High sensitivity scanning microcalorimetry can be used to monitor the changes in phase composition of liposomes as small or large molecules permeate the outer surface, the bilayer, and finally the interior. In this case a very slow dissolving drug suspension was monitored using DMPC liposomes at pH 7. Note the gradual change in phase composition over time. This technique can be used to develop in vivo in vitro correlations.
High sensitivity scanning microcalorimetry permits scanning at very
slow rates compared to traditional DSC. This results in improved
temperature resolution of overlapping peaks. The multi-modal behavior
seen above may indicate formation of complexes in the lipid bilayer which
could be undesirable if they were formed in cell walls.