Now, researchers from Kyoto College say they’ve decoded the key: sperm tails exploit a phenomenon referred to as “odd elasticity,” enabling them to maneuver in ways in which sidestep one among Newton’s fundamental legal guidelines of movement.
The findings, printed by researchers Kenta Ishimoto, Clément Moreau, and Kento Yasuda, assist resolve a decades-old puzzle: how sperm can journey swiftly via thick cervical mucus or gel-like fluids that ought to sluggish such tiny swimmers to a crawl.
The physics drawback within the micro world
On the human scale, swimmers push water backward to propel ahead, with inertia balancing the forces. However on the microscopic stage, inertia disappears and is changed by syrupy drag, a state of affairs physicists name low Reynolds quantity movement.
In such situations, a easy back-and-forth flick of a tail wouldn’t work. As an alternative, objects like sperm should carry out a steady, asymmetrical wiggle sample that by no means repeats in reverse, permitting ahead movement.
Odd elasticity: The tail’s secret weapon
Utilizing high-speed video of human sperm and the inexperienced alga Chlamydomonas, the staff mapped tail actions in “form area” and created an elastic matrix to calculate inside forces. They discovered that the tails are powered by molecular motors that always inject power as a substitute of performing like passive springs.
This creates odd elasticity, an imbalance the place a bend in a single a part of the tail sends pressure via the complete construction with out a mirrored counterforce. The result’s a touring wave that strikes ahead with out an equal push in the other way.
Biology and robotics
The examine means that as odd elasticity will increase, so does propulsion velocity. This explains how human sperm beat their tails round 20 instances per second, even in thick fluids.
The precept additionally applies to different microscopic swimmers like algae, and will encourage smooth robots that navigate via viscous environments utilizing related mechanics, with out rotating motors.
Rethinking newton in lively methods
The work doesn’t overturn Newton’s third regulation, which nonetheless governs passive methods. As an alternative, it exhibits that drive symmetry could be bypassed in lively methods, the place power is consistently absorbed and expended.
In nature, this flexibility might assist sperm adapt their swimming mechanics in response to chemical cues or modifications in viscosity on their approach to the egg.