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I claim:
1. A matrix transdermal drug delivery device, comprising:
(a) a backing substrate;
(b) a matrix containing a silicone, creep resistant, pressure sensitive
adhesive atop at least portions of said backing substrate, the silicon
pressure sensitive adhesive comprising (i) from about 60 to about 30 parts
by weight of a silicon fluid; (ii) from about 40 to about 70 parts by
weight of a silicate resin, wherein the total parts of the silicone fluid
and silicate resin equal 100 parts; and (iii) from about 1.0 to about 20.0
weight percent based on the weight of the silicone pressure sensitive
adhesive of a cohesive strengthening agent selected from the group
consisting of nonionic surfactants, fatty acid esters of glycerol, and
solid particulate materials, said soild particulate materials being
selected from the group consisting of metallic salts of fatty acids,
metallic salts of phosphoric acid, metallic salts of carbonic acid,
polysaccharides, carboxypolymethylene, polyvinyl pyrrolidone,
polyvinylalcohol, and amorphous precipitated silicas having a surface area
of between about 10 and 200 m.sup.2 /g, the adhesive matrix including
compositions selected from the group consisting of drugs, co-solvents,
enhancers, excipients, and mixtures thereof where the silicone pressure
sensitive adhesive is compatible with said drugs, co-solvents, enhancers
and excipients; and
(c) a release liner contacted on the matrix.
2. The matrix transdermal drug delivery device of claim 1, wherein the
drugs are selected from the group consisting of cardiovascular agents,
antiarrthymic agents, antianginal agents, antibiotics, antifungals,
antimicrobials, antihypertensives, analgesics, local anesthetics,
contraceptives, hormonal supplements, anti-smoking agents, appetite
suppressants, hypnotics, anxiolytics, and mixtures thereof.
3. The matrix transdermal drug delivery device of claim 1, wherein the
co-solvents, enhancers and excipients are selected from the group
consisting of fatty acid esters, polyols, surfactants, terpenes, glycerol
esters, polyethylene glycol esters, amides, sulfoxides, lactams, nonionic
surfactants, sorbitan esters, and mixtures thereof.
4. The matrix transdermal drug delivery device of claim 1, wherein the
matrix is between about 1 and about 15 mils thick.
5. A matrix transdermal drug delivery device, comprising:
(a) a backing substrate;
(b) a matrix which is a polymer atop at least portions of said backing
substrate, the matrix containing compositions selected from the group
consisting of drugs, excipients, enhancers, co-solvents and mixtures
thereof, where the matix is compatible with said compositions;
(c) a silicone, creep resistant, pressure sensitive adhesive disposed in a
layer atop at least portions of the polymer matrix; the silicone pressure
sensitive adhesive comprising (i) from about 60 to about 30 parts by
weight of a silicone fluid; (ii) from about 40 to about 70 parts by weight
of a silicate resin, wherein the total parts of the silicone fluid and
silicate resin equal 100 parts; and (iii) from about 1.0 to about 20.0
weight percent based on the weight of the silicone pressure sensitive
adhesive of a cohesive strengthening agent selected from the group
consisting of nonionic surfactants, fatty acid esters of glycerol, and
solid particulate materials, said solid particulate materials being
selected from the group consisting of metallic salts of fatty acids,
metallic salts of phosphoric acid, metallic salts of carbonic acid,
polysaccharides, carboxypolymethylene, polyvinyl pyrrolidone,
polyvinylalcohol, and amorphous precipitated silicates having a surface
area of between about 10 and 200 m.sup.2 /g, and
(d) a release liner attached to the silicone pressure sensitive adhesive.
6. The matrix transdermal drug delivery device of claim 5, wherein the
drugs are selected from the group consisting of cardiovascular agents,
antiarrthymic agents, antianginal agents, antibiotics, antifungals,
antimicrobials, antihypertensives, analgesics, local anesthetics,
contraceptives, hormonal supplements, anti-smoking agents, appetite
suppressants, hypnotics, anxiolytics, and mixtures thereof.
7. The matrix transdermal drug delivery device of claim 5, wherein the
co-solvents, enhancers and excipients are selected from the group
consisting of fatty acid esters, polyols, surfactants, terpenes, glycerol
esters, polyethylene glycol esters, amides, sulfoxides, lactams,
surfactants, sorbitan esters, and mixtures thereof.
8. The matrix transdermal drug delivery device of claim 5, wherein the
matrix is between about 1 and about 15 mils thick.
9. A reservoir transdermal drug delivery device, comprising:
(a) a backing substrate;
(b) a reservoir attached to at least portions of the backing substrate,
said reservoir containing compositions selected from the group consisting
of drugs, co-solvents, enhancers, excipients, and mixtures thereof;
(c) a silicone pressure sensitive adhesive attached to the reservoir and to
portions of the backing substrate not covered by the reservoir; the
silicone pressure sensitive adhesive comprising (i) from about 60 to about
30 parts by weight of a silicone fluid; (ii) from about 40 to about 70
parts by weight of a silicate resin, wherein the total parts of the
silicone fluid and silicate resin equal 100 parts; and (iii) from about
1.0 to about 20.0 weight percent based on the weight of the silicone
pressure sensitive adhesive of a cohesive strengthening agent selected
from the group consisting of nonionic surfactants, fatty acid esters of
glycerol, and solid particulate materials, said solid particulate
materials being selected from the group consisting of metallic salts of
fatty acids, metallic salts of phosphoric acid, metallic salts of carbonic
acid, polysaccharides, carboxypolymethylene, polyvinyl pyrrolidone,
polyvinylalcohol, and amorphous precipitated silicas having a surface area
of between about 10 and 200 m.sup.2 /g, and
(d) a release liner attached to the silicone pressure sensitive adhesive.
10. The reservoir transdermal drug delivery device of claim 9, wherein the
drugs are selected from the group consisting of cardiovascular agents,
antiarrthymic agents, antianginal agents, antibiotics, antifungals,
antimicrobials, antihypertensives, analgesics, local anesthetics,
contraceptives, hormonal supplements, anti-smoking agents, appetite
suppressants, hypnotics, anxiolytics and mixtures thereof.
11. The reservoir-type transdermal drug delivery device of claim 9, wherein
the co-solvents, enhancers and excipients are selected from the group
consisting of fatty acid esters, polyols, surfactants, terpenes, glycerol
esters, polyethylene glycol esters, amides, sulfoxides, lactams, nonionic
surfactants, sorbitan esters and mixtures thereof.
12. The reservoir transdermal drug delivery device of claim 9, wherein the
silicone pressure sensitive adhesive is between about 1 and about 15 mils
thick.
13. The reservoir transdermal drug delivery device of claim 10, further
comprising a rate controlling membrane, said rate controlling membrane
being positioned over said reservoir and sealing the reservoir between the
backing substrate and the rate controlling membrane.
14. The matrix transdermal drug delivery device of claim 1, wherein the
cohesive strengthening agent is selected from the group consisting of
calcium stearate, magnesium stearate, sodium stearate, calcium carbonate,
calcium phosphate, polyvinylalcohol, xanthan gum, and silicas.
15. The matrix transdermal drug delivery device of claim 1, wherein the
cohesive strengthening agent has a particle size ranging from about 0.018
to about 100 microns.
16. The matrix transdermal druge delivery device of claim 1, wherein the
cohesive strengthening agent is present in an amount of between about 5
and about 15 weight percent.
17. The matrix transdermal drug delivery device of claim 5, wherein the
cohesive strengthening agent is selected from the group consisting of
calcium stearate, magnesium stearate, sodium stearate, calcium carbonate,
calcium phosphate, polyvinylalcohol, xanthan gum, and silicas.
18. The matrix transdermal drug delivery device of claim 5, wherein the
cohesive strengthening agent has a particle size ranging from about 0.018
to about 100 microns.
19. The matrix transdermal drug delivery device of claim 5, wherein the
cohesive strengthening agent is present in an amount of between about 5
and about 15 weight percent.
20. The reservoir transdermal drug delivery device of claim 9, wherein the
cohesive strengthening agent is selected from the group consisting of
calcium stearate, magnesium stearate, sodium stearate, calcium carbonate,
calcium phosphate, polyvinylalcohol, xanthan gum, and silicas.
21. The reservoir transdermal drug delivery device of claim 9, wherein the
cohesive strengthening agent has a particle size ranging from about 0.018
to about 100 microns.
22. The reservoir transdermal drug delivery device of claim 9, wherein the
cohesive strengthening agent is present in an amount of between about 5
and about 15 weight percent. |
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Claims |
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Description |
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TECHNICAL FIELD
This invention relates to silicone pressure sensitive adhesive compositions
having improved cohesive strength and stability, and transdermal-type drug
delivery devices and related medical devices for using the compositions.
BACKGROUND OF THE INVENTION
A pressure sensitive adhesive is generally a material which adheres to a
surface with slight pressure and releases from the surface with negligible
transfer of the adhesive to the surface. The most common examples are the
adhesives used in bandages to cover wounds. Silicone pressure sensitive
adhesives in particular have found use in transdermal drug delivery
applications which involve the adherence of a drug-containing patch to a
patient's skin, due to the fact that silicone pressure sensitive adhesives
are acceptable for topical use.
In transdermal drug delivery patches, ingredients such as co-solvents and
excipients have been added to the silicone pressure sensitive adhesive
compositions to improve efficacy. Co-solvents are typically added to
increase drug solubility in the composition, and excipients are typically
added to enhance drug release from or through the composition.
However, when silicone pressure sensitive adhesives are formulated with or
come in contact with co-solvents, excipients, drugs such as nicotine-based
drugs, or skin penetration enhancers such as propylene glycolmonolaurate
or glycerol monoleate, the silicone pressure sensitive adhesive often
becomes plasticized, losing tack, adhesiveness, and resistance to flow.
Such instances occur (1) in matrix-type drug delivery patches where a drug
is formulated into a silicone pressure sensitive adhesive and (2) in
reservoir-type drug delivery patches where a silicone pressure sensitive
adhesive is on the surface of a drug delivery device containing a
reservoir of a drug. In the former type of patch, the silicone pressure
sensitive adhesive is in intimate contact with the drug and other possible
plasticizing additives. In the latter type of patch, the silicone pressure
sensitive adhesive is present to provide means for attaching the device to
a patient's skin. In this device, drugs or other materials from the
reservoir either pass through or otherwise may come in contact with the
silicone pressure sensitive adhesive.
The problem with either device is that the additives cause reduction in
cohesive strength. Cohesive strength causes the adhesive to adhere to a
substrate such as a patch and prevents flow or transfer of the pressure
sensitive adhesive onto either the release liner which protects the
silicone pressure sensitive adhesive before use or onto the patient's skin
following removal of the patch while maintaining adequate adhesion of the
patch to the skin. The cohesive strengthening agent further prevents flow
of the pressure sensitive adhesive beyond the edges of the patch during
storage and/or use.
It is, therefore, a primary object of the invention to provide a pressure
sensitive adhesive composition which has good cohesive strength and is
resistant to cold flow when formulated or contacted with drugs,
co-solvents, excipients or skin penetration enhancers.
SUMMARY OF THE INVENTION
A silicone pressure sensitive adhesive composition which meets the object
of the invention is disclosed which is compatible with drugs, excipients,
co-solvents and skin penetration enhancers while allowing for the addition
of a cohesive strengthening agent to reduce cold flow. The silicone
pressure sensitive adhesive comprises a silicone fluid, a silicate resin
and a cohesive strengthening agent. By the addition of a cohesive
strengthening agent, an improved silicone pressure sensitive adhesive is
produced which retains the adhesive on the substrate, without compromising
the adhesion of the adhesive to the skin of the patient wearing the
bandage or patch.
In meeting the object of the invention, a silicone pressure sensitive
adhesive includes a cohesive strengthening agent selected from the group
consisting of nonionic surfactants, fatty acid esters of glycerol, said
nonionic surfactants and said fatty acid esters being substantially
insoluble in said mixture, as well as solid particulate materials selected
from the group consisting of metallic salts of fatty acids, metallic salts
of phosphoric acid, metallic salts of carbonic acid, polysaccharides,
carboxypolymethylene, polyvinylpyrrolidone, polyvinylalcohol and amorphous
precipitated silicas having a surface area of less than approximately 200
m.sup.2 /g and between about 10 and 200 m.sup.2 /g.
BRIEF DESCRIPTION OF DRAWINGS
The nature and extent of the present invention will be clear from the
following detailed description of the particular embodiments thereof,
taken in conjunction with the appendant drawings, in which:
FIG. 1 shows a pressure sensitive adhesive sandwiched between a backing
substrate and a release liner;
FIG. 2 shows a matrix-type delivery device for a bioactive agent or drug in
place within a transdermal patch;
FIG. 3 shows a liquid reservoir-type transdermal drug delivery device; and
FIG. 4 shows, a solid state reservoir-type transdermal drug delivery device
.
DETAILED DESCRIPTION OF THE INVENTION
Generally, the silicone pressure sensitive adhesive compositions of the
present invention include a silicone pressure sensitive adhesive
containing (i) a silicone fluid, (ii) a silicate resin, and (iii) a
cohesive strengthening agent. The silicone pressure sensitive adhesive of
the present invention includes a cohesive strengthening agent in order to
overcome the problems of excessive cold flow or creep presented by the
pressure sensitive adhesives of the prior art. Cold flow or creep refer to
viscoelastic flow of the adhesive solids under stress. Resistance to cold
flow is referred to as creep resistance. This is defined by, Carl A.
Dahlquist, "Creep", Handbook Of Pressure Sensitive Adhesive Technology 2nd
ed., (Van Nostrand Runhold, New York, N.Y., 1989), p. 97. As can be seen
by the test results of the Examples below, the addition of the cohesive
strengthening agents of the present invention substantially reduces cold
flow. By reducing the cold flow, a superior product can be made which
keeps the adhesive more on the bandage or patch, with less of the adhesive
transferring to the skin of the patient wearing the bandage or transdermal
patch without compromising the adhesion of the bandage to the skin of the
patient. As one can remember, previous bandages left a sticky residue on
the skin when it was removed. This invention alleviates this problem
substantially.
I. SUITABLE SILICONE PRESSURE SENSITIVE ADHESIVES
One suitable class of silicone pressure sensitive adhesives which may be
employed in the silicone pressure sensitive adhesive compositions of this
invention consists of a mixture of (i) a silanol end-blocked
polydiorganosiloxane fluid, e.g. a polydimethylsiloxane polymer, and (ii)
a trimethylsilyl end-blocked polysilicate resin such as a silicate resin
consisting of a benzene-soluble resinous copolymer containing
silicon-bonded hydroxyl radicals and consisting essentially of
triorganosiloxy units of the formula R.sub.3 SiO.sub.1/2 and
tetrafunctionalsiloxy units of the formula SiO.sub.4/2 in a ratio of about
0.6 to 0.9 triorganosiloxy units for each tetrafunctionalsiloxy unit
present in the copolymer, wherein each R is a monovalent organic radical
independently selected from the group consisting of hydrocarbon radicals
of from 1 to 6 inclusive carbon atoms. U.S. Pat. No. 2,736,721 to Dexter,
et al. and U.S. Pat. No. 2,814,601, to Currie, et al. are hereby
incorporated by reference to teach such or similar silicone pressure
sensitive adhesives.
Another class of suitable silicone pressure sensitive adhesives for use
according to this invention is that or those similar to U.S. Pat. No.
2,857,356, to Goodwin, Jr., which is also hereby incorporated by
reference. The Goodwin, Jr. patent teaches silicone pressure sensitive
adhesives which consist of a mixture of ingredients comprising (i) a
cohydrolysis product of a trialkyl hydrolyzable silane and alkyl silicate,
wherein the cohydrolysis product contains a plurality of silicon-bonded
hydroxy groups, and (ii) a linear, high viscosity organopolysiloxane fluid
containing silicon-bonded hydroxy groups.
The silicone fluid and the silicate resin may optionally be condensed
together according to a procedure such as the procedure described in
Canadian Patent 711,756 to Pail, which patent is hereby incorporated by
reference. In such a condensation reaction, the silicate resin and the
silicone fluid are mixed together in the presence of a catalytic amount of
a silanol condensation catalyst, and then the silicate resin and the
silicone fluid are condensed, for example, by heating under reflux
conditions for 1 to 20 hours. Examples of silanol condensation catalysts
are primary, secondary, and tertiary amines, carboxylic acids of these
amines and quaternary ammonium salts.
Another class of suitable pressure sensitive adhesives to use according to
the invention are those compositions described in U.S. Pat. Nos. 4,591,622
and 4,584,355 to Blizzard et al., U.S. Pat. No. 4,585,836 to Homan et al.,
and U.S. Pat. No. 4,655,767 to Woodard et al., which patents are hereby
incorporated by reference. Generally, these pressure sensitive adhesives
consist of a blend of (i) a silicate resin and (ii) a silicone fluid which
are chemically treated to reduce the silicon-bonded hydroxyl content of
the blend. These adhesives may optionally be condensed as described
immediately above prior to the chemical treatment.
In addition, the various types of silicone pressure sensitive adhesives may
be blended to achieve blended characteristics. Preferably, for the
greatest improvement in cohesive-strength, the silicone pressure sensitive
adhesive contains some silanol radicals, preferably greater than 200 ppm,
and, more preferably, greater than 400 ppm.
Typically, the most practical pressure sensitive adhesive for use in this
invention includes a high molecular weight polydimethylsiloxane as the
silicone fluid, since this fluid is the most economical and the most
readily available of the silicone fluids.
The other adhesive component, the silicate resin, preferably has a
molecular weight ranging from about 2,000 to about 4,000. The resin is
employed in amounts from about 40 to about 70 parts by weight in the
silicone pressure sensitive adhesive, while the silicone fluid is employed
from about 60 to about 30 parts by weight, wherein the total parts of the
silicate resin and the silicone fluid equal 100 parts. The silicone
pressure sensitive adhesive composition contains no less than 100 ppm of
silanol radicals and preferably contains between 200 ppm and 1200 ppm of
silanol radicals.
The silicone pressure sensitive adhesive compositions of this invention may
also contain the aforementioned ingredients: drugs, co-solvents,
excipients, skin penetration enhancers or organic solvents for dissolving
the silicone polymer and the silicate resin. Suitable organic solvents may
have reinforcing excipients dispersed therein for dissolving the
polydimethylsiloxane polymer and silicate resin, and should have a
Hildebrand solubility parameter ranging from between about 5 to 10
cal.sup.1/2 /cm.sup.3/2, and optimally between about 8 and 9 cal.sup.1/2
/cm.sup.3/2. Examples of suitable organic solvents include aromatics such
as toluene and xylene; aliphatics such as heptane and hexane; chlorinated
solvents such as 1, 1, 1-trichloroethane and trichlorotrifluoroethane;
fluorocarbons such as Freon 113 (Freon PCA) available from DuPont de
Nemours, E. I. Co., Wilmington, Del.; aliphatic esters such as ethyl
acetate; and mixtures thereof.
The silicone pressure sensitive adhesives used in this invention are not
considered to be silicone adhesives which are "silicone rubbers", which
generally refer to non-tacky vulcanized rubber used as structural
adhesives. The most common type of silicone rubber consists of a mixture
of a polydimethysiloxane gum, a filler (such as fumed silica or other
inorganic, non-resinous material), a crosslinker, and optionally, a
catalyst. These structural adhesives are cured to a fully rubberized
state. The silicone pressure sensitive adhesives employed in this
invention are tacky (or sticky) to the touch without the addition of
plasticizers and typically adhere to a substrate after mild pressure is
applied and therefore are referred to as pressure sensitive adhesives. The
silicone pressure sensitive adhesives may be cured or "rubberized" after
being mixed with the cohesive strengthening agent as discussed below.
However, even after the curing, the silicone pressure sensitive adhesive
composition remains tacky.
The process of curing or crosslinking silicone pressure sensitive adhesives
is known in the art. For example, see "Silicone Pressure Sensitive
Adhesives" by D. F. Merrill in the Handbook Of Pressure Sensitive Adhesive
Technology, edited by D. Satas (Van Nostrand Reinhold, Florence, Ky.,
1982), pages 344-352 and "Formulating Silicone Pressure Sensitive
Adhesives For Application Performances" by L. A. Sobieski in Making It
Stick in '86, Advances In Pressure Sensitive Tape Technology, seminar
proceedings (Pressure Sensitive Tape Council, Deerfield, Ill., 1986),
pages 1-5, both sources being hereby incorporated by reference.
Generally, however, for drug delivery applications, the silicone pressure
sensitive adhesive compositions are not crosslinked because either (1) the
crosslinking temperature is too high for the drugs or (2) the additives
needed for crosslinking are nonbiocompatible ingredients. A silicone
pressure sensitive adhesive composition is generally considered not
crosslinked if it can be dissolved in a solvent.
Another difference between silicone pressure sensitive adhesives suitable
for use in the present invention and unsuitable silicone rubbers lies in
the fact that silicone pressure sensitive adhesives are usually fillerless
or contain low amounts, e.g., less than about 5 weight %, of fillers, such
as fumed silica or other inorganic reinforcing fillers known in the
silicone art. On the other hand, silicone rubbers typically contain about
15-35 weight % filler. Fillers are usually not desired in high quantities
in silicone pressure sensitive adhesives, because high quantities often
cause the silicone pressure sensitive adhesives to lose tack and
adhesiveness and to increase in viscosity, making it more difficult to
apply a coating of the silicone pressure sensitive adhesive.
II COHESIVE STRENGTHENING AGENT
The cohesive strengthening agents utilized in the invention are generally
insoluble in an adhesive polymer or solution, and have a mean particle
size ranging from about 0.5 to about 100 microns. The melting point for
the cohesive strengthening agents should be greater than about 100.degree.
C. Specifically, the cohesive strengthening agents useful for the present
invention include those selected from the group consisting of: 1) nonionic
surfactants; 2) fatty acid esters of glycerol; and solid particulate
materials selected from the group consisting of 3) metallic salts of fatty
acids; 4) metallic salts of phosphoric acid; 5) metallic salts of carbonic
acid; 6) polysaccharides; 7) carboxypolymethylene; 8)
polyvinylpyrrolidone; 9)polyvinylalcohol; and 10) amorphous precipitated
silicas having a surface area of between about 10 and about 200 m.sup.2
/g, with a particle size range of between about 0.018 and 100 microns.
These cohesive strengthening agents are individually described below.
1) Nonionic surfactants. Nonionic surfactants which are useful as the
cohesive strengthening agent include those that are not generally soluble
in the silicone pressure sensitive adhesives. Thus, they form a two-phase
composition when mixed with the silicone pressure sensitive adhesive. In
particular, nonionic surfactants having a hydrophilic-lipophilic balance
(HLB) of between 7 and 14 are suitable. A specific example of such a
surfactant is nonylphenoxypoly(ethyleneoxy)ethanol, an ethoxylated alkyl
phenol that conforms generally to the formula:
C.sub.9 H.sub.19 C.sub.6 H.sub.4 (OCH.sub.2 CH.sub.2).sub.n OH
where n has an average value of 9, and is sold under the trademark IGEPAL
Co-630, which is owned by GAF Chemicals Corp., and is available from GAF
Chemicals Corp, of Wayne, N.J. 07470. IGEPAL, Co-630 has an HLB value of
about 13.
2) Fatty acid esters of glycerol. Fatty acid esters of glycerol useful as
the cohesive strengthening agent generally have a high polarity and are
also substantially insoluble in silicone pressure sensitive adhesives.
Examples of such fatty acid esters of glycerol include cottonseed oil,
corn oil, peanut oil, sesame oil, and coconut oil. These oils are oily
liquids at room temperature with the exception of coconut oil which is
semi-solid at room temperature.
3) Metallic salts of fatty acids. Examples of metallic salts of fatty acids
which have been found suitable as cohesive strengthening agents include
calcium stearate, magnesium stearate, and sodium stearate. A suitable
calcium stearate is Calcium Stearate RSN.RTM. 11-4, commercially available
from Mallinckrodt Inc, St. Louis, Mo. 63147, which contains about 9-10.5
weight percent calcium oxide, has a particle size from 1.7 to 60 microns,
and a specific surface area from 5.76 to 7.44 m.sup.2 /g. A suitable
magnesium stearate is commercially available from Mallinckrodt Inc., St.
Louis, Mo. 63147 and has a specific surface area from 2.45-7.93 m.sup.2
/g. Calcium stearate is the preferred stearate of the three stearates due
to its performance in increasing cohesive strength of the silicone
pressure sensitive adhesive.
4) and 5) Metallic salts of phosphoric and carbonic acid. The preferred
metallic salt of phosphoric acid includes dibasic calcium phosphate, while
the preferred metallic salt of carbonic acid is calcium carbonate.
6) Polysaccharides. Examples of polysaccharides which are useful as
cohesive strengthening agents in the present invention include celluloses,
xanthan gum, pectin, guar gum, and karaya gum. Polysaccharides contain
hydroxyl radicals which are believed to be useful for bonding with the
silanol radicals of the silicone pressure sensitive adhesives. Suitable
polysaccharides may be celluloses which can include microcrystalline
cellulose, powdered cellulose, methylcellulose, ethylcellulose, sodium
carboxymethylcellulose. Microcrystalline cellulose has the general formula
(C.sub.6 H.sub.10 O.sub.5).sub.n, where n is about 220, with a molecular
weight of about 36,000, an average particle size of about 20 to about 100
microns, and a specific surface area from about 10 to about 21 m.sup.2 /g.
Powdered cellulose has the general formula of (C.sub.6 H.sub.10
O.sub.5).sub.n, where n is about 1500, with a molecular weight of about
243,000 and a particle size of from about 1 to about 250 microns.
Methylcellulose is a long chain substituted cellulose ether of about
50-1500 anhydroglycose units containing about 26-32 % methoxyl groups.
7) Carboxypolymethylene. Another cohesive strengthening agent thought to be
useful is carboxypolymethylene is also known as "carbomer". Generally, it
is a crosslinked polymer of acrylic acid having about 0.75-2.0 weight
percent polyalkylsucrose having the empirical formula: (C.sub.3 H.sub.4
O.sub.2).sub.x. (C.sub.3 H.sub.5 -sucrose).sub.y with molecular weights
from about 1.times.10.sup.6 to about 4.times.10.sup.6.
8 ) Polyvinylpyrrolidones. Polyvinylpyrrolidones are also thought to be
useful as the cohesive strengthening agent. They generally have the
empirical formula (C.sub.6 H.sub.9 NO).sub.n, with a mean molecular weight
from about 10,000 to about 700,000.
9) Polyvinylalcohol. Furthermore, polyvinylalcohols may be useful as the
cohesive strengthening agent, having the empirical formula (C.sub.2
H.sub.4 O).sub.n, with an average molecular weight of from about 30,000 to
about 200,000, and a melting point of about 228.degree. C.
10) Amorphous precipitated silicas. Amorphous precipitated silicas which
have been found to be especially suitable as the cohesive strengthening
agents of this invention include amorphous precipitated silicas having a
surface area of between about 10 and about 200 m.sup.2 /g, and a particle
size ranging from about 0.018 to about 100 microns. One such commercially
available silica is "SILENE" 732D, available from PPG Industries, Inc.,
Pittsburgh, Pa., owner of the trademark "SILENE". "SILENE" 732D is an
amorphous precipitated hydrated silica product which typically contains
about 88 weight percent silica on a dry basis and about 7 weight percent
water, with an average particle size of about 0.072 microns, a BET surface
area of about 30 m.sup.2 /g, and a pH of from about 8.5 to about 9.
Generally, the cohesive strengthening agents are insoluble in the silicone
pressure sensitive adhesive, thus forming a dispersion or suspension of
cohesive strengthening agent microparticles in the adhesive matrix. In
addition, they are approved pharmaceutical additives. Many of the cohesive
strengthening agents have the ability to hydrogen-bond to the silanol
radicals of the silicone pressure sensitive adhesive due to the presence
of carboxyl or hydroxyl radicals on the cohesive strengthening agents.
Tests have shown that the cohesive strengthening agents of the present
invention increase the viscosity of the silicone pressure sensitive
adhesive at room temperature.
When mixed with the silicone fluid and silicate resin to practice this
invention, the cohesive strengthening agents are desirably employed from
about 1.0 to about 20.0 weight percent and, more desirably, from about 5.0
to about 15.0 weight percent based on the total weight of the silicone
pressure sensitive adhesive composition. The three main components of this
invention may be made by mixing the ingredients in any order. However,
reaction or treatment of the ingredients, e.g., condensing according to
the procedure of the previously mentioned Pail patent or chemically
treating according to the previously mentioned Blizzard et al., etc.
patents, may require completion prior to the addition of the cohesive
strengthening agent.
Referring now to the drawings, FIG. 1 illustrates a tape including a
silicone pressure sensitive adhesive generally denoted by the numeral 10
which comprises a backing substrate 12, a pressure sensitive adhesive
layer 14 and a release liner 16. This figure illustrates the basic
configuration of a tape with a pressure sensitive adhesive made in
accordance with the present invention. Possible uses for this embodiment
are for bandages, wound dressings and medical transfer tapes. Hereinbelow
are described more embodiments, with reference to the other figures.
With reference to the remaining drawings, the silicone pressure sensitive
adhesive compositions of this invention are especially suitable for
assisting in delivering a bioactive agent, such as a drug, to a bioactive
agent-accepting substrate, such as a patient's skin. The silicone pressure
sensitive adhesive compositions of this invention may be employed in three
types of bioactive agent delivery modes. The first mode is a matrix-type
of delivery device for the bioactive agent or drug. The matrix-type
delivery device is usually a dermal patch which delivers the bioactive
agent locally.
As shown in FIG. 2, this matrix-type delivery device is generally shown as
20 and comprises at least three layers. The first layer is a backing
substrate 22 which may be permeable or occlusive to water vapor
transmission from skin. The second layer is a matrix 24 atop at least
portions of the backing substrate. The matrix may be one of two
embodiments. In a first embodiment, as shown in FIG. 2, the matrix is made
up of the silicone, creep resistant, pressure sensitive adhesive. The
adhesive matrix may contain, and is compatible with compositions selected
from the group consisting of drugs, excipients, enhancers, co-solvents,
and mixtures thereof, shown at 26. In a second embodiment (not shown) the
matrix is made up of a polymer. The polymer matrix may contain and is
compatible with compositions selected from the group consisting of drugs,
excipients, enhancers co-solvents, and mixtures thereof. In this second
embodiment, the silicone, creep-resistant, pressure sensitive adhesive is
disposed in a layer atop at least portions of the polymer matrix. The
matrix is between about 1 and about 15 mils thick. The final layer is a
pressure sensitive adhesive release liner 28 contacted on the matrix. The
liner is between about 1 and 15 mils thick and preferably between about 5
and 10 mils thick.
The matrix-type drug delivery device as shown in FIG. 2 may include various
drugs selected from the group consisting of cardiovascular agents,
antiarrthymic agents, antianginal agents, antibiotics, antifungals,
antimicrobials, antihypertensives, analgesics, local anesthetics,
contraceptives, hormonal supplements, anti-smoking agents, appetite
suppressants, hypnotics, anxiolytics and mixtures thereof. Also included
may be co-solvents, enhancers and excipients selected from the group
consisting of fatty acid esters, polyols, surfactants, terpenes, glycerol
esters, polyethylene glycol esters, amides, sulfoxides, lactams, nonionic
surfactants, sorbitan esters and mixtures thereof.
As shown in FIGS. 3 and 4, the second mode of delivery is a reservoir-type
transdermal drug delivery device. Generally, this mode is applied to the
skin to deliver the bioactive agent to treat systemic disease. FIG. 3
shows a liquid containing reservoir-type drug delivery device generally
denoted as numeral 30 which comprises a minimum of five layers from top to
bottom. The first layer 32 is a backing substrate. The second layer 34
includes a liquid reservoir which may contain bioactive agents or other
compositions selected from the group consisting of drugs, excipients,
enhancers, co-solvents, and mixtures thereof. The reservoir-type
transdermal drug delivery device as shown in FIG. 3 may include various
drugs selected from the group consisting of cardiovascular agents,
antiarrthymic agents, antianginal agents, antibiotics, antifungals,
antimicrobials, antihypertensives, analgesics, local anesthetics,
contraceptives, hormonal supplements, anti-smoking agents, appetite
suppressants, hypnotics, and anxiolytics, and mixtures thereof. Also
included may be co-solvents, enhancers and excipients selected from the
group consisting of fatty acid esters, polyols, surfactants, terpenes,
glycerol esters, polyethylene glycol esters, amides, sulfoxides, lactams,
nonionic surfactants, sorbitan esters and mixtures thereof. The third
layer 36 is a rate controlling membrane positioned such that the reservoir
34 is sealed between the backing substrate 32 and the rate controlling
membrane 36. This membrane acts as the rate controlling mechanism for the
delivery of the liquid drug(s), co-solvents, enhancers and excipients,
from the reservoir 34. The fourth layer 38 is a pressure sensitive
adhesive which should be compatible with any of the drugs, excipients and
co-solvents present in the liquid reservoir. The fifth layer 40 is a
silicone pressure sensitive adhesive release liner. The release liner is
between about 1 and 15 mils thick and preferably between about 1 and 3
mils thick. The bioactive agent of the liquid reservoir 34 may then pass
from the reservoir through the attached rate controlling membrane 36 and
the adhesive layer 38, and then into the skin of the patient to deliver
the drug.
FIG. 4 shows a solid state reservoir-type transdermal drug delivery device.
This device is denoted generally by numeral 50 and includes a first layer
52 which is a backing substrate. The second layer constitutes a solid
reservoir 54 which may contain one or more bioactive agents of other
compositions selected from the group consisting of drugs, excipients and
co-solvents indicated at 56. The same drugs, excipients and co-solvents
may be used as the liquid containing reservoir as shown in FIG. 3. The
third layer of FIG. 4 is a pressure sensitive adhesive layer 58 which is
compatible with the drugs, excipients and co-solvents. The fourth layer is
a release liner 60. The liner 60 averages between 1 and 15 mils thick and
is preferably between 1 and 3 mils thick. An additional layer (not shown)
comprising a rate controlling membrane may be positioned between the solid
reservoir 54 and the adhesive 58 in order to control the rate of delivery
of the drug(s) and excipient(s). The surface area of both the matrix-type
and reservoir-type delivery device generally ranges between 1.0 and 700
cm.sup.2. This range is not to be construed as limiting, as any size
device may utilized with the PSA of the present invention.
The adhesive layer of both the matrix-type and reservoir-type delivery
devices, shown in FIGS. 2-4, may include one or a combination of
co-solvents, enhancers and excipients which increase solubility of the
drug in the adhesive matrix, enhance skin permeation to the drug, or
enhance drug release from the system.
The presence of the cohesive strengthening agents in the adhesives of the
present invention permits the use of drugs, excipients, co-solvents, and
skin penetration enhancers which usually adversely effect the cohesive
strength of prior art silicone pressure sensitive adhesives not containing
any cohesive strengthening agents. Preferably, the cohesive strengthening
agents have a melting point of greater than 40.degree. C. and a Hildebrand
solubility parameter between about 5 and 15 cal.sup.1/2 /cm.sup.3/2. The
addition of the cohesive strengthening agents taught herein significantly
reduces flow and improves creep resistance of silicone adhesives utilized
to deliver a bioactive agent, such as a drug to a substrate, such as a
patient's skin.
The following examples of the invention are meant to be illustrative only
and should not be construed as limiting the invention which is properly
delineated in the appended claims. In the following examples, all parts
and percentages are by weight unless otherwise specified.
EXAMPLES
The basic silicone pressure sensitive adhesive prepared without the
cohesive strengthening agent may be prepared as follows. Once this basic
formulation was prepared, Examples A-F were made by adding various
cohesive strengthening agents, testing them and tabulating the results.
The basic adhesive formulations include two main components: a silicate
resin and a silicone fluid. In this preparation, we will be discussing
Adhesives I, II, and III. They are made from various combinations of
Resins A-1, A-2 and trimethylsiloxy end-blocked polydimethylsiloxane
(PDMS) Fluid A as described below.
Resin A-1 is a xylene solution of a resinous copolymeric siloxane prepared
from 45 parts of sodium silicate and 20 parts of Me.sub.3 SiCl
(Me.dbd.CH.sub.3) according to the method of U.S. Pat. No. 2,676,182 to
Daudt, et al., which is hereby incorporated by reference, and contains
Me.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units in a ratio of
approximately 0.75:1.0, and has a nonvolatile content typically about
69-71%, an acid number in the range of 0.3 to 1.4, a viscosity in the
range of 10-14 centipoise at 25.degree. C. in hexane solution, and a
silicon-bonded hydroxyl content of about 2.5 weight percent based on a
100% non-volatilized content and a number average molecular weight range
of between 2,000 to 4,000.
Resin A-2 is Resin A-1 which has been devolatilized (100% non-volatile
content).
PDMS Fluid A is a homogeneous mixture of a hydroxyl end-blocked
polydimethylsiloxane having a number-average molecular weight range of
between 40,000 to 100,000 with minor amounts of cyclic
polydimethylsiloxane having degrees of polymerization between 4 and 30,
the mixture having a viscosity between 12,000 and 15,000 centipoise as
measured using a Brookfield Viscometer Model HAF with spindle #3 at 10
RPM's.
Adhesive I, a 50 wt % solution of a high silanol containing silicone
pressure sensitive adhesive in xylene solvent was prepared by
homogeneously mixing 34.0 parts by weight of Resin A-2, 34.0 parts by
weight xylene, and 31.0 parts by weight PDMS Fluid A. The mixture was then
heated to 100.degree. C. and anhydrous ammonia was passed through the
mixture at a rate of 11 ml/min/lb of non-volatile component of the mixture
for approximately 2 hours. The mixture was then stripped to greater than
99% non-volatile content and redissolved in hexane to a non-volatile
content of 50 wt %.
Adhesive II, a 50 wt % solution of a low silanol containing silicone
pressure sensitive adhesive in xylene solvent, was prepared by
homogeneously mixing 34.0 parts by weight of Resin A- | | |
