Rare genetic mutations occur more often in schizophrenia patients, researchers find .


DNA sequence. Credit: schulergd / sxc.hu

A new study by University of California, Los Angeles (UCLA) scientists adds to the understanding of the genetic architecture of schizophrenia.

Past research has shown the impact of commonly occurring genetic variants on a person’s risk of developing schizophrenia. This new study focused instead on rare coding mutations that affect protein function. It found that patients with schizophrenia have a higher-than-normal share of these mutations.

“While we cannot point to specific mutations that play a causal role in schizophrenia, we show that schizophrenia patients collectively have more of these mutations than unaffected individuals,” said Loes Olde Loohuis, the study’s first author and a postdoctoral fellow at UCLA’s Center for Neurobehavioral Genetics. The center is part of the university’s Jane and Terry Semel Institute for Neuroscience & Human Behavior.

The findings are reported in Nature Communications.

“Genes that are affected by these mutations play a key role in fetal brain development,” said Roel Ophoff, the study’s senior author and a principal investigator at the Center for Neurobehavioral Genetics. “Our finding further supports the hypothesis that schizophrenia is a disorder that may originate during the early stages of brain development.”

A professor of psychiatry and human genetics, Dr. Ophoff has conducted research on the genetic basis of schizophrenia for the past decade. He is also one of the founding members of the Psychiatric Genomics Consortium’s schizophrenia study group. The consortium is an international collaboration of researchers investigating the genetics of schizophrenia and related disorders.

Schizophrenia affects some 2 to 3 million people in the U.S. — about 1 percent of the population. It is characterized by hallucinations, delusions and disorganization, and can take a tremendous toll on patients and their families. Schizophrenia can cause a significant loss in quality of life, including unemployment and estrangement from loved ones. A better understanding of the causes of the disease may lead to better options for treating it.

Ophoff and his colleagues used an array-based technology to screen for 250,000 DNA coding variants in more than 1000 schizophrenia patients from the Netherlands and compared these samples to those from unaffected individuals. They found that the patients with schizophrenia had more of these variants than patients without schizophrenia. The researchers confirmed these findings in another cohort consisting of more than 13,000 schizophrenia patients and control subjects from the UK.

“Even though it’s well-known that schizophrenia has a large genetic component, the specific biological mechanisms at work are not well understood,” Ophoff said, “Our research shows that rare coding variants throughout the human genome also contribute to this complex genetic architecture.”

Physicists propose new definition of time crystals—then prove such things don’t exist


Few years, physicists have been intrigued by a hypothetical system called a “quantum time crystal,” which has the unusual property of exhibiting periodic motion in its ground state, which is its state of lowest energy. This behavior is unexpected, as it suggests that the system can move even when it doesn’t seem to have enough energy to do so. Ever since time crystals were first proposed in 2012 by Frank Wilczek, physicists have raised serious doubts over their existence, with a few studies already disproving their existence in specific cases.

time crystals

Although at this point it seems likely that time crystals are merely hypothetical concepts, physicists want to be as certain as possible that they do not exist before permanently laying the idea to rest.

With this motivation, physicists Haruki Watanabe at the University of California at Berkeley and Masaki Oshikawa at the University of Tokyo have published a paper in Physical Review Letters in which they first propose a precise of time crystals, and then prove a no-go theorem that rules out the possibility of their existence when defined in this way.

“The original proposal of Wilczek was about a , and we proved its impossibility quite generally,” Watanabe told Phys.org. “We also managed to extend the argument for a ground state (at zero temperature) to a more general ‘‘ state (at non-zero temperatures). These two situations are what we usually discuss for spontaneous symmetry breaking. Thus, we would like to stress that, in our opinion, the spontaneous breaking of time translation symmetry in the standard sense has been proven impossible. In this respect, we believe that our result pretty much settles the debate.”

Yet, as the physicists explain more below, a few open questions still remain.

Time crystals and ordinary crystals

Because a precise mathematical definition of time crystals has been lacking until now, it has understandably been difficult to settle the question of their existence. Watanabe and Oshikawa’s general definition of time crystals resembles the definition of ordinary crystals. Both definitions are based on “long-range order,” which refers to a crystal’s characteristic structure of a highly ordered pattern that repeats over long distances. In ordinary crystals, such as diamonds, long-range order accounts for the periodic geometric shape. In time crystals, according to the new definition, long-range order describes the oscillating motion over time.

When investigating whether time crystals defined in this way actually exist, Watanabe and Oshikawa explain that the key criteria is that the term “crystal” should be reserved for systems that exhibit correlated, coherent behavior. However, due to thermodynamic reasons, they show that a system cannot exhibit this type of behavior at any temperature, and so no real system can be considered a time crystal by this definition.

Overall, the results show that, while ordinary crystals can and do exist, time crystals cannot exist. The only difference between the two is that the first involves spatial long-range order while the second involves temporal long-range order. Although space and time are often considered to be closely related, together forming the “fabric of spacetime,” the findings here emphasize a subtle yet fundamental difference between space and time—with a result that allows for the existence of crystals in one dimension, but forbids them in the other.

Time crystals in equilibrium

There is one minor caveat to the physicists’ definition of time crystals: it requires that the system exist in a state of equilibrium, which is basically the state that a system acquires after a long time without any external forces acting on it. It’s well-known that some non-equilibrium systems exhibit spontaneous oscillations, as demonstrated by a swinging pendulum. However, the researchers explain that these systems should not be considered time crystals without further justification.

“The oscillation of a pendulum or the quantum oscillation in the AC Josephson effect have been known for a long time, and they are not surprising because they are not in thermal equilibrium,” Oshikawa explained. “Certainly they should not be regarded as time crystals. This is a trivial example of periodic motion seen when the system is not in a ground state or in thermal equilibrium. The motion of the pendulum with a small amplitude can be described by a harmonic oscillator, and essentially the same behavior can occur in quantum and classical systems. … Ordinary crystals, on the other hand, can certainly be realized in equilibrium at low enough temperatures.”

With that being said, the scientists also explained that it may still be possible to realize true time crystals in a state of non-equilibrium, but doing so would require formulating a new definition and answering several controversial questions.

“Although it is in the textbooks that any state will approach thermal equilibrium after leaving it for a long enough time—and this has been supported in countless numbers of experiments—this is a highly nontrivial statement and is still under active study,” Watanabe said. “Even if it is true after an infinitely long time, if it requires an unrealistically long time (for example, longer than the age of the universe) to reach the equilibrium, it would be rather irrelevant for actual observation.

“We may generalize the definition of to non-thermal/non-equilibrium setups, and we expect more works along this line. For example, we can easily come up with two interesting open questions one can ask: First, can excited eigenstates [quantum mechanical states] show a time-dependent long range order? This question is related to a recent hot topic, the so-called ‘many-body localization.’ Second, can discrete time translation be spontaneously broken? The continuous time translation cannot be spontaneously broken as we explained above. However, when a system is periodically driven (this makes the problem non-equilibrium), the relevant symmetry is discrete time translation.

“Time crystals may be realized in some way in a non-equilibrium setup, but we would need an appropriate definition for that (as we explained above, there are many systems that show periodic motion rather trivially and we should not include them). As far as we are aware of, there is no positive evidence suggesting such a possibility so far, however.”

First-in-Class Heart Failure Drug Receives FDA Approval


The FDA today approved sacubitril/valsartan (Entresto) for treating heart failure.   The treatment is expected to decrease hospital admissions and extend the life for patients with heart failure with reduced ejection fraction.   Entresto was tested in a trial of more than 8000 patients and was shown to reduce the rate of cardiovascular death and hospitalization related to heart failure when compared with enalapril. Many patients involved in the trial were also taking approved heart failure treatments, such as beta-blockers, diuretics, and mineralocorticoid antagonists.   According to drug manufacturer Novartis, Entresto was able to reduce the risk of death from cardiovascular causes by 20%, reduce heart failure hospitalizations by 21%, and reduce the risk of all-cause mortality by 16%.   Common side effects may include hypotension, hyperkalemia, and renal impairment. Patients may also experience angioedema, especially among African-American patients and those with a prior history of angioedema.   Pharmacists and other health care professionals should make sure patients taking Entresto should not be on any drug from the angiotensin converting enzyme (ACE) inhibitor class, because they may be at greater risk of angioedema. According to the FDA, use of an ACE inhibitor and Entresto should be separated by 36 hours.   Entresto should also not be taken by pregnant women, as the treatment may pose a risk to an unborn baby.   Novartis recently announced it would not use a pay-per-pill method for Entresto; instead, it will use a clinical outcomes-based pricing model. Patients will get a discount for the drug when they purchase it, but they may have to pay more later if Entresto proves to reduce hospital admissions and associated costs. Sales are expected to be strong for the heart failure medicine. The drug is “beyond what [clinicians have] been able to do previously with therapies that we have currently,” Tom Frank, PharmD, BCPS, told Pharmacy Times in an exclusive interview.   The FDA had granted priority review to Novartis’ investigational drug, which had previously been called LCZ696. It was designed to boost the heart’s protective neurohormonal systems and suppress its more harmful systems, thereby alleviating the strain on the heart, according to the manufacturer.  “Heart failure is a leading cause of death and disability in adults,” Norman Stockbridge, MD, PhD, director of the Division of Cardiovascular and Renal Products in the FDA’s Center for Drug Evaluation and Research, said in a press release. “Treatment can help people with heart failure live longer and enjoy more active lives.”

A Spotlight on Sunscreen Regulation.


There may be nothing new under the sun, but the U.S. Food and Drug Administration (FDA) is facing calls for something new under the agency’s authority over sunscreens. In recent months, the FDA has declined to permit use of eight new sunscreen ingredients without additional data, although those ingredients have been used in Europe for more than 5 years and despite the recent passage of a U.S. law intended to expedite the marketing-approval process for new products. The controversy says as much about the challenges facing the agency as it does about sunscreen regulation.

Melanoma is a significant public health problem. Each year, 75,000 people in the United States are diagnosed with and 10,000 die from the disease .

New Cases of Melanoma of the Skin and Deaths per 100,000 Persons, 1992 through 2012.).1 The primary cause of melanoma is known: DNA damage resulting from exposure to ultraviolet radiation. Nevertheless, melanoma rates have been increasing for decades. Reducing exposure to ultraviolent radiation, from both the sun and artificial sources such as tanning beds, is essential to prevention.

In 2012, the FDA determined that sunscreens blocking a broad spectrum of ultraviolet radiation with a sun protection factor (SPF) of 15 or greater could be marketed as reducing the risk of skin cancer. However, it did not remove from the market other sunscreens, such as those with a lower SPF that may only help prevent sunburns. As a result, some Americans may be purchasing “sunscreens” without knowing that there’s no evidence that they protect against cancer. In addition, many Americans fail to use sunscreen as recommended altogether.

Most broad-spectrum sunscreens marketed in the United States contain oxybenzone or avobenzone to block the type of ultraviolet radiation, known as UVA, that is most closely linked to cancer. Since 1999, the FDA has approved one new ingredient, ecamsule, for use in limited formulations for this purpose. In 2002, the agency established a mechanism for considering data from experience elsewhere, including in European countries, where sunscreens are regulated as cosmetics and other ingredients are widely used. But the agency did not take action on applications submitted through this pathway for more than a decade.

In 2013, advocates for patients with melanoma, dermatologists, and manufacturers of new ingredients came together in a coalition called Public Access to SunScreens (PASS). This group argued that the new ingredients would result in products that are more attractive to consumers, such as longer-lasting products that don’t require frequent reapplication. Expressing its dismay over the lack of action on the pending sunscreen applications, the coalition pressed Congress to impose tighter deadlines for FDA decision making. This approach, however, did not fully consider the agency’s framework for review of sunscreens, resource needs, and public health role.

With respect to new prescription drugs, the FDA generally moves faster than European regulatory agencies, and it approved 41 products in 2014 — the most in 18 years. Key to this pace is the fact that under U.S. regulatory law, the agency tailors its approval decisions to the data at hand, receives extra resources (from user fees) for drug reviews, and if problems emerge after approval, has the ability to move quickly with a range of actions to protect the public. Although this process is well suited to individual new therapeutics, it is cumbersome for many products intended to be sold over the counter in a wide variety of formulations and concentrations.

Over-the-counter products such as sunscreens are usually regulated through an entirely different process designed for products posing little to no risk, under the standard of “generally recognized as safe and effective.” There is no product-specific approval decision; rather, the agency must issue proposed and final rules, with multiple opportunities for public comment, before authorizing each class of products. As with other agency regulations, rules for over-the-counter products generally require economic analyses, with clearance often required from both the Department of Health and Human Services and the White House Office of Management and Budget.

Unlike review of new prescription drugs, the pathway for over-the-counter products is supported by no additional resources. Between procedural requirements and inadequate resources, over-the-counter product regulation proceeds in slow motion as compared with the rest of the agency. Rulemaking typically consumes many years, or even decades. Existing sunscreen ingredients, for example, are not, even now, the subject of a final regulation by the agency.

Once issued, rules for over-the-counter products allow companies to manufacture a broad array of formulations and dosages and to market them extensively. The agency has little ability to require the collection of data on long-term safety or efficacy. Even if new troubling safety information on over-the-counter products comes to light, the FDA cannot alter its approach quickly. Instead, it must begin the laborious rulemaking process all over again. These limitations understandably lead to a cautious approach to approving products, such as sunscreens, that are designed for long-term use by millions of children and adults in the absence of disease.

Indeed, in early 2014, the FDA released letters finding insufficient evidence to consider several of the new sunscreen ingredients “generally recognized as safe and effective.” Then, in September, an FDA advisory committee recommended that the agency collect a broad set of data for evaluating all new sunscreen ingredients, including data on skin irritation, carcinogenicity, and developmental toxicology.2

At the end of the year, with the support of the PASS coalition, Congress passed and President Barack Obama signed bipartisan legislation called the Sunscreen Innovation Act. The new law set deadlines for FDA review and removed several procedural requirements for agency action. However, the legislation provided no new resources, no new authority for postmarketing safety, and little new flexibility for the agency in the review process.

Soon after the law’s passage, the FDA released a proposed decision to reject all eight pending ingredients, citing multiple gaps in data, including key safety studies and reports of adverse events in countries where relevant products are marketed.

The agency’s proposal provoked a swift and angry response. In a press release, the PASS coalition stated that the agency “demonstrates clear disregard for increased rates of melanoma and the public’s demand for latest sunscreen technology.”3 The Wall Street Journal editorial board stated that “the agency’s willful culture of control and delay is the real public-health menace. . . . The only solution is to strip the sunscreen police of all powers over the stuff.”4

These attacks missed their mark. It’s no surprise that the FDA would act cautiously given the scientific advice it’s received and a legal structure that essentially provides it with just one tool: authorizing extensive marketing of multiple products and formulations. Understanding the FDA means recognizing that the framework for over-the-counter products is not designed to promote innovation, even innovation with potential public health benefits.

In my view, Congress should try again and pass legislation establishing an alternative approval pathway that combines the flexibility of the new drug pathway with the ability to simultaneously approve multiple formulations and concentrations. The FDA should be able to negotiate with sponsors to get the right data without years of rulemaking, establish postmarketing data requirements, consult with other countries’ regulators to establish consistent standards where possible, and move quickly in the event that safety concerns emerge. Congress should provide additional resources to facilitate timely analysis and review. That this path is viable is evidenced by the fact that the one approval of a product with a new sunscreen ingredient in the past decade came through the new drug pathway.

More timely and flexible review can expand sunscreen options for consumers and complement other measures to reduce melanoma prevalence. Promising steps include FDA efforts to discourage use of tanning beds and initiatives by the Centers for Disease Control and Prevention to promote prevention measures. The federal government should also reconsider whether it makes sense to continue allowing some products to be marketed as sunscreen without evidence of protection against cancer. After all, the ultimate goal is to make meaningful progress against this public health problem.

Switzerland begins postal delivery by drone


http://m.economictimes.com/slideshows/nation-world/switzerland-begins-postal-delivery-by-drone/slideshow/47998181.cms?utm_source=facebook.com&utm_medium=referral&utm_campaign=ETFBMain

Fish oil pills: A $1.2 billion industry built, so far, on empty promises.


For anyone wondering about whether to take a fish oil pill to improve your health, the Web site of the National Institutes of Health has some advice.

Yes. And no.

One page on the Web site endorses taking fish oil supplements, saying they are likely effective for heart disease, because they contain the “beneficial” fatty acids known as omega-3s.

But another page suggests that, in fact, the fish oil pills seem useless: “Omega-3s in supplement form have not been shown to protect against heart disease.”

“I can see how you might think that there is some inconsistency,” Paul R. Thomas, a scientific consultant in NIH’s Office of Dietary Supplements wrote in response to questions about the NIH pages.

Few issues better reflect the American confusion over diet.

People in the United States spend about $1.2 billion annually for fish oil pills and related supplements even though the vast majority of research published recently in major journals provides no evidence of a health benefit.

The “accrual of high-level evidence,” according to a review of studies published last year in an American Medical Association journal, shows “that the supplements lack efficacy across a range of health outcomes.”

While the persistent popularity of fish oil may reflect the human weakness for anything touted as a life-extending elixir, it also reflects that, even among scientists, diet notions can persist even when stronger evidence emerges contradicting them. Scientists, sometimes, are reluctant to let go of ideas.

“Unfortunately, it’s a common situation,” said John P.A. Ioannidis, a professor at Stanford University who has critiqued the methods and findings in nutritional research.

Too often, in the view of Ioannidis and colleagues, claims that one food or another has a particular health effect persist long after they have been contradicted by more exacting research.

For example, his research showed that various claims regarding vitamin E, estrogen and beta-carotene continued to find an audience among scientists — as reflected in scientific papers — even when initial claims about them appear to have been trounced.

“What we have found is that the original papers continue to be cited well after they have been refuted,” he said. “These claims do not easily die away.”

Sorting through warnings
American consumers have long had to sort through confusing contradictions over what food is healthful to eat. And the trouble lies partly in the realm of science, where researchers sometimes have developed diet advice that, despite weakness in the supporting evidence, has been urged on the public.

This year, for example, a federal advisory panel recommended withdrawing the government’s long-standing warning about consuming foods rich in cholesterol, decades after scientists began to argue that the warning was wrongheaded.

Likewise, the long-lived admonition that Americans are using too much salt is facing a strong challenge from research published in prominent medical journals.

The dispute over fish oil and its fatty acids known as omega-3s, meanwhile, is part of a long and confusing debate about the role of fats in the American diet. As far back as 1977, the U.S. Dietary Goals, a forerunner of the federal government’s influential U.S. Dietary Guidelines, called for Americans to eat more carbohydrates and eat less fat. That position is now widely regarded as misguided.

A closer look at the fish oil recommendation shows how health authorities first recommended fish oil despite mixed evidence, then let the recommendation stand even as studies suggesting their worthlessness mounted.

The result can be confusion.

The American Heart Association, for example, recommends that some people with heart disease “may want to talk to their doctor about [omega-3] supplements.” But when the association was asked for an expert to explain the recommendation, that expert, former AHA president Robert Eckel, said that the recommendation needs to be revised.

“It would be a good time for that to be updated,” Eckel said. “Almost all studies of fish oil supplements show no benefit. I really feel this remains unproven.”

An AHA spokesman added: “AHA guideline committees are always reviewing guidelines and assessing whether updates are needed. AHA cannot discuss any guidelines or statements that are currently in the works.”
As for the confusing advice on the NIH Web site, Thomas said the page that endorses fish oil was provided to the NIH by a third party that assesses diet advice.

“Their conclusion that fish oil omega-3s are likely effective for heart disease is generous,” he said. “Whether fish oil can help healthy people prevent or reduce their risks of cardiovascular disease when taken over months and years is still an open scientific question.”

A fish oil story
The fish oil story begins with the account of its discovery. In the 1970s, two Danish scientists, Hans Olaf Bang and Jorn Dyerberg, visited remote Inuit villages in northwest Greenland.

The people in those villages ate mostly whale, seals and fish, according to the scientists. While orthodox thinking at the time suggested that a diet so rich in animal fat would cause heart disease, reports of heart attacks there were very few. Bang and Dyerberg were intrigued.

During their visit, they drew blood samples of 130 Inuits. The samples showed low levels of cholesterol and triglycerides, which are viewed as markers of heart disease.

Eventually, the two formally would hypothesize that the low levels of heart disease among the Inuit was caused by the omega-3s in their fishy diets.

One of the first major tests of this idea was published in the British medical journal the Lancet in 1989. The test, often referred to as the DART study, looked at more than 2,000 Welsh men who had suffered heart attack; some were told to eat more oily fish. That group, it turned out, was 29 percent less likely to die over the next two years.

The demand for fish oil was about to grow. Pharmacies and health food stores were stocking up on fish oil supplements in the ’80s, and by the mid-90s, the industry counted sales in the tens of millions.

But it wasn’t until the early 2000s that the market began to soar. In part, the enthusiasm stemmed from the advice from the broadly influential American Heart Association.

In 2002, the association issued a “Scientific Statement” concluding that “omega-3 fatty acids have been shown in epidemiological and clinical trials to reduce the incidence of cardiovascular disease.”
The statement, however, was based on mixed evidence. Some of the observational studies at the time showed that eating fish provided a benefit; others didn’t. Two randomized trials showed a benefit, while a third didn’t. At the same time, consuming fish and fish oil didn’t show harmful effects, either.

Bill Harris, one of the three authors of the AHA statement, said that currently the “evidence is unclear” on the benefits of fish oils.

But “it all made a lot of sense at the time,” said Harris, now a professor at the University of South Dakota. He is also president of OmegaQuant, a company that analyzes the content of foods. “There seemed to be a benefit, and they were safe, so there was just no downside. Everything looked good, so why not do it?”

The AHA continues to endorse the use of fish oil, suggesting that people with heart disease, particularly those who don’t eat much fish, “may want to talk to their doctor about supplements.”

In 2003, some of the researchers who conducted the early and influential DART study published the results of a follow-up. Of 3,000 Welsh men with angina — a chest pain caused by coronary heart disease — some were advised to eat oily fish or take fish oil supplements. This time, the fish group patients were more likely to die, and the researchers said it was particularly worse for those taking the fish oil pills.

“The excess risk [of cardiac death] was largely located among the subgroup given fish oil capsules,” they reported.

That finding didn’t stop the growth in sales of fish oil pills, however, even though the pages of the academic journals were filling with evidence that fish oil has no benefits.

Andrew Grey and Mark Bolland, researchers at the University of Auckland in New Zealand, for example, last year reviewed fish oil research published in major journals between 2005 and 2012 based on randomized clinical trials. Twenty-two of the 24 studies showed no benefit, according to their work published in JAMA Internal Medicine.

It is possible that fish oil has health benefits that scientific experiments are not sensitive enough to detect.
Most trials have focused on the effects of fish oil on people who have had a history of heart trouble. The trouble with those studies is that such patients are typically taking an array of heart medicines, such as statins, blood thinners and beta blockers. It is possible, scientists say, that the effects of the fish oil can’t be detected among the effects of the other medicines.

An ongoing trial of 26,000 people, however, will focus on the effects of fish oil on a broader set of patients — including those who don’t already have heart disease or use multiple heart medicines.

JoAnn E. Manson, principal investigator of the trial and chief of preventive medicine at the Harvard-affiliated Brigham and Women’s Hospital in Boston, said that it is biologically plausible that omega-3s could protect against heart disease, though there’s not enough evidence to recommend fish oil supplements routinely.

“It’s amazing how popular the fish oil supplements have become without conclusive evidence of their efficacy,” she said.

In the absence of clear messages from health authorities, however, consumers are faced with a barrage of unproven promises.

“The omega-3s [EPA and DHA] in fish oil help support a healthy heart,” according to Nature Made, one company that sells the supplements.

“Their benefits go far beyond the heart,” says Nordic Naturals, which boasts of offering the “#1 selling fish oil in the U.S.”

And Dr. Tobias, another leading fish oil company, suggests that the pills help defend against a remarkable array of ailments. It says “supportive but not conclusive studies indicate benefits of Omega 3 essential fatty acids” for heart disease, dementia, ­Alzheimer’s, arthritis, symptoms of asthma, pneumonia, depression, suicide, wrinkles, acne and psoriasis.

“At the end of the day, omega-3s are healthy fats,” said Adam Ismail, executive director of the Global Organization for EPA and DHA Omega-3s, an industry group. “We believe they prevent heart disease.”

Reptile skin inspires super-slippery steel surfaces.


White-light interferometry images of the textured surfaces showing the two different patterns of scales

The skins of two slithery reptiles – the ball python and a type of lizard known as the sandfish skink – have inspired researchers to create a new kind of super-slippery biomimetic material. By etching patterns similar to those found on these creatures into the surface of steel, Christian Greiner and Michael Schäfer of the Karlsruhe Institute of Technology were able to cut friction by as much as 40%. The researchers say that the work could help to minimize friction in tiny mechanical devices where lubricants cannot be used.

The skin of some snakes and lizards is unusual in that it is slippery when the creature moves forward but resistant to movement in the opposite direction. Apart from allowing the creatures to propel themselves forward, this low friction associated with forward motion combined with the skin’s high resistance to wear has made it an attractive model for researchers seeking to develop new materials. In 2012, for example, scientists were inspired by the skin of the sandfish to create a material that is highly resistant to wear by sand and other particles.

Overlapping scales

Greiner and Schäfer created their reptile-inspired patterns on flat steel surfaces 7.5 mm in diameter using a technique called laser surface texturing. The two patterns they studied were inspired by the overlapping scales found on the python and sandfish, with each scale being oval shaped and about 50 μm long.

The scales protrude about 5 μm from the surface and overlap each other to form columns. In one pattern the columns are isolated from each other, whereas in the other pattern the columns overlap each other (see figure above).

The patterned surfaces were then slid across a smooth, dry sapphire surface at a constant speed of 0.1 m/s and downward force of 2 N. When compared with a smooth steel surface, the isolated columns had 40% lower friction, whereas the overlapping columns had a 22% reduction. The researchers had expected friction to be lower because the species they mimicked live in dry environments and do not secrete oils or other liquids onto their skin. However, they were amazed by the size of the reduction.

Leaping forward

“If we’d managed just a 1% reduction in friction, our engineering colleagues would have been delighted; 40% really is a leap forward and everyone is very excited!” says Greiner. Indeed, when the textured surfaces were lubricated with mineral oil, they experienced greater friction than did a smooth lubricated surface.

The researchers believe that their discovery could help to reduce friction in machines that cannot be lubricated. These include nanometre and micron-sized devices in which lubricants tend to gum up moving parts, rather than help them move. Potential applications include reducing friction in the sensors used in anti-lock braking systems, computer hard-disk drives, accelerometers used in mobile phones and machines that operate under vacuum conditions.

Unlike reptile skin, which has low friction when moving in only one direction, the new textured surfaces have reduced friction in at least two directions. Surfaces with unidirectional friction reduction could be used to create snake-inspired robots that would be useful for exploring extremely dusty environments on Earth or even in space. Greiner is currently trying to develop textured polymer surfaces that mimic the unidirectional nature of reptile skin.

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