Help making an STL model solid (instead of hollow)

Hey all you gurus…I’ve got an .stl file of an anatomical heart. It is currently hollow. What I need to do is plug any holes and make it solid. My goal is to use that to go on to make a keyed hollow mold, using the solid .stl as the empty space within a 2-piece block. Once I print that on my SLA printer, I hope to use it to cast some of these hearts in resin of some type, or possibly silicone rubber.
I understand that the aorta and other veins and arteries that lead into the currently hollow heart must all be plugged properly (mesh modified?). Unfortunately, this is beyond my current skill level. Anyone willing to take a look? I’m attaching the .stl here. (2.2 MB)


I can’t speak to your file info, but check with those folks that work out of classroom one casting medical stuff - they may have some tips on materials.

MeshMixer can probably do what you want… if I understand what you want correctly.

One would select and delete the indented surfaces.

Then use Inspector, Auto-Repair with a smooth fill.

Here’s a good, short instructional video.

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Thanks, man. I’ll try it.

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It’s a bit tedious, but wasn’t that hard and pretty forgiving. Fight the urge to use a larger brush for selection.

David, your arteries are now clogged…

I THINK this is what you’re looking for. There’s a more efficient way to select using “face groups”. Played around for a bit. I have ZERO MeshMixer experience so I imagine there are better ways still.

I removed all the internal mesh so it is a true solid. Took some time, but I think you will find that resin slicers, especially Lychee, will be happier. The model is fully repaired, normals are correct and it doesn’t self intersect.

HeartCastable.stl (2.0 MB)


You’re awesome, man! I worked several hours on it last night, and was going to just give up and take a 3D print, plug the holes with clay, then use that to make the mold. I owe you one!


It worked perfectly. Let’s see how it does on my resin printer…