Personally, from a health perspective, I like the idea of using a pure metal as a coil. This means if I am being contaminated with metallic nano-particles, well at least I only have one type to worry about (and not 3 or 4 such as is the case with alloys like kanthal). This is why titanium is looking more and more promising to my layman, high-school drop-out eyes. It isn't a "heavy metal" like nickel or chromium and is generally considered (
there is some debate) to be inert in the human body. It is used in biomedical implants (try that with nickel or chromium). It is not a known carcinogen (it is class 2B, which is a "possible carcinogen." This classification was based solely on animal studies). Titanium also seems pretty corrosion resistant, even at high temps.
There are animal studies out there that suggest inhaling TiO2 might have some adverse effects, but those are animal studies and, to my knowledge, have not been replicated in humans. Also, the results vary based on the species being tested (rat studies have showed lung tumor growth, but the same tests on mice and hamsters did not which I find very interesting considering they are all rodents). The human studies I have looked at (workers in factories, etc) vary in the results. Some show no correlation between TiO2 inhalation and cancer, while others show a very slight (but statistically significant) increase in cancer risk. However, these studies did not provide a dose-response relationship so there's no way to know if the levels of TiO2 in the air between the two groups were similar. We do know that inhaling anything but pure air can have deleterious effects as it is believed that any nano-particle (no matter the element) can be dangerous depending on its shape, crystalline structure, etc. Nonetheless, even if there is a theoretical risk with TiO2 nano-particles, it certainly cannot be greater than the very well known (and quite nasty) effects of the heavy metals like nickel, lead, tin, chromium, etc.
Years from now we will all probably look back on this and laugh. Once we have a lot more science under the belt, I think we will find that we wasted our time with metal safety. More than likely if there's any real dangers in e-cigs, it's going to be in the flavorings (I just have a hunch about this). I just don't feel that we are heating our coils (of any type) hot enough to expose ourselves to levels of metals that matter. We aren't working in environments where TiO2 will be floating around at high concentrations. Maybe I am wrong, but I hope not. I do hope, however, that there are studies done on these metals as they relate to vaping, as I am not suggesting it should be an area that is ignored.
When I "worry" about vaping safety I am more concerned with what compounds are in all those tasty flavors and whether my juice is being heated to a point where the chemical structure of the solvents and flavors are degrading into carbonyl compounds.
I got most of the info above from an
excellent study I found that examined the literature in regard to the safety of Ti particles. It seems pretty comprehensive.