title: Vitamin-E blended and infused highly cross-linked polyethylene for total hip arthroplasty: a comparison of three-dimensional crystalline morphology and strain recovery behavior.
abstract: Vitamin-E (α-tocopherol) is now recognized worldwide as one of the most promising antioxidant agents for highly cross-linked polyethylene (HXLPE) used in total joint replacements. In the contemporary manufacturing processes, two alternative methods are currently accepted to incorporate this antioxidant into polyethylene microstructure: (i) blending vitamin-E before consolidation and radiation crosslinking; (ii) infusing vitamin-E via a homogenizing heat treatment after radiation crosslinking. However, the effects of these technological differences on crystalline morphology and mechanical behavior of polyethylene remains to be fully elucidated. The aim of this paper is to quantitatively evaluate the microstructural differences of commercially available vitamin-E blended and infused HXLPE liner (referred to as Liner BL and IF, respectively). For this purpose, confocal/polarized Raman spectroscopy was used to systematically examine the three-phase percentages (amorphous (αa), crystalline (αc), and intermediate third phase (αt)), preferential molecular orientation (θp), and degree of crystalline anisotropy (〈P2(cosβ)〉). Additionally, we compared the time-dependent deformation of Liner BL and IF as obtained by uniaxial stress relaxation tests followed by strain recovery. Distinctive features of the near-surface αc, θp, and〈P2(cosβ)〉 were clearly observed within the first 35μm in the two studied liners. Despite the equivalent level of the bulk αc and 〈P2(cosβ)〉, higher restoring force against a uniaxial strain was observed in Liner IF, which reflects a higher crosslink density in its amorphous phase. On the other hands, a higher degree of surface orientational randomness was detected in Liner BL, which is structurally more beneficial for minimizing the in-vivo occurrence of strain-softening-assisted wear.
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan; Department of Bone and Joint Biomaterial Research, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Masaoka
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Kengo
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Shishido
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tateiwa
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Kubo
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, Kyoto 606-8585, Japan. Electronic address: pezzotti@kit.ac.jp.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
mesh_terms: D000975:Antioxidants / Q000008:administration & dosage; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D003432:Cross-Linking Reagents / Q000737:chemistry; D004343:Drug Implants / Q000138:chemical synthesis*; D055119:Elastic Modulus; D006622:Hip Prosthesis; D008422:Materials Testing; D008968:Molecular Conformation; D011095:Polyethylenes / Q000737:chemistry*; D013314:Stress, Mechanical; D013718:Tensile Strength; D014783:Viscosity; D014810:Vitamin E / Q000008:administration & dosage* / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D004343:Drug Implants; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D014810:Vitamin E
keywords: Microstructure; Polyethylene; Raman spectroscopy; Strain; Vitamin-E