Orientational dynamics of human sperm swimming along walls facing noise

MATIAS A. BETTERA MARCAT; ADOLFO J. BANCHIO; VERONICA I. MARCONI

Congreso; Fluidos 2021 / XVI Meeting on Recent Advances in Physics of Fluids and its Applications; 2021

Nowadays it is well known in the physics community that many microswimmers prefer to swim along walls, but the specific orientation mechanism, dynamics or adhesion to surfaces for each species are complicated issues, still unrevealed. Particularly, ?pushers?swimmers, as E. Coli bacteria or sperm cells are found more likely following surfaces. This produces an excess of population density which presumably plays a crucial role in the development of bacteria biofilms. Sperm cells are believed to follow the boundaries as an orientation mechanismthrough the fertilisation in the complex live environment of the female reproductive tract. Under laboratory conditions, microfluidics devices had been essential in order to characterise the microswimmer behaviour near surfaces. Recently we have reported human sperm velocity recovery under ultraconfined conditions, with a nice agreement between model and experiments [1]. We proposed a model of the sperm motility including cells lateral heading and torque that aligns them close to the walls.In this work we explore even further our sperm model over torque and cell internal noise: from the cellular individual dynamics, as their statistics of characteristic times close to the walls, to the population dynamics, as the spatial distribution. We study linear and cubic torque dependence with the orientation angle relative to the surfaces. The calculated characteristic times of spermatic cells swimming along walls are residence, alignment and escape times. A wide range of torque intensity and rotational diffusion coefficient were swept. We find a region in parameter space where the residence times are reduced, although for large torque they diverge.Although the wall accumulation is a population average, it presents a similar behaviour to residence times. At relevant biological and physical scales for micro-swimmers, the residence time and the wall accumulation are reduced up to one order of magnitude when the torque is present.