Protein Driven Patterning of Self-Assembled Cubosomic Nanostructures: Long Oriented Nanoridges

Cubosome-carrying bacterial cellulose membrane as a versatile drug delivery platform

Using advanced nanotechnology membranes has opened up new possibilities in the field of biomedicine, particularly for controlled drug delivery and especially for topical use. Bacterial cellulose membranes (BCM), particularly, have gained prominence owing to their distinctive attributes, including remarkable water retention, safety, biodegradability, and tunable gas exchange. However, they are aqueous matrices and, for this reason, of limited capacity for incorporation of apolar compounds. Cubosomes are lipid nanoparticles composed of a surfactant bicontinuous reverse cubic phase, which, owing to their bicontinuous structure, can incorporate both polar and apolar compounds. Therefore, these particles present a promising avenue for encapsulating and releasing drugs and biomolecules due to their superior entrapment efficiency. In this study, we aim to extend earlier investigations using polymeric hydrogels for cubosome immobilization, now using BCMs, a more resilient biocompatible matrix. Phytantriol cubosome-loaded BCMs were prepared by three distinct protocols: ex situ incorporation into wet BCMs, ex situ incorporation by swelling of dry BCMs, and an in situ process with the growth of BCMs in a sterile medium already containing cubosomes. Our investigation revealed that these methodologies ensured that cubosomes remained integral, uniformly distributed, and thoroughly dispersed within the membrane, as confirmed using Small-Angle X-ray Scattering (SAXS) and high-resolution confocal microscopy. The effective incorporation and sustained release of diclofenac were validated across the different BCMs and compared with hyaluronic acid (HA) hydrogel in our previous studies. Furthermore, the resistance against cubosome leaching from the three BCM and HA hydrogel samples was quantitatively evaluated and contrasted. We hope that the outcomes from this research will pave the way for innovative use of this platform in the incorporation and controlled release of varied active agents, amplifying the already multifaceted applicability of BCMs.

Cubosome-based cosmeceuticals: a breakthrough in skincare

Nanotechnology in skin cosmetics has revolutionized robust skincare formulations, enabling the delivery of therapeutic agents to achieve the effective concentration at the targeted site of action. Lyotropic liquid crystals (LLCs) are emerging as a potential nanoparticle delivery system owing to their biocompatible and biodegradable nature. Within the space of LLCs, the structural and functional relationships of cubosomal characteristics are investigated as drug delivery vehicles for a potential application in skincare. The objective of this review is to describe the structure, preparation methods and the potential application of cubosomes for the successful delivery of cosmetic agents.

Freeze-Fracture Electron Microscopy on Domains in Lipid Mono- and Bilayer on Nano-Resolution Scale

Freeze-fracture electron microscopy (FFEM) as a cryofixation, replica, and transmission electron microscopy technique is unique in membrane bilayer and lipid monolayer research because it enables us to excess and visualize pattern such as domains in the hydrophobic center of lipid bilayer as well as the lipid/gas interface of lipid monolayer. Since one of the preparation steps of this technique includes fracturing the frozen sample and since during this fracturing process the fracture plane follows the area of weakest forces, these areas are exposed allowing us to explore pattern built up by lipids and/or intrinsic proteins but also initiated by peptides, drugs, and toxins reaching into these normally hard to access areas. Furthermore, FFEM as a replica technique is applicable to objects of a large size range and combines detailed imaging of fine structures down to nano-resolution scale within images of larger biological or artificial objects up to several tens of micrometers in size.Biological membranes consist of a multitude of components which can self-organize into rafts or domains within the fluid bilayer characterized by lateral inhomogeneities in chemical composition and/or physical properties. These domains seem to play important roles in signal transduction and membrane traffic. Furthermore, lipid domains are important in health and disease and make an interesting target for pharmacological approaches in cure and prevention of diseases such as Alzheimer, Parkinson, cardiovascular and prion diseases, systemic lupus erythematosus, and HIV. As a cryofixation technique, FFEM is a very powerful tool to capture such domains in a probe-free mode and explore their dynamics on a nano-resolution scale.

Advances in structural design of lipid-based nanoparticle carriers for delivery of macromolecular drugs, phytochemicals and anti-tumor agents

The present work highlights recent achievements in development of nanostructured dispersions and biocolloids for drug delivery applications. We emphasize the key role of biological small-angle X-ray scattering (BioSAXS) investigations for the nanomedicine design. A focus is given on controlled encapsulation of small molecular weight phytochemical drugs in lipid-based nanocarriers as well as on encapsulation of macromolecular siRNA, plasmid DNA, peptide and protein pharmaceuticals in nanostructured nanoparticles that may provide efficient intracellular delivery and triggered drug release. Selected examples of utilisation of the BioSAXS method for characterization of various types of liquid crystalline nanoorganizations (liposome, spongosome, cubosome, hexosome, and nanostructured lipid carriers) are discussed in view of the successful encapsulation and protection of phytochemicals and therapeutic biomolecules in the hydrophobic or the hydrophilic compartments of the nanocarriers. We conclude that the structural design of the nanoparticulate carriers is of crucial importance for the therapeutic outcome and the triggered drug release from biocolloids.

Self-assembled stable sponge-type nanocarries for Brucea javanica oil delivery

Sponge-type nanocarriers (spongosomes) are produced upon dispersion of a liquid crystalline sponge phase formed by self-assembly of an amphiphilic lipid in excess aqueous phase. The inner organization of the spongosomes is built-up by randomly ordered bicontinuous lipid membranes and their surfaces are stabilized by alginate chains providing stealth properties and colloidal stability. The present study elaborates spongosomes for improved encapsulation of Brucea javanica oil (BJO), a traditional Chinese medicine that may strongly inhibit proliferation and metastasis of various cancers. The inner structural organization and the morphology characteristics of BJO-loaded nanocarriers at varying quantities of BJO were determined by cryogenic transmission electron microscopy (Cryo-TEM), small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Additionally, the drug loading and drug release profiles for BJO-loaded spongosome systems also were determined. We found that the sponge-type liquid crystalline lipid membrane organization provides encapsulation efficiency rate of BJO as high as 90%. In vitro cytotoxicity and apoptosis study of BJO spongosome nanoparticles with A549 cells demonstrated enhanced anti-tumor efficiency. These results suggest potential clinical applications of the obtained safe spongosome formulations.

In Vitro Modulation of TrkB Receptor Signaling upon Sequential Delivery of Curcumin-DHA Loaded Carriers Towards Promoting Neuronal Survival

PURPOSE

To in vitro investigate the capacity of carrier-free and lipid-nanoparticle (NP)-encapsulated phytochemical compounds to prevent neuronal damage through neurotrophin potentiating activities. Delivery of molecules promoting the neurotrophin receptor signaling in the central nervous system (CNS) present ongoing interest for combination therapy development.

METHODS

Super-resolution Stimulated Emission Depletion (STED) microscopy imaging and flow cytometry analysis were employed to study the expression of the neurotrophin TrkB receptor in a neuronal cell model, which is highly responsive to binding of brain-derived neurotrophic factor (BDNF). Dual drug-loaded nanoparticle formulations, prepared by self-assembly of lyotropic lipids and PEGylated amphiphile derivatives, were delivered to differentiated human neuroblastoma SH-SY5Y cells subjected to degenerative conditions.

RESULTS

The expression of BDNF in the intra and extracellular domains was quantified by ELISA and flow cytometry after sequential treatment of the degenerating SH-SY5Y cells by neurotherapeutic formulations. Flow cytometry was also used to assess the phosphorylation of the transcription factor cAMP response element-binding protein (CREB) in the intracellular domain as a result of the treatment by nanoformulations.

CONCLUSION

Over time, dual drug formulations (curcumin and docosahexaenoic acid (DHA)) promoted the neuronal survival and repair processes through enhanced BDNF secretion and increased phosphorylation of CREB as compared to untreated degenerating cells.

Mesoporous self-assembled nanoparticles of biotransesterified cyclodextrins and nonlamellar lipids as carriers of water-insoluble substances

Soft mesoporous hierarchically structured particles were created by the self-assembly of an amphiphilic deep cavitand cyclodextrin βCD-nC₁₀ (degree of substitution n = 7.3), with a nanocavity grafted by multiple alkyl (C₁₀) chains on the secondary face of the βCD macrocycle through enzymatic biotransesterification, and the nonlamellar lipid monoolein (MO). The effect of the non-ionic dispersing agent polysorbate 80 (P80) on the liquid crystalline organization of the nanocarriers and their stability was studied in the context of vesicle-to-cubosome transition. The coexistence of small vesicular and nanosponge membrane objects with bigger nanoparticles with inner multicompartment cubic lattice structures was established as a typical feature of the employed dispersion process. The cryogenic transmission electron microscopy (cryo-TEM) images and small-angle X-ray scattering (SAXS) structural analyses revealed the dependence of the internal organization of the self-assembled nanoparticles on the presence of embedded βCD-nC₁₀ deep cavitands in the lipid bilayers. The obtained results indicated that the incorporated amphiphilic βCD-nC₁₀ building blocks stabilize the cubic lattice packing in the lipid membrane particles, which displayed structural features beyond the traditional CD nanosponges. UV-Vis spectroscopy was employed to characterize the nanoencapsulation of a model hydrophobic dimethylphenylazo-naphthol guest compound (Oil red) in the created nanocarriers. In perspective, these dual porosity carriers should be suitable for co-encapsulation and sustained delivery of peptide, protein or siRNA biopharmaceuticals together with small molecular weight drug compounds or imaging agents.

Cubosome Topologies at Various Particle Sizes and Crystallographic Symmetries

The nanoparticles built of bicontinuos lyotropic phases of cubic symmetry are studied within the framework of the Landau-Brazovskii functional that correctly predicts the structure of soft monocrystals and thin films of bicontinuos lyotropic phases. A detailed description of the geometry and topology of cubosomes is presented. This level of description of the internal structure of cubosomes is not easily accessible by experimental techniques. I show that the internal structure of the cubosomes may be extremely rich.

Identification of large channels in cationic PEGylated cubosome nanoparticles by synchrotron radiation SAXS and Cryo-TEM imaging

Extra-large nanochannel formation in the internal structure of cationic cubosome nanoparticles results from the interplay between charge repulsion and steric stabilization of the lipid membrane interfaces and is evidenced by cryogenic transmission electron microscopy (Cryo-TEM) and synchrotron radiation small-angle X-ray scattering (SAXS). The swollen cubic symmetry of the lipid nanoparticles emerges through a shaping transition of onion bilayer vesicle intermediates containing a fusogenic nonlamellar lipid. Cationic amphiphile cubosome particles, thanks to the advantages of their liquid crystalline soft porous nanoarchitecture and capability for multi-drug nanoencapsulation, appear to be of interest for the design of mitochondrial targeting devices in anti-cancer therapies and as siRNA nanocarriers for gene silencing.

Sterically stabilized spongosomes for multidrug delivery of anticancer nanomedicines

SAXS patterns of drug-loaded lipid nanocarriers stabilized by polysorbate P80 (left); cryo-TEM image of BAI-BJO-spongosomes-2 (right).

Neurotrophin delivery using nanotechnology

Deficits or overexpression of neurotrophins cause neurodegenerative diseases and psychiatric disorders. These proteins are required for the maintenance of the function, plasticity and survival of neurons in the central (CNS) and peripheral nervous systems. Significant efforts have been devoted to developing therapeutic delivery systems that enable control of neurotrophin dosage in the brain. Here, we suggest that nanoparticulate carriers favoring targeted delivery in specific brain areas and minimizing biodistribution to the systemic circulation should be developed toward clinical benefits of neuroregeneration. We also provide examples of improved targeted neurotrophin delivery to localized areas in the CNS.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Earliest stage of the tetrahedral nanochannel formation in cubosome particles from unilamellar nanovesicles

Studies of nonequilibrium lipid polymorphism at the nanoscale contribute to the in-depth understanding of the structural pathways for formation of aqueous channels and emerging of channels-network ordering in liquid-crystalline (LC) nanovehicles. We present experimental structural evidence for the smallest tetrahedral-type lipid membrane aggregate, which involves completely formed nanochannels and occurs as an early intermediate state during the bilayer vesicle-to-cubosome particle transition. Nanovehicles are generated from a self-assembled lipid mixture and studied by means of high-resolution cryogenic transmission electron microscopy (cryo-TEM) and synchrotron radiation small-angle X-ray scattering (SAXS). The investigated lipid membrane composition allows for the stabilization of long-lived intermediates throughout the unilamellar vesicle-to-cubosome nanoparticle (NP) transformation at ambient temperature. The observed small cubosomic particles, with well-defined water channels, appear to be precursors of larger cubic membrane structures, thus confirming the theoretical modeling of nanochannel-network growth in diamond-type cubic lipid particles. The reported structural findings, highlighting that bilayer vesicle membrane packing and fusion are required for nanochanneled cubosome particle formation, are anticipated to advance the engineering of small lipid NPs with controllable channels for biomolecular loading and release.

Characterization of oil-free and oil-loaded liquid-crystalline particles stabilized by negatively charged stabilizer citrem

The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H(2)) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid-water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H(2) phase in hexosomes and the hydrophilic core of the L(2) phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs.

Small-Angle X-ray Scattering Investigations of Biomolecular Confinement, Loading, and Release from Liquid-Crystalline Nanochannel Assemblies

This Perspective explores the recent progress made by means of small-angle scattering methods in structural studies of phase transitions in amphiphilic liquid-crystalline systems with nanochannel architectures and outlines some future directions in the area of hierarchically organized and stimuli-responsive nanochanneled assemblies involving biomolecules. Time-resolved small-angle X-ray scattering investigations using synchrotron radiation enable monitoring of the structural dynamics, the modulation of the nanochannel hydration, as well as the key changes in the soft matter liquid-crystalline organization upon stimuli-induced phase transitions. They permit establishing of the inner nanostructure transformation kinetics and determination of the precise sizes of the hydrophobic membraneous compartments and the aqueous channel diameters in self-assembled network architectures. Time-resolved structural studies accelerate novel biomedical, pharmaceutical, and nanotechnology applications of nanochannel soft materials by providing better control of DNA, peptide and protein nanoconfinement, and release from diverse stimuli-responsive nanocarrier systems.

Phase behavior of lipid-based lyotropic liquid crystals in presence of colloidal nanoparticles

We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.

Self-assembled multicompartment liquid crystalline lipid carriers for protein, peptide, and nucleic acid drug delivery

Lipids and lipopolymers self-assembled into biocompatible nano- and mesostructured functional materials offer many potential applications in medicine and diagnostics. In this Account, we demonstrate how high-resolution structural investigations of bicontinuous cubic templates made from lyotropic thermosensitive liquid-crystalline (LC) materials have initiated the development of innovative lipidopolymeric self-assembled nanocarriers. Such structures have tunable nanochannel sizes, morphologies, and hierarchical inner organizations and provide potential vehicles for the predictable loading and release of therapeutic proteins, peptides, or nucleic acids. This Account shows that structural studies of swelling of bicontinuous cubic lipid/water phases are essential for overcoming the nanoscale constraints for encapsulation of large therapeutic molecules in multicompartment lipid carriers. For the systems described here, we have employed time-resolved small-angle X-ray scattering (SAXS) and high-resolution freeze-fracture electronic microscopy (FF-EM) to study the morphology and the dynamic topological transitions of these nanostructured multicomponent amphiphilic assemblies. Quasi-elastic light scattering and circular dichroism spectroscopy can provide additional information at the nanoscale about the behavior of lipid/protein self-assemblies under conditions that approximate physiological hydration. We wanted to generalize these findings to control the stability and the hydration of the water nanochannels in liquid-crystalline lipid nanovehicles and confine therapeutic biomolecules within these structures. Therefore we analyzed the influence of amphiphilic and soluble additives (e.g. poly(ethylene glycol)monooleate (MO-PEG), octyl glucoside (OG), proteins) on the nanochannels' size in a diamond (D)-type bicontinuous cubic phase of the lipid glycerol monooleate (MO). At body temperature, we can stabilize long-living swollen states, corresponding to a diamond cubic phase with large water channels. Time-resolved X-ray diffraction (XRD) scans allowed us to detect metastable intermediate and coexisting structures and monitor the temperature-induced phase sequences of mixed systems containing glycerol monooleate, a soluble protein macromolecule, and an interfacial curvature modulating agent. These observed states correspond to the stages of the growth of the nanofluidic channel network. With the application of a thermal stimulus, the system becomes progressively more ordered into a double-diamond cubic lattice formed by a bicontinuous lipid membrane. High-resolution freeze-fracture electronic microscopy indicates that nanodomains are induced by the inclusion of proteins into nanopockets of the supramolecular cubosomic assemblies. These results contribute to the understanding of the structure and dynamics of functionalized self-assembled lipid nanosystems during stimuli-triggered LC phase transformations.

Freeze-fracture electron microscopy on domains in lipid mono- and bilayer on nano-resolution scale

Freeze-fracture electron microscopy (FFEM) as a cryo-fixation, replica, and transmission electron microscopy technique is unique in membrane bilayer and lipid monolayer research because it enables us, to excess and visualize pattern such as domains in the hydrophobic center of lipid bilayer as well as the lipid/gas interface of the lipid monolayer. Since one of the preparatory steps of this technique includes fracturing the frozen sample and, since during this fracturing process the fracture plane follows the area of weakest forces, these areas are exposed allowing us to explore the pattern built up by lipids and/or intrinsic proteins and which are also initiated by peptides, drugs, and toxins reaching into these normally hard to access areas. Furthermore, FFEM as a replica technique is applicable to objects of a large size range and combines detailed imaging of fine structures down to nano-resolution scale within images of larger biological or artificial objects up to several ten's of micrometers in size.Biological membranes consist of a multitude of components which can self-organize into rafts or domains within the fluid bilayer characterized by lateral inhomogeneities in chemical composition and/or physical properties. These domains seem to play important roles in signal transduction and membrane traffic. Furthermore, lipid domains are important in health and disease and make an interesting target for pharmacological approaches in cure and prevention of diseases such as Alzheimer, Parkinson, cardiovascular and prion diseases, systemic lupus erythematosus and HIV. As a cryofixation technique FFEM is a very powerful tool to capture such domains in a probe-free mode and explore their dynamics on a nano-resolution scale.

Long-living intermediates during a lamellar to a diamond-cubic lipid phase transition: a small-angle X-ray scattering investigation

To generate nanostructured vehicles with tunable internal organization, the structural phase behavior of a self-assembled amphiphilic mixture involving poly(ethylene glycol) monooleate (MO-PEG) and glycerol monooleate (MO) is studied in excess aqueous medium by time-resolved small-angle X-ray scattering (SAXS) in the temperature range from 1 to 68 degrees C. The SAXS data indicate miscibility of the two components in lamellar and nonlamellar soft-matter nanostructures. The functionalization of the MO assemblies by a MO-PEG amphiphile, which has a flexible large hydrophilic moiety, appears to hinder the epitaxial growth of a double diamond (D) cubic lattice from the lamellar (L) bilayer structure during the thermal phase transition. The incorporated MO-PEG additive is found to facilitate the formation of structural intermediates. They exhibit greater characteristic spacings and large diffusive scattering in broad temperature and time intervals. Their features are compared with those of swollen long-living intermediates in MO/octylglucoside assemblies. A conclusion can be drawn that long-living intermediate states can be equilibrium stabilized in two- or multicomponent amphiphilic systems. Their role as cubic phase precursors is to smooth the structural distortions arising from curvature mismatch between flat and curved regions. The considered MO-PEG functionalized assemblies may be useful for preparation of sterically stabilized liquid-crystalline nanovehicles for confinement of therapeutic biomolecules.

Characterization and potential applications of nanostructured aqueous dispersions

The present article highlights recent advances and current status in the characterization and the utilization of nanostructured aqueous dispersions in which the submicron-sized dispersed particles envelope a distinctive well-defined self-assembled interior. The scope of this review covers dispersions of both inverted-type liquid-crystalline particles (cubosomes, hexosomes, micellar cubosomes, and sponge phases), and microemulsion droplets (emulsified microemulsions, EMEs). Recent investigations that have attempted to shed light on the characterization and the control of confined nanostructures of aqueous dispersions are surveyed, as these nanoobjects are attractive for various pharmaceutical and food applications. The focus has been placed on three main subjects: (1) our findings on the formation of EMEs and the modulation of the internal nanostructure, exploring how variations in temperature, oil content, and lipid composition significantly affect the confined nanostructures; (2) recent developments in the field of electron microscopy: using the tilt-angle cryo-TEM method or cryo-field emission scanning electron microscopy (cryo-FESEM) for observing the three dimensional (3D) morphology of non-lamellar liquid-crystalline nanostructured particles (cubosome and hexosome particles); and (3) recent studies on the utilization of nanostructured dispersions as drug nanocarriers.

Self-assembly in monoelaidin aqueous dispersions: direct vesicles to cubosomes transition

BACKGROUND

In the present study, synchrotron small-angle X-ray scattering (SAXS) and Cryo-TEM were used to characterize the temperature-induced structural transitions of monoelaidin (ME) aqueous dispersion in the presence of the polymeric stabilizer F127. We prove that the direct transition from vesicles to cubosomes by heating this dispersion is possible. The obtained results were compared with the fully hydrated bulk ME phase.

METHODOLOGY/PRINCIPAL FINDINGS

Our results indicate the formation of ME dispersion, which is less stable than that based on the congener monoolein (MO). In addition, the temperature-dependence behavior significantly differs from the fully hydrated bulk phase. SAXS findings indicate a direct L(alpha)-V(2) internal transition in the dispersion. While the transition temperature is conserved in the dispersion, the formed cubosomes with internal Im3m symmetry clearly contain more water and this ordered interior is retained over a wider temperature range as compared to its fully hydrated bulk system. At 25 degrees C, Cryo-TEM observations reveal the formation of most likely closely packed onion-like vesicles. Above the lamellar to non-lamellar phase transition at 65 degrees C, flattened cubosomes with an internal nanostructure are observed. However, they have only arbitrary shapes and thus, their morphology is significantly different from that of the well-shaped analogous MO cubosome and hexosome particles.

CONCLUSIONS/SIGNIFICANCE

Our study reveals a direct liposomes-cubosomes transition in ME dispersion. The obtained results suggest that the polymeric stabilizer F127 especially plays a significant role in the membrane fusion processes. F127 incorporates in considerable amount into the internal nanostructure and leads to the formation of a highly swollen Im3m phase.

Calcium triggered L alpha-H2 phase transition monitored by combined rapid mixing and time-resolved synchrotron SAXS

Background

Awad et al. [1] reported on the Ca²⁺-induced transitions of dioleoyl-phosphatidylglycerol (DOPG)/monoolein (MO) vesicles to bicontinuous cubic phases at equilibrium conditions. In the present study, the combination of rapid mixing and time-resolved synchrotron small-angle X-ray scattering (SAXS) was applied for the in-situ investigations of fast structural transitions of diluted DOPG/MO vesicles into well-ordered nanostructures by the addition of low concentrated Ca²⁺ solutions.

Methodology/Principal Findings

Under static conditions and the in absence of the divalent cations, the DOPG/MO system forms large vesicles composed of weakly correlated bilayers with a d-spacing of ∼140 Å (L_α-phase). The utilization of a stopped-flow apparatus allowed mixing these DOPG/MO vesicles with a solution of Ca²⁺ ions within 10 milliseconds (ms). In such a way the dynamics of negatively charged PG to divalent cation interactions, and the kinetics of the induced structural transitions were studied. Ca²⁺ ions have a very strong impact on the lipidic nanostructures. Intriguingly, already at low salt concentrations (DOPG/Ca²⁺>2), Ca²⁺ ions trigger the transformation from bilayers to monolayer nanotubes (inverted hexagonal phase, H₂). Our results reveal that a binding ratio of 1 Ca²⁺ per 8 DOPG is sufficient for the formation of the H₂ phase. At 50°C a direct transition from the vesicles to the H₂ phase was observed, whereas at ambient temperature (20°C) a short lived intermediate phase (possibly the cubic Pn3m phase) coexisting with the H₂ phase was detected.

Conclusions/Significance

The strong binding of the divalent cations to the negatively charged DOPG molecules enhances the negative spontaneous curvature of the monolayers and causes a rapid collapsing of the vesicles. The rapid loss of the bilayer stability and the reorganization of the lipid molecules within ms support the argument that the transition mechanism is based on a leaky fusion of the vesicles.

Tuning curvature and stability of monoolein bilayers by designer lipid-like peptide surfactants

This study reports the effect of loading four different charged designer lipid-like short anionic and cationic peptide surfactants on the fully hydrated monoolein (MO)-based Pn3m phase (Q(224)). The studied peptide surfactants comprise seven amino acid residues, namely A(6)D, DA(6), A(6)K, and KA(6). D (aspartic acid) bears two negative charges, K (lysine) bears one positive charge, and A (alanine) constitutes the hydrophobic tail. To elucidate the impact of these peptide surfactants, the ternary MO/peptide/water system has been investigated using small-angle X-ray scattering (SAXS), within a certain range of peptide concentrations (R Collapse

Key Words Collapse

MESH Headings

• Anions
• Lipid Bilayers
• Lipids/chemistry
• Models, Molecular
• Peptides/chemistry
• Scattering, Radiation
• Surface-Active Agents/chemistry
• Temperature

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Grants Collapse

Affiliation(s)

Anan Yaghmur Institute of Biophysics and Nanosystems Research (IBN), Austrian Academy of Sciences, Graz, Austria.
Peter Laggner
Shuguang Zhang
Michael Rappolt

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Control of the internal structure of MLO-based isasomes by the addition of diglycerol monooleate and soybean phosphatidylcholine

This work describes the effect of two different surfactants on the internal nanostructure of the kinetically stabilized isasomes (internally self-assembled particles or "somes"), which are a new family of colloidal particles (cubosomes, hexosomes, micellar cubosomes, and emulsified microemulsions, EME). The stabilization of these systems is performed by using the polymeric stabilizer F127. We demonstrate that the internal structure of these oil-free and oil-loaded dispersed particles can be modulated by varying the lipid composition. To achieve this goal, we replaced part of our primary lipid monolinolein (MLO) with diglycerol monooleate (DGMO) or soybean phosphatidylcholine (PC). We found that DGMO has a counter effect to that of tetradecane (TC) and allows us to tune back the self-assembled nanostructure in the TC-loaded dispersions from H2 (hexosomes) to Im3m (cubosomes). Although TC has a higher impact on confined structures than does DGMO, we demonstrate that the addition of DGMO significantly affects the internal structure of the TC-solubilized dispersions and favors the formation of large water channels. PC can also be used to modify the internal structure for MLO-based systems. It is somehow different from DGMO due to the fact that the fully hydrated Pn3m cubic structure in the presence of PC for the TC-free dispersion is preserved after dispersing. The results also indicate that PC is less effective than DGMO for tuning back the TC-loaded internal structure from H2 to cubic phase, in which it makes the confined structure less ordered. In addition, we found that DGMO has a significant effect on the internal structure of isasomes. It increases the water solubilization capacity for dispersed and nondispersed bulk phases. In contrast to the MLO-based dispersions, the present results indicate that F127 plays an important role in the internal structure of these dispersions due to its penetration into the oil-free cubic phase changing the symmetry from Pn3m to Im3m.

Detailed Structure of Diamond-Type Lipid Cubic Nanoparticles

Supramolecular three-dimensional self-assembly of nonlamellar lipids with fragments of the protein immunoglobulin results in a bicontinuous cubic phase fragmented into nanoparticles with open water channels (cubosomes). The structure of the diamond-type cubic nanoparticles is characterized experimentally by freeze-fracture electron microscopy, and it is mathematically modeled with nodal surfaces emphasizing the fluid-like undulations of the cubosomic interfaces. Based on scaling-up and scaling-down approaches, we present stable and intermediate-kind nanoparticles resulting from the cubosomic growth. Our results reveal the smallest stable diamond-type cubosomic entity that can serve as a building block of more complex nanostructured fluid drug delivery vehicles of therapeutic proteins. The evidence presented for lipid-bilayer undulations in the surface region of the protein/lipid cubosomes could have important consequences for possible applications of these hierarchically organized porous nanoparticles.

Proteocubosomes: nanoporous vehicles with tertiary organized fluid interfaces

Proteocubosomes are nanostructured open-nanochannel hierarchical fluid vehicles characterized by a cubic lattice periodicity of the lipid/protein supramolecular assembly (protein-loaded cubosomes). They are obtained here at very high hydration levels by a three-dimensional (3D) self-assembly process, which exploits a protein-directed 3D patterning and fragmentation to create a new, tertiary-level structural order of fluid lipid/water interfaces. Our freeze-fracture electron microscopy study reveals that the proteocubosome structures are built up by patterned assemblies of nanocubosomes, which comprise 3D nanoporous fracture surfaces throughout. Complex cubosomic architectures, involving arrays of nanodroplets (larger than 20 nm) inside the proteocubosome particles, are established at high resolution. The soft-matter hierarchical nanocompartment formations display internal aqueous pores belonging to the D-type lipid cubic lattice nanochannel system that is proven by synchrotron X-ray diffraction. The reported nanostructured fluid may give rise to novel applications in nanofluidic biomimetic devices, porous protein drug delivery vehicles, nanoscale enzymatic bioreactors, and protein-encapsulating fluid nanomaterials.