Effects of Chemical Characteristics on the Surface Mechanical Properties of Block Copolymer Micelles at the Air-Water Interface

Every year, over 200,000 individuals in the US suffer from acute respiratory distress syndrome (ARDS). ARDS has a high mortality of ~ 40%, while there is no lung surfactant (LS) drug that is effective in treating this disease. To address this need, our laboratory has recently developed a fully synthetic polymer lung surfactant (PLS) therapeutic (polystyrene-poly(ethylene glycol) (PS-PEG) nano micelles) that can perform the surface tension-lowering function in the lungs of an ARDS patient that are deficient of natural LS. PLS produces near-zero surface tension (under high compression) by formation of insoluble monolayers at the air-water interface. In the present work, in order to understand the effect of polymer chemistry on PLS performance, the surface mechanical and molecular conformational properties of nano micelles formed by various different block copolymers (i.e., block copolymers having different hydrophobic polymer blocks and/or different hydrophilic PEG chain end groups (hydroxy vs. methoxy)) have been investigated by surface tension-area isotherm, ¹H NMR spectroscopy, and water contact angle measurements. We found that micelles derived from block copolymers with stronger hydrophobicity, higher glass transition temperatures, and the less hydrophilic methoxy group at the chain end produced greater surface tension-reducing effects, which makes them more suitable for use in ARDS treatment. A complete understanding of how the chemical characteristics of polymers affect their surface mechanical behavior will enable us to design improved PLS candidate materials for applications in ARDS therapy.