Method for preparing particles comprising metal oxide coating and particles with metal oxide coating

Abstract

The invention relates to a process for coating a solid, water-insoluble particulate matter, with a metal oxide comprising: (a) contacting the solid, water-insoluble particulate matter with an ionic additive and an aqueous medium to obtain a dispersion of said particulate matter having positive charges on its surface; (b) subjecting the particulate matter to a coating procedure comprising precipitating a metal oxide salt onto the surface of the particulate matter to form a metal oxide layer thereon to thereby obtain particulate matter coated by a metal oxide coating layer; (c) repeating step (b) at least 4 more times; and (d) aging said coating layer. The invention further relates to particles comprising a particulate matter coated by a metal oxide layer, to a use of the particles for topical administration, and to a method for preventing, reducing, or eliminating pests at a locus, using the particles.

What is claimed is: 
     
         1 . A method for treating a surface condition in a subject, comprising topically administering onto the surface a composition comprising an effective amount of dispersed particles comprising solid benzoyl peroxide particulate matter encapsulated by a metal oxide coating, wherein the metal oxide coating comprises four or more layers, wherein the outermost portion of the metal oxide coating being substantially free of benzoyl peroxide; wherein,
 (i) the coated particles having leaching of less than 5% w/w, of the benzoyl peroxide in the composition until administered to the skin;   (ii) the coated particles release an effective amount of benzoyl peroxide when the composition is in contact with the surface;   (iii) the time for releasing 50% w/w of the benzoyl peroxide being at least two-fold longer when in coated form than the time to dissolution of benzoyl peroxide particles of the same particle size diameter when in free form under identical conditions.   
     
     
         2 . The method of  claim 1 , wherein said surface is skin or mucosal membrane. 
     
     
         3 . The method of  claim 1 , wherein said surface condition is a disease or disorder selected from the group consisting of acne, infection, inflammation, pruritus, psoriasis, seborrhea, contact dermatitis, rosacea, and a combination thereof. 
     
     
         4 . The method of  claim 1 , wherein said metal oxide is selected from Silica, Titania, Alumina, Zirconia, ZnO, and mixtures thereof. 
     
     
         5 . The method of  claim 4 , wherein the metal oxide is silica. 
     
     
         6 . The method of  claim 1 , wherein the weight ratio of the metal oxide to said particulate matter is in the range of 1:99 to 40:60. 
     
     
         7 . The method of  claim 1 , wherein the four or more layers of said metal oxide has a thickness of 0.1-10 micron. 
     
     
         8 . The method of  claim 1 , wherein the metal oxide coating comprises between 4 to 1000 layers, more preferably 4 to 300 layers, more preferably 4 to 100 layers. 
     
     
         9 . The method of  claim 1 , wherein the solid benzoyl peroxide particles encapsulated by a metal oxide coating have a diameter of between 0.5-100 micron. 
     
     
         10 . Particles comprising solid benzoyl peroxide particulate matter encapsulated by a metal oxide coating, wherein the metal oxide coating comprises four or more layers; wherein
 the outermost portion of the metal oxide coating being substantially free of benzoyl peroxide   the coated particles having teaching of less than 5% w/w, of the benzoyl peroxide in the composition until administered to the skin;   the coated particles release an effective amount of benzoyl peroxide when the composition is in contact with the surface; and   the time for releasing 50% w/w of the benzoyl peroxide being at least two-fold longer when in coated form than the time to dissolution of benzoyl peroxide particles of the same particle size diameter when in free form under identical conditions.   
     
     
         11 . The particles of  claim 10 , wherein said metal oxide coating has a thickness of 0.1-10 micron. 
     
     
         12 . Particles comprising solid benzoyl peroxide particulate matter encapsulated by a metal oxide coating, wherein the metal oxide coating comprises four or more layers, wherein the outermost portion of the metal oxide coating being substantially free of benzoyl peroxide; wherein the particles are prepared by the following steps:
 a) contacting in a medium consisting of an aqueous medium, the solid benzoyl peroxide particulate matter, with a first cationic additive being a cationic surfactant, to obtain a dispersion of said benzoyl peroxide particulate matter in said aqueous medium, said benzoyl peroxide particulate matter having positive charges on its surface;   b) adding an aqueous solution of a metal oxide salt to said dispersion of said benzoyl peroxide particulate matter, under conditions wherein said metal oxide salt precipitates onto the surface of said benzoyl peroxide particulate matter, and acidifying to thereby form a solid, water-insoluble benzoyl peroxide particulate matter that has a metal oxide layer coated thereon;
 b1) contacting, in a medium consisting of an aqueous medium, said benzoyl peroxide particulate matter coated with a metal oxide layer of the preceding step with a surface adhering additive being one or both of (i) a second cationic additive being a cationic polymer and (ii) a non-ionic additive, to obtain a dispersion of said coated benzoyl peroxide particulate matter having an adhering additive on the surface thereof in said aqueous medium; 
 b2) bringing the dispersion obtained in step (b1) into contact with an aqueous solution of a metal oxide salt, under conditions wherein said metal oxide salt precipitates onto the surface of said coated benzoyl peroxide particulate matter, and acidifying to thereby form a solid, water-insoluble benzoyl peroxide particulate matter that has a further metal oxide layer coated thereon; 
   c) repeating steps (b1) and (b2) at least 3 more times; and   d) after completion of step (c), aging the metal oxide layer to form an aged, coated, solid, water-insoluble benzoyl peroxide particulate matter having a coating thickness in the range of 0.1-10 micron.