Few problems to biological healing :
- You need the resources to replace or repair what was hurt.
- You need time for cells to replicate enough to replace or repair what was hurt.
Without any kind of cheating, you can't make the time go faster or make resources magically appear in the body of the anyone near.
But, what could be somewhat credible with still a bit of handwavium :
Your Sanators are somehow constantly emitting a cloud of UBERCELLS around them. These UBERCELLS have three particularities :
- They will naturally copy the genome of first nearest cell they meet (maybe by eating it, first) which is not a UBERCELL.
- They have a very fast reproduction rate.
- They are very big. Which mean they can replicate to a thousands smaller cells without breaking a sweat before lacking resources.
So what you obtain is what could be parent to a "stem cell spray".
Stem cells are (real) non-differentiated cells than can differentiate into every possible cells of an individual (they are the kind you find in an embryo) and are presently being researched and used to grow tissues for transplant or even fight some sicknesses. (Awesome stuff, really).
Stem cells would probably die if you directly sprayed them on an injury but UBERCELLS don't. Because they are very strong and hardworking, they just pick up the job of the closest cells and help them during the healing process. Which is exactly what you are looking for.
The Sanator decline any responsibility concerning the following :
- In case of infection by a virus of the host, the UBERCELL may occasionnaly hasten death.
- If the UBERCELLS come into contact with a cancerous cell, the host won't like it either.
EDIT : UBERCELLS only work on eucaryotes, aka cells with nucleus. Which prevent any kind of bacterial disaster.