Nanotube Coatings Strengthen Implants

Originally Published MDDI February 2005

R&D DIGEST

Maria Fontanazza

Nanotube research could lead to the development of bioactive coatings that make implanted devices last longer and increase their compatibility with body tissues.

Researchers at Purdue University (West Lafayette, IN) are aligning carbon nanotubes in the same orientation as that found in real bones. This technique reflects how natural collagen fibers and ceramic crystals are positioned in the body. The study team believes that the nanotubes will adhere to bone rapidly and could lower the risk of implant rejection.

“We've envisioned the process of aligning the nanotubes in polymers or other substances that could be used as a coating on top of traditional implant materials, such as a titanium-based hip or knee implant,” says Thomas Webster, an assistant professor of biomedical engineering at Purdue. “We haven't seen anyone else aligning carbon nanostructures to control cell morphology on the surfaces of implants.”

According to Webster, tissues in the body are basically nanostructures, and the materials used for implants are smoother than tissues at the nanoscale level. Therefore, he says, implanting materials with nanometer features and a seemingly natural roughness could help trick bone cells into accepting them. Earlier studies at Purdue also revealed that bone growth on carbon nanofiber–based materials was improved compared with that on traditional titanium, a material that doesn't have nanometer features.

Researchers use two ways of aligning the nanotubes, which are about 60 nm in diameter. The first technique involves passing an electrical charge through a mixture of nanotubes in a polymer. The current causes the nano-tubes to align in the same direction and, as the polymer sets, the tubes stay in the same position.

In the second method, researchers pour the nanotubes into grids of narrow channels. The tubes align owing to the space constraints, and remain in position even when the grid is removed. Merging both methods is a possibility, since electricity may stimulate bone growth and the grid technique could help enhance bone-to-cell adhesion.

“It's not just a short-term event. We're seeing the cells form bone faster on these aligned arrays,” says Webster. “We hypothesize that this would fix the implant faster and more efficiently in the body, because the existing bone surrounding the implant has the same aligned fiber orientation.”

All cells require proteins to attach to a surface. When a hip implant is inserted into the body, proteins will absorb into the surface of the implant within milliseconds, and the cells will recognize what type of proteins are present. If they like the proteins, they'll stick to the implant, but if they don't, they won't, says Webster. Researchers believe that the bone cells like the nanofibers, which is why they're recognizing and attaching to grow successfully. “This is exactly how it's done in the body. To do it synthetically outside the body should strengthen and increase the lifetime of an artificial joint or implant.”

The National Science Foundation (Arlington, VA) has been funding the research through its Nanoscale Exploratory Research program.

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