3D Prints and Food


We recently ran a post about a cute little 3D printed elephant that could dispense booze. The design didn’t actually have the plastic touching the liquid — there was a silicone tube carrying the shots. However, it did spark a conversation at the secret Hackaday bunker about how safe it is to use 3D printed objects for food. In particular, when I say 3D printing, I’m talking fused deposition modeling. Yes, there are other technologies, but most of us are printing using filament laid out in layers with a hot nozzle.

There’s a common idea that ABS is bad in general, but that PET and PLA are no problem because there are food-safe versions of those plastics available. However, the plastic is only a small part of the total food safety picture. Let me be clear: I am not a medical professional and although my computers have run a few plastics plants in years past, I am not really an expert on polymer chemistry, either. However, I don’t use 3D printed materials to hold or handle food and while you might not drop dead if you do, you might want to reconsider.

It is true that some plastics are not food safe. The US Food and Drug Administration (FDA) talks about “food contact substances” and has a lot of technical reading on the subject including this mostly readable introduction. There’s even a database with lots of materials (not just plastics) that are food safe.

However, even if some plastics can be food safe, that doesn’t mean that the $11 spool you bought on eBay is actually food safe. You don’t usually know who made it, how impure it is, or what’s been added to it for pigmentation or to modify other properties. However, let’s assume you locate food-grade filament from a trusted supplier. Is that the only problem? Turns out, it isn’t even the biggest problem.

Bacteria

Paradoxically, the biggest problem is microscopic. If you cook or store food much, you probably know that everything you eat is full of bacteria and other little critters. Leave some leftovers out tonight if you don’t believe that. If you make a cup using injection molding with a food-safe plastic, you shouldn’t have a problem as long as you wash the thing after each use. A 3D printed object, though, is going to have little cracks and spaces, especially where the layers make contacts. These are perfect places for germs to hide and multiply. Some foods, too, are worse than others. Raw eggs and meat, for example, are notorious for having dangerous bacterial growth.

There are two schools of thought here. If you are making something disposable, this might not be a big deal. Whatever bacteria get trapped wind up in the trash. The other thing people will do is use a food-safe sealant like polyurethane or silicone to cover the food contact surfaces. Of course, now you need to be sure the sealant is really food grade. In the case of the elephant, it wasn’t so much a sealant as just running a tube through the plastic.

There has been work on making antibacterial plastics. The video below shows one such plastic and it is even dishwasher safe.