AMERICAN CERAMIC SOCIETY

X-ray of artificial knee implant.
improved the spatial structure of the
material—but not enough to eliminate
all fatigue wear. They hit on a wellperforming
cartilage sample when they
doused the mix with a gamma radiation
burst. They says this irradiated combination
breaks the main polymer chains
without disrupting the overall structure
of the artificial cartilage. The free radicals
are recrosslinked, improving the
mechanical and tribological properties
of the materials.
According to a news release, the
group believes the irradiated cartilage
composite “could toughen up plastic
joints in joint replacement surgeries
and make them strong enough to last
for years.”
The release continues, “As a result
of the gamma burst, there is no way for
microscopic fractures to be propagated
throughout the material because there
are no long stretches of polymer.”
Xue and others in the group say the
composite has an advantage on alter-
American Ceramic Society Bulletin, Vol. 90, No. 9 | www.ceramics.org
(Credit: F. Jacquot; Wikipedia.)
native artificial joint coatings, such as
nylon and nonstick polymers, because
the polymers produce debris that ultimately
causes inflammation and pain.
They also believe the composite is
more “biocompatible” and may be a
good host for the of addition of bonegenerating
cells.
The work was published in a paper
in the International Journal of Biomedical
Engineering and Technology (doi:0.1504/
IJBET.2011.042495). n
The fuzzy line between biology
and materials science: Using
DNA to build new materials
In an interesting twist on designing
and engineering materials, a group at
New York University led by Paul M.
Chaikin and Nadrian C. Seeman, has
demonstrated that DNA can be used to
assemble complex new materials that
are not necessarily organic.
According to a NYU news release
the NYU scientists created artificial
DNA “tile motifs,” which are short,
nanometer-scale arrangements of DNA.
In the group’s novel approach each
tile serves as a letter— say an “A” or
a “B”—that recognizes and binds to
complementary letters A’ or B’. This
parallels the natural world’s DNA replication
process, where complementary
matches between bases-adenine (A)
pairs with thymine (T) and guanine
(G) pairs with cytosine (C)—to form
its familiar double helix.
However, the NYU researchers take
the DNA a big step farther. Their tile
motif, called BTX (bent triple helix
molecules, each containing three DNA
double helices) differs from ordinary
DNA in a major feature: The BTX
code is not limited to just four letters.
In principle, the BTX motif-based code
can contain quadrillions of different
letters and tiles that combine—still in
pairs—to form a six-helix bundle.
To begin the self-replication of the
BTX tile arrays, the researchers create
a “seed” word to begin to catalyze multiple
generations of identical arrays. In
the work reported in a recent issue of
Nature (doi:10.1038/nature10500), the
NYU group used a BTX seed that consisted
of a sequence of seven tiles, or in
their terminology, a seven-letter “word.”
The self-replication process begins
with placing the seed in a chemical
solution, where it assembles complementary
tiles to form a “daughter BTX
array”— i.e., a complementary word.
The daughter array then is separated
from the seed by heating the solution to
approximately 40°C. The process then
is repeated. The daughter array binds
with its complementary tiles to form a
“granddaughter array.” It is the granddaughter
arrays that represent the self-
NYU scientists have developed artificial structures consisting of triple helix molecules
containing three DNA double helices that can self-replicate. In the above illustration, two
BTX domains are paired by two lateral connections (another two existing connections are
not shown). The cross-section view shows two of the four helices that are formed by the
lateral cohesive interactions.
(Credit: Paul Chaikin, Nadrian Seeman; Nature.)
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