Human Ancestors Lived on Shaky Ground

Our earliest ancestors preferred to settle in locations that have something in common with cities such as San Francisco, Naples and Istanbul -- they are often on active tectonic faults in areas that have an earthquake risk or volcanoes, or both.
An international team of scientists has established a link between the shape of the landscape and the habitats preferred by our earliest ancestors. The research, by scientists at the University of the Witwatersrand, South Africa, the University of York and the Institut de Physique du Globe Paris (IPGP), is published in the March 2011 issue of the Journal of Human Evolution.

The four-year study examines the geomorphology (literally the shape of the landscape) around ancient sites in southern Africa.

Lead author, South African Dr Sally Reynolds, a palaeoanthropologist at Witwatersrand who conducted the research during a postdoctoral fellowship at IPGP, says: "We were stunned when during a fieldwork trip in South Africa in 2007, Professor Geoffrey King and I discovered evidence that hominin sites such as Taung, Sterkfontein and Makapansgat, show landscape features in combinations that are not random, but result from tectonic motions, such as earthquakes."

Several lines of scientific evidence suggest that Australopithecus africanus (like the 'Mrs Ples' fossil from Sterkfontein) was adapted to mixed, or mosaic habitats -- landscapes with trees and open grassland, with some wetland marshy areas. The study suggests that it was the type of mosaic environment created by tectonic earth movements near rivers or lakes.

These features including cliffs, sedimented valleys, river gorges and drier plateau areas in close proximity of about 10 kilometres, are created when sections of Earth's crust move in response to pressure, then blocks of land are lifted up, while others are forced downwards. When this happens next to a river, the result is the creation of wetland, marshy areas close to drier plateaus and areas of erosion.

Professor Geoff Bailey, from the University of York, who is the lead author on an accompanying paper, also published in the same issue of the Journal of Human Evolution, confirms: "This link between earthquakes and human habitation is one we've long suspected was there. Regions vulnerable to earthquake and volcanic activity often create landscapes with long-term benefits for human settlement. But the tragic events in Christchurch are a graphic illustration of the attendant risk of these locations."

Professor King, a tectonic geomorphologist at the IPGP, adds: "The original idea was developed in Greece over a decade ago, with the surprising discovery that the sites there were clearly associated with ongoing tectonic activity.

"Even though South Africa appears to be tectonically stable, there are landscape features that indicate that modest levels of activity are preserved in the hard, southern African rocks. This means that the landscape model we developed in Greece is equally applicable to East Africa, and now also to the well-known fossil sites of the South Africa's Cradle of Humankind World Heritage Site."

Dr Reynolds, who is also an honorary research fellow at the School of Natural Sciences and Psychology at Liverpool John Moores University, explains "Our hominin ancestors would have been unaware of the tectonic influence on their habitats, but instead would have been attracted by the range of food and shelter offered."

The combination of drinking water, steep cliffs that provided shelter from predators, together with a range of feeding sources constitute the key ingredients for an ideal habitat for our ancestors.

New Observations of the Giant Planet Orbiting Beta Pictoris

Astronomy & Astrophysics publishes new high angular resolution observations of the giant planet orbiting the star β Pictoris. Located at 63.4 light-years from the Sun, β Pic is a very young star of about 12 million years old [1], which is 75% more massive than our Sun. β Pic is well known for harboring an extended and structured circumstellar disk. It was actually the first star to have its disk directly imaged more than 25 years ago. In 2009, a giant planet was seen orbiting within the disk. With an orbital distance of 8 to 15 astronomical units (AU), β Pictoris b is the closest exoplanet to its star that has ever been imaged. This planet offers a new opportunity to study the planetary formation processes, in particular the interactions between the planets and their native disks.
An international team of astronomers [2] observed the β Pic system, using the VLT/NaCo instrument at 2.18 μm, previous observations having been made near 4 μm. They detected the planet again and compared these new observations with the previous ones. Combining all the data together shows that the planet is moving around the star, as expected from the previous data. Analyzing these new observations, the team was then able to measure the mass of the planet, around 7 to 11 times the mass of Jupiter, and its effective temperature, between 1100 and 1700°C [3].

These new data already tell us something about the formation of the planet, especially because the system is very young. The planet β Pic b is still warm, implying that it has retained most of the primordial heat acquired during its formation. If it has been formed in a similar way to the giant planets of our solar system [4], its mass and temperature cannot be explained by some evolutionary models that hypothesize a total release of the energy acquired during the accretion of disk materials.

Forthcoming observations of β Pictoris b with NaCo and also with the next generation VLT instrument SPHERE should soon provide more details about its atmosphere and orbital properties and about the way this companion influences the surrounding disk material.

[1] The β Pictoris system is much younger than our solar system formed 4.5 billion years ago.

[2] The team of astronomers includes M. Bonnefoy, A.-M. Lagrange, G. Chauvin, D. Ehrenreich, D. Mouillet (IPAG, Grenoble, France), A. Boccaletti, D. Rouan, D. Gratadour (LESIA-Observatoire de Paris, Meudon, France), D. Apai (Space Telescope Institute, Baltimore, USA), F. Allard (CRAL-ENS, Lyon, France), J.H.V Girard (ESO, Santiago, Chile), M. Kasper (ESO, Garching, Germany).

[3] The effective temperature of a planet is the surface temperature it would have if it radiated as a "black body," that is, if it absorbed all the radiation coming from its star and re-emitted all back into space. For example, Earth's effective temperature is about -18°C, while its actual surface temperature is 14°C on average.

[4] The giant planets of our solar system (Jupiter, Saturn, Uranus, and Neptune) were most likely formed inside the circumstellar disk surrounding the Sun from embryos of solid material (ice, silicates) that swallowed surrounding gases from the disk.

Black Holes: A Model for Superconductors?

Black holes are some of the heaviest objects in the universe. Electrons are some of the lightest. Now physicists at the University of Illinois at Urbana-Champaign have shown how charged black holes can be used to model the behavior of interacting electrons in unconventional superconductors.

"The context of this problem is high-temperature superconductivity," said Phillips. "One of the great unsolved problems in physics is the origin of superconductivity (a conducting state with zero resistance) in the copper oxide ceramics discovered in 1986." The results of research by Phillips and his colleagues Robert G. Leigh, Mohammad Edalati, and Ka Wai Lo were published online in Physical Review Letters on March 1 and in Physical Review D on February 25.

Unlike the old superconductors, which were all metals, the new superconductors start off their lives as insulators. In the insulating state of the copper-oxide materials, there are plenty of places for the electrons to hop but nonetheless -- no current flows. Such a state of matter, known as a Mott insulator after the pioneering work of Sir Neville Mott, arises from the strong repulsions between the electrons. Although this much is agreed upon, much of the physics of Mott insulators remains unsolved, because there is no exact solution to the Mott problem that is directly applicable to the copper-oxide materials.

Enter string theory -- an evolving theoretical effort that seeks to describe the known fundamental forces of nature, including gravity, and their interactions with matter in a single, mathematically complete system.

Fourteen years ago, a string theorist, Juan Maldacena, conjectured that some strongly interacting quantum mechanical systems could be modeled by classical gravity in a spacetime having constant negative curvature. The charges in the quantum system are replaced by a charged black hole in the curved spacetime, thereby wedding the geometry of spacetime with quantum mechanics.

Since the Mott problem is an example of strongly interacting particles, Phillips and colleagues asked the question: "Is it possible to devise a theory of gravity that mimics a Mott insulator?" Indeed it is, as they have shown.

The researchers built on Maldacena's mapping and devised a model for electrons moving in a curved spacetime in the presence of a charged black hole that captures two of the striking features of the normal state of high-temperature superconductors: 1) the presence of a barrier for electron motion in the Mott state, and 2) the strange metal regime in which the electrical resistivity scales as a linear function of temperature, as opposed to the quadratic dependence exhibited by standard metals.

The treatment advanced in the paper published in Physical Review Letters shows surprisingly that the boundary of the spacetime consisting of a charged black hole and weakly interacting electrons exhibits a barrier for electrons moving in that region, just as in the Mott state. This work represents the first time the Mott problem has been solved (essentially exactly) in a two-dimensional system, the relevant dimension for the high-temperature superconductors.

"The next big question that we must address," said Phillips, "is how does superconductivity emerge from the gravity theory of a Mott insulator?"

This research was supported by the NSF DMR-0940992 and the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center, Award Number DE- AC0298CH1088, and by DOE grant FG02-91-ER40709. The conclusions presented are those of the authors and not necessarily those of the funding agencies.

California Islands Give Up Evidence of Early Seafaring: Numerous Artifacts Found at Late Pleistocene Sites on the Channel Islands

Evidence for a diversified sea-based economy among North American inhabitants dating from 12,200 to 11,400 years ago is emerging from three sites on California's Channel Islands.

Reporting in the March 4 issue of Science, a 15-member team led by University of Oregon and Smithsonian Institution scholars describes the discovery of scores of stemmed projectile points and crescents dating to that time period. The artifacts are associated with the remains of shellfish, seals, geese, cormorants and fish.

Funded primarily by grants from the National Science Foundation, the team also found thousands of artifacts made from chert, a flint-like rock used to make projectile points and other stone tools.

Some of the intact projectiles are so delicate that their only practical use would have been for hunting on the water, said Jon Erlandson, professor of anthropology and director of the Museum of Natural and Cultural History at the University of Oregon. He has been conducting research on the islands for more than 30 years.

"This is among the earliest evidence of seafaring and maritime adaptations in the Americas, and another extension of the diversity of Paleoindian economies," Erlandson said. "The points we are finding are extraordinary, the workmanship amazing. They are ultra thin, serrated and have incredible barbs on them. It's a very sophisticated chipped-stone technology." He also noted that the stemmed points are much different than the iconic fluted points left throughout North America by Clovis and Folsom peoples who hunted big game on land.

The artifacts were recovered from three sites that date to the end of the Pleistocene epoch on Santa Rosa and San Miguel islands, which in those days were connected as one island off the California coast. Sea levels then were 50 to 60 meters (about 160-200 feet) below modern levels. Rising seas have since flooded the shorelines and coastal lowlands where early populations would have spent most of their time.

Erlandson and his colleagues have focused their search on upland features such as springs, caves, and chert outcrops that would have drawn early maritime peoples into the interior. Rising seas also may have submerged evidence of even older human habitation of the islands.

The newly released study focuses on the artifacts and animal remains recovered, but the implications for understanding the peopling of the Americas may run deeper.

The technologies involved suggest that these early islanders were not members of the land-based Clovis culture, Erlandson said. No fluted points have been found on the islands. Instead, the points and crescents are similar to artifacts found in the Great Basin and Columbia Plateau areas, including pre-Clovis levels at Paisley Caves in eastern Oregon that are being studied by another UO archaeologist, Dennis Jenkins.

Last year, Charlotte Beck and Tom Jones, archaeologists at New York's Hamilton College who study sites in the Great Basin, argued that stemmed and Clovis point technologies were separate, with the stemmed points originating from Pacific Coast populations and not, as conventional wisdom holds, from the Clovis people who moved westward from the Great Plains. Erlandson and colleagues noted that the Channel Island points are also broadly similar to stemmed points found early sites around the Pacific Rim, from Japan to South America.

Six years ago, Erlandson proposed that Late Pleistocene sea-going people may have followed a "kelp highway" stretching from Japan to Kamchatka, along the south coast of Beringia and Alaska, then southward down the Northwest Coast to California. Kelp forests are rich in seals, sea otters, fish, seabirds, and shellfish such as abalones and sea urchins.

"The technology and seafaring implications of what we've found on the Channel Islands are magnificent," said study co-author Torben C. Rick, curator of North American Archaeology at the Smithsonian Institution. "Some of the paleo-ecological and subsistence implications are also very important. These sites indicate very early and distinct coastal and island subsistence strategies, including harvest of red abalones and other shellfish and fish dependent on kelp forests, but also the exploitation of larger pinnipeds and waterfowl, including an extinct flightless duck.

"This combination of unique hunting technologies found with marine mammal and migratory waterfowl bones provides a very different picture of the Channel Islands than what we know today, and indicates very early and diverse maritime life ways and foraging practices," Rick said. "What is so interesting is that not only do the data we have document some of the earliest marine mammal and bird exploitation in North America, but they show that very early on New World coastal peoples were hunting such animals and birds with sophisticated technologies that appear to have been refined for life in coastal and aquatic habitats."

The stemmed points found on the Channel Islands range from tiny to large, probably indicating that they were used for hunting a variety of animals.

"We think the crescents were used as transverse projectile points, probably for hunting birds. Their broad stone tips, when attached to a dart shaft provided a stone age shotgun-approach to hunting birds in flight," Erlandson said. "These are very distinctive artifacts, hundreds of which have been found on the Channel Islands over the years, but rarely in a stratified context, he added. Often considered to be between 8,000 and 10,000 years old in California, "we now have crescents between 11,000 and 12,000 years old, some of them associated with thousands of bird bones."

The next challenge, Erlandson and Rick noted, is to find even older archaeological sites on the Channel Islands, which might prove that a coastal migration contributed to the initial peopling of the Americas, now thought to have occurred two to three millennia earlier.

The 13 co-authors on the study with Erlandson and Rick were: Todd J. Braje, professor of anthropology at Humboldt State University in Arcata, Calif.; UO anthropology professors Douglas J. Kennett and Madonna L. Moss; Brian Fulfrost of the geography department of San Francisco State University; Daniel A. Guthrie of the Joint Science Department, Claremont McKenna, Scripps and Pitzer Colleges of Claremont, Calif.; Leslie Reeder, anthropology department of Southern Methodist University in Dallas, Texas; Craig Skinner of the Northwest Research Obsidian Studies Laboratory in Corvallis, Ore.; Jack Watts of Kellogg College at Oxford University, United Kingdom; and UO graduate students Molly Casperson, Nicholas Jew, Brendan Culleton, Tracy Garcia and Lauren Willis.

New Kinds of Superconductivity? Physicists Demonstrate Coveted 'Spin-Orbit Coupling' in Atomic Gases

Physicists at the Joint Quantum Institute (JQI), a collaboration of the National Institute of Standards and Technology (NIST) and the University of Maryland-College Park, have for the first time caused a gas of atoms to exhibit an important quantum phenomenon known as spin-orbit coupling. Their technique opens new possibilities for studying and better understanding fundamental physics and has potential applications to quantum computing, next-generation "spintronics" devices and even "atomtronic" devices built from ultracold atoms.
In the researchers' demonstration of spin-orbit coupling, two lasers allow an atom's motion to flip it between a pair of energy states. The new work, published in Nature, demonstrates this effect for the first time in bosons, which make up one of the two major classes of particles. The same technique could be applied to fermions, the other major class of particles, according to the researchers. The special properties of fermions would make them ideal for studying new kinds of interactions between two particles -- for example those leading to novel "p-wave" superconductivity, which may enable a long-sought form of quantum computing known as topological quantum computation.

In an unexpected development, the team also discovered that the lasers modified how the atoms interacted with each other and caused atoms in one energy state to separate in space from atoms in the other energy state.

One of the most important phenomena in quantum physics, spin-orbit coupling describes the interplay that can occur between a particle's internal properties and its external properties. In atoms, it usually describes interactions that only occur within an atom: how an electron's orbit around an atom's core (nucleus) affects the orientation of the electron's internal bar-magnet-like "spin." In semiconductor materials such as gallium arsenide, spin-orbit coupling is an interaction between an electron's spin and its linear motion in a material.

"Spin-orbit coupling is often a bad thing," said JQI's Ian Spielman, senior author of the paper. "Researchers make 'spintronic' devices out of gallium arsenide, and if you've prepared a spin in some desired orientation, the last thing you'd want it to do is to flip to some other spin when it's moving."

"But from the point of view of fundamental physics, spin-orbit coupling is really interesting," he said. "It's what drives these new kinds of materials called 'topological insulators.'"

One of the hottest topics in physics right now, topological insulators are special materials in which location is everything: the ability of electrons to flow depends on where they are located within the material. Most regions of such a material are insulating, and electric current does not flow freely. But in a flat, two-dimensional topological insulator, current can flow freely along the edge in one direction for one type of spin, and the opposite direction for the opposite kind of spin. In 3-D topological insulators, electrons would flow freely on the surface but be inhibited inside the material. While researchers have been making higher and higher quality versions of this special class of material in solids, spin-orbit coupling in trapped ultracold gases of atoms could help realize topological insulators in their purest, most pristine form, as gases are free of impurity atoms and the other complexities of solid materials.

Usually, atoms do not exhibit the same kind of spin-orbit coupling as electrons exhibit in gallium-arsenide crystals. While each individual atom has its own spin-orbit coupling going on between its internal components (electrons and nucleus), the atom's overall motion generally is not affected by its internal energy state.

But the researchers were able to change that. In their experiment, researchers trapped and cooled a gas of about 200,000 rubidium-87 atoms down to 100 nanokelvins, 3 billion times colder than room temperature. The researchers selected a pair of energy states, analogous to the "spin-up" and "spin-down" states in an electron, from the available atomic energy levels. An atom could occupy either of these "pseudospin" states. Then researchers shined a pair of lasers on the atoms so as to change the relationship between the atom's energy and its momentum (its mass times velocity), and therefore its motion. This created spin-orbit coupling in the atom: the moving atom flipped between its two "spin" states at a rate that depended upon its velocity.

"This demonstrates that the idea of using laser light to create spin-orbit coupling in atoms works. This is all we expected to see," Spielman said. "But something else really neat happened."

They turned up the intensity of their lasers, and atoms of one spin state began to repel the atoms in the other spin state, causing them to separate.

"We changed fundamentally how these atoms interacted with one another," Spielman said. "We hadn't anticipated that and got lucky."

The rubidium atoms in the researchers' experiment were bosons, sociable particles that can all crowd into the same space even if they possess identical values in their properties including spin. But Spielman's calculations show that they could also create this same effect in ultracold gases of fermions. Fermions, the more antisocial type of atoms, cannot occupy the same space when they are in an identical state. And compared to other methods for creating new interactions between fermions, the spin states would be easier to control and longer lived.

A spin-orbit-coupled Fermi gas could interact with itself because the lasers effectively split each atom into two distinct components, each with its own spin state, and two such atoms with different velocities could then interact and pair up with one other. This kind of pairing opens up possibilities, Spielman said, for studying novel forms of superconductivity, particularly "p-wave" superconductivity, in which two paired atoms have a quantum-mechanical phase that depends on their relative orientation. Such p-wave superconductors may enable a form of quantum computing known as topological quantum computation.

Some Antarctic Ice Is Forming from Bottom

Scientists working in the remotest part of Antarctica have discovered that liquid water locked deep under the continent's coat of ice regularly thaws and refreezes to the bottom, creating as much as half the thickness of the ice in places, and actively modifying its structure. The finding, which turns common perceptions of glacial formation upside down, could reshape scientists' understanding of how the ice sheet expands and moves, and how it might react to warming climate, they say.
The study appears in this week's early online edition of the journal Science; it is part of a six-nation study of the invisible Gamburtsev Mountains, which lie buried under as much as two miles of ice.

Ice sheets are well known to grow from the top as snow falls and builds up annual layers over thousands of years, but scientists until recently have known little about the processes going on far below. In 2006, researchers in the current study showed that lakes of liquid water underlie widespread parts of Antarctica. In 2008-2009, they mounted an expedition using geophysical instruments to create 3-D images of the Gamburtsevs, a range larger than the European Alps. The expedition also made detailed images of the overlying ice, and subglacial water.

"We usually think of ice sheets like cakes--one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom--a really thick layer," said Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory and a project co-leader. "Water has always been known to be important to ice sheet dynamics, but mostly as a lubricant. As ice sheets change, we want to predict how they will change. Our results show that models must include water beneath." The Antarctic ice sheet holds enough fresh water to raise ocean levels 200 feet; if even a small part of it were to melt into the ocean, it could put major coastal cities under water.

The scientists found that refrozen ice makes up 24% of the ice sheet base around Dome A, a 13,800-foot-high plateau that forms the high point of the East Antarctic ice sheet, at 3.8 million square miles roughly the size of the continental United States. In places, slightly more than half the ice thickness appears to have originated from the bottom, not the top. Here, rates of refreezing are greater than surface accumulation rates. The researchers suggest that such refreezing has been going on since East Antarctica became encased in a large ice sheet some 32 million years ago. They may never know for sure: the ice is always moving from the deep interior toward the coast, so ice formed millions of years ago, and the evidence it would carry, is long gone.

Deeply buried ice may melt because overlying layers insulate the base, hemming in heat created there by friction, or radiating naturally from underlying rock. When the ice melts, refreezing may take place in multiple ways, the researchers say. If it collects along mountain ridges and heads of valleys, where the ice is thinner, low temperatures penetrating from the surface may refreeze it. In other cases, water gets squeezed up valley walls, and changes pressure rapidly. In the depths, water remains liquid even when it is below the normal freezing point, due to pressure exerted on it. But once moved up to an area of less pressure, such supercooled water can freeze almost instantly. Images produced by the researchers show that the refreezing deforms the ice sheet upward.

"When we first saw these structures in the field, we thought they looked like beehives and were worried they were an error in the data," Bell said. "As they were seen on many lines, it became clear that they were real. We did not think that water moving through ancient river valleys beneath more than one mile of ice would change the basic structure of the ice sheet."

Because the ice is in motion, understanding how it forms and deforms at the base is critical to understanding how the sheets will move, particularly in response to climate changes, researchers say. "It's an extremely important observation for us because this is potentially lifting the very oldest ice off the bed," said Jeff Severinghaus, a geologist at Scripps Institution of Oceanography in San Diego who was not involved in the study. He said it could either mean older ice is better preserved -- or, it could "make it harder to interpret the record, if it's shuffled like a deck of cards."

From November 2008 to January 2009, the researchers did fieldwork around a California-size part of Dome A. Using aircraft equipped with ice penetrating radars, laser ranging systems, gravity meters and magnetometers, they flew low-altitude transects back and forth over the ice to draw 3-D images of what lay beneath. The aim was to understand how the mountains arose, and to study the connections between the peaks, the ice sheet, and subglacial lakes. They were also hunting for likely spots where future coring may retrieve the oldest ice. The work took place near the Southern Pole of Inaccessibility, the point farthest away from any ocean, and much harder to reach than the South Pole itself. They lived in isolated field camps, enduring high winds and temperatures ranging down to minus 40 degrees C.

"Understanding these interactions is critical for the search for the oldest ice and also to better comprehend subglacial environments and ice sheet dynamics," said Fausto Ferraccioli, a scientist with the British Antarctic Survey who also helped lead the project. "Incorporating these processes into models will enable more accurate predictions of ice sheet response to global warming and its impact on future sea-level rise."

The researchers now will look into how the refreezing process acts along the margins of ice sheets, where the most visible change is occurring in Antarctica. Based on their data, a Chinese team also hopes to drill deep into Dome A in the next two or three years to remove cores that would trace long-ago climate shifts. They hope to find ice more than a million years old.

Other co-authors of the paper include Timothy T. Creyts, Indrani Das, Nicholas Frearson and Michael Wolovik, of Lamont-Doherty; Hugh Corr, Thomas Jordan and Kathryn Rose of the British Antarctic Survey; David Braaten of the Center for Remote Sensing of Ice Sheets at Kansas University; Detlef Damaske of Germany's Federal Institute for Geosciences and Resources; and Michael Studinger of the NASA Goddard Space Flight Center in Maryland.

The work was funded by the U.S. National Science Foundation and launched in conjunction with the International Polar Year, a 2007-2009 effort to study the poles by thousands of scientists from more than 60 nations. Support also came from the Natural Environment Research Council of Britain; the Australian Antarctic Division; and the Polar Research Institute of China.

Scientists Create Cell Assembly Line: New Technology Synthesizes Cellular Structures from Simple Starting Materials

Borrowing a page from modern manufacturing, scientists from the Florida campus of The Scripps Research Institute have built a microscopic assembly line that mass produces synthetic cell-like compartments.
The new computer-controlled system represents a technological leap forward in the race to create the complex membrane structures of biological cells from simple chemical starting materials.

"Biology is full of synthetic targets that have inspired chemists for more than a century," said Brian Paegel, Scripps Research assistant professor and lead author of a new study published in the Journal of the American Chemical Society. "The lipid membrane assemblies of cells and their organelles pose a daunting challenge to the chemist who wants to synthesize these structures with the same rational approaches used in the preparation of small molecules."

While most cellular components such as genes or proteins are easily prepared in the laboratory, little has been done to develop a method of synthesizing cell membranes in a uniform, automated way. Current approaches are capricious in nature, yielding complex mixtures of products and inefficient cargo loading into the resultant cell-like structures.

The new technology transforms the previously difficult synthesis of cell membranes into a controlled process, customizable over a range of cell sizes, and highly efficient in terms of cargo encapsulation.

The membrane that surrounds all cells, organelles and vesicles -- small subcellular compartments -- consists of a phospholipid bilayer that serves as a barrier, separating an internal space from the external medium.

The new process creates a laboratory version of this bilayer that is formed into small, cell-sized compartments.

How It Works

"The assembly-line process is simple and, from a chemistry standpoint, mechanistically clear," said Sandro Matosevic, research associate and co-author of the study.

A microfluidic circuit generates water droplets in lipid-containing oil. The lipid-coated droplets travel down one branch of a Y-shaped circuit and merge with a second water stream at the Y-junction. The combined flows of droplets in oil and water travel in parallel streams toward a triangular guidepost.

Then, the triangular guide diverts the lipid-coated droplets into the parallel water stream as a wing dam might divert a line of small boats into another part of a river. As the droplets cross the oil-water interface, a second layer of lipids deposits on the droplet, forming a bilayer.

The end result is a continuous stream of uniformly shaped cell-like compartments.

The newly created vesicles range from 20 to 70 micrometers in diameter -- from about the size of a skin cell to that of a human hair. The entire circuit fits on a glass chip roughly the size of a poker chip.

The researchers also tested the synthetic bilayers for their ability to house a prototypical membrane protein. The proteins correctly inserted into the synthetic membrane, proving that they resemble membranes found in biological cells.

"Membranes and compartmentalization are ubiquitous themes in biology," noted Paegel. "We are constructing these synthetic systems to understand why compartmentalized chemistry is a hallmark of life, and how it might be leveraged in therapeutic delivery."