Decoration of biomembrane with polymer may improve its physical properties, biocompatibility, and stability. In this study, we employ the inverted fluorescence microscopy to characterize the polylysine (PLL) induced shape transformation of the negatively charged giant unilamellar vesicles (GUVs) in low ionic medium. It is found that PLL may be adsorbed to the 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1, 2-dioleoyl-sn-glycero-3-phosphatidic acid (DOPA) binary mixture vesicles, resulting in the attachment between the membranes, the formation of the ropes, and rupture of the GUVs. The response of GUVs generally is enhanced with the increase of the negatively charged DOPA in the membranes. The experimental observations are concluded as follows. Firstly, for the PLL induced attachment of GUVs, the attachment area grows gradually with time. Secondly, ropes can only be found in relatively large GUVs. However, the hollow structure is not discernable from the fluorescence imaging. Thirdly, after the rupture of GUVs, some phase-separated-like highly fluorescence lipid domains form in the adjacent intact vesicles. Through careful discussion and analysis, we show that on the one hand, the positively charged PLL adheres to the negatively charged membrane surface, bridging the neighboring GUVs and drawing the originally electrical repulsive vesicles together. The contact zone between GUVs expands with the increasing adsorption of PLL in this area. And the local high fluorescence areas in the GUVs originate from the PLL induced membrane attachment as well. Some membrane segments from ruptured vesicles are adsorbed to the particular areas of GUV, forming a few lipid patch structures above the latter membrane. On the other hand, PLL is adsorbed to the membrane area enriched in the negatively charged DOPA, reversing the surface charge of the upper leaflet and deteriorating the stability of the lipid bilayer. The original equilibrium of the system is broken by the change of the electrical interaction between the neighboring lipid domains as well as the interaction between the domain and water-dispersed PLL. The lipid packing density and inter-lipid force are affected by the PLL adsorption. Lipid membranes have to bud to release the stress built in the spontaneous curvature incompatibility in the two leaflets. The system may become stable again after buds grown into rods with a certain length. All in all, this study deepens the understanding of the interaction mechanism between lipid membrane and oppositely charged polymer. The conclusions obtained will provide valuable reference for the further studies on the polymer-GUV application areas including drug delivery, control release, cell deformation, micro-volume reaction, and gene therapy.

Osmotic pressure can break the fluid balance between intracellular and extracellular solutions. In hypo-osmotic solution, water molecules, which transfer into the cell and burst, are driven by the concentrations difference of solute across the semi-permeable membrane. The complicated dynamic processes of the intermittent burst have been previously observed. However, the underlying physical mechanism has yet to be thoroughly explored and analyzed. Here, the intermittent release of inclusion in giant unilamellar vesicles was investigated quantitatively, applying the combination of experimental and theoretical methods in the hypo-osmotic medium. Experimentally, we adopted highly sensitive EMCCD to acquire intermittent dynamic images. Notably, the component of the vesicle phospholipids affected the stretch velocity, and the prepared solution of the vesicle adjusted the release time. Theoretically, we chose equations numerical simulations to quantify the dynamic process in phases and explored the influence of physical parameters such as bilayer permeability and solution viscosity on the process. It was concluded that the time taken to achieve the balance of giant unilamellar vesicles was highly dependent on the structure of the lipid molecular. The pore lifetime was strongly related with the internal solution environment of giant unilamellar vesicles. The vesicle prepared in viscous solution accessed visualized long-lived pore. Furthermore, the line tension was measured quantitatively by the release velocity of inclusion, which was in the same order of magnitude as the theoretical simulation. In all, the experimental values well matched the theoretical values. Our investigation clarified the physical regulatory mechanism of intermittent pore formation and inclusion release, which had an important reference for the development of novel technologies such as gene therapy based on transmembrane transport as well as controlled drug delivery based on liposomes.

Supported lipid bilayer (SLB) based biosensors have been applied in biomedical applications such as rapid detection of antigens and cytochromes. It is generally believed that SLB can be formed by the adsorption and spontaneous rupture of vesicles on substrate. Recent findings highlight the importance of investigating the adsorption and rupture of individual vesicles during the SLB formation. Here, we used total internal reflection fluorescence microscopy (TIRFM) to characterize the spatiotemporal kinetics of the front spreading at patch boundary. The mixture of labeled and unlabeled vesicles permitted us to identify individual vesicle or patch on the surface. TIRFM was employed to investigate the adsorption, rupture of vesicles, and spreading of the patch front. Using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and TIRFM characterizations, we found that the size of vesicles has a significant effect on the front spreading at the patch boundary. Quantification of the number of patches and patches area displays that smaller vesicles are more prone to the formation of patches. The front spreading at the patch boundary was followed using the average front growth velocity (<i>v</i>_<i>afv</i>), which indicates that the <i>v</i>_<i>afv</i> of 40 nm vesicles is one order of magnitude larger than that of the 112 nm vesicles. Both theoretical analysis and experimental observation show that the smaller vesicles can attain the higher concentration on the surface (<i>C</i>) and diffusivity in the medium. The global growth theoretical model (GGM) presents that, for the patches with same surface area and vesicle exposure time, the growth of the patch depends on <i>C</i> and the lipid loss percentage during the vesicle rupture. The calculated lipid loss of the smaller vesicles is slightly higher than that of the larger vesicles, while <i>C</i> plays a dominating role in deciding the disparity of the patch growth between the different vesicles. The study promotes the understanding of the growth mechanism of patches on the surface. It demonstates the critcial role of the supply of vesicles in this process and provides a enlightenment for the investigation of reassemble of lipids on nanoscale.