Marie-Alice Guedeau-Boudeville

Pearling Instabilities of Membrane Tubes with Anchored Polymers

We have studied the pearling instability induced on hollow tubular lipid vesicles by hydrophilic polymers with hydrophobic side groups along the backbone. The results show that the polymer concentration is coupled to local membrane curvature. The relaxation of a pearled tube is characterized by two different well-separated time scales, indicating two physical mechanisms. We present a model, which explains the observed phenomena and predicts polymer segregation according to local membrane curvature at late stages.

Coiling of Cylindrical Membrane Stacks with Anchored Polymers

(Received 22 April 1999) We study experimentally a coiling instability of cylindrical multilamellar stacks of phospholipid membranes, induced by polymers with hydrophobic anchors grafted along their hydrophilic backbone. We interpret our experimental results in terms of a model in which local membrane curvature and polymer concentration are coupled. The model predicts the occurrence of maximally tight coils above a threshold polymer concentration. Indeed, only maximally tight coils are observed experimentally. Our system is unique in that coils form in the absence of twist and adhesion. The coil motif is ubiquitous in a wide range of natural contexts. One-dimensional filaments of mutant bacteria [1], supercoiled DNA molecules [2], and tendrils of climbing plants [3] all exhibit a writhing instability as a result of forcing or interaction with an external agent. Such systems are dominated by elastic properties, and the appearance of coils is a result of the relief of twist. In this paper we show that coiling can also be effected in cylindrical multilamellar tubes of phospholipid bilayers, by anchoring hydrophilic polymers with hydrophobic side groups grafted along the backbone. This system is unique in that, in contrast with the above examples, fluid membranes cannot support any twist. Yet coils are

Coiling instability of multilamellar membrane tubes with anchored polymers.

We study experimentally a coiling instability of cylindrical multilamellar stacks of phospholipid membranes, induced by polymers with hydrophobic anchors grafted along their hydrophilic backbone. Our system is unique in that coils form in the absence of both twist and adhesion. We interpret our experimental results in terms of a model in which local membrane curvature and polymer concentration are coupled. The model predicts the occurrence of maximally tight coils above a threshold polymer occupancy. A proper comparison between the model and experiment involved imaging of projections from simulated coiled tubes with maximal curvature and complicated torsions.

Structure and Thermorheology of Concentrated Pluronic Copolymer Micelles in the Presence of Laponite Particles

Small-angle neutron scattering and thermorheology techniques are used to investigate in detail the effect of laponite particles in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, block copolymers in the concentrated regime. At high polymer concentration or temperature, the micellar solutions exhibit a phase transition from fluid to crystal due to crowding of the micelles. The addition of laponite is found to disturb this phase transition. The adsorption of the copolymer unimers onto laponite in large amounts describes these findings. It is shown that the preferred adsorption of the copolymer chains results in a sufficient increase in free volume for the remaining micelles to yield the observed enhancement of the structural disorder.

Rheology and calorimetry of microtextured colloidal polycrystals with embedded laponite nanoparticles

We investigate the rheological properties of copolymer-nanoparticle aqueous solutions and their connection to the thermodynamic and structural behavior. The samples are formed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer micellar solutions with embedded anisotropic colloidal laponite nanoparticles. The concentrated micellar solutions exhibit a temperature induced phase transition from fluid to crystal. Addition of laponite nanoparticles is found to promote the formation of polycrystallized micellar micrograins, above the transition temperature, instead of a cubic monocrystal. This polycrystallization is associated with the confinement of the nanoparticles, which play the role of impurities, in interstices between the micrograins. The analysis and comparison of the experimental data show that the presence of nanoparticles above the transition temperature has the effect to gradually reduce storage modulus and the enthalpy needed to gel the same amount of copolymer co...

TEMPERATURE DEPENDENT MEMBRANE PHASE REORGANIZATION IN GIANT VESICLES

Abstract Giant unilamellar vesicles (GUV) from diacetylenic phospholipid, 1,2 bis (heptacosa-8,10-diynoyl)-sn-glycero-3-phosphocholine (DC6,15PC), have been prepared by applying electric field to the aqueous dispersion maintained above its chain melting transition temperature (Tm) of 58.9°C. Previous studies have shown that large vesicles (∼1 μm or greater diameter) of the diacetylenic lipid transform into the tubule morphology when the temperature of the dispersion medium is dropped below its Tm but these giant vesicles (200 μm diameter) are stable far below Tm. Then within a 2° temperature range at about 32°C (26° below Tm) the giant vesicles suddenly collapse, leaving oddly branched structures. Giant vesicles formed from the saturated lipid 1,2 distearoyl phosphatidylcholine, by contrast, remain intact as the temperature is lowered, eventually adhering to one another to form a gel.