sterilizing polycarbonate

[aag 6]

I am using a U5S to print parts to be used in a cell-culture environment, and they need to be sterile. I am tending towards polycarbonate since it seems to be the most heat-resistant of all the "easy-to-print" materials. I was wondering: what is the highest temperature that a PC-printed model will withstand without deforming? This is crucial, as it will determine my choice of sterilization method. 

[TimonR 21]

Hi @aag,

 

Interesting application you're working on.

So what's your intended sterilization procedure? Does this involve chemicals as well?

I actually think that CPE+ might be a more suitable material from application perspective (PCTG is basically developed for sterilization and chemical resistance). However, it is somewhat difficult to print (warping). Small objects in combination with Magigoo PC and a brim should work on your S5.

I'll look up some HDT (temperature resistance under 'small' load of 0.45 MPa) and VST (softening temperature) for Ultimaker materials.

PC (t): HDT of 104 C and 115C VST

CPE+: HDT of 100 C and 109C VST (CPE+ is a PCTG polymer = PETG with additional chem and heat resistance basically)

PETG: HDT of  76 C and 83C VST

Other option could be PP (which also has high chemical resistance + decent temperature resistance), but this material is more flexible and warps also quite a bit (brim + Magigoo PP should help).

PP: HDT of 64C and VST of 99C (basically you can use it up to 99C but it will become more flexible at higher temperatures.

Hope this helps!

[geert_2 558]

Also, from the very beginning keep in mind that 3D-prints have lots of indents and pores where dirt accumulates easily, due to their layer lines and extruded "sausages". You need to consider smooth printability too, to minimize these.

 

Also consider a material that can be post-processed and polished well, to remove most of the roughness. Not all plastics can be polished well, some are too fibrous and get ragged.

 

How sterile does it have to be: only "free from living organisms", or also free from any accumulation of dirt and dead organisms? Those non-living accumulations could be toxic for your cultures, or they could be undesired food (proteins, fats, hydrocarbons), or they could just change things.

 

Heat won't remove the "dead bodies". But any agressive chemicals and solvents that would, would also attack the plastic, and/or seep into it. And thus later-on evaporate from the plastic and destroy or alter your cultures.

 

If UV-light might also be an option for desinfecting, then you need UV-resistant plastic. And preferably UV-transparent too.

 

So I would at least go for transparent plastic, if possible. Then you can see if there is anything inside, or entrapped air.

 

Avoid ethylene-oxide (etox) for desinfecting: it is extremely dangerous: causes severe chemical burns that you don't feel until 24h laters, when your tissue is dead and needs to be amputated. It is cancerous. And it is *extremely* explosive: it exothermically reacts with almost everything, decomposes and explodes. And it can explode in concentrations from 3% to 100%, thus almost always. The spark from dropping a metal tool is enough to make it explode.

 

For the least amount of gaps, entrapped air, and ridges in your models, print as slow as you can, at or below the minimum temp for the material (otherwise it decomposes in the nozzle due to sitting there for too long), and at the thinnest possible layers. See these tests: layer-heigt from left to right (mm): 0.4; 0.3; 0.2; 0.1; 0.06, all from a 0.4mm nozzle. Printing speeds: top-row 50mm/s, bottom row: 10mm/s. Text caps-height is 3.5mm, leg width is 0.5mm, depth is 1.0mm.

 

 

The model: 20mm x 10mm x 10mm, with hollow watermark halfway

 

Best-quality block (0.06mm layers, 10mm/s): left as printed, right after polishing a bit.

 

[AndersK 59]

There is FDA compliant Nylon available with a working temp of 110°C.

Even if the material itself is compliant doesnt automatically mean the final print is but it should be able to sterilize both with steam and UV

 

As said, surface finnish is crucial. Shotblasting with glass beads, buffing, cleaning and coating with epoxi is one way of getting smooth surfaces.

[aag 6]

Thank you for all your exhaustive and interesting comments. Here comes a couple of clarifications. Ethylene oxide is actually the sterilizing agent of choice for materials that cannot be heated to the common autoclaving temperature (121 degrees or, for prion inactivation, 134 degrees). Medical instruments such as for example endoscopes are always sterilized with ethylene oxide. The sterilizer keeps the material inside until the ethylene oxide has disappeared. There is absolutely no safety concern about this procedure, which is very well established. 

Achieving sterility means that no living organism, no bacteria and no viruses will be present. The existence of debris is irrelevant to the sterility requirement.

For clarity, the intention is not to grow cells on the 3D printed material. The intent is to create a moat that will be filled with a mixture of saline and low melting agarose, which will allow for homogeneous humidity and temperature around the tissue culture area.

Again, thank you very much.

[mwbarre1 0]

We've Autoclave sterilized Sheet PC (purchased from McMaster-Carr) at about 123C but it has a slower drying profile. It can be sensitive to mis-calibration.

 

When we cannot Autoclave, we use X-Ray to sterilize, however, I don't know the intensity or dosage.