The RoboBee is only slightly larger than a penny. Credit: Harvard Microrobotics Laboratory
The first step was to perform experiments to determine the effects of oscillation on the newly designed robotic legs and leg joints. This involved manually disturbing the leg and then releasing it, capturing the resulting oscillations on high-speed video. This showed that the leg and joint essentially acted as an “underdamped spring-mass-damper model,” with a bit of “viscoelastic creep” for good measure. Next, the team performed a series of free-fall experiments with small fiberglass crash-test dummy vehicles with mass and inertia similar to RoboBee’s, capturing each free fall on high-speed video. This was followed by tests of different takeoff and landing approaches.
The final step was running experiments on consecutive takeoff and landing sequences using RoboBee, with the little robot taking off from one leaf, hovering, then moving laterally before hovering briefly and landing on another leaf nearby. The basic setup was the same as prior experiments, with the exception of placing a plant branch in the motion-capture arena. RoboBee was able to safely land on the second leaf (or similar uneven surfaces) over repeated trials with varying parameters.
Going forward, Wood’s team will seek to further improve the mechanical damping upon landing, drawing lessons from stingless bees and mosquitoes, as well as scaling up to larger vehicles. This would require an investigation into more complex leg geometries, per the authors. And RoboBee still needs to be tethered to off-board control systems. The team hopes one day to incorporate onboard electronics with built-in sensors.
“The longer-term goal is full autonomy, but in the interim we have been working through challenges for electrical and mechanical components using tethered devices,” said Wood. “The safety tethers were, unsurprisingly, getting in the way of our experiments, and so safe landing is one critical step to remove those tethers.” This would make RoboBee more viable for a range of practical applications, including environmental monitoring, disaster surveillance, or swarms of RoboBees engaged in artificial pollination.
It’s well understood that spiders have poor eyesight and thus sense the vibrations in their webs whenever prey (like a fly) gets caught; the web serves as an extension of their sensory system. But spiders also exhibit less-understood behaviors to locate struggling prey. Most notably, they take on a crouching position, sometimes moving up and down to shake the web or plucking at the web by pulling in with one leg. The crouching seems to be triggered when prey is stationary and stops when the prey starts moving.
But it can be difficult to study the underlying mechanisms of this behavior because there are so many variables at play when observing live spiders. To simplify matters, researchers at Johns Hopkins University’s Terradynamics Laboratory are building crouching spider robots and testing them on synthetic webs. The results provide evidence for the hypothesis that spiders crouch to sense differences in web frequencies to locate prey that isn’t moving—something analogous to echolocation. The researchers presented their initial findings today at the American Physical Society’s Global Physics Summit in Anaheim, California.
“Our lab investigates biological problems using robot physical models,” team member Eugene Lin told Ars. “Animal experiments are really hard to reproduce because it’s hard to get the animal to do what you want to do.” Experiments with robot physical models, by contrast, “are completely repeatable. And while you’re building them, you get a better idea of the actual [biological] system and how certain behaviors happen.” The lab has also built robots inspired by cockroaches and fish.
The research was done in collaboration with two other labs at JHU. Andrew Gordus’ lab studies spider behavior, particularly how they make their webs, and provided biological expertise as well as videos of the particular spider species (U. diversus) of interest. Jochen Mueller’s lab provided expertise in silicone molding, allowing the team to use their lab to 3D-print their spider robot’s flexible joints.
Crouching spider, good vibrations
A spider exhibiting crouching behavior. Credit: YouTube/Terradynamics Lab/JHU
The first spider robot model didn’t really move or change its posture; it was designed to sense vibrations in the synthetic web. But Lin et al. later modified it with actuators so it could move up and down. Also, there were only four legs, with two joints in each and two accelerometers on each leg; real spiders have eight legs and many more joints. But the model was sufficient for experimental proof of principle. There was also a stationary prey robot.
It’s the “hydrophilic capillary-enhanced adhesion”of gecko feet that most interested the authors of this latest paper. Per the World Health Organization, 684,000 people die and another 38 million are injured every year in slips and falls, with correspondingly higher health care costs. Most antislip products (crampons, chains, studs, cleats), tread designs, or materials (fiberglass, carbon fiber, rubber) are generally only effective for specific purposes or short periods of time. And they often don’t perform as well on wet ice, which has a nanoscale quasi-liquid layer (QLL) that makes it even more slippery.
So Vipin Richhariya of the University of Minho in Portugal and co-authors turned to gecko toe pads (as well as those of toads) for a better solution. To get similar properties in their silicone rubber polymers, they added zirconia nanoparticles, which attract water molecules. The polymers were rolled into a thin film and hardened, and then a laser etched groove patterns onto the surface—essentially creating micro cavities that exposed the zirconia nanoparticles, thus enhancing the material’s hydrophilic effects.
Infrared spectroscopy and simulated friction tests revealed that the composites containing 3 percent and 5 percent zirconia nanoparticles were the most slip-resistant. “This optimized composite has the potential to change the dynamics of slip-and-fall accidents, providing a nature-inspired solution to prevent one of the most common causes of accidents worldwide,” the authors concluded. The material could also be used for electronic skin, artificial skin, or wound healing.
This isn’t the first time scientists have looked to the mantis shrimp as an inspiration for robotics. In 2021, we reported on a Harvard researcher who developed a biomechanical model for the mantis shrimp’s mighty appendage and built a tiny robot to mimic that movement. What’s unusual in the mantis shrimp is that there is a one-millisecond delay between when the unlatching and the snapping action occurs.
The Harvard team identified four distinct striking phases and confirmed it’s the geometry of the mechanism that produces the rapid acceleration after the initial unlatching by the sclerites. The short delay may help reduce wear and tear of the latching mechanisms over repeated use.
New types of motion
The operating principle of the Hyperelastic Torque Reversal Mechanism (HeTRM) involves compressing an elastomeric joint until it reaches a critical point, where stored energy is instantaneously released. Credit: Science Robotics, 2025
Co-author Kyu-Jin Cho of Seoul National University became interested in soft robotics as a graduate student, when he participated in the RoboSoft Grand Challenge. Part of his research involved testing the strength of so-called “soft robotic manipulators,” a type often used in assembly lines for welding or painting, for example. He noticed some unintended deformations in the shape under applied force and realized that the underlying mechanism was similar to how the mantis shrimp punches or how fleas manage to jump so high and far relative to their size.
In fact, Cho’s team previously built a flea-inspired catapult mechanism for miniature jumping robots, using the Hyperelastic Torque Reversal Mechanism (HeTRM) his lab developed. Exploiting torque reversal usually involves incorporating complicated mechanical components. However, “I realized that applying [these] principles to soft robotics could enable the creation of new types of motion without complex mechanisms,” Cho said.
Now he’s built on that work to incorporate the HeTRM into a soft robotic arm that relies upon material properties rather than structural design. It’s basically a soft beam with alternating hyperelastic and rigid segments.
“Our robot is made of soft, stretchy materials, kind of like rubber,” said Cho. “Inside, it has a special part that stores energy and releases it all at once—BAM!—to make the robot move super fast. It works a bit like how a bent tree branch snaps back quickly or how a flea jumps really far. This robot can grab things like a hand, crawl across the floor, or even jump high, and it all happens just by pulling on a simple muscle.”
Over the last few years, Virginia Tech scientists have been looking to the octopus for inspiration to design technologies that can better grip a wide variety of objects in underwater environments. Their latest breakthrough is a special switchable adhesive modeled after the shape of the animal’s suckers, according to a new paper published in the journal Advanced Science.
“I am fascinated with how an octopus in one moment can hold something strongly, then release it instantly. It does this underwater, on objects that are rough, curved, and irregular—that is quite a feat,” said co-author and research group leader Michael Bartlett. “We’re now closer than ever to replicating the incredible ability of an octopus to grip and manipulate objects with precision, opening up new possibilities for exploration and manipulation of wet or underwater environments.”
As previously reported, 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.
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. Back in 2022, 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 result was Octa-Glove, a wearable system for gripping underwater objects that mimicked the arm of an octopus.
Improving the Octa-Glove
Grabbing and releasing underwater objects of different sizes and shapes with an octopus-inspired adhesive. Credit: Chanhong Lee and Michael Bartlett
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 team used a neoprene wetsuit glove as a base for the wearable glove, incorporating the adhesive elements and sensors in each finger, with flexible pneumatic tubes inserted at the base of the adhesive elements.
Enlarge/ Researchers have developed soft, stretchable “jelly batteries” that could be used for wearable devices or soft robotics.
University of Cambridge
Inspired by the electric shock capabilities of electric eels, scientists have developed a soft, stretchable “jelly” battery ideal for wearable devices or soft robotics, according to a new paper published in the journal Science Advances. With further testing in living organisms, the batteries might even be useful as brain implants for targeted drug delivery to treat epilepsy, among other conditions.
As previously reported, the electric eel produces its signature electric discharges—both low and high voltages, depending on the purpose for discharging—via three pairs of abdominal organs composed of modified muscle cells called electrocytes, located symmetrically along both sides of the eel. The brain sends a signal to the electrocytes, opening ion channels and briefly reversing the polarity. The difference in electric potential then generates a current, much like a battery with stacked plates.
Vanderbilt University biologist and neuroscientist Kenneth Catania is one of the most prominent scientists studying electric eels these days. He has found that the creatures can vary the degree of voltage in their electrical discharges, using lower voltages for hunting purposes and higher voltages to stun and kill prey. Those higher voltages are also useful for tracking potential prey, akin to how bats use echolocation. One species, Volta’s electric eel (Electrophorus voltai), can produce a discharge of up to 860 volts. In theory, if 10 such eels discharged at the same time, they could produce up to 8,600 volts of electricity—sufficient to power 100 light bulbs.
Mimicking Mother Nature
For soft robotics or wearable electronics applications, soft and stretchy devices with tissue-like electronic properties are required. However, “It’s difficult to design a material that is both highly stretchable and highly conductive since those two properties are normally at odds with one another,” said co-author Stephen O’Neill of the University of Cambridge. “Typically, conductivity decreases when a material is stretched.” So he and his colleagues decided to model their jelly battery design on the layered structure of the electric eel’s electrocytes. Whereas conventional electronics employ rigid materials with electrons to carry the charges, this battery would use ions as charge carriers, like the electric eels.
Enlarge/ The self-healing jelly batteries can stretch to over 10 times their original length without affecting their conductivity.
University of Cambridge
Hydrogels—3D polymer networks composed of 60 percent water—were the obvious choice since they confer the ability to precisely control mechanical properties and can mimic human skin. They are usually made of neutrally charged polymers, but O’Neill et al. added a charge to their polymers, altering the salt component to make them sticky enough to squish together into multiple layers. This builds up a larger energy potential.
The stickiness of the hydrogels comes from the reversible bonds that form between the different layers, thanks to barrel-shaped molecules that act a bit like “molecular handcuffs,” per the authors. So, the jelly batteries can stretch without separating the layers and without any loss of conductivity. Furthermore, “We can customize the mechanical properties of the hydrogels so they match human tissue,” said co-author Oren Scherman. “Since they contain no rigid components such as metal, a hydrogel implant would be much less likely to be rejected by the body or cause the build-up of scar tissue.” That makes them promising for future biomedical applications.
Another stretchy battery
Enlarge/ This lithium-ion battery has entirely stretchable components and stable charging and discharging capacity over time.
Shi Wang et al., ACS Energy Letters, 2024
In related research, a new paper published in the journal ACS Energy Letters described the fabrication of a lithium-ion battery with stretchable components, including an electrolyte layer that can expand by 5,000 percent. The battery can retain its charge storage capacity after nearly 70 charge/discharge cycles. Rather than using a liquid electrolyte, a team of Chinese scientists incorporated the electrolyte into a polymer layer fused between two flexible electrode films.
The electrodes consisted of a thin film of conductive paste embedded with silver nanowires, carbon black, and lithium-based cathode or anode materials onto a plate. They applied a layer of flexible polydimethylsiloxane (used in contact lenses) on top of the paste, followed by a lithium salt, highly conductive liquid, and stretchy polymer ingredients. When zapped with light, all those components formed a solid rubber-like stretchy layer that could still transport lithium ions. This was topped with another electrode film, and the entire device was then sealed in a protective coating. This battery had a roughly six times higher average charge capacity at a fast-charging rate than a similar device with a traditional liquid electrolyte.
