Light-Sensitive Hydrogel Inspired by Cephalopods

Innovation: Academia

Rutgers University

2021

Image: Vlad Tchompalov / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Smart hydrogel from Rutgers University contains a light-sensing nanomaterial that enables it to change shape when exposed to light.

Benefits

Flexible
Color-changing
Versatile

Applications

Medical implants
Soft robots
Protective equipment

UN Sustainable Development Goals Addressed

Goal 9: Industry Innovation & Infrastructure
Goal 12: Responsible Production & Consumption

The Challenge

Electronic displays are found everywhere and have made remarkable advances in recent years. However, they are still made from rigid materials, which limits the size and shape they can take. It also limits their use in numerous applications, such as color changing materials and medical devices.

Innovation Details

The light-sensing hydrogel contains an artificial chromatophore, which mimics the color-changing structures found in cephalopods. The artificial chromatophore is made from a nanomaterial that reacts to light. When the hydrogel senses light, the nanomaterial deforms, functioning as a kind of ‘artificial muscle’ that contracts or expands in response to changes in light. The hydrogel can be combined with 3D printed stretchy material that changes color, allowing for a camouflage-like effect.

Overview of the innovation. Photo: D. Han et al./Rutgers University.

Biological Model

Cephalopods such as squid and cuttlefish often use adaptive camouflage to blend in with their surroundings. They are able to match colors and surface textures of their surrounding environments by adjusting the and iridescence of their skin. On the skin surface, chromatophores (tiny sacs filled with red, yellow, or brown pigment) absorb light of various wavelengths. Once visual input is processed, the cephalopod sends a signal to a nerve fiber, which is connected to a muscle. That muscle relaxes and contracts to change the size and shape of the chromatophore. Each color chromatophore is controlled by a different nerve, and when the attached muscle contracts, it flattens and stretches the pigment sack outward, expanding the color on the skin. When that muscle relaxes, the chromatophore closes back up, and the color disappears. As many as two hundred of these may fill a patch of skin the size of a pencil eraser.