Sperm and Algae Defy Fluid Dynamics with ‘Odd Elasticity,’ New Research Reveals
Scientists have discovered that sperm tails and algal flagella move with an unexpected efficiency, seemingly bypassing a fundamental principle of physics governing movement in viscous fluids. A new study published in PRX Life details how these microscopic appendages propel themselves thru thick environments without the energy loss typically predicted by the “scallop theorem.” The findings could revolutionize the design of micro-robots and deepen our understanding of biological movement.
Typically, the high viscosity of fluids like cytoplasm should severely hinder the wave-like motion of flagella, dissipating energy and limiting propulsion. Yet, sperm and single-celled algae like Chlamydomonas globosa navigate these environments with remarkable ease. Researchers have now pinpointed a key factor: an ”odd elasticity” within the flagella themselves, allowing them to bend and move without important energy loss to the surrounding fluid.
The team’s modeling revealed that this odd elasticity alone didn’t fully explain the observed propulsion. They subsequently identified a new metric – an “odd elastic modulus” - to characterize the unique internal mechanics of these biological whips. ”From solvable simple models to biological flagellar waveforms for Chlamydomonas and sperm cells, we studied the odd-bending modulus to decipher the nonlocal, nonreciprocal inner interactions within the material,” the researchers concluded in their published paper.
This discovery has implications beyond fundamental biology. The principles governing flagellar movement could inform the advancement of self-assembling robots capable of navigating complex, viscous environments. Furthermore, the modeling techniques employed in the study may provide insights into collective behavior in other biological systems. The research builds on previous work exploring highly viscous fluids and their impact on movement, and also advancements in the design of self-assembling robots.
