Active fluids: rheological properties and response to light of suspensions of Synechocystis sp. CPCC 534
Abstract
Despite our current understanding of active fluid mechanics, more knowledge is required to fully understand their rheological properties, response to light, and details of the interactions between cells in diluted suspensions.
The focus of this thesis is on investigating the rheological properties of suspensions of cyanobacterium Synechocystis sp. CPCC 534 under shear, induced by stirring. Experiments were conducted at different stirring rates and results are compared with the stationary condition. A notable increase in growth and biomass of Synechocystis sp. under various shear conditions was observed and the yield was nearly doubled. Besides, the data showed Newtonian behavior for suspensions at different cell concentrations. Although cell concentration displayed a perceptible rise in the viscosity of suspensions, this rise is smaller than the one predicted for suspensions of hard spheres.
Moreover, experiments were carried out on diluted suspension of Synechocystis sp. CPCC 534 in a microfluidic chamber to investigate the response of cells to the light and cell-cell interactions. The cells were exposed to the light of the laser pointer and a white LED. Cell tracking was performed by image processing in Python programing language. It was observed that cells display an alternating intermittent motion that consists of high motility “run phases” and immobile “tumble phases”. Comparing the probability distributions of the ensembled-averaged mean square displacement (EMSD), and velocity variations with time, revealed that cells detect light and spend more time running with high-speed motility under white LED light, while spending more time tumbling when exposed to laser pointer light. Moreover, the frequency of cell-cell interactions shows that exposure to any light sources decreases the number of interactions significantly. The preliminary design and experimental setup of a multichannel microfluidic device are provided as well.