Microemulsions for Sprayable Delivery and Other Topics: Literature Findings

By: Charles Fox, Independent Consultant

Posted: March 30, 2010, from the April 2010 issue of Cosmetics & Toiletries.

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MO₂CQ(CH₂)₂(SiR₄R₅O)_p SiR₆R7(CH₂)₂QCOOM     Eq. 2

In Eq. 1, R1-3 = silyloxy groups, A = alkylene groups and M = metal or organic cations. In Eq. 2, R4-7 = hydrocarbyl groups, M = metal or organic cations and Q = alkylene groups. Adding trimethylsilyl undecylenate dropwise to 1,1,1,3,5,5,5-heptamethyltrisiloxane in the presence of a platinum catalyst produced an adduct useful for cleansing compositions.

Measuring antioxidative power: Graf et al. reviewed the antioxidative power of formulations over their lifetime and described unique actives superior to vitamins.¹⁴ The human skin is situated at the interface of the organism and its environment and is thus exposed to a variety of physical and chemical assaults. Exposure to ionizing, UV radiation or xenobiotics generates free radicals in excessive quantities that quickly overwhelm tissue antioxidants and stress-degrading pathways. There is an apparent need for providing the skin with potent antioxidants to prevent accelerated aging processes. Commonly used antioxidants vitamin C and its derivatives or vitamin E are effective but highly unstable during storage. Ideal anti-photoaging concepts should provide maximum efficacy paired with excellent stability and galenic elegance.

In the described study, cosmetic formulations containing different antioxidants were tested for their antioxidative power (AP) directly after processing and after different periods of time at different storage conditions. Vitamin-containing formulations show a dramatic decrease in AP, and some show undesirable discolorations. The company presented bis-ethylhexyl hydroxydimethoxy benzylmalonated as an antioxidant that did not show Galenic disadvantages such as yellowing of the formulation. The company also found it to remain stable without a loss in antioxidative activity and therefore recommends the antioxidant for antiaging products and sunscreens.

Microemulsions for sprayable delivery: Payne et al. disclosed the use of microemulsions as sprayable delivery systems.¹⁵ Many desired cosmetic ingredients such as organic sunscreens, vitamins, essential oils and ester emollients are not water-soluble. Commercial products that incorporate these materials are typically opaque emulsions. Microemulsion technology can therefore be utilized to create a clear to translucent water-based active delivery system without the use of ethanol or other short-chain alcohol, which can be drying to the skin. Additionally, using microemulsion technology in sprayable delivery systems allows for environmentally friendly manufacturing processes.