Obstructed interior holes after curing elastic resin

I am making medical models with the elastic resin on the Form2. These models have lots of spaces- arteries and veins. While these spaces are perfectly clear after the cleaning phase, the curing process seems to cause many of these interior lumens become obstructed. Entire small sections that started out as holes become solid. I have turned off all interior supports so these spaces should be clear.
Does anyone else have this issue? Thoughts on resolving it? What during the curing process can cause this? Thanks!

It may still have something to do with the washing process. It’s good to make sure the interior spaces are thoroughly flushed and clear of uncured resin before curing, and if they’re open-ended so that you can spray compressed air or gas (gently through them, that can help.

If thin areas of the part are soaked in IPA for too long, though, they can swell, and so it can also be helpful to make sure the part is not only clear of uncured resin but dry of any wash IPA or other solvent that might still be carrying a curable amount of resin in it.

If you can take a before and after picture, that might help reveal what’s going on, or if you could share a representative section of a model this happens with, I’d be interested to try reproducing the problem.

You can try with a syringe filled with API to flush the arteries using a small needle. Even if the holes have a closed end it helps.

It also depends on how thin they are, if it’s less than ~ 0.5mm then it’s probably going to fill in.

Could you also share what type of models you are making and how they are turning out otherwise other than the wash/curing issue reported here, for those of us also interested in making medical models of veins and arteries?

I am making models of liver arteries. They are not complicated- they are modeled on a single plane over 2D fluoro pictures not 3D CT data- but the interior lumens are correct size to the patient models. Using elastic resin.

They finally started to turn out ok but I’ve learned a couple of things:

  1. Running a print overnight to clean in the morning seems to make the resin too brittle to clean properly. I suggest printing and cleaning in the same day
  2. I did use a small syringe with a flexible hypotube at the end to disperse IPA further into the model. This was very useful but needed to be applied to all of the vessel openings.
  3. I cleaned it before the initial bath, after removing from the print base, and again after the final bath. The lumens remained clear after curing, so even though that’s a lot of cleaning, I think it was worth it.
  4. I also ran a catheter through the lumens to push out the resin. Whatever tool you use, be aware it will come out very gunky and possibly not re-useable.

Thank you for reporting your observations, @jennlucky. Glad to hear you made it work!

  1. As the cured elastic absorbs IPA/swells, it will get more fragile/brittle/weaker. It may be possible to reverse this by letting it air out for a long time after washing to evaporate the absorbed IPA.
  2. The elastic resin is pretty viscous, so hand-flushing may be necessary for negative spaces that are narrow and/or long, where the circulating action of the Wash may not reach.

We’re always excited to hear about applications like this at Formlabs.

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