Interesting process. This stuff is in the same chemical class as "GreatStuff" foam spray. The chemical reaction that forms the finished polymer is exothermic (heat releasing) and in some cases can self-heat up to 200F. I'm assuming the overcome this problem by:
1. picking less exothermic reactant molecules (hundreds to choose from)
2. using the minimum amount of material needed. if expands x30 times, you don't need much to start with.

As for getting it out, based on several different papers I found I think the foam is NOT injected into the abdominal cavity but rather underneath the torso muscles but outside the membrane surrounding the "gut sack". This way it doesn't get intertwined with all the intestines and organs. The hardened block does need to be surgically removed, but that's probably a minor part of the surgery needed to fix the original wound.

-Blast