Meritxell Llinàs

Production of reference materials for the detection and size determination of silica nanoparticles in tomato soup.

A set of four reference materials for the detection and quantification of silica nanoparticles (NPs) in food was produced as a proof of principle exercise. Neat silica suspensions were ampouled, tested for homogeneity and stability, and characterized for total silica content as well as particle diameter by dynamic light scattering (DLS), electron microscopy (EM), gas-phase electrophoretic molecular mobility analysis (GEMMA), and field-flow fractionation coupled with an inductively coupled mass spectrometer (FFF-ICPMS). Tomato soup was prepared from ingredients free of engineered nanoparticles and was spiked at two concentration levels with the silica NP suspension. Homogeneity of these materials was found sufficient to act as reference materials and the materials are sufficiently stable to allow long-term storage and distribution at ambient temperature, providing proof of principle of the feasibility of producing liquid food reference materials for the detection of nanoparticles. The spiked soups were characterized for particle diameter by EM and FFF-ICPMS (one material only), as well as for the total silica content. Although questions regarding the trueness of the results from EM and FFF-ICPMS procedures remain, the data obtained indicate that even assigning values should eventually be feasible. The materials can therefore be regarded as the first step towards certified reference materials for silica nanoparticles in a food matrix.

Studies on Controlled Release of Hydrophilic Drugs from W/O High Internal Phase Ratio Emulsions

Formation of high internal phase ratio emulsions (HIPREs) has been studied in water/Cremophor WO7/soybean oil and water/Cremophor WO7/liquid paraffin systems. Two hydrophilic model drugs, clindamycin hydrochloride (CH) and theophylline (TP), were incorporated in HIPREs with a water concentration of 90% and an oil/surfactant (O/S) weight ratio of 60:40 and their release was determined in vitro at 25 degrees C. The release of both model drugs from HIPREs was much slower than from aqueous solutions. In aqueous solution the release pattern of both actives was identical. In contrast, a clearly distinct release pattern from HIPREs was observed: The release of CH, which is freely soluble in water, was very slow, regardless of the emulsion system, while the release of TP, which is slightly soluble in water, was faster. By changing the pH of the dispersed phase of HIPREs, which in turn affects solubility, drug release was modulated. An increase in the solubility of TP in the dispersed phase by a factor of roughly 4.5 produced a decrease in the diffusion coefficient of two orders of magnitude. These results show for the first time the key role of drug solubility in the release from W/O-HIPREs.

Influence of nonionic branched-chain alkyl glycosides on a model nano-emulsion for drug delivery systems

The effect of incorporating new nonionic glycolipid surfactants on the properties of a model water/nonionic surfactant/oil nano-emulsion system was investigated using branched-chain alkyl glycosides: 2-hexyldecyl-β(/α)-D-glucoside (2-HDG) and 2-hexyldecyl-β(/α)-D-maltoside (2-HDM), whose structures are closely related to glycero-glycolipids. Both 2-HDG and 2-HDM have an identical hydrophobic chain (C16), but the former consists a monosaccharide glucose head group, in contrast to the latter which has a disaccharide maltose unit. Consequently, their hydrophilic-lipophilic balance (HLB) is different. The results obtained have shown that these branched-chain alkyl glycosides affect differently the stability of the nano-emulsions. Compared to the model nano-emulsion, the presence of 2-HDG reduces the oil droplet size, whereas 2-HDM modify the properties of the model nano-emulsion system in terms of its droplet size and storage time stability at high temperature. These nano-emulsions have been proven capable of encapsulating ketoprofen, showing a fast release of almost 100% in 24h. Thus, both synthetically prepared branched-chain alkyl glycosides with mono- and disaccharide sugar head groups are suitable as nano-emulsion stabilizing agents and as drug delivery systems in the future.

Design and in vitro evaluation of biocompatible dexamethasone-loaded nanoparticle dispersions, obtained from nano-emulsions, for inhalatory therapy.

Polymeric nanoparticle dispersions containing dexamethasone (DXM) have been prepared from O/W nano-emulsions of the water/polysorbate 80/[4 wt% poly(lactide-co-glycolide) acid+0.18 wt% DXM in ethyl acetate] system by a low-energy method at 25°C. Nano-emulsions were formed at O/S ratios between 45/55 and 72/25 and water contents above 70 wt% by the phase inversion composition (PIC) method. The mean hydrodynamic diameter of nano-emulsions with a constant water content of 90 wt% and O/S ratios from 50/50 to 70/30 was below 350 nm as assessed by dynamic light scattering. The nanoparticles obtained from these nano-emulsions (by solvent evaporation) showed mean diameters of around 130 nm, as determined by transmission electron microscopy image analysis. Therapeutic concentrations of DXM were encapsulated in the nano-emulsions prior to nanoparticle preparation. DXM entrapment efficiency of the nanoparticle dispersion (above 74 wt%) decreased at increasing O/S ratios of the precursor nano-emulsion while DXM loading, which was around 10 mg/100 mL, showed the reverse tendency. DXM release from nanoparticle dispersions was about an order of magnitude slower than from an aqueous solution. In vitro studies performed in a lung carcinoma cell line and in vitro haemolysis studies performed in red blood cells revealed a dose-dependent toxicity and haemolytic response, respectively. The as-prepared nanoparticle dispersions were non-toxic up to a concentration of 40 μg/mL and non-haemolytic up to a concentration of 1 mg/mL. After purification, nanoparticle dispersions were non-toxic up to a concentration of 90 μg/mL. These results allow concluding that these polymeric nanoparticle dispersions are good candidates for inhalatory therapy.

Studies on the formation of polymeric nano-emulsions obtained via low-energy emulsification and their use as templates for drug delivery nanoparticle dispersions.

Ethylcellulose nanoparticles have been obtained from O/W nano-emulsions of the water/polyoxyethylene 10 oleyl ether/[ethyl acetate+4wt% ethylcellulose] system by low energy-energy emulsification at 25°C. Nano-emulsions with droplet sizes below 200nm and high kinetic stability were chosen for solubilising dexamethasone (DXM). Phase behaviour, conductivity and optical analysis studies of the system have evidenced for the first time that both, the polymer and the drug play a role on the structure of the aggregates formed along the emulsification path. Nano-emulsion formation may take place by both, phase inversion and self-emulsification. Spherical polymeric nanoparticles containing surfactant, showing sizes below 160nm have been obtained from the nano-emulsions by organic solvent evaporation. DXM loading in the nanoparticles was high (>90%). The release kinetics of nanoparticle dispersions with similar particle size and encapsulated DXM but different polymer to surfactant ratio were studied and compared to an aqueous DXM solution. Drug release from the nanoparticle dispersions was slower than from the aqueous solution. While the DXM solution showed a Fickian release pattern, the release behaviour from the nanoparticle dispersions was faster than that expected from a pure Fickian release. A coupled diffusion/relaxation model fitted the results very well, suggesting that polymer chains undergo conformational changes enhancing drug release. The contribution of diffusion and relaxation to drug transport in the nanoparticle dispersions depended on their composition and release time. Surfactant micelles present in the nanoparticle dispersion may exert a mild reservoir effect. The small particle size and the prolonged DXM release provided by the ethylcellulose nanoparticle dispersions make them suitable vehicles for controlled drug delivery applications.

Transdermal delivery of forskolin from emulsions differing in droplet size

The skin permeation of forskolin, a diterpene isolated from Coleus forsholii, was studied using oil in water (O/W) emulsions as delivery formulations and also an oil solution for comparative purposes. Two forskolin-loaded emulsions of water/Brij 72:Symperonic A7/Miglyol 812:Isohexadecane, at 0.075 wt% forskolin concentration were prepared with the same composition and only differing in droplet size (0.38 μm and 10 μm). The emulsions showed high kinetic stability at 25 °C. In vitro study of forskolin penetration through human skin was carried out using the MicroettePlus(®) system. The concentration of the active in the receptor solution (i.e. ethanol/phosphate buffer 40/60, v/v) was analyzed by high performance liquid chromatography with UV detection. The obtained results showed that forskolin permeation from the emulsions and the oil solution, through human skin, was very high (up to 72.10%), and no effect of droplet size was observed.

New insights on the mechanisms of drug release from highly concentrated emulsions

High kinetic stability water-in-oil high internal phase ratio emulsions (W/O-HIPREs) have been obtained in a 0.5% Theophylline (TP) aqueous solution/Cremophor WO7/liquid paraffin system at 25 °C. The release of TP has been studied from HIPREs with pH values of the dispersed phase ranging between 2 and 12. Although the release from aqueous solutions was not influenced by pH, the release from HIPREs depended strongly on the pH of the dispersed phase. Increasing the solubility of TP in the dispersed phase, its apparent diffusion coefficient decreased over two orders of magnitude. Two different physico-chemical models have been applied to describe the diffusion of TP, showing an excellent agreement with experiments and confirming the role of the structure of the emulsions and the solubility of the drug. It has been shown that only non-ionized species are able to cross the interfacial film. Therefore, at pH>pKa diffusion is limited by the concentration of non-ionized species inside the emulsion droplets, while at pH<pKa diffusion is determined by the interfacial film. This demonstrates that solubility of the diffusing molecule can have a higher effect on release from HIPREs than the interfacial film properties.

NLCs as a potential carrier system for transdermal delivery of forskolin

Nanostructured lipid carriers (NLC) composed of the substances generally recognized as safe (GRAS) were obtained by using a hot high-pressure homogenization technique (HPH). The influence of the number of homogenization cycles and concentration of a decyl glucoside surfactant on the NLC properties were studied. The systems stability was assessed by macroscopic observation, light backscattering and zeta potential measurements. NLC particle size was measured using dynamic light scattering (DLS). The kinetically stable formulations were loaded with forskolin and selected for in vitro drug permeation study using the Franz cell method. Concentration of forskolin in the receptor solution (i.e. ethanol/PBS mixture) was analyzed with high performance liquid chromatography (HPLC) with UV detection. The obtained results have shown that NLC formulations could be used as effective carriers for forskolin permeation through the skin.

Nano-emulsions as vehicles for topical delivery of forskolin

Two O/W forskolin-loaded nano-emulsions (0.075% wt.) based on medium chain triglycerides (MCT) and stabilized by a nonionic surfactant (Polysorbate 80 or Polysorbate 40) were studied as forskolin delivery systems. The nano-emulsions were prepared by the PIC method. The mean droplet size of the nano-emulsions with Polysorbate 80 and Polysorbate 40 with oil/surfactant (O/S) ratios of 20/80 and 80% water concentration, measured by Dynamic Light Scattering (DLS), was of 118 nm and 111 nm, respectively. Stability of the formulations, as assessed by light backscattering for 24 h, showed that both nano-emulsions were stable at 25°C. Studies of forskolin in vitro skin permeation from the nano-emulsions and from a triglyceride solution were carried out at 32°C, using Franz-type diffusion cells. A mixture of PBS/ethanol (60/40 v/v) was used as a receptor solution. The highest flux and permeability coefficient was obtained for the system stabilized with Polysorbate 80 (6.91±0.75 µg · cm-2·h-1 and 9.21 · 10-3±1.00 · 10-3 cm · h-1, respectively) but no significant differences were observed with the flux and permeability coefficient value of forskolin dissolved in oil. The obtained results showed that the nano-emulsions developed in this study could be used as effective carriers for topical administration of forskolin.