ARLINGTON, Va., Dec. 3, 2004 -- Stronger than steel, more durable than diamond, carbon nanotubes can be aligned to stimulate bone growth in a way that might make better and longer lasting artificial joints.

Research led by biomedical engineer Thomas Webster, Ph.D., of Purdue University demonstrates two ways of aligning the tiny carbon tubes to mimic the surfaces of collagen fibers and ceramic crystals found in natural bone. The engineered surface attracts and holds a higher percentage of developing bone cells (osteoblasts) than conventional surfaces do.

Artificial joints depend upon a tight bond between bone and a man-made surface, such as titanium. The current research suggests that carbon nanotubes might form a seal between natural bone and artificial joints, creating implants that are stronger and longer-lasting than those currently available.

Carbon nanotubes have a surface texture in the realm of 100 nanometers, or billionths of a meter. Conventional artificial joint materials have much larger surface textures. Titanium has features on the micron scale, 1,000 times larger than carbon nanotubes. As a result, titanium attracts fewer bone cells.

Webster's group experimented with two approaches for making nanotubes align in parallel, like rails in a fence, rather than fall into a jumble.

In the first approach, the group mixed the nanotubes in a polymer and then applied an electric current. Since nanotubes all share the same electrical charge, each tube was pulled into parallel with its neighbor. When the poylmer hardened, the nanotubes were fixed in alignment.

The second method involved pouring nanotubes into tiny channels, forcing the tubes to line up parallel with the channels. The channels were removed, leaving the aligned nanotubes behind.

Both batches of nanotubes were added to cultures of bone cells and given time to intermingle. After two hours, samples were removed and examined. The researchers found that 80 percent of the bone cells stuck to the nanotubes, about twice the rate observed using unaligned nanotubes.

"In a very short period of time, we're already seeing a big improvement in how well the cells stick to the nanotubes," Webster said. The culture was allowed to grow for seven days, at which time the bone cells were still holding strong.

The research is encouraging but many questions remain unanswered. Webster's study spanned a relatively short period -- seven days -- so longer studies will be needed. The work was also in a cell culture, rather than a live organism. Toxicity is also an issue because carbon nanotubes are poisonous under certain conditions. Yet the research has taken a first step toward using nanotechnology to improve one of the most common surgical procedures, joint replacement.

Webster and his colleageus, Tongwoo Khang, Minbaek Lee, Sun Namkung and Seunghun Hong, presented their findings at recent meetings of the Biomedical Engineering Society and the Society for Biomaterials.

Contact:
Thomas Webster, Purdue University
Frank Blanchard, The Whitaker Foundation