Sponges: Not Just for Cleaning Anymore

The deep-sea sponge commonly known as Venus’s Flower Basket may be primitive in terms of its perch on the evolutionary tree, but it is a masterpiece of underwater engineering. Now, researchers are studying this sponge to develop new strategies for a range of applications, from architecture to fiber optics.

This research is part of a larger field called biomimetics, which applies designs found in nature to human engineering problems.

“Traditionally, physical scientists don’t look into biology, but it’s a real gold mine for research,” said Joanna Aizenberg, a materials scientist at Bell Labs in New Jersey who works on the sponge.

Bio-inspired materials and devices are cropping up everywhere, from construction to fashion. The waxy leaves of a lotus plant inspired a water resistant paint called Lotusan, and the scales of a pinecone led to a line of ventilated clothing that adapts to both its wearer and the weather.

Natural structures, like Venus’s Flower Basket, can be instructive to engineers because their architecture is based on a “bottom-up” process, explained Aizenberg. In other words, the final sophisticated assembly is created from the fewest parts possible.

In contrast, human engineering is based on “top-down” manufacturing, which involves more materials than necessary to produce a final product. For example, the tiny silicon chips used in computers were not that small to begin with. Rather, they started out as large crystals of silica that were polished and carved down to form a chip.

The intricate structure of Venus’s Flower Basket consists of several levels of complexity, or hierarchies, which contribute to an overall cylindrical structure. At the first level is a protein core, wrapped by several circular layers of tiny balls of silica—the main ingredient of glass. Those layers—which are held together by a natural glue—form a strand of fiber called a spicule.

The spicules are then bundled together like straws and arranged into a grid, resembling the caning of a kitchen chair. Other spicules are added diagonally for extra support, like crossbeams in a building.

The grid forms a cylindrical cage. And to prevent the cylinder from twisting in on itself, there are reinforcing ridges that spiral around the outside of the cylinder, like those of a screw. The result is exquisite: a 20-centimeter tube of translucent threads tightly knit together.

“This is one of the most amazing structures I have seen in sponges—but maybe not only in sponges…maybe in all organisms I’ve seen,” said Aizenberg.

Though it may appear flimsy, the sponge is deceptively resilient—probably because of its structural hierarchy. To test this idea, members of Aizenberg’s team, led by Peter Fratzl, a biomaterials professor at the Max Planck Institute, are studying three dimensional models of the sponge.

By performing mechanical tests on the models, these researchers hope to determine which components of the skeleton are critical to the sponge’s overall strength and which—if any— are non-functional, at least from an engineering perspective.

What the team is finding is that Venus’s Flower Basket seems to be woven to perfection.

“Not only is it not over-designed, it’s optimally designed for the amount of material that it has to use,” said James Weaver from the Institute of Collaborative Biotechnologies at the University of California, Santa Barbara, and who works with members of Aizenberg’s team. According to Weaver, the structural elements could be applied to design safer and more robust buildings.

And while the structure of the sponge might be architecturally inspiring, so are the materials used to build it. Although the glass-like portions of the sponge are prone to breakage, its interlocking layers of natural glue absorb cracks, preventing them from spreading. Those layers are more complex than some of the synthetic adhesives used today, wrote George Mayer, a materials science and engineering professor at the University of Washington, in last November’s Science.

By understanding how the sponge produces its complex skeleton, researchers could learn new design strategies for making fracture-resistant materials. The field of fiber optics—part of the telecommunications industry—is one area that could benefit.

Fiber optical threads are used to send information over long distances. But tiny defects on their surface make them prone to breakage. On the other hand, the spicules found in Venus’s Flower Basket are much stronger because of their built-in fracture resistance, said Weaver, who is also part of UCSB’s Materials Research Laboratory. And according to Mayer, they could have an enormous impact on the fiber optic industry.

For researchers like Aizenberg and her team, there are several challenges in developing materials inspired by sponges. First, researchers must understand the biological processes through which a sponge makes its skeleton. Then, they must adapt the lessons learned to the development of new, high-performance materials that could be made in the lab. They’re also hoping to make these synthetic materials under milder temperatures, like those found in the sea.

Once the initial challenges of sponge-inspired research are met, there are still other hurdles—such as the costs involved in producing a new material, as well as time constraints. Mass-producing new technology takes a while, explained Fratzl. However, if researchers are able to achieve more “bottom-up” processes in the lab that rely on fewer starting materials and lower temperatures, the costs might go down over the long run.

“There are many ingenious designs in nature which can be transferred to technical systems,” Fratzl wrote from Germany. “Chemistry has a lot to learn from the way nature does materials synthesis.”