Anomalous solubilization behavior of dimyristoylphosphatidylcholine liposomes induced by sodium dodecyl sulfate micelles

The solubilization dynamics of dimyristoylphosphatidylcholine (DMPC) liposomes, as induced by sodium dodecyl sulfate (SDS), were investigated; this investigation was motivated by several types of atypical behavior that were observed in the solubilization in this system. The liposomes and surfactants were mixed in a microchip, and the solubilization reaction of each liposome was observed using a microscope. We found that solubilization occurred not only via a uniform dissolution of the liposome membrane, but also via a dissolution involving the rapid motion of the liposome, or via active emission of protrusions from the liposome surface. We statistically analyzed the distribution of these patterns and considered hypotheses accounting for the solubilization mechanism based on the results. When the SDS concentration was lower than the critical micelle concentration (CMC), the SDS monomers entered the liposome membrane, and mixed micelles were emitted. When the SDS concentration was higher than the CMC, the SDS micelles directly attacked the liposome membrane, and many SDS molecules were taken up; this caused instability, and atypical solubilization patterns were triggered. The size dependence of the solubilization patterns was also investigated. When the particle size was smaller, the SDS molecules were found to be homogeneously dispersed throughout the whole membrane, which dissolved uniformly. In contrast, when the particle size was larger, the density of SDS molecules increased locally, instability was induced, and atypical dissolution patterns were often observed.