Lamellar–micelle transition in a hydrogel induced by polyethylene glycol grafting

Abstract

We demonstrate, for the first time, a distinct change of the bulk properties of a hydrogel based on the lamellar–micelle transition. The hydrogel consists of thousands of periodical stacks of bilayer membranes, poly(dodecyl glyceryl itaconate) (PDGI), inside a dilute polyacrylamide network. Along with a bright structure color, the hydrogel exhibits a strong anisotropy in its bulk properties. By grafting a short chain polymer lipid, poly(ethylene glycol) dodecyl ether (C₁₂EO₂₃), to the bilayer membrane, sharp changes in the structure color, swelling and modulus of the hydrogel are observed in a narrow C₁₂EO₂₃ concentration range. These changes are ascribed to the structure transition of the single domain lamellar phase to the multi-domain micelle phase of PDGI, induced by the excluded volume effect of two dimensionally grafted poly(ethylene glycols) (PEG). By controlling the water permeable nano-channels formed during the structure transition, a specific molecular diffusion and recognition are demonstrated. This lamellar bilayer hydrogel could be a new insight into the lipid bilayer system to investigate the nature of biological membranes by the bulk behaviors of hydrogels.