This IRG includes three thrust areas. These thrust areas are intimately related in several ways: the overlapping participation of the investigators, the common experimental methods and biopolymer materials, and the common theme of materials under constraint resulting in new properties. More important, they explore
this common theme on several levels of complexity. The first thrust deals with constraints on individual molecules, the second with the structure of large condensed arrays of molecules, and the third with the spatial and temporal organization of "active matter", dynamical arrays of interacting objects. All three levels are vital to understanding living systems, and combined, they have the potential for creating novel nano-structured material systems.
The first thrust area will study the effects of localization of biopolymers both in vivo and in vitro,
bridging the gap between traditional biological and physical studies. In cells, confinement of
macromolecules to very small and crowded volumes has major consequences for structure and dynamics.
We will explore this rich and important subject that is crucial to biological function. We will use
microfluidic devices for in vitro studies of the confinement of DNA, microtubules and actin, correlating
the results with fluorescence microscopy studies of processes involving DNA dynamics in yeast cell
nuclei.
The second thrust area will study the effects of chirality in frustrating long range order in both
crystals and membranes, resulting in complex new structures. Although frustration can result in
macroscopic modulated phases, like the beautiful twisted grain boundary phases and the cholesteric blue
phases, it can also lead to finite self-limiting self-assembled structures. Self assembly of molecular
components into ordered arrays is a dominant theme in materials science. However, chirality, the twisted
internal structure of the elementary units, can result in twisted aggregates not compatible with long range
order. The result can be novel structures such as twisted filaments and ribbons, and complex arrangement
of membranes and pores. This may produce simple models for some cell components, which are also
constructed by self-limiting self-assembly.
The third thrust area, perhaps the most exciting and novel, will study "active matter," with the initial
focus on two examples which sound quite different, but have fundamental concepts in common, and are
capable of producing similar spatial and temporal patterns. The first is the dynamical nematic liquid
crystal, composed of actin filaments that are constantly polymerizing at one end, and de-polymerizing at
the other, leading to the travel of each filament relative to its surroundings. We will study the resulting
formation of spatial and temporal patterns, some of which play an important role in cellular dynamical
processes, such as cell division. The second is a dense array of droplets each containing an oscillating
chemical reaction, either a controlled array produced by microfluidics or randomly packed nano-droplets
in a microemulsion. Interactions among the droplets by diffusion of reagents produce a rich variety of
pattern formation and temporal self organization, which we will study by careful variation of the
parameters of these systems. These will be the first precisely controllable experimental model systems of
active matter ever formulated and analyzed, an important innovation in this exciting new area.
