Cosmetic or dermatological gels based on microemulsions

Details Cosmetic or dermatological gels based on microemulsions Cosmetic or dermatological gels based on microemulsions

1999-06-18

2003-12-23

Dodson, Shelley A. (Department: 1616)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Cosmetic, antiperspirant, dentifrice

C424S078030, C424S484000, C424S486000, C514S937000, C514S938000, C514S941000, C514S943000, C514S944000

Reexamination Certificate

active

06667044

ABSTRACT:

This application is a 371 application of PCT/EP 97/05418 (WO 98/15254), which was filed on Oct. 2, 1997.
The present invention relates to cosmetic or dermatological gels based on microemulsions, in particular such gels for cosmetic and dermatological formulations. As a particular embodiment, the present invention relates to cosmetic or dermatological gels based on microemulsions of the water-in-oil type, processes for their preparation and their use for cosmetic and medical purposes.
Cosmetic skin care is primarily to be understood as meaning that the natural function of the skin as a barrier against environmental influences (for example dirt, chemicals and microorganisms) and against the loss of endogenous substances (for example water, natural fats and electrolytes) is intensified or re-established.
If this function is impaired, increased absorption of toxic or allergenic substances or attack by microorganisms and as a consequence toxic or allergic skin reactions may occur.
The aim of skin care is furthermore to compensate the loss of fats and water from the skin caused by daily washing. This is important particularly if the natural capacity for regeneration is not adequate. Skin-care products should furthermore protect against environmental influences, in particular against the sun and wind, and delay ageing of the skin.
Medical topical compositions as a rule comprise one or more medicaments in an active concentration. For simplicity, reference is made to the legal provisions of the Federal Republic of Germany (for example cosmetics legislation, legislation on foodstuffs and medicaments) for a clear distinction between cosmetic and medical use and corresponding products.
Gels are customary cosmetic and dermatological formulation forms which have become more and more wide-spread particularly in recent times.
In the technical sense, gels are understood as meaning: relatively dimensionally stable, easily deformable disperse systems of at least two components, which as a rule comprise a—usually solid—colloidally divided substance of long-chain molecular grouping (for example gelatin, silicic acid or polysaccharides) as the matrix-forming phase and a liquid dispersant (for example water). The colloidally; divided substance is often called a thickener or gelling agent. It forms a three-dimensional network in the dispersant, it being possible for individual particles present in colloidal form to be linked to one another more or less firmly via electro-static interaction. The dispersant, which surrounds the network, is distinguished by electrostatic affinity for the gelling agent, i.e. a predominantly polar (in particular: hydrophilic) gelling agent preferably gels a polar dispersant (in particular: water), whereas a predominantly non-polar gelling agent preferably gels non-polar dispersants.
Strong electrostatic interactions, which are realized, for example, in hydrogen bridge bonds between the gelling agent and dispersant, but also between dispersant molecules with one another, can lead to a high degree of crosslinking of the dispersant as well. Hydro-gels can comprise water to the extent of almost 100% (alongside, for example, about 0.2-1.0% of a gelling agent), and at the same time have an entirely solid consistency. The water content is present here in ice-like structural elements, so that gels entirely justify the origin of their name [from lat. “gelatum”=“frozen” by the alchemistic term “gelatina” (16th century) for the modern term “gelatin”].
Lipogels and oleogels (of waxes, fats and fatty oils) as well as carbogels (from paraffin or petrolatum) are furthermore also customary in cosmetic and pharma-ceutical galenics. In practice, a distinction is made between oleogels, which are in practically anhydrous form, hydrogels, which are practically fat-free, and oil/water gels which are ultimately based on O/W or W/O emulsions but in which features of a gel structure are additionally also realized. Gels are usually transparent. In cosmetic and pharmaceutical galenics, gels are as a general rule distinguished by a semi-solid, often free-flowing consistency.
In simple emulsions, in the one phase, finely dispersed droplets of the second phase (water droplets in W/O or lipid vesicles in O/W emulsions) enclosed by an emulsifier shell are present. The droplet diameters of the usual emulsions are in the range from about 1 &mgr;m to about 50 &mgr;m. Without further colouring additives, such “macroemulsions” are milky white in colour and opaque. Finer “macroemulsions”, the droplet diameters of which are in the range from about 10
−1
&mgr;m to about 1 &mgr;m, again without colouring additives, are bluish-white in colour and non-transparent.
It is the property of micellar and molecular solutions having particle diameters of less than about 10
−2
&mgr;m to appear clear and transparent.
The droplet diameter of transparent or translucent microemulsions, on the other hand, is in the range from about 10
−2
&mgr;m to about 10
−1
&mgr;m. Such microemulsions usually have a low viscosity.
So-called surfactant gels are furthermore customary formulations of the prior art. These are ,understood as being systems which, in addition to water, have a high concentration of emulsifiers, typically more than about 25% by weight, based on the total composition. If oil components are solubilized in these surfactant gels, which is their technical name, microemulsion gels, which are also called “ringing gels” are obtained. Cosmetically more elegant microemulsion gels can be obtained by addition of nonionic emulsifiers, for example alkyl polyglycosides. Here also, the high content of emulsifiers is a disadvantage.
An advantage of microemulsion gels is that active compounds can be present in finely disperse form in the disperse phase. Another advantage is that, because of their low viscosity, they can be sprayed. When micro-emulsions are used as cosmetics, corresponding products are distinguished by a high cosmetic elegance.
It is known per se to link the droplets of a low-viscosity, in particular thinly liquid microemulsion with crosslinking substances with one another, in order to obtain the three-dimensional network of a gel in this manner.
Chain-like, hydrophilic molecules which contain a hydrophobic radical on each of the two chain ends are described in Nachr. Chem. Techn. Lab. 43 (1995) No. 1, page 9 et seq for crosslinking microemulsion droplets. Those hydrophobic radicals are immersed in the micro-emulsion droplets, the hydrophilic chain regions being in the continuous aqueous phase. In the strict sense, it is certainly not necessary for the hydrophobic radicals to be “immersed”. In individual cases, it can also be entirely sufficient if the hydrophobic radicals come into contact with the surface of the microemulsion droplets by hydrophobic interaction and remain stuck to these more or less firmly.
Crosslinkers which are mentioned in the above reference are polyoxyethylene glycols with oleyl groups as hydrophobic end groups.
A disadvantage of microemulsions, and therefore also of the microemulsion gels of the prior art, is that a high content of one or more emulsifiers must always be employed, since the low droplet size results in a high interface between the phases, which as a rule must be stabilized by emulsifiers.
The use of the customary cosmetic emulsifiers is indeed acceptable per se. Nevertheless, emulsifiers, like any chemical substance in the end, can cause allergic reactions or reactions based on hypersensitivity of the user in an individual case.
It is thus known that particular photodermatoses are induced by certain emulsifiers, and also by various fats, and simultaneously exposure to sunlight. Such photodermatoses are also called “Majorca acne”. An object of the present invention was therefore to develop sun-screen products.
As particular embodiments, the present invention thus relates to cosmetic and dermatological light protection formulations, in particular skin-care cosmetic and dermatological light protection formulations.
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