Week of September 19, 2005

Honey, I shrunk the robotic inchworm

Researchers from Dartmouth College and the Massachusetts Institute of Technology have made tiny mobile robots that are steerable. Although scientists have previously made tiny mechanical devices from silicon, most of the devices are stuck in place, and those that can move can only do so in a straight line.

The Dartmouth-MIT microrobot is made from a single piece of 250-by-60-by-10 micron silicon. Human hair is about 75 microns in diameter.

The robot has a rectangular body and a steering arm that protrudes from its left side. It moves inchworm fashion, with the steering arm pivoting the device by making contact with the surface. To turn right, the device pivots through a full loop.

Microrobots like these could eventually be used to manipulate individual cells in the body or in a biochip, repair computer chips and investigate hazardous environments.

Don't worry about these particular tiny robots sneaking around your desk drawers, medicine cabinet or body parts, though. They only move around a special surface that provides power and control signals.

(A Steerable, Untethered, 250 X 60 µm MEMS Mobile Micro-Robot, 12th International Symposium of Robotics Research, San Francisco, October 12-15, 2005)

Nano wireless

Fireflies, heart cells and pendulum clocks synchronize with others of their kind. The same turns out to be true for nanoscale electromagnets, which can be used to transmit and receive microwaves.

An experiment conducted by researchers at the National Institute of Standards and Technology (NIST) and Hitachi San Jose Research Center, and a second experiment by researchers at Freescale Semiconductor Inc., show that a pair of nanoscale magnetic oscillators in close proximity synchronize. And as the oscillators vibrate in tandem, their output power increases exponentially.

The oscillators are thin magnetic layers sandwiching a non-magnetic layer. The magnetic layers are oriented in opposite directions, and under a direct electrical current, their electrons align in opposite directions, causing the device's overall magnetic orientation to rapidly oscillate. These oscillations cause waves of magnetic alignment to ripple through the electrons in surrounding material. The waves from a pair oscillators in close proximity interact in such a way that they synchronize.

Arrays of nano-oscillators could be used to communicate information sans wires between parts of a computer chip or between computer chips within devices.

(Mutual Phase-Locking of Microwave Spin Torque Nano-Oscillators, Phase-Locking in Double-Point-Contact Spin-Transfer Devices, Nature, September 15, 2005)

RNA nanotech takes on cancer

One of the great hopes for biomedical nanotechnology is that it could lead to cancer treatments that are more effective and less harmful than today's chemical and radiation therapies.

Researchers from Purdue University have developed nanoparticles that seek out, infiltrate and destroy cancer cells. The 25-nanometer-diameter particles consist of short strands of RNA, the messenger molecule that carries out instructions encoded in DNA for building the proteins that regulate the body's biochemical processes.

The particles are made up of three hybrid RNA strands that include molecules that find, mark or attack cancer cells. The strands are combined into a triangular nanoparticle small enough to penetrate cancer cells.

The RNA nanoparticles interrupted the growth of human breast cancer cells in laboratory tests and blocked tumor growth in mice, according to the researchers.

The researchers developed some of their RNA-manipulation techniques two years ago by building an RNA nanomotor.

(Controllable Self-Assembly of Nanoparticles for Specific Delivery of Multiple Therapeutic Molecules to Cancer Cells Using RNA Nanotechnology, Nano Letters, September 14, 2005)

Physics finds file-folder formula

Natural networks like predator-prey relationships, social networks like jazz musician collaborations, and artificial networks like the Internet all have a scale-free structure, meaning they have a few nodes -- animals, people or sites -- with many links, and many nodes with just a few links. In these cases, the structure arises from the uncoordinated collective action of many nodes.

The network of file folders in individuals' computer files also has a scale-free structure, even though the structure is coordinated -- people decide how to set up their file folders. Researchers from Leipzig University in Germany and the Mediterranean Institute for Advanced Studies (IMEDEA) used statistical physics to study the file directory trees of 63 computer users and developed a model that describes the file folder structure.

The researchers found that file directory structures are strikingly similar despite the lack of constraints on how people organize their files. The work promises to improve tools for organizing and accessing information.

(Scaling in the Structure of Directory Trees in a Computer Cluster, Physical Review Letters, September 16, 2005)

Bits and pieces

Electrically-driven crystal growth powers a nanomotor; a self-assembled plastic film that changes shape when it hits water or a pH change shows promise for biomedical applications; an inexpensive supercapacitor manufacturing process builds portable power into electronic devices.