Although α gel appears white homogeneous gel state, it often comprises a α type hydrated crystal phase, a water phase, and additional crystal phases that form a multiphase system depending on the situation. Further, as a simple preparation process, ingredients are often heated to be melted, then cooled down after homogenization. These facts may possibly be the reasons of difficulties for engineers to comprehension of the α gel. In this article, a new method of characterization of a water phase in the α gel that was carried out by our group in addition to the previous studies on the α gel.

In this short review, α-gels formed by ternary mixtures of amino acid-based gemini surfactant (12-GsG-12, s is the spacer chain length, 2, 5, and 8), long-chain alcohol (1-hexadecanol, C16OH), and water have been discussed in terms of their structures and physicochemical properties. When compared with the α-gels formed with a single-chain surfactant (12-Glu), characteristic features of the “gemini-based α-gels” are summarized as follows; (i) lesser amount of C16OH requiring the formation of “saturated” α-gel, under the normalization by the number of alkyl chains of the surfactants, (ii) lower melting point, (iii) larger d-spacing suggesting the greater amount of water incorporated between lamellar sheets, and (iv) lower viscosity at a given water concentration. Future directions regarding this research topic are also addressed.

Intercellular lipids of the stratum corneum play an important role in maintaining healthy skin. Forming lamellar structures of intercellular lipids parallel to the skinsurface contributes to water holding property and barrier function of the stratum corneum. The new skincare formulation technique, “α-gel containing a large amount of water” with pseudo-ceramide, has been developed for forming “intercellular lipids-like” lamellar film on skin.

The biomimetic formulation and the study of intercellular lipids are reviewed from a skin care cosmetic point of view.

Tranexamic acid cetyl ester hydrochloride (TXC), which is synthesized by chemically modifying the tranexamic acid with the hydrophobic C16-chain, is utilized as an active ingredient in cosmetics. The chemical structure results in the higher hydrophobicity than water-soluble tranexamic acid which accelerate percutaneous absorption through stratum corneum. Although TXC was designed for the sake of the transdermal permeability to enhance bioavailability, we are interested in its structure as cationic amphiphile. Binary mixtures at different compositions showed a variety of self-assembling structures. Comparing with the general cationic surfactant systems, the TXC/water system showed highly organized orientation of liquid crystal, the higher Krafft temperature, and the lower critical micellar concentration due to its strong inter-molecular interaction between cyclohexyl groups which is a rigid six-membered ring conformation in the molecule. Upon addition of a long-chain alcohol, furthermore, α-gel can be formed. We also observed a unique α-gel phase consisting of dual channels in the quaternary water/TXC/cetyl alcohol/batyl alcohol system, named “Bicontinuous Alpha-Gel (BAG)”, which is beneficial for emulsification of various oils. In this review, we interpret the physicochemical properties of TXC and the hierarchical structure of α-gel, and introduce cosmetic performance of the α-gel formulation such as skin permeation of TXC and sensory effect.