Agents

URI

https://hdl.handle.net/11511/94196

Collections

Graduate School of Natural and Applied Sciences, Thesis