Sun-Min Yu, UMass Amherst and Steve Granick, UMass Amherst

Your cells constantly generate and conduct electricity that runs through your body to perform various functions. One such example of this bioelectricity is the nerve signals that power thoughts in your brain. Others include the cardiac signals that control the beating of your heart, along with other signals that tell your muscles to contract.

As bioengineers, we became interested in the epithelial cells that make up human skin and the outer layer of people’s intestinal tissues. These cells aren’t known to be able to generate bioelectricity. Textbooks state that they primarily act as a barrier against pathogens and poisons; epithelial cells are thought to do their jobs passively, like how plastic wrapping protects food against spoilage.

To our surprise, however, we found that wounded epithelial cells can propagate electrical signals across dozens of cells that persist for several hours. In this newly published research, we were able to show that even epithelial cells use bioelectricity to coordinate with their neighbors when the emergency of an injury demands it. Understanding this unexpected twist in how the body operates may lead to improved treatments for wounds.

Discovering a new source of bioelectricity

Don’t laugh: Our interest in this topic began with a gut feeling. Think of how your skin heals itself after a scratch. Epithelial cells may look silent and calm, but they’re busy coordinating with each other to extrude damaged cells and replace them with new ones. We thought bioelectric signals might orchestrate this, so our intuition told us to search for them.

Almost all the vendors we contacted to obtain the instrument we needed to test our idea warned us not to try these experiments. Only one company agreed with reluctance. “Your experiment won’t work,” they insisted. If we made the attempt and found nothing worthwhile to study, they feared it would make their product look bad.

But we did our experiments anyway – with tantalizing results.

We grew a layer of epithelial cells on a chip patterned with what’s called a microelectrode array – dozens of tiny electric wires that measure where bioelectric signals appear, how strong the signals are and how fast they travel from spot to spot. Then, we used a laser to zap a wound in one location and searched for electric signals on a different part of the cell layer.

Several hours of recording confirmed our intuition: When faced with the emergency need to repair themselves, bioelectrical signals appear when epithelial cells need a quick way to communicate over long distances.

We found that wounded epithelial cells can send bioelectric signals to neighboring cells over distances more than 40 times their body length with voltages similar to those of neurons. The shapes of these voltage spikes are also like those of neurons except about 1,000 times slower, indicating they might be a more primitive form of intercellular communication over long distances.

Powering the bioelectric generator

But how do epithelial cells generate bioelectricity?

We hypothesized that calcium ions might play a key role. Calcium ions show up prominently in any good biology textbook’s list of major molecules that help cells function. Since calcium ions regulate the forces that contract cells, a function necessary to remove damaged cells after wounding, we hypothesized that calcium ions ought to be critical to bioelectricity.

To test our theory, we used a molecule called EDTA that tightly binds to calcium ions. When we added EDTA to the epithelial cells and so removed the calcium ions, we found that the voltage spikes were no longer present. This meant that calcium ions were likely necessary for epithelial cells to generate the bioelectric signals that guide wound healing.

We then blocked the ion channels that allow calcium and other positively charged ions to enter epithelial cells. As a result, the frequency and strength of the electrical signals that epithelial cells produce were reduced. These findings suggest that while calcium ions may play a particularly crucial role in allowing epithelial cells to produce bioelectricity, other molecules may also matter.

Further research can help identify those other ion channels and pathways that allow epithelial cells to generate bioelectricity.

Improving wound healing

Our discovery that epithelial cells can electrically speak up during a crisis without compromising their primary role as a barrier opens doors for new ways to treat wounds.

Previous work from other researchers had demonstrated that it’s possible to enhance wound healing in skin and intestinal tissues by electrically stimulating them. But these studies used electrical frequencies many times higher than what we’ve found epithelial cells naturally produce. We wonder whether reevaluating and refining optimal electric stimulation conditions may help improve biomedical devices for wound healing.

Further down the road of possibility, we wonder whether electrically stimulating individual cells might offer even more healing potential. Currently, researchers have been electrically stimulating the whole tissue to treat injury. If we could direct these electrical signals to go specifically to where a remedy is needed, would stimulating individual cells be even more effective at treating wounds?

Our hope is that these findings could become a classic case of curiosity-driven science that leads to useful discovery. While our dream may carry a high risk of failure, it also offers potentially high rewards.

Sun-Min Yu, Postdoctoral Research Fellow in Polymer Science and Engineering, UMass Amherst and Steve Granick, Professor of Polymer Science and Engineering, UMass Amherst

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Jiaxin Zhong, Penn State and Yun Jing, Penn State

What if you could listen to music or a podcast without headphones or earbuds and without disturbing anyone around you? Or have a private conversation in public without other people hearing you?

Our newly published research introduces a way to create audible enclaves – localized pockets of sound that are isolated from their surroundings. In other words, we’ve developed a technology that could create sound exactly where it needs to be.

The ability to send sound that becomes audible only at a specific location could transform entertainment, communication and spatial audio experiences.

What is sound?

Sound is a vibration that travels through air as a wave. These waves are created when an object moves back and forth, compressing and decompressing air molecules.

The frequency of these vibrations is what determines pitch. Low frequencies correspond to deep sounds, like a bass drum; high frequencies correspond to sharp sounds, like a whistle.

Controlling where sound goes is difficult because of a phenomenon called diffraction – the tendency of sound waves to spread out as they travel. This effect is particularly strong for low-frequency sounds because of their longer wavelengths, making it nearly impossible to keep sound confined to a specific area.

Certain audio technologies, such as parametric array loudspeakers, can create focused sound beams aimed in a specific direction. However, these technologies will still emit sound that is audible along its entire path as it travels through space.

The science of audible enclaves

We found a new way to send sound to one specific listener: through self-bending ultrasound beams and a concept called nonlinear acoustics.

Ultrasound refers to sound waves with frequencies above the human hearing range, or above 20 kHz. These waves travel through the air like normal sound waves but are inaudible to people. Because ultrasound can penetrate through many materials and interact with objects in unique ways, it’s widely used for medical imaging and many industrial applications.

In our work, we used ultrasound as a carrier for audible sound. It can transport sound through space silently – becoming audible only when desired. How did we do this?

Normally, sound waves combine linearly, meaning they just proportionally add up into a bigger wave. However, when sound waves are intense enough, they can interact nonlinearly, generating new frequencies that were not present before.

This is the key to our technique: We use two ultrasound beams at different frequencies that are completely silent on their own. But when they intersect in space, nonlinear effects cause them to generate a new sound wave at an audible frequency that would be heard only in that specific region.

Crucially, we designed ultrasonic beams that can bend on their own. Normally, sound waves travel in straight lines unless something blocks or reflects them. However, by using acoustic metasurfaces – specialized materials that manipulate sound waves – we can shape ultrasound beams to bend as they travel. Similar to how an optical lens bends light, acoustic metasurfaces change the shape of the path of sound waves. By precisely controlling the phase of the ultrasound waves, we create curved sound paths that can navigate around obstacles and meet at a specific target location.

The key phenomenon at play is what’s called difference frequency generation. When two ultrasonic beams of slightly different frequencies, such as 40 kHz and 39.5 kHz, overlap, they create a new sound wave at the difference between their frequencies – in this case 0.5 kHz, or 500 Hz, which is well within the human hearing range. Sound can be heard only where the beams cross. Outside of that intersection, the ultrasound waves remain silent.

This means you can deliver audio to a specific location or person without disturbing other people as the sound travels.

Advancing sound control

The ability to create audio enclaves has many potential applications.

Audio enclaves could enable personalized audio in public spaces. For example, museums could provide different audio guides to visitors without headphones, and libraries could allow students to study with audio lessons without disturbing others.

In a car, passengers could listen to music without distracting the driver from hearing navigation instructions. Offices and military settings could also benefit from localized speech zones for confidential conversations. Audio enclaves could also be adapted to cancel out noise in designated areas, creating quiet zones to improve focus in workplaces or reduce noise pollution in cities.

This isn’t something that’s going to be on the shelf in the immediate future. For instance, challenges remain for our technology. Nonlinear distortion can affect sound quality. And power efficiency is another issue – converting ultrasound to audible sound requires high-intensity fields that can be energy intensive to generate.

Despite these hurdles, audio enclaves present a fundamental shift in sound control. By redefining how sound interacts with space, we open up new possibilities for immersive, efficient and personalized audio experiences.

Jiaxin Zhong, Postdoctoral Researcher in Acoustics, Penn State and Yun Jing, Professor of Acoustics, Penn State

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Kate Kilpatrick, The Conversation

In Philadelphia, fatal overdoses are the No. 3 cause of death after heart disease and cancer. That’s been the case each year since 2016, except in 2020 and 2021 when COVID-19 deaths outpaced overdose deaths. The vast majority of fatal overdoses in Philly involve the synthetic opioid fentanyl.

Data on overdose deaths in Philly in 2024 is not yet available. However, new research shows that drug deaths are dropping in all 50 states and the District of Columbia.

Still, opioid overdose deaths in Philadelphia remain what public health researchers call a “wicked problem.” These are complex, multifaceted challenges that are constantly changing and have no clear solution.

The Conversation U.S. published several articles over the past year that sought to untangle various threads of this wicked problem in Philadelphia. Here are four essential reads.

1. Overdose deaths down – but still high

Philadelphia’s 7% drop in fatal overdoses in 2023 is notable. Still, opioid use disorder claimed the lives of over 1,100 residents that year – more than three times as many lives as 10 years earlier.

Ben Cocchiaro, assistant clinical professor of family medicine and community health at Drexel University, explains one likely reason why overdoses in Philly spiked in the first place: the unpredictable potency of the city’s street fentanyl supply.

“Local drug-testing efforts found as much as a fiftyfold difference in potency between bags of fentanyl that appear identical,” Cocchiaro writes. “It’s like cracking a beer and not knowing whether drinking it will get you mildly buzzed or send you to the graveyard.

2. ‘Tranq’ wounds proliferate

Forensic testing has revealed that over 90% of street heroin and fentanyl samples in Philly now contain xylazine, an animal tranquilizer with no FDA-approved use in humans.

Rachel McFadden is an emergency room nurse at the Hospital of the University of Pennsylvania and also works at a walk-in clinic in North Philadelphia that serves people who use drugs. Before xylazine, she says, most of the wounds she saw were minor skin infections that she treated with antibiotics.

But that changed in late 2019.

“Participants at the wound care clinic started to come in with a different kind of wound. They were filled with black and yellow dead tissue and tunneled deep into the skin. They were not wounds from infection but rather from tissue death or necrosis,” McFadden writes.

McFadden explains the protocol for treating these serious wounds, which involves removing the dead tissue, administering antimicrobials and antibiotics for the inflammation and infection, and keeping the wound moist and dressed. She says it’s also important that people’s other basic needs, including food, shelter and a place to shower, are met so they can properly heal.

3. A new treatment for withdrawal

The combination of fentanyl and xylazine in Philly street opioids has made withdrawal symptoms far more excruciating than those experienced by heroin users in the past.

That’s according to Kory London, an emergency room doctor and associate professor of emergency medicine at Thomas Jefferson University. London says these withdrawal symptoms lead many patients who are addicted to opioids to discharge themselves from the hospital before their treatment is complete.

“Patients with opioid use disorder will often do whatever they can to stay out of the hospital due to fear of withdrawal,” he writes. “Asking how withdrawal symptoms are managed, therefore, is often their first priority when hospitalized. We see this even when they have conditions that require complicated and time-sensitive treatments.

Beginning in 2022, London and colleagues began experimenting with new approaches to treating “tranq” dope withdrawal in Philly. The new protocols reduced the likelihood of these patients leaving early by more than half – from 10% to just under 4%.

4. Industrial chemical BTMPS has unknown risks

Philadelpha’s public health department has issued health alerts about xylazine and medetomidine becoming more prevalent in the city’s street opioid supply.

Researchers Karli Hochstatter and Fernando Montero at Columbia University are part of a team that tests fentanyl samples collected in the Kensington neighborhood of Philadelphia each month. Those tests have turned up a new adulterant: an industrial chemical known as BTMPS that is used in making plastics.

“We first detected BTMPS in Philadelphia in June 2024. We found it in two of the eight samples – 25% – that we collected that month. By November 2024, 12 of 22 samples – or 55% – contained BTMPS,” Hochstatter and Montero write. “What’s more, the amount, or concentration, of this industrial chemical in the drug samples often exceeded the amount of fentanyl.”

BTMPS has not been studied in humans, but rat studies reveal exposure – at far lower levels than what is found in the Philly fentanyl samples – can cause heart defects, serious eye damage and death.

This story is a roundup of articles from The Conversation’s archives.

Read more of our stories about Philadelphia.

Kate Kilpatrick, Philadelphia Editor, The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.