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Doctors may one day have the ability to inject a
solution of nanotubes into a bone fracture, and then wait for the new tissue to
grow and heal.
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Scientists have shown for the first time that carbon
nanotubes make an ideal scaffold for the growth of bone
tissue. The new technique could change the way doctors treat
broken bones, allowing them to simply inject a solution of
nanotubes into a fracture to promote healing.
The report appears in the June 14 issue of the American Chemical
Society's journal Chemistry of Materials.
The success of a bone graft depends on the ability of the
scaffold to assist the natural healing process. Artificial bone
scaffolds have been made from a wide variety of materials, such as
polymers or peptide fibers, but they have a number of drawbacks,
including low strength and the potential for rejection in the body.
"Compared with these scaffolds, the high mechanical strength,
excellent flexibility and low density of carbon nanotubes make them
ideal for the production of lightweight, high-strength materials
such as bone," says Robert Haddon, Ph.D., a chemist at the
University of California, Riverside, and lead author of the paper.
Single-walled carbon nanotubes are a naturally occurring form of
carbon, like graphite or diamond, where the atoms are arranged like
a rolled-up tube of chicken wire. They are among the strongest known
materials in the world.
Bone tissue is a natural composite of collagen fibers and
hydroxyapatite crystals. Haddon and his coworkers have demonstrated
for the first time that nanotubes can mimic the role of collagen as
the scaffold for growth of hydroxyapatite in bone.
"This research is particularly notable in the sense that it
points the way to a possible new direction for carbon nanotube
applications, in the medical treatment of broken bones," says
Leonard Interrante, Ph.D., editor of Chemistry of Materials
and a professor in the department of chemistry and chemical biology
at Rensselaer Polytechnic Institute in Troy, N.Y. "This type of
research is an example of how chemistry is being used everyday,
world-wide, to develop materials that will improve peoples' lives."
The researchers expect that nanotubes will improve the strength
and flexibility of artificial bone materials, leading to a new type
of bone graft for fractures that may also be important in the
treatment of bone-thinning diseases such as osteoporosis.
In a typical bone graft, bone or synthetic material is shaped by
the surgeon to fit the affected area, according to Haddon. Pins or
screws then hold the healthy bone to the implanted material. Grafts
provide a framework for bones to regenerate and heal, allowing bone
cells to weave into the porous structure of the implant, which
supports the new tissue as it grows to connect fractured bone
segments.
The new technique may someday give doctors the ability to inject
a solution of nanotubes into a bone fracture, and then wait for the
new tissue to grow and heal.
Simple single-walled carbon nanotubes are not sufficient, since
the growth of hydroxyapatite crystals relies on the ability of the
scaffold to attract calcium ions and initiate the crystallization
process. So the researchers carefully designed nanotubes with
several chemical groups attached. Some of these groups assist the
growth and orientation of hydroxyapatite crystals, allowing the
researchers a degree of control over their alignment, while other
groups improve the biocompatibility of nanotubes by increasing their
solubility in water.
"Researchers today are realizing that mechanical mimicry of any
material alone cannot succeed in duplicating the intricacies of the
human body," Haddon says. "Interactions of these artificial
materials with the systems of the human body are very important
factors in determining clinical use."
The research is still in the early stages, but Haddon says he is
encouraged by the results. Before proceeding to clinical trials,
Haddon plans to investigate the toxicology of these materials and to
measure their mechanical strength and flexibility in relation to
commercially available bone mimics.
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The American Chemical Society is a nonprofit organization,
chartered by the U.S. Congress, with an interdisciplinary membership
of more than 158,000 chemists and chemical engineers. It publishes
numerous scientific journals and databases, convenes major research
conferences and provides educational, science policy and career
programs in chemistry. Its main offices are in Washington, D.C., and
Columbus, Ohio.
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