Tech
Cracks in flexible electronics run deeper than expected: Study points to potential fix
From health monitors and smartwatches to foldable phones and portable solar panels, demand for flexible electronics is growing rapidly. But the durability of those devices—their ability to stand up to thousands of folds, flexes and rolls—is a significant concern.
New research by engineers from Brown University has revealed surprising details about how cracks form in multilayer flexible electronic devices. The team shows that small cracks in a device’s fragile electrode layer can drive deeper, more destructive cracks into the tougher polymer substrate layer on which the electrodes sit. The work overturns a long-held assumption that polymer substrates usually resist cracking.
“The substrate in flexible electronic devices is a bit like the foundation in your house,” said Nitin Padture, a professor of engineering at Brown and corresponding author of the study published in npj Flexible Electronics. “If it’s cracked, it compromises the mechanical integrity of the entire device. This is the first clear evidence of cracking in a device substrate caused by a brittle film on top of it.”
The layers used in flexible electronics have specific jobs. The top layer conducts electricity across the surface to keep the device running. That layer is usually made of special ceramic oxide materials because they are transparent and also good conductors, which is essential for things like display screens, sensors and solar cells. But ceramics are brittle and prone to cracking, so the substrate’s job is to add some toughness. Substrates are generally made from polymer materials that are highly flexible and resist cracking.
While using these materials to make flexible solar cells, Anush Ranka, a postdoctoral researcher at Brown who performed the work as a Ph.D. student in materials science, became increasingly curious about the mechanism by which fatigue can degrade performance. He decided to take a closer look at the cracking processes.
For the study, Ranka made small experimental devices using various types of ceramic electrodes and polymer substrates. He then subjected them to bending tests and used a powerful electron microscope to examine the cracks. In places where he found cracks in the ceramic layer, he used a focused ion beam—a kind of nanoscale sandblaster—to etch away the ceramic and reveal the substrate directly beneath a ceramic crack.
The work showed that cracks in the ceramic layer often drive deeper cracks into the substrate. The effect occurred across ceramic and polymer combinations, suggesting this is a common—and surprising—failure mechanism in flexible electronics.
Once cracks form deep in the polymer, the researchers say, they become permanent structural defects. With repeated bending, these cracks widen, misalign or fill with debris, which then prevents the ceramic crack faces from reconnecting. That causes electrical resistance to increase and device performance to degrade.

Working with Haneesh Kesari, a Brown engineering professor who specializes in theoretical and applied mechanics, and solid mechanics Ph.D. student Sayaka Kochiyama, the researchers analyzed this cracking problem. They showed that a mismatch in the elastic properties of the two layers was driving the deep cracking phenomenon in the substrate. Understanding the cracking mechanism led the team toward a potential fix: Adding a third layer of material between the ceramic and the substrate that mitigates the elastic mismatch.
“We created a design map that identified hundreds of polymers that—with the correct thickness—could potentially mitigate this elastic mismatch and prevent cracking in a wide range of electrode-substrate combinations,” said Padture, who leads Brown’s Initiative for Sustainable Energy. “Using this design map, we were able to choose a specific polymer for the third layer and experimentally demonstrate the feasibility of our approach.”
The researchers are hopeful that the design diagram will make for more durable devices. Just as important, however, is the discovery that cracks do indeed affect polymer substrates—a fact that was not apparent before this research.
“We’re essentially solving a problem people didn’t know they had,” Padture said. “We think this could significantly improve the cyclic life of flexible devices.”
More information:
Anush Ranka et al, Cracking in polymer substrates for flexible electronic devices and its mitigation, npj Flexible Electronics (2025). DOI: 10.1038/s41528-025-00470-z
Citation:
Cracks in flexible electronics run deeper than expected: Study points to potential fix (2025, September 9)
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Tech
A Billionaire-Backed Startup Wants to Grow ‘Organ Sacks’ to Replace Animal Testing
As the Trump administration phases out the use of animal experimentation across the federal government, a biotech startup has a bold idea for an alternative to animal testing: nonsentient “organ sacks.”
Bay Area-based R3 Bio has been quietly pitching the idea to investors and in industry publications as a way to replace lab animals without the ethical issues that come with living organisms. That’s because these structures would contain all of the typical organs—except a brain, rendering them unable to think or feel pain. The company’s long-term goal, cofounder Alice Gilman says, is to make human versions that could be used as a source of tissues and organs for people who need them.
For Immortal Dragons, a Singapore-based longevity fund that’s invested in R3, the idea of replacement is a core strategy for human longevity. “We think replacement is probably better than repair when it comes to treating diseases or regulating the aging process in the human body,” says CEO Boyang Wang. “If we can create a nonsentient, headless bodyoid for a human being, that will be a great source of organs.”
For now, R3 is aiming to make monkey organ sacks. “The benefit of using models that are more ethical and are exclusively organ systems would be that testing can be meaningfully more scalable,” Gilman says. (R3’s name comes from the philosophy in animal research known as the three R’s—replacement, reduction, and refinement—developed by British scientists William Russell and Rex Burch in 1959 to promote humane experimentation.)
New drugs are often tested in monkeys before they’re given to human participants in clinical trials. For instance, monkeys were critical during the Covid-19 pandemic for testing vaccines and therapeutics. But they’re also an expensive resource, and their numbers are dwindling in the US after China banned the export of nonhuman primates in 2020.
Animal rights activists have long pushed to end research on monkeys, and one of the seven federally funded primate research facilities across the country has signaled it would consider shutting down and transitioning into a sanctuary amid growing pressure. The US Centers for Disease Control and Prevention is also winding down monkey research, part of a bigger trend across the government to reduce reliance on animal testing.
As a result, Gilman says, there aren’t enough research monkeys left in the US to allow for necessary research if another pandemic threat emerges. Enter organ sacks.
Organ sacks would in theory offer advantages over existing organs-on-chips or tissue models, which lack the full complexity of whole organs, including blood vessels.
Gilman says it’s already possible to create mouse organ sacks that lack a brain, though she and cofounder John Schloendorn deny that R3 has made them. (For the record, Gilman doesn’t like the term “brainless” to describe the organ sacks. “It’s not missing anything, because we design it to only have the things we want,” she says.) Gilman and Schloendorn would not say how exactly they plan to create the monkey and human organ sacks, but said they are exploring a combination of stem-cell technology and gene editing.
It’s plausible that organ sacks could be grown from induced pluripotent stem cells, says Paul Knoepfler, a stem cell biologist at the University of California, Davis. These stem cells come from adult skin cells and are reprogrammed to an embryonic-like state. They have the potential to form into any cell or tissue in the body and have been used to create embryo-like structures that resemble the real thing. By editing these stem cells, scientists could disable genes needed for brain development. The resulting embryo could then be incubated until it grows into organized organ structures.
Tech
A Mysterious Numbers Station Is Broadcasting Through the Iran War
“Tavajoh! Tavajoh! Tavajoh!” a man’s voice announces, before going on to narrate a string of numbers in no apparent order, slowly and rhythmically. After nearly two hours, the calls of “Attention!” in Persian stop, only to resume again hours later.
The broadcast has been playing twice a day on a shortwave frequency since the start of the US-Israel attack on Iran on February 28.
According to Priyom, an organization which tracks and analyses global military and intelligence use of shortwave radio, using established radio-location techniques, the broadcast was first heard as the US bombing of Iran began. It has since played on the 7910 kHz shortwave frequency like clockwork—at 02.00 UTC and again at 18.00 UTC.
Over the weekend, Priyom said it had identified the likely origin of the broadcast. Using multilateration and triangulation techniques, the group traced the signal to a shortwave transmission facility inside a US military base in Böblingen, southwest of Stuttgart, Germany.
The site lies within a restricted training area between Panzer Kaserne and Patch Barracks, with technical operations possibly linked to the US army’s 52nd Strategic Signal Battalion, headquartered nearby.
That identification narrows the field, but it does not reveal who is behind the transmissions or who they are meant for.
The two-hour-long transmission is divided into five to six segments, each lasting up to 20 minutes. Each opens with “Tavajoh!” before shifting into a string of numbers in Persian, sometimes punctuated with an English word or two. Five days into the broadcast, radio jammers were heard attempting to block the frequency. The following day, the transmission shifted to a different frequency—7842 kHz.
Radio communication experts believe the broadcast is likely part of a Cold War–era system known as number stations.
The Return of the Numbers
Number stations are shortwave radio broadcasts that play strings of numbers or codes that sound random—like the one now heard in Iran. “It is an encrypted radio message used by foreign intelligence services, often as part of a complex operation by intelligence agencies and militaries,” says Maris Goldmanis, a Latvian historian and avid numbers stations researcher.
Number stations are most commonly associated with espionage. “For intelligence agencies, it is important to communicate with their spies to gather intelligence,” says John Sipher, a former US intelligence officer who served 28 years in the CIA’s National Clandestine Service. “This is not always possible in person due to political constraints or conflict. This is where number stations come in.”
While the use of number stations can be traced back to the First World War, they gained prominence during the US-Soviet Cold War. As espionage grew more sophisticated, governments used automated voice transmissions of coded numbers to communicate with agents, Goldmanis says. Citing declassified KGB and CIA documents, he adds that number stations were widely used during this period, often as Morse code transmissions and, in many cases, as two-way communications, with agents reporting back using their own shortwave transmitters.
“Nowadays, you have various satellite and encrypted communications technologies,” Sipher says. “But during the Cold War and even before that, governments had to find ways to do this without being noticed, and broadcasting coded messages was one way to communicate with your assets discreetly.”
The apparent randomness of the numbers means they can be understood only with a codebook, Sipher adds. “Nobody can make heads or tails of it or understand what it says unless you have the codebook that can give you hints to decrypt the code,” he says, noting that such systems must be set up and coordinated in advance.
A Signal Without a Sender
While the likely origin of the signal may now be clearer, its purpose and intended recipient remain unknown.
Because the broadcasts are encrypted and designed to be covert, those details may remain unclear for years, Goldmanis says. The structured nature of the transmission—its fixed schedule and consistent use of frequencies—further suggests it is part of a planned operation.
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