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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).
http://www.mddionline.com/article/literature-review-biological-safety-parylene-c
"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):
http://www.pcimag.com/articles/parylene-coatings-and-applications
"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.
Comments
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Huh. I've seen plenty of discussion of replacement hips/knees etc being parylene-coated. More reading to do, it seems. ",)
Thanks!
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the main purpose of parylene is that tissue grows and sticks to it. so it keeps stuff in place. since hip/knee implants are usaly ceramic/stainless steel or other materials that are already bioinert it pretty much only gives the tissue something to stick to. a few holes here and there would do no harm.
as for magnets. holes in the parylene would reveal the toxic magnet itself. we all know the possible consequences.
guess one way would be to get magnets that are coated twice. one with a strudy bio-inert material such as ptfe. and another thin layer with parylene for biocompatiblity.
