Polyhedral Vesicles Research Articles

Binding of curvature-inducing proteins onto biomembranes

In this paper, we review the theoretical analyses and simulations of the interactions between curvature-inducing proteins and biomembranes. Laterally isotropic proteins induce spherical budding, whereas anisotropic proteins such as Bin/Amphiphysin/Rvs (BAR) superfamily proteins, induce tubulation. Both types of proteins can sense the membrane curvature. We describe the theoretical analyzes of various transitions of protein binding accompanied by a change in various properties, such as the number of buds, the radius of membrane tubes, and the nematic order of anisotropic proteins. Moreover, we explain the membrane-mediated interactions and protein assembly. Many types of membrane shape transformations (spontaneous tubulation, formation of polyhedral vesicles, polygonal tubes, periodic bumps, network structures, etc.) have been demonstrated by coarse-grained simulations. Furthermore, traveling waves and turing patterns under the coupling of reaction-diffusion dynamics and membrane deformation are described.

Fabrication of pH/H2O2-responsive polyhedral oligomeric silsesquioxane self-assembled fluorescent vesicles for enhanced in vivo anti-tumor efficacy.

Aim: The rational design of a fluorescence imaging-guided, highly efficient multiresponsive delivery system is important for improving drug delivery efficiency. Materials and methods: Herein, pH/H2O2-responsive polyhedral oligomeric silsesquioxane (POSS) molecule functionalized 4-(phenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)amino)benzaldehyde (OTB) copolymer (PEG-POSS-OTB) was synthesized to encapsulate doxorubicin (DOX) for precise drug delivery. Results: The self-assembly fluorescent vesicles exhibited excellent pH/H2O2-responsive drug release properties under physiological conditions and efficient drug-targeting ability. In vitro, compared with the DOX group, PEG-POSS-OTB fluorescent vesicles exhibited improved drug delivery and reduced toxicity. Importantly, we performed a proof-of-concept study demonstrating that PEG-POSS-OTB fluorescent vesicles were a high-efficiency nanoassembly drug-delivery platform for improving drug delivery efficiency. In vivo studies demonstrated that PEG-POSS-OTB vesicles with enhanced stability could be used in targeted drug delivery and controlled intelligent release.

Shape Transformaiton of Biomembrane Induced by Banana-Shaped Protein Rods: Tubulation and Formation of Polyhedral Vesicles

In living cells, morphology of biomembranes is regulated by various proteins. Many of these proteins contain a banana-shaped binding module called BAR (Bin-Amphiphysin-Rvs) domain. We have studied how anisotropic spontaneous curvatures of banana-shaped protein rod induce effective interaction between the proteins and change membrane shapes by using implicit-solvent meshless membrane simulations [1-3].We found that the self-assembly of the rods is divided to two directional assemblies at the low rod density [1] and polyhedral vesicles and polygonal tubes are formed at the high density [2]. We also revealed that a small spontaneous curvature perpendicular to the rod can remarkably alter the tubulation dynamics at high rod density whereas minor effects are only obtained at low density [3]. A percolated network, which suppresses tubule protrusion, is intermediately formed for negative perpendicular curvatures.[1] Noguchi, H. (2014) EPL 108, 48001.[2] Noguchi, H. (2015) J. Chem. Phys. 143, 243109.[3] Noguchi, H. arXiv:1503.00973.

Formation of polyhedral vesicles and polygonal membrane tubes induced by banana-shaped proteins.

The shape transformations of fluid membranes induced by curved protein rods are studied using meshless membrane simulations. The rod assembly at low rod density induces a flat membrane tube and oblate vesicle. It is found that the polyhedral shapes are stabilized at high rod densities. The discrete shape transition between triangular and buckled discoidal tubes is obtained and their curvature energies are analyzed by a simple geometric model. For vesicles, triangular hosohedron and elliptic-disk shapes are formed in equilibrium, whereas tetrahedral and triangular prism shapes are obtained as metastable states.

Polyhedral vesicles with crystalline bilayers formed from catanionic surfactant mixtures of fluorocarbon and hydrocarbon amphiphiles

Salt-free catanionic mixtures of perfluorononanoic acid (C8F17COOH) and tetradecyltrimethylammonium hydroxide (TTAOH) in aqueous solution show rich and interesting self-assembly properties. With the addition of TTAOH to a C8F17COOH solution, a structural transition from polyhedral vesicles with crystalline bilayers to spherical vesicles with fluid bilayers was observed at room temperature, which was demonstrated by cryo- and FF-TEM observations, DSC and WAXS measurements. It is interesting that both uni-lamellar and multi-lamellar polyhedral vesicles were formed in these fluoro- and hydrocarbon catanionic surfactant mixtures. SAXS measurements were performed to determine the interlamellar spacing of the multi-lamellar polyhedral vesicles. The driving force for the formation of the polyhedral vesicles was the crystallization of the C8F17COO− – TTA+ ion pairs in the bilayers, which induced the excess anionic surfactants to be segregated and concentrated to produce the vertices of the polyhedral vesicles. Besides, the rheological results show that the rheological properties of the C8F17COOH/TTAOH system are greatly affected by the fluorocarbon chains due to their high rigidity and Krafft point. The solutions consisting of polyhedral vesicles have high viscoelasticity and high yield stress values while spherical vesicle solutions are not viscoelastic.

Periodic three-dimensional assemblies of polyhedral lipid vesicles

We theoretically study the structure of periodic bulk assemblies of identical lipid vesicles. In our model, each vesicle is represented as a convex polyhedron with flat faces, rounded edges, and rounded vertices. Each vesicle carries an elastic and an adhesion energy and in the limit of strong adhesion, the minimal-energy shape of cells minimizes the weighted total edge length. We calculate exactly the shape of the rounded edge and show that it can be well described by a cylindrical surface. By comparing several candidate space-filling polyhedra, we find that the oblate shapes are preferred over prolate shapes for all volume-to-surface ratios. We also study periodic assemblies of vesicles whose adhesion strength on lateral faces is different from that on basal or apical faces. The anisotropy needed to stabilize prolate shapes is determined and it is shown that, at any volume-to-surface ratio, the transition between oblate and prolate shapes is very sharp. The geometry of the model vesicle assemblies reproduces the shapes of cells in certain simple animal tissues.

Polyhedral non-ionic surfactant vesicles.

Large polyhedral (2-10 microns) non-ionic surfactant vesicles (niosomes) formed from mixtures of a hexadecyl diglycerol ether (C16G2), a cholesteryl poly-24-oxyethylene ether (solulan C24) and a low level of cholesterol are being investigated as slow-release systems for ophthalmic, subcutaneous or intramuscular administration. The phase-diagram of this three-component system has been constructed and these polyhedral vesicles are found to be in the gel (L beta) phase. Confocal laser-scanning microscopy was used to confirm the complex morphology of these vesicles. The thermo-responsive nature of release of entrapped carboxyfluorescein and nicotinamide adenine dinucleotide has been studied; release is increased with increase in temperature (37 degrees C) even though the polyhedral vesicles still maintain their polyhedral shape at this temperature. The results indicate that the thermo-responsive features of the niosomes are a result of reversible changes in bi-layer permeability caused by temperature-mediated alteration in the membrane-packing characteristics of the polyethoxylated cholesterol ether.

Isolated Fluid Polyhedral Vesicles

A fluorinated salt-free catanionic system leads to the formation of spherical vesicles that transform over time into polyhedral vesicles. This is the first example of isolated faceted vesicles with fluid bilayers.

Microtubules formed by capillary extrusion and fusion of surfactant vesicles

Polyhedral non-ionic surfactant vesicles formed from mixtures of polyoxyethylene-5-cetyl ether (C 16EO 5) or polyoxethylene-5-stearyl ether (C 18EO 5) with poly-24-oxyethylene cholesteryl ether (Solulan C24) and low amounts of cholesterol, when extruded from microcapillaries under pressure fuse to form multi-lamellar tubules up to about 80 μm in length. The diameter of the extruded tubules depends on the exit diameter of the capillaries used, in this paper generally around 1 μm. Under some circumstances, instead of linear tubules, the tubules form as concentric whorls which can be unraveled into their constituent tubules, indicating the strength of the systems. Vesicles can be formed within these tubular structures to act as a model for vesicular flow in elastic capillaries. Microparticles encapsulated with the primary polyhedral vesicles after extrusion are seen within the tubules, promising the possibility of a model for the study of microparticle flow within vessels. Preliminary studies on the use of the tubules as templates for polymerisation are also presented.

Polyhedral vesicles: a Brownian dynamics simulation.

Polyhedral vesicles with a large bending modulus of the membrane, such as a gel phase lipid membrane, were studied using a Brownian dynamics simulation. The vesicles exhibited various polyhedral morphologies such as tetrahedron and cube shapes. We clarified two types of line defects on the edges of the polyhedrons: cracks of both monolayers at the spontaneous curvature of the monolayer C0<0, and a crack of the inner monolayer at C0> or =0. The inner monolayer curved positively around the latter defect. Our results suggest that the polyhedral morphology is controlled by C0.

The effect of processing variables on the physical characteristics of non-ionic surfactant vesicles (niosomes) formed from a hexadecyl diglycerol ether

Niosomes are vesicles formed by self-assembly of non-ionic surfactants. In this investigation, the effects of processing variables, particularly temperature and sonication, on the physical characteristics and phase transitional behaviour of two niosomal systems based on a hexadecyl diglycerol ether (C 16G 2) have been studied. Systems containing C 16G 2, cholesterol and poly-24-oxyethylene cholesteryl ether (Solulan C24) in the molar ratios 91:0:9 and 49:49:2 were prepared by aqueous dispersion of films, followed by examination of 5(6)-carboxyfluorescein entrapment, particle size and morphology. The thermal behaviour was examined using high sensitivity differential scanning calorimetry (HSDSC) and hot stage microscopy, while the effects of sonication were studied in terms of size and morphology, both immediately after preparation and on storing for 1 h at room temperature and 60°C. Polyhedral niosomes were formed from systems containing C 16G 2 and Solulan C24 alone, while cholesterol-containing systems formed spherical vesicles mixed with tubular structures; the polyhedral systems were found to have a larger particle size and higher CF entrapment efficiency. HSDSC studies showed the polyhedral systems to exhibit an endotherm at 45.4°C and a corresponding exotherm at 39.1°C on cooling which were ascribed to a membrane phase transition; no equivalent transition was observed for the cholesterol containing systems. Hot stage microscopy showed the polyhedral vesicles to convert to spherical structures at ∼48°C, while on cooling the spherical vesicles split into smaller structures and reverted to the polyhedral shape at ∼49°C. Sonication resulted in the polyhedral vesicles forming spherical structures which underwent a particle size increase on storage at room temperature but not at 60°C. The study suggests that the polyhedral vesicles undergo a reversible transition to spherical vesicles on heating or sonication and that this morphological change may be associated with a membrane phase transition.