Transition to collective motion of spermatozoa in different confinements and at variable temperatures

Sperm motility and its collective motion is a subject still poorly investigated. We aim at studying different environmental conditions that can and do affect the motility of sperm cells, focusing into transitions to collective motion. With increasing concentration of swimmers, sperm cells in a suspension can switch from random motion to organised collective turbulence, which we call "spermulence". This phase transition is strongly influenced by the boundaries of the system, which influence conditions for the transition to spermulence. Complexity of the boundary may lead to oscillatory modes where the flow in suspension reverses periodically. Moreover, the confinement can be used by the swimming sperm cells as an efficient strategy to progress towards a point and this particular phenomenon can be important when designing methods for artificial insemination. In addition to the confinement, other environmental conditions, such as temperature and fluid viscosity, would influence the motion of sperm cells. We demonstrate that cells change the radius of curvature of their trajectories when swimming in a hotter environment. This change in trajectory will result in formation of ring-like structures in a two dimensional system, thatwill turn into a oscillatory motion,with waves propagating throughout the entire system. Self-organisations on such a wide scale and with such consistency have not been yet seen in the spermatozoa investigations. While working with sperm cells, a new method for swarming bacterial experiments has been invented, allowing for bacteria to live on an agar plate and move in the space for long times compared to their usual live span in devices. This techniques allow bacteria to swarmfor hours on agar surface previously modified with the desired structure