Smooth operators: Teflon microfluidic chips

The growing number of research and development efforts focused on microfluidics speaks to the technology’s promise of a potentially broad range of applications, largely in highly-integrated single-chip medical devices. However, the materials currently used to fabricate these labs-on-a-chip and other microfluidic devices have significant limitations, including absorption of small nonpolar and weakly polar molecules, adsorption of biomolecules, and the material’s molecules leaching into the microfluidic channel. The good news is that researchers have overcome these obstacles using microfluidic channels made entirely of Teflon, which supports cellular activity similar to that found in current materials. Moreover, whole-Teflon microchannels have gas permeability levels that permit cells to be cultured in-channel for extended periods of time.

The researchers, led by Prof. Hongkai Wu at Hong Kong University of Science and Technology’s Department of Chemistry, faced a number of obstacles to designing and developing a microfluidic chip that was optimally inert yet suitable to machining. “Currently, there are two major types of materials for microfluidic chips,” Wu explains to PhysOrg.com. “One is inorganic, such as glass and silicon. Unfortunately, fabrication of micropatterns and bonding chips of these materials are difficult and require sophisticated equipment. The other class of materials is plastics, including polydimethylsiloxane (PDMS) – the most widely-used – poly(methyl methacrylate) (PMMA), and polyurethane. Chips in plastics are easier to fabricate than in glass, but they have their own problems,” including the adsorption, absorption and leaching mentioned above, as well as being incompatible with organic solvents, all of which greatly limit their microfluidic chip applications.

“For example,” Wu continues, “they will be unsuitable for highly-sensitive analysis because the analyte will be lost by absorption if it’s a small, non/weakly polar molecule or by adsorption on channel walls if it’s a large molecule. For all of these reasons, we chose Teflon, which is well-known for its high degrees of inertness, non-adhesiveness and resistance to solvents.” Moreover, the Teflon compounds Wu used – perfluoroalkoxy (PFA) and fluorinated ethylenepropylene (FEP) – have melting points above 260 °C (one of the highest in thermoplastics) and are optically transparent (although less so than PDMS and glass).

At the same time, Teflon had its own challenges. For example, Wu notes, “Teflon’s superior inertness causes two major obstacles: one in micropatterning the material and the other in bonding patterned chips. Prior to our work, there were only several very expensive and complicated lithographic methods using high-energy radiation to effectively micropattern Teflon.”

In addition, Wu continues, “tight bonding of Teflon chips is rather difficult. Both bonding temperature and pressure need to be precisely controlled to overcome the problems that come from residue internal stress and plastic flow. “Initially we tried to bond the Teflon channel without pressure (as for bonding glass chips) and with constant pressure (as for bonding PMMA chips),” says Wu, “but neither worked. We needed an effective and convenient method to bond and thereby seal the Teflon channels.”

Overcoming these two obstacles led to the team’s two key innovations, micropatterning Teflon materials and bonding Teflon chips. “We established a very simple and easy-access method to fabricate three-dimensional Teflon micro- and nanostructures. The Teflon PFA and FEP substrates we used are melt-processable, so they could be hot-embossed using a template – an ideal way is to generate micropatterns in photoresist and then transfer the structure into the mold.”

But another problem arose. “Teflon’s melting points of substrates are much higher than those of photoresist. We therefore introduced a specially-treated intermediate thermosetting master to overcome the gap between low-melting-point photoresist master and a high-melting-point replica, allowing us to cast the master at milder temperatures into the replica and then use it at elevated temperatures to mold the patterns into Teflon.”

Their method was adapted from traditional soft-lithography, which previously wasn’t applicable to high-melting-point substrates. “Normal PDMS severely leaches gas above 150 °C, creating bubbles that make it impossible to mold micropatterns into Teflon. With our treated PDMS replica, we now can mold any micropatterns that are formed in photoresist by photolithography into thermoplastics (including Teflon) at as high as 350 °C.”

The team also designed a very simple and highly efficient method that solved the problems that have been encountered for a long time when bonding Teflon chips. This thermobonding process is based on different thermal expansion factors of Teflon materials (slightly higher than that of stainless steel) and the holding scaffold (stainless steel screw clamps) during bonding. “The bonding pressure is automatically controlled,” Wu explains. “When temperature is raised and the two Teflon plates are not bonded, Teflon expands more than the clamps and so the pressure is high. Once the two plates are bonded, the pressure is automatically released.”

Wu is already looking at future innovations and improvements. “We want to develop a smaller on-chip microvalve. The current nanoliter valve is still relatively large, so we’re working on reducing its volume to the picoliter range.” The team is also interested in advances in Teflon itself. “The optical transparency of our current whole-Teflon chip is still lower than that of PDMS and glass chips, so optical detection can be performed only when the optical path length of the Teflon chip is less than 2 mm. If the Teflon materials become as transparent as PDMS or glass, we will have more freedom in designing the microchips. But,” he acknowledges, “this depends on the design of new Teflon materials.”

In terms of the new chip’s most promising near-term and future applications, Wu comments that “since the whole-Teflon device is extremely inert and super-clean, it is superior for applications involving corrosive chemicals, strong solvents, high and low temperatures, and pressurized processes. It is antifouling and biocompatible, and therefore well suitable for quantitative and biological analysis. Interestingly, various biological cells can attach and grow well inside the Teflon channels – so it expands the applications of microfluidics to all these areas that were previously difficult. It is particular advantageous when accurate quantitative information is required.”

Beyond this Wu sees an even wider range of possibilities. “We also believe that Teflon materials are superior to PDMS for commercial applications of microfluidics due to their outstanding stability and reliability. Teflon could be a next-generation microchip material with very broad use, such as serving as standard equipment for flow reactors, microanalysis and bioassay. Moreover, they can also be used under extreme conditions – for example, on a space shuttle.”

Perhaps the ultimate application of Wu’s Teflon microfluidic technology will derive from the intersection of further miniaturization and biocompatibility. “We can mold Teflon pattern down to submicron range and fabricate sealed Teflon channels within the scale of 10 um. Since Teflon materials have outstanding biocompatibility and have long been used for implantations in human body, such as catheters, miniaturized Teflon microfluidic devices might be used for in-vivo diagnostics, drug delivery and flow control.”

More information:
* Whole-Teflon microfluidic chips, PNAS Published online before print May 2, 2011, DOI:10.1073/pnas.1100356108
* Department of Chemistry, Hong Kong University of Science and Technology

Copyright 2011 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

When Will Scientists Grow Meat in a Petri Dish?

Meat grown in a laboratory could provide high-protein food sources free of the environmental and ethical concerns that accompany large-scale livestock operations. Yet progress has been slow, in no small part due to the ­difficulty scientists have securing funding for their research.One promising strategy involves growing embryonic stem cells from livestock in a culture, then coaxing them to transform into muscle cells.Even if research is successful, some people question whether the public would ever develop a taste for meat engi­neer­ed in the lab.

Editor's note: This article appears in print with the title "Inside the Meat Lab."

It is not unusual for visionaries to be impassioned, if not fanatical­, and Willem van Eelen is no exception. At 87, van Eelen can look back on an extraordinary life. He was born in Indonesia when it was under Dutch control, the son of a doctor who ran a leper colony. As a teenager, he fought the Japanese in World War II and spent several years in prisoner-of-war camps. The Japanese guards used prisoners as slave labor and starved them. “If one of the stray dogs was stupid enough to go over the wire, the prisoners would jump on it, tear it apart and eat it raw,” van Eelen recalls. “If you looked at my stomach then, you saw my spine. I was already dead.” The experience triggered a lifelong obsession with food, nutrition and the science of survival.

One obsession led to another. After the Allies liberated Indonesia, van Eelen studied medicine at the University of Amsterdam. A professor showed the students how he had been able to get a piece of muscle tissue to grow in the laboratory. This demonstration inspired van Eelen to consider the possibility of growing edible meat without having to raise or slaughter animals. Imagine, he thought, protein-rich food that could be grown like crops, no matter what the climate or other environmental conditions, without killing any living creatures.

If anything, the idea is more potent now. The world population was just more than two billion in 1940, and global warming was not a concern. Today the planet is home to three times as many people. According to a 2006 report by the Food and Agriculture Organization, the livestock business accounts for about 18 percent of all anthropogenic greenhouse gas emissions—an even larger contribution than the global transportation sector. The organization expects worldwide meat consumption to nearly double between 2002 and 2050.

Meat grown in bioreactors—instead of raised on farms—could help alleviate planetary stress. Hanna Tuomisto, a Ph.D. candidate at the University of Ox­ford, co-authored a study last year on the potential environmental impacts of cultured meat. The study found that such production, if scientists grew the muscle cells in a culture of cyanobacteria hydrolysate (a bacterium cultivated in ponds), would involve “approximately 35 to 60 percent lower energy use, 80 to 95 percent lower greenhouse gas emissions and 98 percent lower land use compared to conventionally produced meat products in Europe.”

As it is, 30 percent of the earth’s ice-free land is used for grazing livestock and growing animal feed. If cultured meat were to become viable and widely consumed, much of that land could be used for other purposes, including new forests that would pull carbon out of the air. Meat would no longer have to be shipped around the globe, because production sites could be located close to consumers. Some proponents imagine small urban meat labs selling their products at street markets that cater to locavores.

The Only Choice Left
Even Winston Churchill thought in vitro meat was a good idea. “Fifty years hence, we shall escape the absurdity of growing a whole chicken in order to eat the breast or wing by growing these parts separately under suitable medium,” he predicted in a 1932 book, Thoughts and Adventures. For most of the 20th century, however, few took the idea seriously. Van Eelen did not let it go. He worked all kinds of jobs—selling newspapers, driving a taxi, making dollhouses. He established an organization to help underprivileged kids and owned art galleries and cafes. He wrote proposals for in vitro meat production and eventually plowed much of his earnings into applying for patents. Together with two partners, he won a Dutch patent in 1999, then other European patents and, eventually, two U.S. patents. In 2005 he and others finally convinced the Dutch Ministry of Economic Affairs to pledge €2 million to support in vitro meat research in the Netherlands—the largest government grant for such research to date.

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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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What's the label? Helping to unravel the role of nature in biosynthetic pathways

Terpenoids are a very large and diverse class of compounds which includes certain hormones, flavors, and drugs, such as steroids, cinnamon or menthol, and antibacterials. They are found in all living organisms, but their biosynthesis is not yet fully understood. To learn more about how plants or animals make these important natural products, chemists typically turn to labeling experiments.

In these experiments, synthetic compounds are used that carry a tag or isotopic label, that is, heavy versions of atoms are chemically introduced into the precursors of biomolecules. These marked precursors are then fed to organisms. Just where these tags appear in natural terpenoids tells researchers more about how the organism made the compounds. Mevalonolactone (MVA) is an important precursor for terpenoids, and Jeroen S. Dickschat and a team of scientists from Braunschweig (Germany) have now prepared a series of labeled MVA derivatives that will help to unravel the biosynthesis of terpenoids, as they report in the European Journal of Organic Chemistry.

Chemists are able to follow the incorporation of isotopic labels into natural products by standard analytical methods. This is one of the most basic approaches used to determine biosynthetic pathways, as the method is only limited by the availability of the labeled compounds. Deuterated derivatives carrying a heavy version of hydrogen are a good choice for the study of terpenoids, as several steps in their biosynthesis can include rearrangements of hydrogen atoms. Deuterated MVAs have been used in the past to unravel the assembly of terpenoids; however, their availability is limited. The synthesis of such materials can be highly complex and laborious, and the isotopically labeled starting materials or reagents can be expensive. Therefore, short, efficient, and flexible routes that allow isotopic labeling at specific locations are required.

Thus, the authors set out to develop a synthetic route to deuterated MVA derivatives that allows for the independent introduction of deuterium into any position or into any combination of different positions using low-cost deuterated reagents. The team demonstrated that MVA could be labeled by using classical organic chemistry transformations, and importantly, the introduction of deuterium at any carbon atom in MVA was possible. The applicability of their route was demonstrated in the synthesis of five exemplary MVA derivatives with deuterium incorporation at different and specific locations. With the possibility to prepare new labeled MVA derivatives, scientists will now be able to address several important questions in the biosynthetic investigations of terpenoids.

More information: Jeroen S. Dickschat, Synthesis of Deuterated Mevalonolactone Isotopomers, European Journal of Organic Chemistry, Permalink to the article: http://dx.doi.org/ … oc.201100188

Provided by Wiley (news : web)

Splitting water for renewable energy simpler than first thought?

An international team, of scientists, led by a team at Monash University has found the key to the hydrogen economy could come from a very simple mineral, commonly seen as a black stain on rocks.

Their findings, developed with the assistance of researchers at UC Davis in the USA and using the facilities at the Australian Synchrotron, was published in the journal Nature Chemistry on May 15, 2011.

Professor Leone Spiccia from the School of Chemistry at Monash University said the ultimate goal of researchers in this area is to create a cheap, efficient way to split water, powered by sunlight, which would open up production of hydrogen as a clean fuel, and leading to long-term solutions for our renewable energy crisis.

To achieve this, they have been studying complex catalysts designed to mimic the catalysts plants use to split water with sunlight. But the new study shows that there might be much simpler alternatives to hand.

"The hardest part about turning water into fuel is splitting water into hydrogen and oxygen, but the team at Monash seems to have uncovered the process, developing a water-splitting cell based on a manganese-based catalyst," Professor Spiccia said.

"Birnessite, it turns out, is what does the work. Like other elements in the middle of the Periodic Table, manganese can exist in a number of what chemists call oxidation states. These correspond to the number of oxygen atoms with which a metal atom could be combined," Professor Spiccia said.

"When an electrical voltage is applied to the cell, it splits water into hydrogen and oxygen and when the researchers carefully examined the catalyst as it was working, using advanced spectroscopic methods they found that it had decomposed into a much simpler material called birnessite, well-known to geologists as a black stain on many rocks."

The manganese in the catalyst cycles between two oxidation states. First, the voltage is applied to oxidize from the manganese-II state to manganese-IV state in birnessite. Then in sunlight, birnessite goes back to the manganese-II State.

This cycling process is responsible for the oxidation of water to produce oxygen gas, protons and electrons.

Co-author on the research paper was Dr Rosalie Hocking, Research Fellow in the Australian Centre for Electromaterials Science who explained that what was interesting was the operation of the catalyst, which follows closely natures biogeochemical cycling of manganese in the oceans.

"This may provide important insights into the evolution of Nature's water splitting catalyst found in all plants which uses manganese centres," Dr Hocking said.

"Scientists have put huge efforts into making very complicated manganese molecules to copy plants, but it turns out that they convert to a very common material found in the Earth, a material sufficiently robust to survive tough use."

The reaction has two steps. First, two molecules of water are oxidized to form one molecule of oxygen gas (O2), four positively-charged hydrogen nuclei (protons) and four electrons. Second, the protons and electrons combine to form two molecules of hydrogen gas (H2).

The experimental work was conducted using state-of-the art equipment at three major facilities including the Australian Synchrotron, the Australian National Beam-line Facility in Japan and the Monash Centre for Electron Microscopy, and involved collaboration with Professor Bill Casey, a geochemist at UC Davis.

"The research highlights the insight obtainable from the synchrotron based spectroscopic techniques -- without them the important discovery linking common earth materials to water oxidation catalysts would not have been made," Dr Hocking said.

It is hoped the research will ultimately lead to the development of cheaper devices, which produce hydrogen.

The work was primarily funded by the U.S. National Science Foundation and the U.S. Department of Energy Monash University, the Australian Research Council through the Australian Centre of Excellence for Electromaterials Science, and the Australian Synchrotron.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Monash University.

Journal Reference:

Rosalie K. Hocking, Robin Brimblecombe, Lan-Yun Chang, Archana Singh, Mun Hon Cheah, Chris Glover, William H. Casey, Leone Spiccia. Water-oxidation catalysis by manganese in a geochemical-like cycle. Nature Chemistry, 2011; DOI: 10.1038/nchem.1049

Plastic products leach toxic substances

Many plastic products contain hazardous chemicals that can leach to the surroundings. In studies conducted at the University of Gothenburg, a third of the tested plastic products released toxic substances, including 5 out of 13 products intended for children.

"Considering how common plastic products are, how quickly the production of plastic has increased and the amount of chemicals that humans and the environment are exposed to, it is important to replace the most hazardous substances in plastic products with less hazardous alternatives," says Delilah Lithner of the Department of Plant and Environmental Sciences at the University of Gothenburg.

Plastics exist in many different chemical compositions and are widespread in the society and the environment. Global annual production of plastics has doubled over the past 15 years, to 245 million tonnes in 2008. The plastic polymers are not regarded as toxic, but there may be toxic residual chemicals, chemical additives and degradation products in the plastic products that can leach out as they are not bound to the plastic polymer. Plastics also cause many waste problems.

In her research, Lithner studied the toxicity of 83 randomly selected plastic products and synthetic textiles. The newly purchased products were leached in pure (deionised) water for 1?? days. The acute toxicity of the water was then tested using water fleas (Daphnia magna).

"A third of all the 83 plastic products and synthetic chemicals that were tested released substances that were acutely toxic to the water fleas, despite the leaching being mild. Five out of 13 products that were intended for children were toxic, for example bath toys and buoyancy aids such as inflatable armbands," says Delilah Lithner.

The products that resulted in toxic water were soft to semi-soft products made from plasticised PVC or polyurethane, as well as epoxy products and textiles made from various plastic fibres. The toxicity was mainly caused by fat-soluble organic substances.

Lithner also studied the chemicals used to make around 50 different plastic polymers and has identified the plastic polymers for which the most hazardous chemicals are used. They were then ranked on the basis of the environmental and health hazard classifications that exist for the chemicals. Examples of plastic polymers made from the most hazardous chemicals are certain polyurethanes, polyacrylonitriles, PVC, epoxy and certain styrene copolymers. The results are of great benefit for further assessing environmental and health risks associated with plastic materials.

Provided by University of Gothenburg (news : web)