SAXS AND WAXS STUDY OF UHMWPE AFTER IRRADIATION

 

H.Synková, M. Šlouf, J. Baldrian, P. Schmidt, A. Marek

 

Institute of Macromolecular Chemistry, Academy of Science of the Czech Republic, Heyrovského náměstí 2, 16206 Praha, Czech Republic; synkova@imc.cas.cz

 

Ultra-high molecular weight polyethylene (UHMWPE) is used in arthroplasty as a part of total joint replacements (TJR) due to its excellent friction properties. Nevertheless, one of the main causes of TJR failures is the wear of UHMWPE, which is believed to induce osteolysis. In recent years, wear resistance of UHMWPE was enhanced by crosslinking with ionizing radiation such as accelerated electrons (b-irradiation) or gamma rays (g-irradiation).

In this study, both b- and g-irradiation were used to crosslink UHMWPE. Samples were irradiated with various doses from 0 to 200kGy. After that the specimens were remelted, i.e. heated above the melting temperature, in order to deactivate free radicals formed during irradiation, whose presence leads to oxidative degradation of material. Several remelting procedures were tested and the results were compared from the point of view of oxidation damage and macroradicals content.

Both irradiation and thermal treatment result in considerable changes in both molecular and supermolecular structure of the polymer, which influences not only its wear resistance, but also other mechanical properties. We followed the structural changes by small- and wide-angle X-ray scattering (SAXS and WAXS). As supplementary methods we used scanning electron microscopy (SEM), infrared spectroscopy (IR), electron paramagnetic resonance (EPR) and solubility tests. Combination of all above mentioned techniques allowed (i) to propose a model of structural changes during irradiation and thermal treatment and (ii) to draw some conclusions concerning optimal thermal treatment of UHMWPE.

 

This work was supported by the Grant Agency of the Czech Republic (grant GACR 106/04/1118) and by the Academy of Sciences of the Czech Republic (project AVOZ4050913).