In recent years, with the rapid development of the internet, a large number of online influencers, skincare experts, WeChat official accounts and Weibo influencers have emerged. As consumers’ understanding of cosmetics has deepened and their demands for quality and efficacy have continued to rise, the cosmetics market is shifting from concept-based marketing to efficacy-based marketing.

Among the key challenges is how to enhance the efficacy and bioavailability of active ingredients in cosmetics—a pressing issue in their application. To address this, scientists have conducted in-depth research into various formulation technologies and active ingredient delivery systems.

Below, we’ll take a look at some commonly used systems in colloid chemistry~

★★★ Micellar Solubilisation

Micelles refer to aggregates formed when an excess of surfactant is dissolved in water: the hydrophobic groups attract one another and aggregate to form a core, whilst the hydrophilic groups face outwards to form a shell. These aggregated structures are known as micelles, which can take various shapes, such as spherical, layered or rod-shaped.

Advantages of micellar solubilisation: Micelles form spontaneously and are thermodynamically stable systems. With particle sizes ranging from just 10 nm to 100 nm, they form transparent aqueous dispersions.

Disadvantages of micellar solubilisation: Due to the high surfactant content, the active ingredient loading is low. Consequently, only small amounts are added to the final product; otherwise, the cosmetic may cause significant irritation. Furthermore, aqueous formulations are prone to foaming when shaken or applied.

★★★ Microemulsion

Microemulsions are somewhat similar to micelles; they are also thermodynamically stable systems formed spontaneously from oil, water, surfactants and co-surfactants. The difference lies in the ratio of ingredients, which differs from that of micelles: microemulsions can carry a higher concentration of active ingredients, whilst the amount of surfactant used is slightly lower.

Advantages of microemulsions: Microemulsions range in size from 10 to 100 nm; when dispersed in water, they form transparent or semi-transparent systems. Microemulsions generally have low viscosity and a high active ingredient loading capacity.

Disadvantages of microemulsions: The technology required to form microemulsions is relatively complex, demanding extreme precision in the structure and proportions of surfactants; this makes them difficult to achieve in practice and challenging to characterise.

★★★ Lipid-like Vesicles

Generally speaking, these are self-assembled structures formed from synthetic surfactants, also known as lipid-like vesicles or liposomes. Lipid-like vesicles are formed spontaneously by synthetic surfactants.

Advantages of lipid-like vesicles: Firstly, their unique bilayer membrane structure is similar to that of cell membranes, offering good compatibility and cellular permeability. Secondly, the manufacturing process is relatively simple; a surfactant concentration of 5–20 per cent is sufficient to form multilayer vesicles.

Disadvantages of lipid vesicles: the synthetic surfactants used are prone to introducing impurities, are highly irritating to the skin, and are thermodynamically unstable.

When it is necessary to form a stable multilayer vesicle gel, an even higher concentration of surfactant is required.

★★★ Liposomes

Liposomes are a common carrier system formed by encapsulating active ingredients within a phospholipid bilayer; they represent one of the earliest and most mature passive targeting formulations.

Advantages of liposomes:

● The phospholipids forming the encapsulating layer are of natural origin and constitute a core component of cell membranes; they are safe, reliable, have good biocompatibility and excellent permeability;

● The bilayer formed by phospholipids is structurally similar to the cell membrane, ensuring good permeability;

● Liposomes have a very fine, smooth and unique skin feel.

Disadvantages of liposomes: Following freezing tests at temperatures below the freezing point, liposomes are unable to regain their original particle size.

ADVANTAGES OF LIPOSOMES

★★★ Nanoemulsion

Nanoemulsions, similar in structure to microemulsions, are semi-transparent emulsions containing extremely small particles; they are also classified as oil-in-water (O/W) and water-in-oil (W/O) types. Nanoemulsions are thermodynamically unstable systems; the use of surfactants, co-surfactants and external energy aids in their formation and ensures their kinetic stability.

Advantages of nanoemulsions: The particle size of nanoemulsions is controllable; they offer good permeability; they are relatively convenient to formulate; and they are readily absorbed.