Classical Emulsion Research Articles

Caffeic Acid in Dermatological Formulations: In Vitro Release Profile and Skin Absorption.

Caffeic acid (CA) is a cinnamic acid derivative, found in many vegetable products, with powerful antioxidant activity, the ability to increase collagen production and capacity to prevent premature aging of the skin. The classic emulsions of CA are widely used by the consumer to provide a pleasant, refreshing sensorial experience; however, preparations developed in the form of dry film are presented as a technological alternative due to its facile and safe transportation. The aim of this study was to evaluate the release, permeation, and retention of CA in a film and emulsion through in vitro experiments. The release evaluation of CA from the emulsion and the film was performed using modified Franz diffusion cells, with an area of 1.77 cm², using Microette equipment (Hanson Research) with a cellulose membrane. The evaluation of the permeation of CA from the formulations was conducted using a similar technique of release, except that a biological membrane was used. High release of active compound and reduced permeation was observed, indicating that CA was able to be retained in the epidermis/dermis, where it should have the desired action. The concentration of caffeic acid in the skin was higher for the film formulation than for the emulsion. This demonstrates a greater efficiency of this type of innovative release system, besides its facile and safe transportation. The formulations tested in this paper can release caffeic acid with a Higuchi kinetic profile, in which release of active ingredient occurs by a diffusion process. The film formulations exhibited a lower permeation rate and higher retention in the skin, which is essential for a cosmetic product. The concentration of CA in the skin was also higher for the film formulation when compared to the emulsion. This demonstrates a greater efficiency of this type of innovative release system, in addition to its easy and safe transportation. Therefore, it is possible to suggest CA as a promising substance for dermal use due to its antioxidant, anti-inflammatory, antimicrobial, and collagen production stimulating activity.

Formulation and Composition Effects in Phase Transitions of Emulsions Costabilized by Cellulose Nanofibrils and an Ionic Surfactant.

Cellulose nanofibrils (CNF) offer great prospects as a natural stabilizer of colloidal dispersions and complex fluids for application in food, pharma, and cosmetics. In this study, an ionic surfactant (sodium dodecyl sulfate, SDS) was used as emulsifier of oil-in-water and water-in-oil emulsions that were further costabilized by addition of CNF. The adsorption properties of SDS in both, CNF dispersions and emulsions, as well as the influence of composition (CNF and SDS concentration) and formulation (ionic strength, oil, and CNF types) on the phase behavior were elucidated and described in the framework of Windsor systems. At low salinity, the phase transition of emulsions containing CNF and SDS at low concentrations was controlled by molecular transfer in the oil-in-water system. Irregular droplets and "bi-continuous" morphologies were observed at medium and high salinity for systems containing high CNF and SDS concentrations. Water-in-oil emulsions were only possible at high salinity and SDS concentrations in the presence of small amounts of CNF. The results revealed some subtle differences in CNF interfacial activity, depending on the method used for their isolation via fiber deconstruction, either from microfluidization or aqueous counter collision. Overall, we propose that the control of emulsion morphology and stability by addition of CNF opens the possibility of developing environmentally friendly complex systems that display high stability and respond to ionic strength following the expectations of classical emulsion systems.

A comparative study on kinetics and substrate specificities of Phospholipase A1 with Thermomyces lanuginosus lipase

The mechanism of lipase binding to the lipid-water interface is crucial for substrate specificity and kinetic properties. In this study, the chain-length specificity, regiospecificity and substrate specificity of Phospholipase A1 (PLA1) and its parent enzyme Thermomyces lanuginosus lipase (TLL) have been investigated using a classical emulsion system. The results show that both PLA1 and TLL are 1,3-regioselective lipases. Additionally, the hydrolytic activity of PLA1 is comparatively lower on short-chain triacylglyceride (TAG) and higher on phosphatidylcholine (PC) than the hydrolytic activity of TLL. Further, the results obtained with monolayer film techniques demonstrate that the C-terminal region regulates the binding of PLA1 to PC. A hypothesis is presented according to which the α9 helix of C-terminal region in PLA1 not only controls the opening of lid but also serves as a membrane anchor that assists in binding to PC. These findings bring new insight into rational design of novel lipases with intriguing functionalities.

Recent Studies of Pickering Emulsions: Particles Make the Difference.

In recent years, emulsions stabilized by micro- or nanoparticles (known as Pickering emulsions) have attracted much attention. Micro- or nanoparticles, as the main components of the emulsion, play a key role in the preparation and application of Pickering emulsions. The existence of particles at the interface between the oil and aqueous phases affects not only the preparation, but also the properties of Pickering emulsions, affording superior stability, low toxicity, and stimuli-responsiveness compared to classical emulsions stabilized by surfactants. These advantages of Pickering emulsions make them attractive, especially in biomedicine. In this review, the effects of the characteristics of micro- and nanoparticles on the preparation and properties of Pickering emulsions are introduced. In particular, the preparation methods of Pickering emulsions, especially uniform-sized emulsions, are listed. Uniform Pickering emulsions are convenient for both mechanistic research and applications. Furthermore, some biomedical applications of Pickering emulsions are discussed and the problems hindering their clinical application are identified.

One Pot Synthesis of a Polyisoprene Polyrotaxane and Conversion to a Slide‐Ring Gel

Synthesis of a cyclodextrin (CD) polyrotaxane is achieved for the first time by simultaneous free radical polymerization of isoprene, threading by CD, and stoppering by copolymerization of styrene. This reaction is performed in an eco-friendly manner in an aqueous medium similar to classical emulsion polymerization. Threaded CD rings of the polyrotaxane are cross-linked by hexamethylene diisocyanate, leading to highly elastic slide-ring gels.

Starch-based Pickering emulsions for topical drug delivery: A QbD approach

Pickering emulsions are stabilized by solid particles instead of surfactants and have been widely investigated in pharmaceutical and cosmetic fields since they present less adverse effects than the classical emulsions. A quality by design (QbD) approach was applied to the production of w/o emulsions stabilized by starch. A screening design was conducted to identify the critical variables of the formula and the process affecting the critical quality properties of the emulsion (droplet size distribution). The optimization was made by establishing the Design Space, adjusting the concentration of starch and the quantity of the internal aqueous phase. The emulsion production process was, in turn, adjusted by varying the time and speed of stirring, to ensure quality and minimum variability. The stability was also investigated, demonstrating that an increase in starch concentration improves the stability of the emulsion. Rheological and mechanical studies indicated that the viscosity of the emulsions was enhanced by the addition of starch and, to a higher extent, by the presence of different lipids. The developed formulations was considered non-irritant, by an in vitro assay using human cells from skin (Df and HaCat) with the cell viability higher than 90% and, with self-preserving properties. Finally, the QbD approach successfully built quality in Pickering emulsions, allowing the development of hydrophilic drug-loaded emulsions stabilized by starch with desired organoleptic and structural characteristics. The results obtained suggest that these systems are a promising vehicle to be used in products for topical administration.

Sol–gel microencapsulation of oil phase with Pickering and nonionic surfactant based emulsions

Sol–gel polycondensation was used to encapsulate two different kinds of core with a silica shell, i.e. castor oil which is considered as a model active agent, and bisphenol A bis(diphenyl phosphate), an insoluble liquid fire retardant. The influence of the nature of the emulsifier was also studied, i.e. Pickering emulsion based on the interface stabilization performed by the organization of solid nanoparticles was compared to a classical emulsion process using a non-ionic surfactant. The influence of both cores and emulsifiers on the stability of emulsion was studied by granulometric analysis, optical microscopy and macroscopic morphology (from nacked-eye observations). The sol–gel encapsulation efficiency was assessed by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. Finally, thermal stability of microcapsules was evaluated by thermogravimetric analysis (TGA). Results show that both Pickering and classical emulsions processing allow successful sol–gel encapsulation of castor oil and bisphenol A bis (diphenyl phosphate) with a satisfying thermal stability for textile application. However, the use of Pickering emulsion with nanoparticles provides more highly stable emulsions and promotes silica shell formation.

Surfactant Assisted Emulsion Crystallization of Hydrogenated Castor Oil

In this paper, the crystallization mechanism of hydrogenated castor oil (HCO) is studied. In contrast to what occurs for a classical emulsion crystallization, the surfactant present in the aqueous phase is shown to enable an aqueous phase driven crystallization forming nonspherical, sometimes highly elongated, crystals. The presence of surfactant appears to be crucial, as it increases the solubility of HCO and sustains crystal growth of aqueous crystals. This is demonstrated by linking the formation of these nonspherically shaped crystals with a required relatively high solubility obtained by adding surfactant. The solubilized HCO concentration versus the crystal shapes is presented for four different surfactants as a function of the surfactant concentration: amine oxide, sodium and monoethylamine linear alkylbenzenesulfonate and sodium dodecyl sulfate. Furthermore, under certain conditions the emulsified HCO is shown to completely crystallize in the aqueous phase, even if at the start of the crystallizat...

Nanoprecipitation is more efficient than emulsion solvent evaporation method to encapsulate cucurbitacin I in PLGA nanoparticles

Cucurbitacin I is a hydrophobic molecule that exerts a degree of polarity, which is expected to complicate its loading in PLGA nanoparticles by the classical emulsion solvent evaporation technique. In the current study, variants of emulsion solvent evaporation method were used to prepare PLGA nanoparticles of cucurbitacin: CI-NP1 (single emulsion starting with 1000μg drug), CI-NP2 (double emulsion starting with 250μg drug), and CI-NP3 (double emulsion starting with 500μg drug). On the other hand, CI-NP4 was prepared by nanoprecipitation (starting with 1000μg drug). In CI-NP1, cucurbitacin I encapsulation efficiency (EE) was 1.29%. The employment of double emulsion, in CI-NP2 and CI-NP3, increased cucurbitacin I EE to 4.8% and 7.96%, respectively. Nanoprecipitation significantly increased the EE of cucurbitacin I to 48.79% in CI-NP4. It is likely that cucurbitacin I escapes with the organic solvent after the emulsification step to the aqueous phase leading to ineffective entrapment in the polymeric matrix. Avoiding emulsification seems efficient in increasing cucurbitacin I disposition in the instantly-precipitating NPs. Therefore, nanoprecipitation method increases cucurbitacin I entrapment in PLGA NPs and possibly other water-insoluble polar drugs.

Sulfonated poly(pentafluorostyrene): Synthesis & characterization

Abstract Preparation of a high molecular weight polypentafluorostyrene (PFS) and sulfonated polypentafluorostyrene (sPFS) is described in this paper. The high molecular weight PFS was obtained via classical emulsion polymerization reaction, which increased the molecular weight of PFS of about one order of magnitude higher than the one of the commercial polymer. The molecular weight is a crucial factor for the film forming properties of a polymer membrane, following the concept the higher–the better. Furthermore, we post-sulfonated the PFS by 100% (one sulfonic acid per styrene unit). This provided a polymer possessing very high ion-exchange capacity (IEC = 3.4 mmol g − 1 ) with functional group coupled to the relatively flexible side units (phenyl rings). The phenyl rings are fluorinated which enhanced the nucleophilic substitution reaction (introduction of the functional groups) and reduced the pKa value of the resulting sulfonic acid (pKa = − 2). The morphology of sPFS, studied by Small Angle Neutron and X-rays Scattering, revealed a high ordering of a nano-phase-separated system. All these factors raised the conductivity to one of the highest measured on polyelectrolyte (σ = 36 mS cm − 1 at T = 160 °C, p (H 2 O) = 10 5 Pa). This value is one order of magnitude higher than the conductivity of Nafion 117 measured under the same conditions.

Modeling of the Temperature Profile in an Ethylene Polymerization Fluidized-Bed Reactor in Condensed-Mode Operation

Condensed-mode operation of an ethylene polymerization fluidized-bed reactor is of great significance in academic and industrial circles. Based on the classical emulsion–bubble two-phase model, thi...

Novel approaches to improve the particle size distribution prediction of a classical emulsion polymerization model

A recent investigation on the homopolymerization of styrene (Hosseini et al., 2012a) showed that the classical population balance models are incapable of predicting the evolution of the breadth of the experimental particle size distributions correctly when a high resolution discretization method is used to suppress the numerical errors. Also by re-tuning the model parameters the model predictions did not fit the experimental results which points to a structural inadequacy of the conventional deterministic growth models in describing the experimentally observed broadening phenomenon. Two novel approaches are suggested in this work to improve the predictions. In the first approach, a possibly size dependent stochastic term is added to the deterministic growth kernel to account for the inhomogeneities of the growth process. The probability distribution of the resulting stochastic differential equation evolves over time based on the Fokker–Planck equation. The parameters of the (possibly size dependent) dispersion term of the Fokker–Planck equation are used as tuning parameters to fit the model to the experimental results. In the second approach, the growth kernel is extracted from the characteristics of the transient experimental particle size distributions. The extracted growth kernel is described in terms of the states of the system which affect the growth phenomenon. The advantages and disadvantages of both approaches are highlighted.

Snowballing Radical Generation Leads to Ultrahigh Molecular Weight Polymers

Styrene is the classical monomer obeying zero-one kinetics in radical emulsion polymerization. Accordingly, particles that are less than 100 nm in diameter contain either one or no growing radical(s). We describe a unique photoinitiated polymerization reaction accelerated by snowballing radical generation in a continuous flow reactor. Even in comparison to classical emulsion polymerization, these unprecedented snowballing reactions are rapid and high-yielding, with each particle simultaneously containing more than one growing radical. This is a consequence of photoinitiator incorporation into the nascent polymer backbone and repeated radical generation upon photo-irradiation.

Emulsion polymerization of styrene using irreversible addition–fragmentation chain transfer agents: effect on the course of the polymerization and molecular weight

The emulsion polymerization of styrene with three different chain transfer agents (CTAs) based on irreversible addition–fragmentation chain transfer (AFCT) mechanism was first reported in this work. The influences of these irreversible AFCT agents on the rate of polymerization, particle size, and molecular weight were investigated. It was found that the intrinsic activity and desorption behaviors of the CTAs determined the efficiency for molecular weight control, rate of polymerization, and particle size in the emulsion polymerization. It has been demonstrated that the rate of polymerization and particle size decreased dramatically in the presence of the irreversible AFCT agents with high chain transfer constant (ethyl α-p-toluenesulfonyl-methacrylate), meanwhile, the molecular weight of the polystyrene could not be controlled well, whereas the irreversible AFCT agents with low chain transfer constant (butyl(2-phenylallyl)sulfane and 2,3-dichloropropene) had a slight effect on the polymerization rate, particle size, and were fairly well for molecular weight control over the whole conversion range in the emulsion polymerization of styrene. The average number of radicals per particle and the number-average molecular weight were calculated by classical radical emulsion polymerization theory, and the experimental results were in good agreement with the results of model calculations, when the irreversible AFCT agents were used as CTAs. The effect of chain transfer agents on the kinetics and nucleation in the emulsion polymerization of styrene can be attributed to desorption of chain-transferred radicals from the polymer particles. The results of this work show that butyl(2-phenylallyl)sulfane as CTA in emulsion polymerization of styrene provides the best balance between the rate of polymerization and the efficiency for molecular weight control conflicting tendencies.

Application of a Novel Initiator on Acrylic Emulsion Polymerization

New initiator of FFM6 is used to initiate the acrylic emulsion polymerization. The influences of concentration of FFM6 (c[I]) and polymerization temperature (T) on polymerization reaction rate (Rp) were discussed.Rpis proportional to (c[I])1.4which is different with classical emulsion polymerization whoseRpis proportion to (c[I])0.4, that indicate polymerization mechanism of the reaction in the study is different with classical mechanism. The value ofEa, 56.4 kJ/mol, is lower than the value of general radical polymerization’sEa(80.0-96.0 kJ/mol), which indicates the FFM6 can initiate acrylic emulsion polymerization at a lower temperature compared with the other kinds of initiator.

Novel Micro- and Nano-particles Cellulose Based Pickering Emulsions.

AbstractEmulsions are usually metastable systems of two non-miscible phases stabilized by surface active species like surfactant molecules. Emulsions stabilized by solid colloidal particles adsorbed at the interface (Pickering emulsions) offer some competitive advantages with respect to classical emulsions. Most studies published up to now concern emulsions stabilized by inorganic (metallic oxides, exfoliated clays, carbonates and phosphates) or polymeric particles while biomass derived alternatives have only been explored to a limited extent. For the first time, we report the stabilization of emulsions by unmodified cellulose nanocrystals [1, 2] . Cellulose nanocrystals were produced from bacterial cellulose and used to form Pickering emulsions. We demonstrate by SEM that the nanocrystals are adsorbed at the oil/water interface. We also study the size distribution of the droplets that was found to range around 4μm in diameter with very narrow dispersity. The stability of the emulsions was also investigated. The fabrication of new armored microparticles exposing cellulose acicular nanocrystals from cellulose nanocrystals opens opportunities to build materials from low cost and environmental friendly resource.

Formulation of Dry Emulsion for Topical Applications

Dry emulsions were investigated for their possible use in cosmetic and pharmaceutical fields and an extract of Vitis vinifera leaves was obtained and characterized in terms of quality and quantitative levels, which can be introduced in a selected dry emulsion formulation. Several pre-dry emulsions were prepared, six of which were chosen as a consequence of their satisfying physico-chemical and over-time stability characteristics. They were successively freeze-dried and reconstituted after optimising the reconstitution modalities and characterized by optical microscopy, granulometric and thermal analysis, FTIR analysis, rheology, and texture studies. The best formulation was chosen to introduce Vitis vinifera dry extract prepared by percolation: a fair increase in anthocians stability was noted over time in dry emulsions as compared with classic emulsions.

Topical delivery of lipophilic drugs from o/w Pickering emulsions

Surfactant-free emulsions stabilized by solid particles (Pickering emulsions) have been evaluated in the terms of skin absorption of lipophilic drugs. The behavior of three formulations: a surfactant-based emulsion, a Pickering emulsion stabilized by silica particles and a solution in triglyceride oil, were compared in order to assess the effect of the surface coating of Pickering emulsions as new dosage forms for topical application. Such comparative investigation was performed in vitro on excised pig skin in Franz diffusion cells with all-trans retinol as model lipophilic drug. Surfactant-based (classical, CE) and Pickering (PE) oil-in-water emulsions containing retinol were prepared with the same chemical composition (except the stabilizing agent: surfactant or silica particles), the same droplet size and the same viscosity. No permeation through the skin sample was observed after 24 h exposure because of the high lipophilic character of retinol. Penetration of retinol was 5-fold larger for both CE and PE than for the solution in triglyceride. The distribution of retinol inside the skin layers depended significantly on the emulsions type: the classical emulsion allowed easy diffusion through the stratum corneum, so that large amounts reached the viable epidermis and dermis. Conversely, high storage of retinol inside the stratum corneum was favored by the Pickering emulsion. The retinol content in stratum corneum evaluated by skin stripping, demonstrated the increased retinol accumulation from PE. Therefore Pickering emulsions are new drug penetration vehicles with specific behavior; they are well-suited either for targeting the stratum corneum or aimed at slow release of drug from stratum corneum used as a reservoir to the deeper layers of skin.

Pickering w/o emulsions: Drug release and topical delivery

The skin absorption from Pickering emulsions as a new dosage form was investigated for the first time. Pickering emulsions are stabilized by adsorbed solid particles instead of emulsifier molecules. They are promising dosage forms that significantly differ from classical emulsions within several features. The skin permeation of a hydrophilic model penetrant (caffeine) was investigated from a w/o Pickering emulsion and compared to a w/o classical emulsion stabilized with an emulsifier. Both emulsions had the same composition and physicochemical properties in order to focus on the effect of the interfacial layer on the drug release and skin absorption processes. The highest permeation rates were obtained from the Pickering emulsion with a pseudo-steady state flux of 25μgcm−2h−1, threefold higher than from a classical emulsion (9.7μgcm−2h−1). After 24h exposure, caffeine was mostly in the receptor fluid and in the dermis; cumulated amounts of caffeine were higher for the Pickering emulsion. Several physicochemical phenomena were investigated for clearing up the mechanisms of enhanced permeation from the Pickering emulsion. Among them, higher adhesion of Pickering emulsion droplets to skin surface was disclosed. The transport of caffeine adsorbed on silica particles was also considered relevant since skin stripping showed that aggregates of silica particles entered deeply the stratum corneum.

Batch and Semicontinuous Styrene–Butadiene Emulsion Copolymerization Reactions

AbstractIn this work an experimental and simulation study of batch and semicontinuous styrene/butadiene emulsion copolymerization process was developed. The mathematical model combines the classical emulsion copolymerization equations, with mass balances, partitioning of components among all liquid phases, micellar and homogenous nucleation mechanisms and mass transfer equations between liquid and gaseous phases. Simulation results show good agreement with experimental measurements of conversion, average particle diameter and pressure.