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Building upon our previous studies on interactions of amphiphilic Janus nanoparticles with glass-supported lipid bilayers, we study here how these Janus nanoparticles perturb the structural integrity and induce shape instabilities of membranes of giant unilamellar vesicles (GUVs). We show that 100 nm amphiphilic Janus nanoparticles disrupt GUV membranes at a threshold particle concentration similar to that in supported lipid bilayers, but cause drastically different membrane deformations, including membrane wrinkling, protrusion, poration, and even collapse of entire vesicles. By combining experiments with molecular simulations, we reveal how Janus nanoparticles alter local membrane curvature and collectively compress the membrane to induce shape transformation of vesicles. Our study demonstrates that amphiphilic Janus nanoparticles disrupt vesicle membranes differently and more effectively than uniform amphiphilic particles. 

In this study, we report the complex effects of charged lipids on the interaction between amphiphilic Janus nanoparticles and lipid bilayers. Janus nanoparticles are cationic on one hemisphere and hydrophobic on the other. We show that the nanoparticles, beyond threshold concentrations, induce holes in both cationic and anionic lipid bilayers mainly driven by hydrophobic interactions. However, the formation of these defects is non-monotonically dependent on ionic lipid composition. The electrostatic attraction between the particles and anionic lipid bilayers enhances particle adsorption and lowers the particle concentration threshold for defect initiation, but leads to more localized membrane disruption. Electrostatic repulsion leads to reduced particle adsorption on cationic bilayers and extensive defect formation that peaks at intermediate contents of cationic lipids. This study elucidates the significant role lipid composition plays in influencing how amphiphilic Janus nanoparticles interact with and perturb lipid membranes. 

Self-assembled lipid tubules are unique supramolecular structures in cell functions. Lipid tubules that are engineered in vitro are of great interest for technological applications ranging from the templated synthesis of nanomaterials to drug delivery. Herein, we report a study to create long lipid tubules from a mono-unsaturated lipid, 1-stearoyl-2-oleoyl- sn-glycero -3-phosphocholine (SOPC), due to the effect of calcium ions. We found that calcium ions at mM concentrations promote the self-assembly of SOPC lipids into inter-connected hollow lipid tubes that are μm thick and as long as a few millimeters. Higher calcium concentration leads to an increase in the numbers of lipid tubules formed, but has little effect on tubule diameter. Calcium ions also stabilize lipid tubules, which break up upon the removal of ions. We showed that the lipid tubule-promoting effect is general for divalent ions. We were able to vary the morphology of lipid tubules from thin tube to “strings of pearls” structures or increase the tubule thickness by mixing SOPC with other lipids of different spontaneous curvature effects. Our results reveal that the divalent charges of calcium ions and the asymmetric mono-unsaturated structure of SOPC acyl chains act in combination to cause the formation of lipid tubules.