Bioactive film helps medical implants bond with bone

The process, developed in partnership with Cambridge University and the University of Texas at San Antonio, involves coating polymer implants with a bioactive film. Testing was carried out on a polymer called polyether ether ketone, or PEEK, which is used in implants due to its similar mechanical properties to bone. PEEK itself doesn’t bond well with bone however, and this is what drove the study, published this week in Materials Science and Engineering.

Previously, PEEK had been coated with hydroxyapatite (HA), a calcium phosphate that promotes osteobonding.However, the HA coating could only be applied to flat surfaces and had never been tested on an implant in a living creature.

"We can now use our technique to coat the entire surface of an implant, and testing HA-coated implants in an animal model has given us very promising results," said Afsaneh Rabiei, a professor of mechanical and aerospace engineering at NC State.

The first step of the process involves coating the PEEK implant with a thin film of yttria-stabilised zirconia (YSZ). A layer of HA is then applied, which is heated using microwaves. During this heating, the YSZ layer acts as a shield that protects the PEEK from melting. The heat also gives the HA a crystalline structure that makes it more stable in the body, meaning that the calcium phosphate will dissolve more slowly, which promotes bonding with surrounding bone.