Tag Archives: bio-inspired

Innovative plant: How does the dandelion drift its seeds?

How far do you think a dandelion seed can drift from its base plant?

The Common Dandelion (Taraxacum officinale) primarily relies on wind flow to scatter its seeds. The dandelion seed has a fluffy structure that enables it to hold the most prolonged wind-based dispersal record. Commonly the seeds land 2 meters away from their mother plant. Still, in windy, dry weather favored by the dandelion, the seeds can fly up to 30 kilometers and even far (150 kilometers in some conditions). The vital point in this extraordinary adventure of the dandelion is flying with a constant velocity and having a short descent time, which means it should stay stable in the air for a relatively long time.

A study tried to illuminate the mystery behind the dandelion seeds’ ability to stay aloft in the air. Researchers attempted to mimic the dandelion flight using similarly structured silicon disks in a wind tunnel that simulated the airflow around the pappus. Pappus, the flying seed of the dandelion, consists of radially oriented filaments, each interacting with other adjacent ones, resulting in a reduction in the airflow. They compared the flight of natural seeds collected from one plant with several silicon disks with different porosities.

Dandelion seeds and silicon disks in wind tunnel
Wind tunnel experiment, modified from Cathal Cummins & et al. 2018
vortex ring above pappus
Pappus & separated vortex ring, modified from Madeleine Seale & et al. 2019

Their results showed that when pappus separates into the air,  it forms an air bubble detached from its surface above it. This air bubble, known as a vortex, is unique to the dandelion seed. When the pappus is released in the air, it takes some time to reach a steady point, in which the vortex becomes symmetrical. An important feature affecting this symmetry is the porosity of the pappus, defined by the number of filaments and their dimension in each pappus— generally, the more the porosity, the steadier the flight. The best porosity for a stable vortex ring is greater than 84.97%, and the vortex ring begins to separate as the porosity falls below 77.42%. The experiment also indicated that the vortex is axisymmetric in low velocities, but it begins to lose its symmetry as the Reynolds increases.

Pappus with water drops on it
Pappus in moisture, photo by enfantnocta

This phenomenal plant has evolved techniques for mass germination, even in the absence of wind! Pappus’s hairy structure enables it to attach to an animal’s skin and soil particles, assuring the dandelion to have enough seed dispersion during the flowering season. More interestingly, the dandelion is known to have an informed dispersal in response to environmental fluctuations. When the plant experiences root herbivory, it intensifies the seed dispersal. The flight distance may vary from meters to kilometers to assure good germination in the absence of threatening conditions. Imagine a rainy day; the moist weather condition makes the pappus’ bristles come close together, reducing the possibility of separating from the plant. The moisture makes the current spot a suitable choice to stay. So even the detached seeds prefer to fall close to their base plant. 

It worth mentioning that this remarkable plant also inspired areas of science. In their study of Mars exploration, researchers presented a primary model of a dandelion-inspired rover. Considering the harsh environmental condition on Mars, other excavators find the wind flow as an obstacle that results in damaged parts and incomplete missions. In contrast, the new dandelion-shaped rovers use the wind flow as an accelerating point to explore locations on Mars that other robots couldn’t access.

Dandelion-shaped Mars rovers
Dandelion-shaped rovers ,modified from Michelle Sherman & et al. 2020

Which is more stable, washing machines or birds? The answer might surprise you

What do birds and washing machines have in common? Shockingly, it’s not the ability to wash clothes. Rather, most birds and washing machines are great examples of vibration isolation systems.

Now that’s cool and all – but what is a vibration isolation system?

Better known as a mass-spring-damper system, vibration isolators are generally a mechanical or industrial mechanism that can reduce the amount of vibrational energy produced by a system. Vibration isolators are incredibly important; studies show “undesirable vibrations” can shorten a machine’s service life and even permanently damage the machine and those using it. Considering this, engineers are constantly improving upon current vibration control systems, and are now looking to birds for inspiration.

But why birds? Well, to understand this, let’s consider a bird as a simple mass-spring-damper system.

Avian vibration isolation system represented as mass-spring-damper-system
Simple approximation of avian vibration isolation system as mass-spring-damper system. Taken from the 2015 study: ‘The role of passive avian head stabilization in flapping flight.”

First, visualize vibrations as an oscillating force stemming from the bird’s body moving back-and-forth. Vibrational forces can be generated by the flapping of wings, unexpected gusts, and/or movement of legs. Now, if we continue up from the body to the neck, we can see where avian skeletal and muscular structure really begins to “show off its feathers.”

Characterized as a multi-layered structure, the avian neck contains many sections of “hollow” bones, connected by surrounding muscles. The structural units (muscles and bones) of the avian neck have properties of both springs and dampers, optimizing them for vibration isolation.

Simplified representation of multi-layered neck as spring-damper structure

For starters, we see the muscles largely act as springs. Springs have the unique ability to move a body with its vibrations. This behavior is present in the muscles connected to the bone segments, in that they are capable of instantaneously compressing, elongating and twisting in response to rapid changes in the body’s movement. This elastic response prevents not only the head, but the whole bird, from shaking when bombarded when vibrations from any form of movement.

Simplified visualization of multi-layered spring-damper structure. The transparent grey portion represents the hollow bone, which is connected by the black lines, or strong spring-like muscles. The empty space between each unit would consist of the softer, damper-like muscle. Taken from the 2021 study: “A novel dynamics stabilization and vibration isolation structure inspired by the role of avian neck.”

Alternatively, the muscles, primarily those not connected to bone, can act as dampers. Effective dampers are similarly identified by the ability to move with vibrations; however, they can dissipate some of the vibrational energy as heat, or store energy until relaxed. The interior muscles are capable of slowly deforming (changing shape) if exposed to steady vibrations, allowing for dissipation of excessive vibrational energy.

But hey, what about those bones?

The avian neck has nearly three times the number of bone sections than most mammals, on top of muscles entirely surrounding the neck. This drastically increases the bird’s flexibility, helping it maneuver through sharp positional changes, thereby further limiting the effect of vibrational forces.

Finally, what makes the avian vibration isolator truly superior is its passive activation. As engineers at Shanghai Jiao Tong University point out, manmade passive vibration isolators fall short because they require sensors and input energy to adjust for “shocks and random vibrations.” As previously explained, the multi-layered neck is well equipped to handle random oscillations, yet, more importantly, the bird’s neck muscles can passively change position to brace for incoming vibrations.

A recent study from Stanford University proved this concept by recording a whooper swan’s reaction to different strength gusts. They found that swan’s neck adjusted to protect the head, and that even when the flapping doubled, the movement of the head reduced by a quarter. Finally, it is important to note that passive activation is not limited to the sky; researchers have found that mainly terrestrial birds like chickens and pigeons have a similar neck structure and system for maintaining stability and clear vision.

Overall, continuing to study the avian vibration isolation system could prove very beneficial for many different applications. For a more in-depth look at the current work out, check-out the studies referenced throughout the article. Otherwise, enjoy watching this chicken work its body control magic!

Mercedes-Benz “Chicken” Magic Body Control Advertisement, highlighting the chicken’s amazing head stabilization ability.

sticks and stones may break my bones but dirt will wash right off

There you are, sitting in the park eating your spaghetti picnic on your favorite picnic blanket when your pollen allergy acts up. You let out a sneeze powerful enough to compete with Aeolus’ bag of wind, but now your spaghetti is all over your favorite picnic blanket. You immediately go to rinse it off, but your fine Italian sauce has thoroughly soaked in. If only nature had a solution to keep a surface clean. Enter: the lotus leaf.

The lotus leaf is renowned for its ability to stay clean in murky environments. This characteristic of the plant is regularly attributed to its superhydrophobic surface features and chemistry. A superhydrophobic surface is a surface which can maintain a contact angle with water above 150o and is correlated with a low free surface energy—which really means water pools and rolls off rather than soaking into the surface.

Nearly perfectly spherical water droplet on an artificially prepared surface

Modified from Zorba et al. 2008

A key attribute of the superhydrophobic surface is a hierarchical micro- and nanostructure. The microstructure is composed of plant cells grown in little mounds known as a “papillae” with small channels for air flow in between called “stomata.” The nanostructure is composed of hair-like wax crystal towers (epicuticular wax) built on the peaks of the papillae topography. The elevated wax towers combined with the stomata trap air and reduce the contact area of the water with the surface. The epicuticular wax chemistry reduces the adhesion to the towers themselves by being naturally hydrophobic.

Graphic of water drop resting across uneven wax pillars on a lotus leaf

Modified from Zorba et al. 2008

The tips of the wax towers create the largest repelling forces which form larger contact angles, while shorter towers can actually produce adhesive forces that reduce the contact angle. If the air is displaced and filled with water, the contact angle will decrease due to the water-water adhesion which “pulls” the droplet to the surface. Similarly, if the surface is damaged, the wax can be removed and decrease the surface’s hydrophobicity. The wax is naturally soft material and prone to mechanical damage increasing water adhesion and reducing the self-cleaning abilities of the leaf.

The papillae topography is the key to the robustness of the lotus leaf hydrophobicity. The papillae create natural valleys and creases which—like the tops—are still densely packed with wax hairs. When the surface is impacted, only the top of the papillae are exposed to the mechanical force so the wax tubules in the valleys are left undeformed and maintain their hydrophobic characteristics.

Water beads on rain jacket

Photo by Chase Pellerin via Gear Patrol

Hydrophobic surfaces have many applications in everyday life, for example rain jackets and umbrellas perform their best when they are hydrophobic. Manufacturing processes rely on hydrophobic surfaces to reduce oxidation and stay clean in past-paced environments, and your favorite picnic blanket would be much less prone to spaghetti stains if it were hydrophobic. Nature has solutions to keeping surfaces clean; we just have to recognize them.

the hairy feet of the gecko

Have you ever thought about what it would be like to walk on walls? If you’ve ever watched a Spiderman movie or watched a gecko maneuver around its habitat, you probably have. While geckos don’t fight crime, their climbing ability is as fantastic as that of any superhero. Geckos have one of the most unique climbing adaptations of any animal, and scientists are examining the source of this ability to see if human technology could one day achieve something similar.

Geckos are able to cling to almost any surface, no matter how smooth or rough it is. They are also able to detach quickly and easily from these surfaces as they climb. This climbing ability is due to tiny hairs, called setae, on the bottoms of their feet that can only be seen with a microscope. Each hair branches off into even smaller fibers called spatulae. Each gecko has about three million setae, and a billion spatulae! When the gecko places its foot on a surface, these hairs cling to the surface and form intermolecular bonds, called Van der Waals bonds, with the molecules of that surface. These bonds are strong enough to hold the gecko in place, but can be broken easily when the gecko lifts up its foot.

A close-up view of the bottom of a gecko foot, with the microscopic hairs visible.
Close-up of setae on gecko foot. Image by Science Photo Library

In addition to enabling the gecko to attach itself to surfaces, these hairs on the bottom of the gecko’s feet have the ability to clean themselves. If the gecko did not have some sort of ability to clean its feet, dust and dirt would get stuck on the gecko’s feet and break the connection between the feet and the surface. However, the hairs on the gecko’s feet are shaped so that it is difficult for water to stick to the feet. When the gecko gets water on its foot, the water rolls off of it and takes any particles of dirt with it.

Scientists have long been fascinated by the gecko’s ability to stick to surfaces, and many have been working on creating adhesives with fibers similar to the hairs on the bottom of the gecko’s feet. These adhesives are dry, like the gecko’s feet, and can be attached firmly and removed easily. The possibilities for application of adhesives like this are vast in number, and include everyday fasteners as well as use in electronics, robotics, and even outer space technology. One of the areas being explored by scientists is the use of these adhesives in the medical industry. The manufacture of gecko-hair fibers for bandages could mean farewell to the pain of removing a bandage, as well as the sticky residue left behind on your skin. This type of adhesive could even one day replace stitches after surgery.

Polymer fibrillar adhesive based on gecko foot Setae. Image by G.J. Shah, M. Sitti.

Most people probably don’t think about geckos very often apart from what they see in advertisements for car insurance. But for some scientists, these creatures hold the key to a world of possibilities. So next time you’re at the pet store, take a look in the lizard tanks and watch the geckos climb. Someday, thanks to those geckos, humans might be able to do the same thing.

Read more: https://steemit.com/science/@herpetologyguy/what-makes-gecko-feet-so-sticky

Soft Robotics: Humanizing the Mechanical

Cassie the robot, created by Dr. Mikhail Jones at Oregon State University
Cassie the Robot, developed by Mikhail Jones, Faculty Research Assistant in Mechanical Engineering at Oregon State University.

In media and science-fiction, robots have stereotypically, and perhaps somewhat unfairly, been depicted as mechanical, stiff assemblies of moving joints and complicated circuitry. While this still holds true for many robots designed today, whether for industry or research, the past few years have seen a growing interest in soft robotics in academia, industry, and popular culture. As the name implies, many research groups have begun investing in constructing robots from compliant, softer materials.

Stickybot, a gecko-inspired robot.
Stickybot, a biomimetic robot.

Inspired by the way organisms in nature survive and adapt to their surroundings (formally known as biomimicry), the advantages of soft robotic components lie in their flexibility, sensitivity, and malleability – delicate tasks or interactions involving other people would be better accomplished by robots made of compliant materials rather than one that could potentially cause harm to the object or person. To that end, many of the applications of soft robotic research have already seen results in the medical industry, from invasive surgery to assistive exosuits. By taking inspiration from biological creatures or mechanisms, softer materials like rubbers and plastics can be actuated to accomplish tasks conventional, “hard” robots could struggle with.

Animation of pneumatic muscle.
Animation of pneumatic air muscle used as robotic actuators.

The most common method of moving these robotic parts is with changes in internal pressure. By creating a “hard”, skeletal frame, and surrounding it with soft, sealed membranes, changes in pressure allow the designer to control its components precisely. By decreasing the pressure and creating a vacuum, the robotic section would shrink or crumple, and increasing it would do the opposite. Researchers at Harvard developed “artificial muscles” by taking this concept a step further; using origami, they were able to design soft robotic mechanisms that could orient themselves into tunable positions as the pressure was changed inside the membrane (as a side note, origami is used in a surprising number of research fields, one of the most famous being satellite deployment). Compared to the challenge of precisely controlling prismatic (sliding) joints and servos in conventional robotics, the compliance of the materials used allow for finer control and smaller ranges of applied forces that are better suited for precise tasks.

Animation of a person demonstrating the Miura fold on a piece of paper
The Miura fold pictured here is often used to deploy large surfaces while minimizing volume, such as for satellites.

Another significant advantage of soft robots over their stiff counterparts is their adaptability to environmental conditions. Generally speaking, robots do not do well in water (or lava, for that matter), but it would have little effect on robots covered in a sealed, pressurized “skin”. This is what inspired NASA in 2015 to fund research into soft robots that could explore the oceans of one of Jupiter’s moons, Europa.  Similarly, a light-activated underwater robotic manta ray was designed at a centimeter scale to study the effect of environmental cues on controllable robots.

Schematic and pictures of soft robot design.
A soft-legged robot with walking capabilities.

While research in soft robotics is still relatively new, it has the potential to significantly affect the role of robots in our daily lives. As a softer, safer, and more environmentally robust alternative to “hard” robots, wearable robotic devices, exploratory robotic fish, and personal medical attendants could soon become commonplace for the general public.

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