Micropatterned model membrane with quantitatively controlled separation of lipid phases

Abstract

The localization of lipids and proteins in microdomains (lipid rafts) is believed to play important functional roles in the biological membrane. Herein, we report on a micropatterned model membrane that mimics lipid rafts by quantitatively controlling the spatial distribution of lipid phases. We generated a composite membrane of polymeric and fluid lipid bilayers by lithographic polymerization of diacetylene phospholipid(1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine: DiynePC). The composite membrane comprised polymer free-region (R₀), partially polymerized region (R₁), and fully polymerized region (R₂). As a ternary mixture of saturated lipid, unsaturated lipid, and cholesterol was introduced into the voids between polymeric bilayers, liquid-ordered (L_o) and liquid-disordered (L_d) lipid phases were accumulated in R₀ and R₁, respectively. Local enrichment of L_d phase in R₁ (and L_o phase in R₀) was enhanced with a heightened coverage of polymeric bilayer in R₁, supporting the premise that polymeric bilayer domains are inducing the phase separation. The pattern geometry (the area fractions of R₀ and R₁) also affected the enrichment due to the balance of gross L_o/L_d area fractions. Therefore, we could control the local L_o/L_d ratios by modulating the pattern geometry and polymer coverage in R₁. Micropatterned model membrane with quantitatively controlled distribution of L_o/L_d phases offers a new tool to study the functional roles of lipid rafts by enabling to separate membrane-bound molecules according to their affinities to L_o and L_d phases.