Sea sponges give us a lesson in engineering

John Hopton for redOrbit.com – @Johnfinitum

The life of the Venus’ flower basket, a sea sponge, depends on being able to remain attached to the ocean floor, from which it takes all of its nutrients. If it were to get torn from the bottom and washed away, it would be deader than chivalry in no time.

To combat this threat, it has developed bodily structures to anchor it; structures with fascinating strength-giving properties which could give us some tips for structural engineering.

Tiny, hair-like appendages made essentially of glass hold the creatures to their seafloor homes. According Brown University engineers, the strength of these lifelines, known as basalia spicules, lies in their remarkable internal structure.

The most interesting aspect of that structure is the use of layers of decreasing thickness from the center outwards. Despite looking like a sex toy knitted by someone’s gran, it appears as if these sea creatures have executed mind-blowing organic engineering.

The spicules, each only 50 microns in diameter, are made of a silica (glass) core surrounded by 10 to 50 concentric cylinders of glass, and are separated by an ultra-thin layer of an organic material. The walls of each cylinder gradually decrease in thickness moving from the core toward the outside edge of the spicule.

Nature is great at math

When Haneesh Kesari, assistant professor of engineering at Brown, first saw this structure, he wasn’t sure what to make of it. But the pattern of decreasing thickness piqued his interest.

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

“If it can’t anchor, it can’t survive,” he added. “So we thought this internal structure must be contributing to these spicules being a better anchor.”

Kesari worked with graduate student Michael Monn to build a mathematical model of the spicules’ structure. Among the model’s assumptions was that the organic layers between the glass cylinders allowed the cylinders to slide against each other.

“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 said.

The model predicted that the structure’s load capacity would be greatest when the layers decrease in thickness toward the outside, just as was initially observed in actual spicules. Kesari and Monn then worked with James Weaver and Joanna Aizenberg of Harvard’s Wyss Institute for Biologically Inspired Engineering, who have worked with this sponge species for years.

Comparing the layer thicknesses predicted by the mechanics model to the actual layer thicknesses in samples from sponges, the team found that predictions made by the model matched very closely with the observed layer thicknesses in the samples.

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

In this knowledge, we can come to one of only two conclusions: 1) Venus’ flower basket sea sponges have secretly completed mathematical modelling at post-graduate level, or 2) nature is the freaking boss.

And as if that wasn’t a happy enough story, it turns out chivalry isn’t dead after all. Watch as this man horse opens the door for his lady horse friend:

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