[ExI] "Chemical signalling drives nanomachines"

[Damien Broderick]

[I don't know how new this really is--the slur 
between nano and micro is irritating:]

http://www.cosmosmagazine.com/node/1913


Chemical signalling drives nanomachines

Friday, 28 March 2008
by Anna Canale-Parola
Cosmos Online

SYDNEY: Scientists have found a way to make 
minute synthetic bubbles, known as microcapsules, 
move by mimicking the behaviour of biological 
cells. The technique brings us one step closer to 
nanomachines with applications ranging from drug delivery to fuel cells.

The team from the University of Pittsburgh in the 
U.S. have used computational modelling to 
demonstrate how the controlled motion of these 
microcapsules could be manipulated to do tasks at the microscopic scale.

The technique could eventually be applied to 
procedures such as targeted drug delivery, where 
the capsules would be directed though the body to 
a target site and then "exploded" by heat from 
lasers, releasing the particles of drugs within them.

Bold and exciting

"This is a very bold and exciting idea," enthused 
Michael Cortie, director of the Institute for 
Nanoscale Technology at the University of 
Technology Sydney (UTS), who was not involved in 
the research. "It goes one step further in the 
direction of trying to achieve a nanorobot."

To make the discovery, chemical engineer Anna 
Balazs, and her team used computer simulations to 
design a system of microscopic capsules that move 
by communicating in the same way that organic 
cells do. They report the find this week in the 
American Chemical Society journal ACSNano.

"Biological cells communicate through a complex 
chemical process where a signalling cell secretes 
molecules that are then detected by receptors on 
the target cell," says the study. "We show how 
one microcapsule 'signals' to another and thereby 
initiates the motion of both."

The team's simulation models two fluid-filled 
polymer capsules resting on a surface within a 
viscous fluid. One of these, the "signalling" 
capsule, contains nanoparticles – tiny particles 
less than 100 nanometres across (one nanometre is 
a billionth of a metre) - which diffuse through 
the porous shell and into the surrounding fluid.

These particles affect the adhesive properties of 
the surface, making parts of it less or more 
sticky. The second "target" capsule is attracted 
to the more sticky part of the surface, and so 
moves towards to it. This movement affects the 
fluid around the first (signalling) capsule – 
think of the wake left by a boat moving in water – and drives it to follow.

The nanoparticles therefore act as a stimulus, 
causing first one, then both capsules to move. 
Continuous motion (and stopping) can be achieved 
by carefully altering some of the system 
variables, such as the size of the capsule, the 
density of the host fluid and the absorption properties of the surface.

Balazs describes the groundbreaking nature of 
their work: "It is the first study to predict how 
to get two inanimate microscopic objects – the 
microcapsules – to effectively communicate with 
each other and thereby carry out a concerted action – namely, motion."

Fundamental insights

The find also provides insight into the 
fundamental processes that control the movement 
of biological cells as they respond to chemicals 
in their environment. But the potential 
applications for moveable nanomachines are what the experts are excited about.

"These communicating microcapsules could be used 
in microfluidics, which are small-scale devices 
used to carry out rapid biological assays or to 
perform synthesis of minute quantities of 
chemicals," said Balazs. "It is bringing us 
closer to the goal of designing "smart materials" 
that can autonomously perform specific functions."

"The possibilities for this kind of small-scale 
technology are very optimistic," added Michael 
Cortie. "If everyone systematically works on the 
problems faced [in nanotechnology research], we 
will have breakthroughs that could make a 
tangible difference to human health and the energy problem."

"This is a really cool piece of work," agreed 
Mike Ford, an associate professor of 
nanotechnology also at UTS in Sydney. "The work 
is more at the level of basic science, however 
one could imagine a raft of applications that 
might spring out of this work later down the 
track, such as controlling the motion of 
micro-objects in liquids and enforcing collective motion."