{"id":20464,"date":"2021-05-02T11:58:10","date_gmt":"2021-05-02T06:13:10","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=20464"},"modified":"2021-05-02T11:58:14","modified_gmt":"2021-05-02T06:13:14","slug":"synthetic-gelatin-like-material-mimics-lobster-underbellys-stretch-and-strength","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/synthetic-gelatin-like-material-mimics-lobster-underbellys-stretch-and-strength\/","title":{"rendered":"Synthetic gelatin-like material mimics lobster underbelly\u2019s stretch and strength"},"content":{"rendered":"\n
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A lobster\u2019s underbelly is lined with a thin, translucent membrane that is both stretchy and surprisingly tough. This marine under-armor, as\u00a0MIT engineers reported<\/a>\u00a0in 2019, is made from the toughest known hydrogel in nature, which also happens to be highly flexible. This combination of strength and stretch helps shield a lobster as it scrabbles across the seafloor, while also allowing it to flex back and forth to swim.<\/p>\n\n\n\n

Now a separate MIT team has fabricated a hydrogel-based material that mimics the structure of the lobster\u2019s underbelly. The researchers ran the material through a battery of stretch and impact tests, and showed that, similar to the lobster underbelly, the synthetic material is remarkably \u201cfatigue-resistant,\u201d able to withstand repeated stretches and strains without tearing.<\/p>\n\n\n\n

If the fabrication process could be significantly scaled up, materials made from nanofibrous hydrogels could be used to make stretchy and strong replacement tissues such as artificial tendons and ligaments.<\/p>\n\n\n\n

The team\u2019s results are published today in the journal Matter<\/em>. The paper\u2019s MIT co-authors include postdocs Jiahua Ni and Shaoting Lin; graduate students Xinyue Liu and Yuchen Sun; professor of aeronautics and astronautics Raul Radovitzky; professor of chemistry Keith Nelson; mechanical engineering professor Xuanhe Zhao; and former research scientist David Veysset PhD \u201916, now at Stanford University; along with Zhao Qin, assistant professor at Syracuse University, and Alex Hsieh of the Army Research Laboratory. <\/p>\n\n\n\n

Nature\u2019s twist<\/strong><\/p>\n\n\n\n

In 2019, Lin and other members of Zhao\u2019s group developed a new kind of fatigue-resistant material made from hydrogel<\/a> \u2014 a gelatin-like class of materials made primarily of water and cross-linked polymers. They fabricated the material from ultrathin fibers of hydrogel, which aligned like many strands of gathered straw when the material was repeatedly stretched. This workout also happened to increase the hydrogel\u2019s fatigue resistance.<\/p>\n\n\n\n

\u201cAt that moment, we had a feeling nanofibers in hydrogels were important, and hoped to manipulate the fibril structures so that we could optimize fatigue resistance,\u201d says Lin.<\/p>\n\n\n\n

In their new study, the researchers combined a number of techniques to create stronger hydrogel nanofibers. The process starts with electrospinning, a fiber production technique that uses electric charges to draw ultrathin threads out of polymer solutions. The team used high-voltage charges to spin nanofibers from a polymer solution, to form a flat film of nanofibers, each measuring about 800 nanometers \u2014 a fraction of the diameter of a human hair.<\/p>\n\n\n\n

They placed the film in a high-humidity chamber to weld the individual fibers into a sturdy, interconnected network, and then set the film in an incubator to crystallize the individual nanofibers at high temperatures, further strengthening the material.<\/p>\n\n\n\n

They tested the film\u2019s fatigue-resistance by placing it in a machine that stretched it repeatedly over tens of thousands of cycles. They also made notches in some films and observed how the cracks propagated as the films were stretched repeatedly. From these tests, they calculated that the nanofibrous films were 50 times more fatigue-resistant than the conventional nanofibrous hydrogels.<\/p>\n\n\n\n

Around this time, they read with interest a study by Ming Guo, associate professor of mechanical engineering at MIT, who characterized the mechanical properties of a lobster\u2019s underbelly. This protective membrane is made from thin sheets of chitin, a natural, fibrous material that is similar in makeup to the group\u2019s hydrogel nanofibers.<\/p>\n\n\n\n

Guo found that a cross-section of the lobster membrane revealed sheets of chitin stacked at 36-degree angles, similar to twisted plywood, or a spiral staircase. This rotating, layered configuration, known as a bouligand structure, enhanced the membrane\u2019s properties of stretch and strength.<\/p>\n\n\n\n

\u201cWe learned that this bouligand structure in the lobster underbelly has high mechanical performance, which motivated us to see if we could reproduce such structures in synthetic materials,\u201d Lin says.<\/p>\n\n\n\n

Angled architecture<\/strong><\/p>\n\n\n\n

Ni, Lin, and members of Zhao\u2019s group teamed up with Nelson\u2019s lab and Radovitzky\u2019s group in MIT\u2019s Institute for Soldier Nanotechnologies, and Qin\u2019s lab at Syracuse University, to see if they could reproduce the lobster\u2019s bouligand membrane structure using their synthetic, fatigue-resistant films.<\/p>\n\n\n\n

\u201cWe prepared aligned nanofibers by electrospinning to mimic the chinic fibers existed in the lobster underbelly,\u201d Ni says.<\/p>\n\n\n\n

After electrospinning nanofibrous films, the researchers stacked each of five films in successive, 36-degree angles to form a single bouligand structure, which they then welded and crystallized to fortify the material. The final product measured 9 square centimeters and about 30 to 40 microns thick \u2014 about the size of a small piece of Scotch tape.<\/p>\n\n\n\n

Stretch tests showed that the lobster-inspired material performed similarly to its natural counterpart, able to stretch repeatedly while resisting tears and cracks \u2014 a fatigue-resistance Lin attributes to the structure\u2019s angled architecture.<\/p>\n\n\n\n

\u201cIntuitively, once a crack in the material propagates through one layer, it\u2019s impeded by adjacent layers, where fibers are aligned at different angles,\u201d Lin explains.<\/p>\n\n\n\n

The team also subjected the material to microballistic impact tests with an experiment designed by Nelson\u2019s group. They imaged the material as they shot it with microparticles at high velocity, and measured the particles\u2019 speed before and after tearing through the material. The difference in velocity gave them a direct measurement of the material\u2019s impact resistance, or the amount of energy it can absorb, which turned out to be a surprisingly tough 40 kilojoules per kilogram. This number is measured in the hydrated state.<\/p>\n\n\n\n

\u201cThat means that a 5-millimeter steel ball launched at 200 meters per second would be arrested by 13 millimeters of the material,\u201d Veysset says. \u201cIt is not as resistant as Kevlar, which would require 1 millimeter, but the material beats Kevlar in many other categories.\u201d<\/p>\n\n\n\n

It\u2019s no surprise that the new material isn\u2019t as tough as commercial antiballistic materials. It is, however, significantly sturdier than most other nanofibrous hydrogels such as gelatin and synthetic polymers like PVA. The material is also much stretchier than Kevlar. This combination of stretch and strength suggests that, if their fabrication can be sped up, and more films stacked in bouligand structures, nanofibrous hydrogels may serve as flexible and tough artificial tissues.<\/p>\n\n\n\n

\u201cFor a hydrogel material to be a load-bearing artificial tissue, both strength and deformability are required,\u201d Lin says. \u201cOur material design could achieve these two properties.\u201d<\/p>\n\n\n\n

This research was supported, in part, by MIT and the U. S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT.<\/p>\n","protected":false},"excerpt":{"rendered":"

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