There is always a colleague from the company next door who hitches a ride during my commute. He brings along cheap sandwiches to share for breakfast. Nature also has its own annoying free riders, such as the remora, which attaches itself to sharks. It feeds on the prey that the shark drops or pieces of old skin it sheds.
Nature's free riding has been reborn as a technological concept that benefits both people and ecosystem health. It is an adhesive device modeled after the suction structure found on the head of the remora. It attaches to the stomach wall to monitor for acid reflux and to release medication. It can also deliver gene therapies and monitor the underwater environment by attaching to fish.
◇ Mimicking suction cups with silicone rubber and shape memory alloy
Giovanni Traverso, a professor in the Department of Mechanical Engineering at the Massachusetts Institute of Technology (MIT), and his research team noted on the 23rd of last month that they developed a mechanical adhesive device inspired by the suction (吸盤) structure of the remora, which attaches to other marine animals and can maintain its grip on smooth surfaces for days to weeks.
Despite its name, the remora is not a type of shark. Unlike shark species that are cartilaginous fish, it belongs to the bony fish family of the order Perciformes. While the remora appears to be upside down attached to a shark, it actually swims upright, using its suction cup on top of its head. The remora attaches to large marine animals like sharks to travel long distances effortlessly and to avoid other predators. It consumes prey that its host drops or dead tissue that comes off the skin.
The research team mimicked the suction of the remora. The remora attaches the soft tissue on the outer part of the suction cup to the shark's body. Before doing this, it expels water inside to create a negative pressure that is lower than the outside pressure. This is similar to pressing a toilet cleaning tool to suck out air and sticking it to the toilet. The research team made the suction cup from silicone rubber.
In the center of the suction cup is a thin lamella, oriented vertically relative to the body length, resembling the radiator grille of a car. These create individual small adhesive spaces, making it possible to stick to the irregular surface of a host. The number of lamellae varies by species of remora.
Scientists discovered the suction of remoras from 32 million years ago in fossils. Research teams at the New Jersey Institute of Technology found in 2019 that a suction cup mimicking the remora must have at least six lamellae to be effective in adhesion, which aligns with fossil evidence.
The researchers created the lamellae structure using a shape memory alloy. This alloy lies flat at low temperatures and stands upright when it reaches body temperature, around 37 degrees Celsius. When the temperature drops, it returns to its original flat shape, allowing for separation. The tips of the remora's lamellae have spiny structures measuring hundreds of micrometers (1 micrometer is 1/1,000,000 meters) that bond to the shark's skin. The tips of the lamellae were designed with micro-needle structures similar to those of the remora.
◇ Monitoring acid reflux and delivering medications
The artificial suction cup has been named MUSAS, an abbreviation of the English title "Mechanical Underwater Soft Adhesion System." The research team confirmed that MUSAS can adhere to various soft surfaces, including porcine stomach tissue, surgical gloves, and live wrasse.
The artificial suction cup could transform into a medical device. The research team attached a suction cup equipped with an electric resistance sensor to a pig's esophagus. This enabled the detection of gastric acid reflux, indicating that it could be a medical device to monitor the condition of patients with gastroesophageal reflux disease for 24 hours.
It is difficult to administer proteins or genetic materials via the gastrointestinal tract because they are broken down before absorption. Patients need to visit hospitals frequently for prolonged intravenous injections. Additionally, the digestive organs are lined with slippery mucosa, making it challenging for medical devices to adhere. The artificial suction cup modeled after the remora can attach effortlessly to the stomach wall, releasing medications slowly over several days to weeks.
The research team delivered drugs used for the prevention and treatment of human immunodeficiency virus (HIV) infection by attaching the artificial suction cup to the stomach wall of pigs. Gene therapies can also be delivered in the same way. They revealed that large molecules, such as ribonucleic acid (RNA), could be attached and delivered using the micro-needles at the tips of the lamellae. They confirmed that they were able to deliver fluorescent genes copied from RNA to the cheeks and esophagus of pigs, causing a fluorescent effect. The research team stated they would investigate whether vaccines could also be delivered in the same manner.
◇ Delivering electronic drugs for obesity and protecting marine ecosystems
Professor Traverso noted that in 2023, he developed a device that activates hormones that regulate appetite by providing electric stimulation. This is referred to as an electronic drug for obesity. The sensation of satiety occurs when the stomach expands, sending signals to the brain through the vagus nerve. When the brain releases hormones like insulin, it triggers feelings of fullness and leads to the cessation of eating, while simultaneously reducing levels of the hunger hormone ghrelin.
The electronic drug creates vibrations in the stomach to artificially stimulate the vagus nerve and produce feelings of fullness. The team observed that administering pills to animals 20 minutes before eating not only triggered the release of hormones indicating satiety but also reduced the animals' intake by about 40%. They stated that it is possible to combine the electronic drug for obesity with the artificial suction cup to ensure stable operation on the stomach wall.
The artificial suction cup can benefit not only humans but also the health of marine ecosystems. By attaching temperature sensors to the artificial suction cup, they successfully measured the water temperature while fish swam quickly. Robots can similarly attach to marine animals in the same manner. Researchers at Beihang University in Beijing, China, attached a device mimicking the remora's suction cup to the material of aircraft windows (plexiglass) in 2017. The adhesive strength was 340 times that of the suction cup's weight.
While scientists have applied adhesive materials modeled after gecko lizards and tree-dwelling frog feet to robots, their effectiveness decreases in water or on slippery surfaces. The suction cup mimicking the remora does not face such issues. It is an opportunity to give back to nature the price of the free ride.
References
Nature (2025), DOI: https://doi.org/10.1038/s41586-025-09304-4
Science Advances (2023), DOI: https://doi.org/10.1126/sciadv.adj3003
Bioinspiration & Biomimetics (2019), DOI: https://doi.org/10.1088/1748-3190/ab3895
Science Robotics (2017), DOI: https://doi.org/10.1126/scirobotics.aan8072