4.6. Gelation temperature and rheological measurements
The gelation of poloxamer solution is known to be a reversible
process, i.e. gels revert to free-flowing solutions when the temperature
drops below the critical gel temperature (CGT). If the gelation
temperature is higher than 36 C, the formulation will remain liquid
at body temperature, and thus does not control the release
of ALA. It would be convenient to have a gelation temperature between
30 and 36 C, to be liquid at room temperature, and thus
could be spread efficiently on the skin, and form a gel instantly
upon contact with the skin [24]. The CGTs of 20 and 30% w/w of