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Chemical Reaction: Controlled Release

By: Steve Herman
Posted: March 5, 2008, from the March 2008 issue of GCI Magazine.

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Scent strips manufactured by Arcade Marketing Inc. had been used in regional magazines, but, in 1983, Giorgio Armani Cosmetics’ Giorgio went national and, for the first time, included mail order envelopes with the encapsulated scent samples. Scented blotters were taxed by postal authorities as actual product, but the scent strip was not, giving the new format a clear monetary advantage. The combination of microencapsulation, quirks in postal regulations and judicious use of zip codes in circulation strategy fueled a fragrance craze.

Other Delivery Methods

Beyond microencapsulation, liposomes and porous polymers are the most common controlled release forms for cosmetics. A liposome is a spherical vesicle composed of a bilayer membrane. The membrane can consist of a phospholipid and cholesterol or have surfactant components. Liposomes usually contain a core of aqueous solution, but they can be empty. Hydrophobic chemicals can dissolve in the membrane, enabling liposomes to deliver both hydrophobic and hydrophilic molecules.

Porous polymers act like sponges; examples are copolymerizing styrene and divinylbenzene. The ratio of the two components determines the pore size. There is a limit to pore size of about 30 Å, because beyond that physical stability is compromised and the pores collapse. Macroporous polymers have a pore size independent of crosslinking. They are formed around “porogens,” which act like placeholders when polymerization occurs and then leave a void. Typical pore sizes are 100–300 Å.

Another controlled release method involves turning the active ingredient into an ester. Delivery of menthol converted to menthyl glutarate or a menthyl succinate, for example, allows a prolonged cooling effect. The activating theory is that the ester bond will be broken by esterases in the skin. A related concept is unimolecular micelles, developed at Rutgers University by Kathryn Ulrich.

They can be single molecules with a hydrophilic core covalently bonded to several polymers with lipophilic terminations. A combination of a sugar, fatty acids and polyethylene glycols yields a biocompatible structure. Using linkages such as esters or amines that break under known conditions, the molecule becomes biodegradable and activates under specific environments.