Vesicle Deformation Research Articles

Correlation between adhesion strength and phase behaviour in solid-supported lipid membranes

Fundamental understanding of vesicle adhesion in the size range ≤ 200 nm is of major importance when addressing biologically relevant processes involving the presence of small vesicles like exosomes or endosomes. Using quartz crystal microbalance with dissipation monitoring, we investigate the correlation between vesicle deformation and eventual membrane rupture on surfaces with different adhesion levels, as well as their respective thermotropic phase transitions. In particular, phase transitions of solid-supported membranes on Au resemble the cooperative behaviour of lipid membrane transitions in bulk. In contrast, solid-supported membranes on SiO2 exhibit broadened ‘double-peak’ transitions, rendering a ‘decoupling’ effect during melting due to stronger interactions with SiO2. This paper provides a comprehensive view of the correlation between size, geometry and phase transitions observed in the layer of adsorbed lipid vesicles/membranes. It paves the way to explore structural changes on more complex biointerfaces by acoustic-based sensors.

Design and Characterization of Ethosomes for Transdermal Delivery of Caffeic Acid.

The present investigation describes a formulative study aimed at designing ethosomes for caffeic acid transdermal administration. Since caffeic acid is characterized by antioxidant potential but also high instability, its encapsulation appears to be an interesting strategy. Ethosomes were produced by adding water into a phosphatidylcholine ethanol solution under magnetic stirring. Size distribution and morphology of ethosome were investigated by photon correlation spectroscopy, small-angle X-ray spectroscopy, and cryogenic transmission electron microscopy, while the entrapment capacity of caffeic acid was evaluated by high-performance liquid chromatography. Caffeic acid stability in ethosome was compared to the stability of the molecule in water, determined by mass spectrometry. Ethosome dispersion was thickened by poloxamer 407, obtaining an ethosomal gel that was characterized for rheological behavior and deformability. Caffeic acid diffusion kinetics were determined by Franz cells, while its penetration through skin, as well as its antioxidant activity, were evaluated using a porcine skin membrane–covered biosensor based on oxygen electrode. Ethosome mean diameter was ≈200 nm and almost stable within three months. The entrapment of caffeic acid in ethosome dramatically prolonged drug stability with respect to the aqueous solution, being 77% w/w in ethosome after six months, while in water, an almost complete degradation occurred within one month. The addition of poloxamer slightly modified vesicle structure and size, while it decreased the vesicle deformability. Caffeic acid diffusion coefficients from ethosome and ethosome gel were, respectively, 137- and 33-fold lower with respect to the aqueous solution. At last, the caffeic acid permeation and antioxidant power of ethosome were more intense with respect to the simple solution.

Interaction of Alpha-Synuclein and Its Mutants with Rigid Lipid Vesicle Mimics of Varying Surface Curvature.

Abnormal aggregation of alpha-synuclein (α-syn), an intrinsically disordered neuronal protein, is strongly implicated in the development of Parkinson's disease. Efforts to better understand α-syn's native function and its pathogenic role in neurodegeneration have revealed that the protein interacts with anionic lipid vesicles via adoption of an amphipathic α-helical structure; however, the ability of α-syn to remodel lipid membranes has made it difficult to decipher the role of vesicle surface curvature in protein binding behavior. In this study, sodium dodecyl sulfate (SDS)-coated gold nanoparticles (AuNPs), which mimic bilayer vesicle architecture, were synthesized in order to conduct a systematic investigation into the binding interaction of α-syn and two of its mutants (A30P and E46K) with rigid lipid vesicle mimics of defined surface curvature. By incorporating a rigid AuNP core (∼10-100 nm), the ability of α-syn to remodel the vesicle mimics was removed and their surface curvature could be fixed. Proteomics studies showed that, upon binding of free α-syn to the surface of SDS-AuNPs, the N-terminus of α-syn became less solvent accessible, whereas its C-terminus became more accessible. Interestingly, α-syn's non-amyloid-β component (NAC) region also exhibited increased solvent accessibility, suggesting that α-syn bound to rigid vesicle-like structures could possess heightened aggregation propensity and therefore pathogenicity. Additionally, both the A30P and E46K mutations were found to adopt distinct binding modes on the mimics' surface. In contrast with previous reports, similar binding affinities were observed for WT, A30P, and E46K α-syn toward SDS-AuNPs of all sizes, indicating the potential importance of vesicle deformability in determining α-syn binding behavior.

Flavosomes, novel deformable liposomes for the co-delivery of anti-inflammatory compounds to skin.

Flavosomes, novel deformable liposomes for the topical delivery of anti-inflammatory compounds have been developed and characterized in this study. The carriers were prepared by incorporating flavonoids, specifically quercetin and dihydroquercetin, into transfersome and evaluated as a potential topical delivery system for meloxicam (MX), a potent hydrophobic NSAID (non-steroidal anti-inflammatory drug). Characterization of the flavosomes was conducted in terms of their vesicle size, zeta potential, entrapment efficiency and deformability index. Ex vivo skin permeation and confocal laser scanning microscopy studies demonstrated that the flavosome formulations improved the skin permeation of meloxicam compared to that for transfersomes. The dermal and transdermal delivery of meloxicam using these formulations has the potential of being a promising alternative to conventional oral delivery of non-steroidal anti-inflammatory drugs (NSAIDs) with enhanced local and systemic onset of action and reduced gastrointestinal side effects.

Exploring the Promising Potential of High Permeation Vesicle-Mediated Localized Transdermal Delivery of Docetaxel in Breast Cancer To Overcome the Limitations of Systemic Chemotherapy.

The currently available systemic chemotherapy for treating breast cancer often results in serious systemic side effects and compromises patient compliance. The distinct anatomical features of human breasts (e.g., embryological origin of breast skin, highly developed internal lymphatic and venous circulation, and the presence of mammary fat layers) help in preferential accumulation of drugs into breasts after topical application on breast region. This unique feature is termed as localized transdermal delivery which could be utilized for effectively delivering anticancer agents to treat breast cancer and reducing the systemic side effects by limiting their presence in blood. However, the clinical effectiveness of this drug delivery approach is highly limited by barrier properties of skin reducing the permeation of anticancer drugs. In the present work, we have developed high permeation vesicles (HPVs) using phospholipids and synergistic combination of permeation enhancers (SCOPE) to improve the skin permeation of drugs. Docetaxel (DTX) was used as a model drug for hypothesis testing. The optimized SCOPE mixture composed of sodium oleate/sodium lauryl ether sulfate/propylene glycol in 64:16:20% w/w ratio. DTX HPVs were prepared using phospholipid: SCOPE, 8:2% w/w ratio. DTX HPVs exhibited as a uniform deformable vesicles with size range 124.2 ± 7.6 nm, significantly improved skin permeation profile, and sustained drug release until 48 h. Superior vesicle deformability, better vesicle membrane fluidization, and SCOPE mediated enhancement in skin fluidization were the prime factors behind enhancement of DTX permeation. The improved cellular uptake, reduced IC50 values, and higher apoptotic index of DTX HPVs in MCF-7 and MDA-MB-231 cells ensured the therapeutic effectiveness of HPV based therapy. Also, HPVs were found to be predominantly internalized inside cells through clathrin and caveolae-dependent endocytic pathways. Bioimaging analysis in mice confirmed the tumor penetration potential and effective accumulation of HPVs inside tumors after topical application. In vivo studies were carried out in comparison with marketed intravenous DTX injection (Taxotere) to compare the effectiveness of topical chemotherapy. The topical application of DTX HPV gel in tumor bearing mice resulted in nearly 4-fold tumor volume reduction which was equivalent to intravenous Taxotere therapy. Toxicity analysis of DTX HPV gel in comparison with intravenous Taxotere dosing showcased remarkably lower levels of toxicity biomarkers (aspartate transaminase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and creatinine), indicating improved safety of topical chemotherapy. Overall results warranted the effectiveness of topical DTX chemotherapy to reduce tumor burden with substantially reduced risk of systemic toxicities in breast cancer.

Deformation and poration of giant unilamellar vesicles induced by anionic nanoparticles

The interaction of anionic magnetite nanoparticles (MNPs) of size 18 nm with negatively charged giant unilamellar vesicles (GUVs) formed from a mixture of neutral dioleoylphosphatidylcholine (DOPC) and negatively charged dioleoylphosphatidylglycerol (DOPG) lipids has been investigated. It has been obtained that NPs induces the deformation of spherical GUVs. The reaction of other GUVs on NPs consists in the appearance of pores in their membranes. We focused the effect of electrostatics on the interaction of charged membranes with MNPs. To study the influence of the surface charge of GUVs on the processes under consideration, we varied the fraction of DOPG in the vesicles from 0 to 100%. We examined the influence of salt concentration in the range of 50−300 mM NaCl concentration. To describe the degree of deformation, a special parameter compactness was introduced. The pore formation in the membranes of GUVs was investigated by the leakage of sucrose. The compactness increases with time and also NPs concentration. The fraction of deformed GUVs increases with the increase of surface charge density of membranes as well as the decrease of salt concentration in buffer. The value of compactness for neutral membrane is 1.25 times higher than that of charged ones. The fraction of deformed GUVs become constant after 20 min, however it increases with NPs concentration. The time taken for stochastic pore formation is less for charged membrane than neutral one. The physical mechanism explaining the experimental results obtained in these investigations.

Shape transition and hydrodynamics of vesicles in tube flow

The steady motion and deformation of a lipid-bilayer vesicle translating through a circular tube in low Reynolds number pressure-driven flow are investigated numerically using an axisymmetric boundary element method. This fluid-structure interaction problem is determined by three dimensionless parameters: reduced volume (a measure of the vesicle asphericity), geometric confinement (the ratio of the vesicle effective radius to the tube radius), and capillary number (the ratio of viscous to bending forces). The physical constraints of a vesicle -- fixed surface area and enclosed volume when it is confined in a tube -- determine critical confinement beyond which it cannot pass through without rupturing its membrane. The simulated results are presented in a wide range of reduced volumes [0.6, 0.98] for different degrees of confinement; the reduced volume of 0.6 mimics red blood cells. We draw a phase diagram of vesicle shapes and propose a shape transition line separating the parachute-like shape region from the bullet-like one in the reduced volume versus confinement phase space. We show that the shape transition marks a change in the behavior of vesicle mobility, especially for highly deflated vesicles. Most importantly, high-resolution simulations make it possible for us to examine the hydrodynamic interaction between the wall boundary and the vesicle surface at conditions of very high confinement, thus providing the limiting behavior of several quantities of interest, such as the thickness of lubrication film, vesicle mobility and its length, and the extra pressure drop due to the presence of the vesicle. This extra pressure drop holds implications for the rheology of dilute vesicle suspensions. Furthermore, we present various correlations and discuss a number of practical applications.

Effect of C60 nanoparticles on elasticity of small unilamellar vesicles composed of DPPC bilayers**Project supported by the National Natural Science Foundation of China (Grant No. 61475196).

The interaction between C60 nanoparticles and biomembranes has been of great interest in researches over the past decades due to their novel applications as well as potential cytotoxicity. In this work, we study the deformation of the small unilamellar vesicles composed of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers infiltrated with C60 nanoparticles of different molecular concentrations through coarse-grained molecular dynamics simulations. By employing the Helfrich spontaneous curvature model, the bending modulus and the spontaneous curvature of the vesicles with C60 nanoparticles of different concentrations are obtained according to the simulation data. The results show that the bending modulus and the spontaneous curvature of pure DPPC vesicle membranes are approximately 1.6 × 10−19 J and 1.4 nm−1, respectively. Both of them increase linearly approximately as the C60 concentration increases from 0 to 16.3%. The density profiles of vesicles, the order of lipid packing and the diffusion characteristics of DPPC and C60 are also investigated.

Synaptotagmin-1/Ca2+Overcomes Inefficiency of SNARE Complex in Dilating the Fusion Pore

In the neuron, membrane fusion is the fundamental process in which neurotransmitters are released to the synapse. It is believed that the SNARE complex is the minimal fusion machinery that drives synaptic membrane fusion. Membrane fusion transits the hemifusion state and the fusion pore prior to the complete merging of two membranes. However, it is hotly debated how far SNARE complexes can carry along the membrane fusion pathway. There is evidence that shows the SNARE complex is not even sufficiently potent to go beyond hemifusion. But, there is other evidence that shows it has the capacity to sustain a small fusion pore. Yet, it is unclear if SNARE complexes can dilate the fusion pore. Here we use an in vitro single vesicle-to-supported bilayer fusion assay to investigate fusion pore dilation by employing 10 kD dextran-rhodamine B (diameter ∼ 6 nm) as the fluorescent content probe. The results show that the SNARE complex alone is inefficient at dilating and stabilizing the fusion pore. This results in pore contraction before full content release. However, the addition of synaptotagmin-1 and Ca2+ promotes dilation of the fusion pore for nearly all docked vesicles with a lower tendency of contraction than with SNAREs alone. Surprisingly, we observe a fluorescence signal consistent with deformation of vesicles to a flattened discus shape. We propose a hypothetical mechanistic model by which SNAREs and particularly, synaptotagmin-1/Ca2+ help dilate the fusion pore by stabilizing the membrane curvature.

Skin permeation and thermodynamic features of curcumin-loaded liposomes.

This work describes the development of liposomes encapsulating curcumin (CURC) aiming to provide insights on the influence of CURC on the thermodynamic and skin permeation/penetration features of the vesicles. CURC-loaded liposomes were prepared by hydration of lipid film, in the 0.1-15% CURC:DPPC w/w ratio range. The obtained formulations were characterized for their size distribution, zeta potential and vesicle deformability, along with their thermodynamic properties and ex vivo skin penetration/permeation ability. Liposome size was 110-130 nm for all formulations, with fairly narrow size distribution (polydispersity index was ≤0.20) and a zeta potential mildly decreasing with CURC loading. DSC outcomes indicated that CURC interferes with the packing of DPPC acyl chains in liposome bilayer when CURC percentage was at least 10%, leading to a more fluid state than blank and low-payload vesicles. Consistently, the deformability index of liposomes with 15% CURC:DPPC was strongly increased compared to other formulations. This is congruent with ex vivo skin penetration/permeation results, which showed how more deformable liposomes showed an improved deposition in the epidermis, which acts as a reservoir for the active molecule. Altogether, results hint at a possible application of high payload liposomes for improved topical dermal accumulations of actives.

Comment on "Acoustic deformation for the extraction of mechanical properties of lipid vesicle populations".

In a recent paper, Silva etal. [Phys. Rev. E 99, 063002 (2019)10.1103/PhysRevE.99.063002] consider the deformation of vesicles in response to the acoustic radiation stresses of ultrasonic standing waves. An important part of the analysis concerns the quadrupole projection of the radial component of radiation stress on a spherical vesicle having a radius much smaller than the acoustic wavelength evaluated with a software-aided expansion approach. Here we note that their projection agrees with results previously found for compressible spheres in the corresponding limit [J. Acoust. Soc. Am. 69, 1499 (1981)10.1121/1.385785] provided an error in Eq. (B5) of Silva etal. is corrected.

A Nitsche-type variational formulation for the shape deformation of a single component vesicle

This paper concerns the development of a finite-element formulation using Nitsche’ method for the phase-field model to capture an equilibrium shape of a single component vesicle. The phase-field model derived from the minimization of the curvature energy results in a nonlinear fourth-order partial differential equation. A standard conforming Galerkin formulation thus requires C1-elements. We derive a nonconforming finite-element formulation that can be applied to C0-elements and prove its consistency. Continuity of the first derivatives across interelement boundaries is weakly imposed and stabilization of the method is achieved via Nitsche’s method. The capability of the proposed finite-element formulation is demonstrated through numerical study of the equilibrium shapes of axisymmetric single component vesicles along with budding and fission phenomena.

Polyunsaturated Phospholipid Modified Membrane Degradation Catalyzed by a Secreted Phospholipase A2.

To optimize the compositions of the lipid-based nanomedicine and to advance understanding of the roles of polyunsaturated phospholipids in biological membranes, this study examined the effects of polyunsaturated phospholipids on the degradation of giant unilamellar vesicles catalyzed by a secreted phospholipase A2 (sPLA2) using fluorescence microscopy. Molecular interfacial packing, interaction, and degradation of the films containing various mixing ratios of saturated and polyunsaturated phospholipids were quantified using a Langmuir trough integrated with synchrotron X-ray surface scattering techniques. It was found that a high molar fraction (0.63 and above) of polyunsaturated phospholipids not only enhanced the rate of sPLA2-catalyzed vesicle degradation but also changed the vesicle deformation process and degradation product morphology. Hydrolysis of the saturated phospholipids generated highly ordered liquid crystal domains, which was reduced or prohibited by the presence of the polyunsaturated phospholipids in the reactant film.

Mechanistic insights into high permeation vesicle-mediated synergistic enhancement of transdermal drug permeation.

Aim: To design a nanocarrier platform for enhanced transdermal drug permeation. Materials& methods: Gel-based high permeation vesicles (HPVs) were developed and their performance in terms of transdermal flux improvement, in vitro release and skin irritancy was assessed. The mechanistic insights of permeation enhancement were explored using confocal laser scanning microscopy, ATR-FTIR, DSC and P31 NMR. Results: HPVs exhibited as vesicles with uniform size (∼150nm), extended drug-release profile (∼48h) and improved transdermal flux. HPVs were also nontoxic and nonirritant to skin. Enhanced vesicle deformability, improved vesicle membrane fluidity and synergistic permeation enhancement action of synergistic combination of permeation enhancer components was found to be responsible for HPV-mediated permeation enhancement. Conclusion: Overall, the study established that HPVs demonstrate a promising therapeutic advantage over conventional transdermal drug carriers.

Temperature dependent self-organization of DMPC membranes promoted by intermediate amounts of the saponin aescin

The plant-derived biosurfactant aescin is naturally present in many plants and is used for treatment of disorders such as varicose veins and inflammation of veins. The hemolytic activity of this saponin is attributed to its interaction with cholesterol in the red blood cell membrane. This work investigates the phase and aggregation behavior of saponin-containing model membranes consisting of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The aescin concentrations studied range from 1 mol% to 7 mol% with respect to the total lipid content. The methods of choice to elucidate the structural picture are small-angle scattering of X-rays (SAXS) and neutrons (SANS) and cryogenic transmission electron microscopy (cryo-TEM). SANS and SAXS revealed that at lower aescin contents vesicular structures are conserved and vesicles tend to aggregate already at aescin contents of around 1 mol%. Aggregation and vesicle deformation effects are found to be stronger when the phospholipids are in the Lβ′ phase. With increasing aescin content, mixed structures, i.e. aggregated and deformed vesicles and solubilized bilayer fragments, are present. This was proven for a sample with 4 mol% aescin by cryo-TEM. An increasing aescin amount leads to membrane decomposition and free standing bilayers which tend to build stacks at high temperature. These stacks are characterized by SAXS using the modified Caillé theory. Analyses and model dependent fitting reveal formation of well-defined structures beginning at 7 mol% aescin.

Effects of DC Magnetic Fields on Magnetoliposomes

A modification of the co-precipitation method was used to prepare Magnetic nanoparticles (MNPs). After characterization, using Transmission Electron Microscopy and hysteresis loops analysis, we found that the nanoparticles are superparamagnetic with different geometries and size average of 12 nm. Magnetoliposomes (MLs), were prepared by rehydration, and we were able to encapsulate the superparamagnetic nanoparticles (SNPs) inside the liposomes. A DC magnetic field was applied to study the effects of the confined SNPs. Digitalized images taken from an inverted phase contrast microscope show that vesicles display two behaviors when a magnetic DC field was applied: encapsulated SNPs assembly in a pearl-chain formation and, in other cases, MLs deform in the direction of the magnetic field. Deformations are explained by analyzing the forces exerted by the magnetic field over the surface of the otherwise spheroidal vesicle. We found that tangential forces squeeze ML deforming them in a rhombohedral-like shape. When the initial surface tension of ML is high, we observe no deformation of the membrane vesicle, and instead, the pearl-chain formation of the SNPs in the inner medium of the vesicle is observed in the direction of the applied magnetic field. A dipole-dipole interaction explains this pearl-chain formation where complete disperse SNPs are observed when the magnetic field is switched off.

A theoretical study on the dynamics of a compound vesicle in shear flow.

The dynamics of nucleate cells in shear flow is of great relevance in cancer cells and circulatory tumor cells where they determine the flow properties of blood. Buoyed by the success of giant unilamellar vesicles in explaining the dynamics of anucleate cells such as red blood cells, compound vesicles have been suggested as a simple model for nucleate cells. A compound vesicle consists of two concentric unilamellar vesicles with the inner, annular and outer regions filled with aqueous Newtonian solvents. In this work, a theoretical model is presented to study the deformation and dynamics of a compound vesicle in linear shear flow using small deformation theory and spherical harmonics with higher order approximation to the membrane forces. A coupling of viscous and membrane stresses at the membrane interface of the two vesicles results in highly nonlinear shape evolution equations for the inner and the outer vesicles which are solved numerically. The results indicate that the size of the inner vesicle (χ) does not affect the tank-treading dynamics of the outer vesicle. The inner vesicle admits a greater inclination angle than the outer vesicle. However, the transition to trembling/swinging and tumbling is significantly affected. The inner and outer vesicles exhibit identical dynamics in the parameter space defined by the nondimensional rotational (Λan) and extensional (S) strength of the general shear flow. At moderate χ, a swinging mode is observed for the inner vesicle while the outer vesicle exhibits tumbling. The inner vesicle also exhibits modification of the TU mode to IUS (intermediate tumbling swinging) mode. Moreover, synchronization of the two vesicles at higher χ and a Capillary number sensitive motion at lower χ is observed in the tumbling regime. These results are in accordance with the few experimental observations reported by Levant and Steinberg. A reduction in the inclination angle is observed with an increase in χ when the inner vesicle is replaced by a solid inclusion. Additionally, a very elaborate phase diagram is presented in the Λan-S parameter space, which could be tested in future experiments or numerical simulations.

The Mechanisms of Action of Triindolylmethane Derivatives on Lipid Membranes.

The effects of new synthetic antibacterial agents – tris(1-pentyl-1H-indol-3-yl)methylium chloride (LCTA-1975) and (1-(4-(dimethylamino)-2,5-dioxo-2,5-dihydro-1H-pyrrol-3-yl)-1H-indol-3-yl)bis(1-propyl- 1H-indol-3-yl)methylium chloride (LCTA-2701 – on model lipid membranes were studied. The ability of the tested agents to form ion-conductive transmembrane pores, influence the electrical stability of lipid bilayers and the phase transition of membrane lipids, and cause the deformation and fusion of lipid vesicles was investigated. It was established that both compounds exert a strong detergent effect on model membranes. The results of differential scanning microcalorimetry and measuring of the threshold transmembrane voltage that caused membrane breakdown before and after adsorption of LCTA-1975 and LCTA-2701 indicated that both agents cause disordering of membrane lipids. Synergism of the uncoupling action of antibiotics and the alkaloid capsaicin on model lipid membranes was shown. The threshold concentration of the antibiotic that caused an increase in the ion permeability of the lipid bilayer depended on the membrane lipid composition. It was lower by an order of magnitude in the case of negatively charged lipid bilayers than for the uncharged membranes. This can be explained by the positive charge of the tested agents. At the same time, LCTA-2701 was characterized by greater efficiency than LCTA-1975. In addition to its detergent action, LCTA-2701 can induce ion-permeable transmembrane pores: step-like current fluctuations corresponding to the opening and closing of individual ion channels were observed. The difference in the mechanisms of action might be related to the structural features of the antibiotic molecules: in the LCTA-1975 molecule, all three substituents at the nitrogen atoms of the indole rings are identical and represent n-alkyl (pentyl) groups, while LCTA-2701 contains a maleimide group, along with two alkyl substituents (n-propyl). The obtained results might be relevant to our understanding of the mechanism of action of new antibacterial agents, explaining the difference in the selectivity of action of the tested agents on the target microorganisms and their toxicity to human cells. Model lipid membranes should be used in further studies of the trends in the modification and improvement of the structures of new antibacterial agents.

Shape deformation of a vesicle under an axisymmetric non-uniform alternating electric field

We suggest that non-uniform electric fields that are commonly used to study vesicle dielectrophoresis can be employed in hitherto relatively unexplored areas of vesicle deformation (for electromechanical characterization) and electroporation. Conventionally, the tension generated in vesicles is commonly modeled to be entropic or enthalpic in origin. A comparison of the configuration of a vesicle in the enthalpic and entropic regimes as well as the cross over between the two regimes during vesicle deformation has eluded understanding. A lucid demonstration of this concept is provided by the study of vesicle deformation under axisymmetric quadrupole electric field and the shapes of the vesicles obtained using the entropic and the enthalpic approaches, show significant differences. A strong dependence of the final vesicle shapes on the ratio of electrical conductivities of the fluids inside and outside the vesicle as well as on the frequency of the applied quadrupole electric field is observed. A comparison with experimental data from the literature is also made. Moreover, an excess area dependent transition between the entropic and enthalpic regimes is observed. The method could be used to estimate electromechanical properties of the vesicle.

Novel Findings about Double-Loaded Curcumin-in-HPβcyclodextrin-in Liposomes: Effects on the Lipid Bilayer and Drug Release

In this study, the encapsulation of curcumin (Cur) in “drug-in-cyclodextrin-in-liposomes (DCL)” by following the double-loading technique (DL) was proposed, giving rise to DCL–DL. The aim was to analyze the effect of cyclodextrin (CD) on the physicochemical, stability, and drug-release properties of liposomes. After selecting didodecyldimethylammonium bromide (DDAB) as the cationic lipid, DCL–DL was formulated by adding 2-hydroxypropyl-α/β/γ-CD (HPβCD)–Cur complexes into the aqueous phase. A competitive effect of cholesterol (Cho) for the CD cavity was found, so cholesteryl hemisuccinate (Chems) was used. The optimal composition of the DCL–DL bilayer was obtained by applying Taguchi methodology and regression analysis. Vesicles showed a lower drug encapsulation efficiency compared to conventional liposomes (CL) and CL containing HPβCD in the aqueous phase. However, the presence of HPβCD significantly increased vesicle deformability and Cur antioxidant activity over time. In addition, drug release profiles showed a sustained release after an initial burst effect, fitting to the Korsmeyer-Peppas kinetic model. Moreover, a direct correlation between the area under the curve (AUC) of dissolution profiles and flexibility of liposomes was obtained. It can be concluded that these “drug-in-cyclodextrin-in-deformable” liposomes in the presence of HPβCD may be a promising carrier for increasing the entrapment efficiency and stability of Cur without compromising the integrity of the liposome bilayer.