In their new study, researchers tested three types of PEEK implants in a rabbit model: PEEK implants with no coating; PEEK implants with an HA coating treated only with microwaves; and PEEK implants with an HA coating treated with both microwaves and brief exposure to an autoclave in order to enhance the HA's crystalline structure.
The researchers used microscopic evaluations of tissue cells and three-dimensional X-ray imaging to assess the performance of all three types of implants. Eighteen weeks after surgery, the researchers found that both types of HA-coated implants had more than double the bone formation of PEEK alone, with comparable bone density. The HA-treated implants also had higher bone-to-implant contact ratios than PEEK alone.
"These results indicated an improved implant fixation in the body, decreasing the chances of loosening of the implant after surgery and the need for revision surgery to remove and replace the implant," Rabiei says. "This improvement is due to increased regenerated bone volume around coated implants compared to uncoated PEEK."
The researchers also did biomechanical testing on the implants, assessing their "toughness," or how well the implant bonded to the surrounding bone.
To test this, the researchers conducted what is called biomechanical push-out testing, in which force is applied to an implant until it is dislodged. These results are measured in terms of work as Newton millimeters (N-mm).
At 18 weeks, it took approximately 299.1 N-mm of work to dislodge implants coated with microwave-treated HA and about 312.5 N-mm to dislodge implants coated with microwave and autoclave-treated HA. This compares to about 183.9 N-mm of work needed to dislodge unmodified PEEK implants.
"It is notable that these results were achieved on completely smooth surfaces of PEEK, while our subsequent studies have indicated that by slightly increasing the surface roughness of PEEK prior to coating, we can accomplish even higher adhesion strength of two-layer HA/YSZ coatings that would require even higher work to dislodge," Rabiei says.
"Whether looking at bone growth or toughness, HA-coated samples outperformed uncoated PEEK implants," Rabiei says. "This treatment will probably increase the cost of an implant marginally, but should help minimize the need for follow-up surgeries - which means HA-treated implants will more than pay for themselves over time."
"And the extent of the cost increase remains unclear," Rabiei adds. "We are not aware of any health risks associated with HA or YSZ - both of which are used in devices already approved by the FDA for long-term implantation. As a result, we may not need additional clinical trials before HA-coated implants can be used in clinical practice. We're investigating that now, and are looking for industry partners to help us commercialize the technique."References
The paper, "Hydroxyapatite coating on PEEK implants: biomechanical and histological study in a rabbit model
," is published online in the journal Materials Science and Engineering C. Lead author of the paper is John Durham, a postdoctoral researcher at NC State. Co-authors are Matthew Allen of Cambridge; and Sergio Montelongo, Joo Ong and Teja Guda of UT-San Antonio. The work was supported by the National Institute of Dental and Craniofacial Research of the National Institutes of Health under award number R21DE022925.Source