Sponges anchor glass houses with precisely engineered glass hairs | The American Ceramic Society

Sponges anchor glass houses with precisely engineered glass hairs

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I might have a thing for marine creatures—coral, limpets, mollusks, algae, starfish, more mollusks—but they are just so darn interesting.

Some sea creatures are interesting because they’re just plain weird. Take for example jellyfish, which lack pretty much every anatomical feature that we associate with a living creature.

And then there are creatures like tardigrades, which look like little faceless Jabba the Hutts and are practically indestructible—they can survive space, dessication, extreme hot, extreme cold, radiation, and pretty much any other tortuous environment you can imagine.

And like many other components of nature, marine creatures (weird and unweird alike) are an inspiration for engineering smarter, stronger, and better materials.

New research from Brown University shows that another kind of marine creature is engineered for maximal strength—the glass sea sponge.

Sea sponges are also on the weird creature list. They have no digestive, nervous, or circulatory systems, but instead filter morsels of food out of the passing water. They don’t hunt, don’t blink, don’t think—they just sit there, passive and unaware, yet alive.

The Venus flower basket, also called the glass sponge, is a particularly pretty sponge variety—as its name suggests, the sponge resembles glass. It extracts silicic acid from seawater and converts it into silica, which the creature secretes to form a glass-cage structure to call home.

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Venus flower baskets in the wild. Credit: NOAA Photo Library; Flickr CC BY 2.0

The glass sponge also has hair-like appendages called spicules that anchor it tight to the deep sea floor, an important feature for a filter feeder. The spicules are only 50 μm in diameter, yet are strong enough to keep the sponges anchored tight.

When Brown researchers examined cross-sections of these thin and fragile-looking fibers, they found that they have a solid silica core surrounded by concentric rings of silica, each layer separated by a very thin organic layer. Each silica fiber contains 10–50 concentric layers that decrease in thickness as they move outwards from the core.

“It was not at all clear to me what this pattern was for, but it looked like a figure from a math book,” senior author Haneesh Kesari says in the press release. “It had such mathematical regularity to it that I thought it had to be for something useful and important to the animal.”

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The complex glass-like skeleton of a Venus flower basket, or glass sponge. Credit: Brown University

The Brown researchers used simulations to show that this particular configuration of layers is key to the fibers’ strength.

“We prepared a mechanical model of this system and asked the question: Of all possible ways the thicknesses of the layers can vary, how should they vary so that the spicule’s anchoring ability is maximized?” Kesari says in the press release.

Assuming that the organic material in between the silica layers allowed them to slide against one another, the model showed that the sponge’s spicule structure was optimized for load capacity. The researchers confirmed that the measurements aligned with those in over a hundred spicule samples.

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A mathematical model, right, predicted that the thickness of nested glass cylinders should decrease from the core to the exterior to optimize strength. Studies of hundreds of spicules, left, showed that was exactly the case in nature. Credit: Brown University

“It appears that the arrangement and thicknesses of these layers does indeed contribute to the spicules’ strength, which helps make them better anchors,” Kesari says in the release.

The knowledge could help develop stronger structures of any material by showing which internal structures optimize strength of the structure overall.

Lead author Michael Monn adds in the release, “In the engineered world, you see all kinds of instances where the external geometry of a structure is modified to enhance its specific strength—I-beams are one example. But you don’t see a huge effort focused toward the internal mechanical design of these structures.”

The paper, published in the Proceedings of the National Academy of Sciences, is “New functional insights into the internal architecture of the laminated anchor spicules of Euplectella aspergillum” (DOI: 10.1073/pnas.1415502112).