Surfactant-rich biocompatible microemulsions as effective carriers of methylxanthine drugs

Suspension of micro- and nanoplastic test materials: Liquid compatibility, (bio)surfactants, toxicity and environmental relevance

Micro- and nanoplastics have been detected in environmental compartments from the highest mountains to the deepest seas. They have been shown to be present at almost all trophic levels, and within humans they have been detected in numerous organs and human stool. Whilst their ubiquitous nature is indisputable, little is known about the health risks they may present. Much current research is focussed on the production of test materials with which to perform the necessary health studies. An important aspect of this is the correct storage and suspension of the materials to ensure they remain stable both chemically and with regards to size and shape. In this review, we look at the chemical stability of nine common polymers in a range of liquids; first with the use of commercial compatibility charts and then with a more quantitative approach using Hansen solubility parameters. We then look at stability with regards to particle agglomeration, whether and how stable compositions can be predicted, and which dispersants can be added to increase stability. Finally, we discuss the role of bio-surfactants and the eco-corona and how these may offer a route to both better stability and environmental relevance.

Natural Amphiphilic Shellac Nanoparticle-Stabilized Novel Pickering Emulsions with Droplets and Bi-continuous Structures

Shellac is a natural amphiphilic substance, and its nanoparticles can be used to stabilize Pickering emulsions with droplets and bi-continuous structures. In this study, shellac nanoparticles (SNPs) were produced through the anti-solvent method, and these SNPs were used to produce a series of Pickering emulsions. Fourier transform infrared results showed that SNPs were generated through hydrogen bonding and hydrophobic effects. The contact angle of SNPs was 122.3°, indicating that hydrophobicity was their dominant characteristic. According to the results of confocal laser scanning microscopy, the Pickering emulsions stabilized by SNPs showed oil-in-water, bi-continuous structure, and water-in-oil characteristics, which were dependent on the oil-phase content. The resistance value of the emulsified part of these Pickering emulsion systems significantly increased at an oil-phase ratio of 80-90% (more than 10⁵ MΩ), as compared with the 10-70% oil-phase content (around 1 MΩ). The viscosity of SNP-stabilized Pickering emulsions with bi-continuous structures was highest at 40% oil-phase content. The porous material prepared by using Pickering emulsions with bi-continuous structures as a template had an interconnected structure and was able to absorb both water and oil. This study indicated that these amphiphilic SNPs readily form bi-continuous structures and effectively stabilize Pickering emulsions with droplets. These SNPs are expected to have increased application in food and pharmaceutical industries.

Formation of sacha inchi oil microemulsion systems: effects of non-ionic surfactants, short-chain alcohols, straight-chain esters and essential oils

BACKGROUND

This study reports the formation of sacha inchi oil (SIO) microemulsions for food and cosmetic applications. Effects of non-ionic surfactants, short-chain alcohols, essential oil and straight-chain esters on the phase behavior and formulation of U-type microemulsion were investigated. Pseudo ternary phase diagrams were constructed to assess the influence of these factors using water titration method. Structural transitions were measured along several water dilution lines using conductivity and viscosity tools.

RESULTS

Among four different surfactants, Tween 80 solubilized the maximum oil and induced the formation of a U-type microemulsion system. Oil solubilization was decreased in the presence of short-chain alcohols. In addition, the system containing straight-chain esters as the cosolvent showed a higher expansion effect in the U-type areas than that containing essential oils. Finally, upon water dilution of three systems with SIO/ethyl acetate of 1:1, 1:2 and 1:3, microstructural transition from W/O to bicontinuous occurred at 200 g kg^-1 (w/w) water content, and then to O/W structure at 650 g kg^-1 (w/w) water content.

CONCLUSION

Straight-chain esters as cosolvent is a potential strategy to extend the dilutability of SIO microemulsions. © 2021 Society of Chemical Industry.

Impact of drug aggregation on the structural and dynamic properties of Triton X-100 micelles

Surfactants are used in a wide range of chemical and biological applications, and for pharmaceutical purposes are frequently employed to enhance the solubility of poorly water soluble drugs. In this study, all-atom molecular dynamics (MD) simulations and small-angle neutron scattering (SANS) experiments have been used to investigate the drug solubilisation capabilities of the micelles that result from 10 wt% aqueous solutions of the non-ionic surfactant, Triton X-100 (TX-100). Specifically, we have investigated the solubilisation of saturation amounts of the sodium salts of two nonsteroidal anti-inflammatory drugs: ibuprofen and indomethacin. We find that the ibuprofen-loaded micelles are more non-spherical than the indomethacin-loaded micelles which are in turn even more non-spherical than the TX-100 micelles that form in the absence of any drug. Our simulations show that the TX-100 micelles are able to solubilise twice as many indomethacin molecules as ibuprofen molecules, and the indomethacin molecules form larger aggregates in the core of the micelle than ibuprofen. These large indomethacin aggregates result in the destabilisation of the TX-100 micelle, which leads to an increase in the amount of water inside of the core of the micelle. These combined effects cause the eventual division of the indomethacin-loaded micelle into two daughter micelles. These results provide a mechanistic description of how drug interactions can affect the stability of the resulting nanoparticles.

Preparation and insecticidal performance of sustained-release cinnamon essential oil microemulsion

BACKGROUND

To improve the utilization rate of cinnamon essential oil and compensate for the shortcomings of its easy decomposition and oxidation, the microemulsion of cinnamon essential oil was prepared using Tween 80 and anhydrous ethanol as surfactant and cosurfactant, respectively. The effects of the surfactant type, K_m value, preparation temperature and aqueous pH on the quality of the microemulsion were studied via a pseudo-ternary phase diagram. The slow-release performance of cinnamon essential oil microemulsion and the control performance of the insect repellent package on the rice weevil were characterized.

RESULTS

The results showed that, when Tween 80 was used as a surfactant and anhydrous ethanol was used as a cosurfactant, the K_m value was 3:1, preparation temperature was 40 °C, aqueous pH was 5 and prepared cinnamon essential oil microemulsion was of the O/W type. The microemulsion had strong stability and a 81.5-nm concentrated particle size distribution, and possessed excellent embedding and sustained-release effects. The prepared insect repellent active package prolongs the use time and the effect of cinnamon essential oil. The repellent rate of the rice weevil was as high as 100% after 48 h, and the contact mortality and fumigation mortality rates of the rice weevil also reached 96.67% and 86.67%, respectively, after 96 h.

CONCLUSION

The prepared cinnamon essential oil microemulsion and active packaging had a good sustained-release effect. © 2021 Society of Chemical Industry.

Preparation and physicochemical stability of tomato seed oil microemulsions

In this study, microemulsions were fabricated using tomato seed oil, water, Tween 80 and citric acid, and then the physicochemical characteristics and the influence of environmental stress were investigated. The physicochemical properties of the microemulsions were evaluated by transmission electron microscopy (TEM), mean particle diameter, polydispersity index (PDI) and conductivity. The phase diagrams of tomato seed oil/Tween 80/citric acid/water microemulsions were constructed under different pHs and ionic strengths. Storage stability of the systems was investigated at 4, 37 and 65°C, and changes in turbidity and lipid oxidation products were monitored. Nano-size zeta potential analyzer results demonstrated that the mean particle diameter and polydispersity index of tomato seed oil microemulsions were 14 nm and 0.014. The transition from W/O to O/W could be detected from electrical conductivity and viscosity data with the increasing of water content. The results showed that the microemulsion areas decreased with increasing pH and NaCl concentrations. What is more, the study proved that tomato seed oil microemulsions exhibited a good storage stability. PRACTICAL APPLICATION: In this study, the preparation of tomato seed oil microemulsion can not only make full use of the nutritional value of tomato seed oil, but also ensure the effective protection of the nutrients contained in it, and improve the problem of adding difficult. By using microemulsion as delivery carrier of tomato seed oil, the application of tomato seed oil in food, cosmetics and other fields could be enhanced. Therefore, the preparation of tomato seed oil microemulsion provides a theoretical basis for production practice.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Development and Study of Nanoemulsions and Nanoemulsion-Based Hydrogels for the Encapsulation of Lipophilic Compounds

Biocompatible nanoemulsions and nanoemulsion-based hydrogels were formulated for the encapsulation and delivery of vitamin D₃ and curcumin. The aforementioned systems were structurally studied applying dynamic light scattering (DLS), electron paramagnetic resonance (EPR) spectroscopy and viscometry. In vitro studies were conducted using Franz diffusion cells to investigate the release of the bioactive compounds from the nanocarriers. The cytotoxicity of the nanoemulsions was investigated using the thiazolyl blue tetrazolium bromide (MTT) cell proliferation assay and RPMI 2650 nasal epithelial cells as in vitro model. DLS measurements showed that vitamin D₃ and curcumin addition in the dispersed phase of the nanoemulsions caused an increase in the size of the oil droplets from 78.6 ± 0.2 nm to 83.6 ± 0.3 nm and from 78.6 ± 0.2 nm to 165.6 ± 1.0 nm, respectively. Loaded nanoemulsions, in both cases, were stable for 60 days of storage at 25 °C. EPR spectroscopy revealed participation of vitamin D₃ and curcumin in the surfactants monolayer. In vitro release rates of both lipophilic compounds from the nanoemulsions were comparable to the corresponding ones from the nanoemulsion-based hydrogels. The developed o/w nanoemulsions did not exhibit cytotoxic effect up to the concentration threshold of 1 mg/mL in the cell culture medium.

Microemulsions as nano-reactors for the solubilization, separation, purification and encapsulation of bioactive compounds

Bioactive components possess various functionalities and are most interested for different food, nutraceutical and pharmaceutical formulations. The current review will discuss the preparation methods and fabrication techniques to design microemulsions (MEs) for the solubilization, separation, encapsulation and purification of various agro-food bioactive compounds. ME systems have shown suitable potential in enhancing oil recovery, protein extraction, and isolation of bioactive compounds. Moreover, the capability of ME based systems as drug and nutraceutical delivery cargos, and synthesis of various organic and inorganic nanoparticles, especially using biopolymers, will be investigated. ME liquid membranes are also developed as nano-extractor/nano-reactor vehicles, capable of simultaneous extraction, encapsulation or even synthesis of hydrophilic and lipophilic bioactive compounds for food, nutraceutical and drug applications.

Microstructure and biopharmaceutical performances of curcumin-loaded low-energy nanoemulsions containing eucalyptol and pinene: Terpenes' role overcome penetration enhancement effect?

The objective of this work was to develop low-energy nanoemulsions for enhanced dermal delivery of curcumin, using monoterpene compounds eucalyptol (EUC) and pinene (PIN) as chemical penetration enhancers. Spontaneous emulsification was the preparation method. All formulations contained 10% of the oil phase (medium-chain triglycerides (MCT), or their mixture with EUC or PIN). Formulations were stabilized by the combination of polysorbate 80 and soybean lecithin (surfactant-to-oil-ratio=1). Concentration of curcumin was set to 3 mg/ml. Average droplet diameter of all tested formulations ranged from 102 nm to 132 nm, but the ones containing monoterpenes had significantly smaller size compared to the MCT formulation. Such finding was profoundly studied through electron paramagnetic resonance spectroscopy, which proved that the presence of monoterpenes modified the nanoemulsions' interfacial environment, resulting in droplet size reduction. The release study of curcumin (using Franz cells) demonstrated that the cumulative amount released after 6 h of the experiment was 10.1 ± 0.2% for the MCT nanoemulsions, 13.9 ± 0.1% and 14.0 ± 0.2% for PIN and EUC formulations, respectively. In vivo tape stripping revealed their performances in delivering curcumin into the skin, indicating the following order: EUC>MCT>PIN. The formulation with EUC was clearly the most successful, giving the highest cumulative amount of curcumin that penetrated per surface unit: 34.24±5.68 µg/cm². The MCT formulation followed (30.62±2.61 µg/cm²) and, finally, the one with PIN (21.61±0.11 µg/cm²). These results corelated with curcumin's solubility in the chosen oils: 4.18±0.02 mg/ml for EUC, 1.67±0.04 mg/ml for MCT and 0.21±0.01 mg/ml for PIN. Probably, higher solubility in the oil phase of the nanoemulsion promoted curcumin's solubility in the superficial skin layers, providing enhanced penetration.

Enhancement of the solubility and antioxidant capacity of α-linolenic acid using an oil in water microemulsion

The applications of α-linolenic acid (ALA) in the food industry are restricted due to its poor water solubility and antioxidant stability. This study concentrates on developing an ALA-loaded microemulsion (ALA-ME) to enhance its solubility and antioxidant capacity. The formulation of the microemulsion was investigated based on pseudoternary phase diagrams. The ALA-ME was characterized by using electrical conductivity, viscosity and transmission electron microscopy (TEM). The microstructure of the ALA-ME was probed using nuclear magnetic resonance (¹H-NMR). The results proved that ALA-ME consisted of spheroidal droplets with 20-40 nm diameter. A structural transformation from water in oil (W/O) to oil in water (O/W) occurred, as seen from the electrical conductivity determination. The ¹H-NMR results revealed a transition of the ALA position encapsulated from the core area of the microemulsion to the lipophilic layer of the surfactant. Furthermore, two microstructural models of ALA-ME were proposed. The antioxidant evaluation demonstrated that the ALA antioxidant capacity in microemulsions was enhanced to about 80% compared with that of ALA in oil solution.

Reverse Micelles As Antioxidant Carriers: An Experimental and Molecular Dynamics Study

Water-in-oil microemulsions with biocompatible components were formulated to be used as carriers of natural antioxidants, such as hydroxytyrosol (HT) and gallic acid (GA). The system was composed of a mixture of natural surfactants, lecithin and monoglycerides, medium chain triglycerides, and aqueous phase. A dual approach was undertaken to study the structure and dynamics of these complicated systems. First, experimental data were collected by using adequate techniques, such as dynamic light scattering (DLS) and electron paramagnetic resonance (EPR) spectroscopy. Following this, a coarse-grained molecular dynamics (CGMD) study based on the experimental composition using the MARTINI force field was conducted. The simulations revealed the spontaneous formation of reverse micelles (RMs) starting from completely random initial conformations, underlying their enhanced thermodynamic stability. The location of the bioactive molecules, as well as the structure of the RM, were in accordance with the experimental findings. Furthermore, GA molecules were found to be located inside the water core, in contrast to the HT ones, which seem to lie at the surfactant interfacial layer. The difference in the antioxidants' molecular location was only revealed in detail from the computational analysis and explains the RM's swelling observed by GA in DLS measurements.

Water-in-oil microemulsions versus emulsions as carriers of hydroxytyrosol: an in vitro gastrointestinal lipolysis study using the pHstat technique

W/O microemulsions are digested at a lower rate than emulsions, mainly because their high contents in emulsifiers result in a strong inhibition of gastric lipolysis.

Biocompatible colloidal dispersions as potential formulations of natural pyrethrins: a structural and efficacy study

Biocompatible colloidal dispersions of the micro- and nanoemulsion type based on lemon oil terpenes, polysorbates, water, and glycerol were used for the formulation of pyrethrins, botanical insecticides derived from the white pyrethrum daisy, Tanacetum cinerariifolium. The proposed formulation is based on pyrethrin-containing water-in-oil (W/O) microemulsions that could be diluted in one step with an aqueous phase to obtain kinetically stable oil-in-water (O/W) nanoemulsions. Structural characteristics of the micro- and nanoemulsions were evaluated by electron paramagnetic resonance (EPR) spectroscopy, dynamic light scattering (DLS), small angle X-ray scattering (SAXS), and electrical conductivity. Dynamic properties of the surfactant monolayer as evidenced by EPR measurements were affected by the water content, the surfactant, and also the presence of the biocide. DLS and SAXS experiments of the nanoemulsions indicated the existence of two populations of oil droplets dispersed in the aqueous phase, globular droplets of 36-37 nm in diameter, and also larger droplets with diameters >150 nm. All of the applied techniques for structural determination revealed the participation of the biocide in the nanostructure. The insecticidal effect of the encapsulated natural pyrethrin was evaluated in laboratory bioassays upon a target-insect pest, the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) in eggplant, and was found to be increased compared to the commercial pyrethrin formulation.

Microemulsion versus emulsion as effective carrier of hydroxytyrosol

Two edible Water-in-Oil (W/O) dispersions, an emulsion that remains kinetically stable and a microemulsion which is spontaneously formed, transparent and thermodynamically stable, were developed for potential use as functional foods, due to their ability to be considered as matrices to encapsulate biologically active hydrophilic molecules. Both systems contained Medium Chain Triglycerides (MCT) as the continuous phase and were used as carriers of Hydroxytyrosol (HT), a hydrophilic antioxidant of olive oil. A low energy input fabrication process of the emulsion was implemented. The obtained emulsion contained 1.3% (w/w) of surfactants and 5% (w/w) aqueous phase. The spontaneously formed microemulsion contained 4.9% (w/w) of surfactants and 2% (w/w) aqueous phase. A comparative study in terms of structural characterization of the systems in the absence and presence of HT was carried out. Particle size distribution obtained by Dynamic Light Scattering (DLS) technique and interfacial properties of the surfactants' layer, examined by Electron Paramagnetic Resonance (EPR) spectroscopy indicated the involvement of HT in the surfactant membrane. Finally, the proposed systems were studied for the scavenging activity of the encapsulated antioxidant toward galvinoxyl stable free radical showing a high scavenging activity of HT in both systems.