Emulsions may sound unfamiliar just by their name. But if you often drink dairy products, eat vegetable salads, and use emulsion skincare products, then emulsions are actually your inseparable "life good friends."

In the cosmetics industry, emulsions are commonly used in products such as moisturizing creams and facial cleansers to provide moisturizing and hydrating effects.

In the food industry, emulsions are often used in the preparation of dairy products, condiments, and salad dressings.

In the pharmaceutical industry, emulsions are usually used in the preparation of oral or topical medications, which helps the stability and absorption of the drugs.

Emulsions are a special dispersed system composed of immiscible water phases, oil phases, and emulsifiers. They can make one liquid phase (such as the oil phase) dispersed in the form of numerous micrometer-sized droplets in another liquid phase (such as the water phase) after emulsification.In general, emulsions are widely used mixtures with a variety of applications and functions.

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However, it was previously difficult to spontaneously form a water-oil emulsion (emulsion) dispersion system.

The reason lies in the fact that mixing water and oil increases the liquid-liquid interface, thereby increasing the overall energy of the mixed system.

Therefore, the most common method of emulsification is stirring and high-speed shearing. By cutting the liquid into small droplets, the droplets are then stabilized by an emulsifier, thus forming an emulsion.

However, the force of stirring or high-speed shearing on the liquid is not uniform, which can result in uneven size distribution of the formed emulsion droplets, ranging from as small as 1-2 micrometers to as large as tens or even hundreds of micrometers, severely affecting the overall performance and related applications of the emulsion.Emulsions are often used as soft templates to prepare microcapsules and microspheres. The latter are widely used in the fields of drug delivery, biomedical detection, and functional materials. Therefore, researchers have never stopped their studies on monodisperse emulsions.

Currently, the mainstream preparation methods for monodisperse emulsions are microfluidics and membrane emulsification.

Microfluidic technology involves the design and fabrication of microchannels, as well as the matching conditions of liquid flow rates. This technology can prepare monodisperse emulsion droplets from microchannels and collect them.

Membrane emulsification technology utilizes the design of pores in the membrane material, allowing the liquid flowing through the membrane to enter another dispersed phase with uniform size, thus achieving the purpose of preparing uniform emulsions.

Monodisperse emulsions, welcome new preparation methods.However, the above two methods each have their strengths and weaknesses. Based on this, Professor Jiang Hang from Jiangnan University and his collaborators have proposed a new method for preparing monodisperse emulsions. Compared to traditional methods, it can eliminate the steps of designing microchannels and membrane pores.

Specifically, this method still builds on the traditional shear emulsification method and does not require the addition of extra auxiliary equipment and devices. At the same time, they have made good use of nature's gift - natural bee pollen.

Bee pollen is widely available and comes in a variety of types. Most importantly, the microscopic morphology and size of bee pollen of the same variety are very uniform and have a very stable pollen wall.

So, they dispersed bee pollen in the form of micro-particles evenly in water and used it as the aqueous phase. Then, the D5 silicone oil dispersion of hydrophobic silica nanoparticles was used as the oil phase, where the silica nanoparticles played the role of interfacial stabilization.

During high-speed shear emulsification, the aqueous phase will still be sheared into droplets of different sizes and dispersed in the oil phase. The difference is that the addition of bee pollen limits the shearing of some of the aqueous phase droplets and makes their size close to the size of the bee pollen.Subsequently, after a simple low-speed centrifugation process, it is possible to obtain monodisperse emulsion droplets loaded with single bee pollen grains, which can then be used to prepare monodisperse microcapsules.

Bee pollen is widely present in nature and is a natural carrier of genetic material from plants. The pollen wall is composed of two layers: a hard outer wall made of sporopollenin and an inner wall based on polysaccharides.

The interior cavity of natural pollen is mainly filled with cytoplasm and spore plasma substances, including biomolecules and organelle clumps. Studies have shown that the interaction of certain pollen components with the human immune system may be responsible for the occurrence of pollen allergies.

To eliminate potential allergic reactions, pollen must first undergo a defatting process to remove some proteins and lipids from the outer wall. Then, using acid or alkali treatment methods, residual proteins and spore plasma organs within the pollen particles are removed.

The treated pollen becomes a natural source of hollow microcapsules, making it suitable for encapsulating various active substances, such as oils, proteins, and nanoparticles.After defatting and protein removal, the surface of pollen particles exhibits a large number of micro-scale and nano-scale pores and openings. These channel structures will affect the encapsulation effect of active substances within the hollow pollen microcapsules.

Therefore, they combine the concept of emulsion interface engineering with hollow pollen microcapsules, utilizing the inherent characteristics of the natural pollen outer wall to create a monodisperse double-layer microcapsule system to slow down or avoid the leakage of encapsulated active substances.

It is expected that in a few years, the achievements of this research will have important application prospects in the fields of active substance encapsulation and delivery in food, cosmetics, biomedicine, and other fields.

Refined engraving in the microcosm, and the essence of nature hidden within small droplets.In fact, nature is both magical and full of mysteries, and many original scientific research works are inspired by nature. As early as five years ago, Jiang Hang had already begun to pay attention to bio-based colloids derived from nature, with bee pollen being one of his focuses.

During his doctoral studies, he followed Professor Wei Tao from the Chinese University of Hong Kong to study emulsions and microcapsules, thus gaining an understanding of monodisperse emulsions. After joining Jiangnan University, Jiang Hang set the topic of bee pollen microcapsules for his students.

Initially, he just wanted to see what kind of phenomenon would occur when bee pollen was encapsulated in an emulsion. Since the size of bee pollen is very uniform, could it be possible to encapsulate only one pollen particle in a single emulsion droplet to achieve the effect of a monodisperse emulsion?

Based on this, they set the topic of monodisperse Pickering emulsions based on bee pollen.

Firstly, they selected camellia pollen as the research object, D5 silicone oil as the oil phase, and aerosol silica as the emulsifying particles. By adding bee pollen and performing high-speed shearing and homogenization emulsification, the resulting emulsion would have two distinctly different size distributions.One type is a large emulsion droplet encapsulating a single pollen grain (greater than 30 micrometers), and the other is a small emulsion droplet formed by high-speed shearing with a size less than 5 micrometers.

Subsequently, a low-speed centrifugation operation is adopted to effectively separate the emulsion droplets of the two size distributions, thereby collecting a monodisperse oil-in-water type Pickering emulsion.

However, the yield of the monodisperse emulsion prepared by this method is heavily dependent on the amount of pollen particles.

Too little addition of pollen can significantly enhance the monodispersity of the emulsion, but the yield is very low. An excessive amount of pollen added may lead to the encapsulation of multiple pollen grains in the emulsion droplets, which in turn affects the overall uniformity of the emulsion.

For this reason, they continuously optimized factors affecting the preparation, such as the oil phase-water phase volume ratio, shearing speed, and the amount of pollen added, and determined the preferred conditions for the preparation of monodisperse emulsions. It was found that even when the concentration of pollen reaches 20% of the aqueous phase, it can still ensure that a single pollen grain is encapsulated in the emulsion droplets.However, the morphology of bee pollen varies among different varieties. Thus, they selected many bee pollens from different plant sources, including rapeseed pollen, which is representative of spherical shapes, and sunflower pollen, which is representative of spiky shapes.

Interestingly, natural bee pollen has its own fluorescent properties. By fluorescently staining the aqueous phase and silica particles, it is possible to clearly observe the encapsulation of single pollen particles by monodisperse Pickering emulsions through confocal laser scanning microscopy, and also to characterize the three-dimensional structure of the emulsion.

They also found that the shape of the pollen does indeed affect the morphology of the droplets. Particularly notable is the sunflower pollen, whose spiky structure can further prevent the coalescence of droplets, forming highly symmetrical and stable monodisperse droplet structures.

Although the use of pollen particles can prepare monodisperse emulsion droplets, the pollen itself occupies most of the internal aqueous phase space, which is not conducive to the encapsulation of active substances in the emulsion and microcapsule systems.

To this end, they obtained natural pollen microcapsules with hollow cavities through methods of defatting and deproteinization. Subsequently, using the pollen microcapsules instead of natural pollen, they found that it was still possible to form monodisperse droplets encapsulating a single pollen microcapsule.In this way, many active substances can be pre-encapsulated in pollen microcapsules, and then encapsulated again within the water phase of the emulsion droplets through emulsification.

Subsequently, through the interfacial sol-gel reaction, the research team found it easy to solidify a protective shell of silica material outside the pollen microcapsules once more, thus serving as a second "protective shield" for the active substances in case of leakage from the pollen microcapsules. With this, the research officially came to an end.

Recently, the related paper was published in Advanced Functional Materials[1] with the title "Harnessing the Power of Nature: Monodisperse Pickering Emulsion Droplets and Yolk-Shell Microcapsules Utilizing Bee Pollen Particles."

Professor Hang Jiang from Jiangnan University and graduate student Hengxing Yu from Jiangnan University are the co-first authors, while Professor Bernard P. Binks from the University of Hull and Professor Tao Wei from the Chinese University of Hong Kong served as the corresponding authors.

In the future, Professor Jiang hopes to continue expanding the study of monodisperse emulsion methodology, as well as conducting research on intelligent encapsulation systems based on pollen microcapsules, thereby bringing more practical applications.