Aerosols are tiny droplets or solid particles suspended in the air, and they surround us constantly. Some are large enough to see, such as springtime pollen, while others, like viruses that circulate during flu season, are far too small for the human eye. A few can even be sensed by taste, including the fine salt particles carried on ocean winds.

PhD student Andrea Stöllner, a member of the Waitukaitis and Muller groups at ISTA, studies the behavior of ice crystals that form within clouds. To better understand how these crystals gather charge, she works with model aerosols made from very small, transparent silica spheres.

Together with former ISTA postdoc Isaac Lenton, ISTA Assistant Professor Scott Waitukaitis and collaborators, Stöllner has created a technique that uses two intersecting laser beams to trap, stabilize, and electrically charge a single silica particle. This setup opens the door to new investigations into how cloud electrification begins and how lightning is sparked.

Building a Stable Laser Trap

Andrea Stöllner works at a large laboratory table filled with polished metal components. Green laser beams cross the space, bouncing from mirror to mirror. A slow, steady hissing noise comes from the table, similar to air leaking from a tire. “It’s an anti-vibration table,” Stöllner says, pointing out how it protects the lasers from small disturbances in the room or from nearby equipment, which is essential for extremely precise measurements.

The beams travel through a series of aligned parts before converging into two narrow streams that enter a sealed container. Where they meet, they create a concentrated point of light that can hold small particles in place. These “optical tweezers” keep drifting aerosols suspended long enough to study them. When a particle is caught, a bright green flash appears, confirming that the trap has successfully grabbed a glowing, perfectly round aerosol particle.

“The first time I caught a particle, I was over the moon,” Stöllner recalls of her breakthrough moment two years earlier, just before Christmas. “Scott Waitukaitis and my colleagues rushed into the lab and took a short glimpse at the captured aerosol particle. It lasted exactly three minutes, then the particle was gone. Now we can hold it in that position for weeks.”

Achieving this level of control took nearly four years. The experiment began with an earlier version developed by Lenton. “Originally, our setup was built to just hold a single particle, analyze its charge, and figure out how humidity changes its charges,” Stöllner says. “But we never came this far. We found out that the laser we are using is itself charging our aerosol particles.”

How Lasers Knock Electrons Loose

Stöllner and her colleagues discovered that the particles gain charge through a “two-photon process.”

Aerosol particles usually carry almost no net charge, with electrons (negatively charged entities) orbiting within each atom. Laser beams are made of photons (particles of light traveling at the speed of light). When two photons strike the particle at the same moment and are absorbed together, they can remove a single electron. Losing that electron gives the particle one unit of positive charge, and with continued exposure, the particle becomes progressively more positively charged.

For Stöllner, identifying this process has opened new opportunities. “We can now precisely observe the evolution of one aerosol particle as it charges up from neutral to highly charged and adjust the laser power to control the rate.”

As the charge builds, the particle also begins to lose charge again in sudden, short bursts. These spontaneous discharges hint at behaviors that may occur naturally in the atmosphere.

High above, cloud particles may undergo similar cycles of charge buildup and release.

Searching for Lightning’s First Spark

Thunderstorm clouds contain a mix of ice crystals and larger chunks of ice. As these collide, they trade electrical charges. Over time, the cloud becomes so electrically imbalanced that lightning forms. One idea is that the earliest spark of a lightning bolt could arise directly from charged ice crystals. Yet the exact mechanism behind lightning formation remains unresolved. Other theories propose that cosmic rays start the process because the charged particles they produce accelerate within existing electric fields. According to Stöllner, the current scientific view is that, in both scenarios, the electric field inside clouds appears too weak to initiate lightning on its own.

“Our new setup allows us to explore the ice crystal theory by closely examining a particle’s charging dynamics over time,” Stöllner explains. While natural ice crystals in clouds are much larger than the silica particles used in the lab, the team hopes that understanding these small-scale effects will reveal the larger processes that create lightning. “Our model ice crystals are showing discharges and maybe there’s more to that. Imagine if they eventually create super tiny lightning sparks — that would be so cool,” she adds with a smile.

“Most living organisms, including humans, cannot survive even briefly in the vacuum of space,” says lead author Tomomichi Fujita of Hokkaido University. “However, the moss spores retained their vitality after nine months of direct exposure. This provides striking evidence that the life that has evolved on Earth possesses, at the cellular level, intrinsic mechanisms to endure the conditions of space.”

Asking Whether Moss Could Survive Beyond Earth

Fujita began exploring the possibility of “space moss” while studying plant evolution. He was impressed by mosses’ ability to colonize the harshest environments on Earth. “I began to wonder: could this small yet remarkably robust plant also survive in space?”

To investigate, Fujita’s team exposed Physcomitrium patens, also known as spreading earthmoss, to a simulated space environment featuring intense UV radiation, extremely high and low temperatures, and vacuum-like conditions.

Testing Moss Structures Under Extreme Stress

The researchers compared three moss forms: protenemata (juvenile moss), brood cells (stress-induced stem cells), and sporophytes (encapsulated spores). They aimed to identify which structure had the greatest likelihood of enduring space.

“We anticipated that the combined stresses of space, including vacuum, cosmic radiation, extreme temperature fluctuations, and microgravity, would cause far greater damage than any single stress alone,” says Fujita.

Their experiments showed that UV radiation posed the biggest threat, and sporophytes clearly outperformed the other structures. Juvenile moss did not survive strong UV exposure or extreme temperatures. Brood cells fared better but still fell short. By contrast, the encased spores showed ~1,000x greater UV tolerance and remained capable of germination even after enduring −196°C for more than a week or 55°C for an entire month.

Why Encased Spores Withstand Harsh Conditions

The team concluded that each spore’s surrounding structure likely absorbs harmful UV light and provides physical and chemical shielding. They suggest that this protective feature may have helped ancient bryophytes, the plant group that includes mosses, move from water to land roughly 500 million years ago and survive repeated mass extinctions.

To determine whether this adaptation held up in real space, the researchers sent sporophytes into orbit.

Launching Moss to the ISS for a Real-World Trial

In March 2022, hundreds of sporophytes traveled to the ISS aboard the Cygnus NG-17 spacecraft. After their arrival, astronauts mounted the samples on the exterior of the station, exposing them to space for 283 days. The specimens later returned to Earth on SpaceX CRS-16 in January 2023 and were brought back to the lab for analysis.

“We expected almost zero survival, but the result was the opposite: most of the spores survived,” says Fujita. “We were genuinely astonished by the extraordinary durability of these tiny plant cells.”

Strong Survival and Healthy Return to Earth

More than 80% of the spores endured the full trip, and all but 11% of those survivors successfully germinated in the laboratory. Measurements of chlorophyll showed normal levels for nearly all pigments, except for a 20% drop in chlorophyll a, a light-sensitive compound. Despite this reduction, the spores remained healthy.

“This study demonstrates the astonishing resilience of life that originated on Earth,” says Fujita.

The team also used their data to build a mathematical model estimating how long the spores might last in similar conditions. Their calculation suggested a potential survival span of up to 5,600 days, or about 15 years, although they stressed that more data is needed for a firm conclusion.

Implications for Growing Life Beyond Earth

The researchers hope these findings support future studies on how extraterrestrial soils might sustain plant life and encourage efforts to use mosses in developing agricultural systems for off-world environments.

“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” says Fujita. “I hope that our moss research will serve as a starting point.”

This work was supported by DX scholarship Hokkaido University, JSPS KAKENHI, and the Astrobiology Center of National Institutes of Natural Sciences.

A research team at Cincinnati Children’s has uncovered a shared and unexpected repair process that may help the body recover from several kinds of muscle damage. The findings were published online on Nov. 21, 2025, in Current Biology. The project was led by first author Gyanesh Tripathi, PhD, and corresponding author Michael Jankowski, PhD, who oversees the Research Division in Cincinnati Children’s Department of Anesthesia and serves as Associate Director of Basic Science Research for the Pediatric Pain Research Center.

The newly identified mechanism involves macrophages, a type of immune cell. These cells are usually known for acting like tiny cleanup crews that remove bacteria, dead cells, and other unwanted material.

A Neuron-Like Repair Signal

“The biggest surprise about this was finding that a macrophage has a synaptic-like property that delivers an ion to a muscle fiber to facilitate its repair after an injury,” Jankowski says. “It’s literally like the way a neuron works, and it’s working in an extremely fast synaptic-like fashion to regulate repair.”

Scientists have long known that macrophages respond to muscle injury by releasing cytokines and chemokines that create inflammation, influence pain, and help drive the growth and regeneration of muscle fibers.

Searching for Pain Relief Leads to a Different Breakthrough

The research team originally aimed to uncover ways to ease pain during recovery after surgery. They were looking for clues that could eventually reduce the need for pain medications that carry significant side effects.

Although they did not find a new approach for pain relief, they identified a process that makes muscle repair occur more quickly. This discovery may support the development of future treatments for muscle wasting and acute injuries. The findings also suggest that macrophages might eventually serve as specialized “delivery vehicles” for cell-based therapies targeting a wider range of medical conditions.

“These are infiltrating macrophages, a very specific type. They’re not ones already residing in the tissue. These come in after damage occurs,” Jankowski says.

Real-Time Evidence of Rapid Muscle Activation

In experiments that used mouse models of two different injury types, researchers examined how macrophages interact with the myofibers that form muscle tissue. They were even able to capture key moments of this activity as it occurred.

By using brief bursts of a designer chemical to activate the macrophages, the team observed these immune cells forming synaptic-like contacts with myofibers. The macrophages then released calcium ions directly to the muscle fibers, accelerating early stages of healing. Within 10 to 30 seconds, the researchers measured bursts of electrical activity inside the damaged muscle.

“This occurs in a very rapid fashion. You can activate the macrophage and make the muscle twitch subtly almost immediately,” Jankowski says.

Healing Effects Seen in Both Injury and Disease Models

The same type of macrophage-driven signaling also helped mice with disease-like muscle damage. After recognizing the injury, the immune cells gathered at the site and triggered waves of activity in the muscle fibers. After 10 days, mice that received this treatment had substantially more new muscle fibers than mice in the control group.

“A similar synaptic-like response worked in both scenarios,” Jankowski says.

Next Research Steps

More work is needed to determine whether human macrophages behave the same way when muscle is injured. If they do, researchers will still need to learn how to guide or control the process in ways that could be safely used as therapy.

The team is also interested in an unexpected outcome: although the infiltrating macrophages sped up healing, they did not appear to reduce acute pain. Understanding why this occurs may help explain why about 20% of children who undergo surgery continue to experience lingering pain afterward.

Looking ahead, the researchers want to explore whether macrophages can deliver other helpful signals or materials to muscle cells.

Cincinnati Children’s co-authors include Adam Dourson, PhD, Fabian Montecino-Morales, PhD, Jennifer Wayland, MS, Sahana Khanna, Megan Hofmann, Hima Bindu Durumutla, MS, Thirupugal Govindarajan, PhD, Luis Queme, MD, PhD, and Douglas Millay, PhD. The Bioanalysis and Imaging Facility at Cincinnati Children’s also contributed to the work.

Funding for this research came from grants provided by the National Institutes of Health (R01NS105715, R01NS113965, R61/R33AR078060, R01AR068286, R01AG082697) and the Cincinnati Children’s Hospital Research Foundation.