Nanotube Technique Repairs Bone Fractures

This new method could change the way clinicians treat broken bones, allowing them to simply inject a nanotube solution into a fracture to promote healing. The success of a bone graft depends on the capability of the scaffold to help in the natural healing process. Synthetic bone scaffolds have been produced from a wide assortment of materials, including peptide fibers or polymers, but they have various disadvantages, such as the potential for rejection in the body and low strength.

"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,” commented Robert Haddon, Ph.D., a chemist at the University of California, Riverside (USA), and lead author of the article, which was published in the June 14, 2005, issue of the journal Chemistry of Materials.

Single-walled carbon nanotubes are a naturally occurring form of carbon, such as a diamond or graphite, where the atoms are arranged like a tube of chicken wire. They are among the strongest known compounds known to man. Bone tissue is a natural complex of collagen fibers and hydroxyapatite crystals. Dr. Haddon and his colleagues have shown 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,” said 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, NY, USA). "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 investigators predict that nanotubes will increase the flexibility and strength of synthetic bone compounds, leading to a new kind of bone graft for breaks that may also be important in the treatment of osteoporosis. In a conventional bone graft, synthetic material or bone is shaped by the surgeon to fit in the affected region, according to Dr. Haddon. Screws or pins then hold the healthy bone to the implanted compound. Grafts offer a framework for bones to heal and regenerate, allowing bone cells to interlace into the porous structure of the implant, which supports the new tissue as it grows to connect broken bone sections.

The new method may soon provide clinicians with the capability to inject a nanotube solution into a bone fracture, and then wait for the new tissue to heal and grow. Simple single-walled carbon nanotubes are not enough, because the growth of hydroxyapatite crystals relies on the capability of the scaffold to draw in calcium ions and begin the crystallization process. Therefore, the scientists carefully designed nanotubes with several chemical groups attached. Some of these groups support the growth and orientation of hydroxyapatite crystals, allowing the scientists a level of control over their alignment, while other groups improve the biocompatibility of nanotubes by increasing their water solubility.

"Researchers today are realizing that mechanical mimicry of any material alone cannot succeed in duplicating the intricacies of the human body,” Dr. Haddon stated. "Interactions of these artificial materials with the systems of the human body are very important factors in determining clinical use.”

The study is still in its preliminary stages, but Dr. Haddon said he is encouraged by the study's findings. Before moving to clinical trials, he plans to assess the toxicity of these compounds and to assess their mechanical flexibility and strength in relation to commercially available bone mimics.




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