Biomemetics This Time: Tunable Photonic Materials

Another Astonishing Design

We have discussed some amazing examples of how species control their color (here and here, for example) and how such technology in nature has inspired engineers creating advanced new technologies such as low-power video displays. Now new research is helping to explain how squids and octopuses change color and it is amazing.

We usually think of color as resulting from chemistry, such as in dyes. But different colors can also result from repeating, detailed submicron geometrical structures at the object’s surface. The new research reveals yet another, even more complex system for manipulating the frequency of light (i.e., the color) coming from squids and octopuses.

It begins with nerve signals which are sent to special cells containing special proteins. The signal causes the proteins to congregate and deep pleats to form in the cell membrane, altering the osmotic pressure and ultimately its refractive index.

Here is how one of the researchers described the process:

Initially, before the proteins are consolidated, the refractive index -- you can think of it as the density -- inside the lamellae and outside, which is really the outside water environment, is the same. There's no optical difference so there's no reflection. But when the proteins consolidate, this increases the refractive index so the contrast between the inside and outside suddenly increases, causing the stack of lamellae to become reflective, while at the same time they dehydrate and shrink, which causes color changes. The animal can control the extent to which this happens -- it can pick the color -- and it's also reversible. The precision of this tuning by regulating the nanoscale dimensions of the lamellae is amazing.

And here is a more technical description, from the journal paper:

Squids have used their tunable iridescence for camouflage and communication for millions of years; materials scientists have more recently looked to them for inspiration to develop new “biologically inspired” adaptive optics. Iridocyte cells produce iridescence through constructive interference of light with intracellular Bragg reflectors. The cell’s dynamic control over the apparent lattice constant and dielectric contrast of these multilayer stacks yields the corresponding optical control of brightness and color across the visible spectrum. Here, we resolve remaining uncertainties in iridocyte cell structure and determine how this unusual morphology enables the cell’s tunable reflectance. We show that the plasma membrane periodically invaginates deep into the iridocyte to form a potential Bragg reflector consisting of an array of narrow, parallel channels that segregate the resulting high refractive index, cytoplasmic protein-containing lamellae from the low-index channels that are continuous with the extracellular space. In response to control by a neurotransmitter, the iridocytes reversibly imbibe or expel water commensurate with changes in reflection intensity and wavelength. These results allow us to propose a comprehensive mechanism of adaptive iridescence in these cells from stimulation to color production. Applications of these findings may contribute to the development of unique classes of tunable photonic materials.

What we see here is a beautiful design consisting of a sequence of highly complex, intricate and finely-tuned mechanisms, molecules and structures allowing these organisms to precisely control their image. There is no scientific evidence that such optical technology arose from random mutations as evolutionists believe. Evolutionists like to call upon natural selection as a sort of natural designer, but that does not help for such intricate designs as these.