Well there obviously haven't been any specfic to the use of e-cigs, but if you look at the main ingredients individually there have. PG for example was studied as early as the 1940s and has been in use since the '50s for various reasons where you'd inhale it (medical inhalers, e.g: asthma, air conditioning in hospitals etc).
Triphammer use natural flavourings, not sure if they use organic fruit etc or just the normal type though. They usually have an 70/30 or 80/20 VG/PG ratio but they will do you some VG only flavours if you ask them on their FB page, the flavour doesn't hold as well in a pure VG juice though. There's also a 20% off code on their FB page.
Haydn.