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Chemical Reaction: Controlled Release

Steve Herman

“Any sufficiently advanced technology is indistinguishable from magic.”    
—Arthur C. Clarke

Active ingredients are the engines that propel treatment products. They are frequently unstable and require customized methods of protection, and, if they are to work, they must be delivered to the right place in active form. The basic challenge is to put something where it doesn’t naturally want to be and ensure it survives intrinsically in hostile conditions. There are many options for controlled release and targeted delivery, and new ones are developed regularly.

The history of encapsulation can be traced as far back as 1927, when capsules were spray-dried with oil-gum acacia coatings, but the real breakout occurred in 1955, when the National Cash Register Company (NCR) received a patent for the process of microencapsulation. The NCR filled its capsules with liquid, and over a period of time and under certain conditions, the capsules would break open, dispensing the liquid.

The manufacture of carbon-free carbon paper was the first commercial application. Using microencapsulated ink and by placing two sheets of paper together, a writer or typist only had to apply pressure on one paper to duplicate what was written or typed onto the other. Now that everyone has computers and printers, it is difficult to appreciate the magnitude of this invention, but it was
a great advance.

More important to the evolution of the fragrance industry, microencapsulation led to the creation of scratch-and-sniff technology, but for a different use than advertising a personal fragrance. The Dayton Power & Light Company was the first company to utilize this technology, sending scratch-and-sniff cards to its customers so that they might distinguish the smell of natural gas.

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.

There are significant delivery issues beyond treatment products. One of the great challenges of the fragrance industry is keeping scent on products incorporated in detergents and fabric softeners. Detergents are designed to wash out oily materials, and fragrances are oily materials.

Raw material suppliers, large fragrance companies and consumer goods companies all have technologies to deal with this situation, many of which are proprietary. Henkel uses a precursor based on salicic acid esters, which anchor fragrance molecules. The esters split through hydrolysis in the laundry process, releasing the fragrance.

MIT scientists have devised remotely controlled nanoparticles that, when pulsed with an electromagnetic field, release drugs. Nanoparticles carry two different drug loads. A remotely generated electromagnetic field releases the first active, and, later, a stronger pulse is used to release the second active. The second active is tethered by a DNA chain twice as long as the first, measured in the number of base pairs.

Green Methods

Green chemistry is being employed to develop revolutionary drug delivery methods that are more effective and less toxic. Chemists at The University of Nottingham (United Kingdom) are developing new methods for coating drugs in plastics, using methods that do not damage the latest generation of delicate biopharmaceutical drugs—which are at the cutting edge of modern medical treatment. Biodegradable polymers are made using supercritical carbon dioxide, eliminating the use of heat or harmful solvents. Using low temperature, delicate bioactive components, such as growth factors or proteins, can be mixed into the polymer without any loss of activity.

Green renewable resources are much in demand, and chicken feathers—typically a waste product—is an unusual and interesting example. The U.S. Department of Agriculture has awarded a four-year, $500,000 bio-based products grant to a University of Delaware research group working to develop advanced materials from chicken feathers and soybean oil. Work has been done using carbonized chicken feather fibers for hydrogen storage5. Hydrogen storage is not a cosmetic application, but this use demonstrates that unexpected sources will arise inevitably as green chemistry evolves and money is dedicated to research.

Technically, it has been a long journey from encapsulating ink to using electromagnetic pulsing to release drugs, and the possibility for future development of controlled release techniques seems boundless. Combined with the cosmetic industry’s constant progress in identifying active ingredients that require stabilization and targeted delivery, the future of ever improving products seems assured.

Steve Herman is the technical sales director for J&E Sozio. He has been an adjunct professor in the Fairleigh Dickinson University Masters in Cosmetic Science program since 1993, teaching Cosmetic Formulation Lab and Perfumery. His book, Fragrance Applications: A Survival Guide, was published by Allured Publishing Corp., Carol Stream, IL, in 2001. He has served as chairman of the SCC’s New York chapter, and was elected to fellow status in 2002.

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