We ended up using India ink, which (according to the encyclopedia of ink* ) is mainly soot.
We were able to isolate it in the HPLC and through some histopath experiments show that it didn’t have any negative local effect between (IIRC) seven and 60 days. Why those times? Protocol was to tattoo on day 0, wait a week for the site to recover, then inject our experimental material on day 7, sacrificing subject animals at D14 (one week), 21, 28, 35, 42, 49, and 56 days.
I don’t think lamp black is really a good idea, but was adequate for our purposes. We didn’t have to do any kind of long term study, just demonstrate that it would not interfere with our work in guinea pigs.
* I actually went to a specialist art store and the owner did indeed go to the back of the store and pull out one of the volumes of a multi-volume work on inks and pigments! I don’t know if it was actually named “The Encyclopedia of Ink”, though I do remember that that’s how he referred to it. He just photocopied the relevant page for me, most of which was the entry for India ink.
But soot is carcinogenic, no? And with soot consisting of nanoparticles small enough to cross the blood-brain barrier, I can imagine a chance of soot-based tattoo substances diffusing into the brain.
We were able to isolate it in the HPLC and through some histopath experiments show that it didn’t have any negative local effect between (IIRC) seven and 60 days. Why those times? Protocol was to tattoo on day 0, wait a week for the site to recover, then inject our experimental material on day 7, sacrificing subject animals at D14 (one week), 21, 28, 35, 42, 49, and 56 days.
I don’t think lamp black is really a good idea, but was adequate for our purposes. We didn’t have to do any kind of long term study, just demonstrate that it would not interfere with our work in guinea pigs.
* I actually went to a specialist art store and the owner did indeed go to the back of the store and pull out one of the volumes of a multi-volume work on inks and pigments! I don’t know if it was actually named “The Encyclopedia of Ink”, though I do remember that that’s how he referred to it. He just photocopied the relevant page for me, most of which was the entry for India ink.