Food Safe 3D Printing: A Study

[Matt Thomas] wanted to answer the question of whether 3D printed structures can be food-safe or even medical-safe, since there is an awful lot of opinion out there but not a lot of actual science about the subject. As a mechanical engineer who dabbles in medical technical matters, he designed as series of tests using a wide range of nasty-sounding pathogens, to find once and for all what works and what does not.

One common argument sprung up from the maker movement response to COVID-19, 3D printed masks and visors. Many of us (this scribe included) printed many thousands of visor frames and ear protectors, using the armies of 3D printers we had available, then distributed them to nursing homes and doctors’ surgeries, and anywhere else that couldn’t get ‘proper’ medical-grade items.

There was much opinion about the risks associated with contamination of such 3D printed structures, due to the allegedly porous nature of the prints. [Matt] has shown with some SEM imaging, that a typical 3D print does not have any detectable porosity, and that the grooves due to the layer lines are so positively huge compared to your average bacterium, as to also be irrelevant.

Cutting to the chase, [Matt] shows that ordinary dish soap and water are totally sufficient to remove 90% or more of all of the pathogens he tested, and that using a mix of culturing swap samples as well as protein detection, that 3D printed parts could be cleaned close to medical standards, let alone those of food handling. Even those pesky biofilms could be quickly dispatched with either a quick rinse in bleach-water or a scrub with baking soda. Does this article clear this up finally? Only you can decide!

We’ve obviously covered the subject of 3D printing masks a fair bit, but it’s not all about PPA, sometimes ventilators need some 3D printing love too. Prusa did some work on the subject of food safety, looking specifically at post-processing for 3D prints, and produced some interesting results.

Thanks to [Keith] for the tip!

43 thoughts on “Food Safe 3D Printing: A Study

    1. If something is medical grade or food grade and food always goes into your body, we should set lower limits for food grade because food grade goes through the mouth/rectal torus compared to medical grade that sometimes does? Just curious.

    2. You and everyone on earth already has plastic in your bloodstream messing up your endocrine system. The time for paranoia is already behind us. Might as well eat out of the 3d-printed bowl.

  1. For food safe, there is more to it. Additives of the plastic can leak out into your food for example. Your nozzle could contaminate your food grade plastic if you have it.

    On the possitive side. I know there is a paper out there that discribes that printing effectively reaches autoclave pressures and temperatures. So your print is sterrile. (If your bed is)

    1. And the article addresses the nozzle contamination issue. The levels of lead or other nasties that can be transferred from the nozzle are negligible (tiny amount of lead in the nozzle, tiny amount of surface area contact with the plastic, tiny amount of transfer from one to the other.) Apparently you should be far, far more concerned about touching your brass house keys (!!).

          1. Lead is everywhere, even your drinking water. It is the amount of lead that is critical, and with the number of hours that a standard brass nozzle lasts in a printer with standard filament (abs, pla, petg), the dosing will not be large in a food-sized print. And certainly, some of it will wash off with soap and water.

            That wouldn’t stop me from swapping to a lead-free nozzle, though, because I’m hypervigilant about those things…partly because I haven’t done the math, and partly because I don’t like any amount of contaminant that can be avoided.

      1. That’s not what this guy said and not the only issue here. The article only considered metal leak from the nozzle but didn’t account for contaminants from the plastic. Things like VOCs are known and taken into account for the designation of food safe and medical grade. We also know that printed parts contains tons of contaminants of that sort.

        Honestly, that was my biggest concern from the beginning. More and more facilities are using UVC and gamma sterilization now which pretty much completely eliminates the porosity argument on their own. But biotic contaminants and inorganic contaminants are the only problems.

    2. Exactly!!! Food safe shouldn’t be used in the title of this…. there is no way I’m going to make a cup of tea in a printed plastic mug.. 90% of all coloured materials contain amounts of not food safe chemicals.

      1. Im the author of this paper and i adress this fully in my actual blog post which im not sure hackaday added or not. In my papet i state its moatly food safe, except for the additives and its best to coat in a epoxy or resin and according to tutle 21 volume 3 of the fda, epoxy and resin is food safe after a full cure:) i can post the link to my full work

      1. I wonder what the layer lines for filament that has absorbed a lot of water looks like. It pops and fizzles due to steam bubbles so if your filament isn’t dry enough that could leave pockmarked layer lines that would be harder to clean.

    1. yeah i was thinking the same thing. “able to be cleaned” is quite a bit different than “will be clean after going through your regular wash.” i’m pretty sure my dishwasher would severely warp the PLA parts i use, and i’m just not very confident in my manual dishwashing to get the grooves clean. i guess a lot depends on your geometry, though…if you avoid inside corners, it’s a lot easier to clean.

      otoh, i simply don’t care :) i use a couple 3d printed things in the kitchen…one odd-sized measuring cup just for water, a couple dry powder funnels, and a dry powder scoop. if they ever got greasy or sticky i might just throw them out. they’re real handy though and i just never wash them.

      1. My pla pint glass has been through the dishwasher a few times. It warps, I fill it with hot water, reshape it with anothe glass pressed in. In theory it’s warping a little less each time…

        Don’t have many printed parts, but have plenty of wooden utensils and boards, which has always made the ‘foodsafe’ crowd seem a bit odd

        1. Yeah, wooden utensils have been in use for as long as carving tools have existed. Studies have shown wood cutting boards are safer than plastic, yet some people still skeev out over them. My mom used to cut meat on right on her wood chopping block and then just wipe it with a wet rag afterwards, and we never got sick from it.

      2. when i say “able to be cleaned” i am literally stating that it is WELL within food safe specs. A surface or part must be below a certain amount of pathogens in order to be deemed clean in the hospital or food environment. For example, in a hospital, ATP readings must be below 10 RLU units in order to be safe, or pass the protein residue tests which i use in my testing. I have an official lab where this was all done

        In a hospital kitchen, sanitizing means to have the surface to SAFE levels. Sterilize means to have it below a specific ID number. We tend to think that sterilization kills everything, it doesnt. Hospital microbiomes are very interesting piece to study. This is what actually gives the hospital its own immune system in a sense.

        and im with you on the “simply dont care piece” i dont really. people are so affraid of getting sick. I dont blame them because being sick SUCKS, but at some point, licking doorknobs to improve your immune system does work hahaha

        For what it is worth, My paper is being peer reviewed as we speak. MIT is interested in my work, and so is the additive manufacture conference and a journal of medicine.

        thanks for your comment:) highly appreciate it

    2. the pathogens are about 200 times smaller than dirt and food particles:) For example, salmonella is about 0.5 microns (2000 times smaller than a mm) in diameter and about 2-5 microns in length. So it needs to have sufficient space in order to reproduce, if not, then it will make a biofilm to protect itself.

  2. I have nothing to do with dishwashing manufacturers, but Dawn = Fairy = very good dishwashing detergent. I once bought a Palmolive dishwashing detergent and, oh my god, I was always forced to open the hot water tap to clean anything. Maybe that was the secret to make the 3D printed parts clean…

  3. I think you are independently discovering why medical and food-grade stuff costs money. It isn’t the materials, it is the testing and certification. (my former PI used to refer to this as discovering hot water). Same in marine or, god forbid, aviation or even worse, aerospace. I know this article focuses on food-grade but for medical use, things need to be either autoclave-safe or at least go through ethylene oxide or radiation sterilization. Pretty much anything can be fully cleaned and sterilized using existing technology, it just costs money.
    Removing 90% of pathogens sounds like a process failure rather than materials failure.

    1. Thats the whole point of my article and findings. I use the exact same methods surgical techs use to check the cleanliness of their tools. In an autoclave, you have to mechanisms to see if the tools are clean, a biological and a chemical. The biological test is a tube with contaminants that die and change color when the autoclave has hit hot enough temps. The chemical test is to make sure the steam went were it was supposed to, then after the clave, they are swabbed using the same swabs i used to test a 3rd time. I did my work in an official lab and we have an autoclave as well as ethylene oxide. You do not have to go through an autoclave to be safe. I am a biomed and aerospace engineer. This is my job haha.

    2. Second, 90% reduction is very good. At the hospital, as long as your ATP readings are less than 10, your safe. You will never get a completely clean tool, but you will get a tool within spec or below the ID number

  4. you can coat anything in enough layers of shellac and make it “food safe”. Depending on the type of alcohol you use as a solvent, of course. mmmm… bug secretions never tasted so yummy.

    of course this means that you trust the original manufacturer to have used a process which does not leave residue. but then again, i’m not eating the shellac, or drinking out of a shellac container. just using it for a surface that may come into contact with food. If you really think about it, aluminum and other alloys with aluminum have been regarded as ‘food safe’ for god knows how long, yet they contribute to alzheimers and early onset dimentia. Good luck with the long term studies. How about plastic cutting boards. microplastics end up in your food every time you cut something on it.

    tl:dr: don’t worry about it too much and use stone, wood, and steel as often as posible, you’re most likely going to get dna breaking chemicals/particles in your over-processed food anyhow straight from the mfg… all FDA and EPA approved, because they don’t work for you, they work for the kickbacks. not to mention ‘forever chemicals’ that break the dna of literally every living thing on the planet .

    1. “Aluminium cookware causes alzheimers” was comprehensively debunked years ago. The original study that started it had alzheimers brains that were preserved in aluminium salts and normal brains which weren’t (oops). Every subsequent study has failed to find a link.

  5. I don’t know how many of you guys have apnea but CPAP masks cost between £60 and £200 each depending on the type model and manufacturer. This article is very interesting to me since it’s very difficult to find a custom fit that avoids leakage, is comfortable and does not leave creases on your face. I’m definitely going to try more mask printing.

  6. This new article does some very interesting work, but the real point is we’ve always known there is a difference between “food safe” or “medically safe” and “safe enough to be used for food handling/medical purposes”. The former is a standard stating the risks of bacteria/chemicals/… are sufficiently low to be widely accepted for long term use in the harshest plausible environment it can. The latter can be very variable with exact use case and environment, single or few-use items aren’t going to need to meet the standards of something regular placed in a dishwasher and blasted with enough hot water to make it leech chemicals. A cookie cutting shape for a few uses doesn’t need to meet the quality of one running on a factory production line non-stop. And something you make yourself is perhaps something where you can just commit to scrubbing it more thoroughly rather than leaving it all down to food-safe design to minimise cleaning needs. This is a really important difference, duration of use and exact application (what state the food is in when touching the part etc…) can mean you’d be perfectly safe in practice to use something even though you wouldn’t want to trust it for long term mass use at scale. In the medical sphere, something which stays solely outside your body (prosthetic or something), or enters a short distance in to a naturally open opening (mouth camera perhaps) on a rare basis, has a much less demanding time being safe in practice than something which gets surgically implanted for a lifetime.

    1. This is 99% food safe. In my conclusion i sate that the ONLY thing left to worry about is the color additives. Once a manufacture can use food safe colors, then your fine. Read the conclusion of my article that is linked:)

      My paper is being peer reviewed right now by a journal of medicine, MIT, and 3 other departments:) I am also hopefully going to the additive manufacture conference to share my work.

      your comment brings up alot of the same questions i have had, hence why i did this.

  7. First, really appreciate your eagerness and creative efforts at testing. It’s important to attempt to prove or dispel various theories, myths, and fears regarding the cleanability and bacterial transmission of 3D printing.

    I read your paper, especially since you mentioned multiple times in this thread that you had submitted it to “peer review” and to “MIT”.

    While I found your paper interesting and creative, I must say it falls way, way below the standards of any peer-reviewed paper I have ever seen or written — unless by peer review you mean a group of your friends or coworkers reading the paper around a round of beers.

    For example, most glaringly, there were no formal footnotes or citations. Your wording was also colloquial and often written in the first person with lots of chatter and informality (e.g., “Fun fact” or “More on this later”. You cited YouTube videos as proof. Your methods while certainly much better than home speculation were still short of typical biomedical methods that I have seen. The paper itself was not organized in typical research format with “Abstract”, “Methods”, “Results”, “Discussion/Conclusions”, etc.

    Again, I really admire, appreciate, and encourage all you have done but calling this a paper submitted for peer review suggest a level of refinement and standard that frankly is not present in your work.

    If you truly want to submit this to a respected peer-reviewed journal or conference, I suggest that you partner with someone who has experience in writing and submitting such papers.

    Please take this as encouragement and as constructive criticism.

    1. LOL, loved the part where you said peer review around some beers haha. that made me laugh. You need to remember, this is a blog post, not the actual paper that is going in for peer review. I have to write it very specific for the journal of medices that i am sending it to. I might stick with one subject matter like “biofilms” etc etc. This blog is NOT the peer reviewed paper. However, i have had my friends read it, but it we had a round of bottled water since that seems to be the new adult drink haha

    2. As for the youtube video, its just ONE video on a concept of alcohol causing strength degeneration on parts. “”Some have asked if IPA can weaken 3d printed parts. For PLA, PLA+, and PETG, the 3 most common thermoplastics, there is no change with their strength after a 12,24, and 48 hour soak in 70% IPA”” Also, the video has a direct link to his research. CNC kitchen is an engineer as well who has done much testing for the community.

      Thnks for the comments and advice, i agree with it all. This is NOT the paper i turned in for review. I would never add humor to a peer review because it might make the reviewers have a stroke haha. The peer review is actually pretty dry and cuts right to the chase.

      I dont think i mention in the paper that i am a biomed and aerospace engineer, which is probably why people think this is the paper im turning in. I think i need to add a disclaimer about that

  8. If you want to test conditions in the home, I would suggest testing for bacterial presence after washing FDM parts in a dishwasher at various settings (e.g., cycle type/length, water temperature, soap type, with/without drying).

    PTEG would generally be better than PLA at least at high water temperature and drying temperatures.

    1. The idea behind my post is that BASIC hand washing can clean parts to safe levels, even with diluted dish soap from a foam dispenser.

      The dishwasher idea is great. I wonder how the powder or liquid soap acts on the surface tension of water? I feel like powder soap doesnt lower it as much, but i could be wrong. ill have to test and see.

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