title: Confocal Raman spectroscopic analysis of cross-linked ultra-high molecular weight polyethylene for application in artificial hip joints.
abstract: Confocal spectroscopic techniques are applied to selected Raman bands to study the microscopic features of acetabular cups made of ultra-high molecular weight polyethylene (UHMWPE) before and after implantation in vivo. The micrometric lateral resolution of a laser beam focused on the polymeric surface (or subsurface) enables a highly resolved visualization of 2-D conformational population patterns, including crystalline, amorphous, orthorhombic phase fractions, and oxidation index. An optimized confocal probe configuration, aided by a computational deconvolution of the optical probe, allows minimization of the probe size along the in-depth direction and a nondestructive evaluation of microstructural properties along the material subsurface. Computational deconvolution is also attempted, based on an experimental assessment of the probe response function of the polyethylene Raman spectrum, according to a defocusing technique. A statistical set of high-resolution microstructural data are collected on a fully 3-D level on gamma-ray irradiated UHMWPE acetabular cups both as-received from the maker and after retrieval from a human body. Microstructural properties reveal significant gradients along the immediate material subsurface and distinct differences are found due to the loading history in vivo, which cannot be revealed by conventional optical spectroscopy. The applicability of the confocal spectroscopic technique is valid beyond the particular retrieval cases examined in this study, and can be easily extended to evaluate in-vitro tested components or to quality control of new polyethylene brands. Confocal Raman spectroscopy may also contribute to rationalize the complex effects of gamma-ray irradiation on the surface of medical grade UHMWPE for total joint replacement and, ultimately, to predict their actual lifetime in vivo.
authors.affiliation: Kyoto Institute of Technology, Ceramic Physics Laboratory, Research Institute of Nanoscience, Sakyo-ku, Matsugasaki, Kyoto 606-8585, Japan. pezzotti@ipc.kit.ac.jp
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kumakura
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Yamada
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tateiwa
authors.forename: Leonardo
authors.initials: L
authors.lastname: Puppulin
authors.forename: Wenliang
authors.initials: W
authors.lastname: Zhu
authors.forename: Kengo
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry; D006622:Hip Prosthesis; D008422:Materials Testing / Q000379:methods*; D018613:Microscopy, Confocal / Q000379:methods*; D008968:Molecular Conformation; D011095:Polyethylenes / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene