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Kyoto, Japan

Leto A.,Piezotech Japan Ltd. | Pezzotti G.,Kyoto Institute of Technology
Physica Status Solidi (A) Applications and Materials Science | Year: 2011

The mechanical properties and the functional behavior of inorganic dielectric materials strongly depend on the stoichiometry imbalance in the material and its structural accommodation. Point defect populations are responsible for departures from the normal stoichiometric formula and clear correlations have been documented between the magnitude of the dielectric constant of a compound and the structural mode by which it accommodates its non-stoichiometry. In this study, we systematically apply the cathodoluminescence (CL) method to local stoichiometry characterizations of advanced silica and barium titanate compounds as paradigm inorganic dielectric materials with amorphous and nanocrystalline structure, respectively. The CL spectral emission is shown here capable not only to clarify the off-stoichiometric characteristics of dielectric devices, but also to provide a useful probe for assessing the local stress state at the interfaces between the dielectric and the conductor materials. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Leto A.,Piezotech Japan Ltd. | Zhu W.,Osaka University | Matsubara M.,Nissan Tamagawa Hospital. | Pezzotti G.,Kyoto Institute of Technology
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

Raman and cathodoluminescence spectroscopic methods were employed for clarifying important stoichiometric and mechanical properties so far missing in the specification of the physical origin of the structural behavior of Oxinium™ femoral head components. Spectroscopy proved helpful in rationalizing the actual physical and chemical reasons behind the mechanical integrity of the ceramic-film/metal-substrate interface, which is responsible for both the good adherence and the surface durability reported in prosthetic applications of Oxinium™ components. Raman spectroscopy coupled with the crack opening displacement (COD) method was used to evaluate the intrinsic fracture toughness of the surface oxide film. In addition, cathodoluminescence spectroscopy provided new evidences on both the oxygen vacancy gradient developed during the metal-oxidation manufacturing process and the bioinertness of Oxinium™ femoral components. © 2013 Elsevier Ltd.

Puppulin L.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Hasegawa M.,Mie University | Pezzotti G.,Kyoto Institute of Technology
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

The impact of adding antioxidant vitamin-E (α-tocopherol) to the microstructure of ultrahigh molecular weight polyethylene (UHMWPE) for total knee arthroplasty has been studied in detail by means of Raman microprobe spectroscopy. Three tibial insert samples prepared by different manufacturing methods were investigated, as follows: (A) a sample manufactured without blending with vitamin E which did not receive any irradiation dose after consolidation but underwent final sterilization in ethylene oxide (EtO); (B) a sample blended with 0.3. wt% of α-tocopherol, an isomer of vitamin E, and manufactured as sample (A); and, (C) a sample in which vitamin E was diffused after being irradiated with 100. kGy dose of γ-ray. Clear microstructural differences were observed in terms of phase contents (i.e., amorphous, crystalline, and intermediate phase fraction), molecular orientation, and the degree of anisotropy between the investigated tibial plates. Vitamin E in the starting resin promoted chain mobility leading to reorganization of the molecular chains. The spectroscopic characterizations helps to rationalize the complex effect of vitamin-E on the UHMWPE microstructure and gives useful information on how significantly any single step of the manufacturing procedures might affect the mechanical properties of the final orthopedic component. © 2014 Elsevier Ltd.

Fukatsu K.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Zhu W.,Osaka University | Sugano N.,Osaka University | And 2 more authors.
Acta Biomaterialia | Year: 2012

The low-temperature polymorphic transformation behavior of two types of commercially available femoral head, both made of 3 mol.% Y 2O 3-stabilized tetragonal ZrO 2 polycrystals (3Y-TZP), was examined by in vitro experiments. Both materials contained a small amount (0.25 wt.%) of Al 2O 3, but they differed slightly in their SiO 2 impurity content, in the morphology and crystallinity of the dispersed Al 2O 3 phase, and in grain size. In vitro experiments were conducted in a water-vapor environment at temperatures in the range 90-134 °C and for periods of time up to 500 h. Despite the materials having the same nominal composition, quite different behaviors were found in the hydrothermal environment for the two types of femoral head investigated. A phenomenological description of the kinetics of monoclinic nuclei formation/growth led to the experimental determination of activation energy values for the environmentally driven polymorphic transformation. From the material physics viewpoint, cathodoluminescence spectroscopy enabled us to rationalize the role of surface stoichiometry on the mechanisms leading to polymorphic transformation. Spectroscopic experiments unveiled some new relevant aspects of surface off-stoichiometry, which lie behind the different phase transformation kinetics experienced by the investigated femoral heads. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Puppulin L.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Wenliang Z.,Osaka University | Sugano N.,Osaka University | And 2 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

The literature on tribological assessments of artificial hip joints usually focuses on correlations between joint composition, size, and specific wear rates, but conspicuously ignores the physical aspects behind the occurrence of degradation mechanisms of friction and wear. Surface degradation in artificial joints occurs because of increases in temperature and local exacerbation of contact stresses inside the moving contact as a consequence of physical and chemical modifications of the sliding surfaces. This article reports about the development of a new pin-on-ball spectroscopy-assisted tribometer device that enables investigating also physical rather than merely engineering aspects of wear processes using in situ Raman and fluorescence techniques. This innovative tribometer is designed to bring about, in addition to conventional tribological parameters, also information of temperature, stress and phase transformations in the femoral heads as received from the manufacturer. Raman and fluorescence spectra at the point of sliding contact are recorded durilng reciprocating hard-on-hard dry-sliding tests. Preliminary results were collected on two different commercially available ceramic-on-ceramic hip joint bearing couples, made of monolithic alumina and alumina-zirconia composites. Although the composite couple showed direct evidence of tetragonal-to-monoclinic phase transformation, which enhanced the coefficient of friction, the specific wear rate was significantly lower than that of the monolithic one (i.e., by a factor 2.63 and 4.48 on the pin and head side, respectively). In situ collected data compared to ex situ analyses elucidated the surface degradation processes and clarified the origin for the higher wear resistance of the composite as compared to the monolithic couple. © 2013 Elsevier Ltd.

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