Bones Grow and Infections Decline

A rougher terrain engineered
on the nanoscale (top) and
microscale (bottom); © T.J.Webster

"We've found a method of coating implants that discourages bacteria growth," said Thomas Webster, an associate professor of engineering at Brown University, "and it does so significantly. The hope is that this technique will lead to safer, longer-lasting implants."

Webster and colleagues knew that abrading or coating implants to produce microscopic bumps, which create a sand-papery surface, aid in bone growth. The team wondered if smaller peaks and craters – ones that measure on the nanometer scale – would work even better.

The engineers chose zinc and titanium oxides as their materials. They took nanoparticles of these ceramics and pressed them into dime-sized discs. They made more discs of the same material with microparticles. Discs with nanostructured surfaces had bumps that measured only .023 microns in diameter. Discs with microstructured surfaces had bumps that measured about 5 microns in diameter.

The engineers put S. epidermidis on the discs and waited an hour. Then they counted the bacteria. The results were dramatic. Microstructured zinc oxide discs were host to 1,000 times more bacteria than the nanostructured zinc oxide discs. Similar, but less striking, results were duplicated on titanium oxide discs.

The engineers conducted similar experiments with bone-forming cells and found that twice as many of these cells grew and formed bone on nanostructured discs. Other indicators of healthy bone growth, such as collagen synthesis, were also stronger with nanostructured discs.

"Surface area seems to be key," Webster said. "With the nanostructured surfaces we created, surface area increased by 25 to 35 percent. We think that this additional area, along with the unique surface energetics of these nanomaterials, gave bone-forming cells more places to adhere. But with bacteria, increased surface area may work the other way, exposing the bugs to more of the germ-fighting properties of the zinc oxide."; Source: Brown University