WHAT ARE LIPOSOMES?
Liposomes are microscopic vesicles that consist of an aqueous center with a phospholipid membrane; phospholipids contain a glycerol bonded to 2 fatty acids and a phosphate group with a polar head. The fatty acid portion of this biomolecule is hydrophobic and is located toward the outside of the lipid bilayer whereas the phosphate group is hydrophilic and faces the aqueous interior. These phospholipid walls are identical to those that comprise other human cell membranes. Liposomes can differ in size, with a range in diameter between 15-3500 nm, and they can be found in unilamellar or multilamellar forms.
Multilamellar vesicles are produced using a low shear method that entails the combination of water and the phospholipids. The phosphate head regions align side by side on the interior of the molecule while the lipid regions align beside one another on the exterior, forming a circular vesicle. These multilamellar vesicles are much larger, having numerous concentric lipid bilayers with integrated aqueous compartments, and are much less stable than the unilamellar versions.
Unilamellar vesicles are small, exceptionally stable molecules, as they are formed via a high shear processing method. These vesicles have a greater Zeta Potential than the typical liposome, which allows for smaller, more uniform particle size with increased stability. Zeta Potential is an indicator of the electronic charge on the surface of any macroscopic material that is in contact with a liquid. This can be used to predict and control the stability of suspensions; the higher the Zeta Potential, the greater the stability of the molecule because the charged particles are able to repel and overcome their innate affinity to assemble.
The skin is the primary protective organ that allows very few foreign objects to penetrate. For this reason, some molecules are unable to effectively penetrate the stratum corneum; for example, actives such as collagen and elastin are too large to permeate efficiently. However, with the liposome as a vehicle we can release these active molecules through several layers of epidermis, but without diffusing too deeply. We are able to discharge hydrophilic and hydrophobic molecules in unison, and yet still manage the texture and efficacy of a topical application.
Liposomes can be used in the delivery of various cosmetic materials, vitamins, and minerals throughout the body, typically to the skin, for an array of advantages such as antioxidant benefits, conditioning, and antimicrobial purposes. The liposomes may attach and fuse to the cellular membranes, releasing their contents into the target cells. Liposomes are available in different transportation forms: dispersed and emulsified. Those that contain solely aqueous materials are known as dispersed liposomes, and they tend to be small and translucent. Liposomes that enclose hydrophobic elements are considered emulsified, and they tend to be larger and more opaque. However, liposomes are very useful in that they are also able to simultaneously transport both oil- and water-soluble actives within one vesicle; the hydrophilic molecules are encapsulated within the aqueous center of the biomolecule, whereas the hydrophobic elements are incorporated into the lipid bilayer.
Along with the capacity to carry hydrophilic and/or hydrophobic molecules, there are many other advantages to using liposomes as delivery mechanisms in skincare and for other cosmetic uses. Along with being nontoxic and noninvasive, the size of the transported molecule will not account as a restriction. In general, liposomes are exceptionally large structures and thus cannot penetrate into the deeper layers of the skin, but they are miscible with the skin’s primary moisture barrier, the peridermal lipids.
There has been intense research in regard to liposomes’ encapsulation capacity in cosmetics because the multifunctional properties lead to an assortment of applications, such as skin regeneration, skin and hair conditioning, anti-aging, and sun protection. Generally liposomes are compatible with the skin in fairly low concentrations such that they do not disrupt the consistency of the skin’s lipid bilayers and are not removed while cleansing the skin.