Switchable positioning of plate-like inclusions in lipid membranes: Elastically mediated interactions of planar colloids in 2D fluids

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Science Advances  02 Apr 2021:
Vol. 7, no. 14, eabf1943
DOI: 10.1126/sciadv.abf1943
  • Fig. 1 A giant unilamellar vesicle containing two phospholipids, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), in a molar ratio of 70/30 and containing a single solid domain.

    The vesicle, suspended in a glucose solution, is imaged in a side view with the solid domain on the left side, making that part of the shape flat. (A) Fluorescence confocal micrograph. (B) Bright field image. (C and D) Schematics at slightly different angles.

  • Fig. 2 Images of vesicles composed of DOPC and DPPC imaged at different focal planes: Equatorial, top, and bottom.

    The second equatorial view is annotated to highlight the curvature in the fluid membrane contour. Solid domains appear dark due to exclusion of a tracer. The three different vesicles, in (A) to (C), are increasingly inflated.

  • Fig. 3 Domain separations are fundamentally stable in time but can be increased or decreased through changes in the excess area.

    (A) Domain separations for four example vesicles with different excess areas. Images for the free vesicles are presented along with images for each vesicle after aspiration, showing differences in excess area and positioning in micropipette. Dv for each vesicle was determined on the basis of the membrane area measured during micropipette aspiration. (B) Example images of the four vesicles from (A), focusing on the domain edges, with a solid line denoting the chosen direction of closest edge-edge separation and dashed lines highlighting alternatives that appear further separated but still measured within no more than a micrometer of the path along the solid line. (C) Normalized and dimensional domain separation in time, as a result of the injection of a drop of DI water near 220 s. Near 60 s, the disturbance in domain separation results from introduction of micropipette nearby but soon recovers. Dv (estimate) = 18.8 μm. (D) Normalized and dimensional domain separation in time as a result of injecting a drop of concentrated glucose solution near 105 s. Dv (estimate) = 10.9 μm. Error bars are the size of the points themselves, with sample error bars on select points at 35, 199, and 350 s in (C) and at 55 and 250 s in (D). Domain separations, when normalized, are divided by Dv.

  • Fig. 4 Measured dependence of spacing between domain edges, normalized on the diameter of an equivalent spherical vesicle.

    Main plot is for free vesicles, while inset shows data, also normalized domain spacing as a function of excess area, obtained for vesicles held at low suction in a micropipette, reducing the excess membrane area and increasing the domain size relative to the spherical part of the vesicle outside the micropipette. Typical error shown: Larger error occurs when domains are on opposite sides of vesicle, requiring imaging top and bottom focal views sequentially. Roman numerals refer to the four vesicles highlighted in Fig. 3A. Gray stars around points indicate a modest indentation in one or both domains of the nature illustrated in Fig. 3Biv.

  • Fig. 5 2D model of domain energetics of fluid-solid composite vesicle.

    (A) Comparison of exact equilibria of the 2D Helfrich energy (colored curves) overlayed on the multi-arc ansatz (gray), as a function of decreasing inflation (1 to 5 correspond to configurations shown in fig. S5 for solid domain fraction 0.2). Fluid domains are colored according to local curvature, with the red/blue color scale of the fluid domain indicating regions of maximal/minimal curvature. (B) Plot of scale energy versus arc separation between solid domains for 0.24 solid fraction and variable excess length. Minima of curves correspond to equilibrium separations, which are plotted in (C) for a range of solid fractions as functions of excess length. (D) Equilibrium configurations for i to vi for 0.24 solid fraction, with fluid portions shown as pink curves and solid domains shown as straight black sections. (E) Schematic highlighting the distribution of fluid bending in separated versus proximal solid domain configurations, with coloring as in (A).

Supplementary Materials

  • Supplementary Materials

    Switchable positioning of plate-like inclusions in lipid membranes: Elastically mediated interactions of planar colloids in 2D fluids

    Weiyue Xin, Hao Wu, Gregory M. Grason, Maria M. Santore

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    • Figs. S1 to S5
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