Tree Frog Inspires New Easy-Off Stickies

Tree Frog Inspires New Easy-Off Stickies

But can they out-stick wall-walking gecko robots? 

	Image: BARNES RESEARCH GROUP
	STICK AROUND:  A new adhesive takes its cue from the sticky toe pads of tree frogs. CLICK HERE FOR FULL IMAGE

Scotch tape, packing tape, Post-its—no man-made adhesive holds a candle to the sticky world of animal adhesives, where geckos scurry across ceilings and tree frogs leap from leaf to leaf on tacky toe pads without missing a step.

Unable to beat nature, researchers have joined it. The ripping sound of Velcro echoes the prickly, sweater-grabbing burdock seeds that inspired the childhood wonder material. Gecko feet bristle with millions of branching, self-cleaning fibers called setae, the inspiration for so-called "gecko tape." Even the "glue" that keeps zebra mussels anchored to rocks has been imitated. 

Now, inspired by the clingy toes of tree frogs and insects, researchers have created a new adhesive that can become up to 30 times stickier on demand or peel off easily, allowing it to re-adhere. Although weaker than ordinary Scotch tape, researchers say the concept may lead to custom-strength, reusable adhesives that peel off without losing their gluey power.

The secret to the film's ability to grip and release, they say, lies in narrow, oil-filled channels just below the surface, reminiscent of the honeycomb grooves on tree frog toe pads and the feet of bush crickets and other insects. Unlike hairy gecko feet, tree frogs and insects secrete a viscous fluid onto their flat, adhesive pads.

Like speed bumps, the grooves slow the growth of cracks that form when adhesives stretch to their breaking point. Adding fluid diffuses the rupture-causing forces on the grooves through the so-called capillary effect, says materials chemist Animangsu Ghatak of the Indian Institute of Technology Kanpur.

Inspired by the concept, Ghatak and his colleagues carved micro-scale tubes in a layer of the polymer PDMS (polydimethyl siloxane), which sticks very weakly on its own, then filled the channels with silicone oil. They sandwiched the film between two plates and pulled the top plate up to test the stickiness. The best results—a 3,000 percent gluey boost—came from tubes 710 microns wide (nearly ten times thicker than a human) filled with moderately viscous oil, the researchers report in Science.

Image: BARNES RESEARCH GROUP
HONEYCOMB GROOVES  in the toe pad of a tree frog, visible under the electron microscope, slow the formation of adhesion-busting cracks. CLICK HERE FOR FULL IMAGE

To switch the adhesive on and off, they added a second layer of tubes to the film, filling one set with oil and the other with air. When the oil was on the bottom, the adhesive held fast, but when it was flipped to the top, the film gave way without leaving a residue, the group reports. Ghatak says the adhesive can re-stick up to 25 times without weakening.

"The results are really exciting," says Phillip Messersmith, associate professor of biomedical engineering at Northwestern University. "To my knowledge, this is the first study describing the use of subsurface features—the air- or silicone-filled channels—to enhance adhesion."

The findings also help solve the mystery of why tree frog and insect pads consist of a stiff outer layer over a fluid-filled one, says biologist Jon Barnes of the University of Glasgow in Scotland, who studies tree frog adherence.

The leading bioinspired adhesive, however, is probably still gecko tape, which has proved its sticking power: Carnegie Mellon University researchers designed a robot that climbed straight up a smooth wall on strips of custom tape. And Messersmith's group unveiled a reusable adhesive in July that combined geckolike hairs with an imitation zebra mussel glue. Voila: the resulting "geckel" tape stuck to wet surfaces as well as dry ones.

Messersmith says the catch with the tree frog adhesive is that the parallel channels work in only one direction, and it could be pricey to manufacture tape with a network of fluid-filled tubes.

So what are the prospects of a real-life, wall-scaling Spider-Man? Messersmith does not rule it out, but notes it is still a long way off. Without self-cleaning, gecko tape would quickly get gunked up, and reusability remains a rare commodity among bioinspired adhesives. "It's remarkable really," he says, "since the essence of tree frog and gecko adhesion is that it is temporary and reversible." 

Cosmic Factories Produce Rubies and Sapphires

Cosmic Factories Produce Rubies and Sapphires

Like enormous jewel factories in the sky, the chaotic environments around some supermassive black holes crank out prodigious amounts of glass, rubies and sapphires, a new study finds

The inevitable breakdown of these materials into simpler components could account for much of the space dust in the universe—dust that is recycled to make stars, planets, and life. 

Traces of these minerals, as well as sand and marble, were recently found by scientists analyzing light from the region around a nearby supermassive black hole using NASA's Spitzer Space Telescope. The black hole was embedded in a quasar, a highly active and incredibly bright galaxy under construction. 

"We were surprised to find what appears to be freshly made dust entrained in the winds that blow away from supermassive black holes," said study team member Ciska Markwick-Kemper of the University of Manchester in the U.K. 

The finding, to be detailed in an upcoming issue of Astrophysical Journal, could also help solve the mystery of where dust used to build the first generation of stars in the universe came from. 

The space dust in our corner of the universe is thought to have been created when ancient stars resembling massive versions of our sun exploded as supernovas at the ends of their lives. But when the universe was new, sun-like stars hadn't been around long enough to die and make dust. So where did the dust needed to make those stars come from? 

One idea is that the dust came from quasars, which are supermassive black holes surrounded by dusty, doughnut-shaped clouds and lots of radiation. They are the most active, budding galaxies known, where gravity lures material in but the resulting pressure blows material away on a constant cosmic tug-of-war that results in high rates of star formation and the creation of  new elements. 

"Quasars are like the Cookie Monster," said study team member Sarah Gallagher of the University of California, Los Angeles. "They can consume less matter than they can spit out in the form of winds." 

To test this theory, Gallagher and her team used Spitzer to investigate PG2112+059, a quasar located in the center of a galaxy about 8 billion light-years away. They found evidence of sand and minerals such as rubies that do not last long in the harsh environment of space, suggesting they were freshly made. 

The researchers plan to look for evidence of dust around other quasars to strengthen their case. It's also possible, they say, that quasars were not the only source of dust in the early universe. 

"Supernovas might have been more important for creating dust in some environments, while quasars were more important in others," Markwick-Kemper said. 

 
This Hubble Space Telescope image, taken December 29, 2005 and released on October 2, 2007...

Study: Bad marriage could damage heart

Study: Bad marriage could damage heart

• Story Highlights
• Study: Bad personal relationships can raise heart disease risk
• Increased stress is probably the key factor
• Previous studies linked health problems with being single
• Current research focused more on quality of important relationships

Marital strife and other bad personal relationships can raise your risk for heart disease, researchers reported Monday.

What it likely boils down to is stress -- a well-known contributor to health problems, as well as a potential byproduct of troubled relationships, the scientists said.

In a study of 9,011 British civil servants, most of them married, those with the worst close relationships were 34 percent more likely to have heart attacks or other heart trouble during 12 years of follow-up than those with good relationships. That included partners, close relatives and friends.

The study, in Monday's Archives of Internal Medicine, follows previous research that has linked health problems with being single and having few close relationships. In the new study, researchers focused more on the quality of marriage and other important relationships.

"What we add here is that, 'OK, being married is in general good, but be careful about the kind of person you have married.' The quality of the relationship matters," said lead author Roberto De Vogli, a researcher with University College in London.

De Vogli said his research team is doing tests to see whether study participants with bad relationships have any biological evidence of stress that could contribute to heart disease. That includes inflammation and elevated levels of stress hormones.

Another recent study also looked at quality of relationships but had different results. There was no association between marital woes in general and risks for heart disease or early death. But it did find, over a 10-year follow-up, that women who keep silent during marital arguments had an increased risk of dying compared with wives who expressed their feelings during fights. What appeared to matter more for men was just being married; married men were less likely to die during the follow-up than single men.

That study, of nearly 4,000 men and women, was published online in July in the journal Psychosomatic Medicine.

In De Vogli's study, men and women with bad relationships faced equal risks. Volunteers filled out questionnaires asking them to rate the person to whom they felt closest on several measures. These included questions about to what extent does that person "give you worries, problems and stress?"

They also were asked about whether they felt they could confide in that person, or whether talking with that person made them feel worse.

Over the following 12 years, 589 participants had heart attacks or other heart problems. Those with the highest negative scores on the questionnaire had the highest risks, even taking into account other factors related to heart disease such as obesity, high blood pressure and smoking.

James Coyne, a University of Pennsylvania psychology professor who also has examined the health impact of social relationships, said De Vogli's results "make intuitive sense." But he said the study found only a weak association that doesn't prove bad relationships can cause heart disease.

"It is still not clear what to recommend," Coyne said.

"Do we tell people who have negative relationships to get therapy? They may have other reasons to do so, but I see no basis for them doing so only to avoid a heart attack," Coyne said.

Ending a bad marriage is not necessarily the answer either, he said, given evidence that being unmarried also could be a risk.

Remote parts of Mont. park said polluted

Remote parts of Mont. park said polluted

Pollution has tainted even the most remote areas of Glacier National Park, and some fish in backcountry waters are so contaminated they could endanger the wildlife eating them, a federal scientist has found.

Dixon Landers of the U.S. Environmental Protection Agency led a three-year study examining pollution that travels in the air.

Landers first hiked into Glacier in 2003. Later he and his team used more than a dozen mules to transport some 2,000 pounds of scientific gear to places such as Snyder Lake, high above the park's McDonald Valley. The researchers took samples that included water, lake sediment, vegetation and fish.

Water tests revealed contamination such as a pesticide that is not used widely in the United States but is applied in Canada, and pesticides that are banned in North America but still are used in some other parts of the world.

Other scientists who have studied water and snow chemistry in Glacier have looked mostly for the "dirty dozen," consisting of pesticides known collectively as persistent organic pollutants, or POPs. Landers' work searched for more than 100 semi-volatile organic compounds, or SOCs.

Both POPs and SOCs have relatively low molecular weights and volatilize easily in the atmosphere when put under heat. They move around the globe, scrubbing out of the air in rain or snow and then vaporizing back into the sky during warmth. Glacier is the kind of cold spot in which they can become trapped.

Landers arrived at the park suspecting it might be a sort of sponge for contaminants transported by powerful jet streams, high-elevation winds known to carry sand and dust from China's Gobi Desert all the way to North American soils. An air mass can move from the Far East to Washington's Olympic National Park in just five days and deliver chemicals unused for decades in this part of the world, he said.

Often concentrations have been small, perhaps too small to be of concern, he indicated.

He wondered what chemicals are at Glacier, whether they posed a risk, where they came from, where they accumulate and how best to measure them.

Studying fish is one way to find answers because chemicals tend to accumulate in fatty tissue and eggs. Some toxins that were small, airborne concentrations build to much higher concentrations within fish and move up the food chain, Landers said.

He found that "for certain contaminants, wildlife exposure thresholds are exceeded for several different species that feed on fish."

Data from Glacier eventually will be compiled with information from eight other parks in the West, providing a baseline for measuring future changes.

Study Reveals 10 Most Terrible Office Behaviors

Study Reveals 10 Most Terrible Office Behaviors

A coworker who takes credit for someone else's work or rattles off obnoxious jokes is engaging in one of the top 10 most offensive workplace no-no's, according to survey results released this week.

These and other workplace misdeeds earned spots on a "Terrible Ten" list of rude working-world behaviors. While discrimination topped the list as most offensive, other highly ranked job-related transgressions occur beyond the office entrance, such as crazy driving.

"The research suggests that people are bothered more by the transgressions of coworkers and strangers than by those of family and friends," said study team member P.M. Forni, director of the Civility Initiative at Johns Hopkins University, which began in 1997 to evaluate the significance of manners and civility in contemporary society.

Out of 30 examples of rude behavior, survey respondents most often indicated the following 10 as most offensive in this order:

1. Discrimination in an employment situation

2. For commuters, erratic/aggressive driving that endangers others

3. Taking credit for someone else’s work

4. Treating service providers as inferiors

5. Jokes or remarks that mock another, including remarks about race, gender, age, disability, sexual preference and religion

6. Children who behave aggressively or who bully others

7. Littering or spitting

8. Misuse of handicapped privileges

9. Smoking in non-smoking places or smoking in front of non-smokers without asking

10. Using cell phones or text messaging in mid-conversation or during an appointment or meeting

For this survey, Forni and his colleagues polled 615 employees of two Baltimore-based companies, along with employees and students at the University of Baltimore, in May 2007. The participants rated 30 examples of rude behavior from 1 (not offensive) to 5 (most offensive).

The top-10 list will be published in Forni's upcoming book, "The Civility Solution: What to do When People Are Rude," due out next spring.