Research Projects

Swimming microorganisms are ubiquitous and important in many branches of science and engineering due to a broad base of applications ranging from pathogenesis, industrial biofouling, or even in geophysical studies of biogenic ocean mixing. Recent technological advancements have also enabled in the development of artificial miroswimmers, with applications in drug delivery and cargo transport. While the typical sizes of these microscopic swimmers is of the order of a few micrometres, by sensing and communicating with their surrounding environment, the resulting interactions often have complex spatio-temporal dynamics on much larger length scales. Of interest from both fundamental and applied standpoints is the migration of these microscopic swimmers in a confined fluid environment. Here, a key feature influencing the microswimmer motion is the fact that it can respond to chemical species in its surroundings, a phenomenon referred to as chemotaxis. Specifically, the coupling between the fluid mediated hydrodynamics, boundary interaction and the spread of the chemical species can modify the swimmer mobility. The proposed project aims at exploring the impact of the above coupling on the swimmer orientation dynamics, for orientable microswimmers navigating through microchannels. Our approach will involve two parts, namely, a theoretical characterization based on a probabilistic description of the swimmer position and orientation and a Langevin dynamics simulation scheme. In the theoretical approach we will determine the orientation probability density function of the microswimmers, which evolves due to convection and rotation by the flow and due to the swimmer’s inherent orientation stochasticity. The chemotactic response will be included via the modification of the stochastic swimmer reorientation, where the coupling to the concentration gradient of the chemical species will appear. The Langevin simulations on the other hand will be a bottom-up approach where the position and orientation of each swimmer will be tracked in space and time. The chemotactic coupling can therefore be tracked at the individual level via the implementation of the stochastic rotations due to orientation tumbling. Here, we will additionally incorporate inter-swimmer interactions via excluded volume effects, which is important owing to possible concentration perturbations induced by chemotaxis. The results of this study will be crucial in understanding how chemotaxis can modify the cross-stream swimmer migration in a channel, an area that is not fully understood. Recent studies neglecting chemotaxis have shown that orientable microswimmers exhibit migration both towards and away from boundaries, and chemotaxis can potentially generate skewed migration responses that can be incipient to formation of biofilm streams. The proposed study is expected to have far reaching consequences in applications involving flow-induced cell sorting and cargo transport through microchannels.