(659g) Understanding the Solubility of Triblock Copolymers With Supported Lipid Bilayers

The interactions of amphiphilic poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers and lipid membranes have been characterized. The solubility of these triblock polymers in a lipid membrane can be changed with temperature leading to the ability to create a tunable insertion within the membrane. Here, we present our results when this system is changed from a free standing lipid membrane to a supported lipid membrane, in which one lipid leaflet is confined by a solid support. With the use of microcantilevers and fluorescence recovery after photobleaching (FRAP), we measure the solubility and interactions of triblock copolymers (F68 and F98) within supported lipid bilayers. Two factors are found to affect the lipid polymer interactions: temperature and number of repeating units in hydrophobic PPO block. For both polymers, the polymer solubility with the membrane was increased with higher temperature on microcantilevers. However, FRAP results show that the polymer with the longer PPO block, F98, significantly hinders the diffusion of lipids, suggesting a highly ordered and expanding structure of lipid bilayer. This conclusion is also confirmed by the copolymer induced surface stress change of lipid bilayer on microcantilevers, and further illustrates the various conformations that these polymers can take on when interacting a supported lipid membrane. These results are also in contrast with that found for free membranes, suggesting that the solid support affects the polymer-lipid interactions. A Langmuir isotherm model and a free area theory are applied to describe the lipid polymer interactions at the sensor surface, assess the binding affinity constants, and analyze the effect of triblock copolymers on lipid lateral diffusion.