An X-ray fluorescence microscopic analysis of the tissue surrounding the multi-channel cochlear implant electrode...

Area of Science:

• Biomaterials science
• Medical device analysis
• Histopathology

Background:

• Long-term implantation of cochlear devices can lead to tissue reactions.
• Understanding the material composition and degradation of implanted electrodes is crucial for device longevity and patient outcomes.

Purpose of the Study:

• To analyze the tissue surrounding University of Melbourne (UOM) and Cochlear Corporation (CI) multi-channel cochlear implant electrode arrays after long-term implantation.
• To identify and characterize particulate material, specifically platinum, within the fibrous tissue capsule using X-ray fluorescence microscopy (XFM).

Main Methods:

• Tissue samples from deceased recipients with UOM, CI-22, and CI-24 implants were analyzed.
• Histological staining (Masson's trichrome) was performed on tissue sections.
• X-ray fluorescence microscopy (XFM) at the Australian Synchrotron was used to identify platinum and determine its chemical state.

Main Results:

• Fibrous tissue capsules of varying thickness and calcification were observed around the implants.
• Dark particulate matter, identified as platinum, was found within macrophages and fibrous tissue near UOM and CI-22 arrays.
• Platinum diffusion into surrounding tissue and the spiral ligament was observed with UOM and CI-22 implants, but not CI-24.

Conclusions:

• Larger platinum particles suggest flaking during UOM electrode manufacturing.
• Diffuse platinum spread around UOM/CI-22 electrodes is likely due to electrolysis from charge imbalance.
• Widespread fine platinum particles may result from corrosion, particularly from UOM electrodes.