Researchers at Brown University in Providence, Rhode Island have created nanoscale surfaces for materials on prosthetic devices that mimic the contours of natural skin. Their findings appear in the April issue of the Journal of Biomedical Materials Research A (paid subscription required).
The goal of biomedical engineers to develop more flexible, functional prosthetics for soldiers and civilians is hampered by the need to keep bacteria from entering the body through the space where a prosthetics device is attached. Thomas Webster, professor of engineering and orthopedics at Brown and colleagues have found two methods to deter bacteria from affecting implants.
Both methods involve modifying the surface of titanium leg implants to promote skin cell growth, thereby creating a natural skin layer and sealing the gap where the device has been implanted into the body. The researchers also created a molecular chain to add skin-growing proteins on the implant to hasten skin growth.
The two methods alter the titanium surface at nanoscale dimensions; 1 nanometer = 1 billionth of a meter. In the first approach, the scientists fired an electron beam of titanium coating at the abutment — the piece of the implant that is inserted into the bone. The beam creates a field of 20-nanometer mounds that imitate the contours of natural skin and trick skin cells into populating the surface and growing additional skin cells. Webster says this is the first time titanium has been shown to attract skin cells in nanoscale.
The second approach involves dipping the abutment into hydrofluoric acid and giving it a jolt of electric current. The electric current with the acid cause the titanium atoms on the abutment’s surface to scatter and regroup as nanotubes rising perpendicularly from the abutment’s surface. As with the nanoscale mounds, skin cells quickly populate the nanotube surfaces.
In lab tests, the researchers report nearly a doubling of skin cell density on implant surfaces. Within five days, the density of skin cells reached the point at which an impermeable skin layer bridging the abutment and the body had been created.
To further promote skin cell growth around the implant, Webster’s team devised a a synthetic molecular chain to bind the protein FGF-2 to the titanium surface. FGF-2 is secreted by the skin to help other skin cells grow, but physically applying FGF-2 to the abutment doesn’t work, as FGF-2 loses its effect when absorbed by the titanium.
Lab tests showed the greatest density of skin cells on abutment surfaces using the nanomodified surfaces and covered with FGF-2. The modified surfaces also created more surface area for FGF-2 proteins than would be available on traditional implants.
The next steps will involve tests on animals, and later human clinical trials. The U.S. Department of Veterans Affairs and National Science Foundation funded the research.
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