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Stronger Artificial Tissues Inspired by the Stretch and Strength of Lobster Underbelly

New hydrogel-based material
Image Source: https://giecdn.azureedge.net/storage/fileuploads/image/2021/04/23/mitflexible-armor-010.jpg?w=736&h=414&mode=crop

Tissue engineering combines biologically active molecules, cells, and scaffolds to develop functional tissues. These tissues can improve, maintain, or restore damaged tissues, including whole organs. Some examples of engineered tissues are artificial cartilage and skin that the FDA approved. In the current setting, however, the use of artificial tissues in human patients is still limited.

New hydrogel-based material

The current application of artificial tissues may soon change. An MIT team developed a hydrogel-based material that imitates the structure of the underbelly of a lobster. In nature, the lobster’s underbelly has a thin, translucent membrane which is very tough and stretchy. According to MIT engineers, the membrane is nature’s toughest known flexible hydrogel. The combination of stretch and strength protects the lobster as it crawls along the seafloor. At the same time, the same membrane helps the lobster flex back and forth so the crustacean can swim.

The MIT engineers who developed the new material ran it through a series of impact and stretch tests and proved that the synthetic material they fabricated is fatigue-resistant. In addition, it has the strength and flexibility to resist repeated strains and stretches without developing a tear.

The engineers think that if the fabrication process of the artificial hydrogel is ramped up, the materials created from the nanofibrous hydrogels could be applied to the production of solid and stretchy replacement tissues such as artificial ligaments and tendons.

Previous researches

Incidentally, some of the team members used to be involved in similar research. In 2019, Shaoting Lin, a postdoctoral fellow, and one of the co-authors of the current study, developed a fatigue-resistant material from hydrogel together with the recent MIT team members. They used ultrathin fibers of hydrogel, which aligned when stretched repeatedly. The process increased the fatigue resistance of the hydrogel.

At that time, they were already thinking that nanofibers in hydrogels would be essential. But, according to Lin, they hoped they could manipulate the fibril structures to maximize their fatigue resistance. 

nanofibers in hydrogels
Image Source: https://scitechdaily.com/images/Bouligand-Nanofibrous-Hydrogel-1536×1024.jpg

Current research

In the latest research, the engineers mixed several techniques to develop more robust nanofibers from a hydrogel. 

The process started with electrospinning, a fiber production technique that uses electric charges to create ultrathin threads from polymer materials. Then, with the high-voltage charges, they made a flat film of nanofibers, each about 800 nanometers, which is only a fraction of the human hair’s diameter. 

Next, they placed the film inside a high-humidity chamber to bind the individual fibers to form a robust and interconnected network. From there, they put the film in an incubator so the individual nanofibers can crystallize to improve the material’s strength. 

The next step is testing the fatigue resistance of the film. They used a machine that stretched the material repeatedly thousands of times. They cut a notch in the film for some tests to see if the tear would increase during the stretching cycles. After the test, they concluded that the artificial hydrogel film was 50 times fatigue-resistant than other nanofibrous hydrogels developed from conventional methods.

On the other hand, they became interested in Ming Guo’s study. Guo is an associate professor at MIT’s mechanical engineering department. He described the mechanical properties of the underbelly of lobsters. In his research, he found that the thin sheets of chitin, the fibrous material that makes up the lobster’s protective membrane, were stacked at 36-degree angles, similar to a spiral staircase or twisted plywood. The arrangement is called bouligand structure, and it is this arrangement that is behind the strength and stretch of the properties of the membrane.  

This is the angled structure that caught the interest the research team. So they recreated it by piling five sheets at the required angle and welded and crystallized them into a single sheet.

The nanofibrous hydrogels will still undergo further tests. But with the encouraging results, these novel materials could have many medical applications.