An octopus spends most of its time crawling around on the seafloor looking for dinner—and trying to avoid becoming it. But when it needs to make a quick move, it can switch into overdrive and jet away. To do this, it sucks water into its mantle and then quickly expels it through a funnel. The funnel helps to act as a steering mechanism and can be pointed to direct the octopus's flight.
Although a pretty basic concept—squid use it, too—we humans have been slow to build anything quite like it. Our underwater propulsion systems are primarily continuous in their power (think propellers and even jet skis and boats). But there are some advantages to this discontinuous system. It's powerful, efficient and stealthful.
Now, a team of researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation in Germany has developed a working prototype for this octopus-inspired propulsion. And it can be 3-D printed in flexible plastics.
The system is composed of four elastomer balls that contain valves and pumps to control the flow of water internally. Water enters one of the chambers and, after being sealed in by a valve, the surrounding structure is collapsed by a piston—much like the squeeze of an octopus's mantel to shoot water out of the funnel. "The system is simple, but effective," Andreas Fischer, an engineer on the project, said in a prepared statement. "When they use it, the octopods can speed up considerably over short distances."
Researchers at the Octopus Integration Project, which is on its way to building an entirely soft-bodied robotic octopus, are also working on the propulsion problem. When I visited the lab in 2011, Francesco Giorgio-Serchi, a postdoctoral fellow at the Center for Sea Technologies and Marine Robotics at Scuola Superiore Sant'Anna in Italy, showed me how they were going about the process. Because they are aiming to replicate the octopus more faithfully, they were actually working with silicone casts of octopus mantles rather than more abstracted shapes. This model is more complex to build—and work with—but it allows them to study the fluid dynamics that octopuses use, such as the vortex ring, in more detail.
The new squeezable jets constructed by the research team in Germany are certainly simpler to make. Melted thermoplastics are fed into 3-D extruders and then each shape is printed from the bottom up. The result is a flexible, scalable component that can withstand high pressures without permanently deforming. Kind of like the octopus.
Illustration courtesy of Ivan Phillipsen