The Remora inspired suction pad mimics the fish's grip ability and offers a glimpse of evolution

Remora fish are famous hitchhikers of the marine world. They have powerful suction disks on their heads to attach like torpedoes to larger hosts that can provide food and safety – from whales to sharks, to boats and divers.

The well known abilities of the disc to generate suction, as well as the friction created by thorny bones in the disc, called lamellae, are essential to remora adhesion in order to keep its host in place. However, the factors that motivated the evolution of Remora's unique disc morphology have long eluded researchers seeking to understand and even design new devices and adhesives that mimic the strange ability of fish to lock on various types. surface without harming its host or spending a lot of energy. often for hours at a time under extreme oceanic forces.

In a study conducted at the New Jersey Institute of Technology (NJIT), the researchers presented a new remora disc of biological inspiration capable of reproducing the passive forces of suction and friction that fuel the fish capacity, demonstrating a 60% higher resistance than that measured. for live remas attached to shark skin.

Using the disk model to explore the evolutionary factors of the remora disk, the researchers claim that the results of the study demonstrate that current live remora species have evolved with increasing numbers of lamellae over time to enhance their power. retention and their ability to attach to larger numbers with smoother surfaces, thus increasing their chances of survival.

The study, presented in Bioinspiration and biomimetics, indicates that the disk model can be used to guide the design of more efficient and less costly adhesive technologies in the future.

"The beauty of Remora's adhesive mechanism lies in the fact that it is essentially the biological tissues that make the bulk of the work," said Brooke Flammang, NJIT biology professor, who led the study. . "The most significant aspect of this research is that our robotic disk relies entirely on the fundamental physics of the adhesive mechanism of the trailers, which allows us to determine biologically relevant performance and better understand the evolution of the disc. This was not possible before with previous designs that required a human operator to control the system. "

The remora fish (of the family Echeneidae), which differs from many of its ancestors close to scavengers, such as cobia (Rachycentron canadum), would have initially begun to attach to hosts on the surface. Rough, shark related, after developing its disk suction of the dorsal fin spines nearly 32 million years ago. The disc of living remorse now has a fleshy outer lip and soft for suction, while the inside of the disc contains many more linear rows of tissue (lamellae) with tissue projections resembling to teeth (spinules), which the fish raises to generate friction against various hosts. body to avoid slipping during hitchhiking.

According to Flammang, while scientists have shed some light on the origins of the modified structure of Remora's fins, the fundamental aspects of the disc's evolution have remained largely unclear.

"The evolution of the remora disc is largely unknown," Flammang said. "There is a fossil remora, Opisthomyzon, in the fossil record that has a disk with fewer lamellae [than today’s remoras] without spinules towards the back of the head ".

Flammang says that this raises two questions: "how" and "why".

"The how comes from the dorsal fin, although the intermediate stages of evolution are not known," explained Flammang. "If you look at the phylogeny of remas, it shows that the species considered the most derived have more lamellae … the" why "is supposed to be related to adhesive performance, but that has never been tested before. "

To find out more, Kaelyn Gamel, the first author of the study and a former Flammang graduate researcher, designed a Remora-inspired record from commercially available 3D printed materials that can independently sustain Attachment to various surfaces and to be modified by adding and removing slats. , allowing the team to study the performance of an increased number of lamellae on shear adhesion.

"The ability of our disk to add and remove slats while acting as a passive system has allowed us to change the degree of friction as well as the ambient pressure in the disc," said Gamel, currently titular. a Ph.D. researcher at the University of Akron. "We were able to compare the difference between no friction, friction and a lot of friction based on the variation of the number of lamellae."

In collaboration with Austin Garner, a researcher at Akron University, the team performed tensile tests with their underwater model disc, experimenting with the lamellar number of the model (up to 12 lamellae) to measure the shear force and the time needed to shoot. the disc of silicone molds with surfaces ranging from completely smooth to those exceeding the roughness of the shark skin (grains 350, 180 and 100).

Overall, the team found that the adhesive performance of their discs was strongly correlated with an increase in disc sipes, observing an "ideal point" in suction power between nine and 12 sipes. When it was modified into 12 lamellae and 294 spinules, the team's disc weighed only 45 grams and withstood 27 N (Newton's forces) for 50 seconds, almost three times more than the strength needed to shoot a remora from a shark. The tests also revealed that a minimum of six coverslips – the number found by coincidence on the fossil opisthomyzon aged 32 million years – was needed to maintain adhesion.

"What is striking with these results is that, for a given disk shape, there is an optimum range in which the phenomena of friction and suction are balanced, and [as their disc size has gotten longer] Remas have evolved to maintain this successful membership, "said Flammang.

The team now indicates that its remora disk model will be used for future evolutionary studies to determine whether attachment by sucking or friction predominated in early Remora ancestors and how the evolution of the form of the disc would affect the adhesion. The disk can also have technical applications in all fields, from medical biosensors to drug delivery devices to remote sensing beacons for ecological studies and monitoring of marine life. "One of the biggest advantages of our design is that it operates autonomously from the system for operation," said Flammang. "This makes it easily scalable for a multitude of new technologies, for medical and scientific purposes."