The knee-specific formula of the tibial inserts and patella components are blended with vitamin E and moderately cross-linked toreduce oxidation and reduce long-term wear.
Re-Melting Not Required
In the case of most highly cross-linked polyethylenes, an anneal or re-melt step occurs following cross-linking to link free radicals (created by the irradiation). Annealing or re-melting polyethylene can reduce mechanical strength properties.
Because vitamin E neutralizes the negative effects of free radicals,2 an anneal or re-melt step is rendered unnecessary. In a material yield strength test, compression molded samples and e+ samples performed statistically the same, while a highly cross-linked re- melted sample exhibited a 12% drop in yield strength.
Maximum Mechanical Strength
The impact of oxygen exposure to e+ samples was evaluated in accelerated aging tests. Un-aged and aged e+ samples yielded the same results during yield strength testing.
Impact testing for the aged e+ sample actually revealed slightly better results than the un-aged sample1, indicating that oxygen has no negative impact on e+.