Synthetic Hydrogel Mimics Lobster Underbelly’s Stretch and Strength

The MIT team has produced a hydrogel-based material that mimics the structure of the lobster’s lower abdomen. This is the toughest known hydrogel in nature.

Membrane structure may provide a robust artificial tissue blueprint.

The lower abdomen of the red shrimp is lined with a thin, translucent film that is elastic and surprisingly durable. This Marine Corps Under Armor Reported by MIT engineers Made from the toughest known hydrogels in nature in 2019, it’s also extremely flexible. This combination of strength and elasticity helps the red shrimp shield as it scrabbles the ocean floor. You can also bend back and forth to swim.

Now another MIT The team produced a hydrogel-based material that mimics the structure of the lobster’s lower abdomen. Researchers have examined the material through a series of stretch and impact tests, and like the lobster’s lower abdomen, the synthetic material is very “fatigue resistant” and can withstand repeated stretches and strains without tearing. Was shown.

If the manufacturing process can be significantly scaled up, materials made from nanofiber hydrogels can be used to create strong elastic replacement tissues such as artificial tendons and ligaments.

Team results were recently published in the journal Matter.. MIT co-authors of this treatise include postdoctoral fellows Jiahua Ni and Shaoting Lin. Graduate students Xinyue Liu and Yuchen Sun; Aerospace Engineering Professor Raul Radovitzky; Chemistry Professor Keith Nelson; Mechanical Engineering Professor Xuanhe Zhao; Former Research Scientist David Veysset PhD ’16, now Stanford University. With Associate Professor Zhao Qin of Syracuse University and Alex Sea of ​​the Army Research Institute.

Bouligand Nanofiber Hydrogel

Image of bouligand nanofiber hydrogel.Credits: Courtesy of researchers

A twist of nature

In 2019, other members of Lin and Zhao’s group will be in a new kind Fatigue resistant material made from hydrogel — A gelatin-like class of material, primarily made of water and cross-linked polymers. They made the material from hydrogel microfibers. It aligned like many strands of straw collected as the material was repeatedly stretched. This training also took place to increase the fatigue resistance of hydrogels.

“At that moment, I felt the importance of hydrogel nanofibers and wanted to manipulate the fibril structure to optimize fatigue resistance,” says Lin.

In their new study, researchers have combined several techniques to create more powerful hydrogel nanofibers. This process begins with electrospinning. Electrospinning is a fiber manufacturing technology that uses an electric charge to draw extrafine threads from a polymer solution. The team used high-voltage charges to spin nanofibers from a polymer solution, forming a flat film of nanofibers of about 800 nanometers, each of which is a fraction of the diameter of human hair.

They placed the film in a high humidity chamber and welded the individual fibers into a sturdy interconnected network, then set the film in an incubator to crystallize the individual nanofibers at high temperatures, further strengthening the material. ..

They tested the fatigue resistance of the film by placing it in a machine that stretches the film repeatedly over tens of thousands of cycles. They also made cuts in some film and observed how the cracks propagated as the film was stretched repeatedly. From these tests, they calculated that nanofiber films are 50 times more fatigue resistant than traditional nanofiber hydrogels.

Notched nanofiber hydrogels that are repeatedly loaded to emphasize how fatigue resistant the material is. Even if there is an existing rift, it can withstand repeated stretches and tensions without further ripping.Credits: Courtesy of researchers

Around this time, they read interestingly a study by Ming Guo, an associate professor of mechanical engineering at MIT, who characterized the mechanical properties of the lower abdomen of red-spotted shrimp. This protective film is made from a thin sheet of chitin, a natural fibrous material similar in composition to the group’s hydrogel nanofibers.

Guo discovered that the cross-section of the lobster membrane revealed a sheet of chitin stacked at a 36-degree angle, like twisted plywood or spiral stairs. This rotating layered structure, known as the boo ligand structure, enhances the stretch and strength properties of the membrane.

“We learned that this boulangerie structure in the lower abdomen of red shrimp has high mechanical performance and motivated us to see if synthetic materials could reproduce such a structure,” says Lin.

Angled architecture

Members of the Ni, Lin, and Zhao groups use synthetic fatigue-resistant films in collaboration with Nelson’s lab, Radovitzky’s lab, and Qin’s lab at Syracuse University at MIT’s Soldier Nanotechnologies Institute. We confirmed whether the boulangerie membrane structure of lobster could be reproduced. ..

“We prepared nanofibers aligned by electrospinning to mimic the kinic fibers present in the lower abdomen of the red shrimp,” says Ni.

After electrospinning the nanofiber films, researchers stacked five films in succession at an angle of 36 degrees to form a single boulangerie structure, which was welded and crystallized to reinforce the material. The final product is 9 square centimeters in size, about 30-40 microns thick, about the size of a small piece of scotch tape.

Stretch tests have shown that lobster-inspired materials work like their natural materials and can be stretched repeatedly while resisting crevices and cracks. This is a fatigue resistant Lin due to the angled architecture of the structure.

“Intuitively, when material cracks propagate through one layer, they are blocked by adjacent layers that align the fibers at different angles,” Lin explains.

The team also subjected the material to microballistic impact testing in an experiment designed by Nelson’s group. They imaged the material while shooting the particles at high speed and measured the velocity of the particles before and after tearing the material. Due to the difference in speed, the impact resistance of the material, that is, the amount of energy that can be absorbed, could be measured directly. It turned out to be surprisingly tough, 40 kilojoules per kilogram. This number is measured in the hydrated state.

Steel Particle Earrings Nanofiber Hydrogel

It is shown that steel particles penetrate the nanofiber hydrogel and slow down and exit. The difference in speed before and after allows researchers to directly measure the impact resistance of a material, the amount of energy it can absorb.Credits: Courtesy of researchers

“That is, a 5mm steel ball fired at 200 meters per second is blocked by a 13mm material,” says Veysset. “It’s not as tolerant as Kevlar, which requires 1 millimeter, but the material outperforms Kevlar in many other categories.”

Not surprisingly, the new material is not as sturdy as the commercially available ballistic missile interception material. However, it is significantly more robust than most other nanofiber hydrogels such as gelatin and synthetic polymers such as PVA. The material is much more elastic than Kevlar. This combination of elasticity and strength can speed up their production, suggesting that nanofiber hydrogels may act as flexible and tough artificial tissues when more films are stacked on the boulangerie structure. I am.

“For a hydrogel material to be a load-bearing artificial tissue, it needs both strength and deformability,” says Lin. “Our Material Design can achieve these two properties.”

Reference: “Strong fatigue-resistant nanofiber hydrogel inspired by lobster lower abdomen”, Jiahua Ni, Shaoting Lin, Zhao Qin, David Veysset, Xinyue Liu, Yuchen Sun, Alex J. Hsieh, Raul Radovitzky, Keith A. Nelson , Xuanhe Zhao, 23 April 2021 Matter..
DOI: 10.1016 / j.matt.2021.03.023

This study was partially supported by MIT and the US Army Institute through MIT’s Soldier Nanotechnology Institute.

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