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'Acoustic cloak' makes objects invisible

Kirsten Doyle
By Kirsten Doyle, ITWeb contributor.
Johannesburg, 19 Jun 2008

'Acoustic cloak' makes objects invisible

Duke University engineers have revealed details of an acoustic cloak fabricated from metamaterials that they claim can render objects invisible to sonar, says Audio Designline.

Although the acoustic cloak has only been mathematically simulated, the engineers claim that devices based on their blueprint can make submarines invisible to sonar. They work by redirecting sound waves around the hull so that they emerge on the other side without distortion.

"We have shown that acoustic cloaks theoretically do exist," said Duke University professor Steven Cummer. "Our recipe shows how to make an acoustic material that essentially opens up a hole in space, making whatever is inside that hole 'disappear'."

Magnetic nanoparticles track cells

Using a gene from a magnetically sensitive bacterium, scientists have genetically engineered mammalian cells to produce magnetic nanoparticles, reports Technology Review. The finding, by a team of Emory University researchers, could give medical researchers a new way to more precisely track cells in the body.

The gene comes from a species of pond-dwelling bacteria that uses it to make tiny particles that function as a kind of biological compass needle. The researchers found that inserting the gene into the DNA of mouse cells caused the cells to produce their own magnetic nanoparticles. When the researchers then injected cells expressing the gene into the brains of live mice, individual cells could be clearly seen with an MRI as a dark blob surrounded by paler normal tissue.

To track cells in an organism, scientists commonly use genetically engineered fluorescent optical markers such as green fluorescent protein (GFP). By precisely controlling where in the genome the GFP gene is inserted, scientists can "tag" particular proteins that they're interested in, and they can track patterns of gene expression as well as particular kinds of cells.

Regenerating lost cartilage

The key to coaxing cells to regenerate might be to make things a little rough for them. Thomas Webster, a bioengineer at Brown University, has been developing implantable materials with nanoscale textures to mimic the roughness of living tissues, reports Technology Review.

Now, his team has found that cartilage cells can adhere to and grow more densely on a surface covered with carbon nanotubes, particularly when they are also exposed to electrical stimulation. Webster believes that surfaces incorporating carbon nanotubes, which are not only textured but are also electrically conductive, could be a promising strategy for designing cartilage implants.

Cartilage has limited ability to heal itself, so loss or injury to the cushioning tissue is a major health problem. Many research labs have developed materials that mimic the properties of cartilage, as well as scaffolds that can be seeded with cartilage cells outside the body and then implanted at the site of cartilage loss. But one of the key problems is getting a patient's native cartilage, a spongy and rather inert material that lacks its own blood supply, to attach to and integrate with an implant.

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