In 2018, a team of French physicists developed a rudimentary mathematical model to describe the deformation of a common type of knit. Their work was inspired when co-author Frédéric Lechenault watched his pregnant wife knitting baby booties and blankets, and he noted how the items would return to their original shape even after being stretched. With a few colleagues, he was able to boil the mechanics down to a few simple equations, adaptable to different stitch patterns. It all comes down to three factors: the “bendiness” of the yarn, the length of the yarn, and how many crossing points are in each stitch.
A simpler stitch
A simplified model of how yarns interact Credit: J. Crassous/University of Rennes
One of the co-authors of that 2018 paper, Samuel Poincloux of Aoyama Gakuin University in Japan, also co-authored this latest study with two other colleagues, Jérôme Crassous (University of Rennes in France) and Audrey Steinberger (University of Lyon). This time around, Poincloux was interested in the knotty problem of predicting the rest shape of a knitted fabric, given the yarn’s length by stitch—an open question dating back at least to a 1959 paper.
It’s the complex geometry of all the friction-producing contact zones between the slender elastic fibers that makes such a system too difficult to model precisely, because the contact zones can rotate or change shape as the fabric moves. Poincloux and his cohorts came up with their own more simplified model.
The team performed experiments with a Jersey stitch knit (aka a stockinette), a widely used and simple knit consisting of a single yarn (in this case, a nylon thread) forming interlocked loops. They also ran numerical simulations modeled on discrete elastic rods coupled with dry contacts with a specific friction coefficient to form meshes.
The results: Even when there were no external stresses applied to the fabric, the friction between the threads served as a stabilizing factor. And there was no single form of equilibrium for a knitted sweater’s resting shape; rather, there were multiple metastable states that were dependent on the fabric’s history—the different ways it had been folded, stretched, or rumpled. In short, “Knitted fabrics do not have a unique shape when no forces are applied, contrary to the relatively common belief in textile literature,” said Crassous.
The No. 1 nuisance with smartphones and smartwatches is that we need to charge them every day. As warm-blooded creatures, however, we generate heat all the time, and that heat can be converted into electricity for some of the electronic gadgetry we carry.
Flexible thermoelectric devices, or F-TEDs, can convert thermal energy into electric power. The problem is that F-TEDs weren’t actually flexible enough to comfortably wear or efficient enough to power even a smartwatch. They were also very expensive to make.
But now, a team of Australian researchers thinks they finally achieved a breakthrough that might take F-TEDs off the ground.
“The power generated by the flexible thermoelectric film we have created would not be enough to charge a smartphone but should be enough to keep a smartwatch going,” said Zhi-Gang Chen, a professor at Queensland University of Technology in Brisbane, Australia. Does that mean we have reached a point where it would be possible to make a thermoelectric Apple Watch band that could keep the watch charged all the time? “It would take some industrial engineering and optimization, but we can definitely achieve a smartwatch band like that,” Chen said.
Manufacturing heaven
Thermoelectric generators producing enough power to run something like an Apple Watch were, so far, made with rigid bulk materials. The obvious problem with them was that nobody would want to wear a metal slab on their wrist or run a power cable from anywhere else to their watch. Flexible thermoelectric devices, on the other hand, were perfectly wearable but offered efficiencies that made them good for low-power health-monitoring electronics rather than more power-hungry hardware like smartwatches.
Back in 2021, generating 35 microwatts per square centimeter in a wristband worn during a typical walk outside was impressive enough to land your research paper in Nature. Today, Chen and his colleagues made a flexible thermoelectric device that performed over 34 times better at room temperature. “To the best of our knowledge, we hold a current record in this field,” Chen says.
“Magic mud” composition and microstructure: (top right) a clean baseball surface; (bottom right) a mudded baseball.
Credit: S. Pradeep et al., 2024
“Magic mud” composition and microstructure: (top right) a clean baseball surface; (bottom right) a mudded baseball. Credit: S. Pradeep et al., 2024
Pradeep et al. found that magic mud’s particles are primarily silt and clay, with a bit of sand and organic material. The stickiness comes from the clay, silt, and organic matter, while the sand makes it gritty. So the mud “has the properties of skin cream,” they wrote. “This allows it to be held in the hand like a solid but also spread easily to penetrate pores and make a very thin coating on the baseball.”
When the mud dries on the baseball, however, the residue left behind is not like skin cream. That’s due to the angular sand particles bonded to the baseball by the clay, which can increase surface friction by as much as a factor of two. Meanwhile, the finer particles double the adhesion. “The relative proportions of cohesive particulates, frictional sand, and water conspire to make a material that flows like skin cream but grips like sandpaper,” they wrote.
Despite its relatively mundane components, the magic mud nonetheless shows remarkable mechanical behaviors that the authors think would make it useful in other practical applications. For instance, it might replace synthetic materials as an effective lubricant, provided the gritty sand particles are removed. Or it could be used as a friction agent to improve traction on slippery surfaces, provided one could define the optimal fraction of sand content that wouldn’t diminish its spreadability. Or it might be used as a binding agent in locally sourced geomaterials for construction.
“As for the future of Rubbing Mud in Major League Baseball, unraveling the mystery of its behavior does not and should not necessarily lead to a synthetic replacement,” the authors concluded. “We rather believe the opposite; Rubbing Mud is a nature-based material that is replenished by the tides, and only small quantities are needed for great effect. In a world that is turning toward green solutions, this seemingly antiquated baseball tradition provides a glimpse of a future of Earth-inspired materials science.”
Recently, construction company ICON announced that it is close to completing the world’s largest 3D-printed neighborhood in Georgetown, Texas. This isn’t the only 3D-printed housing project. Hundreds of 3D-printed homes are under construction in the US and Europe, and more such housing projects are in the pipeline.
There are many factors fueling the growth of 3D printing in the construction industry. It reduces the construction time; a home that could take months to build can be constructed within days or weeks with a 3D printer. Compared to traditional methods, 3D printing also reduces the amount of material that ends up as waste during construction. These advantages lead to reduced labor and material costs, making 3D printing an attractive choice for construction companies.
A team of researchers from the Swiss Federal Institute of Technology (ETH) Zurich, however, claims to have developed a robotic construction method that is even better than 3D printing. They call it impact printing, and instead of typical construction materials, it uses Earth-based materials such as sand, silt, clay, and gravel to make homes. According to the researchers, impact printing is less carbon-intensive and much more sustainable and affordable than 3D printing.
This is because Earth-based materials are abundant, recyclable, available at low costs, and can even be excavated at the construction site. “We developed a robotic tool and a method that could take common material, which is the excavated material on construction sites, and turn it back into usable building products, at low cost and efficiently, with significantly less CO2 than existing industrialized building methods, including 3D printing,” said Lauren Vasey, one of the researchers and an SNSF Bridge Fellow at ETH Zurich.
How does impact printing work?
Excavated materials can’t be used directly for construction. So before beginning the impact printing process, researchers prepare a mix of Earth-based materials that has a balance of fine and coarse particles, ensuring both ease of use and structural strength. Fine materials like clay act as a binder, helping the particles stick together, while coarser materials like sand or gravel make the mix more stable and strong. This optimized mix is designed such that it can move easily through the robotic system without getting stuck or causing blockages.
In recent years, materials scientists experimenting with ceramics have started adding an oxidized form of graphene to the mix to produce ceramics that are tougher, more durable, and more resistant to fracture, among other desirable properties. Researchers at the National University of Singapore (NUS) have developed a new method that uses ultrasound to more evenly distribute graphene oxide (GO) in ceramics, according to a new paper published in the journal ACS Omega. And as a bonus, they collaborated with an artist who used the resulting ceramic tiles to create a unique art exhibit at the NUS Museum—a striking merger of science and art.
As reported previously, graphene is the thinnest material yet known, composed of a single layer of carbon atoms arranged in a hexagonal lattice. That structure gives it many unusual properties that hold great promise for real-world applications: batteries, super capacitors, antennas, water filters, transistors, solar cells, and touchscreens, just to name a few.
In 2021, scientists found that this wonder material might also provide a solution to the fading of colors of many artistic masterpieces. For instance, several of Georgia O’Keeffe’s oil paintings housed in the Georgia O’Keeffe Museum in Santa Fe, New Mexico, have developed tiny pin-sized blisters, almost like acne, for decades. Conservators have found similar deterioration in oil-based masterpieces across all time periods, including works by Rembrandt.
Van Gogh’s Sunflower series has been fading over the last century due to constant exposure to light. A 2011 study found that chromium in the chrome yellow Van Gogh favored reacted strongly with other compounds like barium and sulfur when exposed to sunlight. A 2016 study pointed the finger at the sulfates, which absorb in the UV spectrum, leading to degradation.
Even contemporary art materials are prone to irreversible color changes from exposure to light and oxidizing agents, among other hazards. That’s why there has been recent work on the use of nanomaterials for conservation of artworks. Graphene has a number of properties that make it attractive for art-conservation purposes. The one-atom-thick material is transparent, adheres easily to various substrates, and serves as an excellent barrier against oxygen, gases (corrosive or otherwise), and moisture. It’s also hydrophobic and is an excellent absorber of UV light.
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/ A lot of gold deposits are found embedded in quartz crystals.
One of the reasons gold is so valuable is because it is highly unreactive—if you make something out of gold, it keeps its lustrous radiance. Even when you can react it with another material, it’s also barely soluble, a combination that makes it difficult to purify away from other materials. Which is part of why a large majority of the gold we’ve obtained comes from deposits where it is present in large chunks, some of them reaching hundreds of kilograms.
Those of you paying careful attention to the previous paragraph may have noticed a problem here: If gold is so difficult to get into its pure form, how do natural processes create enormous chunks of it? On Monday, a group of Australian researchers published a hypothesis, and a bit of evidence supporting it. They propose that an earthquake-triggered piezoelectric effect essentially electroplates gold onto quartz crystals.
The hypothesis
Approximately 75 percent of the gold humanity has obtained has come from what are called orogenic gold deposits. Orogeny is a term for the tectonic processes that build mountains, and orogenic gold deposits form in the seams where two bodies of rock are moving past each other. These areas are often filled with hot hydrothermal fluids, and the heat can increase the solubility of gold from “barely there” to “extremely low,” meaning generally less than a single milligram in a liter of water.
The other striking thing about these deposits is that they’re generally associated with the mineral quartz, a crystalline form of silicon dioxide. And that fact formed the foundation for the new hypothesis, which brings together a number of topics that are generally considered largely unrelated.
It turns out that quartz is the only abundant mineral that’s piezoelectric, meaning that it generates a charge when it’s placed under strain. While you don’t need to understand why that’s the case to follow this hypothesis, the researchers’ explanation of the piezoelectric effect is remarkably cogent and clear, so I’ll just quote it here for people who want to come away from this having learned something: “Quartz is the only common mineral that forms crystals lacking a center of symmetry (non-centrosymmetric). Non-centrosymmetric crystals distorted under stress have an imbalance in their internal electric configuration, which produces an electrical potential—or voltage—across the crystal that is directly proportional to the applied mechanical force.”
Quartz happens to be an insulator, so this electric potential doesn’t easily dissipate on its own. It can, however, be eliminated through the transfer of electrons to or from any materials that touch the quartz crystals, including fluids. In practice, that means the charge can drive redox (reduction/oxidation) reactions in any nearby fluids, potentially neutralizing any dissolved ions and causing them to come out of solution.
This has the potential to be self-reinforcing. Once a small metal deposit forms on the surface of quartz, it will ease the exchange of electrons with the fluid in its immediate vicinity, meaning more metal will be deposited in the same location. This will also lower the concentration of the metal in the nearby solution, which will favor the diffusion of additional metal ions into the location, meaning that the fluid itself doesn’t need to keep circulating past the same spot.
Finally, the concept also needs a source of strain to generate the piezoelectric effect in the first place. But remember that this is all happening in an active fault zone, so strain is not in short supply.
And the evidence
Figuring out whether this happens in active fault zones would be extremely challenging for all sorts of reasons. But it’s relatively easy to dunk some quartz crystals in a solution containing gold and see what happens. So the latter is the route the Australians took.
The gold came in the form of either a solution of gold chloride ions or a suspension of gold nanoparticles. Quartz crystals were either pure quartz or obtained from a gold-rich area and already contained some small gold deposits. The crystals themselves were subject to strain at a frequency similar to that produced by small earthquakes, and the experiment was left to run for an hour.
An hour was enough to get small gold deposits to form on the pure quartz crystals, regardless of whether it was from dissolved gold or suspended gold nanoparticles. In the case of the naturally formed quartz, the gold ended up being deposited on the existing sites where gold metal is present, rather than forming additional deposits.
The researchers note that a lot of the quartz in deposits is disordered rather than in the form of single crystals. In disordered material, there are lots of small crystals oriented randomly, meaning the piezoelectric effect of any one of these crystals is typically canceled out by its neighbors. So, gold will preferentially form on single crystals, which also helps explain why it’s found in large lumps in these deposits.
So, this is a pretty compelling hypothesis—it explains something puzzling, relies on well-established processes, and has a bit of experimental support. Given that activity in active faults is likely to remain both slow and inaccessible, the next steps are probably going to involve getting longer-term information on the rate of deposition through this process and a physical comparison of these deposits with those found in natural settings.
This electroactive polymer hydrogel “learned” to play Pong. Credit: Cell Reports Physical Science/Strong et al.
Pong will always hold a special place in the history of gaming as one of the earliest arcade video games. Introduced in 1972, it was a table tennis game featuring very simple graphics and gameplay. In fact, it’s simple enough that even non-living materials known as hydrogels can “learn” to play the game by “remembering” previous patterns of electrical stimulation, according to a new paper published in the journal Cell Reports Physical Science.
“Our research shows that even very simple materials can exhibit complex, adaptive behaviors typically associated with living systems or sophisticated AI,” said co-author Yoshikatsu Hayashi, a biomedical engineer at the University of Reading in the UK. “This opens up exciting possibilities for developing new types of ‘smart’ materials that can learn and adapt to their environment.”
Hydrogels are soft, flexible biphasic materials that swell but do not dissolve in water. So a hydrogel may contain a large amount of water but still maintain its shape, making it useful for a wide range of applications. Perhaps the best-known use is soft contact lenses, but various kinds of hydrogels are also used in breast implants, disposable diapers, EEG and ECG medical electrodes, glucose biosensors, encapsulating quantum dots, solar-powered water purification, cell cultures, tissue engineering scaffolds, water gel explosives, actuators for soft robotics, supersonic shock-absorbing materials, and sustained-release drug delivery systems, among other uses.
In April, Hayashi co-authored a paper showing that hydrogels can “learn” to beat in rhythm with an external pacemaker, something previously only achieved with living cells. They exploited the intrinsic ability of the hydrogels to convert chemical energy into mechanical oscillations, using the pacemaker to apply cyclic compressions. They found that when the oscillation of a gel sample matched the harmonic resonance of the pacemaker’s beat, the system kept a “memory” of that resonant oscillation period and could retain that memory even when the pacemaker was turned off. Such hydrogels might one day be a useful substitute for heart research using animals, providing new ways to research conditions like cardiac arrhythmia.
For this latest work, Hayashi and co-authors were partly inspired by a 2022 study in which brain cells in a dish—dubbed DishBrain—were electrically stimulated in such a way as to create useful feedback loops, enabling them to “learn” to play Pong (albeit badly). As Ars Science Editor John Timmer reported at the time:
Pong proved to be an excellent choice for the experiments. The environment only involves a couple of variables: the location of the paddle and the location of the ball. The paddle can only move along a single line, so the motor portion of things only needs two inputs: move up or move down. And there’s a clear reward for doing things well: you avoid an end state where the ball goes past the paddles and the game stops. It is a great setup for testing a simple neural network.
Put in Pong terms, the sensory portion of the network will take the positional inputs, determine an action (move the paddle up or down), and then generate an expectation for what the next state will be. If it’s interpreting the world correctly, that state will be similar to its prediction, and thus the sensory input will be its own reward. If it gets things wrong, then there will be a large mismatch, and the network will revise its connections and try again.
There were a few caveats—even the best systems didn’t play Pong all that well—but the approach mostly worked. Those systems comprising either mouse or human neurons saw the average length of Pong rallies increase over time, indicating they might be learning the game’s rules. Systems based on non-neural cells, or those lacking a reward system, didn’t see this sort of improvement. The findings provided some evidence that neural networks formed from actual neurons spontaneously develop the ability to learn. And that could explain some of the learning capabilities of actual brains, where smaller groups of neurons are organized into functional units.
Enlarge/ Some solar panels, along with a diagram of a perovskite’s crystal structure.
As the price of silicon panels has continued to come down, we’ve reached the point where they’re a small and shrinking cost of building a solar farm. That means that it might be worth spending more to get a panel that converts more of the incoming sunlight to electricity, since it allows you to get more out of the price paid to get each panel installed. But silicon panels are already pushing up against physical limits on efficiency. Which means our best chance for a major boost in panel efficiency may be to combine silicon with an additional photovoltaic material.
Right now, most of the focus is on pairing silicon with a class of materials called perovskites. Perovskite crystals can be layered on top of silicon, creating a panel with two materials that absorb different areas of the spectrum—plus, perovskites can be made from relatively cheap raw materials. Unfortunately, it has been difficult to make perovskites that are both high-efficiency and last for the decades that the silicon portion will.
Lots of labs are attempting to change that, though. And two of them reported some progress this week, including a perovskite/silicon system that achieved 34 percent efficiency.
Boosting perovskite stability
Perovskites are an entire class of materials that all form the same crystal structure. So, there is plenty of flexibility when it comes to the raw materials being used. Perovskite-based photovoltaics are typically formed by what’s called solution processing, in which all the raw materials are dissolved in a liquid that’s then layered on top of the panel-to-be, allowing perovskite crystals to form across its entire surface. Which is great, except that this process tends to form multiple crystals with different orientations on a single surface, decreasing performance.
Adding to the problems, perovskites are also not especially stable. They’re usually made of a combination of positively and negatively charged ions, and these have to be present in the right ratios to form a perovskite. However, some of these individual ions can diffuse over time, disrupting the crystal structure. Harvesting solar energy, which involves the material absorbing lots of energy, makes matters worse by heating the material, which increases the rate of diffusion.
Combined, these factors sap the efficiency of perovskite solar cells and mean that none lasts nearly as long as a sheet of silicon. The new works tackle these issues from two very different directions.
The first of the new papers tackles stability by using the flexibility of perovskites to incorporate various ions. The researchers started by using a technique called density functional theory to model how different molecules would behave when placed into a spot normally occupied by a positively charged ion. And the modeling got them excited about a molecule called tetrahydrotriazinium, which has a six-atom ring composed of alternating carbon and nitrogen atoms. The regular placement of nitrogens around the ring allows it to form regular interactions with neighboring atoms in the crystal structure.
Tetrahydrotriazinium has a neutral charge when only two of the nitrogens have hydrogens attached to them. But it typically grabs a charged hydrogen (effectively, a proton) out of solution, giving it a net positive charge. This leaves each of its three nitrogens associated with a hydrogen and allows the positive charge to be distributed among them. That makes this interaction incredibly strong, meaning that the hydrogens are extremely unlikely to drift off, which also stabilizes the crystal structure.
So, this should make perovskites much, much more stable. The only problem? Tetrahydrotriazinium tends to react with lots of other chemicals, so it’s difficult to provide as a raw material for the perovskite-forming solution.
On Wednesday, researchers reported that they had developed a drone they’re calling the CoulombFly, which is capable of self-powered hovering for as long as the Sun is shining. The drone, which is shaped like no aerial vehicle you’ve ever seen before, combines solar cells, a voltage converter, and an electrostatic motor to drive a helicopter-like propeller—with all components having been optimized for a balance of efficiency and light weight.
Before people get excited about buying one, the list of caveats is extensive. There’s no onboard control hardware, and the drone isn’t capable of directed flight anyway, meaning it would drift on the breeze if ever set loose outdoors. Lots of the components appear quite fragile, as well. However, the design can be miniaturized, and the researchers built a version that weighs only 9 milligrams.
Built around a motor
One key to this development was the researchers’ recognition that most drones use electromagnetic motors, which involve lots of metal coils that add significant weight to any system. So, the team behind the work decided to focus on developing a lightweight electrostatic motor. These rely on charge attraction and repulsion to power the motor, as opposed to magnetic interactions.
The motor the researchers developed is quite large relative to the size of the drone. It consists of an inner ring of stationary charged plates called the stator. These plates are composed of a thin carbon-fiber plate covered in aluminum foil. When in operation, neighboring plates have opposite charges. A ring of 64 rotating plates surrounds that.
The motor starts operating when the plates in the outer ring are charged. Since one of the nearby plates on the stator will be guaranteed to have the opposite charge, the pull will start the rotating ring turning. When the plates of the stator and rotor reach their closest approach, thin wires will make contact, allowing charges to transfer between them. This ensures that the stator and rotor plates now have the same charge, converting the attraction to a repulsion. This keeps the rotor moving, and guarantees that the rotor’s plate now has the opposite charge from the next stator plate down the line.
These systems typically require very little in the way of amperage to operate. But they do require a large voltage difference between the plates (something we’ll come back to).
When hooked up to a 10-centimeter, eight-bladed propeller, the system could produce a maximum lift of 5.8 grams. This gave the researchers clear weight targets when designing the remaining components.
Ready to hover
The solar power cells were made of a thin film of gallium arsenide, which is far more expensive than other photovoltaic materials, but offers a higher efficiency (30 percent conversion compared to numbers that are typically in the mid-20s). This tends to provide the opposite of what the system needs: reasonable current at a relatively low voltage. So, the system also needed a high-voltage power converter.
Here, the researchers sacrificed efficiency for low weight, arranging a bunch of voltage converters in series to create a system that weighs just 1.13 grams, but steps the voltage up from 4.5 V all the way to 9.0 kV. But it does so with a power conversion efficiency of just 24 percent.
The resulting CoulombFly is dominated by the large cylindrical motor, which is topped by the propeller. Suspended below that is a platform with the solar cells on one side, balanced out by the long, thin power converter on the other.
Meet the CoulombFly.
To test their system, the researchers simply opened a window on a sunny day in Beijing. Starting at noon, the drone took off and hovered for over an hour, and all indications are that it would have continued to do so for as long as the sunlight provided enough power.
The total system required just over half a watt of power to stay aloft. Given a total mass of 4 grams, that works out to a lift-to-power efficiency of 7.6 grams per watt. But a lot of that power is lost during the voltage conversion. If you focus on the motor alone, it only requires 0.14 watts, giving it a lift-to-power efficiency of over 30 grams per watt.
The researchers provide a long list of things they could do to optimize the design, including increasing the motor’s torque and propeller’s lift, placing the solar cells on structural components, and boosting the efficiency of the voltage converter. But one thing they don’t have to optimize is the vehicle’s size since they already built a miniaturized version that’s only 8 millimeters high and weighs just 9 milligrams but is able to generate a milliwatt of power that turns its propeller at over 15,000 rpm.
Again, all this is done without any onboard control circuitry or the hardware needed to move the machine anywhere—they’re basically flying these in cages to keep them from wandering off on the breeze. But there seems to be enough leeway in the weight that some additional hardware should be possible, especially if they manage some of the potential optimizations they mentioned.
Enlarge/ Some of the waste material that ends up part of these bricks.
Seamus Daniel, RMIT University
Researchers at the Royal Melbourne Institute of Technology (RMIT) in Australia have developed special “energy-smart bricks” that can be made by mixing clay with glass waste and coal ash. These bricks can help mitigate the negative effects of traditional brick manufacturing, an energy-intensive process that requires large-scale clay mining, contributes heavily to CO2 emissions, and generates a lot of air pollution.
According to the RMIT researchers, “Brick kilns worldwide consume 375 million tonnes (~340 million metric tons) of coal in combustion annually, which is equivalent to 675 million tonnes of CO2 emission (~612 million metric tons).” This exceeds the combined annual carbon dioxide emissions of 130 million passenger vehicles in the US.
The energy-smart bricks rely on a material called RCF waste. It mostly contains fine pieces of glass (92 percent) left over from the recycling process, along with ceramic materials, plastic, paper, and ash. Most of this waste material generally ends up in landfills, where it can cause soil and water degradation. However, the study authors note, “The utilization of RCF waste in fired-clay bricks offers a potential solution to the increasing global waste crisis and reduces the burden on landfills.”
What makes the bricks “energy-smart”
Compared to traditional bricks, the newly developed energy-smart bricks have lower thermal conductivity: They retain heat longer and undergo more uniform heating. This means they can be manufactured at lower firing temperatures. For instance, while regular clay bricks are fired (a process during which bricks are baked in a kiln, so they become hard and durable) at 1,050° C, energy-smart bricks can achieve the required hardness at 950° C, saving 20 percent of the energy needed for traditional brickmaking.
Based on bricks produced in their lab, they estimated that “each firing cycle led to a potential value of up to $158,460 through a reduction of 417 tonnes of CO2, resulting from a 9.5 percent reduction in firing temperature.” So basically, if a manufacturer switches from regular clay bricks to energy-smart bricks, it will end up saving thousands of dollars on its power bill, and its kilns will release less CO2 into Earth’s atmosphere. Scaled up to the estimated 1.4 trillion bricks made each year, the savings are substantial.
But brick manufacturers aren’t the only ones who benefit. “Bricks characterized by low thermal conductivity contribute to efficient heat storage and absorption, creating a cooler environment during summer and a warmer comfort during winter. This advantage translates into energy savings for air conditioning, benefiting the occupants of the house or building,” the study authors explained.
Tests conducted by the researchers suggest that the residents of a single-story house built using energy-smart bricks will save up to 5 percent on their energy bills compared to those living in a house made with regular clay bricks.
One reason plastic waste persists in the environment is because there’s not much that can eat it. The chemical structure of most polymers is stable and different enough from existing food sources that bacteria didn’t have enzymes that could digest them. Evolution has started to change that situation, though, and a number of strains have been identified that can digest some common plastics.
An international team of researchers has decided to take advantage of those strains and bundle plastic-eating bacteria into the plastic. To keep them from eating it while it’s in use, the bacteria is mixed in as inactive spores that should (mostly—more on this below) only start digesting the plastic once it’s released into the environment. To get this to work, the researchers had to evolve a bacterial strain that could tolerate the manufacturing process. It turns out that the evolved bacteria made the plastic even stronger.
Bacteria meet plastics
Plastics are formed of polymers, long chains of identical molecules linked together by chemical bonds. While they can be broken down chemically, the process is often energy-intensive and doesn’t leave useful chemicals behind. One alternative is to get bacteria to do it for us. If they’ve got an enzyme that breaks the chemical bonds of a polymer, they can often use the resulting small molecules as an energy source.
The problem has been that the chemical linkages in the polymers are often distinct from the chemicals that living things have come across in the past, so enzymes that break down polymers have been rare. But, with dozens of years of exposure to plastics, that’s starting to change, and a number of plastic-eating bacterial strains have been discovered recently.
This breakdown process still requires that the bacteria and plastics find each other in the environment, though. So a team of researchers decided to put the bacteria in the plastic itself.
The plastic they worked with is called thermoplastic polyurethane (TPU), something you can find everywhere from bicycle inner tubes to the coating on your ethernet cables. Conveniently, there are already bacteria that have been identified that can break down TPU, including a species called Bacillus subtilis, a harmless soil bacterium that has also colonized our digestive tracts. B. subtilis also has a feature that makes it very useful for this work: It forms spores.
This feature handles one of the biggest problems with incorporating bacteria into materials: The materials often don’t provide an environment where living things can thrive. Spores, on the other hand, are used by bacteria to wait out otherwise intolerable conditions, and then return to normal growth when things improve. The idea behind the new work is that B. subtilis spores remain in suspended animation while the TPU is in use and then re-activate and digest it once it’s disposed of.
In practical terms, this works because spores only reactivate once nutritional conditions are sufficiently promising. An Ethernet cable or the inside of a bike tire is unlikely to see conditions that will wake the bacteria. But if that same TPU ends up in a landfill or even the side of the road, nutrients in the soil could trigger the spores to get to work digesting it.
The researchers’ initial problem was that the manufacturing of TPU products usually involves extruding the plastic at high temperatures, which are normally used to kill bacteria. In this case, they found that a typical manufacturing temperature (130° C) killed over 90 percent of the B. subtilis spores in just one minute.
So, they started out by exposing B. subtilis spores to lower temperatures and short periods of heat that were enough to kill most of the bacteria. The survivors were grown up, made to sporulate, and then exposed to a slightly longer period of heat or even higher temperatures. Over time, B. subtilis evolved the ability to tolerate a half hour of temperatures that would kill most of the original strain. The resulting strain was then incorporated into TPU, which was then formed into plastics through a normal extrusion process.
You might expect that putting a bunch of biological material into a plastic would weaken it. But the opposite turned out to be true, as various measures of its tensile strength showed that the spore-containing plastic was stronger than pure plastic. It turns out that the spores have a water-repelling surface that interacts strongly with the polymer strands in the plastic. The heat-resistant strain of bacteria repelled water even more strongly, and plastics made with these spores was tougher still.
To simulate landfilling or litter with the plastic, the researchers placed them in compost. Even without any bacteria, there were organisms present that could degrade it; by five months in the compost, plain TPU lost nearly half its mass. But with B. subtilis spores incorporated, the plastic lost 93 percent of its mass over the same time period.
This doesn’t mean our plastics problem is solved. Obviously, TPU breaks down relatively easily. There are lots of plastics that don’t break down significantly, and may not be compatible with incorporating bacterial spores. In addition, it’s possible that some TPU uses would expose the plastic to environments that would activate the spores—something like food handling or buried cabling. Still, it’s possible this new breakdown process can provide a solution in some cases, making it worth exploring further.
