Surface-roughening methods developed by scientists at Brown University (Providence, RI) promote the in-growth of skin cells on titanium implants. Mimicking natural skin, the new implantable material could change the way that orthopedic implants are designed.

Led by Thomas Webster, associate professor of engineering and orthopedics at Brown University, the research team has learned how to modify the surface of titanium leg implants, creating a natural skin layer that can seal the gap between the implant and the body and prevent the growth of infection-causing bacteria. The researchers have also developed a molecular chain for sprinkling skin-growing proteins on the implant surface to hasten skin growth.

Published in the Journal of Biomedical Materials Research A, the scientists' work involved the fabrication of two different nanoscale surfaces. First, using an electron beam, they coated titanium on the implant abutment (the component that is inserted directly into the bone), forming 20-nm mounds that imitate the contours of natural skin and cause skin cells to colonize the surface and grow additional keratinocytes, or skin cells. While Webster knew that a rough nanosurface would promote the regrowth of bone cells and cartilage cells, he was unsure whether it would be able to grow skin cells. This work may be the first time that a nanosurface on a titanium substrate has been shown to attract skin cells.

In the second approach, the scientists anodized the implant abutment by dipping it in hydrofluoric acid and subjecting it to an electric current. This procedure caused the titanium atoms on the abutment's surface to move around and then regroup as hollow, tubular structures that rise perpendicularly from the abutment's surface. As with the nanomounds, this method causes skin cells to quickly colonize the roughened surface.

In vitro tests showed that skin-cell density on the implant surface nearly doubled, leading within five days to the development of an impermeable skin layer bridging the abutment and the body.

To promote skin cell growth around the implant, Webster's team then investigated the use of FGF-2, a protein secreted by the skin to help other skin cells grow. However, because FGF-2 is absorbed by the titanium if it is simply coated on the abutment, the researchers synthesized a molecular chain to bind the proteins to the titanium surface. In vitro tests showed that skin cells formed most readily on those abutment surfaces that had been treated with FGF-2.