Ingredients Penetration Enhancer Systems -

Microencapsulation Delivery System

Introduction

Microencapsulation is a process by which tiny particles of liquid, or solid active ingredient or even a gas, can be surrounded by a second material for the purpose of shielding the material or active ingredient from the surrounding environment. These particles which range in size from 1 µm to seven millimeters, release their contents at a later time depending on the ultimate need or the application. The material inside the microcapsule is referred to as the core, internal phase, or fill, whereas the wall is sometimes called a shell, coating, or membrane. Modification of particles to mask flavors, reactivity, solubility, odor, color, and wetting characteristics is one of the most important yet least understood particle processes.

Microencapsulation can be used for almost any purpose in skin care and cosmeceutical industry. Although most microencapsulation sees its use in the skin care and treatment areas, this process can be used for fragrances, sunscreens, active ingredients, or any material that needs a special delivery system. It can be used to deliver active ingredient (especially large macromolecules, e.g. protein ingredients) into the deeper layer of skin and release the active ingredients at the site where it is most effective. It can also be used to deliver a material into a phase it would otherwise not normally like to go. For example, putting an oil soluble vitamin into a water phase formulation would be difficult if it weren’t for the microencapsulation process. It can be used to encapsulate active ingredients so they can be put into a phase in which they would normally have poor stability. In some cases, a core must be isolated from its surroundings, as in isolating vitamins from the deteriorating effects of oxidation, or slowing down the evaporation rate of a volatile material.

There are many methods that can be utilized to formulate an encapsulation system. There are many different types of encapsulation techniques. Some methods can be used to provide a controlled release (or sustained release) of active materials where a specified amount of drug is released over a specific period of time or at a specific rate., making the effect lasting longer. Some processes and methods are proprietary and there are a number of patents that exist for this technology. This field is still evolving and new systems are being introduced to the industry every day. Microencapsulation will take the cosmetics and personal care industry into new areas of application using actives and sensitive ingredients that are very functional but quite difficult to use.

Delivery system platforms vary dramatically. There are a variety of delivery agents available in the industry today and they may be used for a number of purposes, such as sustaining, improving the stability and mitigating the irritation of actives, delivering actives to the skin surface and enhancing penetration of actives into the skin, as well as allowing insoluble material to be dispersed into a typically incompatible vehicle.

Delivery agents vary widely in chemistry, from polymeric compounds that can be rigid solids or liquid film-forming agents to liposomes based on lecithin and cyclodextrins derived from cyclic carbohydrates. Microspheres and nanospheres (see our Nanotechnology skin care article) may be based on commonly used waxes or polysaccharides. Companies are combining the offering and capabilities of silicone chemistries with organic technologies. The use of silicone elastomer blend (SEB) for delivery of personal care actives is now used for a wide range of actives and not just limited to vitamins, sunscreens, and fragrances. Like their chemistries, the delivery systems also vary in the loading capacity, particle size, penetration ability, and in types of materials they can deliver.

Solid polymeric encapsulates contain vast surface areas that can adsorb or absorb many times their weight in actives. These types of materials generally do not penetrate into the skin and are good mechanisms for time release of actives to the surface of the skin.

Film forming agents can also hold and deposit active ingredients at the skin surface, as well as enhance penetration

Liposomes (and nanospheres) are generally smaller particles and are best utilized for their ability to deliver the actives into the skin. Liposomes consist of fluid multi- or bilayers that are similar to components of cell membranes and thus have the affinity for increased penetration.

Micro-emulsions are popular for use in certain lightweight yet highly potent products such as skin treatment serums. Like emulsions, micro-emulsions are a blend of oil and water-based ingredients that utilize special ingredients, called emulsifiers, which keep each portion of the formulation evenly blended so that each part of the product contains an equal and viable concentration of active ingredients. The important aspect of a micro-emulsion is that it blends the active ingredient droplets into a much smaller or finer droplet than you would find in a normal emulsion. Because the size of the active ingredient droplet can be around 1000 times smaller than that of a normal emulsion, that means that the actives can rapidly penetrate deeper into the skin because the ingredient droplets can fit in between the inter-cellular spaces of the tissue much more efficiently.

Current trends for delivering actives to the skin also include triple emulsions. Triple emulsions are more highly constructed to provide the option of delivery into specific parts of the tissue or even specific cells such as adipocytes. For instance, contouring creams are formulated in a triple emulsion formula in order to deliver slimming and fat burning ingredients directly into the adipocytes. Typically, an average contouring cream would only penetrate into the epidermis. Since our fat cells are located in our adipose tissue (which is much deeper in the body), regular contouring emulsions won’t have much of an effect on those fat cells that are so deep in the skin. Triple emulsions, like regular emulsions, are made of oil and water-based active ingredients. But instead of distributing the oil through the water or vice versa, chemists can actually put water in oil and then redistribute it through another layer of water. So the first “layer” of the emulsion is a water-based active ingredient (for contouring) dissolved into little oil droplets (2nd layer) that have a similar structure to the cellular membranes of a fat cell, creating a miniature “pseudo-adipocyte.” Small appendages are even constructed on the outside of the pseudo-adipocyte membrane to mimic the shape and structure of cell receptors. The last layer of the triple emulsion is achieved when pseudo-adipocytes are dissolved into another water-based texture to distribute and stabilize the structure of the contouring cream.

In the area of nano technology applicable to cosmetics, the companies can focus on nanoemulsions, which are highly adaptable liquid delivery systems that can be tailored to provide desirable properties for a broad range of potential applications, from simple cosmetics to advanced dermatologicals with anti-aging benefits. A nanotechnology company has executed licenses with UCLA for nanoemulsons (including double nanoemulsions) and polypeptides. Encapsulation can be accomplished using micro/nanoparticles, liposomes/vesicles/Nanosome™, micro/nanoemulsions.

Liposome Delivery Systems

Liposomes are small, spherical vesicles which consist of amphiphilic (both water and fat soluble, as opposed to hydrophobic and hydrophillic) lipids, enclosing an aqueous core. The lipids are predominantly phospholipids (e.g. lecithin) which form bilayers similar to those found in biomembranes. In most cases the major component is phosphatidyl choline (lecithin). Depending on the processing conditions and the chemical composition, liposomes are formed with one or several concentric bilayers.

Liposomes are often distinguished according to their number of lamellae and size. Small unilamellar vesicles (SUV), large unilamellar vesicles (LUV) and large multilamellar vesicles (MLV) or multivesicular vesicles (MVV) are differentiated (see figure). SUVs show a diameter of 20 to approximately 100 nm. LUVs, MLVs, and MVVs range in size from a few hundred nanometers to several microns. The thickness of the membrane (phospholipid bilayer) measures approximately 5 to 6 nm.

Large liposomes form spontaneously when phospholipids are dispersed in water above their phase transition temperature. The preparation of SUVs starts usually with MLVs, which then are transformed into small vesicles using an appropriate manufacturing technique, e.g. high-pressure homogenization.

Nonphospholipid liposomes include Niosomes and sphingosomes which are vesicles with a similar structure. In contrast to lecithin (phospholipids) based liposomes, nonionic surfactants, e.g. polyglyceryl alkyl ethers, or sphingolipids make up the bilayer of niosomes and sphingosomes, respectively.

Liposomes which are used as delivery systems, may encapsulate hydrophilic (water soluble) substances in their aqueous core. Amphiphilic (both water and fat soluble) and lipophilic (hydrophobic. i.e. fat soluble) substances, e.g. oil soluble UV filters, can be incorporated into the lipid bilayer. Loaded liposomes as well as non-loaded, empty liposomes, are used in cosmetics. The major effect of empty liposomes is an increase in skin humidity.

Liposomes are an important component of many skin rejuvenation treatments because of the ability of liposomes to encapsulate active anti-aging ingredients and deliver them through the layers of skin right down to the cellular level where they can do the most good.  They can easily penetrate through the layer of the skin. Based on this feature, active ingredients can be incorporated into liposomes to enhance their absorption by the skin and thus their efficacy. In fact, liposome-encapsulation largely reduces the amount of the active ingredient required for effectivness as compared to non- encapsulated, pure active ingredients. This special delivery system serves to provide cells with critical nutrients and the nourishment necessary to promote collagen production.

The skin compatibility of topically applied phospholipids is very high. There are no restrictions concerning their use in foodstuff and cosmetics, neither in the EU nor for regulations of the US Food and Drug Administration; lecithins are generally accepted as safe (GRAS status – Generally Recognized As Safe). However, it is known that high doses of phospholipids which are applied topically over a longer period may lead to irritations on dry and normal skin.

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