Evolution has already solved many of the challenges engineers are confronted with on a daily basis. Think about octopuses, for example. We frequently report on soft robotics here at Gizmodo. Octopuses are essentially brilliant, eight-armed soft robots.
So when it comes to solving other underwater challenges, such as adhesives staying sticky underwater, a team of researchers knew exactly which cephalopod to ask for help. Their new octopus-inspired adhesive could potentially find uses in medicine and other fields of research where things typically get wet or moist. But it's mainly interesting for how it's helped them understand the squid's sticky grip.
"We thought that there would be a secret of how octopuses stick to underwater surfaces, so we started to observe them with curiosity," assistant professor Changhyun Pang from Sungkyunkwan University in South Korea told Gizmodo in an email. "We revealed nature's secret regarding this particular architecture."
Image: Sang-Yul Baik et al
If you've ever seen an octopus tentacle, you'd know it's covered in little suckers, each a deep suction cup with a ball in the middle. Pang and his team wanted to figure out how the tentacles stuck to things underwater, so they made their own tentacles. Rather than a long appendage with protrusions, they instead produced a polymer sheet with dimples tens of micrometres across, each with a little sphere in the middle.
They experimented with various sucker radii, finding that the stickiest adhesive had 50 micrometre dimples arranged fairly densely. They tried several different dimple shapes, and the octopus-inspired one was the stickiest by far under moist conditions, underwater and under oil.
The researchers put their sticker under a microscope to see how it got so sticky. Essentially, each dimple fills with water. When you press down on the back, the whole thing compresses, trapping water beneath the sphere. This leaves a vacuum chamber when you release the pressure.
Image: Sang-Yul Baik et al
Underwater stickiness is a challenge, Emre Kizilkan, researcher from the the Zoological Institute at Kiel University in Germany, told Gizmodo, so he was especially impressed by this octopus-inspired tape. "This absorption of the liquid underwater is quite unique," he said. But he pointed out that it isn't as sticky as dry sticky tape. Scientist Francesca Tramacere from the Istituto Italiano di Tecnologia agreed that there were some things left to do, such as improving the way that the tape un-sticks. That would be especially important if you needed to stick something, such as a Band Aid, to wet skin, for example.
That said, Tramacere was pretty stoked about the whole thing. Pang and his team used her studies of octopus suckers in order to make the adhesive, where she and her coauthors hypothesised how the attachment and detachment process works in octopus suckers. "The authors have confirmed both that morphology of octopus suckers is an amazing source of inspiration for making innovative reversible wet/dry attachment systems," she told Gizmodo in an email, "But also they have provided an experimental confirmation of the attachment hypothesis proposed for octopus in [my past work]."
An underwater adhesive such as this would have a lot of promise as medical tape applied over a wound, according to the paper published today in the journal Nature. It could just be useful for moving things around, or to put on boats to prevent algae from growing on their hulls. And right now, the team thinks they could commercialise their tape in three years.
Octopuses are seriously awesome, and there are a ton of other secrets we might be able to unlock by studying them. Tramacere thought it was especially interesting for its ability to vary its own stiffness, for example. Folks have even tried making octopus tentacle-inspired prosthetic arms.
So clearly, cephalopods are doing something right.