Product Overview
Renovis E-MAX Highly Crosslinked Polyethylene (XLPE) for knee bearings builds on the successes of first generation XLPE by incorporating two innovative technologies:
Vitamin E and mechanical annealing.
• Vitamin E is added to hinder in vivo oxidation, which can cause degradation of the polymer material.
• Mechanically annealing—as opposed to melting—helps maintain mechanical properties.
Thus, Renovis E-MAX Highly Crosslinked Polyethylene provides excellent wear properties, like first generation XLPE, plus oxidative stability and the improved mechanical properties needed in knee applications.
Renovis E-MAX underwent extensive laboratory evaluations, including wear simulator testing.
Excellent Wear Properties
The crosslinking density of Renovis E-MAX for knee was fine-tuned to be about the same as 7 Mrad XLPE and has demonstrated very low wear in hip simulator testing: 74% less wear than conventional polyethylene.
Oxidative Stability under Harsh Testing Conditions
The mechanical anneal eliminates free radicals to near the detection threshold of testing equipment (ESR). After accelerated aging the Renovis E-MAX showed minimal change in free radical content, indicating that the Vitamin E stabilized the free radicals, preventing them from reacting with oxygen. To further test oxidation resistance under extreme conditions, samples were exhaustively extracted to remove as much Vitamin E as possible, and then subjected to accelerated aging. Even under extreme conditions, no positive oxidation index was measured in Renovis E-MAX.
Evenly Distributed Vitamin E
Chemical analysis demonstrated that the Vitamin E is profile is constant throughout Renovis E-MAX, indicating that it is evenly distributed throughout the material. This is because vitamin E is blended with UHMWPE powder before creating the UHMWPE barstock. In contrast, materials into which the vitamin E is diffused after UHMWPE consolidation (e.g. Biomet E1), result in more concentrated levels of vitamin E near the surface.
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