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Year: 2012 (page 36 of 55)

09.08.2012

stretchy gels

A new hydrogel made from polyacrylamide and alginic acid polymers can be stretched up to 20 times its original length before breaking.

A hydrogel is a network of polymers that soaks up lots of water to form a jelly-like material. But most shatter easily and don’t stretch far without breaking. Some of the toughest hydrogels are used to make soft contact lenses, and researchers want to make them more robust, for use in replacement cartilage or as scaffolds for growing artificial organs.

Suo’s hydrogel is made from a mixture of two polymers — alginate and polyacrylamide. Each polymer forms networks using different types of chemical bond: alginate molecules are linked together by ionic bonds, and polyacrylamide molecules by stronger covalent bonds. When the gel is stretched, hit or torn, the ionic bonds can break and reform throughout the material, dissipating energy over a wide area and causing fewer of the covalent bonds to be irreversibly ruptured. The covalent bonds hold the material together, allowing it to spring back to its original shape.

Separately, the two polymers can each form normal hydrogels — but when they are mixed together, the resulting material is far stronger than its constituent parts. The energy needed to fracture the combination hydrogel is on a par with that for natural rubber at 9,000 joules per square metre, and the gel can be stretched to 20 times its original length without breaking. “You can’t even tear it apart with your hands,” says Suo.

More at Nature.com

09.06.2012

branched-chain amino acid deficiency linked to rare form of autism

Lots of interesting reads in Scientific American & Nature these past few weeks.  Ewen Callaway of Nature magazine brings us this story:

A rare, hereditary form of autism has been found — and it may be treatable with protein supplements.

Genome sequencing of six children with autism has revealed mutations in a gene that stops several essential amino acids being depleted. Mice lacking this gene developed neurological problems related to autism that were reversed by dietary changes, a paper published today in Scienceshows1.

“This might represent the first treatable form of autism,” says Joseph Gleeson, a child neurologist at the University of California, San Diego, who led the study. “That is both heartening to families with autism, and also I think revealing of the underlying mechanisms of autism.”

The children came from three families with Middle Eastern ancestry; in each case the parents were first cousins. Studying such families makes the hunt for the rare recessive mutations underlying some forms of autism simpler than it would be among the general population, Gleeson says, because the odds are higher that children will be born with two copies of the recessive mutation.

In each family, Gleeson’s team identified mutations that inactivate the enzyme BCKD-kinase, which normally prevents the body from breaking down branched-chain amino acids called leucine, isoleucine and valine after a meal. Humans cannot synthesize these amino acids and must obtain them from food.

“We predicted that patients would burn through these amino acids,” says Gleeson. The prediction was correct: after eating, the children had low blood levels of the branched-chain amino acids. Mice lacking the gene that codes for BCKD-kinase also had low levels of the amino acids in their blood and tissue.

The sample size of six is extremely limited due to the rarity of the disease, so we don’t know if the result are generalizable. But the results are interesting nonetheless.

09.05.2012

“junk” dna not so junky

Junk DNA

From the New York Times:

The human genome is packed with at least four million gene switches that reside in bits of DNA that once were dismissed as “junk” but that turn out to play critical roles in controlling how cells, organs and other tissues behave. The discovery, considered a major medical and scientific breakthrough, has enormous implications for human health because many complex diseases appear to be caused by tiny changes in hundreds of gene switches.

The findings are the fruit of an immense federal project, involving 440 scientists from 32 labs around the world. As they delved into the “junk” — parts of the DNA that are not actual genes containing instructions for proteins — they discovered it is not junk at all. At least 80 percent of it is active and needed.

The result is an annotated road map of much of this DNA, noting what it is doing and how. It includes the system of switches that, acting like dimmer switches for lights, control which genes are used in a cell and when they are used, and determine, for instance, whether a cell becomes a liver cell or a neuron.

More here.

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