Antivesiculation and Complete Unbinding of Tail-Tethered Lipids.

We report the effect of tail-tethering on vesiculation and complete unbinding of bilayered membranes. Amphiphilic molecules of a bolalipid, resembling the tail-tethered molecular structure of archaeal lipids, with two identical zwitterionic phosphatidylcholine headgroups self-assemble into a large flat lamellar membrane, in contrast to the multilamellar vesicles (MLVs) observed in its counterpart, monopolar nontethered zwitterionic lipids. The antivesiculation is confirmed by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cyro-TEM). With the net charge of zero and higher bending rigidity of the membrane (confirmed by neutron spin echo (NSE) spectroscopy), the current membrane theory would predict that membranes should stack with each other (aka "bind") due to dominant van der Waals attraction, while the outcome of the nonstacking ("unbinding") membrane suggests that the theory needs to include entropic contribution for the nonvesicular structures. This report pioneers an understanding of how the tail-tethering of amphiphiles affects the structure, enabling better control over the final nanoscale morphology.

Design of Nanostraws in Amine-Functionalized MCM-41 for Improved Adsorption Capacity in Carbon Capture.

Polymeric amine encapsulation in high surface area MCM-41 particles for CO2 capture is well established but has the drawback of leaching out the water-soluble polymer upon exposure to aqueous environments. Alternatively, chemical (covalent) grafting amine functional groups from an alkoxysilane such as 3-aminopropyltriethoxysilane (APTES) on MCM-41 offer better stability against this drawback. However, the diffusional restriction exhibited by the narrow uniform MCM-41 pores (2-4 nm) may impede amine functionalization of the available silanol groups within the inner mesoporous core. This leads to incomplete amine functionalization and could reduce the CO2 adsorption capacity in such materials. Our concept to improve access to the MCM-41 interior is based on the incorporation of nanostraws with larger inner diameter (15-30 nm) to create a hierarchical porosity and enhance the molecular transport of APTES. Halloysite nanotubes (HNT) are used as tubular straws that are integrated into the MCM-41 matrix using an aerosol-assisted synthesis method. Characterization results show that the intrinsic structure of MCM-41 remains unaltered after the incorporation of the nanostraws and amine functionalization. At an optimal APTES loading of 0.5 g (X = 2.0), the amine-functionalized composite of MCM-41 with straws (APTES/M40H) has a 20% higher adsorption capacity than the amine-modified MCM-41 (APTES/MCM-41) adsorbent. Furthermore, the CO2 adsorption capacity APTES/M40H doubles that of APTES/MCM-41 when normalized based on the composition of MCM-41 in the composite particle with straws. The facile integration of nanostraws in MCM-41 leading to hierarchical porosities could be effective toward the mitigation of diffusional restriction in porous materials with potential for other catalytic and adsorption technologies.

Lubrication mechanisms of dispersed carbon microspheres in boundary through hydrodynamic lubrication regimes.

HYPOTHESIS: Carbon microspheres have been shown to reduce friction and surface wear at relatively low speeds and high applied loads (i.e., within the boundary lubrication regime). We hypothesize that in dilute colloidal lubricating systems there is an interplay between the size of the carbon microspheres and the lubrication gap size, which determines the dominant lubricating mechanism of the system. EXPERIMENTS: A 60 wt% aqueous glycerol solution was used as the base lubricant and compared to various carbon particle-based lubricant formulations ranging in particle concentrations from 0.05 to 0.30 vol%. The tribological properties of the various lubricant formulations were tested on a pin-on-disk tribometer. A simplified Stribeck plot was produced to understand the changing mechanism of lubrication over a wide range of conditions. FINDINGS: The Stribeck curves show that the carbon microspheres assist lubrication by a rolling mechanism primarily in the boundary lubrication regime. A 0.20 vol% carbon-based lubricant formulation showed the best friction reduction compared to the base lubricant. Increasing speed increases the lubricating gap between the friction pair beyond the size of the particles, thereby nullifying the rolling mechanism of the particles. We introduce a modified specific film thickness parameter to determine the lubrication regime in a particle-lubricant system.

Uncovering the Optimal Molecular Characteristics of Hydrophobe-Containing Polypeptoids to Induce Liposome or Cell Membrane Fragmentation.

Cellular functions of membrane proteins are strongly coupled to their structures and aggregation states in the cellular membrane. Molecular agents that can induce the fragmentation of lipid membranes are highly sought after as they are potentially useful for extracting membrane proteins in their native lipid environment. Toward this goal, we investigated the fragmentation of synthetic liposome using hydrophobe-containing polypeptoids (HCPs), a class of facially amphiphilic pseudo-peptidic polymers. A series of HCPs with varying chain lengths and hydrophobicities have been designed and synthesized. The effects of polymer molecular characteristics on liposome fragmentation are systemically investigated by a combination of light scattering (SLS/DLS) and transmission electron microscopy (cryo-TEM and negative stained TEM) methods. We demonstrate that HCPs with a sufficient chain length (DPn ≈ 100) and intermediate hydrophobicity (PNDG mol % = 27%) can most effectively induce the fragmentation of liposomes into colloidally stable nanoscale HCP-lipid complexes owing to the high density of local hydrophobic contact between the HCP polymers and lipid membranes. The HCPs can also effectively induce the fragmentation of bacterial lipid-derived liposomes and erythrocyte ghost cells (i.e., empty erythrocytes) to form nanostructures, highlighting the potential of HCPs as novel macromolecular surfactants toward the application of membrane protein extraction.

Hydrophobically modified chitosan biopolymer connects halloysite nanotubes at the oil-water interface as complementary pair for stabilizing oil droplets.

The integration of cationic and hydrophobic functionalities into hydrophobically modified chitosan (HMC) biopolymer facilitates complementary emulsion stabilization with negatively charged halloysite clay nanotubes (HNT). Oil-in-water emulsions with smaller droplet sizes and significantly improved interfacial resistance to droplet coalescence are obtained on complementary emulsion stabilization by HNT and HMC compared to the individual emulsifiers alone. Contact angle measurements shows that the adsorption of the cationic HMC onto the negatively charged HNT modifies the surface wettability of the nanotubes, facilitating the attachment of the nanotubes to the oil-water interface. High resolution cryo-SEM imaging reveals that free HMC chains locks the nanotubes together at the oil-water interface, creating a high barrier to droplet coalescence. The emulsion stability is an order of magnitude higher for conditions in which the aqueous HNT dispersion is stabilized by the HMC compared to conditions where the negatively charged HNT is strongly flocculated by the cationic HMC. The hydrophobic interaction between HMC chains, insertion of HMC hydrophobes into the oil phase and electrostatic interactions between HMC and HNT are proposed as key mechanisms driving the increased emulsion stability. For potential application as a dispersant system for crude oil spill treatment, the nanotubular morphology of HNT was further exploited for the encapsulation of the water-insoluble surfactant, sorbitan monooleate (Span 80). The HMC and HNT sterically strengthens the oil-water interfacial layer while release of the Span 80 surfactant from the HNT lumen lowers the oil-water interfacial tension. The concepts advanced here are relevant in the development of environmentally-benign dispersants for oil spill remediation.

Transformation of Lipid Vesicles into Micelles by Adding Nonionic Surfactants: Elucidating the Structural Pathway and the Intermediate Structures.

The phospholipid lecithin (L) and the nonionic surfactant Tween 80 (T) are used together in various contexts, including in drug delivery and oil spill remediation. There is hence a need to elucidate the nanostructures in LT mixtures, which is the focus of this paper. We study these mixtures using cryogenic transmission electron microscopy (cryo-TEM), coupled with dynamic light scattering and small-angle neutron scattering. As the concentration of Tween 80 is increased, the vesicles formed by lecithin are transformed into spherical micelles. We identify bicelles (i.e., disc-like micelles) as well as cylindrical micelles as the key stable nanostructures formed at intermediate L/T ratios. The bicelles have diameters ∼13-26 nm, and the bicelle size decreases as the Tween 80 content increases. We propose that the lecithin lipids form the body of the discs, while the Tween 80 surfactants occupy the rims. This hypothesis is consistent with geometric arguments because lecithin is double-tailed and favors minimal curvature, whereas the single-tailed Tween 80 molecules prefer curved interfaces. In the case of cylindrical micelles, cryo-TEM reveals that the micelles are short (length < 22 nm) and flexible. We are able to directly visualize the microstructure of the aggregates formed by lecithin-Tween 80 mixtures, thereby enhancing the understanding of morphological changes in the lecithin-Tween 80 system.

Integrating Halloysite Nanostraws in Porous Catalyst Supports to Enhance Molecular Transport.

In many porous catalyst supports, the accessibility of interior catalytic sites to reactant species could be restricted due to limitations of reactant transport through pores comparable to reactant dimensions. The interplay between reaction and diffusion in porous catalysts is defined through the Thiele modulus and the effectiveness factor, with diffusional restrictions leading to high Thiele moduli, reduced effectivess factors, and a reduction in the observed reaction rate. We demonstrate a method to integrate ceramic nanostraws into the interior of ordered mesoporous silica MCM-41 to mitigate diffusional restrictions. The nanostraws are the natural aluminosilicate tubular clay minerals known as halloysite. Such halloysite nanotubes (HNTs) have a lumen diameter of 15-30 nm, which is significantly larger than the 2-4 nm pores of MCM-41, thus facilitating entry and egress of larger molecules to the interior of the pellet. The method of integrating HNT nanostraws into MCM-41 is through a ship-in-a-bottle approach of synthesizing MCM-41 in the confined volume of an aerosol droplet that contains HNT nanotubes. The concept is applied to a system in which microcrystallites of Ni@ZSM-5 are incorporated into MCM-41. Using the liquid phase reduction of nitrophenol as a model reaction catalyzed by Ni@ZSM-5, we show that the insertion of HNT nanostraws into this composite leads to a 50% increase in the effectiveness factor. The process of integrating nanostraws into MCM-41 through the aerosol-assisted approach is a one-step facile method that complements traditional catalyst preparation techniques. The facile and scalable synthesis technique toward the mitigation of diffusional restrictions has implications to catalysis and separation technologies.

Aggregation-Enhanced Photoluminescence and Photoacoustics of Atomically Precise Gold Nanoclusters in Lipid Nanodiscs (NANO2).

The authors designed a structurally stable nano-in-nano (NANO2) system highly capable of bioimaging via an aggregation-enhanced NIR excited emission and photoacoustic response achieved based on atomically precise gold nanoclusters protected by linear thiolated ligands [Au25(SC n H2n+1)18, n = 4-16] encapsulated in discoidal phospholipid bicelles through a one-pot synthesis. The detailed morphological characterization of NANO2 is conducted using cryogenic transmission electron microscopy, small/wide angle X-ray scattering with the support of molecular dynamics simulations, providing information on the location of Au nanoclusters in NANO2. The photoluminescence observed for NANO2 is 20-60 times more intense than that of the free Au nanoclusters, with both excitation and emission wavelengths in the near-infrared range, and the photoacoustic signal is more than tripled. The authors attribute this newly discovered aggregation-enhanced photoluminescence and photoacoustic signals to the restriction of intramolecular motion of the clusters' ligands. With the advantages of biocompatibility and high cellular uptake, NANO2 is potentially applicable for both in vitro and in vivo imaging, as the authors demonstrate with NIR excited emission from in vitro A549 human lung and the KB human cervical cancer cells.

Using Microemulsion Phase Behavior as a Predictive Model for Lecithin-Tween 80 Marine Oil Dispersant Effectiveness.

Marine oil dispersants typically contain blends of surfactants dissolved in solvents. When introduced to the crude oil-seawater interface, dispersants facilitate the breakup of crude oil into droplets that can disperse in the water column. Recently, questions about the environmental persistence and toxicity of commercial dispersants have led to the development of "greener" dispersants consisting solely of food-grade surfactants such as l-α-phosphatidylcholine (lecithin, L) and polyoxyethylenated sorbitan monooleate (Tween 80, T). Individually, neither L nor T is effective at dispersing crude oil, but mixtures of the two (LT blends) work synergistically to ensure effective dispersion. The reasons for this synergy remain unexplained. More broadly, an unresolved challenge is to be able to predict whether a given surfactant (or a blend) can serve as an effective dispersant. Herein, we investigate whether the LT dispersant effectiveness can be correlated with thermodynamic phase behavior in model systems. Specifically, we study ternary "DOW" systems comprising LT dispersant (D) + a model oil (hexadecane, O) + synthetic seawater (W), with the D formulation being systematically varied (across 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 L:T weight ratios). We find that the most effective LT dispersants (60:40 and 80:20 L:T) induce broad Winsor III microemulsion regions in the DOW phase diagrams (Winsor III implies that the microemulsion coexists with aqueous and oil phases). This correlation is generally consistent with expectations from hydrophilic-lipophilic deviation (HLD) calculations, but specific exceptions are seen. This study then outlines a protocol that allows the phase behavior to be observed on short time scales (ca. hours) and provides a set of guidelines to interpret the results. The complementary use of HLD calculations and the outlined fast protocol are expected to be used as a predictive model for effective dispersant blends, providing a tool to guide the efficient formulation of future marine oil dispersants.

Spontaneous Formation of Stable Vesicles and Vesicle Gels in Polar Organic Solvents.

The self-assembly of lipids into nanoscale vesicles (liposomes) is routinely accomplished in water. However, reports of similar vesicles in polar organic solvents like glycerol, formamide, and ethylene glycol (EG) are scarce. Here, we demonstrate the formation of nanoscale vesicles in glycerol, formamide, and EG using the common phospholipid lecithin (derived from soy). The samples we study are simple binary mixtures of lecithin and the solvent, with no additional cosurfactants or salt. Lecithin dissolves readily in the solvents and spontaneously gives rise to viscous fluids at low lipid concentrations (∼2-4%), with structures ∼200 nm detected by dynamic light scattering. At higher concentrations (>10%), lecithin forms clear gels that are strongly birefringent at rest. Dynamic rheology confirms the elastic response of gels, with their elastic modulus being ∼20 Pa at ∼10% lipid. Images from cryo-scanning electron microscopy (cryo-SEM) indicate that concentrated samples are "vesicle gels," where multilamellar vesicles (MLVs, also called "onions"), with diameters between 50 and 600 nm, are close-packed across the sample volume. This structure can explain both the elastic rheology as well as the static birefringence of the samples. The discovery of vesicles and vesicle gels in polar solvents widens the scope of systems that can be created by self-assembly. Interestingly, it is much easier to form vesicles in polar solvents than in water, and the former are stable indefinitely, whereas the latter tend to aggregate or coalesce over time. The stability is attributed to refractive index-matching between lipid bilayers and the solvents, i.e., these vesicles are relatively "invisible" and thus experience only weak attractions. The ability to use lipids (which are "green" or eco-friendly molecules derived from renewable natural sources) to thicken and form gels in polar solvents could also prove useful in a variety of areas, including cosmetics, pharmaceuticals, and lubricants.

Does the Solvent in a Dispersant Impact the Efficiency of Crude-Oil Dispersion?

Dispersants, used in the mitigation of oil spills, are mixtures of amphiphilic molecules (surfactants) dissolved in a solvent. The recent large-scale use of dispersants has raised environmental concerns regarding the safety of these materials. In response to these concerns, our lab has developed a class of eco-friendly dispersants based on blends of the food-grade surfactants, soy lecithin (L) and Tween 80 (T), in a solvent. We have shown that these "L/T dispersants" are very efficient at dispersing crude oil into seawater. The solvent for dispersants is usually selected based on factors like toxicity, volatility, or viscosity of the overall mixture. However, with regard to the dispersion efficiency of crude oil, the solvent is considered to play a negligible role. In this paper, we re-examine the role of solvent in the L/T system and show that it can actually have a significant impact on the dispersion efficiency. That is, the dispersion efficiency can be altered from poor to excellent simply by varying the solvent while keeping the same blend of surfactants. We devise a systematic procedure for selecting the optimal solvents by utilizing Hansen solubility parameters. The optimal solvents are shown to have a high affinity for crude oil and limited hydrophilicity. Our analysis further enables us to identify solvents that combine high dispersion efficiency, good solubility of the L/T surfactants, a low toxicity profile, and a high flash point.

Investigation of Amphiphilic Polypeptoid-Functionalized Halloysite Nanotubes as Emulsion Stabilizer for Oil Spill Remediation.

Halloysite nanotubes (HNTs), naturally occurring and environmental benign clay nanoparticles, have been successfully functionalized with amphiphilic polypeptoid polymers by surface-initiated polymerization methods and investigated as emulsion stabilizers toward oil spill remediation. The hydrophilicity and lipophilicity balance (HLB) of the grafted polypeptoids was shown to affect the wettability of functionalized HNTs and their performance as stabilizers for oil-in-water emulsions. The functionalized HNTs having relatively high hydrophobic content (HLB = 12.0-15.0) afforded the most stable oil-in-water emulsions containing the smallest oil droplet sizes. This has been attributed to the augmented interfacial activities of polypeptoid-functionalized HNTs, resulting in more effective reduction of interfacial tension, enhancement of thermodynamic propensity of the HNT particles to partition at the oil-water interface, and increased emulsion viscosity relative to the pristine HNTs. Cell culture studies have revealed that polypeptoid-functionalized HNTs are noncytotoxic toward Alcanivorax borkumensis, a dominant alkane degrading bacterium found in the ocean after oil spill. Notably, the functionalized HNTs with higher hydrophobic polypeptoid content (HLB = 12.0-14.3) were shown to induce more cell proliferation than either pristine HNTs or those functionalized with less hydrophobic polypeptoids. It was postulated that the functionalized HNTs with higher hydrophobic polypeptoid content may promote the bacterial proliferation by providing larger oil-water interfacial area and better anchoring of bacteria at the interface.

Thermoresponsive Coatings on Hollow Particles with Mesoporous Shells Serve as Stimuli-Responsive Gates to Species Encapsulation and Release.

Nanoscale capsule-type particles with stimuli-respondent transport of chemical species into and out of the capsule are of significant technological interest. We describe the facile synthesis, properties, and applications of a temperature-responsive silica-poly( N-isopropylacrylamide) (PNIPAM) composite consisting of hollow silica particles with ordered mesoporous shells and a complete PNIPAM coating layer. These composites start with highly monodisperse, hollow mesoporous silica particles fabricated with precision using a template-driven approach. The particles possess a high specific surface area (1771 m2/g) and large interior voids that are accessible to the exterior environment through pore channels of the silica shell. An exterior PNIPAM coating provides thermoresponsiveness to the composite, acting as a gate to regulate the uptake and release of functional molecules. Uptake and release of a model compound (rhodamine B) occurs at temperatures below the lower critical solution temperature (LCST) of 32 °C, while the dehydrated hydrophobic polymer layer collapses over the particle at temperatures above the LCST, leading to a shutoff of uptake and release. These transitions are also manifest at an oil-water interface, where the polymer-coated hollow particles stabilize oil-in-water emulsions at temperatures below the LCST and destabilize the emulsions at temperatures above the LCST. Cryogenic scanning electron microscopy indicates patchlike particle structures at the oil-water interface of the stabilized emulsions. The silica-PNIPAM composite therefore couples advantages from both the hollow mesoporous silica structure and the thermoresponsive polymer.

Microstructural characteristics of surfactant assembly into a gel-like mesophase for application as an oil spill dispersant.

HYPOTHESIS: Polyoxyethylene (20) sorbitan monooleate (Tween 80) can be incorporated into the gel-like phase formed by L-α-phosphatidylcholine (PC) and dioctyl sulfosuccinate sodium salt (DOSS) for potential application as a gel-like dispersant for oil spill treatment. Such gel-like dispersants offer advantages over existing liquid dispersants for mitigating oil spill impacts. EXPERIMENTS: Crude oil-in-saline water emulsions stabilized by the surfactant system were characterized by optical microscopy and turbidity measurements while interfacial tensions were measured by the spinning drop and pendant drop techniques. The microstructure of the gel-like surfactant mesophase was elucidated using small angle neutron scattering (SANS), cryo scanning electron microscopy (cryo-SEM), and 31P nuclear magnetic resonance (NMR) spectroscopy. FINDINGS: The gel-like phase consisting of PC, DOSS and Tween 80 is positively buoyant on water and breaks down on contact with floating crude oil layers to release the surfactant components. The surfactant mixture effectively lowers the crude oil-saline water interfacial tension to the 10-2 mN/m range, producing stable crude oil-in-saline water emulsions with an average droplet size of about 7.81 µm. Analysis of SANS, cryo-SEM and NMR spectroscopy data reveals that the gel-like mesophase has a lamellar microstructure that transition from rolled lamellar sheets to onion-like, multilamellar structures with increasing Tween 80 content.

A Bottle-around-a-Ship Method To Generate Hollow Thin-Shelled Particles Containing Encapsulated Iron Species with Application to the Environmental Decontamination of Chlorinated Compounds.

Thin-shelled hollow silica particles are synthesized using an aerosol-based process where the concentration of a silica precursor tetraethyl orthosilicate (TEOS) determines the shell thickness. The synthesis involves a novel concept of the salt bridging of an iron salt, FeCl3, to a cationic surfactant, cetyltrimethylammonium bromide (CTAB), which modulates the templating effect of the surfactant on silica porosity. The salt bridging leads to a sequestration of the surfactant in the interior of the droplet with the formation of a dense silica shell around the organic material. Subsequent calcination consistently results in hollow particles with encapsulated iron oxides. Control of the TEOS levels leads to the generation of ultrathin-shelled (∼10 nm) particles which become susceptible to rupture upon exposure to ultrasound. The dense silica shell that is formed is impervious to entry of chemical species. Mesoporosity is restored to the shell through desilication and reassembly, again using CTAB as a template. The mesoporous-shelled hollow particles show good reactivity toward the reductive dichlorination of trichloroethylene (TCE), indicating access of TCE to the particle interior. The ordered mesoporous thin-shelled particles containing active iron species are viable systems for chemical reaction and catalysis.

Impact of the Charge Ratio on the In Vivo Immunogenicity of Lipoplexes.

PURPOSE: The present study investigated the immunogenic potential of different cationic liposome formulations with a DNA plasmid encoding Pfs25, a malaria transmission-blocking vaccine candidate. METHODS: Pfs25 plasmid DNA was complexed with cationic liposomes to produce lipoplexes at different charge ratios of the cationic lipid head group to the nucleotide phosphate (N:P). The formation of lipoplexes was visualized by Cryogenic-TEM. Confocal microscopy of lipoplexes formed with GFP encoding plasmid DNA, and flow cytometry was used to determine their in vitro transfection capability. Two different lipoplex formulations using plasmid DNA encoding Pfs25 were evaluated for in vivo immunogenicity after intramuscular administration in Balb/c mice. Immune sera were analyzed by ELISA. RESULTS: The results demonstrated that the cationic liposome-mediated DNA immunization with an N:P charge ratio of 1:3 (anionic lipoplexes) is more effective than the use of naked plasmid DNA alone. No antibody response was observed when lipoplexes with a higher N:P charge ratio of 10:3 (cationic lipoplexes) were used. Trehalose was added to some lipoplex formulations as a cryoprotectant and adjuvant, but it did not yield any further improvement of immunogenicity in vivo. CONCLUSIONS: The results suggest that Pfs25 plasmid DNA delivered as lipoplexes at a charge ratio of 1:3 elicited strong immunogenicity in mice and may be improved further to match the immune responses of DNA vaccines administered by in vivo electroporation.

Aggregation of cyclic polypeptoids bearing zwitterionic end-groups with attractive dipole-dipole and solvophobic interactions: a study by small-angle neutron scattering and molecular dynamics simulation.

Aggregation behavior of cyclic polypeptoids bearing zwitterionic end-groups in methanol has been studied using a combination of experimental and simulation techniques. The data from SANS and cryo-TEM indicate that the solution contains small clusters of these cyclic polypeptoids, ranging from a single polypeptoid chain to small oligomers, while the linear counterpart shows no cluster formation. Atomistic molecular dynamics simulations reveal that the driving force for this clustering behavior is due to the interplay between the effective repulsion due to the solvation of the dipoles formed by the charged end-groups in each polypeptoid chain and the attractive forces due to dipole-dipole interactions and the solvophobic effect.

Amphiphilic Polypeptoids Serve as the Connective Glue to Transform Liposomes into Multilamellar Structures with Closely Spaced Bilayers.

We report the ability of hydrophobically modified polypeptoids (HMPs), which are amphiphilic pseudopeptidic macromolecules, to connect across lipid bilayers and thus form layered structures on liposomes. The HMPs are obtained by attaching hydrophobic decyl groups at random points along the polypeptoid backbone. Although native polypeptoids (with no hydrophobes) have no effect on liposomal structure, the HMPs remodel the unilamellar liposomes into structures with comparable diameters but with multiple concentric bilayers. The transition from single-bilayer to multiple-bilayer structures is revealed by small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). The spacing between bilayers is found to be relatively uniform at ∼6.7 nm. We suggest that the amphiphilic nature of the HMPs explains the formation of multibilayered liposomes; i.e., the HMPs insert their hydrophobic tails into adjacent bilayers and thereby serve as the connective glue between bilayers. At higher HMP concentrations, the liposomes are entirely disrupted into much smaller micellelike structures through extensive hydrophobe insertion. Interestingly, these small structures can reattach to fresh unilamellar liposomes and self-assemble to form new two-bilayer liposomes. The two-bilayer liposomes in our study are reminiscent of two-bilayer organelles such as the nucleus in eukaryotic cells. The observations have significance in designing new nanoscale drug delivery carriers with multiple drugs on separate lipid bilayers and extending liposome circulation times with entirely biocompatible materials.

Focused Ultrasound-Triggered Release of Tyrosine Kinase Inhibitor From Thermosensitive Liposomes for Treatment of Renal Cell Carcinoma.

This study reports, for the first time, development of tyrosine kinase inhibitor-loaded, thermosensitive liposomes (TKI/TSLs) and their efficacy for treatment of renal cell carcinoma when triggered by focused ultrasound (FUS). Uptake of these nanoparticles into renal cancer cells was visualized with confocal and fluorescent imaging of rhodamine B-loaded liposomes. The combination of TKI/TSLs and FUS was tested in an in vitro tumor model of renal cell carcinoma. According to MTT cytotoxic assay and flow cytometric analysis, the combined treatment led to the least viability (23.4% ± 2.49%, p < 0.001), significantly lower than that observed from treatment with FUS (97.6% ± 0.67%, not significant) or TKI/TSL (71.0% ± 3.65%, p < 0.001) at 96 h compared to control. The importance of this unique, synergistic combination was demonstrated in viability experiments with non-thermosensitive liposomes (TKI/NTSL + FUS: 58.8% ± 1.5% vs. TKI/TSL + FUS: 36.2% ± 1.4%, p < 0.001) and heated water immersion (TKI/TSL + WB43°: 59.3% ± 2.91% vs. TKI/TSL + FUS: 36.4% ± 1.55%, p < 0.001). Our findings coupled with the existing use of FUS in clinical practice make the proposed combination of targeted chemotherapy, nanotechnology, and FUS a promising platform for enhanced drug delivery and cancer treatment.

Microstructure and rheology of particle stabilized emulsions: Effects of particle shape and inter-particle interactions.

Using fumed and spherical silica particles of similar hydrodynamic size, we investigated the effects of particle shape and inter-particle interactions on the formation, stability and rheology of bromohexadecane-in-water Pickering emulsions. The interparticle interactions were varied from repulsive to attractive by modifying the salt concentration in the aqueous phase. Optical microscope images revealed smaller droplet sizes for the fumed silica stabilized emulsions. All the emulsions remained stable for several weeks. Cryo-SEM images of the emulsion droplets showed a hexagonally packed single layer of particles at oil-water interfaces in emulsions stabilized with silica spheres, irrespective of the nature of the inter-particle interactions. Thus, entropic, excluded volume interactions dominate the fate of spherical particles at oil-water interfaces. On the other hand, closely packed layers of particles were observed at oil-water interfaces for the fumed silica stabilized emulsions for both attractive and repulsive interparticle interactions. At the high salt concentrations, attractive inter-particles interactions led to aggregation of fumed silica particles, and multiple layers of these particles were then observed on the droplet surfaces. A network of fumed silica particles was also observed between the emulsion droplets, suggesting that enthalpic interactions are responsible for the determining particle configurations at oil-water interfaces as well as in the aqueous phase. Steady shear viscosity measurements over a range of shear stresses, as well as oscillatory shear measurements at 1Hz confirm the presence of a network in fumed silica suspensions and emulsions, and the lack of such a network when spherical particles are used. The fractal structure of fumed silica leads to several contact points and particle interlocking in the water as well as on the bromohexadecane-water interfaces, with corresponding effects on the structure and rheology of the emulsions. The attenuation of droplet motion due to the formation of a particle network can be exploited for stabilizing emulsions and for modulating their rheology.