Any rescue diver or salvage worker knows it can be tricky to grab hold of slippery objects in a watery environment, particularly if a more delicate touch is required. That’s why scientists looked to the octopus for inspiration when they were developing a novel “OctaGlove,” a wearable system for gripping underwater objects that mimics the arm of an octopus, according to a recent paper published in the journal Science Advances.
There are several examples in nature of efficient ways to latch onto objects in underwater environments, per the authors. Mussels, for instance, secrete adhesive proteins to attach themselves to wet surfaces, while frogs have uniquely structured toe pads that create capillary and hydrodynamic forces for adhesion. But cephalopods like the octopus have an added advantage: The adhesion supplied by their grippers can be quickly and easily reversed, so the creatures can adapt to changing conditions, attaching to wet and dry surfaces.
“When we look at the octopus, the adhesive certainly stands out, quickly activating and releasing adhesion on demand,” said co-author Michael Bartlett, a mechanical engineer at Virginia Tech. “What is just as interesting, though, is that the octopus controls over 2,000 suckers across eight arms by processing information from diverse chemical and mechanical sensors. The octopus is really bringing together adhesion tunability, sensing, and control to manipulate underwater objects.”
From a mechanical engineering standpoint, the octopus has an active, pressure-driven system for adhesion. The sucker’s wide outer rim creates a seal with the object via a pressure differential between the chamber and the surrounding medium. Then muscles (serving as actuators) contract and relax the cupped area behind the rim to add or release pressure as needed. There have been several attempts to mimic cephalopods when designing soft robotic grippers, for example. Bartlett and his colleagues wanted to go one step further and recreate not just the switchable adhesion but also the integrated sensing and control.
The first step was developing a basic octopus-inspired underwater adhesive system as proof of principle. For the adhesion, they designed silicone stalks capped with a pneumatically controlled membrane, mimicking the structure of octopus suckers. These adhesive elements were then integrated with an array of LIDAR optical proximity sensors and a micro-control for the real-time detection of objects. When the sensors detect an object, the adhesion turns on, mimicking the octopus’s nervous and muscular systems.
The next step was to incorporate the system into a wearable glove. The team used a neoprene wetsuit glove as a base, incorporating the adhesive elements (cut into rectangles) and sensors in each finger, with flexible pneumatic tubes inserted at the base of the adhesive elements. Multiple optical sensors were connected to a single microcontroller via a bidirectional multiplexer to operate the pneumatic system in response to the sensor network’s feedback.
“By merging soft, responsive adhesive materials with embedded electronics, we can grasp objects without having to squeeze,” said Bartlett. “It makes handling wet or underwater objects much easier and more natural. The electronics can activate and release adhesion quickly. Just move your hand toward an object, and the glove does the work to grasp. It can all be done without the user pressing a single button.”
The authors note that while the OctaGlove’s system uses optical sensors, it’s possible to use other sensing methods, including chemical or mechanical sensing. “This could be particularly interesting, as it is known that the octopus displays a diverse set of vision, chemical, and mechanical sensing during manipulation,” the authors wrote. They would also like to incorporate haptic feedback in future iterations of the OctaGlove so that users can better customize the system for their underwater gripping needs.
“The glove was a natural starting point for us. I thought it would be neat to have octopus-like abilities on your hand,” Bartlett told New Scientist. “But we could also make a [robot] arm which is more like a tentacle—we could actually make it very biomimetic.”
DOI: Science Advances, 2022. 10.1126/sciadv.abq1905 (About DOIs).
Listing image by Michael Bartlett/Virginia Tech