Science Daily —
Harvard physicists have shown that specially treated diamond coatings
can keep water frozen at body temperature, a finding that may have
applications in future medical implants.

Doctoral
student Alexander Wissner-Gross (above) and Efthimios Kaxiras, Gordon
McKay Professor of Applied Physics, have shown that treated diamond
coatings can keep water frozen at body temperature. (Credit: Stephanie
Mitchell/Harvard News Office)

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Doctoral student Alexander
Wissner-Gross and Efthimios Kaxiras, physics professor and Gordon McKay
Professor of Applied Physics, spent a year building and examining
computer models that showed that a layer of diamond coated with sodium
atoms will keep water frozen up to 108 degrees Fahrenheit.

In
ice, water molecules are arranged in a rigid framework that gives the
substance its hardness. The process of melting is somewhat like a
building falling down: pieces that had been arranged into a rigid
structure move and flow against one another, becoming liquid water.

The computer model shows that whenever a water molecule near the
diamond-sodium surface starts to fall out of place, the surface
stabilizes it and reassembles the crystalline ice structure.

Simulations
show that the process works only for layers of ice so thin they’re just
a few molecules wide — three nanometers at room temperature and two
nanometers at body temperature. A nanometer is a billionth of a meter.

The
layer should be thick enough to form a biologically compatible shield
over the diamond surface and to make diamond coatings more useful in
medical devices, Wissner-Gross said.

The work is not the first
showing that water can freeze at high temperatures. Dutch scientists
had shown previously that ice can form at room temperature if placed
between a tiny tungsten tip and a graphite surface. Kaxiras and
Wissner-Gross’s work shows that ice can be maintained over a large area
at body temperature and pressure.

Device manufacturers have
been considering using diamond coatings in medical implants because of
their hardness. Concerns have been raised, however, because the
coatings are difficult to get absolutely smooth, abrasion of the tissue
surrounding the implant could result, and that diamond might have a
higher chance of causing blood clots than other materials.

Wissner-Gross
said a two-nanometer layer of ice would just fill the pits in the
diamond surface, smoothing it out and discouraging clotting proteins
from attaching to the surface.

“It should be just soft enough and water-friendly enough to smooth out diamond’s disadvantages,” Wissner-Gross said.

Wissner-Gross
and Kaxiras are planning experiments to confirm the computerized
findings in the real world. Wissner-Gross said they expect results
within a year.

“We’re reasonably confident we’ll be able to realize the effect experimentally,” Wissner-Gross said.

Wissner-Gross, who has been a doctoral student at Harvard since 2003,
said the research grew out of an interest in the physical interaction
of nanostructured surfaces with molecules that are biologically
relevant, such as water. Diamond films are growing cheaper,
Wissner-Gross said, and as their cost declines the array of possible
uses of the material grows wider.

“We both had this notion that
it would be very interesting to combine theory with respect to diamond
surfaces with what’s going on in cryobiology,” Wissner-Gross said. “We
were thinking about how we could leverage this long-term trend [of
declining prices] to do something interesting in the medical field.”

Note: This story has been adapted from material provided by Harvard University.