Abstract
Introduction Contemporary highly crosslinked polyethylenes fall into two classes (annealed or remelted). Annealed polyethylenes contain free radicals. Remelted polyethylenes have reduced mechanical properties but no free radicals. SXL provides the advantages of both classes.
Materials and Methods GUR 1020 polyethylene was sequentially crosslinked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (SXL).
The following were measured: free radical concentration (electron spin resonance), oxidation resistance (5 atmospheres of oxygen at 70 degrees C for 14 days), and tensile properties (ASTM D638). Hip simulator wear was determined (MTS machine, 5 million cycles, 1 Hz, Paul load curve with maximum load of 2450 N, alpha fraction bovine calf serum)
Results Free radical concentrations were 14 x 1014 and 1550 x 1014 spins/g for SXL and GUR 1020 irradiated to 3 Mrad in nitrogen (gamma-N2) respectively. Maximum oxidation index was 0.09 for SXL, 0.09 for unirradiated UHMWPE, and 1.27 for gamma-N2.
SXL tensile properties exceeded ASTM F648 and were unchanged by oxidative challenge.
Wear rates were 1.35 and 46 mm3 per million cycles for SXL and gamma-N2 respectively; wear particle sizes were similar.
Discussion and Conclusions Sequential irradiation and annealing provides more complete crosslinking with reduction in free radical level. SXL has the same resistance to oxidative challenge as unirradiated polyethylene. Mechanical properties exceed the ASTM F648 values. Wear is reduced by 97% compared to that of gamma-N2. SXL is the basis for next generation highly crosslinked UHMWPE.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
