title: Strain-induced microstructural rearrangement in ultra-high molecular weight polyethylene for hip joints: A comparison between conventional and vitamin E-infused highly-crosslinked liners.
abstract: Infusion of vitamin E (α-tocopherol) in highly crosslinked ultra-high molecular weight polyethylene (UHMWPE) liners has been conceived to achieve superior oxidation stability while preserving enhanced mechanical properties as compared to post-irradiation remelted liners. However, the presence of an antioxidant in the material microstructure brings an issue of concern in whether a "foreign substance" might reduce radiation crosslinking efficiency and/or change microstructural characteristics by diffusing into UHMWPE. The key to clarify this fundamental issue resides in performing a quantitative evaluation of the obtained material structure and its polymeric chain mobility on the molecular scale. In this paper, a Raman spectroscopic examination is presented of molecular orientation and phase fractions in as-processed vitamin E-infused UHMWPE acetabular liners in comparison with a model (undoped and unirradiated/uncrosslinked) and a conventional (undoped and 33kGy-sterilized by gamma-irradiation) UHMWPE liners. The microstructural responses of structurally different liners to externally applied compressive strain were also monitored. The main results of the spectroscopic analyses can be summarized as follows: (i) preliminary gamma irradiation reduced the fraction of amorphous phase and increased the degree of molecular alignment, the vitamin E-infused liner preserving the crystallinity level achieved by the 100-kGy irradiation injected before infusion; (ii) the presence of vitamin E significantly promoted orientational randomness, which increased with increasing compressive strain magnitude, a phenomenon beneficial to minimize strain-softening-assisted wear phenomena.
authors: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, 160-0023 Tokyo, Japan.
authors: Yasuhito
authors: Y
authors: Takahashi
authors: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, 160-0023 Tokyo, Japan.
authors: Kengo
authors: K
authors: Yamamoto
authors: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, 160-0023 Tokyo, Japan.
authors: Takaaki
authors: T
authors: Shishido
authors: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, 160-0023 Tokyo, Japan.
authors: Toshinori
authors: T
authors: Masaoka
authors: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, 160-0023 Tokyo, Japan.
authors: Toshiyuki
authors: T
authors: Tateiwa
authors: Ceramic Physics Laboratory and Research Institute for Nanoscience, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan.
authors: Leonardo
authors: L
authors: Puppulin
authors: Ceramic Physics Laboratory and Research Institute for Nanoscience, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan. Electronic address: pezzotti@kit.ac.jp.
authors: Giuseppe
authors: G
authors: Pezzotti
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D019245:Compressive Strength; D003432:Cross-Linking Reagents / Q000737:chemistry*; D004058:Diffusion; D055119:Elastic Modulus; D019544:Equipment Failure Analysis; D006622:Hip Prosthesis; D008422:Materials Testing; D008968:Molecular Conformation; D011095:Polyethylenes / Q000737:chemistry*; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013718:Tensile Strength; D014810:Vitamin E / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D014810:Vitamin E
keywords: Microstructure; Raman spectroscopy; Strain; UHMWPE; Vitamin E