Synthesis of composite emulsions and complex foams with the use of microfluidic flow-focusing devices

A method is described for the formation of stable, composite aqueous emulsions of 1) combinations of distinct families of bubbles of nitrogen, 2) combinations of distinct families of droplets of an organic fluid (either perfluoro(methyl)decalin or hexadecane), and 3) combinations of bubbles and droplets. A system of two or three microfluidic flow-focusing units is coupled to a single outlet channel. The composite emulsions can be precisely tuned, both in their composition and in the number fraction of components--either bubbles or droplets--of different types. The use of microfluidic technology, with closely coupled flow-focusing units, guarantees that the emulsions are mixed locally at a controlled local stoichiometry. The emulsions self-assemble in a nonequilibrium process to form a wide variety of highly organized periodic lattices.

Microstructure and structural transition in coconut oil microemulsion using semidifferential electroanalysis

The microemulsification in coconut oil/octadecyltrimethylammonium bromide/iso-pentanol/water system is investigated. The effect of iso-pentanol concentrations on the size of single-phase microemulsion region is discussed. It is found that the maximum microemulsion domain is obtained when cosurfactant (iso-pentanol)-to-surfactant (octadecyltrimethylammonium bromide) mass ratio is 1.5. The diffusion coefficients of ferrocene (electroactive probe) in microemulsion microenvironment are measured by semidifferential electroanalysis. The microstructure and structural transition from water-in-oil to oil-in-water microemulsions through a bicontinuous structure is examined. The results are found to be in agreement with that of conductivity measurements.

Interfacial aspects of water drop formation at micro-engineered orifices

The formation of emulsions with micro-engineered silicon based arrays of micro-orifices is a relatively new technique. Until now, only the preparation of oil-in-water emulsions was studied due to the hydrophilic nature of silicon. This work evaluates the emulsification of water into n-hexadecane with hydrophobized arrays of micro-orifices. We have studied the drop formation rate, the number of active pores and the drop size. In contrast to conventional macroporous membranes used for membrane emulsification, we observed high dispersed phase fluxes up to 4600 L h(-1) m(-2) bar(-1) while all pores being active at applied pressures below 2 times the critical pressure. The drop diameter was independent from the applied pressure difference. We observed a pressure dependent lag time between drop formations at low emulsification pressures. The lag time is related to the rate of surfactant diffusion to the water-oil interface causing a reduction of the interfacial tension. A significant influence of the used hydrophobization agents, perfluorinated octyltrichlorosilane (FOTS) and octyltrichlorosilane (OTS), was found for the resulting drop sizes and the number of active pores.

Development of a w/o/w emulsion for chemical peeling applications containing glycolic acid

Glycolic acid is a member of the AHA family, which occurs naturally in foods and has been used for centuries as a cutaneous rejuvenation treatment. It is used in many cosmetic products as an exfoliant and moisturizer. When glycolic acid is used in greater amounts, however, there are greater cosmetic benefits but also potential for skin irritation as far as burning increases. The aim of this work was to investigate the feasibility of a topical delivery system as a multiple emulsion combining glycolic acid, strontium nitrate, and dexpanthenol in order to optimize the acid's cosmetic properties and lowering its side effects.

Free-choice-profile descriptive analysis of sticks with conditioning agents

Nine formulations to be used as stick bases were manufactured using sodium stearate, propyleneglycol, and water, adding different concentrations of the following conditioning agents: octyldodecanol, PPG-5-ceteth-20, and PPG-15-stearyl ether. Free-choice-profile methodology was used to select the most adequate concentration of the agents in order to improve sensory properties. The sensory descriptors were grouped into four categories: stick aspect, sensations during application, sensations immediately after application, and sensations five minutes after application. Formulations containing 4% and 6% octyldodecanol and 2% PPG-15-stearyl ether were considered inadequate, since they showed unwanted qualities such as exudation, a slow absorption rate, high oiliness, and residue. Formulations containing 2% octyldodecanol; 2%, 4%, and 6% PPG-5-ceteth-20; and 4% and 6% PPG-15-stearyl ether presented different characteristics regarding the four categories of descriptors evaluated, all of them being acceptable considering the properties sought.

Comparing the moisturizing effects of ascorbic acid and calcium ascorbate against that of tocopherol in emulsions

Calcium ascorbate (CAAS), which is a hydrophilic and stable derivative of ascorbic acid (vitamin C) (AA), is commonly used in foods as an antioxidative agent. There are very limited reports on its dermatological use in the literature. In this paper, it is reported that CAAS could be used in place of ascorbic acid, which has chemical stability problems in topicals due to degradation by oxidation. The aim of this study was to investigate the skin-hydrating effect of CAAS compared to those of ascorbic acid and tocopherol (vitamin E) (T), which is a potential skin moisturizer and commonly used in dermocosmetics. Vitamins are incorporated into two kinds of base creams (o/w and w/o emulsion creams), alone and in combinations. Formulations were applied to the inner forearms of volunteers, and skin conductance was measured by using a corneometer. Data obtained were statistically evaluated. It was found that the skin-hydrating effect of CAAS was higher than that of AA and lower than that of T. However, its effect was very close to that of T.

Controlled production of ZnO nanoparticles from zinc glycerolate in a sol–gel silica matrix

The controlled production of ZnO nanoparticles within an amorphous silica matrix is achieved using a new methodology consisting of four stages. First, precursor zinc glycerolate nanoparticles are produced within reversed micelles of glycerol in heptane stabilized by the surfactant Aerosol-OT (bis-ethylhexyl sodium sulfosuccinate, AOT). The surface of these nanoparticles is then modified by exchanging AOT with bis-trimethoxysilyl-ethane (BTME). The surface-modified nanoparticles are copolymerized with tetramethoxysilane (TMOS) to provide a composite silica material, in which the nanoparticles are apparently dissolved, producing a uniform distribution of zinc in the silica matrix. Finally, the conversion of zinc to ZnO is achieved by heating the material at 700 degrees C, leading to a uniform dispersion of very small (<10 nm) ZnO particles within the amorphous matrix. The fluorescence spectrum of the ZnO particles within the matrix is blue-shifted, as expected from the strong quantum confinement achieved. The properties of the system at all stages in this synthetic process are monitored using TEM, XRD, fluorescence and FT-IR spectroscopy. Glycerol forms complexes with many metal ions, so the present procedure may be generalized to provide uniform distributions of metal ions and subsequently metal oxide nanoparticles in amorphous silica.

Controllable preparation of monodisperse O/W and W/O emulsions in the same microfluidic device

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants. Highly uniform droplets ranging from 50 to 400 mum with a polydispersity index (sigma) value of less than 2% were successfully prepared. With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable. Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 0.1-2.0 wt % Span 80 and an aqueous solution with 0.1-2.0 wt % Tween 20 as a continuous-phase flow, respectively. It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device.

Preparation of highly monodisperse W/O emulsions with hydrophobically modified SPG membranes

Experimental investigations on the hydrophobic modification of SPG membranes and the preparation of monodisperse W/O (water-in-oil) emulsions using the modified membranes were carried out. Effects of the osmotic pressure of disperse phase, the average pore size of membranes, emulsifier concentrations in continuous phase and the transmembrane pressure on the average size, size distribution and size dispersion coefficient of emulsions were systematically studied. The stability of W/O emulsions was also investigated. The results showed that SPG membranes took on excellent hydrophobicity through the modification by silane coupler reagent (octyltriethoxysilane) or by silicone resin (polymethylsilsesquioxane). Monodisperse W/O emulsions with size dispersion coefficient of about 0.25, which meant high monodispersity, were successfully prepared by using the hydrophobically modified SPG membranes with average pore sizes of 1.8, 2.0, 2.5, 4.8 and 11.1 microm. When the osmotic pressure was lower than 0.855 MPa, the average size of emulsions was gradually increased while the size dispersion coefficient delta gradually decreased with the osmotic pressure; when the osmotic pressure was higher than 0.855 MPa, both the coefficients kept unvarying. When kerosene was saturated with disperse phase in advance, the average size of emulsions became larger and the monodispersity of emulsions was slightly better than that prepared using unsaturated kerosene. The smaller the pore size of SPG membranes was, the better the monodispersity of the W/O emulsions. The average size and size dispersion coefficient delta were nearly independent on the emulsifier concentrations when the PGPR concentration was in the range from 0.5 to 5.0 wt%, whereas both of them slightly increased as the PGPR concentration was below 0.5 wt%. The effect of the transmembrane pressure on size distributions was slight. Both the average size and size dispersion coefficient delta slightly increased to some extent with the increase of the transmembrane pressure in the experimental range. The stability of the W/O emulsions was dependent on the storage time. The mean size of W/O emulsions decreased gradually with the increase of storage time at the first 35 days, and then kept constant; while the size dispersion coefficient of W/O emulsions was nearly not changed.

Targeting primaquine into liver using chylomicron emulsions for potential vivax malaria therapy

Primaquine (PQ) exerts a broad spectrum of activities against various stages of parasitic malaria. It remains as the only drug that destroys late hepatic stages and latent tissue forms of Plasmodium vivax and Plasmodium ovale. However, systems that can target PQ to liver hepatocytes, where malarial sporozoites reside, are needed to minimize the dose-limiting severe toxicities and side-effects caused by PQ. Recently, a reconstituted artificial chylomicron emulsion was generated using commercially available lipids and was shown to be preferentially taken up by liver hepatocytes following intravenous injection. We proposed to target PQ to hepatocytes by incorporating it into this chylomicron emulsion. We have shown that lipophilized PQ can be readily incorporated into the chylomicron emulsion. The PQ remained inside the emulsion without significant release. Moreover, PQ incorporated inside the emulsion was more stable than free PQ when incubated in serum. Finally, when intravenously injected into mice, the PQ-incorporated chylomicron emulsion led to significantly enhanced accumulation of PQ in liver, when compared to the injection of free PQ. This emulsion could be developed into a promising delivery system to target PQ into hepatocytes for vivax malaria therapy.

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation

Chitosan-coated alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb), owing to nontoxicity of the polymers and mild conditions of the method. The influence of process variables related to the emulsification step and microsphere recovering and formulation variables, such as alginate gelation and chitosan coating, on the size distribution and encapsulation efficiency was studied. The effect of microsphere coating as well its drying procedure on the Hb release profile was also evaluated. Chitosan coating was applied by either a continuous microencapsulation procedure or a 2-stage coating process. Microspheres with a mean diameter of less than 30 microm and an encapsulation efficiency above 90% were obtained. Calcium alginate cross-linking was optimized by using an acid/CaCO(3) molar ratio of 2.5, and microsphere-recovery with acetate buffer led to higher encapsulation efficiency. Hb release in gastric fluid was minimal for air-dried microspheres. Coating effect revealed a total release of 27% for 2-stage coated wet microspheres, while other formulations showed an Hb release above 50%. Lyophilized microspheres behaved similar to wet microspheres, although a higher total protein release was obtained with 2-stage coating. At pH 6.8, uncoated microspheres dissolved in less than 1 hour; however, Hb release from air-dried microspheres was incomplete. Chitosan coating decreased the release rate of Hb, but an incomplete release was obtained. The 2-stage coated microspheres showed no burst effect, whereas the 1-stage coated microspheres permitted a higher protein release.

Continuous contact- and contamination-free ultrasonic emulsification-a useful tool for pharmaceutical development and production

A novel concept was developed here for the continuous, contact- and contamination-free treatment of fluid mixtures with ultrasound. It is based on exciting a steel jacket with an ultrasonic transducer, which transmitted the sound waves via pressurised water to a glass tube installed inside the jacket. Thus, no metallic particles can be emitted into the sonicated fluid, which is a common problem when a sonotrode and a fluid are in direct contact. Moreover, contamination of the fluid from the environment can be avoided, making the novel ultrasonic flow-through cell highly suitable for aseptic production of pharmaceutical preparations. As a model system, vegetable oil-in-water emulsions, fed into the cell as coarse pre-emulsions, were studied. The mean droplet diameter was decreased by two orders of magnitude yielding Sauter diameters of 0.5 microm and below with good repeatability. Increasing the residence time in the ultrasonic field and the sonication power both decreased the emulsion mean diameter. Furthermore, the ultrasonic flow-through cell was found to be well suited for the production of nanoparticles of biodegradable polymers by the emulsion-solvent extraction/ evaporation method. Here, perfectly spherical particles of a volume mean diameter of less than 0.5 microm could be prepared. In conclusion, this novel technology offers a pharmaceutically interesting platform for nanodroplet and nanoparticle production and is well suited for aseptic continuous processing.

Novel asymmetric through-hole array microfabricated on a silicon plate for formulating monodisperse emulsions

We have proposed a novel microchannel (MC) structure for formulating monodisperse emulsions. The emulsification device is a silicon array of microfabricated, asymmetric through-holes with a slit and a circular channel (an asymmetric straight-through MC). The asymmetric through-holes of a uniform size stably yielded monodisperse emulsions with average droplet diameters of 35-41 mum and coefficients of variation of less than 2% by forcing the to-be-dispersed phase into the continuous phase via the through-holes. Their asymmetry enabled the stable formation of monodisperse emulsion droplets by spontaneous transformation, even using a to-be-dispersed phase with a very low viscosity below 1 mPa s. Additionally, the asymmetric straight-through MC with a high-density through-hole layout has the potential for high-throughput formulation of monodisperse emulsions.

Microparticle formation and its mechanism in single and double emulsion solvent evaporation

The emulsification is the first step of the emulsification solvent evaporation method and has been extensively investigated. On the contrary the second step, the solvent transport out from the emulsion droplets that determine the particle morphology and with great influence on the microparticles encapsulation and release behavior has been scarcely studied. This study investigates the mechanism of the solvent elimination from the emulsion droplets and its influence on the particle morphology, encapsulation and release behavior. Usually, the solvent is highly volatile that makes the solvent elimination process very fast thus difficult to observe. In order to observe in detail the microparticle formation, the initial emulsion was monitored by optical microscope under controlled solvent evaporation conditions. The results from the optical microscopic observations corroborated with laser diffractometry analysis showed that in single emulsion formulations, spherical microparticles are formed by accelerated solvent elimination due to the combined effects of high solvent volatility and polymer precipitation. The solvent expulsion accompanied by important shrinkage generates on the microparticle surface a thin layer of nanoparticles attested by scanning electron microscopy and laser diffractometry. During the intense solvent elimination, the encapsulated substance is drained, affecting the loading efficiency. Furthermore, it will concentrate towards the microparticle surface contributing to the initial burst release. In double emulsion formulations, microparticles with different morphologies are generated due to the presence of the aqueous-phase microdroplets inside the emulsion droplet. During the solvent elimination, these microdroplets generally coalesce under the pressure of the precipitating polymer. Depending mainly on the polymer concentration and emulsification energies, the final microparticles will be a mixture of honeycomb, capsule or plain structure. During the shrinkage due to the incompressibility of the inner microdroplets, the precipitating polymer wall around them may break forming holes through which the encapsulated substance is partly expulsed. Through these holes, the encapsulated substance is further partitioning with the external aqueous phase during solvent evaporation and contributes to the initial burst release during the application.

Recent developments in manufacturing emulsions and particulate products using membranes

Membrane emulsification (ME) is a relatively new technique for the highly controlled production of particulates. This review focuses on the recent developments in this area, ranging from the production of simple oil-in-water (O/W) or water-in-oil (W/O) emulsions to multiple emulsions of different types, solid-in-oil-in-water (S/O/W) dispersions, coherent solids (silica particles, solid lipid microspheres, solder metal powder) and structured solids (solid lipid microcarriers, gel microbeads, polymeric microspheres, core-shell microcapsules and hollow polymeric microparticles). Other emerging technologies that extend the capabilities into different membrane materials and operation methods (such as rotating membranes, repeated membrane extrusion of coarsely pre-emulsified feeds) are introduced. The results of experimental work carried out by cited researchers in the field together with those of the current authors are presented in a tabular form in a rigorous and systematic manner. These demonstrate a wide range of products that can be manufactured using different membrane approaches. Opportunities for creation of new and novel entities are highlighted for low throughput applications (medical diagnostics, healthcare) and for large-scale productions (consumer and personal products).

Preparation of Magnetic Microspheres from Water-in-Oil Emulsion Stabilized by Block Copolymer Dispersant

A new method for the preparation of magnetic microspheres is reported. The preparation involved first the dispersion of an aqueous phase, containing magnetite nanoparticles and a water-soluble homopolymer, into droplets in an organic medium using an amphiphilic block copolymer as the dispersant. This was followed by water distillation at a raised temperature from the aqueous droplets to yield polymer/magnetite particles. The structure of the particles was then locked in by a reagent being added to cross-link the water-soluble copolymer block and homopolymer. Since the hydrophobic block of the copolymer consisted of a protected polyester, the removal of the protective moieties from the coronal chains yielded poly(acrylic acid) or other functional polymers to render water dispersibility to the spheres and to enable biomolecule immobilization.

Synthesis and characterization of novel pH-responsive microgels based on tertiary amine methacrylates

Emulsion polymerization of 2-(diethylamino)ethyl methacrylate (DEA) in the presence of a bifunctional cross-linker at pH 8-9 afforded novel pH-responsive microgels of 250-700 nm diameter. Both batch and semicontinuous syntheses were explored using thermal and redox initiators. Various strategies were evaluated for achieving colloidal stability, including charge stabilization, surfactant stabilization, and steric stabilization. The latter proved to be the most convenient and effective, and three types of well-defined reactive macromonomers were examined, namely, monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA), styrene-capped poly[2-(dimethylamino)ethyl methacrylate] (PDMA50-St), and partially quaternized styrene-capped poly[2-(dimethylamino)ethyl methacrylate] (10qPDMA50-St). The resulting microgels were pH-responsive, as expected. Dynamic light scattering and 1H NMR studies confirmed that reversible swelling occurred at low pH due to protonation of the tertiary amine groups on the DEA residues. The critical pH for this latex-to-microgel transition was around pH 6.5-7.0, which corresponds approximately to the known pKa of 7.0-7.3 for linear PDEA homopolymer. The microgel particles were further characterized by electron microscopy and aqueous electrophoresis studies. Their swelling and deswelling kinetics were investigated by turbidimetry. The PDEA-based microgels were compared to poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) microgels prepared with identical macromonomer stabilizers. These PDPA-based microgels had a lower critical swelling pH of around pH 5.0-5.5, which correlates with the lower pKa of PDPA homopolymer. In addition, the kinetics of swelling for the PDPA microgels was somewhat slower than that observed for PDEA microgels; presumably this is related to the greater hydrophobic character of the former particles.

Preparation of finely dispersed O/W emulsion from fatty acid solubilized in subcritical water

A novel method for preparing a finely dispersed oil-in-water emulsion is proposed. Octanoic acid dissolved in water at a high temperature of 220 or 230 degrees C at 15 MPa was combined with an aqueous solution of a surfactant and then the mixture was cooled. When a nonionic surfactant, decaglycerol monolaurate (ML-750) or polyoxyethylene sorbitan monolaurate (Tween 20), was used, fine emulsions with a median oil droplet diameter of 100 nm or less were successfully prepared at ML-750 and Tween 20 concentrations of 0.083% (w/v) and 0.042%, respectively, or higher. The diameters were much smaller than those of oil droplets prepared by the conventional homogenization method using a rotor/stator homogenizer. However, an anionic surfactant, sodium dodecyl sulfate, was not adequate for the preparation of such fine emulsions by the proposed method. Although the interfacial tensions between octanoic acid and the surfactant solutions were measured at different temperatures, they were not an indication for selecting a surfactant for the successful preparation of the fine emulsion by the proposed method.

Microchannel emulsification using gelatin and surfactant-free coacervate microencapsulation

In this study, we investigated the use of microchannel (MC) emulsifications in producing monodisperse gelatin/acacia complex coacervate microcapsules of soybean oil. This is considered to be a novel method for preparing monodisperse O/W and W/O emulsions. Generally, surfactants are necessary for MC emulsification, but they can also inhibit the coacervation process. In this study, we investigated a surfactant-free system. First, MC emulsification using gelatin was compared with that using decaglycerol monolaurate. The results demonstrated the potential use of gelatin for MC emulsification. MC emulsification experiments conducted over a range of conditions revealed that the pH of the continuous phase should be maintained above the isoelectric point of the gelatin. A high concentration of gelatin was found to inhibit the production of irregular-sized droplets. Low-bloom gelatin was found to be suitable for obtaining monodisperse emulsions. Finally, surfactant-free monodisperse droplets prepared by MC emulsification were microencapsulated with coacervate. The microcapsules produced by this technique were observed with a confocal laser scanning microscope. Average diameters of the inner cores and outer shells were 37.8 and 51.5 microm; their relative standard deviations were 4.9 and 8.4%.

Physicochemical Parameters Associated with Nanoparticle Formation in the Salting-Out, Emulsification-Diffusion, and Nanoprecipitation Methods

PURPOSE

The aim of this work was to relate the physicochemical properties of the aqueous and organic phases used for nanoparticle (NP) preparation to the formation of NP produced by salting-out, emulsification-diffusion, and nanoprecipitation.

METHODS

Methacrylic acid copolymer and poly(vinyl alcohol) (PVAL) were selected as NP polymer and emulsifying agent, respectively. Salting-out and emulsification-diffusion NP batches were prepared modifying the PVAL content in the aqueous phase. For nanoprecipitation, NP were produced with variation of the polymer content and type of solvent in the organic phase.

RESULTS

For salting-out and emulsification-diffusion, NP formation was discussed in terms of the emulsification theory. The nanoemulsion obtained during NP preparation was visualized by scanning electron microscopy. Aqueous and organic phases used for NP preparation were characterized by their viscosity and surface tension. NP characteristics such as particle mean size, residual surfactant, suspendability in water after freeze-drying, and morphology were explained in terms of these properties. For nanoprecipitation, NP formation was analyzed considering the diffusion-stranding phenomenon.

CONCLUSIONS

NP formation by salting-out and emulsification-diffusion was related to PVAL chain interactions at the droplet interface (e.g., reduction in the interfacial tension, mechanical stabilization, and steric stabilization) and in the bulk solution (hydrodynamic stabilization). For nanoprecipitation, chi(solvent-water) and delta(delta solvent-water) of the organic phase solvents were well related to the NP characteristics.

Biodistribution Characteristics of Galactosylated Emulsions and Incorporated Probucol for Hepatocyte-Selective Targeting of Lipophilic Drugs in Mice

PURPOSE

Galactosylated emulsions containing cholesten-5-yloxy-N-(4-((1-imino-2-D-thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol) as a "homing device" were developed for hepatocyte-selective drug targeting. The targeting efficiency of galactosylated emulsions was evaluated by a distribution study in mice.

METHODS

Soybean oil/EggPC/cholesterol (Chol) (weight ratio, 70:25: 5) (bare) emulsions and soybean oil/EggPC/Gal-C4-Chol (weight ratio, 70:25:5) (Gal) emulsions were prepared and labeled with [3H]cholesteryl hexadecyl ether (CHE). [14C]probucol as a model lipophilic drug was incorporated in the emulsions or EggPC/Chol/Gal-C4-Chol (Gal) liposomes. Their tissue and intrahepatic distribution were evaluated following intravenous injection in mice.

RESULTS

After intravenous injection, Gal-emulsions were rapidly eliminated from the blood and accumulated in the liver, in contrast to the bare-emulsions. The liver uptake clearance of Gal-emulsions was 3.2- and 1.2-times greater than that of bare-emulsions and Gal-liposomes, respectively. The uptake ratio in liver parenchymal cells (PC) and nonparenchymal cells (NPC) of Gal-emulsions was higher than that of Gal-liposomes, being 7.4 and 3.0, suggesting that Gal-emulsions are an effective PC-selective carrier. The hepatic uptake of Gal-emulsions, but not that of bare-emulsions, was significantly inhibited by the pre-dosing of not only lactoferrin but also Gal-liposomes, suggesting asialoglycoprotein receptor-mediated endocytosis. Furthermore, [14C]probucol incorporated in Gal-emulsions was efficiently delivered to the liver compared with Gal-liposomes.

CONCLUSION

Gal-emulsions have been proven to be an alternative carrier for hepatocyte-selective drug targeting.

Sonication parameters for the preparation of biodegradable nanocapsules of controlled size by the double emulsion method

The main goal of the present work was to study the influence of the sonication process on the characteristics of poly(lactide-co-glycolide) nanocapsules prepared by the water-in-oil-in-water solvent evaporation method. The duration and intensity of sonication were investigated with respect to their ability to modify the size and distribution of the nanocapsule population. It has been demonstrated that the duration of the second mixing step (leading to the w/o/w emulsion) is of greater influence than that of the first step (water-in-oil emulsion) on the final mean particle size. A three-dimensional response surface was drawn up to show that when the second emulsification time increased, the mean size decreased until reaching a plateau. A threshold in sonication intensity also exists, allowing optimization of both parameters and the formation of nanocapsules of controlled size with a rather narrow distribution. The use of a vortex mixer instead of a sonicator during the first mixing step led to nanocapsules with a similar response surface, supporting the idea that the second step is the decisive one. Finally, nanocapsules loaded with methylene blue, a hydrophilic model compound with a positive charge, were characterized and the encapsulation efficiency calculated. Their size and distribution were similar to that of the blank nanocapsules. Entrapment efficiency was independent of duration, intensity, and type of mixing. From these results, it was concluded that nanocapsules of controlled size could be obtained upon optimizing certain process parameters.

Systematic characterization of oil-in-water emulsions for formulation design

Oil-in-water emulsions varying in surfactant concentration and manufacturing process were prepared. About 10 experiments were performed to characterize them. The goal of this research was to find out which tests should systematically be carried out to assess efficiently the stability and the properties of an emulsified preparation. Thus, formulation design requires at least the measurement of the droplet size, the determination of the zeta potential, a TurbiScan analysis, the investigation of the stability under centrifugation and freeze/thaw cycles. If the emulsion contains an active substance, stability under storage at 4 degrees C and microscopic analysis are relevant. Quality control should be improved by measurements of viscosity and pH.

Physicochemical properties to determine the buoyancy of hollow microspheres (microballoons) prepared by the emulsion solvent diffusion method

Hollow microspheres (microballoons) floatable on JPXIII No.1 solution were developed as a dosage form capable of floating in the stomach. Hollow microspheres were prepared by the emulsion solvent diffusion method using enteric acrylic polymers with drug in a mixture of dichloromethane and ethanol. It was found that preparation temperature determined the formation of cavity inside the microsphere and the surface smoothness, determining the floatability and the drug release rate of the microballoon. The correlation between the buoyancy of microballoons and their physical properties, e.g. apparent density and roundness of microballoons were elucidated. The drug loading efficiency of microballoons with various types of drug was investigated and correlated to the distribution coefficient of drug between dichloromethane and water. The optimum loading amount of riboflavin in the microballoon was found to impart ideal floatable properties to the microballoons. On the other hand, little entrapment was observed for aspirin due to the low distribution coefficient; however, entrapment improved to some extent upon reduction of the pH of the process.