A team of American researchers led by Virginia Tech has used 3D printing to create octopus-inspired adhesive suction cups.
Octopuses, along with other members of the cephalopod class, rely on a combination of controllable adhesives and embedded sensors to adhere to and manipulate underwater objects. Many of today’s handling systems based on synthetic adhesives are typically operated by humans without any integrated sensor, which can result in relatively slow activation and release of the adhesion.
A Virginia Tech research team has now developed its own nature-inspired nervous system capable of detecting objects and automatically engaging adhesion in a matter of milliseconds.
By implementing the 3D-printable adhesive skin into a wearable glove, scientists have created a new approach to reliably manipulate objects in an underwater environment.
Mother Nature knows best
To date, efficient and reversible adhesion to underwater surfaces remains a major challenge. In dry environments we can rely on adhesion through van der Waals forces, electrostatic forces and hydrogen bonds, but wet surfaces greatly reduce the efficacy of these phenomena.
Still, evolution has graced the animal kingdom with several methods of creating strong adhesion forces in the wettest of environments, including underwater. For example, clams can secrete special proteins to create a sticky plaque that allows them to stick to almost any surface. Likewise, frogs can secrete fluids through the pads of their toes to activate hydrodynamic forces.
Octopuses are of particular interest because their suckers are able to generate underwater adhesion and suction forces very rapidly while being completely reversible. They are also notable for the sensing and control system that accompanies the suckers, which consists of mechanoreceptors that serve to detect fluid flow, pressure, and surface contact.
This combination provides them with comprehensive information on factors such as attachment and proximity – capabilities that are difficult to achieve in modern synthetic grippers.
Emulating the nervous system of the octopus
Virginia Tech’s octopus-inspired glove features a set of silicone stems covered with pneumatically actuated membranes that act as grippers. The stems were made using 3D printed molds where the silicone elastomer was cast into the molds and cast and cured into custom grip molds.
Each of the adhesive suckers was integrated with an array of optical micro-light detection and ranging (LIDAR) sensors. The gloves also included microcontrollers for real-time object detection and suction control. The team claims that this combination of mechanical and electronic equipment closely mimics the inner workings of the octopus’s nervous system.
When testing the gloves in a series of underwater trials, the researchers found that their device allowed adhesive stresses of more than 60kPa. The adhesion in the gloves can also be switched on and off over 450 times in less than 50 ms, demonstrating excellent reversibility with cycle times faster than those of a real octopus.
The paper concludes: “Although this research is focused on optical sensors, different sensing modalities may also be used in the future. Chemical or mechanical sensors may be synergistic, and this may be of particular interest as the octopus is known to display a diverse array of visual, chemical and mechanical sensations during handling. There are also future opportunities to incorporate tactile feedback into this system to alert the user when the adhesives are activated.
Further details of the research can be found in the paper titled “Octopus-Inspired Adhesive Skins for Smart and Fast-Switching Underwater Adhesion.”
Biomimicry is a common thread in additive manufacturing research, and for good reason. Earlier this year, researchers at ETH Zurich 3D printed artificially colored nanostructures, taking inspiration from butterfly wings. Native to tropical Africa, the wings of the Cynandra opis species are characterized by their vibrant colors. Rather than being pigment-based, however, these colors are structural, meaning they are produced by complex nanostructures on the surface of the wings.
Elsewhere, researchers from the University of Freiburg and the University of Stuttgart have developed a new method for 4D printing wearable medical devices that self-adjust to the patient’s anatomy. Inspired by the reproduction mechanism of the aerial potato plant (Dioscorea bulbifera), the printed systems can be pre-programmed to perform complex movements when exposed to moisture.
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The image shown shows the nervous system of a sucking octopus. Image via Virginia Tech.