Wear measurement of highly cross-linked UHMWPE using a super(7)Be tracer implantation technique

• Published in: Journal of biomedical materials research. Part B, Applied biomaterials Vol. 101B; no. 3; pp. 423 - 429
• Main Authors: Wimmer, Markus A, Laurent, Michel P, Dwiwedi, Yasha, Gallardo, Luis A, Chipps, Kelly A, Blackmon, Jeffery C, Kozub, Raymond L, Bardayan, Daniel W, Gross, Carl J, Stracener, Daniel W, Smith, Michael S, Nesaraja, Caroline D, Erikson, Luke, Patel, Nidhi, Rehm, Karl E, Ahmad, Irshad, Greene, John P, Greife, Uwe
• Format: Journal Article
• Language: English
• Published: 01.04.2013
• Subjects: Crosslinking; Implantation; Nuclei; Polyethylenes; Radioactive tracers; Surgical implants; Tracers; Wear; Wear rate
• ISSN: 1552-4973; 1552-4981
• DOI: 10.1002/jbm.b.32868

The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are therefore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 ( super(7)Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression-molded GUR 1050, were activated with 10 super(9) to 10 super(10) super(7)Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 mu m below the surface. The pins were tested for wear in a six-station pin-on-flat apparatus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and estimated to be 17 plus or minus 3 mu g per million cycles. The conventional-to-cross-linked ratio of the wear rates was 13.1 plus or minus 0.8, in the expected range for these materials. Oxidative degradation damage from implantation was negligible; however, a weak dependence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert. copyright 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 101B: 423-429, 2013.