Videos

Buckled viruses, crumpled shells and folded pollen grains

Presenter
July 24, 2008
Keywords:
  • Ordered states
MSC:
  • 12J15
Abstract
The difficulty of constructing ordered states on spheres was recognized by J. J. Thomson, who discovered the electron and then attempted regular tilings of the sphere in an ill-fated attempt to explain the periodic table. We first discuss how protein packings in buckled virus shells solve a related “Thomson problem”. We then describe the grain boundary scars that appear on colloidosomes, drug delivery vehicles that represent another class of solution to this problem. The remarkable modifications in the theory necessary to account for thermal fluctuations in crumpled amorphous shells of spider silk proteins will be described as well. We then apply related ideas to the folding strategies and shapes of pollen grains during dehydration when they are released from the anther after maturity. The grain can be modeled as a pressurized high-Young-modulus sphere with a weak sector and a nonzero spontaneous curvature. In the absence of such a weak sector, these shells crumple irreversibly under pressure via a strong first order phase transition. The weak sectors (both one and three-sector pollen grains are found in nature) eliminate the hystersis and allow easy rehydration at the pollination site, somewhat like the collapse and subsequent reassembly of a folding chair.