U.S. patent application number 13/359809 was filed with the patent office on 2012-05-31 for dermatological composition.
This patent application is currently assigned to pSiMedica Limited. Invention is credited to Roger Aston, Leigh T. Canham.
Application Number | 20120134917 13/359809 |
Document ID | / |
Family ID | 9897788 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120134917 |
Kind Code |
A1 |
Canham; Leigh T. ; et
al. |
May 31, 2012 |
DERMATOLOGICAL COMPOSITION
Abstract
Dermatological methods of cosmetic, therapeutic, prophylactic,
and/or diagnostic treatment by topically applying compositions
comprising a multiplicity of particles, at least one of the
particles comprising porous and/or polycrystalline silicon.
Included are methods and compositions for sun protection
applications. The use of porous silicon, polycrystalline silicon,
and porous silicon oxide mirrors is disclosed.
Inventors: |
Canham; Leigh T.; (Malvern,
GB) ; Aston; Roger; (Malvern, GB) |
Assignee: |
pSiMedica Limited
Malvern
GB
|
Family ID: |
9897788 |
Appl. No.: |
13/359809 |
Filed: |
January 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11142332 |
Jun 2, 2005 |
8128912 |
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13359809 |
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10344153 |
Feb 10, 2003 |
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PCT/GB01/03633 |
Aug 15, 2001 |
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11142332 |
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Current U.S.
Class: |
424/1.11 ;
423/325; 423/348; 424/401; 424/59; 428/402 |
Current CPC
Class: |
A61P 17/02 20180101;
A61P 17/14 20180101; A61Q 17/04 20130101; A61P 17/00 20180101; A61K
2800/56 20130101; A61P 39/00 20180101; A61K 33/00 20130101; Y10T
428/2982 20150115; Y10S 514/844 20130101; Y10S 514/951 20130101;
A61P 17/10 20180101; A61K 8/25 20130101; A61P 17/06 20180101; A61P
17/08 20180101; A61Q 19/00 20130101; A61P 17/16 20180101 |
Class at
Publication: |
424/1.11 ;
424/59; 424/401; 423/348; 423/325; 428/402 |
International
Class: |
A61K 51/00 20060101
A61K051/00; A61K 8/02 20060101 A61K008/02; B32B 5/16 20060101
B32B005/16; C01B 33/02 20060101 C01B033/02; C01B 33/113 20060101
C01B033/113; A61K 8/25 20060101 A61K008/25; A61Q 17/04 20060101
A61Q017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2000 |
GB |
0020276.2 |
Claims
1.-13. (canceled)
14. A method of protecting the skin or a human or animal from UV
radiation comprising the step of topically applying a
dermatological composition comprising a plurality of particles
comprising polycrystalline silicon.
15. A method according to claim 14 wherein the polycrystalline
silicon has a particle size in a range of 0.01 to 250 .mu.m.
16. A method according to claim 14 wherein the composition
comprises a dermatologically acceptable carrier.
17. A method according to claim 14 wherein the polycrystalline
silicon is resorbable.
18. A method according to claim 14 wherein the composition
comprises a plurality of mirrors made from a plurality of layers of
polycrystalline silicon, each mirror comprising a plurality of
layers, each layer comprising polycrystalline silicon.
19. A method according to claim 18 wherein the composition
comprises a plurality of groups of mirrors, each group reflecting
radiation over a wavelength range that differs from that of the
other groups.
20. A method according to claim 14 wherein the composition further
comprises at least one beneficial substance.
21. A method according to claim 20 wherein the at least one
beneficial substance is selected from the group consisting of a
biological material, a genetic material, a radioactive material, an
antibacterial and a luminescent material.
22. A method according to claim 14 wherein the polycrystalline
silicon is present in the form of polycrystalline silicon
oxide.
23. A dermatological composition comprising a multiplicity of
particles, each particle comprising polycrystalline silicon.
24. A dermatological composition according to claim 23 wherein the
polycrystalline silicon has a particle size in a range of 0.01 to
250 .mu.m.
25. A dermatological composition according to claim 23 wherein the
composition comprises a dermatologically acceptable carrier.
26. A dermatological composition according to claim 23 wherein the
polycrystalline silicon is resorbable.
27. A dermatological composition according to claim 23 wherein the
composition comprises a plurality of mirrors made from a plurality
of layers of polycrystalline silicon, each mirror comprising a
plurality of layers, each layer comprising polycrystalline
silicon.
28. A dermatological composition according to claim 23 wherein the
composition comprises a plurality of groups of mirrors, each group
reflecting radiation over a wavelength range that differs from that
of the other groups.
29. A dermatological composition according to claim 23 wherein the
composition further comprises at least one beneficial
substance.
30. A dermatological composition according to claim 29 wherein the
at least one beneficial substance is selected from the group
consisting of a biological material, a genetic material, a
radioactive material, an antibacterial and a luminescent
material.
31. A dermatological composition according to claim 23 wherein the
polycrystalline silicon is present in the form of polycrystalline
silicon oxide.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/142,332 filed Jun. 2, 2005 (now allowed) which in turn
is a divisional of Ser. No. 10/344,153 (now abandoned) filed Feb.
10, 2003, which in turn is a US national phase of PCT/GB01/03633
filed Aug. 15, 2001, which claims priority of GB 0020276.2 filed
Aug. 18, 2000, the entire content of which is hereby incorporated
by reference in this application.
[0002] This invention relates to a new dermatological composition.
More specifically this invention relates to a new dermatological
composition comprising silicon and/or silicon oxide.
[0003] The term "dermatological composition" covers a huge range of
products that may be applied to the skin. Such products may be used
for the treatment of skin conditions or damaged skin; they may be
used to protect the skin, or for cosmetic purposes; they may even
be used to treat organs located beneath the skin.
[0004] Dermatological compositions are applied to skin in a number
of different forms including creams, pastes, powders, and gels, and
may include components such as oils, pigments, fillers,
surfactants, emollients, basifying/acidifying agents, fragrances,
pharmaceutical products, and particulates.
[0005] Particulates may be used in dermatological compositions for
a variety of reasons. They may be present as a filler, which,
increases the volume of the skin composition. Fillers commonly used
in skin creams include talc, mica, and silica. Alternatively the
particulate may confer colour to the cream, say for cosmetic
purposes. The particulate may be a beneficial substance that
protects or has a beneficial effect upon the skin, or that has a
beneficial effect on organs lying below the skin. Finally the
particulate may be a carrier that interacts with a beneficial
substance in such a manner that the effect of the beneficial
substance is enhanced as a result of the interaction. For example a
carrier may assist in transfer of a beneficial substance through or
into the skin, or it may protect a beneficial substance from other
components in the composition.
[0006] As is well known exposure to direct sunlight may cause
sun-burn, ageing effects, and skin cancer. Cosmetic sunscreen
preparations aim to reduce this risk and often include chemical
compounds which are capable of absorbing certain wavelengths of UV
radiation. Many also incorporate a particulate component having
diameters of 10-150 nm whose purpose is to reflect or scatter
certain wavelengths of UV radiation while remaining optically
transparent on the skin. Although effective, UV absorbing chemicals
may cause sensitisation in some users. The small particles used are
typically of a metal oxide, with titanium and zinc oxides being
particularly common.
[0007] A problem associated with the use of titanium dioxide is
that it has a relatively high refractive index, which causes
whitening when applied to the skin. To overcome this problem
ultrafine particles of titanium dioxide have been used, which cause
less scattering in the visible region. Unfortunately such ultrafine
particles (of titanium oxide, or zinc oxide) suffer from problems
of coagulation which can cause deterioration of their optical
properties. A further problem associated with titanium and zinc
oxides is their hydrophilicity, reducing the water repellent
properties of any composition of which they form a part.
[0008] Dermatological compositions often have to satisfy a number
of criteria such as cosmetic appearance, water resistance, and
stability. The composition should be comfortable to apply and
continue to feel comfortable once applied, for example it should
not cause an allergic reaction and should not cause sensitisation
of the skin.
[0009] The property of stability (the retention of the physical and
chemical properties of the composition after manufacture) includes
stability prior to and after application to the skin. A common
cause of composition instability is the agglomeration of one or
more of the components. Agglomeration of a solid component,
comprising for example nanoparticles, may result in an abrasive or
unpleasant sensation when the composition is applied to the
skin.
[0010] There are thus many problems, or potential problems, to be
taken into account when selecting products for topical application
to human skin; and it is an objective of this invention to provide
a new dermatological composition that ameliorates at least some of
these problems.
[0011] According to a first aspect, the present invention provides
a dermatological composition comprising a multiplicity of
dermatological particles, at least one of the dermatological
particles comprising porous and/or polycrystalline silicon.
[0012] Preferably the dermatological composition comprises a
multiplicity of silicon particles each silicon particle comprising
one or more of: bulk crystalline silicon, porous silicon, amorphous
silicon, and polycrystalline silicon.
[0013] Porous and/or polycrystalline silicon, when located in a
mammalian body, may be degraded to yield silicic acid,
H.sub.4SiO.sub.4. Clinical evidence suggests that exposure to
silicic acid is of value in the treatment of skin complaints such
as psoriasis and conditions associated with the biological ageing
of the skin, hair and nails. For example, studies by Lassus, in the
Journal of International Medical Research, 1997, vol. 25, pp.
206-209 and 1993, vol. 21, pp. 209-215, discuss the results of
tests involving the oral and topical administration of colloidal
silicic acid to groups of patients. Significant improvements were
observed in skin thickness and turgor; alleviation of the symptoms
of chronic plaque-type psoriasis was also observed.
[0014] The effects of supplementing the diets of calves with
silicic acid, H.sub.4SiO.sub.4, has been reported by Colomme et
al., Biological Trace Element Research, 1997 vol. 56, p 153. A 4.9%
increase in dietary silicon over a 23 week period led to a 70%
increase in serum silicon concentration and produced a significant
increase in dermal collagen levels.
[0015] The present invention, therefore provides a composition
which is suited for use as a pharmaceutical product to deliver
silicic acid via the skin. The compostion is suitable for use as a
treatment for conditions affecting the skin, such as psoriasis and
also those which affect the underlying bones and joints, such as
osteoporosis.
[0016] Thin films of porous silicon show good optical transparency,
for example a 20 .mu.m thick film with porosity of 90% provides
greater than 95% transmission in the visible region. Furthermore,
the absorption of UV radiation by porous silicon is high, for
example the absorption coefficient above the direct bandgap of Si
(3.25 eV or 400 nm) is around 5.times.10.sup.4 cm.sup.-1 for a
material with a porosity of 90%. This far exceeds the UV absorption
ability of commonly used metal oxide nanoparticles such as
TiO.sub.2 which has an absorption coefficient of ca. 10.sup.3
cm.sup.-1 at 400 nm. Porous silicon is therefore suitable for use
as a UV radiation screening agent in a sunscreen preparation.
[0017] The dermatological composition may further comprise a
dermatologically acceptable carrier. Preferably the dermatological
carrier comprises a natural or synthetic fat; the fat may be an oil
or a wax.
[0018] High porosity porous silicon has a refractive index
comparable to many commonly used dermatological carriers, making
its concealment by the carrier more effective.
[0019] The dermatological composition may comprise one or more of:
a fatty binder, a filler, a pigment, a volatile oil, an
anti-oxidant, a surfactant, a basifying agent, an acidifying agent,
and a fragrance.
[0020] The dermatological composition may have a composition such
that it is one of: a cream, a lotion, a topical solution, a paste,
a linament, a powder, a gel, a tincture, and an aerosol.
[0021] For pharmaceutical use small quantities of porous and/or
polycrystalline silicon may be effective. Porous and/or
polycrystalline silicon may comprise less than 2% by weight with
respect to the total weight of the composition. Preferably, the
porous and/or polycrystalline silicon comprises at least 2% by
weight with respect to the total weight of the composition.
[0022] Suitably the or each porous and/or polycrystalline silicon
particle has a particle size in the range from 0.01 to 250 .mu.m,
preferably, the particle size is in the range from 0.01 to 0.15
.mu.m and more preferably the particle size is in the range from
0.01 to 0.03 .mu.m.
[0023] Advantageously the dermatological composition comprises a
multiplicity of silicon particles and each silicon particle has a
particle size in the range from 0.01 to 250 .mu.m. More
advantageously, each silicon particle has a particle size in the
range from 0.01 to 0.15 .mu.m. Yet more advantageously each silicon
particle has a particle size is in the range from 0.01 to 0.03
.mu.m.
[0024] The particle size range chosen is dependent on the intended
use of the composition. For use in a sunscreen applications, it may
be desirable for the particles to have a size that scatters
ultraviolet wavelengths. The upper bound to the particle size of
the porous silicon is limited by the need for the composition to be
comfortable in use. Particles which are too large will result in
the composition being granular to the touch and which may cause
abrasion of the skin on application. The dermatological composition
may be used as a deoderant. The dermatological composition may also
be used as a coloured lipstick. Finally, cosmetic aspects may also
have to be taken into account, the particle size influencing the
appearance of the composition on the skin.
[0025] The extent of porosity of the porous silicon has been shown
by the inventors to affect the rate at which it is absorbed by the
mammalian body. Highly porous silicon is more rapidly resorbed than
lower porosity silicon. The porosity is measured in terms of the
fractional void content of the porous silicon.
[0026] Preferably, the dermatological composition comprises porous
silicon and the porous silicon has a porosity of at least 1%, more
preferably, the porous silicon has a porosity of at least 50%.
[0027] Porous silicon may be classified according to the nature of
the porosity. Dependent on the conditions of manufacture, it may be
microporous, with an average pore size of less than 20 .ANG.;
mesoporous, with an average pore size of between 20 and 500 .ANG.;
or macroporous with an average pore size of greater than 500
.ANG..
[0028] For use in the present invention, preferably the
dermatological composition comprises porous silicon and the porous
silicon is microporous or mesoporous, more preferably it is
mesoporous.
[0029] Preferably the porous and/or polycrystalline silicon is
resorbable.
[0030] Advantageously the dermatological composition further
comprises at least one beneficial substance.
[0031] For the purposes of this specification a beneficial
substance is defined as a substance that has a beneficial effect
when administered to the body of an animal or human. The beneficial
substance may be located within the structure of the porous and/or
polycrystalline silicon. If the beneficial substance is resorbable,
then corrosion of the porous and/or polycrystalline silicon may
result in release of the beneficial substance.
[0032] The beneficial substance may be one or more of: a
pharmaceutical material, a biological material, a genetic material,
a radioactive material, an antibacterial agent or a luminescent
material.
[0033] The beneficial substance may be one or more of: insulin,
lidocaine, alprostadil, calcitonin, DNA, RNA, tumour necrosis
factor (TNS), a peptide, cytokine, a hormone, an antibody, a
cytotoxic agent, an adjuvant, a steroid, an antibiotic, a cinamate
derivative, octyl methoxycinnamate, a Salicylate, a benzophenone,
an anthranilate, a dibenzoylmethane, a p-aminobenzoate, a vitamin C
derivative, a .beta. carotene, an .alpha. tocopherol, a thiol, an
antifungal agent, an antiviral agent, and a psoralen.
[0034] Another beneficial substance may be a protein, for example
collagen. It is reputed that collagen has anti-ageing attributes
when applied to the skin. A further beneficial substance may be a
vitamin, for example vitamin E. A yet further beneficial substance
may be a trace mineral. A non-exhaustive list of suitable trace
minerals includes; selenium, manganese, molybdenum, chromium,
vanadium, iodine, fluorine and cobalt.
[0035] In general, trace minerals are needed by the body only in
very small quantities, the recommended daily allowance (RDA) of
certain trace elements can be less than 0.1 mg/day. The effects of
deficiencies are however, well documented. Furthermore, some trace
minerals are required in specific areas of the body. Delivery of
trace minerals in the form of a topical application is therefore
attractive.
[0036] A still further beneficial substance may be a therapeutic
element. Possible therapeutic elements include, lithium, gold,
silver, copper, zinc, and platinum. These elements have widespread
clinical usage for the treatment of chronic conditions; lithium is
used to treat depression, silver and gold have antibacterial
properties, copper and zinc are commonly applied via the skin, and
platinum is used in the treatment of neoplastic diseases. It may
also be desirable to be able to deliver these elements to specific
sites via topical application.
[0037] It is of course intended that the porous silicon may have
more than one beneficial substance incorporated within its
structure.
[0038] Preferably the dermatological composition comprises
derivatised porous silicon. For the purposes of this specification
derivatised porous silicon is defined as porous silicon having a
monomolecular, or monatomic layer that is chemically bonded to at
least part of the surface, including the surface of the pores, of
the porous silicon. The chemical bonding, between the layer and the
silicon, may comprise a Si--C and/or Si--O--C bonding.
[0039] In this way the beneficial substance may be bonded to the
surface of the porous silicon. The porous silicon may also be
derivatised so as to enhance wetting of the porous and/or
polycrystalline silicon particles by other components contained in
the dermatological composition.
[0040] Advantageously the dermatological composition comprises
silicon oxide, more advantageously the dermatological composition
comprises porous and/or polycrystalline silicon oxide. Yet more
advantageously the dermatological composition comprises porous
silicon part of which has been oxidised to form silicon oxide.
[0041] The dermatological composition may comprise a multiplicity
of mirrors, each mirror comprising a plurality of layers, each
layer comprising porous and/or polycrystalline silicon.
[0042] By having a plurality of porous layers, each layer having a
different porosity to layer(s) adjacent to it, and by controlling
the porosity of each layer, the mirror may be made to reflect
radiation over a limited range of wavelengths. The dermatological
composition may comprise a first group of mirrors that reflect
radiation over a first wavelength range, and a second group of
mirrors that reflect radiation over a second wavelength range. The
dermatological composition may comprise several groups of mirrors,
each group reflecting radiation over a wavelength range that
differs from that of the other groups.
[0043] The use of mirrors that reflect different wavelengths may
have two advantages. Firstly it potentially affords protection over
a greater range of wavelengths. Secondly it opens the way for
coloration of the composition using the reflective properties of
the mirrors; in this way the composition may be used to darken the
skin causing it to appear tanned.
[0044] Preferably each mirror may have a largest dimension in the
range 50 nm to 2 mm. More preferably each mirror has a largest
dimension between 100 nm and 1 mm.
[0045] Each mirror may have a largest dimension that is greater
than twice its smallest dimension.
[0046] Advantageously each mirror comprises resorbable porous
silicon.
[0047] The mirrors may reflect electromagnetic radiation away from
the skin of a human to which the dermatological composition has
been applied. If each mirror is resorbable then they will gradually
corrode upon application to the skin. This corrosion will be linked
to a change in the appearance of the composition, and this change
can be used as an indicator of the composition effectiveness.
[0048] Preferably the or each dermatological particle comprises
silicon oxide.
[0049] According to a second aspect the invention provides a
dermatological composition comprising a multiplicity of silicon
oxide mirrors, each silicon oxide mirror comprising a plurality of
layers, each layer comprising porous and/or polycrystalline silicon
oxide.
[0050] By having a plurality of porous layers, each layer having a
different porosity to layer(s) adjacent to it, and by controlling
the porosity of each layer, the mirror may be made to reflect
radiation over a limited range of wavelengths. The dermatological
composition may comprise a first group of mirrors that reflect
radiation over first wavelength range, and a second group of
mirrors that reflect radiation over a second wavelength range. The
dermatological composition may comprise several groups of mirrors,
each group reflecting radiation over a wavelength range that
differs from that of the other groups.
[0051] Preferably each silicon oxide mirror may have a largest
dimension in the range 50 nm to 2 mm. More preferably each silicon
oxide mirror has a dimension between 100 nm and 1 mm.
[0052] Each mirror may have a largest dimension that is greater
than twice its smallest dimension.
[0053] The dermatological composition may further comprise a
dermatologically acceptable carrier. Preferably the dermatological
carrier comprises a natural or synthetic fat; the fat may be an oil
or a wax.
[0054] Porous silicon oxide has a refractive index comparable to
that of commonly used dermatological carriers, making its
concealment by the carrier more effective.
[0055] Preferably the porous silicon oxide is resorbable.
[0056] The dermatological composition may comprise one or more of:
a fatty binder, a filler, a pigment, a volatile oil, an
anti-oxidant, a surfactant, and a fragrance.
[0057] The dermatological composition, may have a composition such
that it is one of a cream, a lotion, a topical solution, a paste, a
linament, a powder, a gel, a tincture or an aerosol.
[0058] According to a third aspect the invention provides a method
of therapeutic or prophylactic treatment of a human or animal body
comprising the steps of: topically applying a dermatological
composition and allowing the dermatological composition to treat
the human or animal; the dermatological composition comprising a
multiplicity of dermatological particles, at least one of the
dermatological particles comprising porous and/or polycrystalline
silicon.
[0059] According to a fourth aspect the invention provides a method
of cosmetic treatment of a human or animal body comprising the
steps of: topically applying a dermatological composition and
allowing the dermatological composition to cosmetically treat the
human or animal; the dermatological composition comprising a
multiplicity of dermatological particles, at least one of the
dermatological particles comprising porous and/or polycrystalline
silicon.
[0060] According to a fifth aspect the invention provides a method
of therapeutic or prophylactic treatment of a human or animal body
comprising the steps of: topically applying a dermatological
composition and allowing the dermatological composition to treat
the human or animal; the dermatological composition comprising a
multiplicity of silicon mirrors, at least one of the mirrors
comprising a plurality of porous and/or polycrystalline silicon
oxide layers, each layer having a different refractive index to the
layer or layers adjacent to it.
[0061] According to a sixth aspect the invention provides a method
of cosmetic treatment of a human or animal body comprising the
steps of: topically applying a dermatological composition and
allowing the dermatological composition to cosmetically treat the
human or animal; the dermatological composition comprising a
multiplicity of mirrors, at least one of the mirrors comprising a
plurality of layers of porous and/or polycrystalline silicon oxide,
each layer having a refractive index that differs from that of the
layer or layers adjacent to it.
[0062] According to a seventh aspect the invention provides a
method of manufacturing a dermatological composition comprising the
step of combining at least one particle, comprising porous and/or
polycrystalline silicon, with a dermatologically acceptable
carrier.
[0063] According to a eighth aspect the invention provides a method
of manufacturing a dermatological composition comprising the step
of combining at least one mirror, the mirror comprising a plurality
of layers of porous and/or polycrystalline silicon oxide each layer
having a refractive index that differs from that of the layer or
layers adjacent to it, with a dermatologically acceptable
carrier.
[0064] According to a ninth aspect, the invention provides a method
of protecting at least part of an animal or human from
electromagnetic radiation, comprising the steps: [0065] (a)
applying a dermatological composition to at least part of the skin
of the animal or human; and [0066] (b) allowing, when at least part
of the skin is exposed to electromagnetic radiation, the
dermatological composition to reflect at least part of the
electromagnetic radiation; wherein step (b) comprises the step of
reflecting at least part of the electromagnetic radiation by means
of a multiplicity dermatological mirrors.
[0067] Each dermatological mirror may comprise a plurality of
porous silicon and/or porous silicon oxide layers. Each porous
silicon and/or porous silicon oxide layer may have a different
porosity to that of its neighbouring layer or layers. Each
dermatological mirror may comprise a plurality of porous silicon
and/or porous silicon oxide layers having alternating high and low
porosities. The low porosity layers may each have a porosity
between 25% and 65%, and the high porosity layers may each have a
porosity between 60% and 95%. Each dermatological mirror may
comprise greater than 10 layers. Each dermatological mirror may
comprise greater than 100 layers. Each dermatological mirror may
comprise greater than 200 layers. Each dermatological mirror may
comprise greater than or equal to 400 layers.
[0068] Each layer of porous silicon and/or porous silicon oxide,
from which the mirrors may be formed, has a different refractive
index to its neighbouring layer or layers, the combined layers
forming a Bragg stack mirror.
[0069] The dermatological composition may comprise a
dermatologically acceptable carrier such as a natural or synthetic
fat. The multiplicity of dermatological mirrors may be in the form
of a powder, the powder being distributed throughout the
carrier.
[0070] Preferably each dermatological mirror comprises one or more
of: bulk crystalline silicon, porous silicon, amorphous silicon,
and polycrystalline silicon.
[0071] Advantageously each dermatological mirror comprises silicon
oxide.
[0072] The dermatological composition may be a sun cream, providing
protection against ultraviolet radiation.
[0073] Each dermatological mirror may comprise porous silicon, and
at least part of the porous silicon may comprise porous
polycrystalline and/or amorphous silicon.
[0074] Step (b) may comprise the step of allowing the multiplicity
of dermatological mirrors to reflect, with a reflectivity peak
between 5 nm and 380 nm, at least part of the electromagnetic
radiation.
[0075] Step (b) may comprise the step of allowing the multiplicity
of dermatological mirrors to reflect, with a reflectivity peak
between 380 nm and 780 nm, at least part of the electromagnetic
radiation.
[0076] Step (b) may comprise the step of allowing the multiplicity
of dermatological mirrors to reflect, with a reflectivity peak
between 740 nm and 100 .mu.m, at least part of the electromagnetic
radiation.
[0077] Step (b) may comprise the step of allowing the multiplicity
of dermatological mirrors to reflect, with a reflectivity peak
between 400 nm and 800 nm, at least part of the electromagnetic
radiation.
[0078] Step (b) may comprise the step of allowing the multiplicity
of dermatological mirrors to reflect, with a reflectivity peak
between 550 nm and 700 nm, at least part of the electromagnetic
radiation.
[0079] Preferably the average particle size of the multiplicity of
dermatological mirrors is in the range 50 nm to 2 mm. More
preferably the average size of the multiplicity of the
dermatological mirrors is between 100 nm and 1 mm.
[0080] The average particle size of the multiplicity of
dermatological mirrors may be in the range 10 nm to 50 microns. The
average particle size of the multiplicity of dermatological mirrors
may be in the range 200 microns to 1 mm.
[0081] The reflectance properties of the multiplicity of
dermatological mirrors may impart colour to the dermatological
composition, or they can be used to reflect undesirable radiation
from the skin to which the composition is applied.
[0082] According to a tenth aspect, the invention provides a
dermatological composition comprising a plurality of dermatological
mirrors.
[0083] Each dermatological mirror may comprise a plurality of
porous silicon and/or porous silicon oxide layers. Each porous
silicon and/or silicon oxide layer may have a different porosity to
that of its neighbouring layer or layers. Each dermatological
mirror may comprise a plurality of porous silicon and/or porous
silicon oxide layers having alternating high and low porosities.
The low porosity layers may each have a porosity between 25% and
65%, and the high porosity layers may each have a porosity between
60% and 95%. Each dermatological mirror may comprise greater than
10 layers. Each dermatological mirror may comprise greater than 100
layers. Each dermatological mirror may comprise greater than 200
layers. Each dermatological mirror may comprise greater than or
equal to 400 layers.
[0084] The dermatological composition may be a sun-cream.
[0085] Preferably each dermatological mirror comprises one or more
of: bulk crystalline silicon, porous silicon, amorphous silicon,
and polycrystalline silicon.
[0086] Each dermatological mirror may comprise silicon oxide. Each
dermatological mirror may comprise porous silicon oxide.
[0087] Each dermatological mirror may comprise porous silicon, and
the porous silicon may comprise porous polycrystalline and/or
porous amorphous silicon.
[0088] Preferably the dermatological composition comprises a
dermatologically acceptable carrier. Advantageously the
dermatological carrier may comprise a natural or synthetic fat such
as an oil or wax. The plurality of dermatological mirrors may be
distributed substantially uniformly throughout the volume of the
dermatological carrier.
[0089] The orientation of each dermatological mirror may be
substantially random.
[0090] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 100 nm and 380 nm.
[0091] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 380 nm and 780 nm.
[0092] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 740 nm and 100 .mu.m.
[0093] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 400 nm and 800 nm.
[0094] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 550 nm and 700 nm.
[0095] Each dermatological mirror may comprise porous silicon
and/or porous silicon oxide, the porous silicon and/or porous
silicon oxide having a structure such that, when each
dermatological mirror is substantially randomly oriented, the
plurality of dermatological mirrors has a peak in its reflectivity
spectrum between 630 nm and 700 nm.
[0096] Each dermatological mirror may substantially consist of
porous silicon.
[0097] Each dermatological mirror may substantially consist of
porous silicon oxide.
[0098] Preferably the average particle size of the plurality of
dermatological mirrors is in the range 50 nm to 2 mm. More
preferably the average particle size of the plurality of the
dermatological mirrors is between 100 nm and 1 mm.
[0099] The average size of the average particle size of the
plurality of dermatological mirrors may be in the range 10 nm to 50
microns. The average size of the average particle size of the
plurality of dermatological mirrors may be in the range 200 microns
to 100 .mu.m.
[0100] At least some of the dermatological mirrors may comprise
silicon oxide having a structure such that it is soluble in human
and/or animal sweat. At least some of the dermatological mirrors
may comprise silicon oxide having a structure such that it is
soluble in simulated human and/or animal sweat.
[0101] At least some of the dermatological mirrors may comprise
silicon having a structure such that it is soluble in human and/or
animal sweat. At least some of the dermatological mirrors may
comprise silicon having a structure such that it is soluble in
simulated human and/or animal sweat.
[0102] At least some of the dermatological mirrors may comprise a
beneficial substance.
[0103] The corrosion of silicon and/or silicon oxide, which may
form part of the dermatological composition, in sweat has several
advantages. As mentioned above, dermatological mirrors may impart
colour to the dermatological composition. Corrosion of the mirrors
in sweat could therefore result in a colour change in the
composition, a colour change that could be used to monitor the
efficacy of the composition, and indicate the need for further
application of the composition.
[0104] Advantageously the dermatological composition comprises a
volatile material. The volatile material may comprise more than one
compound. The volatile material may be a liquid or solid at 20 C
and 760 mm Hg. Preferably the volatile material is a liquid at 20 C
and 760 mm Hg. The volatile material may have a volatility such
that, when 9 g+/-1 g is disposed within a layer of mesoporous
silicon, the mass loss through evapouration at 20 C and 760 mm Hg
is greater than or equal to 0.01 mg per minute over the first two
minutes of measurement.
[0105] The volatile material may be lavender oil and/or Tea Tree
Oil.
[0106] The dermatological mirrors may be of value in imparting a
colour to the dermatological composition; they may even give the
composition a glittering or glinting appearance. At least part of
the volatile material may be distributed in or on the silicon
and/or silicon oxide, from which the dermatological composition is
at least partly formed.
[0107] Advantageously the silicon, from which the plurality of
dermatological mirrors are at least partly formed, comprises porous
silicon, and at least some of the volatile material is disposed in
at least some of the pores of the porous silicon.
[0108] According to an eleventh aspect, the invention provides a
method of delivering a beneficial substance to or through at least
part of the skin of an animal or human, comprising the steps of:
[0109] (a) applying a dermatological composition, comprising a
beneficial substance, to at least part of the skin of the animal or
human; and [0110] (b) allowing the beneficial substance to be
released to or through the skin of the animal and/or human; wherein
the dermatologal composition comprise silicon and/or silicon oxide,
at least part of the beneficial substance being located in or on at
least part of the silicon and/or silicon oxide, and wherein step
(b) comprises the step of allowing the silicon and/or silicon oxide
to corrode in sweat excreted from the skin of the animal or human,
thereby releasing the beneficial substance.
[0111] The dermatological composition may comprise silicon and the
silicon may be selected from one or more of bulk crystalline
silicon, porous silicon, amorphous silicon, and polycrystalline
silicon. Preferably the dermatological composition comprises porous
silicon.
[0112] The dermatological composition may comprise silicon oxide,
and the silicon oxide may be porous silicon oxide.
[0113] The dermatological composition may comprise porous silicon
and the porous silicon may be porous polycrystalline and/or
amorphous silicon.
[0114] The dissolution of silicon and/or silicon oxide in sweat
means that the beneficial substance associated with it may be
released as a result of the dissolution.
[0115] The step of allowing the porous silicon and/pr silicon oxide
to corrode may comprise the step of allowing the porous silicon
and/or silicon oxide to corrode less than or equal to 2 hours after
contact with the sweat.
[0116] The step of allowing the porous silicon and/or porous
silicon oxide to corrode may comprise the step of allowing the
porous silicon and/or silicon oxide to corrode less than or equal
to 6 hours after contact with the sweat.
[0117] The beneficial substance may comprise silicon or a silicon
compound. The beneficial substance may be formed, at least partly
from at least some of the porous silicon.
[0118] The beneficial substance may be one or more of: a
pharmaceutical material, a biological material, a genetic material,
a radioactive material, an antibacterial agent or a luminescent
material.
[0119] The beneficial substance may be one or more of: insulin,
lidocaine, alprostadil, calcitonin, DNA, RNA, tumour necrosis
factor (INS), a peptide, cytokine, a hormone, an antibody, a
cytotoxic agent, an adjuvant, a steroid, an antibiotic, a cinamate
derivative, octyl methoxycinnamate, a Salicylate, a benzophenone,
an anthranilate, a dibenzoylmethane, a p-aminobenzoate, a vitamin C
derivative, a .beta. carotene, an .alpha. tocopherol, a thiol, an
antifungal agent, an antiviral agent, and a psoralen.
[0120] Another beneficial substance may be a protein, for example
collagen. It is reputed that collagen has anti-ageing attributes
when applied to the skin. A further beneficial substance may be a
vitamin, for example vitamin E. A yet further beneficial substance
may be a trace mineral. A non-exhaustive list of suitable trace
minerals includes; selenium, manganese, molybdenum, chromium,
vanadium, iodine, fluorine and cobalt.
[0121] A still further beneficial substance may be a therapeutic
element. Possible therapeutic elements include, lithium, gold,
silver, copper, zinc, and platinum.
[0122] The silicon, from which the dermatological composition may
be at least partly formed, may comprise a multiplicity of silicon
particles. At least some of the silicon particles may comprise
porous silicon.
[0123] The silicon oxide, from which the dermatological composition
may at least partly be formed, may comprise a multiplicity or
silicon oxide particles.
[0124] According to a twelfth aspect, the invention provides a
dermatological composition comprising a multiplicity of porous
silicon particles, each porous silicon particle comprising an outer
layer; characterised in that the outer layer has a composition such
that it corrodes, when it is placed in contact with the skin of an
animal or human.
[0125] The outer layer may comprise gelatin.
[0126] According to an thirteenth aspect the invention provides a
dermatological composition comprising a multiplicity of
dermatological particles.
[0127] Preferably each dermatological particle comprises one or
more of: bulk crystalline silicon, porous silicon, amorphous
silicon, and polycrystalline silicon. More preferably each
dermatological particle comprises porous silicon.
[0128] Certain forms of porous silicon, are photoluminescent,
emitting visible light when illuminated with ultraviolet radiation.
It may therefore be used as a marker to determine whether a
beneficial substance has been administered by the application of a
dermatological composition. Particles of small particles of porous
silicon, invisible under normal conditions, may photoluminesce when
the skin of an animal or human is exposed to the UV radiation.
[0129] Advantageously each dermatological particle comprises
silicon oxide. More advantageously each silicon oxide particle
comprises porous silicon oxide.
[0130] The dermatological composition may further comprise a
dermatologically acceptable carrier. Preferably the dermatological
carrier comprises a natural or synthetic fat; the fat may be an oil
or a wax. The multiplicity of silicon and/or silicon oxide
particles may be distributed throughout the carrier.
[0131] According to a fourteenth aspect, the invention provides the
use of silicon and/or silicon oxide for the manufacture of a
medicament for the delivery of a beneficial substance to or through
at least part of the skin of an animal or human.
[0132] The step of delivering a beneficial substance to or through
at least part of the skin, may comprise the steps of applying a
dermatological composition, comprising the beneficial substance, to
at least part of the skin of the animal or human and allowing the
beneficial substance to be released to or through the skin of the
animal and/or human.
[0133] The dermatological composition may comprise at least part of
the silicon and/or silicon oxide.
[0134] At least part of the beneficial substance may be located in
or on at least part of the silicon and/or silicon oxide and the
step of allowing the beneficial substance to be released may
comprise the step of allowing the silicon and/or silicon oxide to
corrode in sweat excreted from the skin of the animal or human,
thereby releasing the beneficial substance.
[0135] Silicon, used to deliver the beneficial substance, may be
selected from one or more of bulk crystalline silicon, porous
silicon, amorphous silicon, and polycrystalline silicon. Preferably
the silicon comprises porous silicon.
[0136] Silicon oxide, used to deliver the beneficial substance, may
be porous silicon oxide.
[0137] The dissolution of silicon and/or silicon oxide in sweat
means that the beneficial substance associated with it may be
released as a result of the dissolution.
[0138] The step of allowing the porous silicon and/or silicon oxide
to corrode may comprise the step of allowing the porous silicon
and/or silicon oxide to corrode less than or equal to 2 hours after
contact with the sweat.
[0139] The step of allowing the porous silicon and/or porous
silicon oxide to corrode may comprise the step of allowing the
porous silicon and/or silicon oxide to corrode less than or equal
to 6 hours after contact with the sweat.
[0140] The beneficial substance may comprise silicon or a silicon
compound. The beneficial substance may be formed, at least partly
from at least some of the porous silicon.
[0141] The beneficial substance may be one or more of: a
pharmaceutical material, a biological material, a genetic material,
a radioactive material, an antibacterial agent or a luminescent
material.
[0142] The beneficial substance may be one or more of: insulin,
lidocaine, alprostadil, calcitonin, DNA, RNA, tumour necrosis
factor (TNS), a peptide, cytokine, a hormone, an antibody, a
cytotoxic agent, an adjuvant, a steroid, an antibiotic, a cinamate
derivative, octyl methoxycinnamate, a Salicylate, a benzophenone,
an anthranilate, a dibenzoylmethane, a p-aminobenzoate, a vitamin C
derivative, a .beta. carotene, an .alpha. tocopherol, a thiol, an
antifungal agent, an antiviral agent, and a psoralen.
[0143] Another beneficial substance may be a protein, for example
collagen. It is reputed that collagen has anti-ageing attributes
when applied to the skin. A further beneficial substance may be a
vitamin, for example vitamin E. A yet further beneficial substance
may be a trace mineral. A non-exhaustive list of suitable trace
minerals includes; selenium, manganese, molybdenum, chromium,
vanadium, iodine, fluorine and cobalt.
[0144] A still further beneficial substance may be a therapeutic
element. Possible therapeutic elements include, lithium, gold,
silver, copper, zinc, and platinum.
[0145] The silicon, from which the dermatological composition may
be at least partly formed, may comprise a multiplicity of silicon
particles. At least some of the silicon particles may comprise
porous silicon.
[0146] The silicon oxide, from which the dermatological composition
may at least partly be formed, may comprise a multiplicity or
silicon oxide particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0147] The invention will now be described by way of example only
with reference to the following drawings, in which:
[0148] FIG. 1 shows a dermatological composition, according to the
invention, comprising a multiplicity of particles in contact with
human skin;
[0149] FIG. 2 shows one of the particles illustrated in FIG. 1;
[0150] FIG. 3 shows transmission spectra and absorption spectra
comparing bulk crystalline silicon with porous silicon with
differing degrees of porosity;
[0151] FIG. 4 shows an SEM image of a porous silicon mirror prior
to immersion in simulated human sweat;
[0152] FIG. 5 shows an SEM images of a porous silicon mirror after
immersion in simulated human sweat for periods of two, six, and
twenty hours;
[0153] FIG. 6 shows two SEM images, of porous silicon mirrors after
immersion in simulated human sweat for the same period of time, the
immersion being under different conditions for each mirror;
[0154] FIG. 7 shows reflectance spectra for porous silicon, which
is in the form of a film, and also in the form of a powder;
[0155] FIG. 8 shows the effect of oxidation on the reflectance
spectrum of porous silicon mirror;
[0156] FIG. 9a shows a SEM image of a gelatine coated porous
silicon mirror impregnated with Tea Tree Oil;
[0157] FIG. 9b shows EDX plots for a gelatine coated porous silicon
mirror;
[0158] FIG. 10a shows an SEM image of a polycrystalline layer
deposited on a silica substrate; and
[0159] FIGS. 10b and 10c show SEM images of porosified
polycrystalline layers.
PREPARATION OF A FIRST DERMATOLOGICAL COMPOSITION
[0160] A first dermatological composition, according to the
invention, may be prepared by the following process:
Step A1
[0161] Porous silicon was fabricated by anodising a heavily boron
doped CZ silicon wafer with an initial resistivity of 0.01-0.03
.OMEGA.cm. The anodisation was carried out in an electrochemical
cell, as described in U.S. Pat. No. 5,348,618 containing an
electrolyte comprising a 10% solution of hydrofluoric acid in
ethanol. An anodisation current with density of 50 mA cm.sup.-2 was
passed for 12 minutes. This produced a 20 .mu.m thick porous
silicon layer with a porosity of 90% and a mass density of 0.47 mg
cm',
Step B1
[0162] The porous silicon layer may then be detached from the
underlying wafer by increasing the current density, for a few
seconds, to a sufficiently high value that the silicon at the
interface between the porous and bulk crystalline regions is
completely dissolved. It was then supercritically dried as
described by Canham in Nature, vol. 368, (1994) p 133-135.
Step C1
[0163] To produce porous silicon in a particulate form suitable for
use in a dermatological composition the detached layer was
subjected to ultrasonic agitation in a liquid known to allow good
dispersion of silicon powders. Common organic liquids such as
alcohols, ketones or aldehydes were found to be suitable. It was
then necessary to reduce the size of the silicon particles. This
was achieved using a centrifuge as described by Mizuta et al. in
Ceramic Bulletin, vol. 61, (1982), p 872-875. The porous silicon
particulate layer was suspended in n-propanol and centrifuged at
12000 rpm to remove large agglomerates. The supernatant was then
centrifuged at 17000 rpm to give a dispersion of nanoparticulate
porous silicon.
[0164] Alternatively, the particle size may be reduced by milling,
as described by Kerkar et al. in Jn. Am Ceram. Soc., vol 73,
(1990), p 2879-2885. The detached layer is mixed with an organic
liquid such as trichloroethylene and subjected to attrition milling
in a Si.sub.3N.sub.4 container using Si.sub.3N.sub.4 balls for
several hours.
Step D1
[0165] After removal of the organic liquid and drying, the powdered
porous silicon was suitable for use in a dermatological
composition. It was used either without further processing or with
one or more beneficial substances.
[0166] There are a number of methods by which a beneficial
substance may be associated with the silicon particles to be used
in the dermatological composition. The beneficial substance may be
dissolved or suspended in a suitable solvent, the silicon particles
may then be incubated in the resulting solution for a period of
time.
[0167] The beneficial substance may be deposited on the surface of
the implants. If the implants comprise porous silicon, then a
solution of the beneficial substance may be introduced into the
pores of the porous silicon by capillary action. Similarly if the
silicon particles have a cavity then the solution may also be
introduced into the cavity by capillary action. If the beneficial
substance is a solid, but has a sufficiently high vapour pressure
at 20 C then it may be sublimed onto the surface of the silicon
particles. If a solution or suspension of the beneficial substance
can be formed then the substance may be applied to the silicon
particles by successive immersion in the solution/suspension
followed by freeze drying.
[0168] The particle size of the porous silicon was measured by
transmission electron microscopy however any other suitable method
such as laser Doppler particle size analysis, light scattering or
Stokes settling techniques may be used.
Step E1
[0169] A dermatological composition was prepared by blending
powdered porous silicon with a dermatologically acceptable carrier,
such that the percentage of porous silicon comprised about 2% by
weight of the composition. If the carrier comprises an oil, then
the silicon particles may be sprinkled into the oil with stirring
to homogenise the mixture. The oil/porous silicon mixture may then
be combined with other component's, to form the dermatological
composition.
Preparation of a Second Dermatological Composition
[0170] A second dermatological composition, according to the
invention, may be prepared by the following process:
Step A2
[0171] A 0.2 .OMEGA.cm p.sup.- CZ Si substrate is anodized in
H.sub.2O:HF:C.sub.2H.sub.5OH electrolyte, the components of the
electrolyte being present in the ratios 1:1:2 by volume. Current
density is periodically modulated from 30 mAcm.sup.-2 to 120
mAcm.sup.-2 to yield low (corresponding to 30 mAcm.sup.-2) and high
(corresponding to 120 mAcm.sup.-2) porosity layers. Anodisation in
this way results in the formation of a silicon multilayer mirror.
By varying the time intervals over which the two current densities
flow, the stop band (the spectral region of high reflectivity) of
the mirror can be tuned across the visible range and into the
ultraviolet.
[0172] Typical approximate reflectivities of the as-etched porous
silicon mirrors are 99% at 740 nm, 90% at 490 nm, and 50% at 370
nm.
Step B2
[0173] A multiplicity of particulate silicon mirrors may then be
obtained from the single multilayer mirror film by repeating steps
B1 to E1 recited for the first dermatological composition. In this
way the multilayer mirror is detached from the silicon substrate,
formed into silicon particles (at least some of the particles being
a mirror) either ultrasonically or by crushing, combined with one
or more beneficial substances, and finally combined with a suitable
dermatological carrier.
[0174] FIG. 1 shows a number of particulate mirrors 11 that are in
contact with the skin 12. Each particulate mirror 11 comprises a
plurality of layers of porous silicon (see FIG. 2). Radiation 13,
say UV-A radiation, is reflected by the mirrors 11 before the
radiation 13 reaches the skin 12. The particulate mirrors 11 form
part of a dermatological composition, which also comprises a
dermatologically acceptable carrier 14.
[0175] FIG. 2 shows one of the particulate mirrors shown in FIG. 1,
generally indicated by 13. The particulate mirror 13 comprises a
first group of layers 21 and a second group of layers 22, the
porosity of the first group 21 differing from that of the second
group 22.
Preparation of a Third Dermatological Composition
[0176] A third dermatological composition, according to the
invention, may be prepared in the following manner:
Step A3
[0177] The step A2, given for preparation of the second
dermatological composition, is repeated with modulation between 80
mAcm.sup.-2 to 120 mAcm.sup.-2. The porous silicon multi-layer
mirror may then be detached from the underlying wafer by increasing
the current density, for a few seconds, to a sufficiently high
value that the silicon at the interface between the porous and bulk
crystalline regions is completely dissolved. The mirror is then
supercritically dried as described by Canham in Nature, vol. 368,
(1994) p 133-135 and thermally oxidised by heating the multilayer
mirror in dry oxygen at 950 C for five minutes to yield a porous
silicon oxide multilayer mirror. (M Berger et al, Thin Solid Films,
Vol 297, p 237-240, 1997),
Step B3
[0178] A multiplicity of porous silicon oxide mirrors may then be
obtained from the single silicon oxide multilayer mirror by
repeating steps C1 to E1 recited for the first dermatological
composition. In this way the silicon oxide multilayer mirror is
detached from the substrate, formed into particles either
ultrasonically or by crushing, combined with one or more beneficial
substances, and finally combined with a suitable dermatological
carrier.
[0179] The hydrophilicity of the porous silicon oxide mirror may be
increased by wet oxidation of the porous silicon at step A3. By
increasing the hydrophilicity in this way, aqueous solutions may be
used for the ultrasonic and centrifuging processes associated with
step C1.
Preparation of a Fourth Dermatological Composition
[0180] A fourth dermatological composition, according to the
invention, may be prepared in the following manner:
Step A4
[0181] A (100) p-type boron doped wafer with resistivity of 0.01
.OMEGA.cm is anodised galvanostatically at 37 mAcm.sup.-2 in a 1:1
by volume mixture of 46% HF:C.sub.2H.sub.5OH for 3 hours in the
dark to yield a single 300 .mu.m thick layer of porous silicon.
This single layer of porous silicon has an average porosity of 65%.
A high current etch of 400 mAcm.sup.-2 for 5 minutes then releases
the porous layer as a free standing film.
[0182] Subsequent rinsing with ethanol and excess dry hexane was
then carried out without permitting intermediate drying of the
wafers. Derivatization was then carried out, using a Lewis acid
(EtAlCl.sub.2) mediated hydrosilylation to replace the silicon
hydride termination of the wafers. Hydrosilylation was carried out
with 1 dodecyne and yielded a dodecenyl terminated surface. The
Lewis acid mediated hydrosilylation was performed in the following
manner:
[0183] A hexane solution of the Lewis acid (EtAlCl.sub.2) is bought
into contact with the surface of the freshly anodized sample of
porous silicon (comprising a single layer of uniform porosity), 1
dodecyne is then also placed on the surface of the porous silicon
and the consequent reaction is allowed to proceed at an ambient
temperature of 20 C for a period of at least 2 hours. The sample is
then quenched with THF, followed by CH.sub.2Cl.sub.2. The whole
process, from the application of the Lewis acid through to the
quenching with CH.sub.2Cl.sub.2 is performed in an inert
atmosphere. The derivatized sample is then rinsed in ethanol and
dried under an N.sub.2 stream. The resulting surface is capped with
a monolayer of dodecenyl groups.
Step B4
[0184] A multiplicity of silicon particles, each of which comprises
derivatised porous silicon, may then be obtained from the single
layer of derivatised porous silicon by repeating steps C1 to E1
recited for the first dermatological composition. In this way the
single layer of derivatised porous silicon is detached from the
substrate, formed into particles either ultrasonically or by
crushing, combined with one or more beneficial substances, and
finally combined with a suitable dermatological carrier.
Preparation of a Fifth Dermatological Composition
[0185] A fifth dermatological composition, according to the
invention, may be prepared by the following process:
[0186] A layer of polycrystalline silicon was deposited on a glass
substrate by pyrolysis of SiH.sub.4 at 0.3 torr, at 600 to 620 C,
in a Thermco TMX9000 low pressure chemical vapour deposition hot
walled furnace. The glass substrate is then removed by etching in
aqueous HF solution to obtain a free standing layer. The
polycrystalline layer may then be formed into a multiplicity of
silicon particles by ultrasonic treatment or milling as described
step C1 and combined with a dermatologically acceptable carrier as
described at step E1.
[0187] Alternately, the multiplicity of polycrystalline silicon
particles may be porosified by stain etching prior to combination
with the dermatologically acceptable carrier.
Preparation of a Sixth Dermatological Composition
[0188] A sixth dermatological composition, according to the
invention, may be prepared by the following process:
[0189] A mirror comprising multiple layers of polycrystalline
silicon may be deposited on a substrate by PECVD of hydrogen
diluted SiH.sub.4 using electron cyclotron resonance at
temperatures less than 200 C (see Kalkan et al J. Appl Phys, Vol
88, p 555-561 (2000)). The microwave power is modulated
periodically with time to generate a number of layers of
polycrystalline silicon, each layer having a refractive index that
differs from those of its adjacent layer(s). The process is
performed at a pressure between 5 and 12 mtorr, a silane flow rate
of 2 sccm, and a hydrogen flow rate of 40 sccm.
[0190] The polycrystalline mirror may then be formed into a
multiplicity of particulate mirrors by ultrasonic treatment or
milling as described step C1 and combined with a dermatolocially
acceptable carrier as described at step E1.
Transmission Verses Wavelength Characteristics of Porous
Silicon
[0191] FIG. 3 shows transmission T and absorption coefficient A
verses photon energy E spectra for porous and bulk crystalline
silicon. Plot 31 corresponds to a 90% porous silicon layer, which
effectively screens UV radiation with photon energies of 3.87-3.25
eV (320-400 nm) while allowing transmission of lower energy, longer
wavelength visible light. Plot 32 corresponds to 75% porosity
porous silicon; a comparison of plots 31 and 32 shows how the
transmission properties may be altered by altering the porosity of
the porous silicon. Improved UV screening can be achieved by
sacrificing some optical transparency and vice versa. The optical
characteristics of crystalline bulk silicon, shown by plot 33,
displays UV screening capabilities, but shows very poor optical
transparency.
Stability of Porous Silicon in Sweat
[0192] 10 repeat multilayer silicon mirrors, each containing 10 low
porosity and 10 high porosity porous silicon layers, were
fabricated by anodisation at modulated current density for a total
of 156 seconds in 20% ethanoic HF.
[0193] Each of the 10 repeat mirrors was immersed in simulated
human sweat (SHS) for varying periods of time. The preparation of
simulated human sweat was in accordance with ISO standard (3160/2)
and is described by J P Randin in J. Blamed. Mater. Res. 22, 649
(1988). The simulated sweat comprises NaCl (20 g/litre), NH.sub.4Cl
(17.5 g/litre), urea (5 g/litre), acetic acid (2.5 g/litre) and
lactic acid (15 g/litre). The pH was adjusted to 5.5 by addition of
NaOH.
[0194] FIG. 4 shows an SEM image of one of the 10 repeat silicon
mirrors prior to immersion in the simulated human sweat.
[0195] FIG. 5 shows SEM images of one of the ten repeat mirrors
after immersion in SHS for a period of 2, 6, and 20 hours at 25 C.
After 2 hours (FIG. 5(a)) there is minimal change in thickness, but
the topmost high porosity layer has undergone significant attack,
after 6 hours (FIG. 5(b)) there are 18 of the 20 layers remaining,
whilst after 20 hours (FIG. 5(c)) half of the structure has
completely dissolved and the remainder has been affected throughout
its depth to become partially delaminated.
[0196] FIG. 6 shows two mirrors, one of which (FIG. 6(a)) has been
immersed in SHS at 25 C for a period of 2 hours, and one of which
(FIG. 6(b)) has been immersed in SHS at 37 C for 2 hours. The
mirror that had been immersed at 37 C was also simultaneously
illuminated with; UV radiation (2.5 mWcm.sup.-2, 365 nm). The
illumination with UV radiation at elevated temperatures simulates
sunbathing conditions. Comparison of FIGS. 6(a) and 6(b) shows that
illumination with UV and increase in temperature causes an increase
in the corrosion rate.
Reflectance Properties of Porous Silicon and Oxidised Porous
Silicon
[0197] An ultrathick free standing mirror of 300 repeats (600
layers) was fabricated by anodisation in 20% ethanoic HF, at a
modulated current density for a total of 1 hour and 8 minutes (0.7
amps for 9 second intervals and 4.55 amps for 4.5 second intervals,
the switch between low and high current not being
instantaneous).
[0198] Viewed at normal incidence, the front face had a red hue,
the rear face a vivid green colour. FIG. 7(a) shows the
reflectivity spectrum taken from the front face of the intact 150
micron thick film using Ocean Optics 52000 system. The peak in
reflectivity at about 650 nm is consistent with its red appearance.
The film was then crushed into a powder with a pestal and mortar.
The average particle size was approximately 500 microns. FIG. 7(b)
shows a reflectivity spectrum from the powder, under conditions
where a number of randomly oriented particles contributed to the
signal.
[0199] A thinner mirror of the same microstructure, fabricated by
the same method as that used for the 300 repeat mirror, but having
only 100 repeats (200 layers), and still adhered to its silicon
substrate, was subjected to partial oxidation.
[0200] FIG. 8a shows the reflectance spectrum for the 100 repeat
mirror, attached to its substrate. After oxidation the mirror
became pale purple in colour and had a blue-shifted reflectance
peak shown in FIG. 8b. Further oxidation would shift the
reflectance peak out of the visible region and into the near UV
region.
Volatile Agents: Loading of and Release from Porous Silicon
(A) Lavender Oil
[0201] A large flake of a porous silicon membrane, with a dry
weight of 8.0+/-0.1 mg, was immersed at 20 C in 1 ml of Meadows
pure concentrated lavender oil (Lavendula Officinalis) for a period
of 10 minutes. The flake was then given a brief water rinse.
Residual oil on the external surfaces of the flake was then removed
by contact with filter paper, and the flake was re-weighed. In its
initial as-impregnated state the weight of the flake plus lavender
oil was 17.3+/-0.2 mg, falling by 1 mg in the first 2 minutes but
much more gradually thereafter. After 2 hours in air the weight had
fallen to 8.6+/-0.1 mg. The measurements of mass loss were
conducted at 20 C and 760 mm Hg.
(B) Tea Tree Oil
[0202] A segment of a 100 repeat multilayer mirror attached to its
bulk silicon substrate was impregnated with Tea Tree Oil (Melaleica
Alternifolia). After pre-warming the layer to 60 C on a hot plate,
a drop of concentrated oil was pippetted onto the surface. There
was an immediate colour change from green to red and a gradual
increase in the diameter of the circular red region of the mirror
as the oil droplet spread laterally across the outer surface, in
addition to infiltrating the film. Extended application of a stream
of dry nitrogen gas to the affected region caused the original
green colour to gradually reappear.
[0203] The initial application of the oil was repeated on another
segment, but this time a very thin gelatine film was deposited over
the impregnated region to entrap the volatile oil within. This was
achieved by warming 2 g of gelatine in 200 ml of water to 45 C and
then dipping the segment into this solution and allowing the
adsorbed film to solidify by cooling to room temperature in air.
The coated segment was found to retain its red colour. FIG. 9a
shows an SEM image of the gelatine coated mirror. FIG. 9b shows EDX
plots for the top (FIG. 9b(i)), middle (FIG. 9b(ii)), and bottom
(FIG. 9b(iii)) of the layer of porous silicon containing the Tea
Tree Oil and capped with gelatine. The EDX plots show that the oil
(indicated by the carbon and oxygen peaks) has penetrated
throughout the layer of porous silicon.
Alternative Methods of Impregnation
[0204] A sample of porous silicon, either attached to or detached
from a bulk crystalline silicon substrate, may be disposed in a
sealed container above a volatile liquid. The vapour pressure
within the porous silicon may slowly be increased by heating the
volatile material between its melting point and its boiling point.
This approach may be of value for volatile liquids that do not wet
porous silicon or which are prone to solidification on the pore
walls.
Preparation of Porous Polycrystalline Silicon
[0205] FIG. 10a shows a SEM image of a polycrystalline film of
silicon, deposited onto silica by thermal decomposition of silane
at 620 C in a LPCVD reactor. Segments were subjected to a stain
etch in a 50:1 mixture of 40 wt % HF and 70% nitric acid
respectively. After 15 seconds, about half the layer was porosified
(as shown in the SEM image of FIG. 10(b); after 30 seconds the
electrolyte had penetrated through the full thickness of the layer
and has started to create voids in the underlying oxide (FIG.
10(c)).
[0206] The use of porous polycrystalline silicon in dermatological
compositions is of value, since it is much less expensive to
fabricate than porous silicon derived from bulk crystalline
silicon.
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