Hybridization of lipids to monolayer and bilayer membranes of triblock copolymers

Hypothesis: Membranes formed by ABA (hydrophilic-hydrophobic-hydrophilic) triblock copolymers were studied. Bridge- and Loop-conformation of ABA copolymers are identified in the membrane and monolayered, bilayered, and mixed structured membranes can be formed. When lipids co-assemble with ABA copolymers, a hybrid membrane is developed. Experiments: The monolayered (bridge-conformation) and bilayered membranes (loop-conformation) formed by ABA copolymers were investigated by dissipative particle dynamics, and their hybridization with lipids was studied as well. The fraction of loop-conformation in the membrane can be controlled by strong immiscibility between A and B blocks. Findings: The effects of the loop-conformation fraction on the structural, mechanical, and transport properties of the membrane were obtained. The bilayered membrane is thicker than the monolayered membrane, and is easier to stretch and bend. Moreover, the lateral diffusion and permeability of the bilayered membranes are greater. For a hybrid membrane of copolymers and lipids, a homogenous distribution of lipids in the membrane is acquired at low lipid concentrations (ϕ _l ), but a lipid-rich domain emerges as ϕ _l >ϕ _l ^c . The critical lipid concentration (ϕ _l ^c ) is higher in the monolayered membrane, indicating that lipids prefer to hybridize with bridge-conformation rather than loop-conformation. Moreover, the structural incompatibility itself can lead to phase separation in hybrid membranes.