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Hypothesis: Silicone as part of a cochlear implant electrode may be responsible for a foreign body response in the human. Background: Clinical evidence of a foreign body response to a cochlear implant has been reported. In a previous study, particulate material found within the fibrous sheath and within macrophages surrounding a cochlear implant has been identified as being consistent with platinum. However, to date, there has been no histologic evidence of a role for silicone in this cellular immune response. Methods: A total of 44 temporal bone specimens from 36 patients were reviewed by light microscopy for evidence of presumed platinum and/or silicone foreign bodies in an extracellular or intracellular location. Identification of cell type involved in phagocytosis of foreign body material was accomplished using CD163 immunostaining. The identity and source of the foreign body material was confirmed using energy-dispersive X-ray spectroscopy and scanning electron microscopy. Results: Evidence for both platinum and silicone was found in all 44 specimens. In three patients, anti-CD 163 immunostaining demonstrated phagocytized platinum and silicone foreign bodies. In five specimens, energy-dispersive X-ray spectroscopy demonstrated that the birefringent foreign bodies were consistent with silicone. Scanning electron microscopy of two electrodes removed from temporal bones demonstrated small cracks, fragmentation, and small circular defects in the silicone carrier. Conclusion: Histologic evidence of a foreign body response to the presence of platinum and silicone in a cochlear implant has been demonstrated and may be responsible for some reported delayed failures or extrusion.

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Corrugated stainless steel tubing (CSST) has been used for more than 20 years as a replacement for conventional black iron gas piping. CSST has a thinner tubing wall and is susceptible to damage from lightning activity when discharges enter a structure, potentially resulting in perforation of the CSST wall and fire ignition. Grounding has been promoted by CSST manufacturers as a solution to this problem. We use modeling and simulation of voltage potentials and arc currents to evaluate the effects of grounding on the voltage potential across CSST, which can result in arc initiation, and charge through the arc, which can result in melting and perforation of the CSST wall. Our results show multiple scenarios where a 10 kA 10 9 350 s current waveform with 1 X grounding of the CSST still results in voltages greater than the arc initiation threshold of 25 kV and charge through the arc greater than 1.2 C, the perforation threshold we measured. For the case where lightning enters the structure through an outdoor light fixture or chimney, the presence of a grounding wire increases the charge through the arc from 0.13 C to 2.22 C. These results indicate that good grounding of CSST will not necessarily prevent arc initiation nor perforation of the CSST wall by lightning. Good grounding may in fact exacerbate the problem of lightning damage to CSST depending on where lightning enters the building and the electrical parameters of the path to ground.

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