Soft Matter Seminar: Dr. Kenneth Foster

“How Physics and Biology solved the problem of how cilia beat”

Motile cilia are slender cylindrical biological organelles that propagate traveling waves of lateral displacement to propel cells or move fluid. They keep mammalian airways clean, control embryo development braking body symmetry, aid male and female reproduction and move nourishing fluid in the brain. A cilium is typically 200 nm diameter and in length from 10 μm up to even 6 mm. They are nanoelectromechanical machines composed of an excess of 600 unique proteins. They are large enough to incorporate ATP-driven motors down their entire length unlike prokaryotic flagella or archaella making it possible for eukaryotic microorganisms, larvae and sperm to go faster and further than prokaryotes. Addressed in this talk will be the fundamental question of how a bend forms and progresses to produce ciliary beating. We found at the cilium’s attachment to a cell a high-Q mechanical oscillator that initiates a sustained constant-energy traveling wave that propagates to the tip. Because of the energy dissipated during its motion, energy must be continuously supplied along its length. For cilia of constant diameter, the energy propagated does not depend on the availability of ATP energy above a threshold or within a significant range the viscosity of the fluid the cell is swimming through. This talk will present the mechanism of oscillation and how it was derived mostly from biological data made available in 1996 by applying physical principles and how the wave propagates based on biological data from 2018. All this spontaneous behavior is self-organized under entirely local control.