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 .
ACS is the world's largest scientific society.
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
"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."
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
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.
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.
- Jason Gorss
The online version of the research paper cited
above was initially published May 13, 2005, on
the journal's Web site. Journalists can arrange
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Contact: Michael Bernstein