Effects of the interaction and surface morphology of mixed DPoPE/Poloxamer 188 monolayers and thin liquid films

The aim of the present study is to investigate the kinetics and the penetration degree of Poloxamer 188 (P188) of different concentrations to Langmuir lipid monolayers at the air–water interface formed from dipalmitoleoylphosphatidylethanolamine (DPoPE) in different liquid crystalline phase states, lamellar Lα and non-lamellar (inverse hexagonal HII and inverse bicontinuous cubic QII) phases, in static and dynamic conditions. It was found that the penetration of P188 to the DPoPE monolayers in all three lipid phases is very fast, strong and concentration dependent, and the strongest effect was detected for the non-lamellar DPoPE monolayers. Moreover, the dynamic characteristics of the mixed DPoPE + P188 monolayers revealed stronger interactions between P188 and DPoPE in QII phase, than in the other two, and more packed surface structures. In addition, by using Brewster angle microscopy (BAM), the surface morphology of mixed DPoPE + P188 monolayers was determined. The BAM images showed that the addition of P188 to DPoPE monolayers led to decrease in the lipid domain size and to formation of more homogeneous films. Furthermore, the effects of P188 on the hydrodynamic properties and the stability of lipid thin liquid films (LTLFs) were studied. A strong stabilization effect of P188 to the LTLF films was proved. This effect was probably influenced by the appearance of steric repulsion (in addition to the electrostatic repulsion and van der Waals attractive forces). The results suggested that the non-lamellar lipid phases have higher potential to act as a “reservoir” for penetrating agents, and as a pool for membrane repairing substances such as P188.