What is the name of the movie where a guy gets a bullet to the head, and survives because of a gel like gauze?

Could it be Kingsman: The Golden Circle?

When it’s activated, the shrink-wrap rapidly inflates with a swirl of orange and blue gel, which then fills in the hole in his skull. This “bio-foam” is what keeps [the victim] alive until nanites (nano-scale robots) rush in to repair the damage. It may seem like another ridiculous made-up tool in the super-spy toolkit, but its premise is something actual scientists have already considered.

It contains a scene very much like the one you suggest (twice, actually). I came upon it by doing a Google search for film gel cures gunshot wound.