Abstract
Recently, highly crosslinked polyethylenes have emerged as an alternative bearing surface with tremendous potential for clinical success. However, the term highly cross-linked polyethylene refers to a great many materials, each manufactured under drastically different processing parameters, such as type of irradiation, dose, and warm versus cold state. It has been widely shown in laboratory hip simulator testing, that the wear resistance of UHMWPE improves significantly with increasing cross-link density, but the measurement of this parameter is somewhat controversial. While both swell testing of the polyethylene (direct) and trans-vinylene content (indirect) both yield information regarding the actual degree to which the material is crosslinked, no study to date has examined the exact relationship between these two tests. In evaluating the clinical performance of highly crosslinked polyethylenes, it is crucial that they be characterized according to the specific parameters by which they were manufactured. onship. Micro-Fourier Transform Infrared Spectroscopy (FTIR) and swelling measurements were performed on samples irradiated by either electron beam or gamma sources at varying doses, in both the cold and warm state. The trans-vinylene content was obtained from the ratio of the peaks at 965 cm-1 and 2022 cm-1, while the crosslink density was computed from Flory network theory.
The information for crosslink density was plotted versus trans-vinylene content to obtain the precise relationship between these two highly sensitive tests. This information can be used to aid in the clinical evaluation of commercially available highly crosslinked polyethylenes, and to improve our understanding of the very complex relationship between wear and the physical and chemical properties of UHMWPE.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
