One of the chicken's most lasting legacies may eventually include advanced materials such as self-organizing colloids, or optics that can transmit light with the efficiency of a crystal and the flexibility of a liquid.
The unusual arrangement of cells in a chicken's eye constitutes the first known biological occurrence of a potentially new state of matter known as "disordered hyperuniformity," according to researchers from Princeton University and Washington University in St. Louis. Research in the past decade has shown that disordered hyperuniform materials have unique properties when it comes to transmitting and controlling light waves, the researchers report in the journal Physical Review E.
States of disordered hyperuniformity behave like crystal and liquid states of matter, exhibiting order over large distances and disorder over small distances. Like crystals, these states greatly suppress variations in the density of particles — as in the individual granules of a substance — across large spatial distances so that the arrangement is highly uniform. At the same time, disordered hyperuniform systems are similar to liquids in that they have the same physical properties in all directions. Combined, these characteristics mean that hyperuniform optical circuits, light detectors and other materials could be controlled to be sensitive or impervious to certain light wavelengths, the researchers report.
"We've since discovered that such physical systems are endowed with exotic physical properties and therefore have novel capabilities," Torquato said. "The more we learn about these special disordered systems, the more we find that they really should be considered a new distinguishable state of matter."
The discovery of hyperuniformity in a biological system could mean that the state is more common than previously thought, said Remi Dreyfus, a researcher at the Pennsylvania-based Complex Assemblies of Soft Matter lab (COMPASS) co-run by the University of Pennsylvania, the French National Centre for Scientific Research and the French chemical company Solvay. Previously, disordered hyperuniformity had only been observed in specialized physical systems such as liquid helium, simple plasmas and densely packed granules.
"It really looks like this idea of hyperuniformity, which started from a theoretical basis, is extremely general and that we can find them in many places," said Dreyfus, who is familiar with the research but had no role in it. "I think more and more people will look back at their data and figure out whether there is hyperuniformity or not. They will find this kind of hyperuniformity is more common in many physical and biological systems."
The findings also provide researchers with a detailed natural model that could be useful in efforts to construct hyperuniform systems and technologies, Dreyfus said. "Nature has found a way to make multi-hyperuniformity," he said. "Now you can take the cue from what nature has found to create a multi-hyperuniform pattern if you intend to."
Evolutionarily speaking, the researchers' results show that nature found a unique workaround to the problem of cramming all those cones into the compact avian eye, Corbo said. The ordered pattern of cells in most other animals' eyes are thought to be the "optimal" arrangement, and anything less would result in impaired vision. Yet, birds with the arrangement studied here — including chickens — have impeccable vision, Corbo said.
"These findings are significant because they suggest that the arrangement of photoreceptors in the bird, although not perfectly regular, are, in fact, as regular as they can be given the packing constraints in the epithelium," Corbo said.
"This result indicates that evolution has driven the system to the 'optimal' arrangement possible, given these constraints," he said. "We still know nothing about the cellular and molecular mechanisms that underlie this beautiful and highly organized arrangement in birds. So, future research directions will include efforts to decipher how these patterns develop in the embryo.