science

That seems to be what they are trying to control. Just "turning on" the regenerative mechanisms is a fast track to a cancerous growth. This research seems to be aimed at understanding how to provide that mechanism with the chemical instruction of what to grow into. While we aren't there yet, each time a new part of that instruction set is figured out, we get a step closer to regrowing lost tissue. Living organisms are incredibly complex and understanding large, complex processes like growing a limb is going to take a lot of work and time.