Stretching drives Membrane Homogenization of Phase-Separated Supported Lipid Bilayers

Abstract

Cell plasma membranes exhibit heterogeneous lateral organization whose dynamic compartmentalization is critical for processes such as viral infection and fertilization. While membrane tension is known to influence crucial cell remodeling processes, its role in regulating membrane heterogeneous organization remains unclear. To reveal the effect of tension on lateral membrane organization, we used supported lipid bilayers on flexible substrates. These were prepared by rupturing ternary-composition giant unilamellar vesicles exhibiting liquid order-disorder phase coexistence. The phase coexistence is observed using a fluorescent probe that preferentially partitions to the disordered phase. Using a motorized equibiaxial stretching device, we observed progressive homogenization of domain morphology with increasing strain up to a critical strain, beyond which the membrane remains uniform. We define an order parameter based on the relative concentration of the dye in the two phases, which is a proxy for the membrane lateral organization. Order parameter analysis revealed power-law scaling below the critical strain with an exponent {beta} = 1.0 {+/-} 0.3, consistent with an elastic theoretical model predicting {beta} = 1. The progressive broadening of the interfacial region width near the critical strain, and continuous transition to a homogeneous phase, is consistent with a second-order phase transition. These findings indicate that membrane tension may serve as a physical regulator of lateral lipid organization, with implications for how cells use mechanical forces to regulate their structure and function. Significance StatementCell membranes are fundamental structures serving as the interface between a cells interior and its external environment. Membrane tension regulates critical cellular processes, yet how it affects the essential heterogeneous organization of membrane domains remains controversial. We combine artificial supported membranes on flexible substrates with a motorized equibiaxial stretching device, to directly visualize domain morphology under controlled tension. We observed that stretching drives the membrane to become progressively more uniformly distributed until it appears homogeneous. This transformation is consistent with a second-order phase transition. These findings demonstrate that mechanical tension acts as a direct physical regulator of cell membrane structure and lateral lipid organization.