A recent study characterizing the movement of these reproductive cells and single-celled algae shows that human sperm have whip-like tails and propel themselves through viscous fluids, seemingly in line with Newton’s third law of motion. He seems to be rebelling.
Kenta Ishimoto, a mathematical scientist at Kyoto University, and his colleagues are trying to figure out how sperm and other microscopic biological fluids slip through materials that, in theory, should resist their movement. Therefore, we investigated these non-interactions in sperm and other microscopic biological fluids.
When Newton conceived his now famous work laws of motion In 1686, he tried to explain the relationship between physical objects and the forces that act on them using some neat principles, but these principles don’t necessarily apply to microscopic cells wriggling in sticky liquids. It turns out that this is not the case.
Newton’s third law can be summarized as, “For every action, there is an equal and opposite reaction.” It implies a certain symmetry in the nature of opposite forces acting on each other. In the simplest example, when two marbles of the same size collide while rolling along the ground, a force is transferred and they repel each other based on this law.
However, the natural world is chaotic; Not all physical systems We are bound by these symmetries. So-called non-reciprocal interactions manifest themselves in unruly systems of flocking birds. particles in fluid – and swimming sperm.
These motile agents move in a way that exhibits asymmetric interactions with the animals behind them or the surrounding fluid, forming an equal and opposite force loophole to circumvent Newton’s third law.
Because birds and cells generate your own energyEvery time you flap your wings or whip your tail, you add to the system, pushing it far away from equilibrium and the same rules don’t apply.
In a study published in October 2023, Ishimoto and his colleagues analyzed experimental data on human sperm and also modeled sperm movement. green algae, Chlamydomonas. Both are thin and use their bending to swim. Flagellum It protrudes from the cell body and changes shape or deforms to propel the cell forward.
High viscosity fluid This normally dissipates the flagellar energy and prevents most movement of sperm or unicellular algae. But somehow, the resilient flagella are able to propel these cells without provoking a reaction from their surroundings.
The researchers found that in sperm tails and algae flagella,Unusual elasticityThis allows these flexible appendages to move around without losing much energy to the surrounding fluid.
However, this strange elasticity could not fully explain the propulsion force due to the wave-like movement of the flagella. From their modeling studies, the researchers also derived a new term, odd modulus, to describe the internal mechanisms of the flagellum.
“From simple solvable models to biological flagellar waveforms, Chlamydomonas and sperm cells, we studied odd bending modulus to decipher non-local, non-reciprocal internal interactions within the material,” the researchers said. concluded.
This discovery could be useful for designing smaller products. self-assembly robot The researchers say modeling techniques could be used to mimic living materials and at the same time to better understand the principles underlying collective behavior. said.
This study PRX Life.
A previous version of this article was published in October 2023.
