Journey

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 (left pic) 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.(about 42.2 degrees Celsius)

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.”

Adapted from Science Daily

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