New ultrathin materials can pull climate-warming CO2 from the air

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The three most influential gases towards climate change are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. Of these, CO2 is present in the largest amount by far. Its contributions to the greenhouse effect from burning fossil fuels and other combustion processes were noted as far back as 1896 by physical chemist and Nobel Prize winner Svante Arrhenius. Methane and N2O have a greater potential to trap heat, but there is so little of them in the atmosphere that CO2's overall effect is stronger. Planting trees can help remove it because they use CO2 and sunlight to make their own food source via photosynthesis. Reducing the amount made from industry will also help, but regulations are not always easy to come by. What if there was a filter or type of "flypaper" to take CO2 out as fast as it is being made? There just might be.

Image from Pixabay

A special type of metallic material called a MAX phase was discovered naturally in the 1960s, but it took scientists until the 1990s to make them artificially. The name comes from how the three parts are labeled.

• M = elements like the metals vanadium and titanium
• A = elements like aluminum or silicon
• X = carbon alone or carbon plus nitrogen

In the right combination, these form sheets that are one molecule thick for each of the three components. 

Image adapted from Science News Explores

The thinnest material in the world, however, is only one layer (molecule) thick. It is called graphene (from the word graphite because it is pure carbon). It was discovered in 1962 but ignored until 2004, when it was "rediscovered" and investigated. Graphene was found to be an important material for semiconductors, electronics, electric batteries, and composites. But because its chemistry was so simple, it had little other use.

Image of graphene sheet. Each dot represents a carbon atom (Wikipedia)

Because this single layer material has such different properties than the multi-layered MAX phases, scientists hoped to find something even more useful by removing the A element from a MAX phase in order to create a two-layered material they called a MXene (pronounced "max-een"). They did that with chemically etching away aluminum with hydrofluoric acid.

Diagram from Advanced Materials, 2011

Scientists like Michael Naguib at Tulane University have shown that MXenes can be made with many combinations of elements (about 50 now exist), and their properties can also be changed fairly easily. One chemical treatment gives a MXene the ability to soak up CO2. Raw MXenes are a black powder which can dissolve in hydrogen peroxide. That can be used as a paint or later dried in sheets. The amount of surface area from the powder is amazing. Just one gram (1/400 ounce) of MXene has the same surface area as a football field! That gives it a lot of filtering capacity in a small painted patch.

Microscopic photograph of the first MXene (Advanced Materials, 2011)

If MXene is mixed with cellulose (plant cell wall fiber) then an elastomer (rubberizing agent) and dried, it can be used in sheets to filter gas molecules, such as CO2 or methane from natural gas or chimney flue gases. Professor Per Persson, a materials scientist from the Swedish Linköping University, stated that such filters could be used on the top of industrial chimneys to prevent the exhaust from delivering CO2 into the atmosphere. 

Making a gas filtration MXene (figure adapted from Macromolecules, 2022)

One problem in the use of MXenes is the cost of the raw materials such as vanadium ($20/pound), titanium ($0.35/pound), and molybdenum ($5–$15/pound). Another is cleaning the CO2 off a MXene sheet after it has become saturated. Rinsing the sheets with hydrogen under high temperatures removes CO2, which can then be used as starting material for animal feed or methanol. The good news is that MXenes have many more uses:

• Desalination (trapping energy of the sun to purify water by evaporation)
• Waste water treatment (floating on water to evaporate it with 84% efficiency with sun energy)
• Battery technology and energy storage (higher charging rates than lithium-ion batteries; charging batteries faster)
• Nanogenerators (harvesting frictional energy from moving muscles to convert it into electric power)
• Conductive coatings (retaining conductivity even under heavy stretching and bending)
• Sensors and chemical noses (detecting ammonia and acetone, which are indicators of ulcers and diabetes, with lower traces than sensors now used in medical diagnostics)

A vibrating pill could help treat obesity, pig study finds

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They say that weight loss is a matter of taking in fewer calories and burning as many as possible. A sort of supply and demand issue. But is the demand in one's head or stomach, and can that be controlled? Some diets purport stopping eating a meal when one feels 80% full, to allow for the body to catch up to itself and register a real feeling of fullness. But, many people can't control themselves, and so they continue to eat. It can be called making a pig out of oneself, but pigs might prove to be the solution to weight loss after all! Read on.

Image from Pixabay

Why do we feel full when we eat? Surrounding our stomach is a network of nerves called IGLEs (intraganglionic laminar endings). These are connected to nerve clusters called ganglia which run through two layers of smooth muscle outside of the stomach lining. IGLEs detect mechanical pressure from the stomach and send signals to the muscles to loosen or tighten, in order to allow food in or to squeeze it through to the small intestine. When they detect enough pressure, it suggests to the brain that the stomach is filled with food, and it then tells the body to stop.

IGLE nerve in a cross-section of stomach (adapted from Frontiers in Physiology)

If the goal is to force a person to eat less, then giving them a sensation of a full stomach is needed. Drugs are costly and potentially dangerous. Putting in a balloon was done as early as 1979. In 2017, researchers reviewed studies on the effects of inserting a balloon then filling it with saline (salt water) solution directly into the stomach. Lean people have a stomach volume of 1,000 milliliters (4 cups), and obese people's stomach has a volume of 1,920 milliliters (8 cups). So, various makers of stomach balloons allow for them to be inflated to 200, 400, 600, or 800 mL to take up stomach volume. Most balloons are inserted and filled under anesthesia, which adds another layer of complication and cost.

Stomach balloon insertion and inflation (Mayo Clinic)

The 2017 review found mixed results. Whether patients had diet treatment, and whether the balloon was a certain size both affected the results in a 3-month study.

• balloon only (300 mL): 3.2 kg lost + 4.1 kg
• balloon plus diet: 5.1 kg lost + 4.7 kg
• diet only: 6.9 kg lost + 5.9 kg
• no treatment: 0.6 kg lost + 2.5 kg

Researchers at Harvard University wondered whether stimulating the muscles around the stomach lining could be done and what effect that would have. Electrical stimulation was probably not a feasible technique. As far back as 1966, it was known that vibrations like those used in physical therapy massage, when applied to the body, can cause muscles to contract. So, Professor Shriya Srinivasan and a team of scientists at Harvard University developed a small device called a Vibrating Ingestible BioElectronic Stimulator (VIBES) pill which patients could swallow before eating. As the pill rested against the inside of the stomach, its vibrations might cause the brain to think stomach muscles were reacting to a volume of food in the stomach. The VIBES pill is 31 mm (1.2 inches) long and 9.8 mm (0.38 inches) wide.

VIBES pill inside the stomach of a pig (Science Advances 2023)

It has a motor and battery. The pill is coated with gelatin that holds down a pin; when stomach acid dissolves the gelatin, the pin moves to the on position to start the vibration. The vibrating waves trick the IGLEs nerves to send a false signal of an expanding stomach to the vagus nerve and then to the medulla in the brain. When the brain has the illusion that the stomach is full, it then reduces the amount of a "hunger hormone" sent to the body. 

Faking fullness with the VIBES pill (Science Advances, 2023)

Srinivasan's team confirmed what the VIBES pill did as follows. First, they inflated the pig's stomach with an endoscope to 30%, 60%, and 90% of its maximal volume. When they held those volumes for 3 minutes, they recorded electrical impulses from the vagus nerve. They compared those data with what vibrations at 60 Hz, 80 Hz, and 100 Hz did to the nerve. The results were virtually identical.

Top: results showing vagus nerve signal with endoscopic inflation of stomach

Bottom: results showing vagus nerve signal with vibration (from Science Advances, 2023)

Srinivasan and coworkers tested the pill on a dozen Yorkshire pigs 4-6 months old. After two weeks, and 108 meals, the experimental pigs ate less than those given a placebo. Pigs with VIBES pills ate 58.1% of food provided, while the control pigs ate 78.4% of food given to them, a significant difference.

Three pigs were tested further. They had the VIBES treatment, then none, then back on VIBES. Researchers measured the percentage of the meal that they ate during those times. How much they ate returned to normal right away without the pill (left graph, white area), which suggested eating behavior was dependent on the pill's vibrations. They also measured how much weight four pigs gained with and without the VIBES pill. The graph on the right shows less weight gained with VIBES treatment, matching the smaller amount of food eaten.

Data from Science Advances, 2023)

The concept of the VIBES pill is that people will take it before every meal, as the pigs did, and it will eventually find its way out of the body in the feces. No damage was seen to the stomach lining after Srinivasan's experiments were over, even though the pill is right at the maximum size allowed for humans to swallow it. The data from Harvard University will be used to set up human clinical trials. Pigs were chosen for this experiment because their stomach is similar to a human's, not just because of the stereotype of obese people eating like pigs.

Tiny living robots made from human cells surprise scientists

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In 1920, Czech playwright Karel Čapek wrote a science-fiction play called "R.U.R.", which stood for Rossum's Universal Robots, and which was set in the year 2000. This was the first time the word robot had been used. These robots were more like androids, purely organic beings, instead of metallic walking computers. However, they looked like the tin man from the Wizard of Oz. Engineers have since been working on creating microscopic robotic machines to work at the cellular level. But in recent years, scientists have also gone back to the RUR days of organic robots. They are microscopic and composed of living cells. How does that work?

Robots in the play "R.U.R." (Wikipedia)

The benefit of such devices, if they were to exist today, is thought to be in drug delivery, surgery, diagnosis, monitoring of diseases like diabetes, and even cleaning the oceans. In 1959, Nobel Prize winner Richard Feynman even conceived of using tiny machines to more efficiently create new chemicals by directly manipulating atoms. 

What if it microscopic robots didn't require mechanical parts and were disposable? In 2020, teams at the  University of Vermont Advanced Computing Core and the Center for Regenerative and Developmental Biology at Tufts University developed organic microscopic robots. The Vermont group created computer models of potential cell clusters of skin and heart cells from the African frog Xenopus laevis. Skin cell properties were used to help build proposed structures in many shapes because skin cells are made to do that. Heart muscle cells flex, and their properties were added to the "evolutionary algorithm" in the software to determine various functions like movement. The idea was to see which shapes and configurations of these cells would theoretically work together in clusters to create functional organic robots.

100 computer models for functional cell clusters

(adapted from Proceedings of the National Academy of Sciences)

(red=heart cells, blue=skin cells)

After many computer trials, the most successful models were handed off to Tufts U. Scientists there then peeled apart cells from Xenopus embryos and put them in groups. The cells clumped together to form a cluster of many cells. Then, with tiny tweezers, the researchers poked and prodded the clusters into the shapes of the computer models. Each one took several hours to build, but eventually these became the living, moving "xenobots", named after the frog source. 

Computer model and colorized xenobot cell cluster (University of Vermont)

Just under a millimeter (0.04 inches) wide, they are about 3 times the size of a period in Times New Roman 12-point font. Tufts U researchers observed them move about in Petri dishes for days or weeks until their internal energy supplies ran out. Movement is caused by hair-like projections called cilia, which move like paddles. Some xenobots had holes in them designed to carry material, but others without holes spontaneously pushed pellets of material together as they moved.

Xenobot spinning, moving, joining other xenobots in a Petri dish (YouTube)

When xenobots were damaged even to the point of being cut nearly in half, they repaired themselves.

Clip from YouTube

But even more amazing is that these clumps of cells were able to reproduce. Instead of just splitting each cell in the cluster, they worked together to gather other cells in the area. Those new clusters became new xenobots that do the same at the "parents". See what the designer has to say:

From YouTube shorts

More recently, in November 2023,  the Tufts U researchers have created "anthrobots", which are cell cluster robots made from human cells, specifically adult lung cells. Instead of 3-4 days, these took 7 days before they showed movement. Also,  from 2,281 of these, about half consistently don't move at all even after 3 weeks, even though they have cilia. The thing is, since they were from lung tissue, the cilia formed on the inside of the clump like it was the lining of the trachea. By adjusting the chemical composition of the medium they lived on in the Petri dish, the researchers changed that to the outside.

Cilia shown in yellow (from Advanced Science)

Anthrobots tend to have 4 types of motion: circular, linear, curvilinear, and eclectic. Examples are shown below from the researchers paper.

From Advanced Science, 2023

Anthrobots come in 8 unique cluster shapes, and each is correlated with a certain amount of cilia. What's more, they follow a scratched line in the Petri dish, which might be useful in later medical research if these are used to follow tissue cuts for repair to take place. See below microscopic tracking of the scratch outlined in yellow and the anthrobot path in pink.

From Advanced Science, 2023)

Taken to the next level, anthrobots have also been shown to fix damaged nerve tissue by forming "superbot" bridges. In the photos below, the top one shows a bridge formed in a cut. The bottom picture simply shows the superbot in red and nerve tissue in green.

From Advanced Science, 2023

Considering how important it is to repair nerve tissue, which normally is next to impossible, the usefulness of these organic robots is pretty clear.

Here's a nice 5-minute video that summarizes this blog article.

Plants can call for help

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Plants are immobile; they can't run away from danger. But they have evolved various ways to protect themselves, for example, with sharp thorns or thick tree bark. Some plants even produce chemicals that are foul-tasting to invaders, which makes them less tasty and more likely to be avoided. Some make toxic substances, and others make chemicals that slow the growth rate of plant eaters. But some have found a way to call for help against predators. How do they do that?

Wasp about to lay eggs inside a caterpillar attacking a plant (Science News Explores)

In the 1980s, University of Amsterdam scientists Marcel Dicke and Maurice Sabelis studied lima bean plants and their enemy, spider mites. When spider mites Tetranychus urticae attacked the plants, the damaged leaves in the top of the plant released 4 chemicals that are different from the ones released when leaves are mechanically damaged by other means. These four were specific "infochemicals" which female predatory mites (P-mites) use to locate and eat the spider mite and its eggs. The infochemicals were specific to attract the P-mites!

Orange predatory mite eating green spider mite (Univ. of CA Integrated Pest Management Program)

Swiss entomologist Thomas Degen in 2012 inoculated corn plant tops with an armyworm caterpillars using a spring-loaded "bazooka" and waited for them to feast on the corn. After that, he measured two things. Growing 6 types of corn in a lab, he placed a plastic bag over the top of the corn where the worms were eating, and using a pair of pumps, Degen could suck out air containing volatile chemicals (volatile means they evaporate easily into the surrounding air) that the plants made and replace it with fresh air. 

Collecting volatile chemicals from plants (Science News Explores)

Then, he analyzed the volatiles and found 36 chemicals were released. Six corn varieties each made different amounts, with the largest amount 15 times more concentrated than the lowest corn variety. And infested plants made more chemicals than controls with no infestations. He also noticed that the size of the worm larvae were smaller when the chemical concentration was higher. 

 

Bazooka inoculator design (Wiseman et al., 1980)

 

Inoculating plants with larvae using a "bazooka" (YouTube)

Degen noticed that in his early experiments in a lab (not the field), his infested plants made 9 times more chemicals than the non-infested controls in the lab. In the field, however, they made only 2.5 times more. One difference was that his lab plants were much younger (9-12 days vs 33-49 days). This got him and others to thinking why the younger plants would do that.

More recently, Lei Wang at the University of Bern in Switzerland has also studied corn to see what chemicals are released, and he saw a similar thing. Older plants don't make as much anti-predator warning chemicals. 

Chemicals from the left plant under attack trigger warning to right plant (modified from Science News Explores)

Nobody knows why young plant leaves do this better than old ones. They might be predisposed to doing it because the plant is still growing instead of at rest, and it may be more vulnerable then. New leaves are on the top of the plants, so the mechanism for chemical release might have evolved to take advantage of wind there. It's a pretty sensitive issue for growing plants, too. Ian Baldwin of the Max Planck Institute for Chemical Ecology in Germany showed as far back as 1983 that even if 7% of leaf damage was sustained by one plant, that was enough to send out a chemical signal in 1.5-2 days to warn neighboring plants. 

Middle plant signaling chemically to its neighbors that it is under attack. 

Note the spots on its leaves indicating insect larvae eating them. (From npr.org)

What is known is that some plants recognize chemicals in the saliva of an attacking insect larva, and that triggers the defensive release of the volatile plant chemicals. This is not limited to one species protecting its neighbors of the same species. Richard Karban (University of California - Davis) showed that damaging sagebrush can cause nearby tobacco plants to produce defensive chemicals. He toned down the name "plant communication" from one to another to a more casual term of "plant eavesdropping" to describe what may actually be happening. This might be because the signaling operates only within 50-100 cm (20-40 inches) from the plant. 

One benefit from these studies was expressed by Wang. Perhaps science could develop crops that are better at doing this and "smarter" to resist predators. 

For an historical perspective on learning how plants defend themselves, check out this link.