Tag Archives: Florida Atlantic University (FAU)

A nanoscale look inside a blacktip shark’s skeleton reveals ‘sharkitecture’

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It’s usually sharkskin that excites scientific attention. (It has nanoscale structures that endow it with special properties See: “Characterization of shark skin properties and biomimetic replication” published July 15, 2024). This May 20, 2025 news item on ScienceDaily shifts attention to the skeleton,

Sharks have been evolving for more than 450 million years, developing skeletons not from bone, but from a tough, mineralized form of cartilage. These creatures are more than just fast swimmers — they’re built for efficiency. Their spines act like natural springs, storing and releasing energy with each tailbeat, allowing them to move through the water with smooth, powerful grace.

Now, scientists are peering inside shark skeletons at the nanoscale, revealing a microscopic “sharkitecture” that helps these ancient apex predators withstand extreme physical demands of constant motion.

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A May 20, 2025 Florida Atlantic University (FAU) news release (also on EurekAlert) by Gisele Galoustian, which originated the news item, delves further into the topic, Note: Links have been removed,

Using synchrotron X-ray nanotomography with detailed 3D imaging and in-situ mechanical testing, researchers from the Charles E. Schmidt College of Science and the College of Engineering and Computer Science at Florida Atlantic University, in collaboration with the German Electron Synchrotron (DESY) in Germany, and NOAA [US National Oceanic and Atmospheric Administration] Fisheries, have mapped the internal structure of blacktip sharks (Carcharhinus limbatus) in unprecedented detail.

Results of the study, published in ACS ]American Chemical Society] Nano, reveal two distinct regions within the blacktip shark’s mineralized cartilage: the corpus calcareum and the intermediale. Though both are composed of densely packed collagen and bioapatite, their internal structures differ significantly. In both regions, mineralized plates are arranged in porous structures, reinforced by thick struts that help the skeleton withstand strain from multiple directions – a critical adaptation for sharks, whose constant swimming places repeated stress on the spine.

At the nanoscale, researchers observed tiny needle-like bioapatite crystals – a mineral also found in human bones – aligned with strands of collagen. This intricate structure gives the cartilage surprising strength while still allowing flexibility.

Even more intriguing, the team discovered helical fiber structures primarily based on collagen – suggesting a sophisticated, layered design optimized to prevent cracks from spreading. Under strain, fiber and mineral networks work together to absorb and distribute force, contributing to the shark’s resilience and flexibility.

“Nature builds remarkably strong materials by combining minerals with biological polymers, such as collagen – a process known as biomineralization. This strategy allows creatures like shrimp, crustaceans and even humans to develop tough, resilient skeletons,” said Vivian Merk, Ph.D., senior author and an assistant professor in the FAU Department of Chemistry and Biochemistry, the FAU Department of Ocean and Mechanical Engineering, and the FAU Department of Biomedical Engineering. “Sharks are a striking example. Their mineral-reinforced spines work like springs, flexing and storing energy as they swim. By learning how they build such tough yet adaptable skeletons, we hope to inspire the design of next-generation materials.” 

In experiments applying mechanical stress on microscopic samples of shark vertebrae, the researchers observed tiny deformations – less than a micrometer – after a single cycle of applied pressure. Interestingly, fractures only occurred after a second round of loading and were contained within a single mineralized plane, hinting at the material’s built-in resistance to catastrophic failure.

“After hundreds of millions of years of evolution, we can now finally see how shark cartilage works at the nanoscale – and learn from them,” said Marianne Porter, Ph.D., co-author and an associate professor in the FAU Department of Biological Sciences. “We’re discovering how tiny mineral structures and collagen fibers come together to create a material that’s both strong and flexible, perfectly adapted for a shark’s powerful swimming. These insights could help us design better materials by following nature’s blueprint.”

Found in warm, shallow coastal waters worldwide, blacktip sharks are sleek, fast-swimming predators known for their incredible agility and speed, reaching up to 20 miles per hour. One of the most striking behaviors they display is leaping and spinning out of the water, often during feeding – an acrobatic move that adds to their mystique.

This research not only enhances the biomechanical understanding of shark skeletons but also offers valuable insights for engineers and materials scientists. 

“This research highlights the power of interdisciplinary collaboration,” said Stella Batalama, Ph.D., dean of the College of Engineering and Computer Science. “By bringing together engineers, biologists and materials scientists, we’ve uncovered how nature builds strong yet flexible materials. The layered, fiber-reinforced structure of shark cartilage offers a compelling model for high-performance, resilient design, which holds promise for developing advanced materials from medical implants to impact-resistant gear.”

Study co-authors are Dawn Raja Somu, Ph.D.; and Steven A. Soini, Ph.D., two recent Ph.D. graduates from the Charles E. Schmidt College of Science; Ani Briggs, a former undergraduate student in the FAU College of Engineering and Computer Science; Kritika Singh, Ph.D.; and Imke Greving, Ph.D., scientists at outstations of the DESY PETRA III X-ray light source operated by Helmholtz-Zentrum Hereon; and Michelle Passerotti, Ph.D., a research fish biologist at NOAA Fisheries.

This research was supported by a National Science Foundation (NSF) grant awarded to Merk; an NSF CAREER Award, awarded to Porter; and seed funding from the FAU College of Engineering and Computer Science and FAU Sensing Institute (I-SENSE). The acquisition of a transmission electron microscope was supported by a United States Department of Defense instrumentation/equipment grant awarded to Merk.

Caption: An X-ray nanotomography reconstruction of the intermedial cartilage of a blacktip shark. The colors indicate the thickness of the struts, with red representing thicker areas and blue indicating thinner ones. Credit: Florida Atlantic University

Here’s a link to and a citation for the paper,

A Nanoscale View of the Structure and Deformation Mechanism of Mineralized Shark Vertebral Cartilage by Dawn Raja Somu, Steven A. Soini, Ani Briggs, Kritika Singh, Imke Greving, Marianne Porter, Michelle Passerotti, and Vivian Merk. ACS Nano 2025, 19, 14, 14410–14421 DOI: https://doi.org/10.1021/acsnano.5c02004 Published April 7, 2025 Copyright © 2025 American Chemical Society

This paper is behind a paywall.

Fortify wood with eco-friendly nano-iron

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An April 28, 2025 news item on ScienceDaily announced an investigation into making wood stronger,

Scientists and engineers are developing high-performance materials from eco-friendly sources like plant waste. A key component, lignocellulose — found in wood and many plants — can be easily collected and chemically modified to improve its properties.

By using these kinds of chemical changes, researchers are creating advanced materials and new ways to design and build sustainably. With about 181.5 billion tons of wood produced globally each year, it’s one of the largest renewable material sources.

Researchers from the College of Engineering and Computer Science at Florida Atlantic University, and collaborators from the University of Miami and Oak Ridge National Laboratory, wanted to find out if adding extremely hard minerals at the nanoscale could make the walls of wood cells stronger — without making the wood heavy, expensive or bad for the environment. Few studies have investigated how treated wood performs at different scales, and none have successfully strengthened entire pieces of wood by incorporating inorganic minerals directly into the cell walls.

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Caption: A microCT image that shows the distribution of the iron mineral in the wood cell wall (in turquoise). Credit: Florida Atlantic University

An April 28, 2025 Florida Atlantic University (FAU) news release (also on EurekAlert) by Gisele Galoustian, which originated the news item, provides more technical details about the work,Note: Links have been removed,

The research team focused on a special type of hardwood known as ring-porous wood, which comes from broad-leaf trees like oak, maple, cherry and walnut. These trees feature large, ring-shaped vessels in the wood that transport water from the roots to the leaves. For the study, researchers used red oak, a common hardwood in North America, and introduced an iron compound into the wood through a simple chemical reaction. By mixing ferric nitrate with potassium hydroxide, they created ferrihydrite, an iron oxide mineral commonly found in soil and water.

Results of the study, published in the journal ACS Applied Materials and Interfaces, revealed that a simple, cost-effective chemical method using a safe mineral called nanocrystalline iron oxyhydroxide can strengthen the tiny cell walls within wood while adding only a small amount of extra weight. Although the internal structure became more durable, the wood’s overall behavior – such as how it bends or breaks – remained largely unchanged. This is likely because the treatment weakened the connections between individual wood cells, affecting how the material holds together on a larger scale.

The findings suggest that, with the right chemical treatment, it’s possible to enhance the strength of wood and other plant-based materials without increasing their weight or harming the environment. These bio-based materials could one day replace traditional construction materials like steel and concrete in applications such as tall buildings, bridges, furniture and flooring.

“Wood, like many natural materials, has a complex structure with different layers and features at varying scales. To truly understand how wood bears loads and eventually fails, it’s essential to examine it across these different levels,” said Vivian Merk, Ph.D., senior author and an assistant professor in the FAU Department of Ocean and Mechanical Engineering, the FAU Department of Biomedical Engineering, and the FAU Department of Chemistry and Biochemistry within the Charles E. Schmidt College of Science. “To test our hypothesis – that adding tiny mineral crystals to the cell walls would strengthen them – we employed several types of mechanical testing at both the nanoscale and the macroscopic scale.”

For the study, researchers used advanced tools like atomic force microscopy (AFM) to examine the wood at a very small scale, allowing them to measure properties such as stiffness and elasticity. Specifically, they employed a technique called AM-FM (Amplitude Modulation – Frequency Modulation), which vibrates the AFM tip at two different frequencies. One frequency generates detailed surface images, while the other measures the material’s elasticity and stickiness. This method gave them a precise view of how the wood’s cell walls were altered after being treated with minerals.

Additionally, the team conducted nanoindentation tests within a scanning electron microscope (SEM), where tiny probes were pressed into the wood to measure its response to force in different areas. To round out their analysis, they performed standard mechanical tests – such as bending both untreated and treated wood samples – to evaluate their overall strength and how they broke under stress.

“By looking at wood at different levels – from the microscopic structures inside the cell walls all the way up to the full piece of wood – we were able to learn more about how to chemically improve natural materials for real-world use,” said Merk.

This combination of small- and large-scale testing helped the researchers understand how the treatment affected both the fine details inside the cell walls and the overall strength of the wood.

“This research marks a significant advancement in sustainable materials science and a meaningful stride toward eco-friendly construction and design,” said Stella Batalama, Ph.D., the dean of the College of Engineering and Computer Science. “By reinforcing natural wood through environmentally conscious and cost-effective methods, our researchers are laying the groundwork for a new generation of bio-based materials that have the potential to replace traditional materials like steel and concrete in structural applications. The impact of this work reaches far beyond the field of engineering – it contributes to global efforts to reduce carbon emissions, cut down on waste, and embrace sustainable, nature-inspired solutions for everything from buildings to large-scale infrastructure.”

Study co-authors are Steven A. Soini, a Ph.D. graduate from the FAU College of Engineering and Computer Science and FAU Charles E. Schmidt College of Science; Inam Lalani, a Ph.D. student at the University of Miami; Matthew L. Maron, Ph.D., a doctoral researcher at the University of Miami; David Gonzalez, a graduate student in the FAU College of Engineering and Computer Science; Hassan Mahfuz, Ph.D., a professor in the FAU Department of Ocean and Mechanical Engineering; and Neus Domingo-Marimon, Ph.D., senior R&D staff scientist, group leader for the Functional Atomic Force Microscopy Group, Oak Ridge National Laboratory.

Here’s a link to and a citation for the paper,

Multiscale Mechanical Characterization of Mineral-Reinforced Wood Cell Walls by Steven A. Soini, Inam Lalani, Matthew L.Maron, David Gonzalez, Hassan Mahfuz, Neus Domingo-Marimon, Vivian Merk. ACS Applied Materials & Interfaces (ACS Appl. Mater. Interfaces) 2025, 17, 12, 18887–18896 DOI: https://doi.org/10.1021/acsami.4c22384 Published: March 12, 2025 Copyright © 2025 American Chemical Society

This paper is behind a paywall.

One last comment, I love wordplay, so I offer my thanks to Gisele Galoustian for the news release’s original title “‘Wood you believe it?’ FAU engineers fortify wood with eco-friendly nano-iron.”

Pioneering bionic hand achieves human-like grip on plush toys, water bottles, and other everyday objects

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This is not a biohybrid hand incorporating ‘living’ and nonliving materials but a hybrid hand incorporating soft and rigid robotics.

A March 5, 2025 news item on ScienceDaily announces work from Johns Hopkins University (JHU; Maryland, US),

Johns Hopkins University engineers have developed a pioneering prosthetic hand that can grip plush toys, water bottles, and other everyday objects like a human, carefully conforming and adjusting its grasp to avoid damaging or mishandling whatever it holds.

The system’s hybrid design is a first for robotic hands, which have typically been too rigid or too soft to replicate a human’s touch when handling objects of varying textures and materials. The innovation offers a promising solution for people with hand loss and could improve how robotic arms interact with their environment.

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A March 5, 2025 Johns Hopkins University (JHU) news release (also on EurekAlert), which originated the news item, provides more details, Note: Links have been removed,

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“The goal from the beginning has been to create a prosthetic hand that we model based on the human hand’s physical and sensing capabilities—a more natural prosthetic that functions and feels like a lost limb,” said Sriramana Sankar, a Johns Hopkins biomedical engineer who led the work. “We want to give people with upper-limb loss the ability to safely and freely interact with their environment, to feel and hold their loved ones without concern of hurting them.”

The device, developed by the same Neuroengineering and Biomedical Instrumentations Lab that in 2018 created the world’s first electronic “skin” with a humanlike sense of pain [mentioned here in a December 14, 2018 posting], features a multifinger system with rubberlike polymers and a rigid 3D-printed internal skeleton. Its three layers of tactile sensors, inspired by the layers of human skin, allow it to grasp and distinguish objects of various shapes and surface textures, rather than just detect touch. Each of its soft air-filled finger joints can be controlled with the forearm’s muscles, and machine learning algorithms focus the signals from the artificial touch receptors to create a realistic sense of touch, Sankar said. “The sensory information from its fingers is translated into the language of nerves to provide naturalistic sensory feedback through electrical nerve stimulation.”

In the lab, the hand identified and manipulated 15 everyday objects, including delicate stuffed toys, dish sponges, and cardboard boxes, as well as pineapples, metal water bottles, and other sturdier items. In the experiments, the device achieved the best performance compared with the alternatives, successfully handling objects with 99.69% accuracy and adjusting its grip as needed to prevent mishaps. The best example was when it nimbly picked up a thin, fragile plastic cup filled with water, using only three fingers without denting it.

“We’re combining the strengths of both rigid and soft robotics to mimic the human hand,” Sankar said. “The human hand isn’t completely rigid or purely soft—it’s a hybrid system, with bones, soft joints, and tissue working together. That’s what we want our prosthetic hand to achieve. This is new territory for robotics and prosthetics, which haven’t fully embraced this hybrid technology before. It’s being able to give a firm handshake or pick up a soft object without fear of crushing it.”

To help amputees regain the ability to feel objects while grasping, prostheses will need three key components: sensors to detect the environment, a system to translate that data into nerve-like signals, and a way to stimulate nerves so the person can feel the sensation, said Nitish Thakor, a Johns Hopkins biomedical engineering professor who directed the work.

The bioinspired technology allows the hand to function this way, using muscle signals from the forearm, like most hand prostheses. These signals bridge the brain and nerves, allowing the hand to flex, release, or react based on its sense of touch. The result is a robotic hand that intuitively “knows” what it’s touching, much like the nervous system does, Thakor said.

“If you’re holding a cup of coffee, how do you know you’re about to drop it? Your palm and fingertips send signals to your brain that the cup is slipping,” Thakor said. “Our system is neurally inspired—it models the hand’s touch receptors to produce nervelike messages so the prosthetics’ ‘brain,’ or its computer, understands if something is hot or cold, soft or hard, or slipping from the grip.”

While the research is an early breakthrough for hybrid robotic technology that could transform both prosthetics and robotics, more work is needed to refine the system, Thakor said. Future improvements could include stronger grip forces, additional sensors, and industrial-grade materials.

“This hybrid dexterity isn’t just essential for next-generation prostheses,” Thakor said. “It’s what the robotic hands of the future need because they won’t just be handling large, heavy objects. They’ll need to work with delicate materials such as glass, fabric, or soft toys. That’s why a hybrid robot, designed like the human hand, is so valuable—it combines soft and rigid structures, just like our skin, tissue, and bones.” 

Other authors include Wen-Yu Cheng of Florida Atlantic University; Jinghua Zhang, Ariel Slepyan, Mark M. Iskarous, Rebecca J. Greene, Rene DeBrabander, and Junjun Chen of Johns Hopkins; and Arnav Gupta of the University of Illinois Chicago.

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Here’s a link to and a citation for the paper,

A natural biomimetic prosthetic hand with neuromorphic tactile sensing for precise and compliant grasping by Sriramana Sankar, Wen-Yu Cheng, Jinghua Zhang, Ariel Slepyan, Mark M. Iskarous, Rebecca J. Greene, Rene DeBrabander, Junjun Chen, Arnav Gupta, and Nitish V. Thakor. Science Advances 5 Mar 2025 Vol 11, Issue 10 DOI: 10.1126/sciadv.adr9300

This paper is open access.

A bioengineered robot hand with its own nervous system: machine/flesh and a job opening

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A November 14, 2017 news item on phys.org announces a grant for a research project which will see engineered robot hands combined with regenerative medicine to imbue neuroprosthetic hands with the sense of touch,

The sense of touch is often taken for granted. For someone without a limb or hand, losing that sense of touch can be devastating. While highly sophisticated prostheses with complex moving fingers and joints are available to mimic almost every hand motion, they remain frustratingly difficult and unnatural for the user. This is largely because they lack the tactile experience that guides every movement. This void in sensation results in limited use or abandonment of these very expensive artificial devices. So why not make a prosthesis that can actually “feel” its environment?

That is exactly what an interdisciplinary team of scientists from Florida Atlantic University and the University of Utah School of Medicine aims to do. They are developing a first-of-its-kind bioengineered robotic hand that will grow and adapt to its environment. This “living” robot will have its own peripheral nervous system directly linking robotic sensors and actuators. FAU’s College of Engineering and Computer Science is leading the multidisciplinary team that has received a four-year, $1.3 million grant from the National Institute of Biomedical Imaging and Bioengineering of the [US] National Institutes of Health for a project titled “Virtual Neuroprosthesis: Restoring Autonomy to People Suffering from Neurotrauma.”

A November14, 2017 Florida Atlantic University (FAU) news release by Gisele Galoustian, which originated the news item, goes into more detail,

With expertise in robotics, bioengineering, behavioral science, nerve regeneration, electrophysiology, microfluidic devices, and orthopedic surgery, the research team is creating a living pathway from the robot’s touch sensation to the user’s brain to help amputees control the robotic hand. A neuroprosthesis platform will enable them to explore how neurons and behavior can work together to regenerate the sensation of touch in an artificial limb.

At the core of this project is a cutting-edge robotic hand and arm developed in the BioRobotics Laboratory in FAU’s College of Engineering and Computer Science. Just like human fingertips, the robotic hand is equipped with numerous sensory receptors that respond to changes in the environment. Controlled by a human, it can sense pressure changes, interpret the information it is receiving and interact with various objects. It adjusts its grip based on an object’s weight or fragility. But the real challenge is figuring out how to send that information back to the brain using living residual neural pathways to replace those that have been damaged or destroyed by trauma.

“When the peripheral nerve is cut or damaged, it uses the rich electrical activity that tactile receptors create to restore itself. We want to examine how the fingertip sensors can help damaged or severed nerves regenerate,” said Erik Engeberg, Ph.D., principal investigator, an associate professor in FAU’s Department of Ocean and Mechanical Engineering, and director of FAU’s BioRobotics Laboratory. “To accomplish this, we are going to directly connect these living nerves in vitro and then electrically stimulate them on a daily basis with sensors from the robotic hand to see how the nerves grow and regenerate while the hand is operated by limb-absent people.”

For the study, the neurons will not be kept in conventional petri dishes. Instead, they will be placed in  biocompatible microfluidic chambers that provide a nurturing environment mimicking the basic function of living cells. Sarah E. Du, Ph.D., co-principal investigator, an assistant professor in FAU’s Department of Ocean and Mechanical Engineering, and an expert in the emerging field of microfluidics, has developed these tiny customized artificial chambers with embedded micro-electrodes. The research team will be able to stimulate the neurons with electrical impulses from the robot’s hand to help regrowth after injury. They will morphologically and electrically measure in real-time how much neural tissue has been restored.

Jianning Wei, Ph.D., co-principal investigator, an associate professor of biomedical science in FAU’s Charles E. Schmidt College of Medicine, and an expert in neural damage and regeneration, will prepare the neurons in vitro, observe them grow and see how they fare and regenerate in the aftermath of injury. This “virtual” method will give the research team multiple opportunities to test and retest the nerves without any harm to subjects.

Using an electroencephalogram (EEG) to detect electrical activity in the brain, Emmanuelle Tognoli, Ph.D., co-principal investigator, associate research professor in FAU’s Center for Complex Systems and Brain Sciences in the Charles E. Schmidt College of Science, and an expert in electrophysiology and neural, behavioral, and cognitive sciences, will examine how the tactile information from the robotic sensors is passed onto the brain to distinguish scenarios with successful or unsuccessful functional restoration of the sense of touch. Her objective: to understand how behavior helps nerve regeneration and how this nerve regeneration helps the behavior.

Once the nerve impulses from the robot’s tactile sensors have gone through the microfluidic chamber, they are sent back to the human user manipulating the robotic hand. This is done with a special device that converts the signals coming from the microfluidic chambers into a controllable pressure at a cuff placed on the remaining portion of the amputated person’s arm. Users will know if they are squeezing the object too hard or if they are losing their grip.

Engeberg also is working with Douglas T. Hutchinson, M.D., co-principal investigator and a professor in the Department of Orthopedics at the University of Utah School of Medicine, who specializes in hand and orthopedic surgery. They are developing a set of tasks and behavioral neural indicators of performance that will ultimately reveal how to promote a healthy sensation of touch in amputees and limb-absent people using robotic devices. The research team also is seeking a post-doctoral researcher with multi-disciplinary experience to work on this breakthrough project.

Here’s more about the job opportunity from the FAU BioRobotics Laboratory job posting, (I checked on January 30, 2018 and it seems applications are still being accepted.)

Post-doctoral Opportunity

Dated Posted: Oct. 13, 2017

The BioRobotics Lab at Florida Atlantic University (FAU) invites applications for a NIH NIBIB-funded Postdoctoral position to develop a Virtual Neuroprosthesis aimed at providing a sense of touch in amputees and limb-absent people.

Candidates should have a Ph.D. in one of the following degrees: mechanical engineering, electrical engineering, biomedical engineering, bioengineering or related, with interest and/or experience in transdisciplinary work at the intersection of robotic hands, biology, and biomedical systems. Prior experience in the neural field will be considered an advantage, though not a necessity. Underrepresented minorities and women are warmly encouraged to apply.

The postdoctoral researcher will be co-advised across the department of Mechanical Engineering and the Center for Complex Systems & Brain Sciences through an interdisciplinary team whose expertise spans Robotics, Microfluidics, Behavioral and Clinical Neuroscience and Orthopedic Surgery.

The position will be for one year with a possibility of extension based on performance. Salary will be commensurate with experience and qualifications. Review of applications will begin immediately and continue until the position is filled.

The application should include:

  1. a cover letter with research interests and experiences,
  2. a CV, and
  3. names and contact information for three professional references.

Qualified candidates can contact Erik Engeberg, Ph.D., Associate Professor, in the FAU Department of Ocean and Mechanical Engineering at eengeberg@fau.edu. Please reference AcademicKeys.com in your cover letter when applying for or inquiring about this job announcement.

You can find the apply button on this page. Good luck!

Omnidirectional fish camouflage and polarizing light

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I find this camouflage technique quite interesting due to some nice writing, from a Nov. 19, 2015 Florida Atlantic University (FAU) news release on EurekAlert,

The vast open ocean presents an especially challenging environment for its inhabitants since there is nowhere for them to hide. Yet, nature has found a remarkable way for fish to hide from their predators using camouflage techniques. In a study published in the current issue of Science, researchers from Harbor Branch Oceanographic Institute at Florida Atlantic University and collaborators show that fish scales have evolved to not only reflect light, but to also scramble polarization. They identified the tissue structure that fish evolved to do this, which could be an analog to develop new materials to help hide objects in the water.

HBOI researchers and colleagues collected more than 1,500 video-polarimetry measurements from live fish from distinct habitats under a variety of viewing conditions, and have revealed for the first time that fish have an ‘omnidirectional’ solution they use to camouflage themselves, demonstrating a new form of camouflage in nature — light polarization matching.

“We’ve known that open water fish have silvery scales for skin that reflect light from above so the reflected intensity is comparable to the background intensity when looking up, obliquely at the fish, as a predator would,” said Michael Twardowski, Ph.D., research professor at FAU’s HBOI and co-author of the study who collaborated with co-author James M. Sullivan, Ph.D., also a research professor at FAU’s HBOI. “This is one form of camouflage in the ocean.”

Typical light coloring on the ventral side (belly) and dark coloring on the dorsal (top) side of the fish also can help match intensity by differential absorption of light, in addition to reflection matching.

Light-scattering processes in the open ocean create spatially heterogeneous backgrounds. Polarization (the directional vibration of light waves) generates changes in the light environment that vary with the Sun’s position in the sky.

Polarization is a fundamental property of light, like color, but human eyes do not have the ability to sense it. Light travels in waves, and for natural sunlight, the direction of these waves is random around a central viewing axis. But when light reflects off a surface, waves parallel to that surface are dominant in the reflected beam. Many visual systems for fish have the ability to discriminate polarization, like built-in polarized sunglasses.

“Polarized sunglasses help you see better by blocking horizontal waves to reduce bright reflections,” said Twardowski. “The same principle helps fish discriminate objects better in water.”

Twardowski believes that even though light reflecting off silvery scales does a good job matching intensity of the background, if the scales acted as simple mirrors they would impart a polarization signature to the reflected light very different from the more random polarization of the background light field.

“This signature would be easily apparent to a predator with ability to discriminate polarization, resulting in poor camouflage,” he said. “Fish have evolved a solution to this potential vulnerability.”

To empirically determine whether open-ocean fish have evolved a cryptic reflectance strategy for their heterogeneous polarized environments, the researchers measured the contrasts of live open-ocean and coastal fish against the pelagic background in the Florida Keys and Curaçao. They used a single 360 degree camera around the horizontal plane of the targets and used both light microscopy and full-body video-polarimetry.

The American Association for the Advancement of Science (AAAS), publisher of Science magazine where the researchers’ study can be found issued a Nov. 19, 2015 news release on EurekAlert further describing the work,

… The study’s insights could pave the way to improvements in materials like polarization-sensitive satellites. Underwater, light vibrates in way that “polarizes” it. While humans cannot detect this vibrational state of light without technology, it is becoming increasingly evident that many species of fish can; lab-based studies hint that some fish have even adapted ways to use polarization to their advantage, including developing platelets within their skin that reflect and manipulate polarized light so the fish are camouflaged. To gain more insights into this form of camouflage, Parrish Brady and colleagues measured the polarization abilities of live fish as they swam in the open ocean. Using a specialized underwater camera (…), the researchers took numerous polarization measurements of several open water and coastal species of fish throughout the day as the sun changed position in the sky, causing subsequent changes in the polarization of light underwater. They found that open water fish from the Carangidae fish family, such as lookdowns and bigeye scad, exhibited significantly lower polarization contrast with their backgrounds (making them harder to spot) than carangid species that normally inhabit reefs. Furthermore, the researchers found that this reflective camouflage was optimal at angles from which predators most often spot fish, such as from directly below the fish and at angles perpendicular to their length. By looking at the platelets of open water fish under the microscope, the team found that the platelets align well on vertical axes, allowing fish to reflect the predictable downward direction of light in the open ocean. Yet the platelets are angled in way that diffuses light along the horizontal axis, the researchers say. They suggest that these different axes work together to reflect a wide range of depolarized light, offering better camouflage abilities to their hosts.

The AAAS has made available a video combining recordings from the researchers and animation to illustrate the research,

Be sure you can hear the audio as this won’t make much sense otherwise.

Here’s a link to and a citation for the paper,

Open-ocean fish reveal an omnidirectional solution to camouflage in polarized environments by Parrish C. Brady, Alexander A. Gilerson, George W. Kattawar, James M. Sullivan, Michael S. Twardowski, Heidi M. Dierssen, Meng Gao, Kort Travis, Robert Ian Etheredge, Alberto Tonizzo, Amir Ibrahim, Carlos Carrizo, Yalong Gu, Brandon J. Russell, Kathryn Mislinski, Shulei Zha1, Molly E. Cummings. Science 20 November 2015: Vol. 350 no. 6263 pp. 965-969 DOI: 10.1126/science.aad5284

This paper is behind a paywall.