Cars are no longer just a means of transportation. They have become rolling hubs of data communication. Modern vehicles regularly transmit information wirelessly to their manufacturers^[1].

However, as cars grow “smarter,” the right to repair them is under siege^[2].

When landing on the surface of the Moon, astronauts can become spatially disoriented, which is when they lose sense of their orientation – they might not be able to tell which way is up. This disorientation can lead to fatal accidents.

Even on Earth, between 1993 and 2013^[1], spatial disorientation led to the loss of 65 aircraft, US$2.32 billion of damages and 101 deaths in the U.S.

Just like any other organism, plants can get stressed. Usually it’s conditions like heat and drought^[1] that lead to this stress, and when they’re stressed, plants might not grow as large or produce as much. This can be a problem for farmers, so many scientists have tried genetically modifying plants^[2] to be more resilient.

But plants modified for higher crop yields tend to have a lower stress tolerance^[3] because they put more energy into growth than into protection against stresses. Similarly, improving the ability of plants to survive stress often results in plants that produce less because they put more energy into protection than into growth. This conundrum makes it difficult to improve crop production^[4].

I have been studying^[5] how the plant hormone ethylene regulates growth and stress responses in plants. In a study published in July 2023^[6], my lab made an unexpected and exciting observation. We found that when seeds are germinating in darkness, as they usually are underground, adding ethylene can increase both their growth and stress tolerance.

Ethylene is a plant hormone

Plants can’t move around, so they can’t avoid stressful environmental conditions like heat and drought. They take in a variety of signals from their environment such as light and temperature that shape how they grow, develop and deal with stressful conditions. As part of this regulation, plants make various hormones^[7] that are part of a regulatory network that allows them to adapt to environmental conditions.

Ethylene^[8] was first discovered as a gaseous plant hormone over 100 years ago^[9]. Since then, research has shown that all land plants that have been studied make ethylene. In addition to controlling growth and responding to stress, it is also involved in other processes such as causing leaves to change color in the fall and stimulating fruit ripening.

Ethylene as a way to ‘prime’ plants

My lab focuses on how plants and bacteria sense ethylene and on how it interacts with other hormone pathways to regulate plant development. While conducting this research, my group made an accidental discovery^[10].

We’d been running an experiment where we had seeds germinating in a dark room. Seed germination is a critical period in a plant’s life when, under favorable conditions, the seed will transition from being dormant into a seedling.

For this experiment, we’d exposed the seeds to ethylene gas^[11] for several days to see what effect this might have. We’d then removed the ethylene. Normally, this is where the experiment would have ended. But after gathering data on these seedlings, we transferred them to a light cart. This is not something we usually do, but we wanted to grow the plants to adulthood so we could get seeds for future experiments.

Several days after placing the seedlings under light, some lab members made the unexpected and startling observation that the plants briefly gassed with ethylene were much larger^[12]. They had larger leaves as well as longer and more complex root systems than plants that had not been exposed to ethylene. These plants continued growing at a faster rate throughout their whole lifetime.

My colleagues and I wanted to know if diverse plant species showed growth stimulation when exposed to ethylene during seed germination. We found that the answer is yes^[13]. We tested the effects of short-term ethylene treatment on germinating tomato, cucumber, wheat and arugula seeds – all grew bigger.

But what made this observation unusual and exciting is that the brief ethylene treatment also increased tolerance to various stresses^[14] such as salt stress, high temperature and low oxygen conditions.

Long-term effects on growth and stress tolerance from brief exposure to a stimulus are often called priming effects. You can think of this much like priming a pump^[15], where the priming helps get the pump started easier and sooner. Studies have looked at how plants grow after priming^[16] at various ages and stages of development. But seed priming^[17] with various chemicals and stresses has probably been the most studied because it is easy to carry out, and, if successful, it can be used by farmers.

How does it work?

Since that first experiment^[18], my lab group has tried to figure out what mechanisms allow for these ethylene-exposed plants to grow larger and tolerate more stress. We’ve found a few potential explanations.

One is that ethylene priming increases photosynthesis, the process plants use to make sugars from light. Part of photosynthesis includes what is called carbon fixation^[19], where plants take CO₂ from the atmosphere and use the CO₂ molecules as the building blocks to make the sugars.

My lab group showed that there is a large increase in carbon fixation – which means the plants are taking in much more CO₂ from the atmosphere.

Correlating with the increase in photosynthesis is a large increase in carbohydrate levels throughout the plant. This includes large increases in starch^[20], which is the energy storage molecule in plants, and two sugars, sucrose^[21] and glucose^[22], that provide quick energy for the plants.

More of these molecules in the plant has been linked to both increased growth^[23] and a better ability for plants to withstand stressful conditions^[24].

Our study^[25] shows that environmental conditions during germination can have profound and long-lasting effects on plants that could increase both their size and their stress tolerance at the same time. Understanding the mechanisms for this is more important than ever and could help improve crop production to feed the world’s population.

Patterns on animal skin, such as zebra stripes and poison frog color patches, serve various biological functions, including temperature regulation^[1], camouflage^[2] and warning signals^[3]. The colors making up these patterns must be distinct and well separated to be effective. For instance, as a warning signal, distinct colors make them clearly visible to other animals. And as camouflage, well-separated colors allow animals to better blend into their surroundings.

In our newly published research in Science Advances, my student Ben Alessio^[4] and I^[5] propose a potential mechanism^[6] explaining how these distinctive patterns form – that could potentially be applied to medical diagnostics and synthetic materials.

A thought experiment can help visualize the challenge of achieving distinctive color patterns. Imagine gently adding a drop of blue and red dye to a cup of water. The drops will slowly disperse throughout the water due to the process of diffusion^[7], where molecules move from an area of higher concentration to lower concentration. Eventually, the water will have an even concentration of blue and red dyes and become purple. Thus, diffusion tends to create color uniformity.

A question naturally arises: How can distinct color patterns form in the presence of diffusion?

Movement and boundaries

Mathematician Alan Turing first addressed this question in his seminal 1952 paper, “The Chemical Basis of Morphogenesis^[8].” Turing showed that under appropriate conditions, the chemical reactions involved in producing color can interact with each other in a way that counteracts diffusion. This makes it possible for colors to self-organize and create interconnected regions with different colors, forming what are now called Turing patterns.

However, in mathematical models, the boundaries between color regions are fuzzy due to diffusion. This is unlike in nature, where boundaries are often sharp and colors are well separated.

Our team thought a clue to figuring out how animals create distinctive color patterns could be found in lab experiments on micron-sized particles, such as the cells involved in producing the colors^[10] of an animal’s skin. My work^[11] and work from other labs^[12] found that micron-sized particles form banded structures^[13] when placed between a region with a high concentration of other dissolved solutes and a region with a low concentration of other dissolved solutes.

In the context of our thought experiment, changes in the concentration of blue and red dyes in water can propel other particles in the liquid to move in certain directions. As the red dye moves into an area where it is at a lower concentration, nearby particles will be carried along with it. This phenomenon is called diffusiophoresis^[16].

You benefit from diffusiophoresis whenever you do your laundry^[17]: Dirt particles move away from your clothing as soap molecules diffuse out from your shirt and into the water.

Drawing sharp boundaries

We wondered whether Turing patterns composed of regions of concentration differences could also move micron-sized particles. If so, would the resulting patterns from these particles be sharp and not fuzzy?

To answer this question, we conducted computer simulations^[18] of Turing patterns – including hexagons, stripes and double spots – and found that diffusiophoresis makes the resulting patterns significantly more distinctive in all cases. These diffusiophoresis simulations were able to replicate the intricate patterns on the skin of the ornate boxfish and jewel moray eel, which isn’t possible through Turing’s theory alone.

Further supporting our hypothesis, our model was able to reproduce the findings of a lab study^[19] on how the bacterium E. coli moves molecular cargo within themselves. Diffusiophoresis resulted in sharper movement patterns, confirming its role as a physical mechanism behind biological pattern formation.

Because the cells that produce the pigments that make up the colors of an animal’s skin are also micron-sized, our findings suggest that diffusiophoresis may play a key role in creating distinctive color patterns more broadly in nature.

Learning nature’s trick

Understanding how nature programs specific functions can help researchers design synthetic systems that perform similar tasks.

Lab experiments have shown that scientists can use diffusiophoresis to create membraneless water filters^[20] and low-cost drug development tools^[21].

Our work suggests that combining the conditions that form Turing patterns with diffusiophoresis could also form the basis of artificial skin patches. Just like adaptive skin patterns in animals, when Turing patterns change – say from hexagons to stripes – this indicates underlying differences in chemical concentrations inside or outside the body.

Skin patches that can sense these changes could diagnose medical conditions and monitor a patient’s health by detecting changes in biochemical markers. These skin patches could also sense changes in the concentration of harmful chemicals in the environment.

The work ahead

Our simulations exclusively focused on spherical particles, while the cells that create pigments in skin come in varying shapes. The effect of shape on the formation of intricate patterns remains unclear.

Furthermore, pigment cells move in a complicated biological environment. More research is needed to understand how that environment inhibits motion and potentially freezes patterns in place.

Besides animal skin patterns, Turing patterns are also crucial to other processes such as embryonic development^[22] and tumor formation^[23]. Our work suggests that diffusiophoresis may play an underappreciated but important role in these natural processes.

Studying how biological patterns form will help researchers move one step closer to mimicking their functions in the lab – an age-old endeavor^[24] that could benefit society.

Water pollution is a growing concern globally, with research estimating^[1] that chemical industries discharge 300-400 megatonnes^[2] (600-800 billion pounds) of industrial waste into bodies of water each year.

As a team of materials scientists^[3], we’re working on an engineered “living material” that may be able to transform chemical dye pollutants from the textile industry^[4] into harmless substances.

Water pollution^[5] is both an environmental and humanitarian issue that can affect ecosystems and human health alike. We’re hopeful that the materials we’re developing could be one tool available to help combat this problem.

Engineering a living material

The “engineered living material^[6]” our team has been working on contains programmed bacteria^[7] embedded in a soft hydrogel material. We first published a paper showing the potential effectiveness of this material in Nature Communications^[8] in August 2023.

The hydrogel^[9] that forms the base of the material has similar properties to Jell-O – it’s soft and made mostly of water. Our particular hydrogel is made from a natural and biodegradable seaweed-based polymer called alginate^[10], an ingredient common in some foods^[11].

The alginate hydrogel provides a solid physical support for bacterial cells, similar to how tissues support cells^[12] in the human body. We intentionally chose this material so that the bacteria we embedded could grow and flourish.

We picked the seaweed-based alginate as the material base because it’s porous and can retain water. It also allows the bacterial cells^[15] to take in nutrients from the surrounding environment.

After we prepared the hydrogel, we embedded photosynthetic – or sunlight-capturing – bacteria called cyanobacteria^[16] into the gel.

The cyanobacteria embedded in the material still needed to take in light and carbon dioxide to perform photosynthesis^[17], which keeps them alive. The hydrogel was porous enough to allow that, but to make the configuration as efficient as possible, we 3D-printed^[18] the gel into custom shapes – grids and honeycombs. These structures have a higher surface-to-volume ratio that allow more light, CO₂ and nutrients to come into the material.

The cells were happy in that geometry. We observed higher cell growth and density over time in the alginate gels in the grid or honeycomb structures when compared with the default disc shape.

Cleaning up dye

Like all other bacteria, cyanobacteria has different genetic circuits^[19], which tell the cells what outputs to produce. Our team genetically engineered^[20] the bacterial DNA^[21] so that the cells created a specific enzyme called laccase^[22].

The laccase enzyme produced by the cyanobacteria works by performing a chemical reaction with a pollutant that transforms it into a form that’s no longer functional. By breaking the chemical bonds, it can make a toxic pollutant nontoxic. The enzyme is regenerated at the end of the reaction, and it goes off to complete more reactions.

Once we’d embedded these laccase-creating cyanobacteria into the alginate hydrogel, we put them in a solution made up of industrial dye pollutant^[23] to see if they could clean up the dye. In this test, we wanted to see if our material could change the structure of the dye so that it went from being colored to uncolored. But, in other cases, the material could potentially change a chemical structure to go from toxic to nontoxic.

The dye we used, indigo carmine^[24], is a common industrial wastewater pollutant usually found in the water near textile plants – it’s the main pigment in blue jeans. We found that our material took all the color out of the bulk of the dye over about 10 days.

This is good news, but we wanted to make sure that our material wasn’t adding waste to polluted water by leaching bacterial cells. So, we also engineered the bacteria to produce a protein that could damage the cell membrane of the bacteria – a programmable kill switch.

The genetic circuit was programmed to respond to a harmless chemical, called theophylline^[25], commonly found in caffeine, tea and chocolate. By adding theophylline, we could destroy bacterial cells at will.

The field of engineered living materials is still developing, but this just means there are plenty of opportunities to develop new materials with both living and nonliving components.