The influence of incubation temperature and surfactant concentration on the interaction between dimyristoylphosphatidylcholine liposomes and poloxamer surfactants.

Differential scanning calorimetry and photon correlation spectroscopy have been used to study the interaction between poloxamers P338 and P407 and dimyristoylphosphatidylcholine (DMPC) liposomes. The extent of the interaction was found to be dependent on the incubation temperature in addition to the poloxamer concentration. At low poloxamer concentrations (0.1-1.0% w/v) an interaction with the phospholipid bilayer was detected by a reduction of the pre-transition enthalpy of DMPC. At higher concentrations (2.0-5.0% w/v), the main phase transition temperature of the liposomes decreased and the endotherm broadened with a shoulder on the high temperature side, indicative of phase separation. Maximum increases in the diameter of small freeze-thaw extruded liposomes were shown to occur at temperatures close to the poloxamer critical micelle temperatures. At higher temperatures and surfactant concentrations there was evidence of solubilization of phospholipid into mixed micelles.