Aligned nanotubes accommodate bone

Natural tissues grow from the ground up molecule by molecule, and in many cases the alignment of each molecule matters. Researchers from Purdue University have found that artificial joints can be improved by mimicking the alignment of collagen fibers and natural ceramic crystals in real bones.

Bones are made from proteins and ceramic crystals whose dimensions are on the nanometer scale; the components of bone are also fiber-like. With this in mind, the researchers are using nanoscale materials that are fiber-like.

Today's nanotechnology techniques make it possible to orient carbon nanotubes and filaments in implant material. Carbon nanotubes are rolled-up sheets of carbon atoms that can be narrower than a nanometer, which is one millionth of a millimeter, or the span of 10 hydrogen atoms.

The researchers' petri-dish experiments show that orienting artificial joint material nanotubes in the same direction made bone cells attach better to the material. It also stimulated the growth of more new bone tissue, which is important for anchoring implanted artificial joints. Finding better artificial joint material is motivated in part by the 15-year lifespan of today's artificial joints.

Aligning the molecules in materials may also make them stronger, according to the researchers.

The researchers used two methods to align nanotubes: aligning a mix of nanotubes and plastic using electric current, and pouring nanotubes into narrow channels on a silicon oxide surface.

The researchers had previously shown that bone-forming cells grow more readily on carbon nanotubes materials than the titanium used in implants.

The material could be used in practical implants in 10 to 15 years, according to the researchers. They presented the research at the Biomedical Engineering Society annual meeting held in Philadelphia October 13 to 16, 2004.