title: An X-ray fluorescence microscopic analysis of the tissue surrounding the multi-channel cochlear implant electrode array.
abstract: OBJECTIVE
  The aim of this study was to analyse the tissue surrounding the University of Melbourne's (UOMs) multi-channel cochlear implant electrode array and cochlear limited replacements, after long-term implantations. In particular, it aimed to identify the particulate material in the fibrous tissue capsule of the arrays implanted in 1978, 1983, and 1998, by using the Australian Synchrotron for X-ray fluorescence microscopy (XFM) to reveal the characteristic spectrum of metal, in particular platinum. This also helped to determine its format and chemical state. Tissue was retrieved following the recipient's death in 2007.
  
  
  METHODS
  Tissue was fixed and sections taken across the UOM and Cochlear Corporation (CI-22 and CI-24) electrode tracks. These were stained with Masson's trichrome. The Australian Synchrotron enabled XFM to accurately identify platinum from its characteristic fluorescence spectrum.
  
  
  RESULTS
  There was a fibrous tissue capsule (about 100-µm thick) and small regions of calcification around the UOM and CI-22 arrays, but a thinner capsule (40-60-µm thick) around CI-24, and a greater degree of calcification. Dark particulate matter was observed within macrophages and especially in fibrous tissue in proximity to the UOM and CI-22 arrays. This was identified as platinum using X-ray fluorescence. There was also diffusion of platinum into the tissue surrounding the UOM and CI-22 electrodes and fine particles had penetrated the spiral ligament.
  
  
  CONCLUSIONS
  The larger particulate matter in the tissue around the UOM and CI-22 arrays suggested that it had flaked off in the manufacturing of the UOM electrodes. The more diffuse spread of platinum in the tissue around the UOM and CI-22 electrodes was likely due to electrolysis, probably from charge imbalance with the bipolar pulses from the UOM implant. This did not occur with the Cochlear CI-24 device. Furthermore, the widespread fine particles of platinum could have also been due to corrosion, especially from the UOM electrodes.
authors.affiliation: a The Australian Synchrotron , Melbourne , Australia.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Spiers
authors.affiliation: b Department of Anatomy and Neuroscience , University of Melbourne , Australia.
authors.forename: Tina
authors.initials: T
authors.lastname: Cardamone
authors.affiliation: b Department of Anatomy and Neuroscience , University of Melbourne , Australia.|c Florey Institute of Neuroscience and Mental Health , Australia.
authors.forename: John B
authors.initials: JB
authors.lastname: Furness
authors.affiliation: d Department of Anatomical Pathology , Austin Hospital, University of Melbourne , Australia.
authors.forename: Jonathan C M
authors.initials: JC
authors.lastname: Clark
authors.affiliation: e Cochlear Corporation , Sydney , Australia.
authors.forename: James F
authors.initials: JF
authors.lastname: Patrick
authors.affiliation: f Centre for Neural Engineering , University of Melbourne , Australia.
authors.forename: Graeme M
authors.initials: GM
authors.lastname: Clark
mesh_terms: D001315:Australia; D001344:Autopsy; D002114:Calcinosis / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology; D003051:Cochlea / Q000737:chemistry / Q000000981:diagnostic imaging / Q000473:pathology; D003054:Cochlear Implants / Q000009:adverse effects*; D004567:Electrodes, Implanted / Q000009:adverse effects*; D006801:Humans; D008264:Macrophages / Q000737:chemistry / Q000473:pathology; D008856:Microscopy, Fluorescence / Q000379:methods*; D052638:Particulate Matter / Q000032:analysis*; D010984:Platinum / Q000032:analysis*; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology; D013995:Time; D014965:X-Rays
chemical_list: D052638:Particulate Matter; D010984:Platinum
keywords: Cochlear implants; Electrodes; Histopathology; Platinum