a concept: its my personal headcanon that dermal regenerators don't work well on Cardassian skin, because they're primarily made and developed in the Federation and most Federation species are Mammalian and don't have scales as a part of their dermal anatomy. They can handle clean cuts (like from surgery), bruises, shallow scrapes, but anything beyond that it's better to let heal the old fashioned way.

So following from this, Julian inventing a regenerator that actually works for species with scales, because what's better than loving someone to the point of invention, to the point of loving not just them, but the world which they love, which made them.