title: Reconciling in vivo and in vitro kinetics of the polymorphic transformation in zirconia-toughened alumina for hip joints: II. Theory.
abstract: In this paper, an updated analytical model for the kinetics of the tetragonal to monoclinic (t→m) polymorphic transformation in ZTA composites for hip joints is proposed and discussed. The model builds upon the so-called Mehl-Avrami-Johnson (MAJ) description of transformation kinetics, which combines two overlapping processes: nucleation of monoclinic sites, and their successive growth. Dependencies on two specific factors are introduced in the model, namely the initial fraction of monoclinic polymorph as received from the manufacturer, and the presence of different types of transition-metal stains (e.g., Ti, CoCr, and Fe) on the ZTA surface. These two factors were studied because clear indications of their potential roles on the environmental stability of implantable ZTA components were found in previous phenomenological analyses of retrievals. Nucleation and growth of monoclinic domains are two key processes whose interplay decides the actual kinetics of the overall transformation process according to two main parameters: an apparent activation energy value function of time and temperature, and a nuclei growth exponent. These parameters were clearly altered by the presence of transition metal contamination, whose effect was incorporated into the model to explain exacerbations of surface degradation. In accordance with a general analytical description of transformation kinetics for isothermal or isochronal evolutions in terms of time and temperature, the modified model of the MAJ description assesses the effect of the initial monoclinic fraction. The updated model has been validated using systematic in vitro experiments, and appears to partly reconcile in vitro and in vivo data of t→m transformation discrepancies in ZTA hip components.
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan. Electronic address: pezzotti@kit.ac.jp.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
authors.affiliation: Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0854, Japan.
authors.forename: Wenliang
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan.
authors.forename: Matteo
authors.initials: M
authors.lastname: Zanocco
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan.
authors.forename: Elia
authors.initials: E
authors.lastname: Marin
authors.affiliation: Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0854, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sugano
authors.affiliation: Amedica Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States.
authors.forename: Bryan J
authors.initials: BJ
authors.lastname: McEntire
authors.affiliation: Amedica Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States; Department of Orthopaedic Surgery, University of Missouri, Columbia, MO 65212, United States.
authors.forename: B Sonny
authors.initials: BS
authors.lastname: Bal
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D006622:Hip Prosthesis; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008956:Models, Chemical; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide
keywords: Activation energy; Hydrothermal treatment; Initial monoclinic volume fraction; Metal stain; Polymorphic transformation; Zirconia-toughened alumina