Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Patent
1991-05-30
1998-10-06
Dodson, Shelley A.
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
424 60, 424400, 424401, A61K 742, A61K 700
Patent
active
058172980
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to coated titanium dioxide particles for use in sunscreen compositions. The term "sunscreen" is used herein to encompass tanning lotions, sunscreens and sunblockers which are intended for topical application to provide protection against the sun's rays or other sources of ultraviolet (UV) radiation.
Conventional sunscreen compositions have been prepared either as oil-in-water or water-in-oil emulsions containing organic sunscreen agents which could be formulated equally successfully in either of the above emulsion systems. More recently sunscreen compositions have been proposed which contain, as the sunscreening agent, titanium dioxide.
Titanium dioxide particles have a tendency to agglomerate and this effect reduces their efficacy as UV screening agents and increases their whiteness on the skin (opacity). Agglomeration also results in the breakdown of emulsions containing such particles and adversely affects their stability during prolonged storage. It is known to coat titanium dioxide particles with compounds such as aluminium stearate and aluminium oxide in order to minimise light-induced reduction and to increase the hydrophobicity of the particles, thereby aiding their dispersion. However, even stearate-coated titanium dioxide particles do not disperse entirely effectively in lipophilic phases such as silicone but tend to form clumps, presumably as a result of interaction between the stearate chains of adjacent particles. The present invention stems from the applicants discovery that coating titanium dioxide particles with phospholipid reduces their tendency to clump and enables the particles to be more effectively dispersed.
The present invention provides titanium dioxide particles having a mean primary particle size of less than 100 nm, each of said particles being substantially coated with phospholipid. It will be understood that the phrases "titanium dioxide particles substantially coated with phospholipid" and "phospholipid-coated titanium dioxide" as used herein describe particles of titanium dioxide to which a substantial number of phospholipid molecules are bonded. The bonding of phospholipid molecules to titanium dioxide particles may occur during an initial coating procedure or may arise spontaneously in situ within the oil phase of a sunscreen composition in which both titanium dioxide and phospholipid are present.
Phospholipids of use in the present invention may be naturally occurring or synthetic phospholipids or mixtures thereof., Naturally occurring phospholipids include, for example, phosphatidyl cholines, phosphatidyl ethanolamines, phosphatidyl serines, phosphatidyl inositols, diphosphatidyl glycerols and sphingomyelins. These natural phospholipids may be prepared from, for example, mammalian brain or liver tissue, egg yolk, soybean or bacterial cell membranes. Numerous synthetic phospholipids are also commercially available and may, for example, be derived from naturally occurring oils such as rapeseed oil which have been partly or fully hydrogenated, selectively esterified to a glycerol backbone and phosphorylated to form specific phosphatidates or mixtures thereof. Other synthetic phospholipids may be derived from naturally occurring phospholipids which have been modified, for example by hydroxylation or ethoxylation.
Phospholipids carry one or two, more usually two C.sub.8-32 alkyl groups bound to a polar phosphorylated alcohol headgroup. The alkyl groups may be straight or branched chain, saturated or unsaturated, and may be optionally substituted, for example, by one or more hydroxyl groups. Preferably the phospholipids of use in the present invention carry two C.sub.8-32 alkyl groups, more particularly C.sub.12-24 alkyl groups. Most preferred phospholipids are phosphatidyl cholines, phosphatidyl ethanolamines, phosphatidyl serines and phosphatidyl inositols and mixtures thereof. A particularly suitable type of phospholipid for coating titanium dioxide particles according to the present invention is phosphatidyl choline. Mixtures of phosphatidyl c
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Elsom Nicola Anne
Galley Edward
Dodson Shelley A.
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