Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2000-08-11
2003-01-28
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C424S401000
Reexamination Certificate
active
06511655
ABSTRACT:
The present invention relates to cosmetic and dermatological preparations of the oil-in-water type, in particular sprayable O/W emulsions, which have a viscosity of less than 2000 mPa·s, and to a method of stabilizing O/W formulations by matching the density of the phases.
Cosmetic preparations are essentially used for skincare. The human skin is man's largest organ and performs numerous vital functions. Having an average area of about 2 m
2
in adults, it has a prominent role as a protective and sensory organ. Amongst its many functions (for example for heat regulation), the barrier function, which prevents the skin (and therefore ultimately the entire organism) from drying out, is by far the most important. At the same time, the skin acts as a protective device against the invasion and the absorption of external substances (e.g. dirt, chemicals, microorganisms). In addition, it has an important role as a regulatory and target organ in human metabolism.
The main aim of cosmetic skincare is to strengthen or rebuild the skin's natural function as a barrier against environmental influences and against the loss of endogenous substances (as well as water, also natural fats, electrolytes etc.).
Another aim of skincare is to compensate for the loss by the skin of lipids and water caused by daily washing. This is particularly important if the natural regeneration ability is inadequate. Furthermore, skincare products should protect against environmental influences, in particular against sun and wind, and delay skin ageing.
The harmful effect of the ultraviolet part of solar radiation on the skin is generally known. Depending on their respective wavelength, the rays have different effects on the skin organ: UV-C radiation having a wavelength of less than 290 nm is absorbed by the ozone layer in the earth's atmosphere and is of no physiological importance. By contrast, rays in the range between 290 nm and 320 nm, the UV-B region, cause erythema, simple sunburn or even burns of varying severity. UV-A radiation (320 to 400 nm) is much more harmful than UV-B radiation with regard to the triggering of photodynamic, specifically phototoxic, reactions and chronic changes in the skin. For example, UV-A radiation on its own under very normal everyday conditions is enough to damage collagen and elastin fibres within a short period. The harmful effect of UV-B radiation can also be further intensified by UV-A radiation.
In addition, even very low radiation dosages can trigger photochemical reactions. These include, in particular, the formation of free radicals, which in turn can trigger uncontrolled secondary reactions as a result of their high reactivity. In order to prevent such reactions, as well as UV filter substances, it is also possible to additionally add antioxidants and/or free-radical scavengers to cosmetic or dermatological formulations.
Medicinal topical compositions usually comprise one or more medicaments in an effective concentration. For the sake of simplicity, in order to clearly distinguish between cosmetic and medicinal use and corresponding products, reference is made to the legal provisions of the Federal Republic of Germany (e.g. Cosmetics Directive, Foods and Drugs Act).
By far the most important type of product in the field of skincare compositions are emulsions. Emulsions are disperse two- or multi-phase systems, cosmetic emulsions consisting of at least one fatty phase (fats and mineral oils, fatty acid esters, fatty alcohols etc.) and at least one water phase (water, glycerol, glycols etc.), which are distributed in the form of very fine droplets in one another using emulsifiers. If the oil phase is finely distributed in the water phase, then this is an oil-in-water emulsion (O/W emulsion, e.g. milk). The basic character of an O/W emulsion is determined by the water, i.e. is less greasy on the skin, is rather matting and absorbs more rapidly into the skin than a W/O emulsion.
Although, when viewed from a thermodynamic viewpoint, emulsions are unstable systems, it is possible to prepare cosmetic emulsions which are stable for years.
An emulsion is described as stable if, over a pregiven period of time, no measurable temporal or spatial changes in the droplet size distribution can be established.
The stability or instability of emulsions depends on a variety of factors. Firstly, the water phase of a W/O emulsion tends, for example, towards sedimentation since the water and oil phases have different densities. The oil phase of an O/W emulsion, accordingly, has a tendency towards creaming.
In addition, because of the forces of attraction between the finely distributed droplets of the disperse phase, drop aggregation can result, where the individual droplets of an aggregate remain initially separate from one another by a thin film of the continuous phase. In this case, the original droplet size distribution only seemingly changes and can in this case be restored by stirring or shaking.
However, the droplets which are in contact can, moreover, also coalesce, which leads to a real change in the droplet size distribution, which can only be changed back by inputting energy. This phenomenon is referred to as coalescence. The more viscous the outer phase of the emulsion, the more slowly the process of coalescence proceeds.
The processes described can occur individually or together. One process often initiates or intensifies the other. Thus, for example, the formation of aggregates in O/W emulsions accelerates creaming of the oil phase. If the disperse state of an emulsion is partially or completely lost, then the two phases separate, and this is referred to as emulsion breaking.
Accordingly, the stabilization of emulsions over a relatively long period of time requires auxiliaries which prevent separation of the two phases, or at least delay it until the emulsion has fulfilled its intended purpose.
These auxiliaries should firstly stabilize the interface by preventing the droplets of the disperse phase from coalescing. In the ideal case, these substances moreover effect repulsion of the droplets, which prevents them from contacting, thus avoiding agglomeration (aggregate formation).
Secondly, auxiliaries are used to counteract creaming or sedimentation of the phases.
Emulsifiers are interface-active substances which are able to prevent the interfacial tension between oil and water phase by positioning themselves preferably at the interface between these two phases. This is made possible as a result of their amphiphilic molecular structure: emulsifiers have at least one polar (hydrophilic) group and at least one nonpolar (lipophilic) group. As a result, they are soluble both in the hydrophilic phase and in the lipophilic phase. The part which is more soluble in the corresponding phase protrudes into this phase and as a result lowers the interfacial tension between the two phases.
The attempt to classify emulsifiers is difficult since they belong to categories which are very different in chemical terms. The more quickly an emulsifier lowers the interfacial tension and the lower the equilibrium value of the interfacial tension, the more effective the emulsifier.
Moreover, emulsifiers also stabilize as a result of the formation of interfacial films and thus “physical” barriers, as a result of which aggregate formation and coalescence of the emulsified particles is prevented. As a result of the positioning of the emulsifier at the interface, the droplets either become charged, so that they mutually repel, or a stable, often high-viscosity or even solid protective layer is formed around the droplets.
However, for the practical preparation of cosmetic or dermatological emulsions, the use of one or more emulsifiers on their own is generally insufficient. Important factors for the stability of cosmetic or dermatological preparations are also:
very fine distribution of the two phases in one another the smaller the dispersed particles, the more stable the emulsion.
high viscosity of the outer phase
a stable interfacial film
a balanced phase volume ratio
The emulsifier system m
Gers-Barlag Heinrich
Müller Anja
Beiersdorf AG
Dees Jose′ G.
DeWitty Robert
Norris & McLaughlin & Marcus
LandOfFree
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