NNanoparticles form in a 3-D-printed microfluidic channel. Each droplet
shown here is about 250 micrometers in diameter, and contains billions
of platinum nanoparticles. CPhoto: Richard Brutchey and Noah Malmstadt,
USC
Nanoparticles form in a 3-D-printed microfluidic channel. Each droplet
shown here is about 250 micrometers in diameter, and contains billions
of platinum nanoparticles. CPhoto: Richard Brutchey and Noah Malmstadt,
USC
anoparticles can be found in everything from drug delivery formulations
to pollution controls on cars to HD TV sets. With special properties
derived from their tiny size and subsequently increased surface area,
they're critical to industry and scientific research.
They're also expensive and tricky to make.
Now, researchers at USC have created a new way to manufacture
nanoparticles that will transform the process from a painstaking,
batch-by-batch drudgery into a large-scale, automated assembly line.
The method, developed by a team led by Noah Malmstadt of the USC Viterbi
School of Engineering and Richard Brutchey of the USC Dornsife College
of Letters, Arts and Sciences, was published in Nature Communications on
Feb. 23.
Consider, for example, gold nanoparticles. They have been shown to be
able to easily penetrate cell membranes without causing any damage - an
unusual feat, given that most penetrations of cell membranes by foreign
objects can damage or kill the cell. Their ability to slip through the
cell's membrane makes gold nanoparticles ideal delivery devices for
medications to healthy cells, or fatal doses of radiation to cancer
cells.
However, a single milligram of gold nanoparticles currently costs about
$80 (depending on the size of the nanoparticles). That places the price
of gold nanoparticles at $80,000 per gram - while a gram of pure, raw
gold goes for about $50.
"It's not the gold that's making it expensive," said Malmstadt. "We can
make them, but it's not like we can cheaply make a 50 gallon drum full
of them."
Right now, the process of manufacturing a nanoparticle typically
involves a technician in a chemistry lab mixing up a batch of chemicals
by hand in traditional lab flasks and beakers.
Brutchey and Malmstadt's new technique instead relies on microfluidics -
technology that manipulates tiny droplets of fluid in narrow channels.
"In order to go large scale, we have to go small," said Brutchey. Really small.
The team 3-D printed tubes about 250 micrometers in diameter - which
they believe to be the smallest, fully enclosed 3-D printed tubes
anywhere. For reference, your average-sized speck of dust is 50
micrometers wide.
They then built a parallel network of four of these tubes, side-by-side,
and ran a combination of two non-mixing fluids (like oil and water)
through them. As the two fluids fought to get out through the openings,
they squeezed off tiny droplets. Each of these droplets acted as a
micro-scale chemical reactor in which materials were mixed and
nanoparticles were generated. Each microfluidic tube can create millions
of identical droplets that perform the same reaction.
This sort of system has been envisioned in the past, but its hasn't been
able to be scaled up because the parallel structure meant that if one
tube got jammed, it would cause a ripple effect of changing pressures
along its neighbors, knocking out the entire system. Think of it like
losing a single Christmas light in one of the old-style strands - lose
one, and you lose them all.
Brutchey and Malmstadt bypassed this problem by altering the geometry of
the tubes themselves, shaping the junction between the tubes such that
the particles come out a uniform size and the system is immune to
pressure changes.
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