User:Haileydw/Bio-inspired photonics

Bioinspired Periodic/Aperiodic Structures

A combination of chemical structure and how it interacts with visible light creates color within organisms' nature. The creation of specific biological photonics requires identifying the chemical components of the structure, the optical response created by the physics and the structure’s function. The complex structures created by nature can range from simple, quasi-ordered structures to hierarchical complex formations.

2-D Structures

Simple Array Structure (Peacock Feathers)

Nature sometimes manipulates the nanostructure, such as its crystal lattice parameters in order to create its patterns and colors. The Barbule (the individual strands of a feather that hold its color) of the peacock is made of an outer layer of keratin and an inner layer containing an array of melanin rods connected by keratin with holes separating them. When the melanin rods are parallel to the lattice arrangement of the structure of the keratin outer layer it creates the brown color. The rest of the colors of the feather are created by changing the spacing of the melanin layers.

Multiple types of structures present in bio photonics

Aperiodic Photonic Structures

Aperiodic Photonic Structures do not have a unit cell and are capable of creating band gaps without the requirement of a high index of refraction difference. Also known as quasi-ordered crystal structure creates blue and green coloring.

3-D Structures

Helicoidal Multilayers

Twisted multilayers where fibers are aligned in the same direction and each layer they are slightly rotated. This structure allows nature to reflect polarized light and creates an intense value due to Bragg reflection.

Molecular Biomimetics

Molecular biomimetics involves the design of optical materials based on specific molecules and/or macromolecules to induce coloration. Molecularly Imprinted Polymers (MIPs) are specifically aimed at sensing macromolecules. They can also form them into specific structures that change color. [2] Pigment-inspired materials aiming for specific molecular light absorption have been developed as for example melanin-inspired films prepared by polymerization of melanin precursors such as dopamine and 5,6-dihydroxyindole to provoke color saturation.  Polydopamine is a synthetic polymer with color properties similar to melanin. It can also act to enhance structural colors. [2] Materials based on the multi-layer stacking of guanine molecular crystals found in living organisms (e.g. fish and chameleons) have been proposed as potential reflective coatings and solar reflectors. Protein-based optical materials, for instance self-assembling reflectin proteins found in cephalopods  and silk, have incited interest in artificial materials for camouflage systems, electronic paper (e-paper) and biomedical applications. Non-protein biological macromolecules such as DNA have also been utilized for bio-inspired optics. The most abundant biopolymer on earth, cellulose, has been also utilized as a principal component for bio-optics. Modification of wood or other cellulose sources can mitigate scattering and absorption of light leading to optically interesting materials such as transparent wood and paper. Cellulose nanocrystals can polarize light. [7]  Cellulose can also be used as nanofibrils or nanocrystals after treatments. One such treatment involves a nitrating agent to form nitrocellulose. Pressure and solvent polarity affect color of a manufactured cellulose membrane, to the point of detection by the naked eye [2].

Responsive Materials

Responsive materials are materials or devices that can respond to external stimuli as they occur. A little bit of time is taken to adjust to the new surroundings, but the idea remains consistent with what is seen in nature. The most commonly used examples are the chameleon or octopus, as their responsive skin allows them to change the color or even the texture of their skin. The mechanisms behind these tactics are called chromatophores, which is a pigment-filled sac that uses muscles and nerves to change the animal’s external appearance. These chromatophores are activated by neuronal activity, so an animal can change its color just by thinking about it. The animal uses another mechanism to be able to know what color or shape to take; a photo-sensitive cell within their skin called opsin is able to detect light (and possibly color). The animal can use these opsins to their advantage to quickly assess their surroundings, before turning on their chromatophores to accurately camouflage to their circumstances.

File:Silvering and Counterillumination.jpg

Silvering and counterillumination mechanisms in a general deep-sea fish

A lot of creatures have camouflage incorporated into their bodies - take the fish in the figure to the right for example. In this hypothetical, the animal can appear in two different ways depending on their surroundings: in the middle of the ocean away from all solid objects, it can appear near-translucent; near the sea floor where potential predators will only sense it from above, it can turn darker to naturally blend in with the rocky bottom. Many fish, such as the marine hatchetfish, use a combination of camouflage techniques to achieve these appearances. Silvering, a common tactic, utilizes highly reflective scales to reflect the surrounding light effectively enough to make the scales appear invisible from the side. Counterillumination, a tactic used more by deep-sea dwellers, uses a luminous organ located in the bottom of the body to emit light in order to appear brighter from underneath. At this angle, the light emitted is at an intensity meant to replicate the sunlight as it appears on the surface of the water. Thus, from below the creature is essentially invisible to many predators.

Within the luminous organ is a laminar structure of photocytes and nerve branches, with relatively small gap junctions between them. It is thought that the vast interconnectivity and the layered structure of these neuro-photocyte units is what allows a deep-sea fish to rapidly respond to a situation with spontaneous luminescence. Because all of the nerves are directly connected to the spinal cord (and by extension, the brain), researchers believe that electronic signals can trigger these photocytes to react. With this line of thinking, scientists are working to develop technology using this type of neuro-photocyte unit.

These biologically-inspired materials can be applied in many different circumstances. This technology can be used to camouflage objects, create a device that can mold its shape yet still retain its desired properties, or even help people in relation to biomedical applications. A coating of this technology can help incorporate a foreign body into a living ecosystem i.e. a human body. The technology of this device allows a person’s antibodies to detect the new object as a non-threat thus permitting easier acceptance of manmade tools into the body, such as a cardiac pacing device to the chest.

Application Examples

Bioinspired antibacterial structural color hydrogel

As a form of application, biophotonics are used in order to indicate antibacterial and self-healing properties. Since the existence of silver nanoparticles prevent bacterial adhesion (there is already bacteria existing in the hydrogel) it causes hydrogel degradation and color fading. This allows for the engineered hydrogel to display with color its integrity after self-healing.

Photonic nanoarchitectures in butterflies and beetles

Nanoarchitectures contribute to the iridescence of butterflies and beetles. Multilayers are common.- typically 1-D or 3-D structure, 2-D is more rare. [6] Disorder and irregularity in the structure are “intentional” and adapted to habitat. The structure has been successfully recreated and can be used as a coating. [8] It is also used in some applications where stable, vibrant color is required. It is flexible enough that it can be designed to have a pattern.  [https://www.sciencedirect.com/science/article/pii/S2666675821000060]