Nav: Home

MIT engineers design beaver-inspired wetsuit material

October 05, 2016

Beavers and sea otters lack the thick layer of blubber that insulates walruses and whales. And yet these small, semiaquatic mammals can keep warm and even dry while diving, by trapping warm pockets of air in dense layers of fur.

Inspired by these fuzzy swimmers, MIT engineers have now fabricated fur-like, rubbery pelts and used them to identify a mechanism by which air is trapped between individual hairs when the pelts are plunged into liquid.

The results, published in the journal Physical Review Fluids, provide a detailed mechanical understanding for how mammals such as beavers insulate themselves while diving underwater. The findings may also serve as a guide for designing bioinspired materials -- most notably, warm, furry wetsuits.

"We are particularly interested in wetsuits for surfing, where the athlete moves frequently between air and water environments," says Anette (Peko) Hosoi, a professor of mechanical engineering and associate head of the department at MIT. "We can control the length, spacing, and arrangement of hairs, which allows us to design textures to match certain dive speeds and maximize the wetsuit's dry region."

Hosoi's co-authors include lead author and graduate student Alice Nasto, postdoc José Alvarado, and applied mathematics instructor Pierre-Thomas Brun, all from MIT, as well as former visiting researcher Marianne Regli, and Christophe Clanet, both of École Polytechnique, in France.

Surfing science

The group's research was motivated by a 2015 trip to Taiwan. Hosoi leads MIT's STE@M (Sports Technology and Education at MIT), a program that encourages students and faculty to pursue projects that help advance sports technologies. In the summer of 2015, Hosoi brought a group of STE@M students to Taiwan, where they visited several sporting goods makers, including the wetsuit manufacturer, Sheico Group.

"They are interested in sustainability, and asked us, 'Is there a bioinspired solution for wetsuits?'" Hosoi says. "Surfers, who go in and out of the water, want to be nimble and shed water as quickly as possible when out of the water, but retain the thermal management properties to stay warm when they are submerged."

When the group returned from the trip, Hosoi assigned the problem to Nasto, encouraging her to find examples in nature that could serve as a design model for warm, dry, streamlined wetsuits. In her literature searches, Nasto zeroed in on semiaquatic mammals, including beavers and sea otters. Biologists had observed that these animals trap, or "entrain" air in their fur.

Nasto also learned that the animals are covered in two types of fur: long, thin "guard" hairs, that act as a shield for shorter, denser "underfur." Biologists have thought that the guard hairs keep water from penetrating the underfur, thereby trapping warm air against the animals' skin. But as Nasto notes, "there was no thorough, mechanical understanding of that process. That's where we come in."

Deep pockets

The team laid out a plan: Fabricate precise, fur-like surfaces of various dimensions, plunge the surfaces in liquid at varying speeds, and with video imaging measure the air that is trapped in the fur during each dive.

To make hairy surfaces, Nasto first created several molds by laser-cutting thousands of tiny holes in small acrylic blocks. With each mold, she used a software program to alter the size and spacing of individual hairs. She then filled the molds with a soft casting rubber called PDMS (polydimethylsiloxane), and pulled the hairy surfaces out of the mold after they had been cured.

In their experiments, the researchers mounted each hairy surface to a vertical, motorized stage, with the hairs facing outward. They then submerged the surfaces in silicone oil -- a liquid that they chose to better observe any air pockets forming.

As each surface dove down, the researchers could see within the hairs a clear boundary between liquid and air, with air forming a thicker layer in hairs closer to the surface, and progressively thinning out with depth. Among the various surfaces, they found that those with denser fur that were plunged at higher speeds generally retained a thicker layer of air within their hairs.

Fur trap

From these experiments, it appeared that the spacing of individual hairs, and the speed at which they were plunged, played a large role in determining how much air a surface could trap. Hosoi and Nasto then developed a simple model to describe this air-trapping effect in precise, mathematical terms. To do this, they modeled the hair surfaces as a series of tubes, representing the spaces between individual hairs. They could then model the flow of liquid within each tube, and measure the pressure balance between the resulting liquid and air layers.

"Basically we found that the weight of the water is pushing air in, but the viscosity of the liquid is resisting flow (through the tubes)," Hosoi explains. "The water sticks to these hairs, which prevents water from penetrating all the way to their base."

Hosoi and Nasto applied their equation to the experimental data and found their predictions matched the data precisely. The researchers can now accurately predict how thick an air layer will surround a hairy surface, based on their equation.

"People have known that these animals use their fur to trap air," Hosoi says. "But, given a piece of fur, they couldn't have answered the question: Is this going to trap air or not? We have now quantified the design space and can say, 'If you have this kind of hair density and length and are diving at these speeds, these designs will trap air, and these will not.' Which is the information you need if you're going to design a wetsuit. Of course, you could make a very hairy wetsuit that looks like Cookie Monster and it would probably trap air, but that's probably not the best way to go about it."
-end-
This research was funded, in part, by the National Science Foundation.

Additional background

ARCHIVE: Tackling challenges at the intersection of engineering and sports

ARCHIVE: Squishy robots

ARCHIVE: Robot builds on insights into Atlantic razor clam dynamics

ARCHIVE: 3 Questions: Anette Hosoi on engineering and the Olympics

Massachusetts Institute of Technology

Related Water Articles:

Water, water, nowhere
Researchers at the University of Pittsburgh's Swanson School of Engineering have found that the unusual properties of graphane -- a two-dimensional polymer of carbon and hydrogen -- could form a type of anhydrous 'bucket brigade' that transports protons without the need for water, potentially leading to the development of more efficient hydrogen fuel cells for vehicles and other energy systems.
Advantage: Water
When water comes in for a landing on the common catalyst titanium oxide, it splits into hydroxyls just under half the time.
What's really in the water
Through a five-year, $500,000 CAREEER Award from the National Science Foundation, a civil and environmental engineering research group at the University of Pittsburgh's Swanson School of Engineering will be developing new DNA sequencing methods to directly measure viral loads in water and better indicate potential threats to human health.
Jumping water striders know how to avoid breaking of the water surface
When escaping from attacking predators, different water strider species adjust their jump performance to their mass and morphology in order to jump off the water as fast and soon as possible without breaking of the water surface.
Water, water -- the two types of liquid water
There are two types of liquid water, according to research carried out by an international scientific collaboration.
Just add water? New MRI technique shows what drinking water does to your appetite, stomach and brain
Stomach MRI images combined with functional fMRI of the brain activity have provided scientists new insight into how the brain listens to the stomach during eating.
UM researchers found shallow-water corals are not related to their deep-water counterparts
A new study led by scientists at the University of Miami Rosenstiel School of Marine and Atmospheric Science found that shallow-reef corals are more closely related to their shallow-water counterparts over a thousand miles away than they are to deep-water corals on the same reef.
Saline water better than soap and water for cleaning wounds, researchers find
Researchers found that very low water pressure was an acceptable, low-cost alternative for washing out open fractures, and that the reoperation rate was higher in the group that used soap.
UTA research predicting lake levels, moving water to yield better data for water providers
A University of Texas at Arlington environmental engineer is creating an integrated decision support tool for optimal operation of water supply systems that will allow water providers to make better decisions about when to turn on pumps to transfer water from one reservoir system to another and when to release water downstream from the reservoirs.
Surfing water molecules could hold the key to fast and controllable water transport
Scientists at UCL have identified a new and potentially faster way of moving molecules across the surfaces of certain materials.

Related Water Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.