As a biologist with a 3D printer, one of the questions I get most often about 3D printed parts is, “Can you autoclave these things?” As it turns out, no, not really. There are only a handful of thermoplastics that can survive the autoclave process, and most of them are not very good for 3D printing. With few exceptions, only polypropylene and blends of polypropylene hold up to repeated autoclave cycles, and polypropylene is, unfortunately, very a difficult material to print. It shrinks a lot when it cools, which causes a lot of warping during printing, and it is very difficult to get molten polypropylene to bond strongly to cooler, solid polypropylene.
It turns out that this is all unnecessary. Fused deposition modeling (FDM) 3D printing involves shoving a rod of thermoplastic into a hot nozzle until it melts and squirts out the nozzle. For most popular 3D printing plastics like ABS and PLA, the nozzle temperature is somewhere between 180C and 260C, and the plastic stays at that temperature for around a minute, depending on what the toolpath looks like. It’s actually a lot like Pasteurization, except way overkill. Get it? Overkill?
Anyway, here’s how FDM 3D printing compares to various Pasteurization (in black) and autoclave (in red) protocols :
Earlier this year, I was wondering about this, and my friend Emily Tung convinced me to just try it. So, on her advice, I heated up the nozzle of my 3D printer to 220C and placed a beaker of sterile liquid LB media under it. I then extruded some plastic until the blob fell into the media. I then incubated it, along with a positive an negative control, at 37C until… well, until nothing. Only the positive control (a short length of raw plastic feedstock) grew anything.
I tweeted this little experiment as it went along, and suddenly I had two collaborators, Kaitlin Flynn in Michele Swanson lab at the University of Michigan, and Luis Zaman in Richard Lenski’s lab at Michigan State University. Kaitlin immediately started suggesting different growth conditions I should try, and Luis, who also has a 3D printer, replicated all of my experiments and invented new variations to try. Because Kaitlin didn’t have a 3D printer of her own, Luis and I 3D printed a bunch of little test parts for her to try out, and mailed them to her. In her spare time, Kaitlin tried culturing the parts under all sorts of different conditions, including with mouse macrophages.
The results are detailed in our new paper On the intrinsic sterility of 3D printing, which is now available as a PeerJ PrePrint as of yesterday.
The tl;dr is that yes, 3D prints are sterile after printing. They are not sterile after touching them with your fingers or dropping them on the floor.