Charging cartilage.

Borrowing a few tricks from the field of electronics, biomedical researchers have developed a new material for growing tissue in the lab. The team, led by Frank Ko of Drexel University in Philadelphia, mixed polymer nanofibers with carbon nanotubes to produce a scaffold for growing cartilage.

For tissue engineering, researchers typically seed a biodegradable polymer scaffold with cells. As the cells proliferate and form new tissue, the scaffold dissolves. However, existing polymers don't have the mechanical properties to support the growth of stiff tissues, such as bone and cartilage, says Ko.

"Cells need to feel at home," he says. "They need the right mechanical stimuli: So, Ko decided to strengthen the polymer scaffold with carbon nanotubes and give it the look and feel of natural collagen, the structural protein in cartilage.

The researchers blended the two materials and fed the mix through a nanofiber-spinning machine. The machine churned out fibers 20 to 500 nanometers in diameter-approximately the same width as natural collagen fibrils. While only 3 to 5 percent of the resulting material was made up of carbon nanotubes, that was enough to increase the material's resistance to deformation by two orders of magnitude.

The composite fiber behaved more like real cartilage than existing polymers do.

Adding carbon nanotubes to the biodegradable polymer also made the scaffolding slightly conductive, says Ko. Scientists have shown that passing a small electrical current through tissue scaffolding can stimulate cell proliferation and encourage connections between cartilage and bone tissue in, say, knee joints.

Cartilage cells added to the nanofiber scaffolds multiplied and produced new collagen. The team plans to test the performance of its scaffolding in animals within a year or so.--A.G.