Motion System Design

Nanotubes used in artificial joints

Artificial joints may someday use tiny carbon tubes and filaments aligned to mimic collagen fibers and natural ceramic crystals in real bones.

Researchers at Purdue University found that bone cells attach better to materials possessing surface bumps smaller than those of conventional materials used to make artificial joints. The smaller features also stimulate the growth of more new bone tissue, critical for the proper attachment of artificial joints once they are implanted.

The researchers found that cell adhesion and growth get even better with so-called nanotubes and nanofibers aligned in the same direction. This orientation is similar to the way collagen and natural ceramic crystals, called hydroxyapatite, are aligned in bone.

Purdue researchers found that about one-third more bone-forming cells, or osteoblasts, attach to carbon nanotubes that possess surface bumps about as wide as 100 nm. Fewer bone cells stick to conventional titanium, often used as bone replacement material, which has surface features on the scale of microns.

The nanometer-scale bumps mimic surface features of proteins and natural tissues, prompting cells to stick better and promoting the growth of new cells. The findings also suggest that use of nanometer-scale materials might cause fewer rejection responses from the body. Rejection eventually weakens the attachment of implants and causes them to become loose and painful. Many times, additional replacement surgery can result.

Aligning the nanotubes to further mimic natural bone also might provide more strength.

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