(267i) Wrinkled Myelin: Surface Wrinkling of Myelin Figures in Aqueous Solutions of Polymers

Lipids can self-assemble into a variety of complex structural morphologies, many of which are ubiquitous in nature. One of these metastable, non-equilibrium lipid assemblies is the class of cylindrical mesophases called myelin figures. Myelins are concentric, cylindrical tubules consisting of alternating layers of thousands of smectically ordered lipid bilayers and water. When hydrated, they comprise of closely spaced tubular protrusions at the lipid-water interface, on the micrometer scale. External stimuli can alter lipid packing and modulate the water layer to induce large-scale morphological transformations. We study how myelins respond to the presence of non-diffusible macromolecular solutes (osmolytes) in the aqueous milieu. Our initial findings suggest that the presence of the osmolytes in the surrounding water induces extended, periodic corrugations of well-defined wavelengths in the exposed myelin surfaces. We find that these structural changes occur because of the osmolytes’ compounding effects on osmotic stress and depletion forces. The osmotic stress partially dehydrates the myelins, producing a propagating axisymmetric undulatory instability responsible for the appearance of the wrinkled surface profile. Depletion forces maximize the solute entropy by bundling the neighboring myelins. These forces shape the myelins in macromolecularly crowded media, achieving a better understanding of the structural formation and on-command control of myelin figures.

Lipids can self-assemble into a variety of complex structural morphologies, many of which are ubiquitous in nature. One of these metastable, non-equilibrium lipid assemblies is the class of cylindrical mesophases called myelin figures. Myelins are concentric, cylindrical tubules consisting of alternating layers of thousands of smectically ordered lipid bilayers and water. When hydrated, they comprise of closely spaced tubular protrusions at the lipid-water interface, on the micrometer scale. External stimuli can alter lipid packing and modulate the water layer to induce large-scale morphological transformations. We study how myelins respond to the presence of non-diffusible macromolecular solutes (osmolytes) in the aqueous milieu. Our initial findings suggest that the presence of the osmolytes in the surrounding water induces extended, periodic corrugations of well-defined wavelengths in the exposed myelin surfaces. We find that these structural changes occur because of the osmolytes’ compounding effects on osmotic stress and depletion forces. The osmotic stress partially dehydrates the myelins, producing a propagating axisymmetric undulatory instability responsible for the appearance of the wrinkled surface profile. Depletion forces maximize the solute entropy by bundling the neighboring myelins. These forces shape the myelins in macromolecularly crowded media, achieving a better understanding of the structural formation and on-command control of myelin figures.