Medical Implant Coating Lowers Rejection Rates

Researchers at North Carolina State University (Raleigh, USA) and Oak Ridge National Laboratory (Oak Ridge, TN, USA) developed a series of functionally graded hydroxyapatite (FGHA) coatings that can be applied on to titanium substrates using ion beam-assisted deposition. The smart coatings mitigate the risk of implant rejection by fostering bone growth into the implant by creating a crystalline layer next to the implant, as well as a mostly amorphous outer layer that touches the surrounding bone. The amorphous layer dissolves over time, releasing calcium and phosphate, which encourages bone growth. The researchers also incorporated silver nanoparticles --using various percentages of silver--throughout the coating to ward off infections, which act as antimicrobial agents while the amorphous layer dissolves. This not only limits the amount of antibiotics the patients will need following surgery, but provides protection from infection at the implant site; moreover, the silver is released more quickly right after surgery, when there is more risk of infection, due to the faster dissolution of the amorphous layer of the coating.

The analysis of the coating's cross-section using transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy showed a decreased crystallinity as well as a distribution of nanoscale (10-50 nm) silver particles from the coating-substrate interface to the top surface of the implant. Both X-ray diffraction and fast Fourier transforms on high-resolution TEM images revealed the presence of hydroxyapatite within the coatings. The study was published in the January 2010 issue of Acta BioMaterialia.

"We call it a smart coating because we can tailor the rate at which the amorphous layer dissolves to match the bone growth rate of each patient,” said coauthor Afsaneh Rabiei, Ph.D., an associate professor of mechanical and aerospace engineering at North Carolina State University. "The bone grows into the coating as the amorphous layer dissolves, resulting in improved bonding, or osseointegration. This bonding also makes the implant more functional, because the bonding helps ensure that the bone and the implant do a better job of sharing the load.”

Related Links:
North Carolina State University
Oak Ridge National Laboratory