Cholera Bacteria Injected in a Soft Gel Shed Light on the Mechanics of How Growing Bodies Respond to Confinement

Researchers from the Massachusetts Institute of Technology (MIT) and Yale University are developing a new theoretical framework that explains the mechanics behind growing bodies taking up the shape of confined spaces.

MIT associate professor Tal Cohen and his colleagues grew cholera bacteria and injected them into a soft gel and observed the architecture of the growing bacterial biofilms at a single resolution as they grew 10,000 times their original size.

JAPAN-LIFESTYLE-FRUITS-OFFBEAT
This photo taken on July 1, 2015 shows senior managing director Mototaka Nishimura of the Shibuya Nishimura luxury fruit shop displaying square (L), pyramid (C) and heart-shaped (R) watermelons at the company's main store in Tokyo. Japanese consumers are used to paying through the nose for fruit, and now the summer's here there's another way for them to empty their wallets: cube and heart-shaped watermelons. TORU YAMANAKA/AFP via Getty Images

Biofilms Adopt Growth Path in Response to Confinement

Researchers reported in their study titled "Nonlinear Inclusion Theory With Application to the Growth and Morphogenesis of a Confined Body," published in the Journal of the Mechanics and Physics of Solids, that the bacterial biofilms have adopted growth paths that follow the shape of the confined space and deformed the surrounding gel.

M.D. Anderson Chair Professor of Mechanical Engineering Pradeep Sharma from the University of Houston said that the recent research is a significant step forward in the study of inclusion problems, which was revolutionized by British scientist John Eshelby in the 1950s.

Sharma, who is not part of the study, explains that one of the key limitations of the British scientist's work is that materials used in the study only deformed slightly that it is hardly seen, SciTech Daily reported. Meanwhile, Cohen's work ingeniously solved that limitation and demonstrated large deformations. He noted that this experiment has explained the mechanics between cell and tissue interactions and solved inclusion problems in soft matter used in soft robotics.

Cohen said that the experimental biofilm system plays a significant role in refining their theory that explains the mechanics behind the response of growing bodies to confinements. Understanding the mechanics could be essential for addressing tumor growth.

Employing Different Approach in Studying Growth Path of Growing Bodies

Cohen's study investigates what will happen to grow bodies in confinement when pushed to the limit, whether they stop growing or break down. The stress could come from extreme loading, shock wave, or stresses brought about by growth.

She said that they looked at growth differently than others. For instance, they see a tree and hypothesize how it grows before creating a theory based on observation. They dissect a system to understand this process microscopically to see the physical principles that induce their morphology. Their open-ended approach is useful in solving problems in both physical and biological systems.

Japan's Cube-Shaped Watermelons

In Japan, cube-shaped watermelons (Cucurbitaceae) are popular. According to Treehugger, Japan has been growing them for 45 years, but last year's batch was extremely large due to good weather that around 260 cube-shaped watermelons were harvested.

Farmers grow these cube-shaped watermelons by training them into square submission by putting them into boxes as they grow to maturity. These cube-shaped watermelons were invented because round watermelons are hard to store and awkward to cut. On the other hand, cube-shaped watermelons can be easily tucked away and stored in small refrigerators of Japanese households.


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