Scientists explain skin fusion at a molecular level

Scientists from the Goethe University (GU) Frankfurt, the European Molecular Biology Laboratory (EMBL) Heidelberg and the University of Zurich explain skin fusion at a molecular level and pinpoint the specific molecules that do the job in their latest publication in the journal ("Quantitative analysis of cytoskeletal reorganization during epithelial tissue sealing by large-volume electron tomography"). In order to prevent death by bleeding or infection, every wound (skin opening) must close at some point. The events leading to skin closure had been unclear for many years. Mikhail Eltsov (GU) and colleagues used fruit fly embryos as a model system to understand this process. Similarly to humans, fruit fly embryos at some point in their development have a large opening in the skin on their back that must fuse. This process is called zipping, because two sides of the skin are fastened in a way that resembles a zipper that joins two sides of a jacket. Perspective view of the zipping area with 17 skin cells "zipping". Membranes are colored in shades of brown and green to discriminate individual skin cells coming from the left or the right. The cells expand various types of protrusions in all directions to find their respective neighbor. The scientists have used a top-of-the-range electron microscope to study exactly how this zipping of the skin works. “Our electron microscope allows us to distinguish the molecular components in the cell that act like small machines to fuse the skin. When we look at it from a distance, it appears as if skin cells simply fuse to each other, but if we zoom in, it becomes clear that membranes, molecular machines, and other cellular components are involved", explains Eltsov. “In order to visualize this orchestra of healing, a very high-resolution picture of the process is needed. For this purpose we have recorded an enormous amount of data that surpasses all previous studies of this kind”, says Mikhail Eltsov. As a first step, as the scientists discovered, cells find their opposing partner by “sniffing” each other out. As a next step, they develop adherens junctions which act like a molecular Velcro. This way they become strongly attached to their opposing partner cell. The biggest revelation of this study was that small tubes in the cell, called microtubules, attach to this molecular Velcro and then deploy a self-catastrophe, which results in the skin being pulled towards the opening, as if one pulls a blanket over. Damian Brunner who led the team at the University of Zurich has performed many genetic manipulations to identify the correct components. The scientists were astonished to find that microtubules involved in cell-division are the primary scaffold used for zipping, indicating a mechanism conserved during evolution. “What was also amazing was the tremendous plasticity of the membranes in this process which managed to close the skin opening in a very short space of time. When five to ten cells have found their respective neighbors, the skin already appears normal”, says Achilleas Frangakis from the Goethe University Frankfurt, who led the study. The scientists hope that their results will open new avenues into the understanding of epithelial plasticity and wound healing. They are also investigating the detailed structural organization of the adherens junctions, work for which they were awarded a starting grant from European Research Council (ERC).

read more "Scientists explain skin fusion at a molecular level"

Nanobubbles dilemma solved after more than twenty years

It was a question that has kept physicists and chemists busy for more than twenty years. Why can tiny bubbles in a liquid supersaturated with gas remain stable for weeks, while according to theoretical expectation they should disappear in a fraction of a second? Prof. dr. ir. Detlef Lohse from the University of Twente's MESA+ research institute found the answer. The research was recently published in the scientific journal ("Pinning and gas oversaturation imply stable single surface nanobubbles"). If a water repellent substrate is immersed in water containing dissolved gas, tiny bubbles can form on the immersed body. These so called surface nanobubbles emerge because the surrounding liquid wants to lose its gas, similar as bubbles emerge in a glass of soda. In the case of the nanobubbles, however, the bubbles are only ten to twenty nanometres in height (one nanometre is one million times smaller than a millimetre), and therefore the (Laplace) pressure in the bubble is very high. According to all the current theories, the bubbles should disappear on their own accord in less than a millisecond, since the gas in the bubbles wants to dissolve in the water again. According to Lohse, this idea is quite similar to a balloon, which - even if it is properly tied - always deflates over time. The reason for this is that a little bit of air constantly leaks through the rubber of the balloon due to diffusion and the high pressure in the balloon. Conclusive explanation In practice, however, the nanobubbles can survive for weeks, as was already observed more than twenty years ago. Nevertheless, scientists failed to find a conclusive explanation for this long lifetime. With the publication of an article in the scientific journal Physical Review E (Rapid Communication), prof. dr. ir. Detlef Lohse and prof. dr. Xuehua Zhang (who besides the UT is also affiliated with the RMIT University in Melbourne) finally provide an explanation for the phenomenon. And they do this with a complete analytical method with relatively simple mathematical formulas. Angle of curvature The reason that the bubbles survive for such a long period of time lies in the pinning of the three phase contact line. Thanks to the pinning, bubble shrinkage implies an increase of the radius of curvature and thus a smaller Laplace pressure. For stable bubbles the outflux originating from the Laplace pressure and the influx due to oversaturation balance. The result is a stable equilibrium. The research not only provides an answer to a fundamental physical and chemical question, but also has all sorts of practical applications. The knowledge can, for example, be used to make catalytic reactions more efficient and for flotation processes, a purification technique that is used a lot in the extraction of minerals. Research Within his Physics of Fluids (POF) Department at the University of Twente, Lohse has already been working on this topic for more than ten years. In this research, he works closely with prof. dr. ir. Harold Zandvliet from the Physics of Interfaces and Nanomaterials (PIN) department. The research is part of the MCEC Gravity Programme, within which the University of Utrecht, the Eindhoven University of Technology and the University of Twente work together on the development of efficient catalytic processes for different energy and material resources, such as fossil fuels, biomass and solar energy. NWO is financing this programme with 31.9 million euros.

read more "Nanobubbles dilemma solved after more than twenty years"

Better battery imaging paves way for renewable energy future

In a move that could improve the energy storage of everything from portable electronics to electric microgrids, University of Wisconsin-Madison and Brookhaven National Laboratory researchers have developed a novel X-ray imaging technique to visualize and study the electrochemical reactions in lithium-ion rechargeable batteries containing a new type of material, iron fluoride. "Iron fluoride has the potential to triple the amount of energy a conventional lithium-ion battery can store," says Song Jin, a UW-Madison professor of chemistry and Wisconsin Energy Institute affiliate. "However, we have yet to tap its true potential." Graduate student Linsen Li worked with Jin and other collaborators to perform experiments with a state-of-the-art transmission X-ray microscope at the National Synchrotron Light Source at Brookhaven. There, they collected chemical maps from actual coin cell batteries filled with iron fluoride during battery cycling to determine how well they perform. The results are published in the journal ("Visualization of electrochemically driven solid-state phase transformations using operando hard X-ray spectro-imaging"). Chemical phase map showing how the electrochemical discharge of iron fluoride microwires proceeded from 0 percent discharge (left), to 50 percent (middle), to 95 percent. (Image: Linsen Li) "In the past, we weren't able to truly understand what is happening to iron fluoride during battery reactions because other battery components were getting in the way of getting a precise image," says Li. By accounting for the background signals that would otherwise confuse the image, Li was able to accurately visualize and measure, at the nanoscale, the chemical changes iron fluoride undergoes to store and discharge energy. Thus far, using iron fluoride in rechargeable lithium ion batteries has presented scientists with two challenges. The first is that it doesn't recharge very well in its current form. "This would be like your smart phone only charging half as much the first time, and even less thereafter," says Li. "Consumers would rather have a battery that charges consistently through hundreds of charges." By examining iron fluoride transformation in batteries at the nanoscale, Jin and Li's new X-ray imaging method pinpoints each individual reaction to understand why capacity decay may be occurring. "In analyzing the X-ray data on this level, we were able to track the electrochemical reactions with far more accuracy than previous methods, and determined that iron fluoride performs better when it has a porous microstructure," says Li. The second challenge is that iron fluoride battery materials don't discharge as much energy as they take in, reducing energy efficiency. The current study yielded some preliminary insights into this problem and Jin and Li plan to tackle this challenge in future experiments. Some implications of this research are obvious — like using portable electronic devices for longer before charging — but Jin also foresees a bigger and broader range of applications. "If we can maximize the cycling performance and efficiency of these low-cost and abundant iron fluoride lithium ion battery materials, we could advance large-scale renewable energy storage technologies for electric cars and microgrids," he says. Some implications of this research are obvious — like using portable electronic devices for longer before charging — but Jin also foresees a bigger and broader range of applications. Jin also believes that the novel X-ray imaging technique will facilitate the studies of other technologically important solid-state transformations and help to improve processes such as preparation of inorganic ceramics and thin-film solar cells. The experiments were performed with the help of Yu-chen Karen Chen-Wiegart, Feng Wang, Jun Wang and their co-workers at Beamline X8C, National Synchrotron Light Source, Brookhaven National Laboratory, and supported by the U.S. Department of Energy Basic Energy Sciences and a seed grant from the Wisconsin Energy Institute. The synthesis of the battery materials in Jin's lab was supported by National Science Foundation Division of Materials Research.

read more "Better battery imaging paves way for renewable energy future"