Properties of alkyl-phosphatidylcholine monolayers in the presence of surface-active three-block copolymers

The interaction of three-block copolymers (poloxamers) with dimyristoyl-phosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayer experiments. The poloxamers selected were BASF PLURONICS F-68, F-88 and F-98. All of them are water-soluble and possess two hydrophilic polyoxyethylene and one hydrophobic polyoxypropylene moiety but differ in molecular weight. These substances and their interfacial behaviour are interesting for the development of targeted drug delivery systems. Monolayer tensiometry revealed the degree of poloxamer penetration in PC monolayers and the changes in monolayer compression/expansion behaviour.Two different experimental protocols were used to determine the surface pressures (π) and areas (A) at “squeeze-out” (compression) and “insertion” (expansion) of the soluble component in the surface layer. The two protocols yielded differences in the “squeeze-out” and “insertion” parameters of the DMPC (DPPC)/Poloxamer systems. The differences disappear when comparing the product πA (2-D – “mechanical work”) for the various combinations of lipids and poloxamers. In all cases (πA)out > (πA)in. This approach reveals a possibility for adequate comparison of monolayer compression/expansion isotherms made by different experimental protocols.