Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITIONS COMPRISING SOLID PARTICLES ENCAPSULATED IN A CROSS-
LINKED SILICONE MATRIX, AND METHODS OF MAKING THE SAME
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of Application No. US12/538,455
filed
August 10, 2009, which claims priority of provisional application
U561/093,882, filed
September 3, 2008.
FIELD OF THE INVENTION
The present invention relates to topical compositions comprising stabilized
particulate
components, as well as methods of making the same.
BACKGROUND OF THE INVENTION
Cosmetic or topical compositions typically comprise one or more particulate
components, such as, for example, pigments or dyes, fillers, thickeners,
sunscreen agents, and
the like. Such particulate components are often insoluble in the respective
solvent or carrier
system and remain dispersed or suspended in the cosmetic or topical
compositions.
However, whenever there are changes in the pH and temperature in the
surrounding
environment, the dispersed or suspended particles may agglomerate with one
another and
precipitate out of the composition. Furthermore, the smaller the particle
size, the larger the
active surface area, and the more susceptible such particulate components are
toward adverse
interactions or interference with other ingredients or components in the
cosmetic or topical
compositions, which may destabilize the cosmetic or topical compositions or
reduce the
overall performance thereof Additionally, particulate components that are less
than 40nm in
size can penetrate into the skin and lead to apoptosis.
There is therefore a continuing need for treating or modifying the particulate
components of cosmetic or topical compositions in order to eliminate or
mitigate the above-
described drawbacks and improve the overall stability of the compositions
without adversely
affecting the chemical and physical properties of the particulate components.
There is also a need for improving the chemical and/or physical properties of
the
particulate components through surface treatment or modification.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a topical composition
comprising a
dispersion of treated particles in a cosmetically or pharmaceutically
acceptable carrier,
wherein each of the treated particles comprises one or more core particles
encapsulated in a
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cross-linked silicone matrix, and wherein each of the treated particles
possesses an electrical
potential in the range of from about -40mV to about -80mV.
In another aspect, the present invention relates to a treated particle
comprising one or
more titanium dioxide or zinc oxide core particles encapsulated in a cross-
linked silicone
matrix, while the treated particle has a particle size ranging from about 1
micron to about 50
microns and possesses an electrical potential in the range of from about -40mV
to about -
80mV.
In a still further aspect, the present invention relates to a method for
forming treated
particles, comprising:
(a) coating one or more core particles having an average particle size ranging
from
about 0.001 micron to about 0.5 micron with an anionic copolymer selected
from the group consisting of acrylates copolymers and methyl vinyl ether and
maleic anhydride (PVM/MA) copolymers, wherein the anionic copolymer
possesses an electrical potential in the range of from about -10mV to about -
100mV;
(b) coating the coated particles of (a) with silicone;
(c) contacting the coated particles of (b) with a cross-linking agent,
wherein the
cross-linking agent comprises a stannous carboxylate capable of effectuating
cross-linking of the silicone coating, thereby forming a cross-linked
structure
with the core particles encapsulated therein; and
(d) reducing the cross-linked structure into treated particles having an
average
particle size ranging from about 1 micron to about 50 microns and possessing
an electrical potential ranging from about -40mV to about -80mV, wherein
each of the treated particles comprises one or more of said core particles
encapsulated in a cross-linked silicone matrix.
Other aspects and objectives of the present invention will become more
apparent from the ensuing description, examples, and claims.
BRIEF DESCRIPTION OF THE DRAWING
The lone figure is a microscope image of a treated particle formed by first
coating TiO2
core particles with silicone, then cross-linking the silicone coating to form
a cross-linked
structure, followed by milling/grinding of the cross-linked structure,
according to one
embodiment of the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
The present invention provides stabilized particulate components that are
useful in
cosmetic or topical compositions, as well as methods for stabilizing
particulate components.
Specifically, the treated particles, which are formed by encapsulating the
particulate
components in a cross-linked silicone matrix, are characterized by an average
particle size that
is at least 10 times, preferably 20 times, more preferably 50 times, and most
preferably 100
times, larger than the average particle size of the initial particulate
components. Each of the
treated particles comprises a cross-linked silicone matrix encapsulating
therein one or more
core particles. Preferably, the physical and/or chemical properties of the
entrapped core
particles pertaining to or associated with their desired activities in the
cosmetic or topical
compositions are not adversely affected, while the significantly larger
treated particles provide
improved structural and spatial stability.
The core particles useful for the present invention can be any particulate
components
that are commonly used in cosmetic or pharmaceutical compositions, which
include, but are
not limited to: mineral pigments and fillers such as, for example, talc,
kaolin, mica, bismuth
oxychloride, chromium hydroxide, barium sulfate, polymethylmethacrylates
(PMMA), boron
nitride, nylon beads, polymeric powders (e.g., BPD 500 powders comprised of
hexamethylene
diisocyanate/trimethylol hexyllactone crosspolymer and silica that is
commercially available
from Kobo Products, Inc. at South Plainfield, NJ), silica, silica beads, lakes
(e.g., aluminum or
calcium lake), metal oxides (e.g., black, yellow or blue iron oxide, chromium
oxide, zinc
oxide, and titanium dioxide), physical and chemical sunscreen agents, and any
other organic
and inorganic powders or particles. Preferably, but not necessarily, the core
particles are
comprised of a material capable of generating free oxygen radicals, and more
preferably a
metal oxide such as zinc oxide or titanium dioxide. The core particles can be
of any regular or
irregular shape, such as, for example, spherical, cubic, cylindrical, planar,
fibrous, laminar,
and the like.
The average particle size of the core particles as used in the present
invention is
preferably less than 1 micron, more preferably from about 0.001 micron to
about 0.5 micron,
and most preferably from about 0.01 to about 0.05 micron. A particularly
preferred example
of the core particles is a manganese modified titanium dioxide particle
commercially available
under the trade name of OptisolTM from Croda, Inc. at Edison, NJ. The core
particle
preferably constitutes about 10 to about 99 percent by weight of the treated
particle, and more
preferably, about 40 to 90 percent by weight of the treated particle.
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Encapsulation of the core particles can be readily achieved in the present
invention by
first coating the core particles with silicone, then contacting the coated
particles with a cross-
linking agent comprising a stannous carboxylate capable of effectuating cross-
linking of the
silicone coating so as to form a cross-linked structure with the core
particles encapsulated
therein, and followed by reducing the cross-linked structure into treated
particles of desired
size.
The silicone as used in the present invention is preferably a silicone with
branched
reactive moieties. The term "branched reactive moieties" as used herein refers
to side chain
moieties that are branching off the polymeric backbone of the hydrophobic
polymer and are
capable of forming chemical bonds (which include, but are not limited to: van
der Waals'
bonds, hydrogen bonds, covalent bonds, and ionic bonds) with the surface of
the core particle.
The branched reactive moieties of the hydrophobic polymer of the present
invention may
include, but are not limited to: amino moieties, imino moieties, halogen
moieties, hydroxyl
moieties, and alkoxyl moieties. While not wishing to be bound by any
particular theory, it is
believed that the polyorganosiloxane backbone of the silicone forms a
continuous coating over
the core particles, while the branched reactive moieties of the silicone
extend inwardly to the
surface of the core particle and form a chemical bond with the core particle,
thereby welding
or anchoring the entire silicone coating onto the core particle.
In a particularly preferred, but not necessary, embodiment of the present
invention, the
silicone is a reactive ethoxy modified silicone with ethoxy or
ethoxysilylethyl branched
moieties, as described in U.S. Patent 6,660,281, the content of which is
incorporated herein by
reference in its entirety for all purposes. Suitable reactive ethoxy modified
silicones are
commercially available under the trade names KF9901, KF9908, KF9909 or KP574
from
Shin-Etsu Silicones of America, Inc., Akron, OH. Most preferably, the
hydrophobic polymer
of the present invention comprises a triethoxysilylethyl
polydimethylsiloxyethyl hexyl
dimethicone, which is commercially available under the trade name KF9909 from
Shin-Etsu.
The silicone is preferably present in an amount of about 0.01 to about 50
percent by total
weight of the treated particle, and preferably, about 0.5 to about 15.0
percent by total weight
of the treated particle.
The silicone as described hereinabove can be coated onto the core particles
using any
known coating technique, such as simple mixing, spray drying, fluid bed
coating, and the like.
Preferably, but not necessarily, the silicone is coated onto the core
particles using techniques
involving localized heat treatment, such as, for example, sonication achieved
by using an
Ultrasonic Processor, model # UPP-400A, Cycles: 20 KHz, available from Sonicor
Instrument
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Corp., Copiague, NY. Typically, the core particles are provided in batches of
from about 100
grams to about 1 kilogram, and each batch is mixed with a solution or
dispersion of silicone.
The mixture is then sonicated to form a silicone coating over the core
particles in a period of
time ranging from about 15 minutes to about 2 hours, and preferably from 10
minutes to about
1 hour. During the sonication, the branched reactive alkoxyl moieties of the
silicone are
energized and consequently form chemical bonds with the surface of the core
particles,
thereby cladding the polyorganosiloxane backbone of the silicone onto the
surface of the core
particles and forming a securely attached silicone coating thereover. After
sonication, the
silicone-coated particles are subjected to a centrifugation step whereby any
residual silicone is
removed from the batch of silicone-coated particles. Finally after
centrifugation, the silicone-
coated particles are dried by placing them in an oven for about 12 to 19 hours
at a temperature
at least sufficient to remove any residual water by evaporation (for example,
about 100 C to
about 120 C).
The silicone-coated particles as described hereinabove are then contacted with
a cross-
linking agent, which is preferably a stannous carboxylate capable of
effectuating cross-linking
of the silicone coating. Suitable stannous carboxylates that can be used as
the cross-linking
agent of the present invention include, but are not limited to stannous salts
of linear or
branched C8-C12 alkyl carboxylic acids, among which stannous octoate is the
most preferred.
Specifically, stannous octoate demonstrates in the present invention the
capability of
effectively cross-linking the silicone as described hereinabove at room
temperature (i.e., 25 C)
upon continuous mixing for a period of time ranging from about 30 seconds to
about 5
minutes, more preferably from about 45 seconds to about 2 minutes, and most
preferably for
about 1 minute.
The mixture is then allowed to sit for from about 1 minute to about 45
minutes, and a
cross-linked structure is thereby formed with the core particles encapsulated
therein. The
cross-linked structure readily conforms to the shape of the container in which
it is allowed to
form. For example, if the mixture is poured onto a flat surface, the cross-
linked structure will
be formed into a flat sheet. For another example, if the mixture is poured
into a cubic
container, the cross-linked structure will be formed into a cube. The cross-
linked structure so
formed is typically a relatively solid structure.
Such cross-linked structure can be subsequently reduced into treated particles
of
desired average particle size by any suitable methods, such as crushing,
grinding, pulverizing,
milling, filtering, and the like. The resulting treated particles preferably
have an average
particle size ranging from about 1 micron to about 50 microns, more preferably
from about 1
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to about 15 microns, and most preferably from about 5 to about 8 microns, as
determined by a
Malvern Particle Size Analyzer, available from Malvern Instrument at
Worcestershire, UK.
The entrapped core particles may account for from about 10% to about 90% of
the total weight
of the resulting treated particles, more preferably 30% to about 75% of the
total weight, and
most preferably from about 40% to about 60% of the total weight. The cross-
linked silicone
may account for from about 5% to about 75% of the total weight of the
resulting treated
particles, more preferably from about 10% to about 60% of the total weight,
and most
preferably from about 30% to about 50% of the total weight. The figure shows a
microscopic
view of a treated particle formed by the process described hereinabove,
according to one
embodiment of the present invention.
It is known that submicron particles, particularly those that are less than
40nm in size,
can penetrate or be engulfed into the skin cells and consequently lead to
apoptosis. The
inventor has discovered that one of the ways to prevent particles from
penetrating into the cells
is to modify the particles to have the same charge as the skin cells. Human
skin and blood cells
are known to be negatively charged, the skin cells possessing a negative
charge of about
-24mV. The inventor has also found that when the particles possess an
electrical potential
which is at least 2.5 to 3 times the electrical potential of skin cells, a
repulsive force between
the particles and the skin is created. As a result, penetration of the
particles into the cells can
be prevented.
Therefore, in a preferred but not necessary embodiment of the present
invention, the
core particles are first coated with an inner layer of an anionic polymer
before being
encapsulated into the cross-linked silicone matrix. Specifically, the core
particles are first
coated with the anionic polymer and then with silicone followed by sonication,
thereby
forming coated particles that each comprises an inner coating of the anionic
polymer and an
outer coating of the silicone. Such coated particles are subsequently treated
by cross-linking
the outer silicone coating in the presence of a cross-linking agent as
described hereinabove to
form the cross-linked structure with the core particles encapsulated therein.
The anionic
polymer is believed to impart a negative charge to the overall treated
particle.
For purposes of the present invention, any anionic polymer possessing an
electrical
potential ranging from about -10mV to -100 mV, more preferably from about -
30mV to -
80mV, which will impart to the treated particle an electrical potential
ranging from about -
40mV to -80mV, more preferably from about -50mV to -70mV, can be used. It is
important to
select a polymer with a suitable electrical potential, because if the
electrical potential of the
treated particle is too low, the repulsion between the skin and the treated
particles would be
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insufficient to prevent the particles from penetrating into the skin. On the
other hand, if the
electrical potential of the treated particles is too high, then the particles
would not disperse
properly when used in a composition. The electrical potential can be measured
by diluting 0.1
part of the specimen in 30 parts of 99% ethanol and using a Zeta potential
analyzer, such as
the Zetasizer Nano available from Malvern Instruments Ltd, Worcestershire, UK.
The Zeta
potential is a measure of the magnitude of charge repulsion or attraction
between particles.
While not wishing to be bound by any particular theory, it is believed that
the particles
of the present invention, possessing an electrical potential ranging from
about -40mV to -
80mV, such as those containing an inner layer of an anionic polymer, will not
settle into the
wrinkles or creases on the skin surface when situated on the surface of the
skin due to the
repulsive forces between the skin and the treated particles. For example,
coating the surface of
the particles (e.g. titanium dioxide) with 2% PVM/MA by total weight of the
treated particles
generates approximately -64mV in a solvent system of water and/or alcohol.
Thus, the two
like charges of the skin cells and the particles repel one another, and this
repulsive force can
be measured.
Furthermore, the negative charge is trapped within the inner layer between the
core
particle and the outer cross-linked silicone matrix, and thereby becoming
localized or
immobilized around the core particle. As a result, a uniform negative charge
is created around
the entire particle. Although not wishing to be bound by any specific theory,
the branched
reactive alkoxyl moieties of the silicone in the outer matrix are believed to
extend through the
inner layer of the anionic polymer onto the surface of the core particle,
preferably forming
chemical bonds therewith to anchor the silicone layer as well as entrap the
inner layer onto the
core particle surface. The anionic polymer preferably has a higher density
than the silicone
but a lower density than the core particle. In this manner, the anionic
polymer and the silicone
can be sequentially coated onto the surface of the core particle, and the
anionic polymer can be
successfully entrapped between the core particle surface and the outer
silicone layer. More
preferably, a density difference of at least 0.01 g/cm3 exists between the
anionic polymer and
the silicone so as to ensure the desired sequential deposition thereof.
Examples of suitable anionic polymers that can be used for forming the inner
layer of
the present invention include, but are not limited to, anionic copolymers such
as acrylates
copolymers and methyl vinyl ether and maleic anhydride (PVM/MA) copolymers.
Acrylates
copolymers include, but are not limited to, the Aculyn series of copolymers
available from
The Dow Chemical Company, Philadelphia, PA. Preferably, the anionic polymer is
a
PVM/MA copolymer, which is commercially available as the Gantrez series of
copolymers
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from International Specialty Products at Wayne, New Jersey. The Gantrez
copolymers
include, for example, Gantrez AN-119, Gantrez AN-139, Gantrez AN-149, Gantrez
AN-169,
Gantrez AN-903, and Gantrez S-97BF. The Gantrez copolymers are white, free-
flowing
powders that are initially insoluble in water, but they can be easily
dispersed in water where
the polymeric anhydride gradually hydrolyzes to produce a transparent solution
of the free
acid. All of the Gantrez copolymers contain methyl vinyl ether and maleic
anhydride moieties
but are differentiated from one another by molecular weights, which range
widely from about
200,000 (for Gantrez AN-119) to about 2,000,000 (for Gantrez AN-179). More
preferably,
the anionic polymer used for forming the inner layer in the present invention
comprises
Gantrez AN-149 or Gantrez S-97BF. The inner layer may be present in an amount
of about
0.2 to 5.0 percent by weight of the treated particle, and preferably, 0.5 to
2.0 percent by weight
of the treated particle.
In another preferred but not necessary embodiment of the present invention, an
active
agent can be co-encapsulated with the core particles into the cross-linked
silicone matrix,
either with or without the inner layer of anionic polymer. The active agent is
preferably a
hydrophilic active agent including, but not limited to: water-soluble
preservatives,
carbohydrates, water-soluble vitamins, amino acids, antioxidants, and water-
soluble extracts of
biological materials. Examples of water-soluble extracts include but are not
limited to,
extracts from, artemia, phytosphingosine, polygonum cuspidatum root, yeast
such as
saccharomyces lysate, thermos thermophillus ferment, birch (Betula alba),
mimosa tenuiflora
(bark) extract, fruit, clove, rye, malt, corn, spelt, millet, barley, oat,
wheat, sesame, cumin,
turmeric, green onion, celery, ginseng, ginger, licorice, carrot, bupleurum
root, Ginkgo biloba
(gingko), Foeniculi Fructus (fennel), kiwi, berry such as Moms bombycis
(mulberry),
Gentiana lutea (gentian), algae such as red algae, Arctium lappa (burdock),
Salvia officinalis
(sage), Lentinus edodes (shiitake mushroom), Perilla frutescens (perilla),
Filipendula
Multijuga, Fucus vesiculosis (bladderwrack, sea weed), peach kernel, Allium
sativum (garlic),
Poria cocos (poria), Humulus lupulus (hops), Mutan Cortex (Moutan Bark),
Pimpinella major,
Lactuca sative (lettuce), Astragalus membranaceous (astragalus) and Rosmarinus
officinalis
(rosemary), Prunus amygdalus (almond), Althea officinale (althea), aloe, Rosae
Fructus (rose
fruit, or Rosa multiflora), Scuttelaria baicalensis (Huang qin), Puerariae
Radix (Pueraria Root,
or Pueraria lobata), chamomile such as Chamomillae Flos (German chamomile),
Gardenia
jasminoides (zhii zi, Gardeniae Fructus), Sophora flavescens Aiton (Sophorae
Radix),
chlorella, rice bran, Paeoniae lactiflora (white peony), ziyu (Sanguisorba
officinalis, burnet),
Moms alba (sang bai pi, mulberry), Glycine max (soybean), Camellia sinensis
(tea), Carthami
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Flos (safflower), Aesculus hippocastanum (horse chestnut), Melissa officinalis
(lemon balm)
and Coicis Semen (Coix lacryma-jobi var. ma-yuen), Angelica keisukei, Arnica
montana
(arnica), Foeniculum officinale (fennel), Isodon japonicus Hara (Isodonis
Herba), Daucus
Carota (carrot), Oryza sativa (rice), Crataegus cuneata (Japanese howthorn),
Acorns calamus
(sweet flag), Crataegus oxycantha (howthorn), Juniperus communis, Ligusticum
wallichii
(Chinese lovage), Swertiae Herba (Swertia Herb), Thymus vulgaris (garden
thyme), Citrus
reticulata (Citrus unshiu), Capsicum tincture, Angelicae sinensis (angelica),
Aurantii
Pericarpium (bitter orange peel), Ruscus aculeatus (butcher's bloom), Vitis
vinifera (grape),
Tilia japonica (lime), Citrus junos and Rosa canina (rose hip), caffeine,
Cinnamomi Cortex
(cinnamon bark) and Eriobotrya japonica Lindl. (loquat), Gambir, Echinacea,
Phellodendri
Cortex (amur cork tree or Phellodendron amurense), Hypericum perforatum (St.
John's wort),
Citrus sinensis (orange), Valeriana fauriei Briquet, Artemisia capillaris
Thunb., Cucumis
sativus (cucumber), Geranii Herba (Geranium Herb), Lithospermum erythrorhizon
Sieb. et
Zucc., Hedera helix, Achillea millefolium (yarrow), Ziziphus jujuba (Chinese
dates),
Calendula officinalis (pot marigold), Houttuynia cordata (Houttuyniae Herba,
Houttuynia
Herba), Potentilla erecta, Petroselinum crispum (parsley), Parietaria
officinalis, Santalum
album (sandalwood), Prunus persica (peach), Centaurea cyanus (cornflower),
Eucalyptus
globulus (eucalyptus) and Lavandula angustifolia (lavender), Persea americana
(avocado),
Nasturtium officinalis (watercress), Symphytum officinale (comfrey), Asarum
sieboldii (wild
ginger), Xanthoxyum piperitum (Japan pepper), Rehmannia glutinosa (di huang),
Mentha
piperita (peppermint), Syzygium aromaticum (clove), Tussilago farfara
(coltsfoot) and
Haematoxylum campechianum (logwood); Oolong tea, Cinchona succirubra (peruvian
bark),
Betula verrucosa (birch) and Glechoma hederacea (ground ivy), milk and royal
jelly, honey,
cysteine and derivatives thereof, ascorbic acid and derivatives thereof, BHA,
BHT, ferulic acid
and derivatives thereof, grapeseed extract, pine bark extract, horseradish
extract,
hydroquinones, rosmarinic acid, coffee robusta seed, caffeic acid, tocopherol
and derivatives
thereof, green tea extract, sodium DNA, sodium ribonucleic acid, octyl, propyl
and dodecyl
gallates, uric acid and thiodiproprionate derivatives. The active agent,
preferably, is an
antioxidant or a natural water-soluble extract having antioxidant activities.
More preferably,
the active agent is a grape seed extract or a French maritime pine tree bark
extract (also
referred to as pycnogenol). The hydrophilic active agent can be present in the
treated particle
of the present invention in an amount of about 0.01 to 50.0 percent, and
preferably, about 0.25
to 30.0 percent by weight of the treated particle.
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The treated particles, according to one preferred embodiment, of the present
invention
as illustrated hereinabove can be readily formed, for example, by adding an
anionic polymer
and optionally a hydrophilic active agent, such as an antioxidant, into a
specific solvent system
to solubilize the anionic polymer and the hydrophilic active agent. The
specific solvent
system for practicing the present invention may contain a single solvent or a
mixture of two or
more solvents. Suitable solvents that can be used for forming such a solvent
system include,
but are not limited to: water, alcohols, and organic solvents, such as ethers,
ketones, aliphatic
hydrocarbons, halogenated hydrocarbons, and the like. Preferably, but not
necessarily, the
solvent system as used in the present invention is an aqueous solvent system
containing water
and optionally one or more alcohols. Core particles to be treated can then be
added into the
aqueous solution of anionic polymer and hydrophilic active agent and mixed
until uniform.
Subsequently, a silicone with branched reactive alkoxyl moieties is added into
the aqueous
solution, preferably with additional water and alcohol. The mixture is then
sonicated for a
sufficient period of time so as to form coated particles having an inner layer
of anionic
polymer and an optional hydrophilic active agent and an outer layer of
hydrophobic polymer
that are securely attached to the core particle, i.e., with little or no
flaking-off A cross-linking
agent, e.g., stannous octoate, is then added into the solution at room
temperature with
continuous mixing. The resulting mixture is next poured into a container and
allowed to sit for
a sufficient period time to thereby forming a cross-linked structure, which is
subsequently
reduced to treated particles of desirable particle size by grinding, milling,
crushing,
pulverizing, filtering, and the like.
When formulated into topical compositions, the treated particles of the
present
invention provide various advantages and benefits that are not available in
their un-
encapsulated or "naked" counterparts. For example, because the core particles
encapsulated in
the cross-linked silicone matrix are sealed off from potentially destabilizing
or degrading
active ingredients in the topical composition, they are significantly more
stable than their un-
encapsulated or "naked" counterparts. Furthermore, if the core particles
contain material or
materials potentially capable of causing generation of reactive oxygen species
(ROS), which
may in turn degrade or otherwise interfere with other active ingredients in
the topical
composition, the encapsulation of such core particles in the cross-linked
silicone matrix
functions to reduce the interference or degradation and improves the overall
stability of the
topical composition. Encapsulation by the cross-linked silicone matrix may
also alter the
hydrophobicity/hydrophilicity of certain core particles that are intrinsically
hydrophilic and
allow such core particles to be formulated into oil or silicone phases that
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incompatible with the un-encapsulated or "naked" hydrophilic particles. It is
important to note
that the desired chemical and/or physical properties of the core particles
should remain
substantially unaffected by the encapsulation described hereinabove.
Although applicable to any cosmetic or topical ingredient or component of
solid,
particulate form, it is believed that the present invention is particularly
useful for stabilizing
solid particles capable of causing generation of reactive oxygen species (ROS)
without
adversely affecting the desired properties of such particles. Reactive oxygen
species (ROS),
such as oxygen ions, free radicals, and peroxides (either inorganic or
organic), are natural
byproducts of the normal metabolism of oxygen by living cells. On one hand,
ROS play
important roles in cell signaling, a process termed redox signaling, and they
are also used by
the immune system to attack and kill pathogens, thereby protecting the living
cells against
invasion by such pathogens. On the other hand, ROS, if not reduced or
eliminated timely,
may cause extensive damage to all components of living cells, including
proteins, lipids, and
DNA. Thus, to maintain proper cellular homeostasis, a balance must be struck
between the
production and consumption of ROS. Various enzymes produced by the living
cells, such as
superoxide dismutase, catalase, and glutathione peroxidase, function as
cellular antioxidants to
eliminate the excess reactive oxygen species. Consequently, the ROS are
present only at low
levels in normal living cells, and the damage caused by them is constantly
repaired by various
cellular repair mechanisms. However, during times of environmental stress, the
ROS levels
can increase dramatically, which may lead to an imbalance between the
production of ROS by
a biological system and the biological system's capability to detoxify the
reactive
intermediates or repair the resulting damages. This cumulates into a situation
commonly
referred to as "oxidative stress." Oxidative stress is involved in many
diseases, such as
atherosclerosis, Parkinson's disease and Alzheimer's disease. Oxidative stress
is also believed
to be a major contributor to the aging process. Certain particles commonly
used in cosmetic
compositions, such as iron oxides, titanium dioxide, and zinc oxide, are known
to cause
generation of ROS, which not only can exert oxidative stress on the skin, but
may also
interfere with other ingredients or components in the cosmetic compositions.
For example,
many organic dyes/colorants, organic sunscreen agents, and other organic
cosmetic ingredients
are known to be susceptible to oxidative decomposition or degradation.
Combined use of the
ROS-releasing particles with such organic cosmetic ingredients may
consequently lead to in
situ decomposition or degradation of such organic cosmetic ingredients and
adversely affect
the overall performance and stability of the cosmetic compositions.
Encapsulation of such
ROS-releasing particles into the cross-linked silicone matrix of the present
invention is
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believed to effectively eliminate or reduce any potential oxidative stress
that such particles
may exert on the skin, and to prevent such particles from causing the
decomposition or
degradation of other cosmetic ingredients. Consequently, the cross-linked
silicone-
encapsulated metal oxide particles of the present invention can be readily
used with organic
compounds that are known to be susceptible to oxidative decomposition or
degradation to
form topical or cosmetic compositions with significantly improved overall
stability and
prolonged shelf life.
The treated particles of the present invention can be added directly to any
pharmaceutically or cosmetically acceptable carrier to form a cosmetic or
topical composition.
For purposes of the present invention, pharmaceutically or cosmetically
acceptable carriers are
substances that are biologically compatible with human skin and can be used to
formulate
active ingredients described hereinabove and/or hereinafter into a cream, gel,
emulsion, liquid,
suspension, powder, nail coating, skin oil, or lotion that can be topically
applied. In the case
where the cosmetically acceptable carrier is in the form of an emulsion, it
may contain from
about 0.1 to 99%, preferably from about 0.5 to 95%, more preferably from about
1 to 80% by
weight of the total composition of water and from about 0.1 to 99%, preferably
from about 0.1
to 80%, more preferably from about 0.5 to 75% by weight of the total
composition of oil. In
the case where the composition is anhydrous, it may comprise from about 0.1 to
90 wt% of oil
and from about 0.1 to 75 wt% of other ingredients such as pigments, powders,
non-aqueous
solvents (such as mono-, di-, or polyhydric alcohols, etc. In the case where
the composition is
in the form of an aqueous based gel, solution, or suspension, it may comprise
from about 0.1
to 99 wt% of water and from about 0.1 to 75 wt% of other ingredients such as
botanicals, non-
aqueous solvents, etc.
The pharmaceutically or cosmetically acceptable carrier or carriers can be
present in
the topical or cosmetic composition of the present invention at an amount
ranging from about
0.1% to about 99.9%, preferably from about 5% to about 99.5%, more preferably
from about
10% to about 99%, and most preferably from about 10% to 90% by total weight of
the topical
or cosmetic composition.
The topical or cosmetic composition may contain one or more skin care actives,
which
are agents that provide benefits to the skin, rather than merely improving the
physical or
aesthetic characteristics of the topical composition. If present, such skin
care actives may
range from about 0.01 to 50%, preferably from about 0.05 to 35% by weight of
the total
composition. Exemplary skin care additives that can be used in the topical or
cosmetic
compositions of the present invention include, but are not limited to:
chemical or physical
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sunscreens, self-tanning agents such as dihydroxyacetone, anti-acne agents
(e.g., resorcinol,
salicylic acid, benzoyl peroxide, and the like), enzyme-inhibiting agents,
collagen-stimulating
agents, agents for the eradication of age spots and keratoses, analgesics,
anesthetics,
antimicrobials (e.g., antibacterials, antiyeast agents, antifungal agents, and
antiviral agents),
-- antidandruff agents, antidermatitis agents, antipruritic agents,
antiemetics, anti-inflammatory
agents, antihyperkeratolytic agents, antiperspirants, antipsoriatic agents,
antiseborrheic agents,
antihistamine agents, skin lightening agents, depigmenting agents, skin
soothing/healing
agents (e.g., aloe vera extract, allantoin, and the like), corticosteroids,
hormones, proteins or
peptides, vitamins and derivatives thereof (e.g., vitamin A, vitamin E,
vitamin B3, vitamin B5,
-- and the like), exfoliants, retinoids (e.g., retinoic acid and retinol),
farnesol, bisabolol,
phytantriol, glycerol, urea, guanidine (e.g., amino guanidine), clotrimazole,
ketoconazole,
miconozole, griseofulvin, hydroxyzine, diphenhydramine, pramoxine, lidocaine,
procaine,
mepivacaine, monobenzone, erythromycin, tetracycline, clindamycin,
meclocyline,
minocycline, hydroquinone, naproxen, ibuprofen, theophylline, cromolyn,
albuterol, topical
-- steroids (e.g., hydrocortisone, hydrocortisone 21-acetate, hydrocortisone
17-valerate, and
hydrocortisone 17-butyrate), betamethasone valerate, betamethasone
diproprionate, benzoyl
peroxide, crotamiton, propranolol, promethazine, and mixtures or derivatives
thereof In a
preferred, but not necessary embodiment of the present invention, the topical
composition
comprises one or more skin care actives selected from the group consisting of
sunscreen
-- agents, self-tanning agents, anti-aging agents, anti-wrinkle agents, anti-
acne agents,
antimicrobials, anti-inflammatory agents, skin-lightening agents, proteins or
peptides, vitamins
and derivatives thereof, exfoliants, ingredients that stimulate DNA repair,
ingredients that
provide immune protection, ingredients that stimulate cell renewal,
ingredients that stimulate
skin barrier repair, moisturizers, and mixtures thereof
In a particularly preferred embodiment of the present invention, the topical
or cosmetic
composition is a sunscreen composition comprising treated particles containing
core particles
formed of zinc oxide, titanium dioxide, or both. As mentioned hereinabove,
zinc oxide or
titanium dioxide particles are known to have photoprotective characteristics
and can therefore
be used as physical sunscreen agents, but their uses in topical or cosmetic
compositions are
-- limited due to their photo-activity, i.e., their tendency to cause
generation of reactive oxygen
species upon exposure to UV light, which may degrade or otherwise interfere
with certain
organic cosmetic ingredients or skin care actives that are susceptible to
oxidative
decomposition or degradation. The encapsulation of zinc oxide and/or titanium
dioxide
particles as described in the present invention is believe to eliminate or
reduce reactive oxygen
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species generated in the vicinity of such particles upon UV exposure, but
without adversely
affecting the sunscreen properties of such particles.
Consequently, the treated particles of the present invention containing zinc
oxide
and/or titanium dioxide can be readily formulated with organic cosmetic
ingredients or skin
care additives that are known to be susceptible to oxidative decomposition or
degradation to
form stable sunscreen compositions with significantly improved overall
stability and
prolonged shelf live. For example, the treated particles containing zinc oxide
and/or titanium
dioxide can be formulated with one or more organic dyes susceptible to
oxidative
decomposition or degradation to form color cosmetic compositions that also
have sunscreen
properties. For another example, the treated particles containing zinc oxide
and/or titanium
dioxide can be formulated with one or more organic sunscreen agents
susceptible to oxidative
decomposition or degradation, thereby forming sunscreen compositions that are
not only
characterized by high SPF values (e.g., SPF 30 or more), but also surprisingly
and
unexpectedly improved overall stability and prolonged shelf life. If present,
such organic
sunscreen agents may range from about 0.1 to 45% by weight of the total
composition.
Exemplary organic sunscreen agents that can be used in combination with the
Ti02-
and/or ZnO-containing treated particles of the present invention include, but
are not limited to
UVA and UVB sunscreens, such as benzophenones and derivatives thereof (e.g.,
benzophenone-3, dioxybenzone, sulisobenzone, octabenzone, hydroxy- and/or
methoxy-
substituted benzophenones, and benzophenonesulfonic acids and salts thereof);
salicylic acid
derivatives (e.g., ethylene glycol salicylate, triethanolamine salicylate,
octyl salicylate,
homomenthyl salicylate, and phenyl salicylate); urocanic acid and derivatives
thereof (e.g.,
ethyl urocanate); p-aminobenzoic acid (PABA) and derivatives thereof (e.g.,
ethyl/isobutyl/glyceryl esters thereof and 2-ethylhexyl p-
dimethylaminobenzoate, which is
also referred to as octyldimethyl PABA); anthranilates and derivatives thereof
(e.g., o-amino-
benzoates and various esters of amino-benzoic acid); benzalmalonate
derivatives;
benzimidazole derivatives; imidazolines; bis-benzazolyl derivatives;
dibenzoylmethanes and
derivatives thereof (e.g., 4-tert-butyl-4'-methoxydibenzoylmethane, which is
commonly
referred to as "avobenzone," and 4-isopropyl-dibenzoylmethane); benzoazole/
benzodiazole/benzotriazoles and derivatives thereof (e.g., 2-(2-hydroxy-5-
methylphenyl)
benzotriazole and methylene bis-benzotriazolyl tetramethylbutylphenol, which
is commonly
referred to as "Tinosorb M"); diphenylacrylates and derivatives thereof (e.g.,
2-ethylhexy1-2-
cyano-3,3-diphenylacrylate, which is commonly referred to as "octocrylene,"
and ethy1-2-
cyano-3,3-diphenylacrylate, which is commonly referred to as "etocrylene");
diesters or
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polyesters containing diphenylmethylene or 9H-fluorene substitutional groups;
2-phenyl-
benzimidazole-5-sulphonic acid (PBSA); 4,4-diarylbutadienes; cinnamates and
derivatives
thereof (e.g., 2-ethylhexyl-p-methoxycinnamate, octyl-p-methoxycinnamate,
umbelliferone,
methylumbelliferone, methylaceto-umbelliferone, esculetin, methylesculetin,
and daphnetin);
camphors and derivatives thereof (e.g., 3-benzylidenecamphor, 4-
methylbenzylidenecamphor,
polyacrylamidomethyl benzylidenecamphor, benzylidene camphor sulfonic acid,
and
terephthalylidene dicamphor sulfonic acid, which is commonly referred to as
"Encamsule");
triazines and derivatives thereof (e.g., 2,4-bis- {[4-(2-ethyl-hexyloxy)-2-
hydroxy]-phenyl} -6-
(4-methoxypheny1)-1,3,5-triazine, which is commonly referred to as "Tinosorb
S");
naphthalates and derivatives thereof (e.g., diethylhexy1-2,6-naphthalate);
naphtholsulfonates
and derivatives thereof (e.g., sodium salts of 2-naphthol-3,6-disulfonic and 2-
naphthol-6,8-
disulfonic acids); dibenzalacetone and benzalacetonephenone;
diphenylbutadienes and
derivatives thereof; di-hydroxynaphthoic acid and salts thereof; o- and p-
hydroxybiphenyldisulfonates; coumarin derivatives ( e.g., 7-hydroxy, 7-methyl,
and 3-phenyl
derivatives thereof); azoles/diazoles/triazoles and derivatives thereof (e.g.,
2-acety1-3-
bromoindazole, phenyl benzoxazole, methyl naphthoxazole, and various aryl
benzotriazoles);
quinine and derivatives thereof (e.g., bisulfate, sulfate, chloride, oleate,
and tannate salts
thereof); quinoline and derivatives thereof (e.g., 2-phenylquinoline and 8-
hydroxyquinoline
salts); tannic acid and derivatives thereof (e.g., hexaethylether derivatives
thereof);
hydroquinone and derivatives thereof; uric acid and derivatives thereof;
vilouric acid and
derivatives thereof, and mixtures or combinations thereof. Salts and otherwise
neutralized
forms of certain acidic sunscreens from the list hereinabove are also useful
herein. These
organic sunscreen agents may be used alone or in combination of two or more.
In addition,
other known animal or vegetable extracts having UV light-absorbing ability may
properly be
used alone or in combination.
Organic sunscreen agents that are particularly useful for the practice of the
present
invention are: 4,4' -t-butyl methoxydibenzoylmethane, 2-ethylhexy1-2-cyano-3,3-
diphenylacrylate, 2-ethylhexylsalicylate, 3,3,5-trimethylcyclohexylsalicylate,
2-ethylhexyl p-
methoxycinnamate, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-
methoxybenzophenone, 2,4-bis- {4-(2-ethyl-hexyloxy)-2-hydroxy]-phenyl} -6-(4-
methoxypheny1)-1,3,5-triazine, methylene bis-benzotriazolyl
tetramethylbutylphenol,
terephthalylidene dicamphor sulfonic acid, diethylhexyl 2,6-naphthalate,
digalloyltrioleate,
ethyl 4-[bis(hydroxypropyl)]aminobenzoate, glycerol p-aminobenzoate,
methylanthranilate, p-
dimethylaminobenzoic acid or aminobenzoate, 2-ethylhexyl p-
dimethylaminobenzoate, 2-
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phenylbenzimidazole-5-sulfonic acid, 2-(p-dimethylaminopheny1)-5-
sulfoniobenzoxazoic
acid, and mixtures or combinations thereof Preferably, 4,4' -t-butyl
methoxydibenzoylmethane is provided in the sunscreen compositions of the
present invention,
either with Ti02-containing treated particles, or ZnO-containing treated
particles, or both.
More preferably, the sunscreen compositions of the present invention further
include a second
organic sunscreen agent selected from the lists provided hereinabove.
The cosmetically acceptable carrier may also contain one or more oils, which
may be
silicone, organic, or mixtures thereof If present, such oils may range from
about 0.1 to 99%
by weight of the total composition and include volatile or non-volatile
silicones such as
cyclomethicone; methyl trimethicone; octamethyltrisiloxane;
decamethyltetrasiloxane;
dodecamethylpentasiloxane; dimethicone; phenyl trimethicone
trimethylsiloxyphenyl
dimethicone; phenyl dimethicone; cetyl dimethicone; dimethicone copolyol,
cetyl dimethicone
copolyol; glycerolated silicones such as lauryl PEG-9 polydimethylsiloxyethyl
dimethicone; or
mixtures thereof. Suitable esters include mono-, di-, or triesters of C4-30
fatty acids and mono-
, di-, or polyhydric C1-20 alcohols, such as fatty acid (e.g., stearyl,
behenyl, and isostearyl)
esters of glycerin, or fatty acid esters of alpha hydroxyl acids such as
citric, malic, or lactic
acids and the like. Suitable hydrocarbons include monomeric or polymeric
olefins or alpha
olefins, such as polyisobutene, polydecene, polybutene, or hydrogenated
derivatives thereof.
The cosmetically acceptable carrier may also comprise one or more humectants.
If
present, they may range from about 0.1 to 20% by weight of the total
composition and include
C1-4 alkylene glycols such as butylene, propylene, ethylene glycol, glycerin
and the like.
The cosmetically acceptable carrier may also contain one or more waxes
preferably
having a melting point ranging from about 30 to 150 C. If present, such waxes
may range
from about 0.1 to 45% by weight of the total composition and include animal,
vegetable,
mineral, or silicone waxes. Examples include alkyl dimethicones stearyl
dimethicone,
candelilla, polyethylene, ozokerite, beeswax, and the like.
The cosmetically acceptable carrier may also comprise one or more
organosiloxane
elastomers, either emulsifying or non-emulsifying. If present, such elastomers
may range
from about 0.1 to 30% by weight of the total composition. Examples of suitable
elastomers
include dimethicone/vinyl dimethicone crosspolymer; dimethicone/dimethicone
PEG/PPG
10/15 crosspolymer; and the like.
The cosmetically acceptable carrier may also include one or more pigments or
powders
or mixtures thereof If present, the suggested range of such pigments or
powders is from about
0.1 to 85% by weight of the total composition. The particle sizes of such
pigments or powders
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may range from about 0.05 to 200 microns but are preferably about 50-100
microns.
Examples of pigments include organic pigments such as D&C or FD&C colors or
Lakes
thereof including blues, browns, reds, etc; or inorganic iron oxides such as
brown, yellow,
green, red, iron oxides. Suitable powders include titanium dioxide, nylon,
PMMA, boron
nitride, mica, and the like.
The cosmetically acceptable carrier may also comprise one or more nonionic
surfactants, particularly if the topical or cosmetic composition of the
present invention is
provided in the emulsion form. If present, such surfactants may range from
about 0.1 to 20%
by weight of the total composition. Suitable surfactants include ethoxylated
fatty C6-30
alcohols such as steareth, beheneth, ceteth where the number following each of
the surfactants
refers to the number of repeating ethylene oxide groups which may range from 2
to 250, e.g.
steareth-2, beheth-30 and so on.
The present invention can be further illustrated in the following non-limiting
examples.
Example I
TiO2 particles were first coated with Gantrez S-97BF polymer and then with
KF9909
silicone fluid under sonication, and the coated particles were then mixed with
more KF9909
silicone fluid in a main beaker and mixed together using a pro mixer
manufactured by
Caframo in Ontario, Canada (Model # BDC 1850) at digital reading of 105 until
a
homogenous mixture was formed. Stannous octoate, which was commercially
available from
Arkema as FascatO 2003 catalyst, was added into the main beaker at room
temperature, and
mixing was resumed for about 1 minute. The resulting mixture was immediate
poured onto a
flat surface and allowed to sit for 30 minutes, thereby forming a cross-linked
flat sheet. The
flat sheet was subsequently reduced to particles by mortar pestle. The
resulting treated
particles had an average particle size ranging from about 1 micron to 10
microns, as measured
under microscope. Such treated particles contained about 85.31 wt% of Ti02,
3.52% Gantrez
S-97BF, 0.41% stannous octoate, and about 12.57 wt% of KF-9909 silicone fluid.
While the present invention has been described hereinabove with reference to
specific
embodiments, features and aspects, it will be recognized that the invention is
not thus limited,
but rather extends in utility to other modifications, variations,
applications, and embodiments,
and accordingly all such other modifications, variations, applications, and
embodiments are to
be regarded as being within the spirit and scope of the present invention.
17
