[naturenews] from [nature.com]
[naturenews]
Published online 16 September 2009 | Nature | doi:10.1038/news.2009.910
News
Why opposites don't always attract
A lucky lab accident helps to explain the mystery of bouncing droplets.
By Geoff Brumfiel
It's a natural fact that opposites attract — or so scientists thought. But a new study of fluid droplets shows that opposites can sometimes bounce right off one another. The results may seem esoteric, but they could have big implications for everything from oil refining to microfluidic 'lab-on-a-chip' technologies.
The work, published today in Nature, began as a laboratory accident. William Ristenpart, a chemical engineer at the University of California at Davis, was studying how the shape of a water column in oil changed as it was drawn towards an electrically charged plate. "I basically messed up," he says. "I was applying a few kilovolts, the system shorted out and the water exploded."
Tiny droplets of water went ricocheting around the oil-filled chamber. But as Ristenpart watched, he noticed something odd: oppositely charged water bubbles seemed to be bouncing off one another. "The first time I saw that I was terribly confused," Ristenpart says.
Charge puzzle
That's because, like other researchers, Ristenpart believed that oppositely charged water droplets would attract each other and form larger drops. This property has long been exploited in the 'electrostatic separation' process used by the petroleum industry to collect and remove bubbles of seawater from crude oil.
Ristenpart and his colleagues studied his laboratory accident for three years, and with the help of high-speed videos and mathematical calculations they now claim to understand the phenomenon. Because of the force of surface tension, water droplets are normally held in tight spheres. But as two electrically charged droplets come close to each other, the spheres begin to warp — and at very short distances, a small bridge of fluid forms between the drops.
When the electrical charge is low, that bridge grows until the drops merge together, but when the charge is high, something else happens: the bridge allows the droplets to exchange their charge and then snaps. The water flows back into the bubbles, and by the time the two drops collide, they are back in their spherical shape. Rather than merging, their surface tension causes them to bounce off one another like beach balls.
Seeing is believing
"Wow, how can that be?" Frieder Mugele, a physicist at the University of Twente in Enschede, the Netherlands, remembers asking himself on first seeing the result. But Mugele says he is wholly convinced by the group's explanation. "The fundamental principle is captured by what they are saying," he says. "It's a very striking phenomenon."
A bigger question is whether the bouncing effect could actually be useful. Many scientists are working to develop microfluidic systems — known as labs-on-a-chip — that can mix small amounts of chemical reagents or biological molecules. Electrical charge is one way that chemicals can be moved around these chips, and the study's authors say that knowledge of the bouncing bubbles could aid their development. Ristenpart says that the work could also find an application in the oil industry, which currently uses building-sized electrostatic separators to remove seawater from crude oil. The American Chemical Society has given Ristenpart's team a grant to see whether their research can create a more efficient separator, he says.
But even if the myriad potential applications don't pan out, Ristenpart is still planning a long future in droplet studies. His group is now looking at unusual collisions in which the droplets break into a pair of daughter drops, one large and one small. "That is not really well understood at all," he says. "There's a lot more thinking to do for sure."
References
1. Ristenpart, W. D., Bird, J. C., Belmonte, A., Dollar, F. & Stone, H. A. Nature 461, 377-380 (2009). | Article
[naturenews]
Published online 16 September 2009 | Nature | doi:10.1038/news.2009.921
News
Colour blindness corrected by gene therapy
Treated monkeys can now see in technicolour.
By Elie Dolgin
Researchers have used gene therapy to restore colour vision in two adult monkeys that have been unable to distinguish between red and green hues since birth — raising the hope of curing colour blindness and other visual disorders in humans.
"This is a truly amazing study," says András Komáromy, a vision researcher and veterinary ophthalmologist at the University of Pennsylvania in Philadelphia, who was not involved in the research. "If we can target gene expression specifically to cones [in humans] then this has a tremendous implication."
About 1 in 12 men lack either the red- or the green-sensitive photoreceptor proteins that are normally present in the colour-sensing cells, or cones, of the retina, and so have red–green colour blindness. A similar condition affects all male squirrel monkeys (Saimiri sciureus), which naturally see the world in just two tones. The colour blindness in the monkeys arises because full colour vision requires two versions of the opsin gene, which is carried on the X chromosome. One version codes for a red-detecting photoreceptor, the other for a green-detecting photoreceptor. As male monkeys have only one X chromosome, they carry only one version of the gene and are inevitably red–green colour blind. A similar deficiency accounts for the most common form of dichromatic color blindness in humans. Fewer female monkeys suffer from the condition as they have two X chromosomes, and often carry both versions of the opsin gene.
"Here is an animal that is a perfect model for the human condition," says Jay Neitz of the University of Washington in Seattle, a member of the team that carried out the experiment.
Neitz and his colleagues introduced the human form of the red-detecting opsin gene into a viral vector, and injected the virus behind the retina of two male squirrel monkeys — one named Dalton in honour of the British chemist, John Dalton, who was the first to describe his own colour blindness in 1794, and the other named Sam. The researchers then assessed the monkeys' ability to find coloured patches of dots on a background of grey dots by training them to touch coloured patches on a screen with their heads, and then rewarding them with grape juice. The test is a modified version of the standard 'Cambridge Colour Test' where people must identify numbers or other specific patterns in a field of coloured dots.
Colour coded
After 20 weeks, the monkeys' colour skills improved dramatically, indicating that Dalton and Sam had acquired the ability to see in three shades (see video). Both monkeys have retained this skill for more than two years with no apparent side effects, the researchers report in Nature1.
Adding the missing gene was sufficient to restore full colour vision without further rewiring of the brain even though the monkeys had been colour blind since birth. "There is this plasticity still in the brain and it is possible to treat cone defects with gene therapy," says Alexander Smith, a molecular biologist and vision researcher at University College London, who did not contribute to the study.
"It doesn't seem like new neural connections have to be formed," says Komáromy. "You can add an additional cone opsin pigment and the neural circuitry and visual pathways can deal with it."
Three human gene therapy trials are currently under way for loss of sight due to serious degeneration of the retina. These phase I safety studies injected a similar type of virus vector (but carrying a different gene) behind the retina as in the monkeys, and people treated have shown no serious adverse effects more than a year after, with some participants reporting marked improvements in vision2. These first human trials — which repair rods, a different type of photoreceptor cell — can be seen as a safety benchmark for any future treatment of cone diseases and colour blindness in humans, says Neitz.
"The biggest issue is that people who are colour blind have very good vision," Neitz says. "So before people are going to want to treat colour blindness you're going to want to ensure that this is completely safe, and that's going to take some work."
References
1. Mancuso, K. et al. Nature advanced online publication, doi:10.1038/nature08401 (2009).
2. Cideciyan, A. V. et al. N. Engl. J. Med. 361, 725-727 (2009).
[naturenews]
Published online 16 September 2009 | Nature | doi:10.1038/news.2009.910
News
Why opposites don't always attract
A lucky lab accident helps to explain the mystery of bouncing droplets.
By Geoff Brumfiel
It's a natural fact that opposites attract — or so scientists thought. But a new study of fluid droplets shows that opposites can sometimes bounce right off one another. The results may seem esoteric, but they could have big implications for everything from oil refining to microfluidic 'lab-on-a-chip' technologies.
The work, published today in Nature, began as a laboratory accident. William Ristenpart, a chemical engineer at the University of California at Davis, was studying how the shape of a water column in oil changed as it was drawn towards an electrically charged plate. "I basically messed up," he says. "I was applying a few kilovolts, the system shorted out and the water exploded."
Tiny droplets of water went ricocheting around the oil-filled chamber. But as Ristenpart watched, he noticed something odd: oppositely charged water bubbles seemed to be bouncing off one another. "The first time I saw that I was terribly confused," Ristenpart says.
Charge puzzle
That's because, like other researchers, Ristenpart believed that oppositely charged water droplets would attract each other and form larger drops. This property has long been exploited in the 'electrostatic separation' process used by the petroleum industry to collect and remove bubbles of seawater from crude oil.
Ristenpart and his colleagues studied his laboratory accident for three years, and with the help of high-speed videos and mathematical calculations they now claim to understand the phenomenon. Because of the force of surface tension, water droplets are normally held in tight spheres. But as two electrically charged droplets come close to each other, the spheres begin to warp — and at very short distances, a small bridge of fluid forms between the drops.
When the electrical charge is low, that bridge grows until the drops merge together, but when the charge is high, something else happens: the bridge allows the droplets to exchange their charge and then snaps. The water flows back into the bubbles, and by the time the two drops collide, they are back in their spherical shape. Rather than merging, their surface tension causes them to bounce off one another like beach balls.
Seeing is believing
"Wow, how can that be?" Frieder Mugele, a physicist at the University of Twente in Enschede, the Netherlands, remembers asking himself on first seeing the result. But Mugele says he is wholly convinced by the group's explanation. "The fundamental principle is captured by what they are saying," he says. "It's a very striking phenomenon."
A bigger question is whether the bouncing effect could actually be useful. Many scientists are working to develop microfluidic systems — known as labs-on-a-chip — that can mix small amounts of chemical reagents or biological molecules. Electrical charge is one way that chemicals can be moved around these chips, and the study's authors say that knowledge of the bouncing bubbles could aid their development. Ristenpart says that the work could also find an application in the oil industry, which currently uses building-sized electrostatic separators to remove seawater from crude oil. The American Chemical Society has given Ristenpart's team a grant to see whether their research can create a more efficient separator, he says.
But even if the myriad potential applications don't pan out, Ristenpart is still planning a long future in droplet studies. His group is now looking at unusual collisions in which the droplets break into a pair of daughter drops, one large and one small. "That is not really well understood at all," he says. "There's a lot more thinking to do for sure."
References
1. Ristenpart, W. D., Bird, J. C., Belmonte, A., Dollar, F. & Stone, H. A. Nature 461, 377-380 (2009). | Article
[naturenews]
Published online 16 September 2009 | Nature | doi:10.1038/news.2009.921
News
Colour blindness corrected by gene therapy
Treated monkeys can now see in technicolour.
By Elie Dolgin
Researchers have used gene therapy to restore colour vision in two adult monkeys that have been unable to distinguish between red and green hues since birth — raising the hope of curing colour blindness and other visual disorders in humans.
"This is a truly amazing study," says András Komáromy, a vision researcher and veterinary ophthalmologist at the University of Pennsylvania in Philadelphia, who was not involved in the research. "If we can target gene expression specifically to cones [in humans] then this has a tremendous implication."
About 1 in 12 men lack either the red- or the green-sensitive photoreceptor proteins that are normally present in the colour-sensing cells, or cones, of the retina, and so have red–green colour blindness. A similar condition affects all male squirrel monkeys (Saimiri sciureus), which naturally see the world in just two tones. The colour blindness in the monkeys arises because full colour vision requires two versions of the opsin gene, which is carried on the X chromosome. One version codes for a red-detecting photoreceptor, the other for a green-detecting photoreceptor. As male monkeys have only one X chromosome, they carry only one version of the gene and are inevitably red–green colour blind. A similar deficiency accounts for the most common form of dichromatic color blindness in humans. Fewer female monkeys suffer from the condition as they have two X chromosomes, and often carry both versions of the opsin gene.
"Here is an animal that is a perfect model for the human condition," says Jay Neitz of the University of Washington in Seattle, a member of the team that carried out the experiment.
Neitz and his colleagues introduced the human form of the red-detecting opsin gene into a viral vector, and injected the virus behind the retina of two male squirrel monkeys — one named Dalton in honour of the British chemist, John Dalton, who was the first to describe his own colour blindness in 1794, and the other named Sam. The researchers then assessed the monkeys' ability to find coloured patches of dots on a background of grey dots by training them to touch coloured patches on a screen with their heads, and then rewarding them with grape juice. The test is a modified version of the standard 'Cambridge Colour Test' where people must identify numbers or other specific patterns in a field of coloured dots.
Colour coded
After 20 weeks, the monkeys' colour skills improved dramatically, indicating that Dalton and Sam had acquired the ability to see in three shades (see video). Both monkeys have retained this skill for more than two years with no apparent side effects, the researchers report in Nature1.
Adding the missing gene was sufficient to restore full colour vision without further rewiring of the brain even though the monkeys had been colour blind since birth. "There is this plasticity still in the brain and it is possible to treat cone defects with gene therapy," says Alexander Smith, a molecular biologist and vision researcher at University College London, who did not contribute to the study.
"It doesn't seem like new neural connections have to be formed," says Komáromy. "You can add an additional cone opsin pigment and the neural circuitry and visual pathways can deal with it."
Three human gene therapy trials are currently under way for loss of sight due to serious degeneration of the retina. These phase I safety studies injected a similar type of virus vector (but carrying a different gene) behind the retina as in the monkeys, and people treated have shown no serious adverse effects more than a year after, with some participants reporting marked improvements in vision2. These first human trials — which repair rods, a different type of photoreceptor cell — can be seen as a safety benchmark for any future treatment of cone diseases and colour blindness in humans, says Neitz.
"The biggest issue is that people who are colour blind have very good vision," Neitz says. "So before people are going to want to treat colour blindness you're going to want to ensure that this is completely safe, and that's going to take some work."
References
1. Mancuso, K. et al. Nature advanced online publication, doi:10.1038/nature08401 (2009).
2. Cideciyan, A. V. et al. N. Engl. J. Med. 361, 725-727 (2009).
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