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FLAgellated MicroswimmErs’ locomotioN in Confined flOws

Periodic Reporting for period 1 - FLAMENCO (FLAgellated MicroswimmErs’ locomotioN in Confined flOws)

Reporting period: 2016-08-01 to 2018-07-31

The objective of this project is to study swimming at the micrometer scale. We are interested in addressing the strategies adopted by microorganisms and cells to achieve propulsion in a fluid environment. Cell motility is critical to accomplish essential surviving tasks, like feeding and evading predators, or specialized functions, as fertilizing the egg cell in the case of spermatozoa. While we can easily acknowledge why motility is important, it is more difficult to understand how cells swim. Swimming at the micro-scale is indeed counterintuitive and challenges the physical intuitions we build living in the macroscopic world.
Our focus is on improving the mathematical and numerical modeling of locomotion at scales that range between a few to hundreds of micrometers to provide computational tools with both a descriptive and predictive power. We are in fact guided by the ambition of improving the fundamental understanding of this phenomenon and using this knowledge to inspire biomimetic robot and the design of microfluidic devices to manipulate and sort motile cells.
An improved modeling capability for the motion of microswimmers has the potential of impacting several fields: microswimmers play a crucial role for a wide range of biological, ecological, and industrial processes, e.g. the fertilization of mammalian ova, production of algal biofuels, and the degradation of particulate organic matter by bacteria. As an example, an important and largely unsolved case is biofouling where immersed surfaces become covered by microorganisms, which affect the surface performance and can even lead to its failure.
The main objectives of this project were the training of the researcher in computational modeling of micro-swimming and the development of numerical and computational models for simulating swimming at the micro-scale and study confined and collective motion.
The specialist training of the experienced researcher was provided by Queen Mary University (Engineering Department), and benefitted from collaborations with the University of Warwick (Physics Department), the International School for Advanced Studies (SISSA) in Trieste, and the University of Padova (Department of Medicine).
The interdisciplinary nature of the institutions allowed the researcher to appreciate the potential of the acquired knowledge for tackling problems relevant to field as diverse as engineering, biology, reproductive medicine and medical diagnostic.
The main scientific results of this action consisted in a thorough theoretical and numerical analysis of the available mathematical models to simulate swimming at the microscale and led to identifying strengths and criticalities of the various approaches. These results have been presented at several international venues (workshops, meeting, symposia, various institutes) as posters, contributed or invited talks and are currently under review for publication in a peer reviewed journal.
Despite the high accuracy of the models considered, the main computational challenge in for simulating collective and confined motion lies in the fact that the calculations are prohibitively expensive when scaled-up to account for complex geometries or multiple swimmers, for this reason most of the efforts in the final stage of the project have focused on experimenting new strategies to accelerate the calculations while retaining their accuracy.
The scientific outcome of this project contributed to improve, through a better comprehension of the mathematical models, our quantitative understanding of phenomena that can be described mainly qualitatively at present. The most recent developments will potentially provide the tools and body of knowledge for controlling and manipulating microswimmers near solid surfaces.
Flow field around the swimming sperm cell averaged over a swimming cycle (far field)
Flow field around the swimming sperm cell averaged over a swimming cycle. The head is shown in black