The how's of skin healing are largely over my head - I'm a surgical tech, so my focus is mostly on surgery setup, knowing the surgery well enough to keep the surgeon equipped with the instrument they need throughout the surgery, tear down and clean up, rinse and repeat. Our education on physiology is pretty limited relative to everyone else in the OR, especially in my case since I was trained to be a surg tech when I joined the Air Force, and the military version is WAY abbreviated and requires no academic background (vs most civilian programs which require college level anatomy & physiology courses, and then actual surg tech school is like 5x as in depth compared to mil). I've only just recently caught up to my civ peers academically bc I took the prereqs for nursing school, for which there's significant overlap with normal surg tech program prereqs. (just finished 1st semester of nursing school, woot woot!!)

...and tbh, grain of salt on civ surg tech program info I just mentioned - that's all 2nd hand info from other techs that I just took at face value. I have no reason to doubt it, but still.

Aaaanywho, my understanding (which is like tip of the iceberg basic) is that the epidermis is mostly just the dead skin cells that flake up to the top to form the outer layer of your skin. The dermis underneath is vascularized, and healing pretty much starts with blood (delivering nutrients and platelets etc). So yeah, wounds heal from the edges inward and from the deeper parts outward. Wide area wounds can be painful af, have a high infection risk, and you lose a lot of fluid through them, so that's where grafts come in to replace that protective outer layer, which acts as a barrier to pathogens and keeps the underlying tissue moist. Even with the mesher, the graft is effectively covered in holes to cover a wider area, but that still acts as a scaffolding for new tissue to form.

I imagine you get used to it, but I feel squeamish just looking at the graft, not to mention the injury that required it!

Yeah you get used to it. Funny thing with the AF: many active duty surgical techs are placed via "open general" which is a recruiting tool to place warm bodies in open job slots as fast as possible. Basically people go to a recruiter, aren't picky about what they want to do once they enlist, so they just let the AF decide for them. Some of them get surg tech, and there's an "Oh shit" moment when they realize medical jobs were on the menu and they're the type that passes out at the sight of blood.... TOO LATE, THEY ALREADY SIGNED! So they finish Basic, go to surg tech school, then go to work at the OR at an on base hospital where they STRUGGLE (in part because they're a source of great fun for the other staff, lol) for about... 4 months. Much after that, them being elbow deep into a stranger's abdomen to hold a bunch of intestines back out of the surgeons way is just another Tuesday, doesn't phase em at all.

Squeamishness is just a matter of exposure; as that increases, so does tolerance.

...also on the off chance anyone reading this is considering enlisting into the AF, do not - DO NOT - go open general unless you're sincerely cool with spending the next 4+ years doing ANY of the jobs listed in general, which is a massive category that could land you as a medic, cop, line cook, roach exterminator, weather, etc. And if you want medical and your recruiter recommends you go "open medical", that doesn't exist - there's a number or email on the back of his business card to file complaints, write that motherfucker up for lying to you. Apparently that's a common trick to get people to sign open general.