Sea sponges stay put with anchors that bend but don't break

Sea sponges known as Venus' flower baskets remain fixed to the sea floor with nothing more than an array of thin, hair-like anchors made essentially of glass. It's an important job, and new research suggests that it's the internal architecture of those anchors, known as basalia spicules, that helps them to do it.

The spicules, each about half the diameter of a human hair, are made of a central silica (glass) core clad within 25 thin silica cylinders. Viewed in cross-section, the arrangement looks like the rings in a tree trunk. The new study by researchers in Brown University's School of Engineering shows that compared to spicules taken from a different sponge species that lacks the tree-ring architecture, the basalia spicules are able to bend up to 2.4 times further before breaking.

"We compared two natural materials with very similar chemical compositions, one of which has this intricate architecture while the other doesn't," said Michael Monn a Brown University graduate student and first author of the research. "While the mechanical properties of the spicules have been measured in the past, this is the first study that isolates the effect of the architecture on the spicules' properties and quantifies how the architecture enhances the spicules' ability to bend more before breaking."

That bendability likely enables the spicules to weave themselves into the silt of the seafloor, helping to assure the sponge's secure attachment. A better understanding of how this internal spicule architecture works might be useful in developing new human-made materials, the researchers say.

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