May 1 2007
Invibio®, a leading provider of biomaterial solutions to the medical device market, today presented findings from research investigating wear rates of its PEEK-OPTIMA® polymer and carbon fiber-reinforced (CFR) PEEK-OPTIMA compound in self-mating wear couples.
The research, presented today in a poster session at the Spine Arthroplasty Society's 7th Annual Global Symposium on Motion Preservation Technology, indicates that self-mating PEEK-OPTIMA-based spinal arthroplasty devices may possess lower wear rates compared to those implants developed using conventional UHMWPE-on-metal material combinations.
"Our screening results indicate that PEEK-OPTIMA polymer offers a low-wear solution, which could be even further reduced by the inclusion of carbon fibers," said Dr. John Devine, senior product development scientist, Invibio. "These observations have been verified by the recent wear results for a PEEK-OPTIMA-based nucleus replacement device, which demonstrated wear rates within the range of metal-on-metal and metal-on-polymer cervical and lumbar total disc replacements."
By using materials with low wear rates, medical device manufacturers can prolong implant life and reduce the need for revision surgery. In addition to possessing lower wear rates, all-polymer self-mating disc arthroplasty devices offer greater radiolucency for imaging system compatibility and eliminate metal ion exposure. Furthermore, all-polymer couples offer a wider degree of design and manufacturing flexibility, such as the ability to reduce device height in a two component cervical artificial disk prostheses.
Materials and Methods
Different material combinations were tested on a four-station device that applied both reciprocation and rotational motion. Samples of PEEK-OPTIMA and CFR PEEK-OPTIMA (PAN based fibers) were tested in a self-mating multi-directional wear testing rig. A 40N load was applied to each station, which resulted in a contact stress of approximately 2MPa. The lubricant used was 24.5% bovine serum (protein content: 15 gl(-1)), which was heated to 37°C. The wear was assessed gravimetrically and each test completed 2 million cycles.
Results
The self-mating wear couple of CFR PEEK-OPTIMA materials produced significantly lower wear factors (0.34 x 10(-6) mm(3)N(-1)m(-1)) than those of UHMWPE-on-metal wear couples (1.1 x 10(-6) mm(3)N(-1)m(-1)). It was also observed that in general the surface of the machined polymeric pin becomes smoother (Sa ≈ 0.1µm) and more negatively skewed during the test, without a significant breaking in period.
Unfilled PEEK-OPTIMA has also shown low wear rates. Recently, a nucleus replacement device composed of unfilled PEEK-OPTIMA was tested under conditions incorporating a cross shear motion profile using modified ISO/DIS 18192 parameters These implants demonstrated a constant average wear rate of 0.45±0.01 mg/million cycles over 10 million cycles, indicating that self-mating PEEK-OPTIMA is relatively insensitive to changes in motion profiles(1).
References
1. A Wear Assessment of NUBAC Under a Cross Shear Motion Profile. T. Brown, Q Bao, T Kilpela, 7th Annual Meeting of Global Symposium on Motion Preservation Technology, Berlin, Germany, 2007.