Cephalopod Skin Sparks Next-Gen Soft Robotics
Cephalopod Skin Sparks Next-Gen Soft Robotics
Squids, cuttlefish, and other cephalopods are masters of disguise. Now, chemists at the University of Nebraska have created skin that mimics these shape-shifting sea creatures.
The skins of octopuses and their cephalopod brethren are some of the most colorful, high-definition, morphing displays evolution has produced. Like a soft, tentacled, stretchable LED TV that can swim, they’re one moment a bright and fluorescent coral, the next a striped alga or a plain sandy beige, and then, just as suddenly, a rough and rocky boulder.
A macroscopic view of the bilayer soft skin, which is encapsulated in a silicone medium to preserve hydration and alignment. Image: Brennan P. Watts, Stephen A. Morin, University of Nebraska-Lincoln.
However astonishing the epidermal fireworks, it’s their ability to mimic their environment that most interests Stephen A. Morin, an Associate Professor in the Department of Chemistry at The University of Nebraska, Lincoln. Morin has created a stretchy silicone and hydrogel skin that can sense changes in its environment and transform accordingly without electricity.
Cephalopod skin is covered with chromatophore organs and tiny pigment sacks whose shape is controlled by radial muscles, allowing them to switch their camo so quickly. Morin has traded those for microscopic arrays of hydrogels that sit on top of a silicone film.
These hyper-spongy hyper-water-loving polymers can suck up enough of the wet material to become 95 percent water, as they can be sensitized to change shape when the light, temperature, or pH of their environment changes. For their paper “Synthetic Chromatophores for Color and Pattern Morphing Skins,” which appeared in Advanced Materials this spring, temperature was the main focus.
Though hydrogels were utilized instead of pigment sacks, their technique still borrows from the tentacled ocean dwellers.
You May Want to Read: Nanocomposite Hydrogels Offer Extended Drug Delivery
“The cephalopod skins, and our skins, and digital print media, are fundamentally using some of the basic properties of halftoning,” said Morin. “Like the dots of a dot matrix printer, the dimensional arrays of gels look different when they change size and shape. So, when they’re fully expanded, they offer a larger fill fraction.”
This simple actuation could give rise to a garment that reports body temperature, humidity, acidity, among other factors, all at the same time, somewhere down the road. Soft robots could also display the state of these parameters, as could any tool or object wrapped in such a skin, all without a battery or a power cord. More complicated signaling could come to creation with multiple layers of hydrogel arrays.
“You can get some interesting interference effects between layers,” Morin said. “You can have regions of alignment and misalignment that give rise to interesting higher-level patterns that you wouldn’t get from just a single array.”
Essentially, the effect allows different parameter combinations for reading at a glance. Incorporating color into the mix will also give rise to many forms of environmentally responsive imaging.
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But achieving the kind of fidelity and vibrancy of a flat screen or an octopus skin is a long way off. For one thing, with the kind of general sensing that they’re working on now, thermal
diffusion would lead to a not very distinct image.
Brennan Watts, a fourth-year doctoral student, looks through a microscope at a checkerboard-patterned hydrogel, with Stephen Morin, associate professor of chemistry. Image: Liz McCue | University Communication and Marketing
If one of the hydrogel skins were on a surface with a small, well-defined hot spot, the heat on the polymer would spread, preventing a sharp-edged reaction. Then there’s the small issue of speed of response—the hydrogel has a seconds-long actuation time. However, Morin’s paper represents the start of this field of research.
“I don’t know if we’re going to be able to make a hydrogel do what an octopus or a cephalopod does,” he said. “An LCD screen where you have RGB pixels that are on and off—that’s certainly a target that we can aim for in the future. You can have gels whose job it is to focus regions of the underlying layer so that they’re part of the image or not part of the image. So the optical landscape, in terms of what’s possible, is quite rich.”
But the more immediate goal of an unpowered sensing and color-shifting skin for soft robotics or wearables is more achievable.
“Ideally we would be able to make materials that can sense their environment, react to it, heal themselves when they’re broken and grow and shrink in response to some sort of a new need,” said Morin. “We would hope that our synthetic materials will execute all of those fundamental functions of sustainability and adaptability that we see in biology.”
Michael Abrams is a technology writer in Westfield, N.J.
A macroscopic view of the bilayer soft skin, which is encapsulated in a silicone medium to preserve hydration and alignment. Image: Brennan P. Watts, Stephen A. Morin, University of Nebraska-Lincoln.
Cephalopod skin is covered with chromatophore organs and tiny pigment sacks whose shape is controlled by radial muscles, allowing them to switch their camo so quickly. Morin has traded those for microscopic arrays of hydrogels that sit on top of a silicone film.
These hyper-spongy hyper-water-loving polymers can suck up enough of the wet material to become 95 percent water, as they can be sensitized to change shape when the light, temperature, or pH of their environment changes. For their paper “Synthetic Chromatophores for Color and Pattern Morphing Skins,” which appeared in Advanced Materials this spring, temperature was the main focus.
Though hydrogels were utilized instead of pigment sacks, their technique still borrows from the tentacled ocean dwellers.
You May Want to Read: Nanocomposite Hydrogels Offer Extended Drug Delivery
“The cephalopod skins, and our skins, and digital print media, are fundamentally using some of the basic properties of halftoning,” said Morin. “Like the dots of a dot matrix printer, the dimensional arrays of gels look different when they change size and shape. So, when they’re fully expanded, they offer a larger fill fraction.”
This simple actuation could give rise to a garment that reports body temperature, humidity, acidity, among other factors, all at the same time, somewhere down the road. Soft robots could also display the state of these parameters, as could any tool or object wrapped in such a skin, all without a battery or a power cord. More complicated signaling could come to creation with multiple layers of hydrogel arrays.
“You can get some interesting interference effects between layers,” Morin said. “You can have regions of alignment and misalignment that give rise to interesting higher-level patterns that you wouldn’t get from just a single array.”
Essentially, the effect allows different parameter combinations for reading at a glance. Incorporating color into the mix will also give rise to many forms of environmentally responsive imaging.
Discover the Benefits of ASME Membership
But achieving the kind of fidelity and vibrancy of a flat screen or an octopus skin is a long way off. For one thing, with the kind of general sensing that they’re working on now, thermal
diffusion would lead to a not very distinct image.
Brennan Watts, a fourth-year doctoral student, looks through a microscope at a checkerboard-patterned hydrogel, with Stephen Morin, associate professor of chemistry. Image: Liz McCue | University Communication and Marketing
“I don’t know if we’re going to be able to make a hydrogel do what an octopus or a cephalopod does,” he said. “An LCD screen where you have RGB pixels that are on and off—that’s certainly a target that we can aim for in the future. You can have gels whose job it is to focus regions of the underlying layer so that they’re part of the image or not part of the image. So the optical landscape, in terms of what’s possible, is quite rich.”
But the more immediate goal of an unpowered sensing and color-shifting skin for soft robotics or wearables is more achievable.
“Ideally we would be able to make materials that can sense their environment, react to it, heal themselves when they’re broken and grow and shrink in response to some sort of a new need,” said Morin. “We would hope that our synthetic materials will execute all of those fundamental functions of sustainability and adaptability that we see in biology.”
Michael Abrams is a technology writer in Westfield, N.J.
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