Characterization of irradiated blends of alpha-tocopherol and UHMWPE

Biomaterials. 2005 Nov;26(33):6657-63. doi: 10.1016/j.biomaterials.2005.04.026.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aging
  • Antioxidants / chemistry
  • Antioxidants / pharmacology
  • Arthroplasty, Replacement, Hip
  • Biocompatible Materials / chemistry*
  • Calorimetry, Differential Scanning
  • Cell Adhesion
  • Cross-Linking Reagents / pharmacology
  • Free Radicals
  • Gamma Rays
  • Lipids / chemistry
  • Materials Testing
  • Models, Chemical
  • Oxygen / chemistry
  • Oxygen / metabolism
  • Polyethylenes / chemistry*
  • Stress, Mechanical
  • Surface Properties
  • Temperature
  • Tensile Strength
  • Time Factors
  • alpha-Tocopherol / chemistry*

Substances

  • Antioxidants
  • Biocompatible Materials
  • Cross-Linking Reagents
  • Free Radicals
  • Lipids
  • Polyethylenes
  • ultra-high molecular weight polyethylene
  • alpha-Tocopherol
  • Oxygen