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Intelligent Machines


New publications, experiments, and breakthroughs in nanotechnology – and what they mean.

DNA Origami
Simple synthesis could bring nanoscale design to the masses.

Source: “Folding DNA to Create Nanoscale Shapes and Patterns”
P. W. K. Rothemund
Nature 440(7082): 297-302

Results: Paul Rothemund, a Caltech computer scientist, has developed a simple technique for building nanometer-scale, two-dimensional structures of any shape or pattern from DNA. So far, he’s made, among other things, smiley faces, the letters “DNA,” and a map of the Western Hemisphere. These structures can also be combined to form larger shapes. Since the shapes “self-assemble” in solution, billions of them can be made at once.

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Why It Matters: DNA is a versatile raw material for nanoscale structures. But past methods of using DNA as a nano building block were slow, labor intensive, and expensive, which limited their use to a handful of labs. The new technique is simple and inexpensive enough for widespread use, Rothemund says. Since a variety of molecules and nanoparticles can be linked to DNA, the technique could be a way of quickly patterning molecules as diverse as proteins and carbon nanotubes, possibly leading to minute electronic devices or “nanoarrays” for studying cells at an unprecedented level of detail.

Methods: Rothemund begins with a solution containing long strands of DNA with a known sequence. He then adds hundreds of different short “staple strands,” each with a sequence designed to latch on to two or three specific sections of the long strand. As the staples connect, they pull these sections together, causing the long strand to fold into the desired shape.

Next Step: Using the technique to make electronics will require the invention of a nanoscale equivalent of the transistor. Also, since any self-assembly process is prone to error, engineers will need to develop fault-tolerant computer architectures. For biological applications, such as sensors that determine the kinds of proteins in a particular cell, researchers will need to find a reliable way to read signals transmitted by the minuscule devices. Rothemund expects that the best applications of the new technique are yet to be imagined.

Knitting Nerves Back Together
Nanofibers allow injured brain and spinal tissue to repair itself.

Source: “Nano Neuro Knitting: Peptide Nanofiber Scaffold for Brain Repair and Axon Regeneration with Functional Return of Vision”
Rutledge Ellis-Behnke et al.
Proceedings of the National Academy of Sciences 103(13): 5054-5059

Results: Using self-assembling nanomaterials, MIT researchers have restored the sight of brain-damaged rodents. After cutting through a structure in hamsters’ brains necessary for vision, neuroscientist Rutledge Ellis-Behnke and colleagues injected the animals with a solution containing short chains of amino acids, called peptides, that when in contact with brain fluids assemble into nanoscale fibers. The resulting mesh of fibers bridges the gap left by the cut and prevents scar tissue from forming, thus allowing neurons to regrow and reëstablish preinjury signal pathways. Seventy-five percent of adult hamsters treated with the technique recovered enough vision to detect and turn toward food.

Why It Matters: Spinal-cord and brain injuries from accidents, strokes, and disease affect millions of Ameri-cans; many of these people never regain lost abilities and functions, largely because scar tissue and inhibitory chemicals prevent damaged tissue from healing. At least over short distances, the experimental nanomaterial seems to overcome these problems in neural tissue. The nanomaterial allows nerve cells to grow and reëstablish connections, which could restore human patients’ lost abilities to walk or talk, even as it restored sight in these experiments.

Methods: In separate experiments on young and adult hamsters, the researchers cut through a brain structure called the optic track, which conveys visual signals, thus blinding the hamsters in one eye. Soon after the cut was made, control animals received an injection of saline at the site of the injury, and test animals received an injection of the peptides. The researchers then tested the animals for the -ability to see and turn toward sunflower seeds and, after euthanizing them, examined their brain tissue to measure the regrowth of neurons.

Next Step: If large-animal studies go well, the treatment could be tested in humans starting within three years. Meanwhile, the researchers are developing ways to speed nerve regrowth, with the goal of reconnecting distant areas of the brain and spinal cord sepa-rated by larger injuries.

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