September 23, 2019
A natural plastic-like material? That's right! Science has come through again combining silk protein from spider webs and wood fibers. Now why didn't I think of that?
Learn about this and more interesting stories from the scientific community in today's issue.
*-- Spider silk, wood combination replicates material advantages of plastic --*
By combining the silk protein from spider web threads with wood cellulose fibers, scientists have created a material featuring strength and extensibility comparable to plastic.
Extensibility is the extent to which a material can be stretched without causing it to tear or break, and until now, scientists have struggled to pair the material property with strength.
To overcome the challenge, scientists turned to two biological ingredients with the target qualities. Cellulose is know for its strength, while the silk threads produced by spiders offer impressive extensibility.
"We used birch tree pulp, broke it down to cellulose nanofibrils and aligned them into a stiff scaffold," Pezhman Mohammadi, researcher at the VTT Technical Research Center of Finland, said in a news release. "At the same time, we infiltrated the cellulosic network with a soft and energy dissipating spider silk adhesive matrix."
Mohammadi worked with scientists at Aalto University to produce the bio-based composite material.
Though silk is produced by silk worms and spiders, scientists at Aalto sourced the silk from bacteria augmented with synthetic DNA.
"Because we know the structure of the DNA, we can copy it and use this to manufacture silk protein molecules which are chemically similar to those found in spider web threads," said Markus Linder, a professor at Aalto. "The DNA has all this information contained in it."
The production process yielded a material with high strength and stiffness, as well as increased toughness. Most importantly, this strength is not compromised when the material is stretched.
Researchers described their new material in the journal Science Advances. The material's qualities are similar to those of plastic, but because it is biodegradable, the new material is more eco-friendly.
"Our work illustrates the new and versatile possibilities of protein engineering. In future, we could manufacture similar composites with slightly different building blocks and achieve a different set of characteristics for other applications," Pezhman said. "Currently we are working on making new composite materials as implants, impact resistance objects and other products."
*-- Engineers build robot fish that keeps pace with yellowfin tuna --*
Engineers have developed an underwater robot capable of matching the movements and speed of yellowfin tuna.
To build the robot, the team of engineers closely studied the physics of fish propulsion. Researchers hope their efforts will eventually inspire a new generation of underwater vehicles, powered by fins and fish-like locomotion instead of propellers.
"Our goal wasn't just to build a robot. We really wanted to understand the science of biological swimming," Hilary Bart-Smith, an engineering professor at the University of Virginia, said in a news release. "Our aim was to build something that we could test hypotheses on in terms of what makes biological swimmers so fast and efficient."
Before researchers could set out to build their robot, the scientists needed to understand how fish move. The team precisely measured the swimming movements of yellowfin tuna and mackerel.
Bart-Smith and her research partners designed a fish-like robot capable of beating its tail fast enough to match the speeds of yellowfin tuna. They named their creation "Tunabot."
After putting Tunabot through a series of tests, scientists compared its swimming performance to the performance of real tuna. The data -- detailed this week in the journal Science Robotics -- showed Tunabot can replicate a yellowfin's top speed.
For the tests, the robot swam in place, held steady by a fishing line. Scientists produced stronger and stronger currents in the test tank to test Tunabot's top speeds. As they increased the current, the robot's tail and whole body perform a fast-paced bending pattern. Researchers used a laser to measure the fluid motion shed by each bend of the robot's body and tail.
"We see in the fish robotics literature so far that there are really great systems others have made, but the data is often inconsistent in terms of measurement selection and presentation," said doctoral student Carl White. "It's just the current state of the robotics field at the moment. Our paper about the Tunabot is significant because our comprehensive performance data sets the bar very high."
Though Tunabot is inspired by yellowfin tuna, researchers aim to eventually build a robot fish that can outrace their biological forefathers.
"Our ultimate goal is to surpass biology," said Bart-Smith. "How can we build something that looks like biology but swims faster than anything you see out there in the ocean?"
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