Ready, Set, Inflate!

When they had to build a project around an engineering principle reflected in nature, four classmates in MEM 435 started out with spiders and snakes and eventually worked their way seaward, zeroing in on the octopus (the plural for which is, exotically, octopodes).

A term of design in the “product development” course and another term in Independent Study to refine the prototype ended with the creation of a teaching aid bound for the Adventure Aquarium in Camden, New Jersey, where its tactile gadgets and colored balloons are sure to inspire young scientists.

With four encased grids of tiny balloons in primary colors that are inflated by depressing pumps, or syringes, the model illustrates how octopodes use ink-filled cells to deploy one of nature’s most adaptive camouflage systems. Called chromatophores, these cells contract and fade or expand and display color in a process that matches the creature’s environment with eerie precision, right down to the texture surrounding it—whether that’s a bed of fire coral or the deep blue of the open ocean.

The challenge of demonstrating this principle for a pack of skeptical young engineers was irresistible for the MEM team. Using the properties of fluid dynamics—specifically, how fluid flows from a set of syringes into the colored balloons—the team developed the OCTOPUS model.

It stands for Octopus Chromatophore Teaching Object Pressurized Using Syringes.

“That was about 90% of the manpower, just figuring out the acronym,” said teammate Stephen St. Raymond, a BS/MS senior in the Department of Mechanical Engineering and Mechanics (MEM).

“The idea behind the class was that you could work with land animals or sea animals, with either the Academy of Natural Sciences or the Aquarium. When we were coming up with animal systems we wanted to mimic, we were just trying to look for really interesting and unique systems that could be found in only a handful of animals,” explained Christian Pirnot, a senior in MEM. “This one, you find only in the octopus, squids, chameleons, cuttlefish, and a few others.”

OCTOPUS team members include St. Raymond, Pirnot, Andrew Leavitt, and Jeffrey Serabo, all MEM members of the Class of ‘19.

Standing around their project in a basement laboratory one afternoon, the team demonstrated how the process works. An octopus actuates its chromatophores by contracting muscles that flush pigment into the cells. The chromatophores become engorged and inflate with color, or contract to display a lack of it. The color change is almost instantaneous.

“They can mimic the color and texture of a coral reef,” said Leavitt. “You’re really not going to know it’s there until you get up to within a couple inches of it and it freaks out and turns black, and then jets off.”

The OCTOPUS model represents a patch of octopus skin. As team members depress select syringes on the model, diverse colored balloons inflate – red or green for coral, for example, or blue for ocean water; in short, whatever shade or shadow an octopus needs as camouflage to prevent detection by predators or prey. From a distance, the inflated balloons provide a blanket of color in much the way thousands of pixels on a display screen form a whole picture. While the balloons do not reflect the spectrum of colors chromatophores utilize, team members said, they provide a strong representation of the biological system.

“Talking to the Aquarium was a big part of our excitement to do this,” said Leavitt. “It’s one of the frequent questions they get, how an octopus changes color. They never had a really good way to display this. They’d had previous projects using LED lights to change the colors, but that doesn’t really fit the biological principles that chromatophores work on.”

The team was one of just a few in recent memory to carry a project from Junior Design into Independent Study and, finally, into the very facilities for which they were intended, according to Drexel Associate Teaching Professor Roger J. Marino. The course partners with the Academy of Natural Sciences of Drexel University and with Adventure Aquarium, both of whom are beneficiaries of completed projects.

“This team was a pleasure to work with because of their enthusiasm for the project and their desire to grow in a professional sense during the development of their prototype,” said Marino. “They accomplished what educators aim for them to achieve: the development of soft skills like interviewing and listening to stakeholders’ needs, and hard skills, like engineering principles and constructability of the design.

“I especially commend them,” he added, “for understanding and meeting the stakeholder’s goal of simplicity of design. That is not always easy to accomplish.”

The OCTOPUS will be delivered to the Aquarium at the end of the term.

Update

Drexel students (l to r) Andrew Leavitt, Christian Pirnot, Jeffrey Serabo and Stephen St. Raymond delivered their OCTOPUS learning aid on Friday, Dec. 14, to Camden’s Adventure Aquarium, where it will be used for special exhibits and classes.

Drexel students deliver their OCTOPUS learning aid to Adventure Aquarium.


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