Recent IP Advances in Polymers For Skin Treatments

The skin is the largest organ in the body. It is a complex organ with an active metabolism and simultaneously functions as the body’s protective barrier against loss of moisture, the intrusion of environmental toxins and harmful electromagnetic radiation. The skin undergoes natural, or intrinsic, aging that leads to fine lines and wrinkling which are prominent signs of senescence. In aged skin, intercellular substances are degraded and the skin’s ability to retard moisture loss is impaired.

Alternatively, extrinsic aging of the skin occurs due to repeated exposure to UV light and environmental pollutants such as cigarette smoke. Actinic aging, due to UV exposure, manifests itself as pronounced and obvious wrinkling. Such deep wrinkling is due to the loss of elasticity of the skin as a consequence of the destruction of elastic fibers in the reticular dermis.

Hyaluronic acid is a high molecular weight polysaccharide that exists naturally within the dermis and contributes to the hydration and elasticity of the skin. Hyaluronic acid has been included in skin treatment compositions for several decades.However, hyaluronic acid, whether injected or topically applied, is rapidly degraded. Consequently, a method for treating skin defects, including wrinkles, embraces creams that contain both hyaluronic acid and an inhibitor of hyaluronic acid degradation.1The preferred inhibitor is glycyrrhetinic acid.

Topically applied high molecular weight hyaluronic acid (500,000 to 3 million Daltons) forms films on the skin that act as barriers against moisture loss. Low molecular weight hyaluronic acid (500 to 50,000 Daltons), on the other hand, is claimed to permeate and moisturize the skin. In this context, topical compositions containing high and low molecular weight hyaluronic acids in combination with anti-inflammatory polysaccharides extracted from elm root bark are claimed to have anti-aging effects on the skin.2

Biodegradable hyaluronic acid combined with amphipathic prepolymers has been disclosed for the purpose of preparing polymeric micelles that can be used for the delivery of topical pharmaceuticals.3


Mitigating Irritation And Inflammation
Estée Lauder researchers have taken a more fundamental look at the causes of skin irritation and its mitigation.4The conventional way of treating skin irritation or inflammation is to apply topical products that contain ingredients that are believed to have anti-irritant or anti-inflammatory properties.

However, there are many biologically reactive pathways that lead to these adverse skin conditions and these ingredients often do not address all of the pathways. The Lauder researchers list the pathways that contribute to skin inflammation as the Adhesion Pathway, the Chemotaxis Pathway, the Collagenase Pathway, the COX Pathway, the Elastase Pathway, the Histamine Pathway, the Histamine Receptor Pathway, the LO Pathway, the PDE Pathway, the PLA-2 Pathway and the VEGF Pathway, and they select ingredients that inhibit each pathway to be included in a composition for normalizing skin.

Skin cleansing usually involves detergents. However, detergents have a tendency to cause skin irritation. There is a need to mitigate the effects of these known irritants. Johnson & Johnson and Lubrizol researchers have taken this approach and they have disclosed that certain non-crosslinked linear acrylic copolymers can lower the irritation potential of surfactants and provide products that are both clear and highly foaming.5The preferred polymers interact with the surfactant and effectively shift the critical micelle concentration (CMC) to higher concentrations, while lowering the critical aggregation concentration; the latter being the concentration at which the surfactant selectively interacts with the polymer rather than adsorbing at the liquid surface (Figure 1).

Delta CMC is defined, in U.S. Patent Application 20100311628, as the difference between the measured CMC for the surfactant + polymer and the surfactant composition alone.

These applicants propose that free surfactant molecules and free surfactant micelles are responsible for irritation of skin and eyes and that binding of the surfactant to the polymer effectively reduces the concentration of free micelles. They measure the difference between the CMC of the surfactant alone and the higher concentration of the surfactant in the presence of polymer; and create a parameter that they call (delta CMC) (Figure 1).Larger values of delta CMC for a particular surfactant are apparently correlated with lowering of the irritation potential. The delta CMC provides a measure that is useful for selecting, comparing and optimizing polymers that reduce the irritation potential of selected surfactant systems. Carbopol Aqua SF-1 was identified as a polymer that exhibited a satisfactory “delta CMC.”

Cationic Complexes
Cationic actives such as hexamidine compounds, cetylpyridinium chloride and amino acids have been advanced as compounds that improve or regulate the luminosity or “glow” of the skin, reduce the appearance of wrinkles and coarse deep lines, fine lines, crevices, bumps and large pores; thicken keratinous tissue; and prevent loss of elasticity, sagging and skin color changes.6

However, it is common practice to include these cationic actives in emulsion forms and the most convenient stabilizers for emulsions are anionic thickeners. Unfortunately, anionic thickeners form ionic complexes with these cationic actives. When such emulsions are applied to skin, the complexes tend to peel off and form undesirable prills on the skin surface. The complexes also bind most of the cationic active and prevent its delivery into the skin. These adverse effects have been addressed by including an anionic pairing agent that competes
selectively to bind the active, making it more hydrophobic to foster its portioning into the oil phase of the emulsion. Once in the oil phase, the cationic is less available to the anionic thickeners that reside essentially in the aqueous phase.

Moreover, when the emulsion is applied to the skin, the ion-pairing agent can release the cationic active and allow it to interact with the skin to improve its appearance and to regulate imperfections. Claimed anionic pairing agents are oleic acid, stearic acid, propionic acid, hexanoic acid, benzoic acid, octadecenedioic acid, retinoic acid, salicylic acid, glycyrrhetinic acid or undecylenoyl phenylalanine neutralized with the bases triethylamine, triethanolamine, sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide or magnesium hydroxide.7

The “gunk” produced by the complexation of polycations and anionic surfactants is also mentioned in U.S. Patent 7,868,208.8 The inventors claim to have overcome the problem by using highly crosslinked cationic or amphoteric polymers formed from di-tertiary amines that are “soft bases” and that contain alkyl groups to confer hydrophobicity. When these polymers are mixed with anionic surfactants, a hazy dispersion is formed which disperses upon further mixing. These compounds are disclosed as being highly substantive to skin and hair, but their high molecular weight mitigates against skin penetration. They are useful for “rinse-off” applications.

Multi-Component Complexes
Skin hygiene traditionally involves the use of soap and water, and thorough cleansing with abrasive soaps entails exfoliation of the skin surface. The inclusion of fibers, filaments and/or particles having core-sheath structures provided improved products for exfoliating while cleansing the skin.9 However, these dispersed elements tended to trap hair and debris with continued use and this gave the product an unsanitary appearance. This problem has been tackled by introducing discrete elements constructed from a water-soluble core and an erodible shell10such as a core of poly(ethylene oxide) and a shell of stearyl alcohol. As these discrete elements are exposed at the surface of a soap bar, the erodible shells are abraded or dissolved and the water-soluble cores readily detach from the surface.
Controlled release of actives, such as ascorbic acid, to the skin may be accomplished by including the active in a multicomponent layer that partially coats a pigment, such as titanium dioxide. Estée Lauder researchers have surprisingly discovered that incomplete coverage of a pigment particle by a hydrophilic coating and a hydrophobic deposit and finish can individually tailor the release of actives to the needs of the skin of the user by the action of the stratum corneum proteases.11

Hydrophobic actives are contained within the hydrophobic deposit and hydrophilic actives are included in the hydrophilic coating. The claimed hydrophobic deposit is dimethicone. The claimed hydrophobic finish is trimethysiloxysilicate and the claimed hydrophilic deposit is selected from water, glycols, glycerin, water-based gums, carbomer/water-based gels, acrylates copolymers, quaternary amine compounds, and/or carbohydrates.

The appearance of wrinkles can be mitigated by mechanical means that depend upon the formation of a tensioning film on the skin to temporarily overcome the sagging of the wrinkled skin underneath. Shiseido researchers have reported that this effect can be achieved by application of a film-forming anionic or amphoteric polyurethane12or by the application of an interpolymer of a polyurethane and a polvinylpyrrolidone/silicone copolymer.13The interpolymer is the material having the INCI name PVP/dimethiconylacrylate/ polycarbamyl and it is exemplified as Pecogel HS-501.

Polymers can be incorporated into skin care formulas to reduce the appearance of wrinkles.

Playing Tricks with Light
Cosmetic artists have long used concealing makeups to hide wrinkles and skin defects, but these products are opacifiers that give the wearer a matte “made-up” look. In recent years there has been a move to foundations that “play tricks” with light to conceal skin blemishes. These products give a more natural look. In this vein, compositions containing a number of distinct particulates have been advanced for the purpose of filling and hiding fine lines and wrinkles.14 The particulates are chosen to have complementary size ranges and this is forwarded as a reason for them to pack closely within facial lines.

The particulates may be chosen from a Markush list of polyethylenes, polymethylsilsesquioxanes, siloxanes, polyamides, polyolefins, polystyrenes, polytetrafluoroethylenes, polyurethanes, polymethacrylates, starch and starch derivatives and composite particles. The first particulate is claimed to be polyethylene having a median particle size from 10 microns to approximately 30 microns. The second particulate is claimed to be starch with a median particle size from 0.5 to 15 microns. The third particulate is claimed to be polymethylsilsesquioxane with a median particle size from 0.5 to approximately 15 microns. The fourth particulate is claimed to be a polyamide with a median particle size from 3 to 20 microns. These particles are delivered in silicone-in-water emulsions which are disclosed to provide a desirable feel to encourage frequent usage, especially to provide chronic or long-term benefit. Silicone elastomers provide the silky, non-greasy feel. The silicone-in-water emulsions are preferred in this case over water-in-silicone emulsions in order to overcome stability problems and processing complexities.

Summary
Recent trends in the use of polymers for the treatment of aged or damaged skin include:

1. Topically applied hyaluronic acid is inhibited against degradation to treat skin wrinkles. Bimodal molecular weight distributions of hyaluronic acid can also be applied to skin; the high molecular weight fraction forms a film on the skin surface and the low molecular weight fraction permeates the skin to mitigate the appearance of wrinkles. This treatment is enhanced by the inclusion of elm root bark as an anti-inflammatory.

2. There are a large number of possible pathways that lead to skin irritation and inflammation. A fundamental approach is to include known actives for each and every one of these pathways in a single treatments composition.

3. Detergent–induced skin irritation can be mitigated by the addition of polymers that effectively raise the CMC of the surfactant composition.

4. Cationic actives can provide beneficial effects on skin, but these actives complex with anionic rheology modifiers to form prills that limit delivery of the active to the skin surface. The cationics can be delivered to the surface from anionic polyelectrolyte-stabilized emulsions if they are paired with a suitable anionic pairing agent that favors partitioning into the oil phase of the emulsion but also favors dissociation of the complex once it reaches the surface of skin. Compatibility with anionic surfactants can also be achieved from crosslinked cationic systems if the cation is a “soft” base.

5. Composite fibers having a water-swellable core and a hydrophobic sheath are useful as exfoliating agents when incorporated into cleansing bars. Pigments that are incompletely coated with hydrophilic layer and hydrophobic finishes can be tailored to controllably release beneficial agents to the skin when activated by stratum corneum proteases.

6. Interpolymers can be used to tension the skin to “smooth” wrinkles. Alternatively, multi-modal particles can be packed into the wrinkles to refract and diffuse light and, therefore, to screen the wrinkles.


References
1. Moutet, Marc; Yadan, Jean-Claude; “Pharmaceutical or cosmetic preparations for topical and/or parenteral application, preparation methods thereof and use of same;” US Patent Application 20100323985, Dec. 23, 2010.
2. Kim, Ki Ho; Kim, Ki Soo; Kim, Young Heui; Kim, Jin Guk; Kim, Kyoung Tae; Han, Chang Sung; Ko, Kang Il; “Anti-aging composition for external use comprising low and high molecular weight hyaluronic acids and the polysaccharides extracted from root bark of Ulmus Davidiana;” U.S. Patent Application 20110003769, Jan. 6, 2011, assigned to Bioland Ltd.
3. Chen, Jui-Hsiang; Tsai, Bin-Hong; Chang, Hsuen-Tseng; Chen, Muh-Lan;Chen, Yu-Hua; Jan, Shu-Hua; Liu, Mei-Jung; “Biodegradable Hyaluronic Acid Derivative, Biodegradable Polymeric Micelle Composition and Pharmaceutical or Bioactive Composition;” US Patent Application 20100316682; Dec. 16, 2010; Assigned to Industrial Technology Institute.
4. Collins, Donald F.;Maes, Daniel H.;Muizzuddin, Neelam; “Methods and compositions for treating skin,” US Patent Application 20100323042; Dec. 23, 2010,TheEstee Lauder Cos.
5. Librizzi; Joseph J.; Walters; Russel M.; Fevola; Michael; Tamareselvy; Krishnan, “Low-irritation compositions and methods of making the same,” US Patent Application 20100311628, Dec. 9, 2010, Johnson & Johnson.
6. Robinson, Larry Rich; Kelm, Gary Robert; Faulk, Denver Michael, “Personal-care composition comprising a cationic active;” US Patent Application 20100305169,ec. 2, 2010, The Procter & Gamble (P&G) Company.
7. Robinson, Larry Rich; Kelm, Gary Robert; Faulk, Denver Michael, “Personal-care composition comprising a cationic active,” US Patent Application 20100305168,Dec. 2, 2010, The P&G Company.
8. O’Lenick, Kevin A.; O’Lenick, Thomas, G.; O’Lenick, Anthony, J.; “Polyquaternary alkyl polymers;” US Patent 7,686,208; Jan. 11, 2011, assigned to Surfatech Corporation.
9. Aleles, Margaret; Burwell, David; Ip, Raymond, “Cleansing bar containing discrete elements;” US Patent 6,818,603. Nov. 16, 2004; Assigned to Johnson & Johnson Consumer Companies, Inc.
10. Eknoian, Michael W.; Brennan Jr., Robert A., Ip, Raymond, Poccia III, John F.; “Cosmetic device comprising discrete elements,” US Patent 7,901,696, March 8, 2011, Assigned to J&J Consumer Companies Inc.
11. Friel, Francis Martin; Lee, Wilson An-Tuen; Shidara, Aya; Mercado, Clara G.; Leaver; Eric John; “Discontinuous Surface coating for particles,” US Patent Application 2011001298, Jan. 20, 2011, The Estée Lauder Companies Inc.
12. Omura, Takayuki; Yokoo, Mihoshi; “Skin cosmetic.” U.S. Patent Application 20110002873; Jan. 6, 2011; assigned to Shiseido Company Ltd.
13. Brault, Delphine;Quevauviller, Florence; Frick; Regine; “Cosmetic method for smoothing wrinkles and fine lines;” US Patent Application 20110014150; Jan. 20, 2011, Chanel Parfums Beaute.
14. Griffiths-Brophy, Susan Adair; Elsbrock, Robert John; “Personal Care Composition,” US Patent Application 20100322983, Dec. 23, 2010, The P&G Company.