Palorchestid marsupials, an extinct group of Australian megafauna, had strange bodies and lifestyles unlike any living species, according to a study released September 13, 2019 in the open-access journal PLOS ONE by Hazel Richards of Monash University, Australia and colleagues.
For most of the last 25 million years, eastern Australia was home to a now-extinct group of marsupials called palorchestids. These animals are well known for their large size, strange tapir-like skulls, and large claws, but so far there has been no detailed study of their limb morphology. In this study, Richards and colleagues examined more than 60 fossil specimens of palorchestids of varying geologic ages to characterize the function and evolution of their arms and legs.
Over the course of their evolution, palorchestids grew larger and stranger. Using limb proportions as a proxy for body size, these authors estimated that the latest and largest of the palorchestids may have weighed over 1,000kg. Furthermore, their forelimbs were extremely muscular and were likely adapted for grabbing or scraping at leaves and branches. Uniquely among known mammals, the elbow joints of the largest palorchestids appear to have been immobile and fixed at roughly a 100-degree angle, so that the arms served as permanently flexed food-gathering tools.
This study provides the first formal description of limb morphology in palorchestid marsupials and reveals a group of giant herbivores that probably filled a niche no longer occupied in modern Australian ecosystems. Fossil remains are still missing for certain parts of the palorchestid body, such as the shoulders and wrists, but the authors are hopeful that more material may be found in existing museum collections.
The authors add: "This study has allowed us for the first time to appreciate just how huge these mega-marsupial palorchestids were, while also providing the first comprehensive view of a strange limb anatomy unprecedented in the mammalian world. This research reveals yet more about the diversity of unique large marsupials that once roamed Australia not so long ago."
From Science Daily
Sep 16, 2019
Hope for coral recovery may depend on good parenting
The fate of the world's coral reefs could depend on how well the sea creatures equip their offspring to cope with global warming.
About half the world's coral has been lost due to warming seas that make their world hostile. Instead of vivid and floral, coral bleach pale as temperatures rise. This happens because the peculiar animal cohabitates with algae, which expel under stress. When that happens, coral lose their color and a life partner that sustains them, so they starve.
Yet, hope occurs in aquariums at the USC campus near downtown Los Angeles and at the Australian Institute of Marine Science. There, biologists study coral's unusual ability to shuffle their so-called symbionts -- the algae colonies inside their cells -- as a coping mechanism to potentially gain an advantage in a changing environment. For the first time, the researchers have shown that adult coral can pass along this ability to shuffle their symbionts to their offspring. It's a process that occurs in addition to traditional DNA transfer, and it's never been seen before until scientists began captive breeding research in labs on both sides of the Pacific Ocean.
"What we're finding is that corals can pass their shuffled complement of algal partners, or symbionts, to their offspring to bestow a potential survival advantage, and that's a new discovery," said Carly Kenkel, an assistant professor of biology at the USC Dornsife College of Letters, Arts and Sciences. "We care about this because coral reefs do so much for us. A reef provides breakwater for storms, fish protein people need and biodiversity we love and find beautiful."
The findings appear in a research paper published today in Scientific Reports.
Scientists have known for a long time that coral and algae live in mutual harmony. The two creatures live as one: a soft-bodied polyp animal similar to a sea anemone or jellyfish and an algae living within its cells. The animal provides algae safety and substances for photosynthesis; the algae produce oxygen, help remove wastes and supply the coral with energy. Corals use the energy to make calcium carbonate, the rigid architecture that builds reefs, while the algae contribute to the creatures' jewel-tone hues that make coral spectacular.
They live amicably together until environmental stress disrupts the partnership. When this happens, some coral succumb whereas others are capable of shuffling their symbionts, favoring some algae over others depending on water conditions, competition or available nutrients. "It's a messy divorce," Kenkel said.
Yet in this breakup, the kids could benefit. Kenkel wanted to understand if parent coral could pass along the reshuffled symbionts to its offspring. It's a tricky proposition because the algae exist independent of the cell nucleus and therefore are not part of the nuclear DNA transfer, parent to offspring, during reproduction.
Her curiosity took her to the Great Barrier Reef and Orpheus Island, off northeast Australia, where she joined scientists from James Cook University and the Australian Institute of Marine Science. The research team focused on a particular coral, Montipora digitata, which is common to the western Pacific Ocean and large swaths of the Great Barrier Reef.
The scientists focused on two consecutive spawning seasons: one under normal conditions during 2015 and the other during the global mass coral bleaching event of 2016. Using DNA sequencing, the scientists screened which corals showed potential to shuffle their symbionts and if the change was reflected in gametes. They found that the numbers and types of algal cells differed considerably from one year to the next, as measured in cell densities and photosynthesis output. It's a finding consistent with other research.
Montipora digitata coral can package algae in their eggs when they reproduce. In looking at the eggs between the two years, they discovered that rearrangements of the algae communities in the adults were also reflected in the coral's eggs, indicating that they could be passed down to offspring from the parents.
"To our knowledge, this is the first evidence that shuffled Symbiodiniaceae (symbiont) communities ... can be inherited by offspring and supports the hypothesis that shuffling in microbial communities may serve as a mechanism of rapid coral acclimation to changing environmental conditions," the study said.
The process is perhaps similar to how mitochondrial DNA works in humans. In that analog, the mitochondria -- an energy-producing unit inside the cell but outside the nucleus -- shares genetic material with offspring via the mother's egg. However, the researchers have not identified the mechanism for transfer in coral; they plan to answer that mystery in the next study.
The findings show coral may be more adaptable than thought, but is it enough?
Corals face an enormous challenge as ocean warming is increasing. According to a United Nations report, the world's coral reefs are at the epicenter for climate change impacts and species loss. If the world warms another 0.9 degrees Fahrenheit, which is likely, coral reefs will probably dwindle by 70% to 90%. A gain of 1.8 degrees, the report says, means 99% of the world's coral will be in trouble.
In some regions, the threat to coral is already severe. For example, as much as 80% of Caribbean Sea coral has been lost in the past three decades, according to the Smithsonian Institution.
Read more at Science Daily
About half the world's coral has been lost due to warming seas that make their world hostile. Instead of vivid and floral, coral bleach pale as temperatures rise. This happens because the peculiar animal cohabitates with algae, which expel under stress. When that happens, coral lose their color and a life partner that sustains them, so they starve.
Yet, hope occurs in aquariums at the USC campus near downtown Los Angeles and at the Australian Institute of Marine Science. There, biologists study coral's unusual ability to shuffle their so-called symbionts -- the algae colonies inside their cells -- as a coping mechanism to potentially gain an advantage in a changing environment. For the first time, the researchers have shown that adult coral can pass along this ability to shuffle their symbionts to their offspring. It's a process that occurs in addition to traditional DNA transfer, and it's never been seen before until scientists began captive breeding research in labs on both sides of the Pacific Ocean.
"What we're finding is that corals can pass their shuffled complement of algal partners, or symbionts, to their offspring to bestow a potential survival advantage, and that's a new discovery," said Carly Kenkel, an assistant professor of biology at the USC Dornsife College of Letters, Arts and Sciences. "We care about this because coral reefs do so much for us. A reef provides breakwater for storms, fish protein people need and biodiversity we love and find beautiful."
The findings appear in a research paper published today in Scientific Reports.
Scientists have known for a long time that coral and algae live in mutual harmony. The two creatures live as one: a soft-bodied polyp animal similar to a sea anemone or jellyfish and an algae living within its cells. The animal provides algae safety and substances for photosynthesis; the algae produce oxygen, help remove wastes and supply the coral with energy. Corals use the energy to make calcium carbonate, the rigid architecture that builds reefs, while the algae contribute to the creatures' jewel-tone hues that make coral spectacular.
They live amicably together until environmental stress disrupts the partnership. When this happens, some coral succumb whereas others are capable of shuffling their symbionts, favoring some algae over others depending on water conditions, competition or available nutrients. "It's a messy divorce," Kenkel said.
Yet in this breakup, the kids could benefit. Kenkel wanted to understand if parent coral could pass along the reshuffled symbionts to its offspring. It's a tricky proposition because the algae exist independent of the cell nucleus and therefore are not part of the nuclear DNA transfer, parent to offspring, during reproduction.
Her curiosity took her to the Great Barrier Reef and Orpheus Island, off northeast Australia, where she joined scientists from James Cook University and the Australian Institute of Marine Science. The research team focused on a particular coral, Montipora digitata, which is common to the western Pacific Ocean and large swaths of the Great Barrier Reef.
The scientists focused on two consecutive spawning seasons: one under normal conditions during 2015 and the other during the global mass coral bleaching event of 2016. Using DNA sequencing, the scientists screened which corals showed potential to shuffle their symbionts and if the change was reflected in gametes. They found that the numbers and types of algal cells differed considerably from one year to the next, as measured in cell densities and photosynthesis output. It's a finding consistent with other research.
Montipora digitata coral can package algae in their eggs when they reproduce. In looking at the eggs between the two years, they discovered that rearrangements of the algae communities in the adults were also reflected in the coral's eggs, indicating that they could be passed down to offspring from the parents.
"To our knowledge, this is the first evidence that shuffled Symbiodiniaceae (symbiont) communities ... can be inherited by offspring and supports the hypothesis that shuffling in microbial communities may serve as a mechanism of rapid coral acclimation to changing environmental conditions," the study said.
The process is perhaps similar to how mitochondrial DNA works in humans. In that analog, the mitochondria -- an energy-producing unit inside the cell but outside the nucleus -- shares genetic material with offspring via the mother's egg. However, the researchers have not identified the mechanism for transfer in coral; they plan to answer that mystery in the next study.
The findings show coral may be more adaptable than thought, but is it enough?
Corals face an enormous challenge as ocean warming is increasing. According to a United Nations report, the world's coral reefs are at the epicenter for climate change impacts and species loss. If the world warms another 0.9 degrees Fahrenheit, which is likely, coral reefs will probably dwindle by 70% to 90%. A gain of 1.8 degrees, the report says, means 99% of the world's coral will be in trouble.
In some regions, the threat to coral is already severe. For example, as much as 80% of Caribbean Sea coral has been lost in the past three decades, according to the Smithsonian Institution.
Read more at Science Daily
The rare molecule weighing in on the birth of planets
Astronomers using one of the most advanced radio telescopes have discovered a rare molecule in the dust and gas disc around a young star -- and it may provide an answer to one of the conundrums facing astronomers.
The star, named HD 163296, is located 330 light years from Earth and formed over the last six million years.
It is surrounded by a disc of dust and gas -- a so-called protoplanetary disc. It is within these discs that young planets are born. Using a radio telescope in the Atacama Desert in Chile, researchers were able to detect an extremely faint signal showing the existence of a rare form of carbon monoxide -- known as an isotopologue (13C17O).
The detection has allowed an international collaboration of scientists, led by the University of Leeds, to measure the mass of the gas in the disc more accurately than ever before. The results show that disc is much heavier -- or more 'massive' -- than previously thought.
Alice Booth, a PhD researcher at Leeds who led the study, said: "Our new observations showed there was between two and six times more mass hiding in the disc than previous observations could measure.
"This is an important finding in terms of the birth of planetary systems in discs -- if they contain more gas, then they have more building material to form more massive planets."
The study -- The first detection of 13C17O in a protoplanetary disk: a robust tracer of disk gas mass -- is published today (12/09/2019) in Astrophysical Journal Letters.
The scientists' conclusions are well timed. Recent observations of protoplanetary discs have perplexed astronomers because they did not seem to contain enough gas and dust to create the planets observed.
Dr John Ilee, a researcher at Leeds who was also involved in the study, added: "The disc-exoplanet mass discrepancy raises serious questions about how and when planets are formed. However, if other discs are hiding similar amounts of mass as HD 163296, then we may just have underestimated their masses until now."
"We can measure disc masses by looking at how much light is given off by molecules like carbon monoxide. If the discs are sufficiently dense, then they can block the light given off by more common forms of carbon monoxide -- and that could result in scientists underestimating the mass of the gas present.
"This study has used a technique to observe the much rarer 13C17O molecule -- and that's allowed us to peer deep inside the disc and find a previously hidden reservoir of gas."
The researchers made use of one of the most sophisticated radio telescopes in the world -- the Atacama Large Millimetre/submillimetre Array (ALMA) -- high in the Atacama Desert.
ALMA is able to observe light that is invisible to the naked eye, allowing astronomers to view what is known as the 'cold universe' -- those parts of space not visible using optical telescopes.
Booth said: "Our work shows the amazing contribution that ALMA is making to our understanding of the Universe. It is helping build a more accurate picture of the physics leading to the formation of new planets. This of course then helps us understand how the Solar System and Earth came to be."
Read more at Science Daily
The star, named HD 163296, is located 330 light years from Earth and formed over the last six million years.
It is surrounded by a disc of dust and gas -- a so-called protoplanetary disc. It is within these discs that young planets are born. Using a radio telescope in the Atacama Desert in Chile, researchers were able to detect an extremely faint signal showing the existence of a rare form of carbon monoxide -- known as an isotopologue (13C17O).
The detection has allowed an international collaboration of scientists, led by the University of Leeds, to measure the mass of the gas in the disc more accurately than ever before. The results show that disc is much heavier -- or more 'massive' -- than previously thought.
Alice Booth, a PhD researcher at Leeds who led the study, said: "Our new observations showed there was between two and six times more mass hiding in the disc than previous observations could measure.
"This is an important finding in terms of the birth of planetary systems in discs -- if they contain more gas, then they have more building material to form more massive planets."
The study -- The first detection of 13C17O in a protoplanetary disk: a robust tracer of disk gas mass -- is published today (12/09/2019) in Astrophysical Journal Letters.
The scientists' conclusions are well timed. Recent observations of protoplanetary discs have perplexed astronomers because they did not seem to contain enough gas and dust to create the planets observed.
Dr John Ilee, a researcher at Leeds who was also involved in the study, added: "The disc-exoplanet mass discrepancy raises serious questions about how and when planets are formed. However, if other discs are hiding similar amounts of mass as HD 163296, then we may just have underestimated their masses until now."
"We can measure disc masses by looking at how much light is given off by molecules like carbon monoxide. If the discs are sufficiently dense, then they can block the light given off by more common forms of carbon monoxide -- and that could result in scientists underestimating the mass of the gas present.
"This study has used a technique to observe the much rarer 13C17O molecule -- and that's allowed us to peer deep inside the disc and find a previously hidden reservoir of gas."
The researchers made use of one of the most sophisticated radio telescopes in the world -- the Atacama Large Millimetre/submillimetre Array (ALMA) -- high in the Atacama Desert.
ALMA is able to observe light that is invisible to the naked eye, allowing astronomers to view what is known as the 'cold universe' -- those parts of space not visible using optical telescopes.
Booth said: "Our work shows the amazing contribution that ALMA is making to our understanding of the Universe. It is helping build a more accurate picture of the physics leading to the formation of new planets. This of course then helps us understand how the Solar System and Earth came to be."
Read more at Science Daily
Antibiotic resistance surges in dolphins, mirroring humans
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| Dolphin swimming. |
Once primarily confined to health care settings, these resistant strains of bacteria are now commonly found in other places, especially marine environments. To date, few studies have looked at long-term trends in antibiotic resistance in pathogens isolated from wildlife populations.
Researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute in collaboration with Georgia Aquarium , the Medical University of South Carolina and Colorado State University, conducted a unique, long-term study (2003 to 2015) of antibiotic resistance among pathogens isolated from bottlenose dolphins (Tursiops truncatus) in Florida's Indian River Lagoon. This lagoon has a large coastal human population and significant environmental impacts.
"In 2009, we reported a high prevalence of antibiotic resistance in wild dolphins, which was unexpected," said Adam M. Schaefer, MPH, lead author and an epidemiologist at FAU's Harbor Branch. "Since then, we have been tracking changes over time and have found a significant increase in antibiotic resistance in isolates from these animals. This trend mirrors reports from human health care settings. Based on our findings, it is likely that these isolates from dolphins originated from a source where antibiotics are regularly used, potentially entering the marine environment through human activities or discharges from terrestrial sources."
Using 13-years of data and the Multiple Antibiotic Resistance (MAR) index, researchers obtained a total of 733 pathogen isolates from 171 individual bottlenose dolphins. Several of the organisms isolated from these animals are important human pathogens.
Results of the study, published in the journal Aquatic Mammals, shows that the overall prevalence of resistance to at least one antibiotic for the 733 isolates was 88.2 percent. The prevalence of resistance was highest to erythromycin (91.6 percent), followed by ampicillin (77.3 percent) and cephalothin (61.7 percent). This is one of the few studies to use the MAR index for bacterial isolates from a marine mammal species.
Resistance to ciprofloxacin among E. coli isolates more than doubled between sampling periods, reflecting recent trends in human clinical infections. Pseudomonas aeruginosa, responsible for respiratory system infections, urinary tract infections, among others, were the highest recorded for any organism and increased during the study period.
The MAR index increased significantly between the periods 2003-2007 and 2010-2015 for P. aeruginosa and Vibrio alginolyticus, a common pathogenic marine Vibrio species found to cause serious seafood-poisoning. For all bacterial isolates, resistance to cefotaxime, ceftazidime and gentamicin increased significantly between sampling periods.
"The Health and Environmental Risk Assessment or HERA Project has helped discover that the emerging bacterial resistance to antibiotics in bottlenose dolphins is prevalent. Bottlenose dolphins are a valuable sentinel species in helping us understand how this affects human and environmental health. Through HERA we've been able to provide a large database of information in order to continue learning from these impressive animals," said Gregory D. Bossart, V.M.D., Ph.D., co-author, senior vice president and chief veterinary officer at Georgia Aquarium. "Antibiotic resistance is one of the most significant risks to public health. As resistance increases, the probability of successfully treating infections caused by common pathogens decreases."
The sampling for the study was conducted and funded in part by the Florida Specialty License Plate fund and Georgia Aquarium with Bossart serving as the HERA lead and permit holder. Swab samples for microbiology were taken from the blowhole, gastric fluid and feces and cultured on standard media under aerobic conditions. The most frequently isolated pathogens were Aeromonas hydrophila, E. coli, Edwardsiella tarda, V. alginolyticus, and S. aureus, pathogens frequently associated with aquatic environments. The dolphins were captured and released back into the Indian River Lagoon as a part of the HERA Project. Sampling took place during June and July each year.
"The nationwide human health impact of the pathogen Acinetobacter baumannii is of substantial concern as it is a significant nosocomial pathogen with increasing infection rates over the past 10 years," said Peter McCarthy, Ph.D., co-author, a research professor and an associate director for education at FAU's Harbor Branch. "In addition to nosocomial infections, resistant strains associated with fish and fish farming have been reported globally. The high MAR index for this bacteria isolated from dolphins in the Indian River Lagoon represents a significant public health concern."
Read more at Science Daily
Sep 15, 2019
Slower growth in working memory linked to teen driving crashes
Research into why adolescent drivers are involved in motor vehicle crashes, the leading cause of injury and death among 16- to 19-year-olds in the United States, has often focused on driving experience and skills. But a new study suggests that development of the adolescent brain may play a critical role in whether a teenager is more likely to crash.
The study finds that slower growth in the development of working memory is associated with motor vehicle crashes, which points to cognitive development screening as a potential new strategy for identifying and tailoring driving interventions for teens at high risk for crashes.
The study, led by researchers at the Annenberg Public Policy Center of the University of Pennsylvania (APPC) and Children's Hospital of Philadelphia (CHOP), is the first longitudinal study of working memory development in relation to vehicle crashes. The paper "Working Memory Development and Motor Vehicle Crashes in Young Drivers" was published today in JAMA Network Open.
The research examines data from 118 youth in Philadelphia who were part of a larger group that participated in a six-wave survey from when they were 10- to 12-year-olds, in 2005, until they were 18- to 20-year-olds, in 2013-14. The survey measured working memory development, as well as associated risk-related traits and behaviors. This group later participated in a follow-up survey on driving experience.
"We found that teens who had slower development in working memory were more likely to report being in a crash," said the lead author, Elizabeth A. Walshe, Ph.D., who is a postdoctoral fellow at the Annenberg Public Policy Center and at the Center for Injury Research and Prevention at CHOP.
Driving and working memory
Working memory, which develops through adolescence into the twenties, is a frontal lobe process associated with complex, moment-to-moment tasks essential to driving. "Safe driving involves scanning, monitoring, and updating information about the vehicle and environment while managing multiple subtasks (e.g., adjusting speed, steering, in-vehicle controls) and distractors (e.g., peer passengers and cell phones)," the researchers said in their paper. All of these tasks challenge working memory, especially when a young driver has not yet fully learned to automate many basic driving routines.
Adolescent drivers have the highest rate of crashes, injuries, and mortality. While poor skills and inexperience explain some of the risk shortly after a new driver receives a license, crash risk is inversely related to age during the early years of driving. In other words, among equally new drivers, those who are 17 years old have a higher crash rate than those who are 20 years old, which suggests a possible developmental link.
"Not all young drivers crash," Walshe said. "So we thought, what is it about those who are crashing? It could be related to variability in working memory development."
Findings
Prior research has shown a link between lower working memory capacity and reckless and inattentive driving, crashes, and poor performance on simulated driving tasks. For the current study, the researchers recruited participants from the Philadelphia Trajectory Study, a broad six-wave study conducted by researchers at APPC and CHOP. Across seven years -- when the adolescents were 11-13 years old to 18-20 years old -- this study measured the change in working memory and other characteristics. Subsequently, in 2015, 118 young adults, including 84 drivers and 34 non-drivers, took the follow-up survey on driving. Among the drivers, 25 reported having a crash history and 59 reported no crash history.
The drivers who reported crashes and those who didn't started from about the same point in working memory capacity though the trends diverged from there. The researchers found that the relative growth of working memory was associated with car crashes within three years after starting to drive. Young drivers whose trajectory of working memory growth was less-than-average in the group were more likely to report being in a crash; drivers with greater-than-average growth in working memory were more likely to say they had not been in a crash.
The analysis controlled for other risk-related factors including reckless driving and drug use.
Driving crashes: "Predictable and preventable"
The researchers say the results have important policy implications. While all 50 states have some type of graduated driver licensing (GDL) program that gradually lifts restrictions for young new drivers, the research suggests that individual assessments of adolescents' cognitive development may play an important part, too.
"If our findings hold up in larger samples with diverse youth, we will need to start assessing cognitive abilities, such as working memory, to see if some adolescents are less ready for independent driving," said Daniel Romer, Ph.D., research director of the Annenberg Public Policy Center and a senior fellow at the Center for Injury Research and Prevention at CHOP. "There is considerable variation in working memory development during the teen years, and some teens may not be as ready to drive on their own without additional assistance."
Flaura K. Winston, M.D., Ph.D., founder and scientific director of the Century for Injury Research and Prevention at CHOP, said that enabling teens to become safe drivers is a health concern for physicians. Prior research has focused on driving skills and experience, but this study examines cognitive development in typical adolescents and suggests that individual variation plays a critical role.
"This research points to the fact that crashes are predictable and preventable," said Winston, who also is an APPC distinguished research fellow. "It focuses attention more on the role of the driver and the driver's clinician. A clinician could identify teens who will be at an increased risk and use 'precision prevention' to tailor anticipatory guidance so that young drivers achieve independent mobility in a safe way."
Precision prevention, Winston said, could provide different types of driver training or a release from driving restrictions at different times based on their development.
Read more at Science Daily
The study finds that slower growth in the development of working memory is associated with motor vehicle crashes, which points to cognitive development screening as a potential new strategy for identifying and tailoring driving interventions for teens at high risk for crashes.
The study, led by researchers at the Annenberg Public Policy Center of the University of Pennsylvania (APPC) and Children's Hospital of Philadelphia (CHOP), is the first longitudinal study of working memory development in relation to vehicle crashes. The paper "Working Memory Development and Motor Vehicle Crashes in Young Drivers" was published today in JAMA Network Open.
The research examines data from 118 youth in Philadelphia who were part of a larger group that participated in a six-wave survey from when they were 10- to 12-year-olds, in 2005, until they were 18- to 20-year-olds, in 2013-14. The survey measured working memory development, as well as associated risk-related traits and behaviors. This group later participated in a follow-up survey on driving experience.
"We found that teens who had slower development in working memory were more likely to report being in a crash," said the lead author, Elizabeth A. Walshe, Ph.D., who is a postdoctoral fellow at the Annenberg Public Policy Center and at the Center for Injury Research and Prevention at CHOP.
Driving and working memory
Working memory, which develops through adolescence into the twenties, is a frontal lobe process associated with complex, moment-to-moment tasks essential to driving. "Safe driving involves scanning, monitoring, and updating information about the vehicle and environment while managing multiple subtasks (e.g., adjusting speed, steering, in-vehicle controls) and distractors (e.g., peer passengers and cell phones)," the researchers said in their paper. All of these tasks challenge working memory, especially when a young driver has not yet fully learned to automate many basic driving routines.
Adolescent drivers have the highest rate of crashes, injuries, and mortality. While poor skills and inexperience explain some of the risk shortly after a new driver receives a license, crash risk is inversely related to age during the early years of driving. In other words, among equally new drivers, those who are 17 years old have a higher crash rate than those who are 20 years old, which suggests a possible developmental link.
"Not all young drivers crash," Walshe said. "So we thought, what is it about those who are crashing? It could be related to variability in working memory development."
Findings
Prior research has shown a link between lower working memory capacity and reckless and inattentive driving, crashes, and poor performance on simulated driving tasks. For the current study, the researchers recruited participants from the Philadelphia Trajectory Study, a broad six-wave study conducted by researchers at APPC and CHOP. Across seven years -- when the adolescents were 11-13 years old to 18-20 years old -- this study measured the change in working memory and other characteristics. Subsequently, in 2015, 118 young adults, including 84 drivers and 34 non-drivers, took the follow-up survey on driving. Among the drivers, 25 reported having a crash history and 59 reported no crash history.
The drivers who reported crashes and those who didn't started from about the same point in working memory capacity though the trends diverged from there. The researchers found that the relative growth of working memory was associated with car crashes within three years after starting to drive. Young drivers whose trajectory of working memory growth was less-than-average in the group were more likely to report being in a crash; drivers with greater-than-average growth in working memory were more likely to say they had not been in a crash.
The analysis controlled for other risk-related factors including reckless driving and drug use.
Driving crashes: "Predictable and preventable"
The researchers say the results have important policy implications. While all 50 states have some type of graduated driver licensing (GDL) program that gradually lifts restrictions for young new drivers, the research suggests that individual assessments of adolescents' cognitive development may play an important part, too.
"If our findings hold up in larger samples with diverse youth, we will need to start assessing cognitive abilities, such as working memory, to see if some adolescents are less ready for independent driving," said Daniel Romer, Ph.D., research director of the Annenberg Public Policy Center and a senior fellow at the Center for Injury Research and Prevention at CHOP. "There is considerable variation in working memory development during the teen years, and some teens may not be as ready to drive on their own without additional assistance."
Flaura K. Winston, M.D., Ph.D., founder and scientific director of the Century for Injury Research and Prevention at CHOP, said that enabling teens to become safe drivers is a health concern for physicians. Prior research has focused on driving skills and experience, but this study examines cognitive development in typical adolescents and suggests that individual variation plays a critical role.
"This research points to the fact that crashes are predictable and preventable," said Winston, who also is an APPC distinguished research fellow. "It focuses attention more on the role of the driver and the driver's clinician. A clinician could identify teens who will be at an increased risk and use 'precision prevention' to tailor anticipatory guidance so that young drivers achieve independent mobility in a safe way."
Precision prevention, Winston said, could provide different types of driver training or a release from driving restrictions at different times based on their development.
Read more at Science Daily
What multilingual nuns can tell us about dementia
A strong ability in languages may help reduce the risk of developing dementia, says a new University of Waterloo study.
The research, led by Suzanne Tyas, a public health professor at Waterloo, examined the health outcomes of 325 Roman Catholic nuns who were members of the Sisters of Notre Dame in the United States. The data was drawn from a larger, internationally recognized study examining the Sisters, known as the Nun Study.
The researchers found that six per cent of the nuns who spoke four or more languages developed dementia, compared to 31 per cent of those who only spoke one. However, knowing two or three languages did not significantly reduce the risk in this study, which differs from some previous research.
"The Nun Study is unique: It is a natural experiment, with very different lives in childhood and adolescence before entering the convent, contrasted with very similar adult lives in the convent," said Tyas. "This gives us the ability to look at early-life factors on health later in life without worrying about all the other factors, such as socioeconomic status and genetics, which usually vary from person to person during adulthood and can weaken other studies."
Tyas added, "Language is a complex ability of the human brain, and switching between different languages takes cognitive flexibility. So it makes sense that the extra mental exercise multilinguals would get from speaking four or more languages might help their brains be in better shape than monolinguals."
The researchers also examined 106 samples of the nuns' written work and compared it to the broader findings. They found that written linguistic ability affected whether the individuals were at greater risk of developing dementia. For example, idea density -- the number of ideas expressed succinctly in written work -- helped reduce the risk even more than multilingualism.
"This study shows that while multilingualism may be important, we should also be looking further into other examples of linguistic ability," said Tyas. "In addition, we need to know more about multilingualism and what aspects are important -- such as the age when a language is first learned, how often each language is spoken, and how similar or different these languages are. This knowledge can guide strategies to promote multilingualism and other linguistic training to reduce the risk of developing dementia."
From Science Daily
The research, led by Suzanne Tyas, a public health professor at Waterloo, examined the health outcomes of 325 Roman Catholic nuns who were members of the Sisters of Notre Dame in the United States. The data was drawn from a larger, internationally recognized study examining the Sisters, known as the Nun Study.
The researchers found that six per cent of the nuns who spoke four or more languages developed dementia, compared to 31 per cent of those who only spoke one. However, knowing two or three languages did not significantly reduce the risk in this study, which differs from some previous research.
"The Nun Study is unique: It is a natural experiment, with very different lives in childhood and adolescence before entering the convent, contrasted with very similar adult lives in the convent," said Tyas. "This gives us the ability to look at early-life factors on health later in life without worrying about all the other factors, such as socioeconomic status and genetics, which usually vary from person to person during adulthood and can weaken other studies."
Tyas added, "Language is a complex ability of the human brain, and switching between different languages takes cognitive flexibility. So it makes sense that the extra mental exercise multilinguals would get from speaking four or more languages might help their brains be in better shape than monolinguals."
The researchers also examined 106 samples of the nuns' written work and compared it to the broader findings. They found that written linguistic ability affected whether the individuals were at greater risk of developing dementia. For example, idea density -- the number of ideas expressed succinctly in written work -- helped reduce the risk even more than multilingualism.
"This study shows that while multilingualism may be important, we should also be looking further into other examples of linguistic ability," said Tyas. "In addition, we need to know more about multilingualism and what aspects are important -- such as the age when a language is first learned, how often each language is spoken, and how similar or different these languages are. This knowledge can guide strategies to promote multilingualism and other linguistic training to reduce the risk of developing dementia."
From Science Daily
New way to target cancer's diversity and evolution
Scientists have revealed close-up details of a vital molecule involved in the mix and match of genetic information within cells -- opening up the potential to target proteins of this family to combat cancer's diversity and evolution.
A team at The Institute of Cancer Research, London, has discovered the three-dimensional structure and function of this 'mix n match' protein, which helps control a process linked to cancer's progression and drug resistance.
The researchers believe the study opens up a potentially exciting new way to tackle drug-resistant cancers and will be exploring the possibility further within the pioneering £75 million new Centre for Cancer Drug Discovery.
The study is published in the Biochemical Journal today (14th September) and was funded by Cancer Research UK with additional support from the Faringdon Fund, which was created by The Institute of Cancer Research (ICR) to get high-risk projects off the ground following a generous philanthropic donation.
Researchers at the ICR investigated the structure and function of a molecule known as DHX8. This belongs to a class of proteins involved in a fundamental process in life called 'alternative splicing', which affects 95 per cent of human genes.
Splicing takes place once the DNA code has been copied into RNA, with certain pieces cut out and the rest stuck together to create a final code that is translated into protein.
In alternative splicing, the bits of RNA that are cut out, or kept in, can be varied to create multiple proteins from a single gene -- increasing the diversity of proteins available to cells.
When alternative splicing goes wrong, it can generate changes to the proteins within cells -- which can lead to cancer, or fuel cancer's diversity, evolution and drug resistance.
Splicing is carried out by a complex made up of proteins and RNA, which constantly changes during the cutting and gluing of the RNA. DHX8 is a crucial member of this complex and helps to release the finished RNA into the cell so it can be translated into protein.
In this new study, the researchers examined how the human DHX8 protein binds to RNA and acts to unravel RNA from the rest of the splicing machinery.
They also determined the first high-resolution X-ray crystal structures of DHX8 with and without RNA -- allowing them not only to visualise the protein's molecular structure but also to gain key clues about its function.
In particular, the study shed light on the roles of specific structural regions of DHX8, including the so-called 'DEAH motif', 'hook loop' and 'hook turn' regions, which were all shown to be vital for DHX8's function.
The researchers next want to study in greater detail how DHX8 can contribute to cancer -- and believe their study will open up ways of blocking members of the protein family as a promising new approach to treatment.
Attempting to combat cancer's diversity is one of the central strategies the ICR is pursuing as part of a pioneering research programme to overcome the ability of cancers to adapt, evolve and become drug resistant.
The ICR -- a charity and research institute -- is raising the final £14 million of a £75 million investment in the new Centre for Cancer Drug Discovery to house a world-first programme of 'anti-evolution' therapies.
Study leader Dr Rob van Montfort, Team Leader in Hit Discovery and Structural Design at The Institute of Cancer Research, London, said:
"Our study has shed new light on the structure and function of a crucial protein involved in the process of alternative splicing, in which genetic information is mixed and matched to create multiple protein molecules from a single gene.
"Cancer cells take advantage of alternative splicing to diversify, evolve and escape the body's regulatory mechanisms. By determining the detailed molecular structure of one of the key protein molecules involved in alternative splicing, we have opened up potentially exciting new avenues for cancer treatment."
Study co-author Professor Paul Workman, Chief Executive of The Institute of Cancer Research, London, said:
"We are excited to study these 'mix and match' proteins further, because we think our findings open up a new route to help block cancer's evolutionary pathways, and potentially overcome drug resistance.
"This is exactly the sort of approach we plan to take within our pioneering new Centre for Cancer Drug Discovery, which once completed will house the world's first 'Darwinian' drug discovery programmed dedicated to overcoming the twin challenges of cancer evolution and drug resistance."
Read more at Science Daily
A team at The Institute of Cancer Research, London, has discovered the three-dimensional structure and function of this 'mix n match' protein, which helps control a process linked to cancer's progression and drug resistance.
The researchers believe the study opens up a potentially exciting new way to tackle drug-resistant cancers and will be exploring the possibility further within the pioneering £75 million new Centre for Cancer Drug Discovery.
The study is published in the Biochemical Journal today (14th September) and was funded by Cancer Research UK with additional support from the Faringdon Fund, which was created by The Institute of Cancer Research (ICR) to get high-risk projects off the ground following a generous philanthropic donation.
Researchers at the ICR investigated the structure and function of a molecule known as DHX8. This belongs to a class of proteins involved in a fundamental process in life called 'alternative splicing', which affects 95 per cent of human genes.
Splicing takes place once the DNA code has been copied into RNA, with certain pieces cut out and the rest stuck together to create a final code that is translated into protein.
In alternative splicing, the bits of RNA that are cut out, or kept in, can be varied to create multiple proteins from a single gene -- increasing the diversity of proteins available to cells.
When alternative splicing goes wrong, it can generate changes to the proteins within cells -- which can lead to cancer, or fuel cancer's diversity, evolution and drug resistance.
Splicing is carried out by a complex made up of proteins and RNA, which constantly changes during the cutting and gluing of the RNA. DHX8 is a crucial member of this complex and helps to release the finished RNA into the cell so it can be translated into protein.
In this new study, the researchers examined how the human DHX8 protein binds to RNA and acts to unravel RNA from the rest of the splicing machinery.
They also determined the first high-resolution X-ray crystal structures of DHX8 with and without RNA -- allowing them not only to visualise the protein's molecular structure but also to gain key clues about its function.
In particular, the study shed light on the roles of specific structural regions of DHX8, including the so-called 'DEAH motif', 'hook loop' and 'hook turn' regions, which were all shown to be vital for DHX8's function.
The researchers next want to study in greater detail how DHX8 can contribute to cancer -- and believe their study will open up ways of blocking members of the protein family as a promising new approach to treatment.
Attempting to combat cancer's diversity is one of the central strategies the ICR is pursuing as part of a pioneering research programme to overcome the ability of cancers to adapt, evolve and become drug resistant.
The ICR -- a charity and research institute -- is raising the final £14 million of a £75 million investment in the new Centre for Cancer Drug Discovery to house a world-first programme of 'anti-evolution' therapies.
Study leader Dr Rob van Montfort, Team Leader in Hit Discovery and Structural Design at The Institute of Cancer Research, London, said:
"Our study has shed new light on the structure and function of a crucial protein involved in the process of alternative splicing, in which genetic information is mixed and matched to create multiple protein molecules from a single gene.
"Cancer cells take advantage of alternative splicing to diversify, evolve and escape the body's regulatory mechanisms. By determining the detailed molecular structure of one of the key protein molecules involved in alternative splicing, we have opened up potentially exciting new avenues for cancer treatment."
Study co-author Professor Paul Workman, Chief Executive of The Institute of Cancer Research, London, said:
"We are excited to study these 'mix and match' proteins further, because we think our findings open up a new route to help block cancer's evolutionary pathways, and potentially overcome drug resistance.
"This is exactly the sort of approach we plan to take within our pioneering new Centre for Cancer Drug Discovery, which once completed will house the world's first 'Darwinian' drug discovery programmed dedicated to overcoming the twin challenges of cancer evolution and drug resistance."
Read more at Science Daily
Sep 14, 2019
How new loops in DNA packaging help us make diverse antibodies
Diversity is good, especially when it comes to antibodies. It's long been known that a gene assembly process called V(D)J recombination allows our immune system to mix and match bits of genetic code, generating new antibodies to conquer newly encountered threats. But how these gene segments come together to be spliced has been a mystery. A new study in Nature provides the answer.
Our DNA strands are organized, together with certain proteins, into a packaging called chromatin, which contains multiple loops. When a cell needs to build a particular protein, the chromatin loops bring two relatively distant DNA segments in close proximity so they can work together. Many of these loops are fixed in place, but cells can sometimes rearrange loops or make new loops when they need to -- notably, cancer cells and immune cells.
The new research, led by Frederick Alt, PhD, director of the Program in Cellular and Molecular Medicine (PCMM) at Boston Children's Hospital, shows in exquisite detail how our immune system's B cells exploit the loop formation process for the purpose of making new kinds of antibodies.
Scanning loops as they form
A pair of enzymes called RAG1 and RAG2, the researchers show, couple with mechanisms involved in making the chromatin loops to initiate the first step of V(D)J recombination -- joining the D and J segments. The RAG 1/2 complex first binds to a site on an antibody gene known as the "recombination center." As the DNA scrolls past during the process of loop formation ("extrusion"), the RAG complex scans for the D and J segments the cell wants to combine. Other factors then impede the extrusion process, pausing the scrolling DNA at the recombination center so that RAG can access the desired segments.
"The loop extrusion process is harnessed by antibody gene loci to properly present substrate gene segments to the RAG complex for V(D)J recombination," says Alt.
While many of the hard-wired chromatin loops are formed and anchored by a factor known as CTCF, the Alt lab shows that other factors are involved in dynamic situations, like antibody formation, that require new loops on the fly. The study also establishes the role of a protein called cohesin in driving the loop extrusion/RAG scanning process.
"While these findings have been made in the context of V(D)J recombination in antibody formation, they have implications for processes that could be involved in gene regulation more generally," says Alt.
Read more at Science Daily
Our DNA strands are organized, together with certain proteins, into a packaging called chromatin, which contains multiple loops. When a cell needs to build a particular protein, the chromatin loops bring two relatively distant DNA segments in close proximity so they can work together. Many of these loops are fixed in place, but cells can sometimes rearrange loops or make new loops when they need to -- notably, cancer cells and immune cells.
The new research, led by Frederick Alt, PhD, director of the Program in Cellular and Molecular Medicine (PCMM) at Boston Children's Hospital, shows in exquisite detail how our immune system's B cells exploit the loop formation process for the purpose of making new kinds of antibodies.
Scanning loops as they form
A pair of enzymes called RAG1 and RAG2, the researchers show, couple with mechanisms involved in making the chromatin loops to initiate the first step of V(D)J recombination -- joining the D and J segments. The RAG 1/2 complex first binds to a site on an antibody gene known as the "recombination center." As the DNA scrolls past during the process of loop formation ("extrusion"), the RAG complex scans for the D and J segments the cell wants to combine. Other factors then impede the extrusion process, pausing the scrolling DNA at the recombination center so that RAG can access the desired segments.
"The loop extrusion process is harnessed by antibody gene loci to properly present substrate gene segments to the RAG complex for V(D)J recombination," says Alt.
While many of the hard-wired chromatin loops are formed and anchored by a factor known as CTCF, the Alt lab shows that other factors are involved in dynamic situations, like antibody formation, that require new loops on the fly. The study also establishes the role of a protein called cohesin in driving the loop extrusion/RAG scanning process.
"While these findings have been made in the context of V(D)J recombination in antibody formation, they have implications for processes that could be involved in gene regulation more generally," says Alt.
Read more at Science Daily
Few people with peanut allergy tolerate peanut after stopping oral immunotherapy
Allergy to peanut, which is often severe, is one of the most common food allergies in the United States. Although previous studies have shown that peanut oral immunotherapy (OIT) -- ingesting small, controlled amounts of peanut protein -- can desensitize adults and children and prevent life-threatening allergic reactions, the optimal duration and dose is unknown. In a study that followed participants after OIT successfully desensitized them to peanut, discontinuing OIT or continuing OIT at a reduced dose led to a decline in its protective effects. The study, published online today in The Lancet, also found that several blood tests administered before OIT could predict the success of therapy. The Phase 2 study was supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH, and may inform who may benefit from peanut OIT and what changes in this experimental treatment should be implemented.
Investigators at Stanford University enrolled 120 people aged 7 to 55 with diagnosed peanut allergy in the Peanut Oral Immunotherapy Study: Safety Efficacy and Discovery, or POISED. While otherwise avoiding peanut throughout the trial, 95 participants received gradually increasing daily doses of peanut protein up to 4 grams, and 25 participants received daily placebo oat flour OIT. After 24 months, participants were given gradually increasing amounts of peanut in a controlled environment, to assess their tolerance. Of those participants who received peanut OIT, 83% passed the peanut challenge without an allergic reaction, while only 4% on placebo OIT did so.
Those on OIT who passed the challenge were then randomized to receive either placebo OIT or were switched to a 300-mg daily dose of peanut protein. One year later, more participants on 300-mg peanut OIT (37%) passed the challenge than those on placebo OIT (13%), confirming insights from smaller trials that desensitization is maintained in only a minority of participants after OIT is discontinued or reduced. Participants who passed food challenges also had lower initial levels of allergic antibodies to peanut protein and other indicators of allergic activity in the blood. Future research will focus on identifying optimal OIT regimens that maintain protection after therapy and will allow for regular food consumption without allergic symptoms.
From Science Daily
Investigators at Stanford University enrolled 120 people aged 7 to 55 with diagnosed peanut allergy in the Peanut Oral Immunotherapy Study: Safety Efficacy and Discovery, or POISED. While otherwise avoiding peanut throughout the trial, 95 participants received gradually increasing daily doses of peanut protein up to 4 grams, and 25 participants received daily placebo oat flour OIT. After 24 months, participants were given gradually increasing amounts of peanut in a controlled environment, to assess their tolerance. Of those participants who received peanut OIT, 83% passed the peanut challenge without an allergic reaction, while only 4% on placebo OIT did so.
Those on OIT who passed the challenge were then randomized to receive either placebo OIT or were switched to a 300-mg daily dose of peanut protein. One year later, more participants on 300-mg peanut OIT (37%) passed the challenge than those on placebo OIT (13%), confirming insights from smaller trials that desensitization is maintained in only a minority of participants after OIT is discontinued or reduced. Participants who passed food challenges also had lower initial levels of allergic antibodies to peanut protein and other indicators of allergic activity in the blood. Future research will focus on identifying optimal OIT regimens that maintain protection after therapy and will allow for regular food consumption without allergic symptoms.
From Science Daily
Chameleon inspires 'smart skin' that changes color in the sun
A chameleon can alter the color of its skin so it either blends into the background to hide or stands out to defend its territory and attract a mate. The chameleon makes this trick look easy, using photonic crystals in its skin. Scientists, however, have struggled to make a photonic crystal "smart skin" that changes color in response to the environment, without also changing in size.
The journal ACS Nano is publishing research led by chemists at Emory University that found a solution to the problem. They developed a flexible smart skin that reacts to heat and sunlight while maintaining a near constant volume.
"Watching a chameleon change colors gave me the idea for the breakthrough," says first author Yixiao Dong, a PhD candidate in Emory's Department of Chemistry. "We've developed a new concept for a color-changing smart skin, based on observations of how nature does it."
"Scientists in the field of photonic crystals have been working for a long time to try to create color-changing smart skins for a range of potential applications, such as camouflage, chemical sensing and anti-counterfeiting tags, " adds Khalid Salaita, senior author of the paper and an Emory professor of chemistry. "While our work is still in the fundamental stages, we've established the principles for a new approach to explore and build upon."
Co-authors of the paper include Alisina Bazrafshan and Dale Combs (Emory PhD students); Kimberly Clarke (an Emory post-doctoral fellow); and Anastassia Pokutta, Fatiesa Sulejmani and Wei Sun (from Georgia Tech's Wallace H. Coulter Department of Biomedical Engineering).
Besides chameleons, many other creatures have evolved the ability to change color. The stripes on a neon tetra fish, for example, turn from deep indigo to blue-green when they swim into sunlight.
The coloration in these organisms is not based on pigments, but on tiny particles in a repeating pattern, known as photonic crystals. The periodicity in these particles causes the material to interfere with wavelengths of light. Although the particles themselves are colorless, the precise spacing between them allows certain light waves to pass through them while rejecting others. The visible colors produced change depending on factors such as lighting conditions or shifts in the distance between the particles. The iridescence of some butterfly wings and the feathers of peacocks are among many other examples of photonic crystals in nature.
If you put strawberries into a blender, Dong explains, the resulting liquid will be red because the color of the strawberries comes from pigment. If you grind up iridescent butterfly wings, however, the result will be a dull powder because the rainbow colors were not based on pigments, but on what is known as "structural color." The structure of the photonic crystal arrays is destroyed when the butterfly wings are ground up.
To mimic chameleons and create an artificial smart skin, scientists have experimented with embedding photonic crystal arrays into flexible, water-containing polymers, or hydrogels. Expanding or contracting the hydrogel changes the spacing between the arrays, resulting in a color change. The problem, however, is that the accordion-like action needed to generate a visible change in hue causes the hydrogel to significantly grow or shrink in size, leading to structural instability and buckling of the material.
"No one wants a camouflage cloak that shrinks to change color," Salaita notes.
Dong was pondering the problem while watching YouTube videos of a chameleon. "I wanted to understand why a chameleon doesn't get bigger or smaller as it changes color, but remains its original size," he says.
In close-up, time-lapsed images of the chameleon changing hues, Dong noticed that the arrays of photonic crystals did not cover the entire skin but were spread out within a dark matrix. As the photonic crystals turned different colors, these patches of color remained the same distance apart. Dong hypothesized that the skin cells making up the dark matrix somehow adjusted to compensate for the shifts in the photonic crystals.
"I wondered if we could design something similar -- a composite structure of photonic crystal arrays embedded into a strain-accommodating matrix," Dong says.
The researchers used magnets to arrange patterns of photonic crystals containing iron oxide within a hydrogel. They then embedded these arrays into a second, non-color-changing hydrogel. The second, springy hydrogel was mechanically matched to the first hydrogel to compensate for shifts in distances between the photonic crystals. When heated, this strain-accommodating smart skin (SASS) changes color but maintains a near-constant size.
Dong also tested the material in sunlight, fabricating SASS films into the shape of a fish, in homage to the neon tetra, as well as into the shape of a leaf. When exposed to natural sunlight for 10 minutes, the SASS films shifted from orange to green, without changing in size.
"We've provided a general framework to guide the future design of artificial smart skins," Dong says. "There is still a long way to go for real-life applications, but it's exciting to push the field another step further."
Read more at Science Daily
The journal ACS Nano is publishing research led by chemists at Emory University that found a solution to the problem. They developed a flexible smart skin that reacts to heat and sunlight while maintaining a near constant volume.
"Watching a chameleon change colors gave me the idea for the breakthrough," says first author Yixiao Dong, a PhD candidate in Emory's Department of Chemistry. "We've developed a new concept for a color-changing smart skin, based on observations of how nature does it."
"Scientists in the field of photonic crystals have been working for a long time to try to create color-changing smart skins for a range of potential applications, such as camouflage, chemical sensing and anti-counterfeiting tags, " adds Khalid Salaita, senior author of the paper and an Emory professor of chemistry. "While our work is still in the fundamental stages, we've established the principles for a new approach to explore and build upon."
Co-authors of the paper include Alisina Bazrafshan and Dale Combs (Emory PhD students); Kimberly Clarke (an Emory post-doctoral fellow); and Anastassia Pokutta, Fatiesa Sulejmani and Wei Sun (from Georgia Tech's Wallace H. Coulter Department of Biomedical Engineering).
Besides chameleons, many other creatures have evolved the ability to change color. The stripes on a neon tetra fish, for example, turn from deep indigo to blue-green when they swim into sunlight.
The coloration in these organisms is not based on pigments, but on tiny particles in a repeating pattern, known as photonic crystals. The periodicity in these particles causes the material to interfere with wavelengths of light. Although the particles themselves are colorless, the precise spacing between them allows certain light waves to pass through them while rejecting others. The visible colors produced change depending on factors such as lighting conditions or shifts in the distance between the particles. The iridescence of some butterfly wings and the feathers of peacocks are among many other examples of photonic crystals in nature.
If you put strawberries into a blender, Dong explains, the resulting liquid will be red because the color of the strawberries comes from pigment. If you grind up iridescent butterfly wings, however, the result will be a dull powder because the rainbow colors were not based on pigments, but on what is known as "structural color." The structure of the photonic crystal arrays is destroyed when the butterfly wings are ground up.
To mimic chameleons and create an artificial smart skin, scientists have experimented with embedding photonic crystal arrays into flexible, water-containing polymers, or hydrogels. Expanding or contracting the hydrogel changes the spacing between the arrays, resulting in a color change. The problem, however, is that the accordion-like action needed to generate a visible change in hue causes the hydrogel to significantly grow or shrink in size, leading to structural instability and buckling of the material.
"No one wants a camouflage cloak that shrinks to change color," Salaita notes.
Dong was pondering the problem while watching YouTube videos of a chameleon. "I wanted to understand why a chameleon doesn't get bigger or smaller as it changes color, but remains its original size," he says.
In close-up, time-lapsed images of the chameleon changing hues, Dong noticed that the arrays of photonic crystals did not cover the entire skin but were spread out within a dark matrix. As the photonic crystals turned different colors, these patches of color remained the same distance apart. Dong hypothesized that the skin cells making up the dark matrix somehow adjusted to compensate for the shifts in the photonic crystals.
"I wondered if we could design something similar -- a composite structure of photonic crystal arrays embedded into a strain-accommodating matrix," Dong says.
The researchers used magnets to arrange patterns of photonic crystals containing iron oxide within a hydrogel. They then embedded these arrays into a second, non-color-changing hydrogel. The second, springy hydrogel was mechanically matched to the first hydrogel to compensate for shifts in distances between the photonic crystals. When heated, this strain-accommodating smart skin (SASS) changes color but maintains a near-constant size.
Dong also tested the material in sunlight, fabricating SASS films into the shape of a fish, in homage to the neon tetra, as well as into the shape of a leaf. When exposed to natural sunlight for 10 minutes, the SASS films shifted from orange to green, without changing in size.
"We've provided a general framework to guide the future design of artificial smart skins," Dong says. "There is still a long way to go for real-life applications, but it's exciting to push the field another step further."
Read more at Science Daily
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