Absence Of Cosurfactant Research Articles

Co-Surfactant-Free Bioactive Protein Nanosheets for the Stabilization of Bioemulsions Enabling Adherent Cell Expansion.

Bioemulsions are attractive platforms for the scalable expansion of adherent cells and stem cells. In these systems, cell adhesion is enabled by the assembly of protein nanosheets that display high interfacial shear moduli and elasticity. However, to date, most successful systems reported to support cell adhesion at liquid substrates have been based on coassemblies of protein and reactive cosurfactants, which limit the translation of bioemulsions. In this report, we describe the design of protein nanosheets based on two globular proteins, bovine serum albumin (BSA) and β-lactoglobulin (BLG), biofunctionalized with RGDSP peptides to enable cell adhesion. The interfacial mechanics of BSA and BLG assemblies at fluorinated liquid-water interfaces is studied by interfacial shear rheology, with and without cosurfactant acyl chloride. Conformational changes associated with globular protein assembly are studied by circular dichroism and protein densities at fluorinated interfaces are evaluated via surface plasmon resonance. Biofunctionalization mediated by sulfo-succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) is studied by fluorescence microscopy. On the basis of the relatively high elasticities observed in the case of BLG nanosheets, even in the absence of cosurfactant, the adhesion and proliferation of mesenchymal stem cells and human embryonic kidney (HEK) cells on bioemulsions stabilized by RGD-functionalized protein nanosheets is studied. To account for the high cell spreading and proliferation observed at these interfaces, despite initial moderate interfacial elasticities, the deposition of fibronectin fibers at the surface of corresponding microdroplets is characterized by immunostaining and confocal microscopy. These results demonstrate the feasibility of achieving high cell proliferation on bioemulsions with protein nanosheets assembled without cosurfactants and establish strategies for rational design of scaffolding proteins enabling the stabilization of interfaces with strong shear mechanics and elasticity, as well as bioactive and cell adhesive properties. Such protein nanosheets and bioemulsions are proposed to enable the development of new generations of bioreactors for the scale up of cell manufacturing.

Evaluating the potential of natural surfactants in the petroleum industry: the case of hydrophobins

Abstract Enhancing oil recovery from currently available reservoirs is a major issue for petroleum companies. Among the possible strategies towards this, chemical flooding through injection of surfactants into the wells seems to be particularly promising, thanks to their ability to reduce oil/water interfacial tension that promotes oil mobilization. Environmental concerns about the use of synthetic surfactants led to a growing interest in their replacement with surfactants of biological origin, such as lipopeptides and glycolipids produced by several microorganisms. Hydrophobins are small amphiphilic proteins produced by filamentous fungi with high surface activity and good emulsification properties, and may represent a novel sustainable tool for this purpose. We report here a thorough study of their stability and emulsifying performance towards a model hydrocarbon mixture, in conditions that mimic those of real oil reservoirs (high salinity and high temperature). Due to the moderate interfacial tension reduction induced in such conditions, the application of hydrophobins in enhanced oil recovery techniques does not appear feasible at the moment, at least in absence of co-surfactants. On the other hand, the obtained results showed the potential of hydrophobins in promoting the formation of a gel-like emulsion ‘barrier’ at the oil/water interface.

Effects of Temperature and Humidity History on Brittleness of α-Sulfonated Fatty Acid Methyl Ester Salt Crystals.

α-Sulfonated fatty acid methyl ester salts (MES), which were made from vegetable sources, are attractive candidates for eco-friendly washing detergents because they have various special features like excellent detergency, favorable biodegradability, and high stability against enzymes. To overcome some disadvantages of powder-type detergents like caking, sorting, and dusting, we studied how temperature and humidity history, as a model for long-term storage conditions, can affect crystalline structures and reduce the brittleness of MES powder. We characterized the crystalline structure of MES grains using small-angle X-ray scattering, wide-angle X-ray scattering, differential scanning calorimetry, and Fourier transform infrared spectroscopy measurements and determined the yield values, which measure the brittleness of MES grains, in shear stress using dynamic viscoelasticity measurements. This study confirmed that MES crystals form three pseudo-polymorphs via thermal or humidity conditioning: metastable crystals (αsubcell), anhydrous crystals (β subcell), and dihydrate crystals (β' subcell). Further, we found that the yield value increases upon phase transition from the β subcell to the β' subcell and from the β' subcell to the αsubcell. Therefore, controlling the thermal and humidity conditioning of MES grains is an effective way to decrease the brittleness of MES powders and can be used to overcome the above mentioned disadvantages of powder-type detergents in the absence of co-surfactants.

A Nonconventional Model of Protocell-like Vesicles: Anionic Clay Surface-Mediated Formation from a Single-Tailed Amphiphile

We report a novel model system of precursor cellular membranes, self-assembled from micellar solution of a common anionic single-tailed amphiphile (STA), including sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). The self-assembly process was mediated with solid surfaces of Mg2Al-CO3 hydrotalcite-like compound (HTlc), an anionic clay, in the absence of cosurfactants or any additives. The resultant STA vesicles were characterized using negative-staining and cryogenic transmission electron microscopies, as well as dynamic light scattering and steady state fluorescence techniques. Interestingly, the obtained STA vesicles displayed good stability even after the removal of the anionic clay surface (ACS), and a self-reproduction phenomenon was observed for the "preformed" STA vesicles when mixing with corresponding STA micellar solutions. More importantly, the micelle-to-vesicle transition for SDS could be still arisen in high-salinity artificial seawater under the ACS mediation. Instead of conventional fatty acid scenario, our finding provides another novel possible model for protocell-like vesicles, which are easily formed under the plausible prebiotic conditions.

Rough glass surface-mediated transition of micelle-to-vesicle in sodium dodecylbenzenesulfonate solutions.

In this paper, we report a micelle-to-vesicle transition in aqueous solution of the anionic single-tailed surfactant (STS) sodium dodecylbenzenesulfonate (SDBS), with the mediation of a rough glass surface (RGS) in the absence of cosurfactants or additives. This transition produced a mixed solution of vesicles and micelles. Interestingly, the obtained SDBS vesicles in the solution displayed good stability during a long-term storage (at least 6 months at room temperature), exposure to high temperature (80 °C for 2 h), and freeze-thawing (-20 or -196 °C for 2 h to approximately 25 °C) after the RGS was removed. Our results confirmed that SDBS could adsorb on the RGS to form bilayers, in which the molecular packing parameter of SDBS was in the range of 1/2-1. The bilayer adsorption and the roughness of the solid surface played an important role in the vesicle formation. In addition, we propose a possible mechanism for the RGS-mediated transition of micelle-to-vesicle in SDBS solutions: SDBS micelles and molecules adsorb on the RGS to form curved bilayers; the curved bilayers detach from the RGS, and then close to form vesicles.

Fabrication of Lipophilic Nanoparticles by Spontaneous Emulsification: Stabilization by Cosurfactants

Lipid nanoparticles are increasingly being used to encapsulate and deliver lipophilic bioactive components in food, pharmaceutical, and personal care products. These nanoparticles can be produced by high-energy or low-energy methods, with the latter approach having advantages in terms of simplicity, lower energy demands, and reduced production costs. In this study, a model system consisting of non-ionic surfactant (Brij 30), hydrocarbon oil (n-octadecane) and aqueous phase (citric acid buffer, pH 3.0) was used to examine the impact of cosurfactants on the stability of nanoemulsions produced by spontaneous emulsification. Initially, the optimum surfactant-to-oil ratio (SOR) for preparing nanoemulsions with small droplets was established: SOR = 0.5. In the absence of cosurfactants, the surfactant-oil–water (SOW) system formed by spontaneous emulsification contained large irregular structures (>10 μm) that remained after dilution. However, addition of cosurfactants (SDS or Tween 80) to the SOW system promoted the formation of nanoemulsions (d < 100 nm) that were stable to droplet growth. The nanoemulsions also had good thermal stability when SDS was used as a cosurfactant (25–90 °C), but underwent rapid coalescence above 50 °C when Tween 80 was used. This study suggests that cosurfactants improve the stability of nanoemulsions by disrupting the formation of liquid crystal like structures and altering the phase inversion temperature.

Modulating lipid droplet intestinal lipolysis by electrostatic complexation with anionic polysaccharides: Influence of cosurfactants

The food, supplement, and pharmaceutical industries are interested in developing delivery systems that can control the biological fate of ingested lipids within the gastrointestinal tract. In this study, a simulated intestinal lipolysis model was used to elucidate the impact of cosurfactants and anionic polysaccharides on the digestion of emulsified fats. Lipid droplets were prepared by membrane homogenization using a globular protein (β-lactoglobulin) as the primary surfactant, and a non-ionic surfactant (Tween 20) as the cosurfactant. Electrostatic complexes were formed by mixing the resulting cationic lipid droplets with anionic alginate molecules. In the absence of cosurfactant, multilayer emulsions were formed consisting of lipid droplets coated by a layer of alginate. In the presence of cosurfactant, microclusters were formed that contained aggregates of alginate-coated lipid droplets linked together. The electrical charge on the complexes remained negative from pH 2 to 7.5, with the complexes formed in the presence of cosurfactant having a lower charge magnitude. The rate and extent of lipid digestion under simulated intestinal lipolysis conditions depended on cosurfactant, alginate, and digestion conditions (fasted versus fed). Under high calcium fed conditions (20 mM Ca2+), lipid digestion was highly suppressed in delivery systems containing alginate but no cosurfactant, which was attributed to the formation of a calcium alginate gel that restricted access of lipase to the lipid droplets. This reduction in lipid digestion could be largely overcome by including cosurfactant in the delivery systems. The information obtained in this study may prove useful for designing oral delivery systems that control the digestion and release of lipids in the gastrointestinal tract.

Microemulsions as Reaction Media for the Synthesis of Mixed Oxide Nanoparticles: Relationships between Microemulsion Structure, Reactivity, and Nanoparticle Characteristics

Phase behavior, dynamics, and structure of W/O microemulsions of the system aqueous solution/Synperonic 13_6.5/1-hexanol/isooctane were studied, with the goal of determining their effect on Mn-Zn ferrite nanoparticle formation, kinetics and characteristics. Microemulsion structure and dynamics were studied systematically by conductivity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), and small-angle neutron scattering (SANS). The main effect of cosurfactant 1-hexanol was a decrease in microemulsion regions as compared to the systems without cosurfactant; nevertheless, overlap of microemulsion regions in the systems with precursor salts (PS) and precipitating agent (PA) was achieved at lower S/O ratios, compared to the system without cosurfactant. At 50 °C, PA microemulsions are nonpercolated, while PS microemulsions are percolated. SANS indicates small prolate ellipsoidal micelles with the absence of free water up to 18 wt % PS solution; DSC studies confirm the absence of free water in this composition range. Kinetic studies show an increase in the reaction rate with increasing concentration of the aqueous solution; but the most significant effect in reaction kinetics was noted when cosurfactant was used, regardless of microemulsion dynamics and structure. On the other hand, the main difference regarding the characteristics of the obtained nanoparticles was observed when bicontinuous microemulsions were used as reaction media which resulted in 8 nm nanoparticles, versus a constant size of ~4 nm obtained with all other microemulsions regardless of aqueous solution content, dynamics, and presence or absence of cosurfactant. The latter effect of constant size is attributed to the fact that the water present is dominantly bound to the EO units of the surfactant.

Transdermal delivery of hydrocortisone from eucalyptus oil microemulsion: Effects of cosurfactants

This study investigated the effects of cosurfactants on the transdermal delivery of hydrocortisone (model drug) from eucalyptus oil microemulsion. Eucalyptus oil which was successfully employed for steroidal drugs was used as the oil. Tween 80 which was readily miscible with eucalyptus oil was used as surfactant. Ethanol, isopropanol and propylene glycol which are relatively tolerable by the skin were employed as cosurfactants. Pseudo-ternary phase diagrams were constructed in the presence and absence of cosurfactants. Microemulsion formulations containing 20% oil, 20% water and 60% of either Tween 80 or 1:1 surfactant/cosurfactant mixture were compared. Incorporation of cosurfactants expanded the microemulsion zone. The cosurfactant free microemulsion was viscous showing pseudo-plastic flow. The cosurfactant containing preparations were less viscous with Newtonian flow. The drug loading and release rate were increased in the presence of cosurfactants with the release depending on the viscosity. Incorporation of hydrocortisone in microemulsion increased the transdermal flux compared to saturated aqueous solution. The presence of cosurfactants increased the transdermal drug flux compared to the cosurfactant free formulation. Ethanol produced the greatest effect followed by propylene glycol and isopropanol. The presence of cosurfactant and its type can thus affect both the phase behavior and the transdermal delivery potential of microemulsion.

Phase inversion temperatures of triton X‐100/1‐butanol/hydrocarbon/water systems

AbstractThe formation of a water‐in‐oil (w/o) microemulsion in Triton X‐100/1‐butanol/alkane/water systems was investigated at 25.0±0.1°C. Phase inversion temperatures in hydrocarbon‐water microemulsions stabilized with Triton X‐100 were determined for different hydrocarbons. It was found that the more soluble the alkane (oil), functioning as a nonionic emulsifier, the lower was the phase inversion temperature, above which oil‐in‐water type microemulsions invert to w/o type. The effect of the presence of cosurfactant was studied. No phase inversion was observed in the absence of cosurfactant. The effect on phase inversion temperature of decreasing or increasing the temperature was evaluated. By definition, phase inversion was not affected by different temperatures.

Influence of Cosurfactants on the Properties of Mesostructured Materials

The effects of the addition of two different types of cosurfactants, n-alkylamine and n-alkyl alcohol, on the phase behavior of silicate-surfactant mesophases and the pore size of the calcined materials have been investigated using X-ray diffraction, N2-sorption, TG-MS, and solid state 1H and 13C NMR spectroscopy. The cosurfactants were added to a standard room-temperature synthesis, which results in a MCM-41 type, hexagonally ordered material in the absence of cosurfactant. Their addition led either to an increase or a decrease of the pore size and d spacing of the hexagonal mesophase, depending on the nature of the polar headgroup and on the chain length of the cosurfactant. For high cosurfactant/surfactant ratios, however, a transition to a lamellar phase was usually observed. The d spacing and the pore size of the hexagonal mesophase can be decreased considerably down to the supermicropore range by addition of butylamine without a marked decrease in the long-range order of the material. The addition of alcohol, on the other hand, resulted in an increase in the d spacing of the hexagonal phase by up to 3 Å. These results are discussed in terms of differences in the ability of the cosurfactants to interact with the silicate as well as cosurfactant-induced changes in the packing parameter.

Phase Behavior of Lecithin–Water Mixtures inn-Hexane and Near-Critical Propane: Influence of Cosurfactants Caprylic Acid and 1-Butanol

The phase behavior of mixtures of water and lecithin in near-critical propane andn-hexane was studied as a function of the overall water concentrationcoverall(water) with and without added cosurfactant. Six different equilibria were identified inn-hexane with increasingcoverall(water) in the absence of cosurfactant, whereas only two different equilibria were observed in the presence of one mole of caprylic acid per mole lecithin. Using near-critical propane as the continuous phase solvent, the phase behavior could be varied as a function of pressure. Cloud-point pressures were determined with and without caprylic acid. An unusual behavior was found for the cloud-point pressure as a function ofcoverall(water). In the absence of cosurfactant, the formation of a highly viscous organogel was observed at low overall water concentrations. This gel formation was reversible and pressure dependent.

SOLUBILIZATION, MICROEMULSIONS AND SURFACE CHEMISTRY OF ETHYL STEARATE IN AQUEOUS SOLUTIONS OF A NONIONIC EMULSIFIER

ABSTRACT The solubilization limit of ethyl stearate in aqueous solutions of the nonionic emulsifier Teric X10 was determined precisely by measurements of the density of the aqueous layer. Interfacial tensions were measured in order to gain some information concerning ageing effects and the behaviour of various species at the interface. A distinction was drawn between those systems occurring below the solubilization limit which are thermodynamically - stable microemulsions and include normal micellar systems, in the presence or absence of cosurfactant; and systems above the solubilization limit which are kinetically - stable microemulsions (miniemulsions) and typically are coarse emulsions. Systems above the solubilization limit achieve thermodynamic equilibrium by separating into two phases.

Liquid-crystalline and microemulsion phase behavior in alcohol-free Aerosol-OT/oil/brine systems

The phase behavior of systems containing the pure anionic surfactant Aerosol OT or sodium bis(2-ethylhexyl) sulfosuccinate was studied as a function of salt concentration, surfactant concentration, alkane carbon number, and water-to-oil ratio. Since the hydrophilic and lipophilic properties of Aerosol OT are nearly balanced, the surfactant forms microemulsions with water and oil in the absence of cosurfactant, allowing for simplified representation of phase behavior. In particular, this property aided in the understanding of transitions between the aqueous surfactant phase behavior and the well-studied oil-rich microemulsion regime. With the addition of salt to dilute alcohol-free surfactant-water mixtures, transitions in the liquid-crystalline phases similar to those seen previously for systems containing petroleum sulfonates and other anionic surfactants with alcohol cosurfactants were found. When hydrocarbons of various chain lengths were equilibrated with the aqueous surfactant solutions, again behavior similar to that of anionic surfactants with alcohol cosurfactants was observed. Pseudoternary diagrams of surfactant-brine-oil were constructed at various brine salinities with n-dodecane as the oil. The assumption that brine acts as a pseudocomponent was found to work best at salinities well below and well above the optimum and at low surfactant concentrations. In any case, the results provide extensive information on phase behavior ofmore » a four-component system containing a pure anionic surfactant, a pure hydrocarbon, and sodium chloride brine over a region of considerable interest for enhanced oil recovery and other applications.« less