Characterization of irradiated blends of alpha-tocopherol and UHMWPE.
Adhesive/abrasive wear in ultra-high molecular weight polyethylene (UHMWPE) has been minimized by radiation cross-linking. Irradiation is followed by melting to eliminate residual free radicals and avoid long-term oxidative embrittlement. However, post-irradiation melting reduces the crystallinity of the polymer and hence its strength and fatigue resistance. We proposed an alternative to post-irradiation melting to be the incorporation of the antioxidant alpha-tocopherol into UHMWPE prior to consolidation. alpha-Tocopherol is known to react with oxygen and oxidized lipids, stabilizing them against further oxidative degradation reactions. We blended GUR 1050 UHMWPE resin powder with alpha-tocopherol at 0.1 and 0.3 wt% and consolidated these blends. Then we gamma-irradiated these blends to 100-kGy. We characterized the effect of alpha-tocopherol on the cross-linking efficiency, oxidative stability, wear behavior and mechanical properties of the blends. (I) The cross-link density of virgin, 0.1 and 0.3 wt% alpha-tocopherol blended, 100-kGy irradiated UHMWPEs were 175+/-19, 146+/-4 and 93+/-4 mol/m3, respectively. (II) Maximum oxidation indices for 100-kGy irradiated UHMWPE previously blended with 0, 0.1 and 0.3 wt% alpha-tocopherol that were subjected to accelerated aging at 80 degrees C in air for 5 weeks were 3.32, 0.09, and 0.05, respectively. (III) The pin-on-disc wear rates of 100-kGy irradiated UHMWPE previously blended with 0.1 and 0.3 wt% alpha-tocopherol that were subjected to accelerated aging at 80 degrees C in air for 5 weeks were 2.10+/-0.17 and 5.01+/-0.76 mg/million cycles, respectively. (IV) Both accelerated aged, alpha-tocopherol-blended 100-kGy irradiated UHMWPEs showed higher ultimate tensile strength, higher yield strength, and lower elastic modulus when compared to 100-kGy irradiated, virgin UHMWPE. These results showed that alpha-tocopherol-blended 100-kGy irradiated UHMWPEs were not cross-linked to the same extent as the 100-kGy irradiated, virgin UHMWPE.
Department of Orthopaedic Surgery, Massachusetts General Hospital, 55 Fruit Street, GRJ 1206, Boston, MA 02114, USA.
Ebru
E
Oral
Evan S
ES
Greenbaum
Arnaz S
AS
Malhi
William H
WH
Harris
Orhun K
OK
Muratoglu
D000375:Aging; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology; D019644:Arthroplasty, Replacement, Hip; D001672:Biocompatible Materials / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002448:Cell Adhesion; D003432:Cross-Linking Reagents / Q000494:pharmacology; D005609:Free Radicals; D005720:Gamma Rays; D008055:Lipids / Q000737:chemistry; D008422:Materials Testing; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011095:Polyethylenes / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D024502:alpha-Tocopherol / Q000737:chemistry*
D000975:Antioxidants; D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D005609:Free Radicals; D008055:Lipids; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D024502:alpha-Tocopherol; D010100:Oxygen