Since ancient times, oil and water have been regarded as the quintessential example of immiscible substances, and emulsifiers (such as surfactants) have played the role of mediating between them. Consequently, the notion that “oil and water cannot mix without the use of emulsifiers” has long been accepted as common wisdom. However, we have come to realize that this conventional wisdom is not necessarily absolute through continued investigation of the mixing behavior of oil and water. Oil and water can mix and form stable emulsions under appropriate conditions even in the absence of emulsifiers. In this article, we discuss the possibility and underlying principles of emulsifier-free emulsification (EfE): a phenomenon once regarded as implausible, in which stable emulsions are formed using only oil and water.

Lipid bilayers constitute the fundamental structural framework of biological membranes and serve as platforms for diverse cellular functions. Among artificial membrane systems, nanodiscs have emerged as unique nanoscale assemblies that preserve the planar structure of lipid bilayers while minimizing their dimensions. Owing to their small size, structural uniformity, and accessibility of both membrane surfaces, nanodiscs have been extensively utilized as model membranes for investigating membrane proteins and membrane-active biomolecules. More recently, their applications have expanded to drug delivery, molecular imaging, and vaccine development.

This article reviews the development of nanodisc technologies from conventional phospholipid bicelles to protein- and polymer-stabilized nanodiscs. Particular emphasis is placed on our studies employing synthetic lipids and amphiphilic polymers. First, organic–inorganic hybrid nanodiscs formed from alkoxysilane-containing lipids are introduced. These nanodiscs possess a siloxane network on the membrane surface, resulting in remarkable structural stability against drying, detergents, and temperature changes. Second, polymer nanodiscs generated by amphiphilic polymethacrylates are described. These polymers provide high molecular design flexibility, enabling control over nanodisc formation and properties. Furthermore, applications of polymer nanodiscs in amyloid inhibition and drug delivery are discussed. These studies demonstrate that nanodiscs are evolving from simple membrane models into versatile functional nanomaterials for biomedical applications.

The effects of glycerol and urea on the microstructure and water homeostasis of the stratum corneum (SC) are summarized and compared based on studies using high-brilliance synchrotron X-ray diffraction (XRD). Time-resolved XRD analyses of human SC during wetting and drying processes revealed that both glycerol and urea suppress the reduction of the coiled-coil α-helix chain distance of soft keratin during drying, indicating enhanced retention of bound water, with glycerol exhibiting a stronger effect than urea. In addition, analysis of the short lamellar structure of intercellular lipids showed that treatment with glycerol or urea prolonged the interval during which the structural volume remained unchanged, reflecting stabilization of interlamellar water within the lipid matrix. These findings indicate that glycerol and urea enhance SC water homeostasis through two complementary mechanisms: stabilization of bound water near the skin surface at approximately 25 wt% and reinforcement of water regulation by the lipid lamellar structure. Owing to these mechanisms, the water content at the SC surface is maintained homeostatically, and this homeostatic state is more effectively strengthened by glycerol than by urea.