Impact of short-chain alcohols on the formation and stability of nano-emulsions prepared by the spontaneous emulsification method

Spontaneous Emulsification of Alkanes Monitored by Multiple Light Scattering

When propylene oxide/ethylene oxide (PO/EO) surfactants were initially placed in the oil phase, long-chain alkanes with poor water solubility were emulsified spontaneously upon contact with the aqueous phase. This formation of oil droplets under static conditions was monitored and the efficiency of spontaneous emulsification was quantified using multiple light scattering (MLS). The effect of the initial surfactant phase on the interfacial tension and moduli was investigated using an interfacial tensiometer. The utilization efficiency of the surfactant and energy under external energy inputs was compared by analyzing the droplet size of the emulsions using microscopic observation and dynamic light scattering. The surfactant with the highest efficiency of spontaneous emulsification could disperse crude oil, which was used to address crude oil spill incidents in cold marine environments. To the best of our knowledge, this is the first study to monitor spontaneous emulsification under static conditions using MLS. This spontaneous emulsification under static conditions depended on the spontaneous diffusion of the PO/EO surfactants from the oil phase into the aqueous phase and on their interactions with the oil molecules. The findings of this study provide insights into the application of MLS to monitoring spontaneous emulsification.

Micellar media effect on the ultrasensitive quantitation of a diuretic medication at nano-scale levels with environmentally benign impact

A novel micelle-augmented spectrofluorimetric method is proposed for the ultrasensitive estimation of bumetanide (BUM) at nanoscale concentrations. The method utilizes the unique properties of micelles to enhance the fluorescence intensity of BUM and measures its native fluorescence at 415 nm after excitation at 267 nm. The proposed method was optimized by evaluating the effect of organized media, buffer pH, and diluting solvent. The method validity was further assessed following the ICH guidelines, where excellent linearity was obtained over a concentration range of 40.0-400.0 ng mL-1, with a correlation coefficient of 0.9999 and a low limit of detection (LOD) of 5.31 ng mL-1. The method was further applied for the determination of BUM in different dosage forms with % recoveries greater than 98%, as well as for content uniformity testing. Ultimately, a comprehensive assessment of the method's environmental impact was performed using different metrics, highlighting the eco-friendly nature of the method and underlining its potential for sustainable analytical practices in pharmaceutical research and beyond.

Influence of physico-chemical properties of two lipoxin emulsion-loaded hydrogels on pre-polarized macrophages: a comparative analysis

Inflammation, a crucial defense mechanism, must be rigorously regulated to prevent the onset of chronic inflammation and subsequent tissue damage. Specialized pro resolving mediators (SPMs) such as lipoxin A4 (LXA4) have demonstrated their ability to facilitate the resolution of inflammation by orchestrating a transition of M1 pro-inflammatory macrophages towards an anti-inflammatory M2 phenotype. However, the hydrophobic and chemically labile nature of LXA4 necessitates the development of a delivery system capable of preserving its integrity for clinical applications. In this study, two types of emulsion were formulated using different homogenization processes:mechanical overhead stirrer (MEB for blank Emulsion and MELX for LXA4 loaded-Emulsion) or Luer-lock syringes (SEB for blank Emulsion and SELX for LXA4 loaded-Emulsion)). Following characterization, including size and droplet morphology assessment by microscopy, the encapsulation efficiency (EE) was determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). To exert control over LXA4 release, these emulsions were embedded within silanized hyaluronic acid hydrogels. A comprehensive evaluation, encompassing gel time, swelling, and degradation profiles under acidic, basic, and neutral conditions, preceded the assessment of LXA4 cumulative release using LC-MS/MS. Physicochemical results indicate that H-MELX (Mechanical overhead stirrer LXA4 Emulsion loaded-Hydrogel) exhibits superior efficiency over H-SELX (Luer-lock syringes LXA4 Emulsion loaded-Hydrogel). While both formulations stimulated pro-inflammatory cytokine secretion and promoted a pro-inflammatory macrophage phenotype, LXA4 emulsion-loaded hydrogels displayed a diminished pro-inflammatory activity compared to blank emulsion-loaded hydrogels. These findings highlight the biological efficacy of LXA4 within both systems, with H-SELX outperforming H-MELX in terms of efficiency. To the best of our knowledge, this is the first successful demonstration of the biological efficacy of LXA4 emulsion-loaded hydrogel systems on macrophage polarization. These versatile H-MELX and H-SELX formulations can be customized to enhance their biological activity making them promising tools to promote the resolution of inflammation in diverse clinical applications.

Nanoemulsions Stable against Ostwald Ripening

Ostwald ripening, the dominant mechanism of droplet size growth for an O/W nanoemulsion at high surfactant concentrations, depends on micelles in the water phase and high aqueous solubility of oil, especially for spontaneously formed nanoemulsions. In our study, O/W nanoemulsions were formed spontaneously by mixing a water phase with an oil phase containing fatty alcohol polyoxypropylene polyoxyethylene ether (APE). By monitoring periodically the droplet size of the nanoemulsions via dynamic light scattering, we demonstrated that the formed O/W nanoemulsions are stable against Ostwald ripening, i.e., droplet growth. In contrast, the nanoemulsion droplets grew with the addition of micelles, demonstrating the pivotal role of the presence of micelles in the water phase in the occurrence of Ostwald ripening. The influence of the initial phase of APE, the oil or water phase in which APE is present, on the micelle formation is discussed by the partition coefficient and interfacial adsorption of APE between the oil and water phase using a surface and interfacial tensiometer. In addition, the spontaneously formed O/W nanoemulsion, which is stable against Ostwald ripening, can be used as a nanocarrier for the delivery of water-insoluble pesticides. These results provide a novel approach for the preparation of stable nanoemulsions and contribute to elucidating the mechanism of instability of nanoemulsions.

Spontaneous Emulsions: Adjusting Spontaneity and Phase Behavior by Hydrophilic-Lipophilic Difference-Guided Surfactant, Salt, and Oil Selection

Spontaneous emulsion behavior has been difficult to predict and could be influenced by many variables including salinity, temperature, and chemical composition of the oil and surfactant. In this work, the hydrophilic-lipophilic difference (HLD) framework was used to predict the formation of spontaneous emulsions using a mixture of Span-80 and SLES surfactants. The spontaneity and emulsion behavior of different systems were modeled by estimating the HLD_mix. The influence of surfactant ratio, salinity, and oil type was investigated. Spontaneous emulsification could only be observed when the HLD_mix was between -0.96 and 1.04. Within this range, a negative HLD_mix resulted in a greater spontaneity to form o/w emulsion, and a w/o emulsion was more likely to form when the HLD_mix was positive. When the HLD_mix was close to 0 (between -0.22 and 0.56 in our systems), emulsions were formed in both the oil and aqueous phases with high spontaneity. A combined effect of ultralow interfacial tension, Span-80 micelle swelling, and interfacial turbulence due to Marangoni effects is likely the main mechanism of the spontaneous emulsification observed in this study. A synergistic reduction in interfacial tension was observed between Span-80 and SLES (<1 mN/m). When the HLD of the system was close to 0, a bicontinuous emulsion phase was formed at the oil-water interface. The bicontinuous emulsion broke-up over time due to the ultralow interfacial tension and interfacial turbulence, forming dispersed oil and water droplets. Results from this work provide a practical method to suggest what surfactant composition, salinity, and oil type could promote (or eliminate) the conditions favorable for spontaneous emulsification.

Formulation and evaluation of norcanthridin nanoemulsions against the Plutella xylostella (Lepidotera: Plutellidae)

Background

Norcantharidin (NCTD), a demethylated derivative of cantharidin (defensive toxin of blister beetles), has been reported to exhibit insecticidal activity against various types of agricultural pests. However, NCTD applications are limited by its poor water solubility and high dosage requirement. Nanoemulsions have attracted much attentions due to the transparent or translucence appearance, physical stability, high bioavailability and non-irritant in nature. In general, nanoemulsions with small droplet size can enhance the bioavailability of drugs, whereas this phenomenon is likely system dependent. In present study, NCTD nanoemulsions were developed and optimized to evaluate and improve the insecticidal activity of NCTD against Plutella xylostella (Lepidotera: Plutellidae) by a spontaneous emulsification method.

Results

Triacetin, Cremophor EL and butanol were selected as the constituents of NCTD nanoemulsions via solubility determination, emulsification efficiency and ternary phase diagram construction. Insecticidal activity of NCTD nanoemulsion was associated with the content of surfactant and cosurfactant: (1) Higher effective toxicity exhibited at Smix (surfactant to cosurfactant mass ratio) = 3:1 that may be associated with the changes in interfacial tension; (2) NCTD nanoemulsion at 3:7 < SOR (surfactant to oil mass ratio) < 6:4 was more effective at lower surfactant level, which was attributed to the relatively slow diffusion rate of NCTD hindering by excess surfactant. Interestingly, nanoemulsions with smaller droplets were not found to be more effective in our study.

Conclusions

The optimized NCTD nanoemulsion (triacetin/Cremophor EL/butanol (60/20/20, w/w)) exhibited effective insecticidal activity (LC₅₀ 60.414 mg/l, LC₉₀ 185.530 mg/l, 48 h) than the NCTD acetone solution (LC₅₀ 175.602 mg/L, LC₉₀ 303.050 mg/L, 48 h). Spontaneous emulsifying nanoemulsion employed to formulate this poor water-soluble pesticide is a potential system for agriculture application.

Electronic supplementary material

The online version of this article (10.1186/s12896-019-0508-8) contains supplementary material, which is available to authorized users.