4 ms·

It's sad because PTFE is the best dry lubricant but you can get close with Tungsten Disulfide nanoparticles. Hexagonal boron nitride is a good bicycle lubricant

It's sad because PTFE is the best dry lubricant but you can get close with Tungsten Disulfide nanoparticles. Hexagonal boron nitride is a good bicycle lubricant additive too and it can actually photocatalytically degrade environmental PFAS! https://ceramics.org/ceramic-tech-today/ceramic-video/video-boron-nitride-destroys-pfoa-genx https://ceramics.org/ceramic-tech-today/ceramic-video/video-...

kragen 4y ago
Tungsten disulfide is enormously more toxic than PTFE. Nanoparticles of anything are usually toxic. Boron nitride might be as nontoxic as PTFE but I wouldn't bet on it.
- orangepurple 4y ago
  I have not seen any evidence showing tungsten disulfide is toxic for either people or the environment in general
  - kragen 4y ago
    Its toxicity isn't well characterized, and isn't especially high, but you can generally assume that metal sulfides with access to water produce either hydrogen sulfide, sulfuric acid, or both. In the case of tungsten disulfide it seems to be sulfuric acid, though the reaction is poorly characterized. Sulfate as such is pretty nontoxic (though it does cause diarrhea) but it doesn't take very much sulfuric acid to lower the pH to fatal levels.
- ncmncm 4y ago
  I think you might be giving PTFE a stronger pass than it merits.
  - kragen 4y ago
    That's always possible, but why do you think so? The list of materials considered biocompatible enough for implants is pretty short, and PTFE is on that list.
    - DoingIsLearning 4y ago
      > The list of materials considered biocompatible enough for implants is pretty short, and PTFE is on that list. Not to stray from the main discussion but biocompatible has a pretty narrow scope. Time effects are not always fully captured, it often boils down to quite literally "we injected this stuff in 50x bunnies' bloodstream or implanted under their derme and none of them died after a month". With any new substance a cautionary principle should be applied, the main issue is Industry is spitting out new substances faster than we can meaningfully study them.
      - kragen 4y ago
        It would be possible for your comment to be farther from the truth, but it would take significant effort. It is incorrect to a degree that demonstrates malicious disregard for the truth, and since it pertains to health risks, people who were to rely on it would be putting their health at risk. You should not have posted it. https://www.fda.gov/medical-devices/biocompatibility-assessment-resource-center/biocompatibility-evaluation-endpoints-contact-duration-periods#permanent-implant https://www.fda.gov/medical-devices/biocompatibility-assessm... https://www.fda.gov/medical-devices/science-and-research-medical-devices/medical-device-material-safety-summaries https://www.fda.gov/medical-devices/science-and-research-med... https://www.fda.gov/media/158495/download https://www.fda.gov/media/158495/download
        DoingIsLearning 4y ago
        I am not sure what was so out of line about my comment. The safety profile you link to itself refers to animal studies. That profile now looks very complete but before we had all those RCTs and clinical surveilance data, someone had to make a decision on wheather or not we can use PTFE in vascular stents _for_humans_. That decision would have relied on initial animal tests (i.e.literally sticking this stuff in bunnies) and some limited trial data. My point is not that FDA are somehow clueless bureaucrats but that everytime we introduce a new substances we are taking an educated risk based on limited (animal) data.

kragen 4y ago

Tungsten disulfide is enormously more toxic than PTFE. Nanoparticles of anything are usually toxic. Boron nitride might be as nontoxic as PTFE but I wouldn't bet on it.

orangepurple 4y ago
I have not seen any evidence showing tungsten disulfide is toxic for either people or the environment in general
- kragen 4y ago
  Its toxicity isn't well characterized, and isn't especially high, but you can generally assume that metal sulfides with access to water produce either hydrogen sulfide, sulfuric acid, or both. In the case of tungsten disulfide it seems to be sulfuric acid, though the reaction is poorly characterized. Sulfate as such is pretty nontoxic (though it does cause diarrhea) but it doesn't take very much sulfuric acid to lower the pH to fatal levels.
ncmncm 4y ago
I think you might be giving PTFE a stronger pass than it merits.
- kragen 4y ago
  That's always possible, but why do you think so? The list of materials considered biocompatible enough for implants is pretty short, and PTFE is on that list.
  - DoingIsLearning 4y ago
    > The list of materials considered biocompatible enough for implants is pretty short, and PTFE is on that list. Not to stray from the main discussion but biocompatible has a pretty narrow scope. Time effects are not always fully captured, it often boils down to quite literally "we injected this stuff in 50x bunnies' bloodstream or implanted under their derme and none of them died after a month". With any new substance a cautionary principle should be applied, the main issue is Industry is spitting out new substances faster than we can meaningfully study them.
    - kragen 4y ago
      It would be possible for your comment to be farther from the truth, but it would take significant effort. It is incorrect to a degree that demonstrates malicious disregard for the truth, and since it pertains to health risks, people who were to rely on it would be putting their health at risk. You should not have posted it. https://www.fda.gov/medical-devices/biocompatibility-assessment-resource-center/biocompatibility-evaluation-endpoints-contact-duration-periods#permanent-implant https://www.fda.gov/medical-devices/biocompatibility-assessm... https://www.fda.gov/medical-devices/science-and-research-medical-devices/medical-device-material-safety-summaries https://www.fda.gov/medical-devices/science-and-research-med... https://www.fda.gov/media/158495/download https://www.fda.gov/media/158495/download
      - DoingIsLearning 4y ago
        I am not sure what was so out of line about my comment. The safety profile you link to itself refers to animal studies. That profile now looks very complete but before we had all those RCTs and clinical surveilance data, someone had to make a decision on wheather or not we can use PTFE in vascular stents _for_humans_. That decision would have relied on initial animal tests (i.e.literally sticking this stuff in bunnies) and some limited trial data. My point is not that FDA are somehow clueless bureaucrats but that everytime we introduce a new substances we are taking an educated risk based on limited (animal) data.