Literature Review: Biological Safety of Parylene C
I was reading a couple of articles about the parylene coating on the magnets (deciding whether to get the bulk magnets and implant 8 of them, or get two of Steve Haworth's silicon-coated magnets), and I found some information which may be interesting to those of you who have already had this done (especially since the fingers are probably a considerably higher-stress application than brain electrodes).
"Schmidt reported stress cracking and pinholing of parylene C after a period of implantation. He implanted 11 parylene Ccoated microelectrodes in the dural matter of 6 monkeys in order to monitor neural responses, and found that the impedance of 8 of the 11 electrodes fell drastically within a few months of implantation.8 Explantation and scanning electron microscopy revealed longitudinal stress cracking in the parylene C coating of some of the electrodes. Others exhibited surface craters (pinholing). The remaining 3 electrodes were still operational upon explantation after 3 years."
Also (admittedly, this is from a journal of paints/coatings rather than a medical journal):
"Deposition of a thin layer of parylene over a cytotoxic surface can render it traumatic to cells." <-- I think this one is likely a misprint, though -- I seriously doubt that coating something toxic with something nontoxic would make the resulting product more toxic.