Wound healing is a pretty amazing thing. I'm a biologist, so I know how it works1, but I still find it fascinating. Four weeks ago, I had a relatively large (but very neat) cut through my body wall, something that ought to be fairly catastrophic -- there's a reason we have all those layers of skin, after all. But now I just have a red scar, and the skin has knitted itself together nicely. That part of the procedure was more or less the handiwork of my body's own processes, without much modern medical intervention. All that is needed is some way of temporarily keeping the edges of the wound together (modern surgical clips, stitches, thorns, soldier ant mandibles, or whatever), and your body does the rest.
I was thinking about this yesterday while watching a couple of plumbers trying to fix my leaking radiator pipe. Why can't we design domestic pipework to heal itself of leaks, like a scab forming over a wound? We could provide the equivalent of a temporary plaster over the hole to slow the flow, then the pipe could gradually seal itself. In this case, the plumbers who originally installed the pipes couldn't even get basic plumbing right, let alone advanced self-healing. The guys yesterday had to open up the wall a bit to find a sound bit of pipe to form the new joint with, and discovered that a) the plastic piping that's supposed to protect the copper pipes from corrosion caused by the plaster stopped half way down the wall, and b) they hadn't actually bothered to solder the upper joint -- it was just slotted together, which goes some way to explaining why it was leaking.
1 ...she writes, desperately trying to recall the details of that lecture many years ago in which the process was explained. It would be more accurate to say that I know roughly how it works. ↑