Squeezing polymers produces chemical energy but raises doubts about implant safety

In a new study, Northwestern University scientists turned to squeezed polymers and free radicals in a search for new energy sources. They found incredible promise but also some real problems. Their report is published by the journal Angewandte Chemie.

The researchers demonstrated that radicals from compressed polymers generate significant amounts of energy that can be used to power chemical reactions in water. This energy has typically been unused but now can be harnessed when polymers are under stress in ordinary circumstances -- as in shoe soles, car tires or when compacting plastic bags.

They also discovered during the study that a silicone polymer commonly used in implants for cosmetic procedures releases a large quantity of harmful free radicals when the polymer is under only a moderate amount of pressure. These findings suggest the safety of certain polymer-based medical implants should be looked at more closely.

"We have established that polymers under stress create free radicals with overall efficiencies of up to 30 percent and shoot the radicals out into the surrounding medium where they can drive chemical reactions," said Bartosz A. Grzybowski, an author of the paper and the Kenneth Burgess Professor of Physical Chemistry and Chemical Systems Engineering. "These radicals can be useful or they can be harmful, depending on the situation."

Grzybowski and his team are the first to use this energy to drive chemical reactions by simply surrounding the compressed polymer with water containing desired reagents.

The radicals created in the polymer migrate toward the polymer/water interface where they produce hydrogen peroxide, which then can drive chemical processes.

"You can get a surprisingly large amount of chemical energy from a polymer under compression," Grzybowski said. "This energy is, in a sense, free for the taking. Under normal circumstances, the energy is virtually never retrieved from deformed polymers, which then age unproductively. But you could recharge a battery from the energy produced by walking or driving a car. And you could capture even more energy when compacting millions of plastic bags."

Grzybowski is also director of Northwestern's Non-Equilibrium Energy Research Center, which is funded by the U.S. Department of Energy.

"We are interested in new sources of chemical energy, and this energy from the simple breaking of polymers' bonds is not being used," he said. "By surrounding the polymer with a medium, such as water, we can produce environmentally friendly chemical energy. One direction we are pursuing is to use this energy to sanitize water in developing countries. This is possible because hydrogen peroxide produced by squeezed polymers kills bacteria."

The researchers confirmed that mechanical deformation -- moderate squeezing -- created free radicals in the polymers. They also determined the number of radicals produced in a polymer under pressure is approximately 1016 (10 to the 16th) radicals per cubic centimeter of polymer -- a substantial amount.

They next filled polymer tubes with water, squeezed the tubes and measured the total number of radicals that migrated into the surrounding solution. They found that nearly 80 percent of the radicals made the trip.

Grzybowski and his team demonstrated they can squeeze a polymer, such as what might be found in a shoe, tire or plastic bag, and get a mechanical-to-chemical energy conversion of up to 30 percent -- approaching the energy efficiency of a car engine.

The hydrogen peroxide produced when a polymer surrounded by water is squeezed can power a variety of chemical reactions, including fluorescence, nanoparticle synthesis and dye bleaching, the researchers showed.

To illustrate the process, they converted a Nike Air LeBron shoe into a "lightning shoe," where the air pockets in the polymeric sole are filled with a solution of a compound that lights up in the presence of radicals. After a person walked in the shoe for 30 minutes or more, enough radicals were created to generate a blue glow visible to the naked eye.

The researchers studied seven different polymers, including a number of particular public interest. Poly(dimethylsiloxane), a silicon-based material commonly used in medical implants, was one of them. In the lab experiments, the medium surrounding the polymer and the amount of pressure exerted on the material were similar to what would be found in the human body, Grzybowski pointed out.

"Our findings are somewhat worrisome since every polymeric implant in the human body experiences mechanical stresses and, as we now know, can produce harmful free radicals and liberate them into surrounding tissues, which may contribute to diseases such as cancer, stroke, myocardial infarction, diabetes and other major disorders," Grzybowski said. "With this knowledge, I am quite happy to have a metal implant in my knee, rather than a polymer implant.

"From a scientific perspective, our work proves yet again that a phenomenon can be useful or harmful depending on how we implement it," he said. "The same polymer can be a useful source of energy when outside of a human body, yet a potential risk hazard when implanted into it."

More information: The title of the paper is "Mechanoradicals Created in 'Polymeric Sponges' Drive Reactions in Aqueous Media." In addition to Grzybowski, other authors of the paper are H. Tarik Baytekin and Bilge Baytekin (who contributed equally).

Provided by Northwestern University (news : web)

Squeezing silicone polymers produces chemical energy, but raises doubts about implant safety

 A polymer is a mesh of chains, which slowly break over time due to the pressure from ordinary wear and tear. When a polymer is squeezed, the pressure breaks chemical bonds and produces free radicals: ions with unpaired electrons, full of untapped energy. These molecules are responsible for aging, DNA damage and cancer in the human body.

In a new study, Northwestern University scientists turned to squeezed polymers and free radicals in a search for new energy sources. They found incredible promise but also some real problems. Their report is published by the journal Angewandte Chemie.

The researchers demonstrated that radicals from compressed polymers generate significant amounts of energy that can be used to power chemical reactions in water. This energy has typically been unused but now can be harnessed when polymers are under stress in ordinary circumstances -- as in shoe soles, car tires or when compacting plastic bags.

They also discovered during the study that a silicone polymer commonly used in implants for cosmetic procedures releases a large quantity of harmful free radicals when the polymer is under only a moderate amount of pressure. These findings suggest the safety of certain polymer-based medical implants should be looked at more closely.

"We have established that polymers under stress create free radicals with overall efficiencies of up to 30 percent and shoot the radicals out into the surrounding medium where they can drive chemical reactions," said Bartosz A. Grzybowski, an author of the paper and the Kenneth Burgess Professor of Physical Chemistry and Chemical Systems Engineering. "These radicals can be useful or they can be harmful, depending on the situation."

Grzybowski and his team are the first to use this energy to drive chemical reactions by simply surrounding the compressed polymer with water containing desired reagents.

The radicals created in the polymer migrate toward the polymer/water interface where they produce hydrogen peroxide, which then can drive chemical processes.

"You can get a surprisingly large amount of chemical energy from a polymer under compression," Grzybowski said. "This energy is, in a sense, free for the taking. Under normal circumstances, the energy is virtually never retrieved from deformed polymers, which then age unproductively. But you could recharge a battery from the energy produced by walking or driving a car. And you could capture even more energy when compacting millions of plastic bags."

Grzybowski is also director of Northwestern's Non-Equilibrium Energy Research Center, which is funded by the U.S. Department of Energy.

"We are interested in new sources of chemical energy, and this energy from the simple breaking of polymers' bonds is not being used," he said. "By surrounding the polymer with a medium, such as water, we can produce environmentally friendly chemical energy. One direction we are pursuing is to use this energy to sanitize water in developing countries. This is possible because hydrogen peroxide produced by squeezed polymers kills bacteria."

The researchers confirmed that mechanical deformation -- moderate squeezing -- created free radicals in the polymers. They also determined the number of radicals produced in a polymer under pressure is approximately 1016 (10 to the 16th) radicals per cubic centimeter of polymer -- a substantial amount.

They next filled polymer tubes with water, squeezed the tubes and measured the total number of radicals that migrated into the surrounding solution. They found that nearly 80 percent of the radicals made the trip.

Grzybowski and his team demonstrated they can squeeze a polymer, such as what might be found in a shoe, tire or plastic bag, and get a mechanical-to-chemical energy conversion of up to 30 percent -- approaching the energy efficiency of a car engine.

The hydrogen peroxide produced when a polymer surrounded by water is squeezed can power a variety of chemical reactions, including fluorescence, nanoparticle synthesis and dye bleaching, the researchers showed.

To illustrate the process, they converted a Nike Air LeBron shoe into a "lightning shoe," where the air pockets in the polymeric sole are filled with a solution of a compound that lights up in the presence of radicals. After a person walked in the shoe for 30 minutes or more, enough radicals were created to generate a blue glow visible to the naked eye.

The researchers studied seven different polymers, including a number of particular public interest. Poly(dimethylsiloxane), a silicon-based material commonly used in medical implants, was one of them. In the lab experiments, the medium surrounding the polymer and the amount of pressure exerted on the material were similar to what would be found in the human body, Grzybowski pointed out.

"Our findings are somewhat worrisome since every polymeric implant in the human body experiences mechanical stresses and, as we now know, can produce harmful free radicals and liberate them into surrounding tissues, which may contribute to diseases such as cancer, stroke, myocardial infarction, diabetes and other major disorders," Grzybowski said. "With this knowledge, I am quite happy to have a metal implant in my knee, rather than a polymer implant.

"From a scientific perspective, our work proves yet again that a phenomenon can be useful or harmful depending on how we implement it," he said. "The same polymer can be a useful source of energy when outside of a human body, yet a potential risk hazard when implanted into it."

Story Source:

The above story is reprinted from materials provided by Northwestern University. The original article was written by Megan Fellman.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

H. Tarik Baytekin, Bilge Baytekin, Bartosz A. Grzybowski. Mechanoradicals Created in “Polymeric Sponges” Drive Reactions in Aqueous Media. Angewandte Chemie, 2012; DOI: 10.1002/ange.201108110

Thin Body of Evidence: Why I Have Doubts about Gary Taubes's Why We Get Fat

When someone divides a complex phenomenon into two basic categories, he invariably oversimplifies and distorts reality. Anyway, there are two basic styles of science journalism, celebratory and critical. Celebratory journalists help us appreciate the cool things scientists discover, whereas critical journalists challenge scientists' claims.

Gary Taubes practices critical science journalism, although calling Gary "critical" is like calling Donald Trump "self-confident." No journalist whacks scientists with more gusto than Gary, whom I've known for 15 years. Gary, who earned his degree in physics and was briefly—and tellingly—an amateur boxer, began his career thumping physicists. His first book, Nobel Dreams (Random House, 1987), asserted that ruthless ambition more than the desire for truth compelled Nobel laureate Carlo Rubbia to seek the particles that mediate the weak nuclear force. (Scientists can be swell-headed! Who knew?) In his next book, Bad Science (Random House, 1993), Gary lambasted the jokers behind the "cold fusion" fiasco of the late 1980s.

Gary's career really took off when he switched his focus from physics to a topic that the masses actually care about: diet. In a lengthy article published in 1998 in Science (for which he has long been a correspondent) Gary raised doubts about the claim that low-salt diets are healthy. In a 2002 cover story for The New York Times Magazine, Gary questioned the truism that people are getting fatter because they eat too much—especially fatty foods—and exercise too little. Carbohydrates, Gary contended, have fueled the epidemic of obesity in the U.S.; cut the carbs and you can eat all the fat and protein you like, just as the controversial diet doctor Robert Atkins has insisted for decades. Gary expanded on the Times article in a dense, 500-plus-page book, Good Calories, Bad Calories (Knopf, 2007), and a newer, much shorter, easier-to-digest sequel, Why We Get Fat (Knopf, 2010).

I have great respect for Gary. He's a science journalist's science journalist, who researches topics to the point of obsession—actually, well beyond that point—and never dumbs things down for readers. I read both of Gary's fat books, invited him to speak about diet at my school two years ago, and discussed the subject with him on Bloggingheads.tv last month. Gary marshals mountains of data in support of his thesis, but I still have misgivings about it. My reaction is partly visceral; the Atkins diet—which prescribes little fruit and vegetables and lots of meat—strikes me as, well, gross. Here is Gary's personal diet, as described on his blog:

"I do indeed eat three eggs with cheese, bacon and sausage for breakfast every morning, typically a couple of cheeseburgers (no bun) or a roast chicken for lunch, and more often than not, a rib eye or New York steak (grass fed) for dinner, usually in the neighborhood of a pound of meat. I cook with butter and, occasionally, olive oil (the sausages). My snacks run to cheese and almonds. So lots of fat and saturated fat and very little carbohydrates." Even disregarding the economic, environmental and ethical issues raised by consuming all this meat, the burden of proof for a diet like Gary's should be quite high.

Gary suggested as much in a 2007 article for The New York Times Magazine, "Do We Really Know What Makes Us Healthy?," which I often assign to students in my science-writing seminar. The article examined the "here-today-gone-tomorrow nature of medical wisdom," such as the claim—touted in the 1990s and retracted a decade ago—that estrogen could improve the health of aging women. Gary noted that even the best-designed epidemiological studies are confounded by factors such as "healthy-user bias," the tendency of people who faithfully adhere to a treatment to be healthier than those who are less compliant—even if the treatment is a placebo. He warned that if a study implies that "some drug or diet will bring us improved prosperity and health," we should "wonder about the unforeseen consequences."

Gary, it seems to me, applies this critical outlook more to high-carb, low-fat diets than to the Atkins diet, which he celebrates for helping him and many others lose weight "almost effortlessly." If the Atkins diet works so well, why hasn't it swept aside its competitors, especially low-calorie, low-fat diets recommended by Weight Watchers and other popular groups? One problem, Gary says, is that many people become addicted to carbs, and their craving makes them fall off the Atkins wagon. Switching from a high-carb, low-fat diet to the Atkins system, Gary also acknowledges in Why We Get Fat, can trigger "weakness, fatigue, nausea, dehydration, diarrhea, constipation," among other side effects. Gary assures readers that they'll reap the benefits if they just stick to Atkins, but he slams advocates of less-fat, more-exercise diets for giving people this same just-stick-to-it advice.

Gary is a big guy, 1.9 meters (six feet, three inches) tall, who weighs over 90 kilograms (200 pounds) and years ago struggled with his weight. Exercise didn't help him slim down, he said, but the Atkins diet did. Because Gary cites his personal experience as evidence, I can cite mine as counterevidence. I'm 1.85 meters (six feet, one inch) tall. I eat lots of carbs, including pasta, bread, rice, potatoes, cookies, cake, pie and three teaspoons of sugar in coffee at least twice a day. I weigh 77 kilograms (170 pounds). I'm just one of those lucky folks, Gary says, whose genes let them chow down carbs without getting fat.

Here is another more significant exception: Many Asian people consume lots of carbs, especially rice, without getting fat. Well, Gary says, that's because these Asians don't ingest as much highly processed sugar—contained in soft drinks, for example—as Americans do. But then why not just cut out these sugary foods instead of almost all carbs? Gary seems to recommend this course in a New York Times Magazine cover story published in April, "Is Sugar Toxic?".

But now we're moving away from the dramatic, celebratory claim that the Atkins diet solves obesity to a more complex perspective: For many people high-carb diets are fine, and the low-carb Atkins diet isn't; different diets work for different people. Reviewing Why We Get Fat in The New York Times, Abigail Zuger, a physician, notes that "in virtually all head-to-head comparisons of various diet plans, the average long-term results have invariably been quite similar—mediocre all around." Given the "remarkable diversity of the human organism," she adds, "it is foolish to expect a single diet to serve all comers." Zuger's take seems reasonable to me.

Toward the end of our Bloggingheads interview, I asked Gary about his family's diet. He answered cagily, but he implied that his wife has
resisted putting their two kids on Atkins. I think that's sensible,
and Gary, when in his critical rather than celebratory mode, probably does, too. Although he insists that the evidence for his diet claims is overwhelming, he acknowledges in an author's note to Why We Get Fat that the claims still need to be "rigorously tested."

So, when Gary divides diets into two basic categories—the Atkins diet, which is good, and all other diets, which are bad—he's oversimplifying and distorting reality. But read his new book with a critical eye, check out my Bloggingheads interview with him and make up your own mind.

Credit: Alfred A. Knopf

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