Influence of diffusive transport on the structural evolution of W/O/W emulsions

Complex Emulsions as an Innovative Pharmaceutical Dosage form in Addressing the Issues of Multi-Drug Therapy and Polypharmacy Challenges

This review explores the intersection of microfluidic technology and complex emulsion development as a promising solution to the challenges of formulations in multi-drug therapy (MDT) and polypharmacy. The convergence of microfluidic technology and complex emulsion fabrication could herald a transformative era in multi-drug delivery systems, directly confronting the prevalent challenges of polypharmacy. Microfluidics, with its unparalleled precision in droplet formation, empowers the encapsulation of multiple drugs within singular emulsion particles. The ability to engineer emulsions with tailored properties-such as size, composition, and release kinetics-enables the creation of highly efficient drug delivery vehicles. Thus, this innovative approach not only simplifies medication regimens by significantly reducing the number of necessary doses but also minimizes the pill burden and associated treatment termination-issues associated with polypharmacy. It is important to bring forth the opportunities and challenges of this synergy between microfluidic-driven complex emulsions and multi-drug therapy poses. Together, they not only offer a sophisticated method for addressing the intricacies of delivering multiple drugs but also align with broader healthcare objectives of enhancing treatment outcomes, patient safety, and quality of life, underscoring the importance of dosage form innovations in tackling the multifaceted challenges of modern pharmacotherapy.

Preparation and stability mechanisms of double emulsions stabilized by gelatinized native starch

Double emulsions are promising carrier systems for foods, pharmaceuticals, and cosmetics. However, their limited stability hinders their practical applications. We used gelatinized starch to develop stable double emulsions as carrier materials. The oil/water/water (O/W/W) double emulsions were formed by 5 wt% native corn starch, while oil/water/oil (O/W/O) double emulsions were formed by 7 wt% native corn starch and high-amylose starch with 60 % and 75 % amylose contents investigated by optical microscopy. Furthermore, the storage stability of double emulsions was revealed by droplet size distribution, microstructure, backscattering, rheological profiles, and low-field nuclear magnetic resonance (LF-NMR) imaging. Results confirmed that the O/W/O double emulsions stabilized by 7 wt% native corn starch had a smaller mean droplet size (11.400 ± 0.424 μm) and excellent storage stability (14 days) than O/W/W and O/W/O double emulsions prepared with high-amylose starch. Such unique double emulsions prepared with gelatinized native corn starch are good candidates of carrier materials.

Impact of fat crystallization on the resistance of W/O/W emulsions to osmotic stress: Potential for temperature-triggered release

Water-in-oil-in-water (W/O/W) emulsions can be designed to encapsulate, protect, and release both hydrophilic and hydrophobic functional compounds. In this study, we examined the impact of crystallizing the fat phase on the resistance of W/O/W emulsions to osmotic stress, with the aim of developing osmotic-responsive systems. Polyglycerol polyricinoleate (PGPR) was used as a hydrophobic surfactant to stabilize the inner water droplets, while Quillaja saponin and whey protein isolate (WPI) were used as hydrophilic surfactants to coat the oil droplets. The impact of fat crystallization was examined by using either a liquid (soybean oil, SO) or semi-solid (hydrogenated soybean oil, HSO) fat as the oil phase. An osmotic stress was generated by establishing a sucrose concentration gradient between the internal and external water phases. Alterations in the droplet size, morphology, and stability of the W/O/W emulsions was measured when the sucrose concentration gradient was changed. The W/O droplets in the SO-emulsions swelled/shrank when the external sucrose concentration was below/above the internal sucrose concentration, which is indicative of water diffusing into/out of the droplets. Conversely, there was no change in the size of the W/O droplets in the HSO-emulsions under the same conditions, which was attributed to the mechanical strength of the fat crystal network resisting swelling or shrinking. HSO-emulsions did exhibit swelling when they were heated above a critical temperature, due to melting of the fat crystals and disruption of the crystal network. Our results demonstrate that crystallization of the oil phase of W/O/W emulsions can prevent water transport due to osmotic stress, which may be useful for developing temperature-triggered delivery systems for application in foods, cosmetics, pharmaceuticals, or personal care products.

Fat crystals: A tool to inhibit molecular transport in W/O/W double emulsions

Water-in-oil-in-water (W/O/W) double emulsions are a promising technology for encapsulation applications of water soluble compounds with respect to functional food systems. Yet molecular transport through the oil phase is a well-known problem for liquid oil-based double emulsions. The influence of network crystallization in the oil phase of W/O/W globules was evaluated by NMR and laser light scattering experiments on both a liquid oil-based double emulsion and a solid fat-based double emulsion. Water transport was assessed by low-resolution NMR diffusometry and by an osmotically induced swelling or shrinking experiment, whereas manganese ion permeation was followed by means of T₂ -relaxometry. The solid fat-based W/O/W globules contained a crystal network with about 80% solid fat. This W/O/W emulsion showed a reduced molecular water exchange and a slower manganese ion influx in the considered time frame, whereas its globule size remained stable under the applied osmotic gradients. The reduced permeability of the oil phase is assumed to be caused by the increased tortuosity of the diffusive path imposed by the crystal network. This solid network also provided mechanical strength to the W/O/W globules to counteract the applied osmotic forces.

Controllable one-step double emulsion formation via phase inversion

Double emulsions, the simplest form of multiple emulsion, have been intensively utilized in various industries as well as in fundamental research. A variety of strategies to effectively form double emulsions have been developed, but no simple yet controlled and scalable technique has been achieved yet. Herein, we examine the mechanism of the entire process of double emulsion formation by phase inversion, and we propose a universal one-step strategy for the formation of an oil/water/oil double emulsion using oil soluble polymers and hydrophobic silica nanoparticles. We demonstrate that this new approach enables control of both the fraction and the number of inner small droplets; even high internal phase double emulsions could be achieved.

Multiple Water-in-Oil-in-Water Emulsion Gels Based on Self-Assembled Saponin Fibrillar Network for Photosensitive Cargo Protection

A gelled multiple water-in-oil-in-water (W₁/O/W₂) emulsion was successfully developed by the unique combination of emulsifying and gelation properties of natural glycyrrhizic acid (GA) nanofibrils, assembling into a fibrillar hydrogel network in the continuous phase. The multiple emulsion gels had relatively homogeneous size distribution, high yield (85.6-92.5%), and superior storage stability. The multilayer interfacial fibril shell and the GA fibrillar hydrogel in bulk can effectively protect the double emulsion droplets against flocculation, creaming, and coalescence, thus contributing to the multiple emulsion stability. Particularly, the highly viscoelastic bulk hydrogel had a high storage modulus, which was found to be able to strongly prevent the osmotic-driven water diffusion from the internal water droplets to the external water phase. We show that these multicompartmentalized emulsion gels can be used to encapsulate and protect photosensitive water-soluble cargos by loading them into the internal water droplets. These stable multiple emulsion gels based on natural, sustainable saponin nanofibrils have potential applications in the food, pharmaceutical, and personal care industries.

Different magnesium release profiles from W/O/W emulsions based on crystallized oils

Water-in-oil-in-water (W/O/W) double emulsions based on crystallized oils were prepared and the release kinetics of magnesium ions from the internal to the external aqueous phase was investigated at T=4°C, for different crystallized lipophilic matrices. All the emulsions were formulated using the same surface-active species, namely polyglycerol polyricinoleate (oil-soluble) and sodium caseinate (water-soluble). The external aqueous phase was a lactose or glucose solution at approximately the same osmotic pressure as that of the inner droplets, in order to avoid osmotic water transfer phenomena. We investigated two types of crystallized lipophilic systems: one based on blends of cocoa butter and miglyol oil, exploring a solid fat content from 0 to 90% and the other system based on milk fat fractions for which the solid fat content varies between 54 and 86%. For double emulsions based on cocoa butter/miglyol oil, the rate of magnesium release was gradually lowered by increasing the % of fat crystals i.e. cocoa butter, in agreement with a diffusion/permeation mechanism. However for double emulsions based on milk fat fractions, the rate of magnesium release was independent of the % of fat crystals and remains the one at t=0. This difference in diffusion patterns, although the solid content is of the same order, suggests a different distribution of fat crystals within the double globules: a continuous fat network acting as a physical barrier for the diffusion of magnesium for double emulsions based on cocoa butter/miglyol oil and double globule/water interfacial distribution for milk fat fractions based double emulsions, through the formation of a crystalline shell allowing an effective protection of the double globules against diffusion of magnesium to the external aqueous phase.

A pendant drop method for the production of calibrated double emulsions and emulsion gels

We introduce a convenient pendant drop method for making double emulsions and emulsion gels in a predictable way.

Preparation of novel silicone multicompartment particles by multiple emulsion templating and their use as encapsulating systems

Multicompartment poly(dimethylsiloxane) particles were produced for the first time using water-in-oil-in-water (W1/O/W2) emulsions as templates. Multiple silicone W1/O/W2 emulsions were successfully prepared by using silicone precursors with a low viscosity. Several formulation parameters were studied to determine their effect on the properties of emulsions and derived particles. It was observed that the mass fraction of the inner aqueous phase (φ(W1)) and the concentration of both the hydrophobic and hydrophilic surfactants played a crucial role in the morphology and stability of the emulsions. Thus, the derived silicone porous particles also showed different characteristics depending on the emulsion formulation because of the templating effect. At low φ(W1) or high concentrations of the hydrophobic surfactant, particles showed smaller pore sizes as a result of more stable inner droplets. On the other hand, high concentrations of the hydrophobic surfactant resulted in an increase in the size of the derived particles, whereas high concentrations of the hydrophilic surfactant caused the opposite effect. In addition, fluorescein was encapsulated into the hydrophobic particles during the synthesis process and released in a controlled manner. The possibility to encapsulate simultaneously but independently two different hydrophilic components inside the same globule was also tested. On the basis of these results, the obtained silicone porous particles are envisioned to have applications in several advanced fields, for instance, as hydrophobic delivery systems.

Partial coalescence of sessile drops with different miscible liquids

Using computer simulations in three spatial dimensions, we examine the interaction between two deformable drops consisting of two perfectly miscible liquids sitting on a solid substrate under a given contact angle. Driven by capillarity and assisted by Marangoni effects at the droplet interfaces, several distinct coalescence regimes are achieved after the droplets' collision.