Designing Saltwater Solutions: Two Students Create Tanks for Derk Joester's Sea Urchins

April 23, 2009

When Derk Joester, assistant professor of materials science and engineering, arrived at McCormick in fall 2007 to teach and perform research on the biological synthesis of mineralized tissue, he knew he had quite a task ahead of him: Joester’s research subjects, sea urchins, would need a home that had ample salt water, was continually oxygenated, and that was kept continually at about 54 degrees Fahrenheit.

“Initially we bought a tank from a company but we very quickly found that it was inconvenient to work with,” he says. The tank, deep and rectangular and designed for fish, wasn’t suited for sea urchins. The urchins would just cling to the walls, and when researchers tried to feed them algae — a food they normally scrape off of rocks — the plants would fall to the bottom uneaten.

All this biomedical engineering students Piotr Maniak and Janesh Lakhoo knew well. They had joined Joester’s group as freshman and regularly cleaned the tank and fed the urchins, which, because of the tank issues, required taking the urchins out of the water, holding an algae leaf to their mouth until they suctioned onto it, then holding the urchin back in the freezing water until it suctioned onto the aquarium wall.

“I was then faced with the possibility of outsourcing to a local company or designing it from scratch,” Joester says. “Designing it here appealed to both our mission as an engineering school and also to Piotr and Janesh.”

So the two students spent the summer of 2008 designing and building a tank system. They first looked at research from other sea urchin tank designs, then went about deciding the geometry of their own tanks.

“We knew we didn’t want a rectangular tank like before,” Maniak says. “And we wanted to be able to access them and feed them easily.” The result was a modified tank with a triangle cross section. But that was just the first step — the students then had to think about what materials would work best for such a tank. The materials couldn’t leach chemicals into the water, and they needed a material that could be molded into their specific shape, so Plexiglas was out.

“We were talking with Steve Jacobson from the machine shop in the Ford building and we came up with the idea of using fiberglass,” Maniak says. “It’s lightweight, cheap, and very strong. Then we considered using foam insulation as the structure, and putting the fiberglass on top of that, which would help to keep the tanks cool.” Lakhoo designed the actual structure using computer-aided design, but the students soon found actually creating the tanks was easier said than done. During their first attempt, they created a boat structure and put the foam pieces inside, then created a mold where they could push the fiberglass down to make the right shape. But they soon found that the epoxy used to make the fiberglass hard stuck to their mold.

“We were left with a very bad looking thing,” Maniak says. They then tried to put the fiberglass on top of the epoxy and insulation, then put it all inside a bag and vacuum the air out to make sure the fiberglass is applied evenly. That, too, did not work out.

“In the end we put the fiberglass in by hand and straightened it out while it hardened to keep the shape,” Lakhoo says. “We also stuck the pieces of foam together using latex caulk to add another barrier to make it water tight.”

From there they tested the prototype with water, and, after finding out it was in fact water tight, they created eight more such tanks in less than a week. But once they had the tanks, they then had to come up with a system to hold the tanks. The two used PVC pipes, which are cheap and resistant to salt water, to construct a shelving unit. To create a water filtration system, they created a system where the water spills over from the tanks onto bacteria balls, which oxygenates the water before it is cooled and pumped back into the tanks. The resulting system, up and running since September, pumps 600 gallons of water a minute.

“The project was really a design from scratch,” Joester says. “It’s not just a mechanical engineering task. It’s a life support system. To come up with a system that actually works is quite a feat.”

The students say the project has taught them more about the engineering process. “We learned about going through all the steps you have to do to come up with a product and make sure it meets the requirements and will last,” Lakhoo says.

“And we learned you have to make constant modifications,” Maniak says. “We still think, how can we make this better? How can we make it more efficient and easy to use?”
Recently, they designed tops for the tanks to reduce splashing, keep the sea urchins from going into the overflow tank, and to reduce evaporation. They’re also working on creating an auto top-off system to make sure there is always water going through the pumps.

“With everything they had to think about — materials, design, systems — this wasn’t a trivial undertaking,” Joester says. “What they came up with is really impressive.”

Joester, who has anywhere from 10 to 40 sea urchins living in the tank at a time, studies their embryos to learn how their endoskeletons are created.

“The idea is that we want to reprogram their machinery,” he says. The sea urchins create an endoskeleton element called a spicule, which is a single crystal. Joester hopes to pattern cells in a certain shape in order to create a crystal spicule in that grows into a certain shape.

“We hope to use engineering to grow crystals in the way we want them to grow using their biological machinery as a black box,” he says. “Right now they grow crystals in cylindrical shapes that curve, and we can’t grow crystals like that in the lab. We need to understand those growth mechanism in order to grow crystals in a bioinspired fashion.”

This research is supported by the National Science Foundation. To read the blog about the tanks’ creating, visit www.nautilus.mccormick.northwestern.edu.

- Emily Ayshford