U.S. patent application number 10/891885 was filed with the patent office on 2008-03-13 for antimicrobial coating for inhibition of bacterial adhesion and biofilm formation.
This patent application is currently assigned to Bacterin Inc.. Invention is credited to Guy Cook, Matt Trebella.
Application Number | 20080063693 10/891885 |
Document ID | / |
Family ID | 35320670 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080063693 |
Kind Code |
A1 |
Cook; Guy ; et al. |
March 13, 2008 |
Antimicrobial coating for inhibition of bacterial adhesion and
biofilm formation
Abstract
The present invention provides antimicrobial coatings for
coating substrate surfaces, particularly medical devices, for
preventing bacterial adhesion and biofilm formation by inhibiting
microbial growth and proliferation on the coating surface. The
antimicrobial coatings are composed of a hydrogel and a bioactive
agent including a substantially water-insoluble antimicrobial
metallic material that is solubilized within the coating.
Antimicrobial coating formulations for obtaining such coatings, and
coating methods are also described.
Inventors: |
Cook; Guy; (Bozeman, MT)
; Trebella; Matt; (Bozeman, MT) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
Bacterin Inc.
|
Family ID: |
35320670 |
Appl. No.: |
10/891885 |
Filed: |
July 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60566576 |
Apr 29, 2004 |
|
|
|
Current U.S.
Class: |
424/443 ;
424/618; 523/122 |
Current CPC
Class: |
A61L 31/10 20130101;
A01N 59/16 20130101; A61L 2300/406 20130101; A61L 27/34 20130101;
A61L 27/54 20130101; A01N 59/16 20130101; A61L 2300/104 20130101;
A61L 31/16 20130101; A61L 29/085 20130101; A61L 2300/606 20130101;
C09D 5/14 20130101; B05D 3/104 20130101; B05D 3/142 20130101; A61L
29/16 20130101; A01N 25/10 20130101; A01N 25/10 20130101 |
Class at
Publication: |
424/443 ;
424/618; 523/122 |
International
Class: |
C09D 5/16 20060101
C09D005/16; A61K 33/38 20060101 A61K033/38 |
Claims
1. An antimicrobial coating for inhibiting microbial adhesion
comprising: a hydrogel layer comprising a three-dimensional
hydrophilic polymer network; and a bioactive agent comprising at
least one substantially water-insoluble antimicrobial metallic
material that is solubilized within the hydrogel layer.
2. The antimicrobial coating of claim 1, wherein the hydrogel layer
is selected from the group consisting of polyvinyl alcohol,
polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid,
polyhydroxyethylmethacrylate, polyvinyl alcohol-glycine co-polymer,
polyvinyl alcohol-lysine co-polymer, and combinations and
copolymers thereof.
3. The antimicrobial coating of claim 1 wherein the hydrogel layer
comprises a polyvinyl alcohol.
4. The antimicrobial coating of claim 1 wherein the bioactive agent
comprises a synthetic or naturally occurring antibiotic, an
antibacterial compound, or combinations thereof.
5. The antimicrobial coating of claim 1, wherein the substantially
water-insoluble antimicrobial metallic material comprises a metal,
a metal alloy, a metal salt, a metal complex, or combinations
thereof.
6. The antimicrobial coating of claim 1, wherein the substantially
water-insoluble antimicrobial metallic material is selected from
the group consisting of silver halides, silver sulfazines, silver
sulfadiazines silver sulfonamides silver sulfonylureas and
combinations thereof.
7. The antimicrobial coating of claim 5 wherein the substantially
water-insoluble antimicrobial metallic material comprises silver
sulfadiazine.
8. The antimicrobial coating of claim 1 further comprising a
stabilizing agent selected from the group consisting of
antioxidants, photostabilizers, free-radical scavengers and
combinations thereof.
9. The antimicrobial coating of claim 8 wherein the stabilizing
agent comprises an antioxidant.
10. The antimicrobial coating of claim 8, wherein the stabilizing
agent comprises a photostabilizer.
11. The antimicrobial coating of claim 8, wherein the antioxidant
is selected from the groups consisting of a lactone, phenolic,
phosphite, thioester, hindered amine, hindered benozoate
benzoate,hindered phenolic, and combinations thereof.
12. The antimicrobial coating of claim 8, wherein the antioxidant
is selected from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-thiazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-thiazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
13. The antimicrobial coating of claim 8, wherein the
photostabilizer comprises a benzoate, benzophenone, benzotriazole,
cyanoacrylate, organo nickel or organo zinc.
14. The antimicrobial coating of claim 8, wherein the stabilizing
agent is selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate or mixtures thereof.
15. The antimicrobial coating of claim 8, wherein the stabilizing
agent comprises TiO.sub.2.
16. The antimicrobial coating of claim 1 wherein the
three-dimensional hydrophilic polymer network is a cross-linked
matrix comprising ionic or covalent chemical bonds, a cryogel or an
interpenetrating polymer network.
17. The antimicrobial coating of claim 16 wherein the
three-dimensional hydrophilic polymer network has a cross-linked
matrix comprising covalent bonds.
18. The antimicrobial coating of claim 1 that inhibits biofilm.
19. A coating composition for providing an antimicrobial coating
for inhibiting microbial adhesion comprising: a hydrophilic
polyfunctional polymer; and a bioactive agent comprising at least
one substantially water-insoluble antimicrobial metallic material
that is solubilized in the coating composition.
20. The coating composition of claim 19, wherein the hydrophilic
polyfunctional polymer is selected from the group consisting of
polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine,
polyacrylic acid, polyhydroxyethylmethacrylate, polyvinyl
alcohol-glycine co-polymer, and polyvinyl alcohol-lysine
co-polymer, and combinations and copolymers thereof.
21. The coating composition of claim 19, wherein the hydrophilic
polyfunctional polymer comprises a polyvinyl alcohol.
22. The coating composition of claim 19, wherein the bioactive
agent is a synthetic or naturally occurring antibiotic, an
antibacterial compound, or combinations thereof.
23. The coating composition of claim 19, wherein the
water-insoluble antimicrobial metallic material comprises a metal,
a metal alloy, a metal salt, a metal complex, or combinations
thereof.
24. The coating composition of claim 19, wherein the
water-insoluble antimicrobial metallic material is selected from
the group consisting of silver halides, silver sulfazines, silver
sulfadiazines silver sulfonamides silver sulfonylureas and
combinations thereof.
25. The coating composition of claim 19, wherein the
water-insoluble antimicrobial metallic material comprises silver
sulfadiazine.
26. The coating composition of claim 19 further comprising a
stabilizing agent.
27. The coating composition of claim 26, wherein the stabilizing
agent is selected from the group consisting of antioxidants,
free-radical scavengers, and combinations thereof.
28. The coating composition of claim 26, wherein the stabilizing
agent comprises an antioxidant.
29. The coating composition of claim 26, wherein the stabilizing
agent comprises a photostabilizer.
30. The coating composition of claim 28, wherein the antioxidant is
a lactone, phenolic, phosphite, thioester, hindered amine, hindered
benzoate, hindered phenolic, and combinations thereof.
31. The coating composition of claim 28, wherein the antioxidant is
selected from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
32. The coating composition of claim 29, wherein the
photostabilizer is selected from the groups consisting of benzoate,
benzophenone, benzotriazole, cyanoacrylate, organo nickel, organo
zinc, and combinations thereof.
33. The coating composition of claim 26, wherein the stabilizing
agent is selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate and mixtures thereof.
34. The coating composition of claim 26, wherein the stabilizing
agent comprises TiO.sub.2.
35. A coating composition for providing an antimicrobial coating
for inhibiting biofilm comprising: a hydrophilic polyfunctional
polymer; and a bioactive agent comprising at least one
substantially water-insoluble antimicrobial metallic material that
is solubilized in the coating composition.
36. An antimicrobial coating for inhibiting microbial adhesion on a
medical device comprising: a hydrogel layer comprising a
three-dimensionally cross-linked polyvinyl alcohol network; and a
bioactive agent comprising silver sulfadiazine that is solubilized
within the hydrogel layer.
37. The antimicrobial coating of claim 36 further comprising a
stabilizing agent.
38. The antimicrobial coating of claim 37, wherein the stabilizing
agent is selected from the group consisting of antioxidants,
photostabilizers, free readical scavengers, and combinations
thereof.
39. The antimicrobial coating of claim 37, wherein the stabilizing
agent comprises TiO.sub.2.
40. An antimicrobial coating for inhibiting biofilm on a medical
device comprising: a hydrogel layer comprising a
three-dimensionally cross-linked polyvinyl alcohol network; and a
bioactive agent comprising silver sulfadiazine that is solubilized
within the hydrogel layer.
41. The antimicrobial coating of claim 40 further comprising a
stabilizing agent.
42. The antimicrobial coating of claim 41, wherein the stabilizing
agent is selected from the group consisting of antioxidants,
photostabilizers, free readical scavengers, and combinations
thereof.
43. The antimicrobial coating of claim 41, wherein the stabilizing
agent comprises TiO.sub.2.
44. A method for forming an antimicrobial coating for inhibiting
microbial adhesion on a substrate material, the method comprising:
depositing at least one layer of a coating material comprising a
hydrophilic polyfunctional polymer and a bioactive agent including
at least one antimicrobial substantially water-insoluble metallic
compound solubilized therein on a substrate material; at least
partially drying the coating material layer; and reacting the
coating material layer with a cross-linking agent to form a surface
immobilized, three-dimensional hydrogel network on the substrate
material.
45. The method of claim 44 wherein the coating material further
comprises a stabilizing agent.
46. The method of claim 45, wherein the stabilizing agent is
selected from the group consisting of antioxidants,
photostabilizers, free-radical scavengers, and combinations
thereof.
47. The method of claim 45, wherein the stabilizing agent comprises
TiO.sub.2.
48. The method of claim 44 further comprising pre-treating the
substrate material and chemically grafting a hydrophilic
polyfunctional material on the substrate material prior to
depositing the coating material layer.
49. A method of inhibiting bacterial adhesion on a substrate
material by providing a surface coating comprising: a hydrogel
layer comprising a three-dimensional hydrophilic polymer network;
and a bioactive agent comprising at least one substantially
water-insoluble antimicrobial metallic material that is solubilized
within the hydrogel layer.
50. A method of inhibiting biofilm by providing a surface coating
on a substrate material comprising: a hydrogel layer comprising a
three-dimensional hydrophilic polymer network; and a bioactive
agent comprising at least one substantially water-insoluble
antimicrobial metallic material that is solubilized within the
hydrogel layer.
51. The method of claim 49 or 50, wherein the substrate material
comprises a metallic material, ceramic, glass, or natural or
synthetic polymers.
52. The method of claim 49 or 50, wherein the substrate material is
part of a medical device or healthcare product.
53. The method of claim 52, wherein the medical device comprises a
catheter, wound drain, needle-less connector, stent or a component
thereof.
54. A method of inhibiting bacterial adhesion and biofilm formation
on a medical device or healthcare product in a physiological
environment by providing a surface coating on a substrate material
comprising: a hydrogel layer comprising a three-dimensional
hydrophilic polymer network; and a bioactive agent comprising at
least one substantially water-insoluble antimicrobial metallic
material that is solubilized within the hydrogel layer.
55. The method of claim 54, wherein the substrate material is part
of a medical device or healthcare product.
56. The method of claim 55, wherein the medical device comprises a
catheter, wound drain, needle-less connector, stent or a component
thereof.
57. A method of manufacturing a coating composition for providing
an antimicrobial coating for inhibiting microbial adhesion, the
method comprising: (i) heating an aqueous acidic solution; (ii)
adding a substantially water-insoluble antimicrobial metallic
material to the heated aqueous acidic solution so as to completely
dissolve the substantially water-insoluble antimicrobial metallic
material; and (iii) adding a hydrophilic polyfunctional polymer to
the heated aqueous acidic solution comprising the dissolved
substantially water-insoluble antimicrobial metallic material so as
to maintain the substantially water-insoluble antimicrobial
metallic material in a solubilized form in the coating
composition.
58. The method of claim 57 wherein the solubilized form of the
substantially water-insoluble antimicrobial metallic material in
the heated aqueous acidic solution is a homogeneous or
substantially homogeneous aqueous phase, wherein the substantially
water-insoluble antimicrobial metallic material and the hydrophilic
polyfunctional polymer are homogeneously dispersed in the coating
composition.
59. The method of claim 57, wherein the hydrophilic polyfunctional
polymer is selected from the group consisting of polyvinyl alcohol,
polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid,
polyhydroxyethylmethacrylate, polyvinyl alcohol-glycine co-polymer,
polyvinyl alcohol-lysine co-polymer, and combinations and
copolymers thereof.
60. The method of claim 57, wherein the hydrophilic polyfunctional
polymer comprises a polyvinyl alcohol.
61. The method of claim 57, wherein the substantially
water-insoluble antimicrobial metallic material is a synthetic or
naturally occurring antibiotic, an antibacterial compound, or
combinations thereof.
62. The method of claim 57, wherein the substantially
water-insoluble antimicrobial metallic material comprises a metal,
a metal alloy, a metal salt, a metal complex, or combinations
thereof.
63. The method of claim 57, wherein the substantially
water-insoluble antimicrobial metallic material is selected from
the group consisting of silver halides, silver sulfazines, silver
sulfadiazines, silver sulfonamides, silver sulfonylureas, and
combinations thereof.
64. The method of claim 57, wherein the substantially
water-insoluble antimicrobial metallic material comprises silver
sulfadiazine.
65. The method of claim 57 further comprising adding a stabilizing
agent.
66. The method of claim 65 wherein the stabilizing agent is
dissolved in the coating composition to form a homogeneous phase or
is suspended in the coating composition as a microparticulate
dispersion.
67. The method of claim 65, wherein the stabilizing agent is
selected from the group consisting of antioxidants,
photostabilizers, free-radical scavengers, and combinations
thereof.
68. The method of claim 65, wherein the stabilizing agent comprises
an antioxidant.
69. The method of claim 65, wherein the stabilizing agent comprises
a photostabilizer.
70. The method of claim 67, wherein the antioxidant is selected
from the groups consisting of lactone, phenolic, phosphite,
thioester, hindered amine, hindered benozoate benzoate, hindered
phenolic, and combinations thereof.
71. The method of claim 68, wherein the antioxidant is selected
from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
72. The method of claim 69, wherein the photostabilizer is a
benzoate, benzophenone, benzotriazole, cyanoacrylate, organo nickel
or organo zinc.
73. The method of claim 65, wherein the stabilizing agent is
selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate and mixtures thereof.
74. The method of claim 65, wherein the stabilizing agent comprises
TiO.sub.2.
75. A method of manufacturing a coating composition for providing
an antimicrobial coating for inhibiting microbial adhesion, the
method comprising: (i) heating an aqueous acidic solution; (ii)
adding a substantially water-insoluble antimicrobial metallic
material to the heated aqueous acidic solution so as to completely
dissolve the substantially water-insoluble antimicrobial metallic
material; and (iii) adding a mixture of a hydrophilic
polyfunctional polymer and a stabilizing agent to the heated acidic
solution comprising the dissolved substantially water-insoluble
antimicrobial metallic material so as to maintain the substantially
water-insoluble antimicrobial metallic material in a solubilized
form in the coating composition.
76. The method of claim 75 wherein the solubilized form of the
substantially water-insoluble antimicrobial metallic material in
the heated aqueous acidic solution is a homogeneous or
substantially homogeneous aqueous phase, wherein the substantially
water-insoluble antimicrobial metallic material and the hydrophilic
polyfunctional polymer are homogeneously dispersed in the coating
solution.
77. The method of claim 75, wherein the hydrophilic polyfunctional
polymer is selected from the group consisting of polyvinyl alcohol,
polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid,
polyhydroxyethylmethacrylate, polyvinyl alcohol-glycine co-polymer,
and polyvinyl alcohol-lysine co-polymer, and combinations and
copolymers thereof.
78. The method of claim 75, wherein the hydrophilic polyfunctional
polymer comprises a polyvinyl alcohol.
79. The method of claim 75, wherein the substantially
water-insoluble antimicrobial metallic material is a synthetic or
naturally occurring antibiotic, an antibacterial compound, or
combinations thereof.
80. The method of claim 75, wherein the substantially
water-insoluble antimicrobial metallic material comprises a metal,
a metal alloy, a metal salt, a metal complex, or combinations
thereof.
81. The method of claim 75, wherein the substantially
water-insoluble antimicrobial metallic material is selected from
the group consisting of silver halides, silver sulfazines, silver
sulfadiazines, silver sulfonamides, silver sulfonylureas, and
combinations thereof.
82. The method of claim 75, wherein the substantially
water-insoluble antimicrobial metallic material comprises silver
sulfadiazine.
83. The method of claim 75 wherein the stabilizing agent is
dissolved in the coating composition to form a homogeneous phase or
is suspended in the coating composition as a microparticulate
dispersion.
84. The method of claim 75, wherein the stabilizing agent is
selected from the group consisting of antioxidants,
photostabilizers, free-radical scavengers, and combinations
thereof.
85. The method of claim 75, wherein the stabilizing agent comprises
an antioxidant.
86. The method of claim 75, wherein the stabilizing agent comprises
a photostabilizer.
87. The method of claim 85, wherein the antioxidant is selected
from the group consisting of lactone, phenolic, phosphite,
thioester, hindered amine, hindered benozoate, hindered phenolic,
and combinations thereof.
88. The method of claim 85, wherein the antioxidant is selected
from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
89. The method of claim 86, wherein the photostabilizer comprises a
benzoate, benzophenone, benzotriazole, cyanoacrylate, organo nickel
or organo zinc.
90. The method of claim 75, wherein the stabilizing agent is
selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate and mixtures thereof.
91. The method of claim 75, wherein the stabilizing agent comprises
TiO.sub.2.
92. A method of coating a substrate material with an antimicrobial
coating for inhibiting microbial adhesion, the method comprising:
(i) depositing at least one layer of a coating composition
comprising a hydrophilic polyfunctional polymer and at least one
bioactive agent comprising at least one substantially
water-insoluble antimicrobial metallic compound solubilized therein
on a substrate material; (ii) at least partially drying the at
least one layer of the coating composition; and (iii) crosslinking
the hydrophilic polyfunctional polymer to form a surface
immobilized, three-dimensional hydrogel network on the substrate
material.
93. The method of claim 92, wherein the coating composition further
comprises a stabilizing agent.
94. The method of claim 93, wherein the stabilizing agent is
selected from the group consisting of antioxidants,
photostabilizers, free-radical scavengers, and combinations
thereof.
95. The method of claim 93, wherein the stabilizing agent comprises
an antioxidant.
96. The method of claim 93, wherein the stabilizing agent comprises
a photostabilizer.
97. The method of claim 95, wherein the antioxidant selected from
the group consisting of lactone, phenolic, phosphite, thioester,
hindered amine, hindered benozoate, hindered phenolic, and
combinations thereof.
98. The method of claim 95, wherein the antioxidant is selected
from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
99. The method of claim 96, wherein the photostabilizer is a
benzoate, benzophenone, benzotriazole, cyanoacrylate, organo nickel
or organo zinc.
100. The method of claim 93, wherein the stabilizing agent is
selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate and mixtures thereof.
101. The method of claim 93, wherein the stabilizing agent
comprises TiO.sub.2.
102. A method of coating a substrate material with an antimicrobial
coating for inhibiting microbial adhesion, the method comprising:
(i) pre-treating the surface of a substrate material with a primer
layer or a surface oxidant; (ii) chemically grafting a hydrophilic
polyfunctional compound onto the substrate material; (iii)
depositing at least one layer of a coating composition comprising a
hydrophilic polyfunctional polymer and at least one bioactive agent
comprising at least one substantially water-insoluble antimicrobial
metallic compound solubilized therein on a substrate material; (iv)
at least partially drying the at least one layer of coating
composition; and (v) crosslinking the hydrophilic polyfunctional
polymer to form a surface immobilized, three-dimensional hydrogel
network on the substrate material.
103. The method of claim 102 wherein pre-treating the surface of
the substrate material comprises coating the surface of the
substrate material with the primer layer on which the antimicrobial
coating is deposited.
104. The method of claim 102 wherein pre-treating the surface of
the substrate material with a surface oxidant comprises subjecting
the substrate material to an oxidation process that is followed by
a chemical grafting reaction rendering the surface hydrophilic, and
compatible with the coating.
105. The method of claim 102 wherein the surface oxidant comprises
plasma.
106. The method of claim 102 wherein the hydrophilic polyfunctional
compound comprises an aliphatic alcohol.
107. The method of claim 102 wherein the hydrophilic polyfunctional
polymer is selected from the group consisting of polyvinyl alcohol,
polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid,
polyhydroxyethylmethacrylate, polyvinyl alcohol-glycine co-polymer,
polyvinyl alcohol-lysine co-polymer, and combinations and
copolymers thereof.
108. The method of claim 102 wherein the hydrophilic polyfunctional
polymer comprises polyvinyl alcohol.
109. The method of claim 102 wherein the bioactive agent is a
synthetic or naturally occurring antibiotic, an antibacterial
compound, or combinations thereof.
110. The method of claim 102 wherein the substantially
water-insoluble antimicrobial metallic compound comprises a metal,
a metal alloy, a metal salt, a metal complex, or combinations
thereof.
111. The method of claim 102 wherein the substantially
water-insoluble antimicrobial metallic compound is selected from
the group consisting of silver halides, silver sulfazines, silver
sulfadiazines, silver sulfonamides, silver sulfonylureas, and
combinations thereof.
112. The method of claim 102 wherein the substantially
water-insoluble antimicrobial metallic compound comprises silver
sulfadiazine.
113. The method of claim 102 wherein the coating composition
further comprises a stabilizing agent.
114. The method of claim 113 wherein the stabilizing agent
comprises an antioxidant or a photostabilizer.
115. The method of claim 113 wherein the stabilizing agent
comprises an antioxidant.
116. The method of claim 113 wherein the stabilizing agent
comprises a photostabilizer.
117. The method of claim 115 wherein the antioxidant is selected
from the group consisting of lactone, phenolic, phosphite,
thioester, hindered amine, hindered benozoate or hindered phenolic,
and combinations thereof.
118. The method of claim 115 wherein the antioxidant is selected
from the group consisting of:
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione;
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)i-
mino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]];
3,5-di-t-butyl-4-hydroxybenzoic acid hexadecyl ester;
alpha-tocopherol; alpha-tocopherol polyetheylene glycol succinate;
alpha-lipoic acid; butylated hydroxy toluene, sodium ascorbate, and
combinations thereof.
119. The method of claim 116 wherein the photostabilizer is
selected from the group consisting of benzoate, benzophenone,
benzotriazole, cyanoacrylate, organo nickel or organo zinc.
120. The method of claim 113 wherein the stabilizing agent is
selected from the group consisting of TiO.sub.2, WO.sub.3,
magnesium silicate and mixtures thereof.
121. The method of claim 113 wherein the stabilizing agent
comprises TiO.sub.2.
122. A method of manufacturing a coating composition for providing
an antimicrobial coating for inhibiting microbial adhesion, the
method comprising: (i) heating an aqueous acidic solution
comprising nitric acid; (ii) adding silver sulfadiazine to the
heated aqueous acidic solution so as to completely dissolve the
silver sulfadiazine; and (iii) adding polyvinyl alcohol to the
heated aqueous acidic solution comprising the silver sulfadiazine
so as to maintain the silver sulfadiazine in a solubilized form in
the coating composition.
123. The method of claim 122 wherein the aqueous acidic solution
comprising nitric acid is heated to a temperature ranging from
about 65 to about 70.degree. C.
124. The method of claim 122 wherein the aqueous acidic solution
comprising nitric acid has a nitric acid concentration of about
70%.
125. The method of claim 122 wherein the polyvinyl alcohol has a
molecular weight ranging from about 89,000 to about 98,000
daltons.
126. A method of manufacturing a coating composition for providing
an antimicrobial coating for inhibiting microbial adhesion, the
method comprising: (i) heating an aqueous acidic solution
comprising nitric acid; (ii) adding silver sulfadiazine to the
heated aqueous acidic solution so as to completely dissolve the
silver sulfadiazine; and (iii) adding a mixture of a polyvinyl
alcohol and micronized titanium dioxide to the heated acidic
solution comprising the dissolved silver sulfadiazine so as to
maintain the silver sulfadiazine in a solubilized form in the
coating composition.
127. The method of claim 126 wherein the aqueous acidic solution
comprising nitric acid is heated to a temperature ranging from
about 65 to about 70.degree. C.
128. The method of claim 126 wherein the aqueous acidic solution
comprising nitric acid has a nitric acid concentration of about
70%.
129. The method of claim 126 wherein the polyvinyl alcohol has a
molecular weight ranging from about 89,000 to about 98,000
daltons.
130. The method of claim 126 wherein the micronized titanium
dioxide has a particle size of about 1 .mu.m.
131. An antimicrobial coating for inhibiting microbial adhesion
comprising: a hydrogel layer comprising a three-dimensional
polyvinyl alcohol network; and a bioactive agent comprising silver
sulfadiazine that is solubilized within the hydrogel layer.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/566,576, filed on Apr. 29, 2004. The entire
teachings of the above application is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an antimicrobial coating
for coating a substrate surface, particularly medical devices that
are likely to become contaminated or have become contaminated with
microorganisms as a result of bacterial adhesion and proliferation
and methods for preventing biofilm formation by inhibiting
microbial growth and proliferation on the surface of medical
devices.
BACKGROUND OF THE INVENTION
[0003] Colonization of bacteria on the surfaces of medical devices
and healthcare products, particularly in implanted devices, result
in serious patient problems, including the need to remove and/or
replace the implanted device and to vigorously treat secondary
infection conditions. Considerable efforts, therefore, have been
directed toward preventing such colonization by the use of
antimicrobial agents, such as antibiotics, that are bound to the
surface of the materials used in such medical devices. The focus of
prior attempts has been to produce a sufficient bacteriostatic or
bactericidal action to prevent microbial colonization on the device
surface.
[0004] As a defense against antimicrobial agents that would affect
their survival and proliferation, many surface adhered
microorganisms form a defense layer comprising a
muco-polysaccharide film called biofilm. Formation of biofilms on
the surface of medical devices can be detrimental to the integrity
of the medical device, present health risks, and prevent sufficient
flow through the lumens of medical devices. Furthermore, biofilms
formed on the device surface recruit non-adhered or "sessile"
microorganisms from the device environment, such as urine or blood,
and enable their propagation. Particulate biofilm matter that
periodically detach from the surface of a medical device or
healthcare product, for example, therefore provide, a continued
source of pathologically infectious microorganisms that can
contaminate the physiological environment in which the medical
device or healthcare product is in contact with, that can result in
serious secondary infections in patients.
[0005] Although coating or cleaning medical devices with
antimicrobial agents, such as antibiotics or antiseptics, can be
effective in killing or inhibiting growth of free-floating or
"planktonic" organisms not adhered to the device surface, such
antimicrobial agents are generally much less active against the
microorganisms that are deeply embedded within the biofilm due to
their inability to penetrate the biofilm. The failure of the
antimicrobial agents to sufficiently remove the microorganisms is
therefore largely due to the protective effect of the biofilm which
prevents diffusion of antimicrobial deep into the biofilm layer to
eliminate the microorganisms proliferating within therein.
[0006] Biofilm associated problems experienced with implantable
medical devices such as catheters, particularly catheters designed
for urinary tract infections, pose a significant risk for
catheterized patients of acquiring secondary infection such as
nosocomial infection in a hospital environment. Such infections can
result in prolonged hospital stay, administration of additional
antibiotics, and increased cost of post-operative hospital care. In
biofilm mediated urinary-tract infections, bacteria are believed to
gain access to the catheterized bladder either by migration from
the collection bag, the catheter by adhering to and proliferating
on the material constituting the catheter material, or by ascending
the periurethral space outside the catheter. Although, the use of
antimicrobially coated catheters wherein antibiotic agents or
antimicrobial compounds are dispersed within the coating have been
reported to reduce the incidence of catheter associated
bacteriuria, such coatings have proven to be largely ineffective in
preventing bacterial adhesion and biofilm formation on the catheter
surface for extended periods, and therefore do not sufficiently
retard the onset of bacterial infection.
[0007] The use of silver compounds in antimicrobial coatings for
medical devices is known in the art. The antiseptic activity of
silver compounds is a well-known property that has been utilized
for many years in topical formulations. Silver is known to possess
antibacterial properties and is used topically either as a metal or
as silver salts due to their ability to generate bactericidal
amounts of silver ions (Ag.sup.+), in which in this bioactive
species, is released to the contacting environment. The
bactericidal and fungistatic effect of the silver ion have been
extensively utilized clinically; for example, silver nitrate, which
is readily soluble (highly ionizable) in water, at concentrations
of 0.5-1% exhibits disinfectant properties and is used for
preventing infections in burns or for prophylaxis of neonatal
conjunctivitis. Silver nitrate however, can cause toxic side
effects at these concentrations, and does cause discoloration of
the skin (Argyria).
[0008] A specific advantage in using the silver ion as
antibacterial agent is the inability of bacteria to acquire
tolerance to the silver ion, which is in contrast to many types of
antibiotics. Unlike antibiotics, the potential for bacterial to
become silver ion resistant is therefore quite low. However, it is
also recognized that silver compounds capable of providing
bactericidal levels of silver ion have reduced photostability, and
tend to discolor in presence of light and or heat as a result of
photoreduction of Ag.sup.+ ion to metallic silver. Furthermore,
commonly used terminal sterilization processes such as gamma or
e-beam radiation of coatings or formulations containing such silver
compounds results in discoloration and loss of activity in such
materials, whether it is in the form a cream, gel or as a coating
on a medical device. Silver compounds that have extremely low
solubility in aqueous solutions such as silver iodide
(K.sub.sp.about.10.sup.-18) and silver sulfide
(K.sub.sp.about.10.sup.-52) on the other hand, are relatively more
photostable but poorly ionized, and hence cannot provide
bactericidal levels of silver ions into the contacting environment.
They are therefore, either weakly antibacterial (bacteriostatic),
or inert.
[0009] Silver compounds with relatively low aqueous solubilities
but sufficient ionization such as silver oxide (Ag.sub.2O) and
silver chloride (AgCl)(K.sub.sp 10.sup.-8 to 10.sup.-9) are weakly
antibacterial and have been used in antimicrobial coatings.
However, they are incorporated as micronized particles suspended
within the coating which effectively reduces the effective
concentration of Ag.sup.+ ions released from such coatings,
resulting in shorter coating efficiency and greater tendency to
fail in bacterially rich or growth promoting environments. Silver
sulfadiazine (AgSD), a substantially water insoluble compound
(K.sub.sp.about.10.sup.-9) has a combination of a weakly
antibacterial sulfadiazine molecule that is complexed with silver.
In contrast to silver nitrate, the solubility of the silver
sulfadiazine complex is relatively low, and hence both silver ion
and sulfadiazine are present only in low concentrations in aqueous
solutions. The antibacterial effect of AgSD in topical formulations
may therefore, persist over a longer period of time before being
washed out at topically treated wound sites. AgSD is therefore,
used in the treatment of wounds, particularly for burns, under the
trademarks Silvadene.RTM. and Flamazine.RTM.. The substantially low
water solubility of AgSD has however, limited its use in
antimicrobial coatings, particularly in thin coatings for medical
devices. Attempts to incorporate AgSD into antimicrobial coatings
involve dispersion AgSD as micronized particles within relatively
hydrophilic polymeric coating materials such as polyethyleneglycol
(PEG) and polyvinylalcohol(PVA) which significantly limits the
ability to obtain high AgSD concentrations in thin coatings,
without compromising coating integrity and mechanical properties.
European patent application EP 83305570 discloses a
polyvinylpyrollidone hydrogel containing micronized AgSD and
cross-linked by e-beam radiation used as an absorbent wound
dressing. . . . Such hydrogel absorbent materials are however, not
suitable for coating of medical devices in which high loading of
particulate AgSD is not achievable. Furthermore, the antimicrobial
efficacy of such coatings are relatively poor because of the
relatively low concentrations of silver (Ag.sup.+) ions in the
coating, and such coatings therefore require additional
water-soluble antimicrobial compounds, such as chlorhexidine to
provide bactericidal levels of antimicrobial agents in the
contacting environment. Such increased elution of the non-silver
agent however, is likely to adversely affect the duration of
coating efficacy, since the coating becomes depleted of the soluble
agent in a relatively short period of time. Such antimicrobial
coatings therefore, are not optimal for medical devices that remain
implanted in the patient for longer periods of time (several days
to weeks).
SUMMARY OF THE INVENTION
[0010] The present invention is based upon the realization that a
substantially water-insoluble antimicrobial material can be
incorporated into a hydrophilic polymeric coating in a
substantially "solubilized` form wherein the water insoluble
antimicrobial material is dispersed homogeneously in a three
dimensional hydrogel network gel, formed by a hydrophilic polymer
in a substantially homogenous manner, thereby enabling
incorporation of high concentrations of a bacteriostatic or
bactericidal material in relatively thin coatings, and resulting in
increased coating antimicrobial efficacy for extended periods. The
coatings of the invention, therefore, inhibit bacterial adhesion
and biofilm formation on coated surfaces such as medical devices
and healthcare products.
[0011] The present invention concerns an antimicrobial coating
comprising a cross-linked polymeric material comprising a
biologically active or "bioactive" agent and at least one
substantially water-insoluble antimicrobial metallic compound
maintained in a substantially "solubilized" form within the coating
that inhibits bacterial adhesion and proliferation on the coating
surface, thereby inhibiting the formation of biofilm. It has been
surprisingly found that maintaining the water-insoluble
antimicrobial metallic compound in a solubilized form within the
hydrogel coating imparts substantially high coating antimicrobial
efficacy that is maintained over an extended duration of time
relative to hydrogel coatings within which the water-insoluble
antimicrobial metallic compound is dispersed as micronized
heterogeneous particles.
[0012] In one aspect, the present invention relates to an
antimicrobial coating on a substrate surface, including surface of
a medical device or healthcare product, comprising a hydrogel layer
and a substantially water-insoluble antimicrobial metallic compound
that is maintained in a substantially "solubilized" form within the
coating, that inhibits bacterial adhesion and biofilm formation on
the coating surface. In particular, the present invention relates
to hydrogel coating comprising a hydrophilic polymer at least a
portion of which is crosslinked to form a hydrophilic 3-dimensional
(3-D) network within which a substantially water insoluble silver
compound is dispersed homogeneously within the coating in a
substantially solubilized form.
[0013] In another aspect, the present invention provides an
antimicrobial coating wherein substantially water-insoluble, poorly
ionizing (weakly active) silver compounds or silver complexes are
rendered more active in a sustained manner over a longer duration
of time by maintaining them in a homogeneously dispersed,
solubilized form within the coating.
[0014] In a further aspect, the present invention provides a
coating formulation comprising a hydrophilic polymeric material and
a substantially water-insoluble metallic antimicrobial compound
that is dispersed in a substantially homogenous phase in the
coating formulation complex structure rendering silver ions stable
against loss of the antiseptic activity and against darkening due
to reduction of the silver ions or the formation of darkly stained
sparingly or insoluble silver compounds.
[0015] In yet another aspect, the present invention provides
principles and methods of introducing the silver compositions
stabilized against the effect of light into catheters, guide-wires,
wound drains, needle-less connectors, or similar medical devices or
instruments.
[0016] In a further aspect the invention provides coating
compositions and coating methods for coating substrate materials,
particularly medical devices, and evaluation of coating biological
activity e including antimicrobial efficacy, and inhibition of
bacterial adhesion and biofilm formation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows images of coated substrates. FIG. 1(a) is an
image of a substrate coated with micronized AgSD in suspension.
FIG. 1b is an image of a substrate coated with AgSD in solution.
The coating in FIG. 1(b) is translucent in appearance.
[0018] FIG. 2 shows coating AgSD elution profiles of static and
dynamic elution assays. FIG. 2(a) is a graph of a static model
elution. FIG. 2(a) is a graph of a dynamic model elution. The
vertical axes represent concentration in micrograms per milliliter
(.mu.g/mL). The horizontal axes represent time in hours.
[0019] FIG. 3 shows coating AgSD elution profiles as a function of
crosslink density. FIG. 3 is a graph showing AgSD elution profiles
of several crosslinked coating compositions comprising solubilized
AgSD and a hydrophobic coating composition comprising micronized
AgSD. The vertical axis represents percent AgSD released from the
coating. The horizontal axis represents time in hours. Crosslink
density is represented by concentration of crosslinking agent.
[0020] FIG. 4 shows Scanning Electron Microscope (SEM) images of
coated and uncoated substrates. FIG. 4(a) is an image of an
uncoated polycarbonate outlet housing. FIG. 4(b) is an image of a
coated polycarbonate outlet housing.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention accordingly describes antimicrobial
coatings comprising a hydrogel layer and a bioactive agent
comprising at least one substantially water-insoluble antimicrobial
metallic material that is homogeneously dispersed and maintained in
a substantially "solubilized" form within the coating,
[0022] The term "solubilize" with reference to the substantially
water-insoluble antimicrobial metallic material in the
antimicrobial coatings of the invention as used herein, refers to a
homogeneous or substantially homogenously dispersed composition of
the substantially water-insoluble antimicrobial metallic material
within in the coating hydrogel layer. The term "solubilized" with
reference to the substantially water-insoluble antimicrobial
metallic material in the antimicrobial coating formulations of the
invention as used herein, refers to a homogeneous or substantially
homogenous dispersion of the substantially water-insoluble
antimicrobial metallic material in the coating formulation or
coating solution of the invention containing the hydrophilic
polymers used to obtain the antimicrobial coatings of the
invention. The term "solubilization" with reference to the
substantially water-insoluble antimicrobial metallic material in
the antimicrobial coatings and antimicrobial coating formulations
of the invention as used herein, refers to the dissolution of the
substantially water-insoluble antimicrobial metallic material in
the coating material or coating formulation in a homogeneous or
substantially homogenous manner.
[0023] By maintaining the water-insoluble antimicrobial metallic
material in a homogeneously dispersed solubilized form, high
concentrations of the water-insoluble antimicrobial metallic
material may be incorporated in relatively thin coatings, which is
not achievable in heterogeneous compositions incorporating it in a
micronized form. The antimicrobial coatings of the invention,
therefore, provide high concentrations of the antimicrobial
metallic material in a contacting aqueous environment over extended
periods of time, and effectively inhibit bacterial adhesion and
biofilm formation on the coating surface. For example, The
"solubilization" of AgSD in the antimicrobial coating of the
invention enables thin coatings comprising high (therapeutic)
levels of AgSD that is up to two orders of magnitude higher with
respect to its soluble levels in water. Such levels in thin
coatings are unachievable with micronized AgSD, thereby precluding
their application to small dimension medical devices, for which a
thin coating (coating thickness dimension of several micrometers
(.mu.M) is an essential prerequisite. Such devices include, but are
not limited to catheters, stents, wound drains, needle-less
connectors, trauma pins etc., that have diameters of only a few
millimeters.
[0024] Although the invention as claimed is not to be construed as
relying upon any hypothesis as to the mode of action, it can be
reasonably inferred that the homogeneous dispersion of the
water-insoluble silver compounds in a "solubilized" form within the
hydrogel coating whereby they are substantially homogeneously
dispersed within the coating, enables incorporation high
concentrations of such silver compounds in relatively thin coatings
per unit area of coating, which in turn, results in bactericidal
Ag.sup.+ ions to be released from the hydrogel coating into the
contacting aqueous environments. Furthermore, the relatively small
coating thickness coupled with the hydrophilic nature of the
polymeric material forming the cross-linked hydrogel coating matrix
enable the facile diffusion of Ag.sup.+ ions from the solubilized
silver compounds homogenously dispersed within the coating, that
results in extended duration of coating antimicrobial efficacy. The
cross-link density in the 3-D hydrogel matrix forming the coating
may be varied to effectively control the diffusion rate of Ag.sup.+
ions released from the coating, thereby providing control over the
duration of coating antimicrobial efficacy. The substantially
water-insoluble silver compounds that are rendered soluble in the
hydrophilic coating formulations of the invention enable high
concentrations of the insoluble silver compounds that are
homogeneously dispersed within the coating to be incorporated into
relatively thin coatings, thereby enabling controlled release of
higher concentration of Ag+ ions per unit area of the coating,
compared to relatively thicker coatings that are required when the
water insoluble silver compounds are present in a heterogeneous
micro-particular phase.
[0025] The hydrogel layer in the antimicrobial coating of the
present invention comprises a three-dimensional network formed by a
hydrophilic polymer by ionic or chemical cross-linking, cryogel
formation, or by an interpenetrating polymeric network. The
hydrophilic polymer of the invention is chosen from polyfunctional
water soluble polymers, including polyfunctional polymers such as,
for example, polyvinyl alcohol, polyvinylpyrrolidone,
polyethyleneimine, polyacrylic acid, polyhydroxyethylmethacrylate,
polylactic acid, polylactide, polyglycolide, poly
epsilon-caprolactone, copolymers and mixtures thereof, poly vinyl
alcohol-glycine co-polymer, and polyvinyl alcohol-lysine
co-polymer. Ionic or chemical crosslinking of the hydrophilic
polymers can be accomplished in the polyfunctional polymers
included in the antimicrobial coatings of the invention. For
example, a hydrogel layer comprising ionically cross-linked
hydrophilic polymer chains by coating a substrate material with the
antimicrobial coating formulation of the invention comprising a
polyfunctional hydrophilic polymer containing coating formulation
and a substantially water-insoluble antimicrobial metallic material
in a solubilized homogeneous dispersion on a substrate surface,
drying the coating to a pre-determined extent and reacting it with
a suitable ionic or chemical crosslinking agent or agents known in
the art. The cross-linking agent is chosen appropriately based on
its ability to effect cross-linking between functional groups
present in the polyfunctional hydrophilic polymer chains. Examples
of ionic cross-linking agents include, but are not limited to,
divalent or trivalent metal halides such as calcium, zinc or copper
halides. Examples of covalent cross-linking agents include, but are
not limited to aldehydes, dialdehydes, alkyl dihalides, alkyl
ditriflates, etc.
[0026] In one embodiment, chemical cross-linking is accomplished in
partially or completely dried coatings on a substrate surface
utilizing the antimicrobial coating formulations of the invention
that comprise a hydrophilic polymer and a solubilized substantially
water-insoluble antimicrobial metallic material, drying the coating
for an appropriate amount of time and reacting it with a chemical
crosslinking agent capable of reacting with the functional groups
in the hydrophilic polymer chains. Cross-link density in the
hydrogel matrix forming the antimicrobial coatings of the invention
may be controlled or pre-determined by varying the concentration of
the cross-linking reaction, by appropriately varying the reaction
time of the cross-linking process, by varying the time between
coating and cross-linking, and/or reaction temperature of the
cross-linking reaction.
[0027] In a currently preferred embodiment, the hydrophilic polymer
in the coating formulation of the invention is poly(vinyl alcohol)
(PVA). Poly(vinyl alcohol), which is commercially available in
several forms that differ in percent hydrolysis and molecular
weight range. The antimicrobial coatings of the present invention
utilizes an optimal combination of these characteristics of PVA,
together with control of cross-link density to pre-determine
coating physical properties, including tensile strength, durability
and pore size. In one preferred embodiment, the PVA in the
antimicrobial coating formulations of the invention has a percent
hydrolysis ranging between 87 to 89%. In another preferred
embodiment, the PVA in the antimicrobial coating of the invention
includes a form with percent hydrolysis of greater than about 99%.
The molecular weight of PVA used in the antimicrobial coating
formulations of the invention ranges between 124,000 to 186,000
daltons. In another embodiment, the molecular weight of PVA ranges
from 89,000 to 98,000 daltons. In a currently preferred embodiment,
the choice of PVA includes, but is not limited to a hydrolysis
percent that are about 87-89% and a molecular range between 124,000
to 186,000 daltons, 99+% hydrolysis, molecular weight range 124,000
to 186,000; a hydrolysis percent that is .gtoreq.99% and a
molecular weight range between 89,000 to 98,000, and combinations
thereof. The PVA in the antimicrobial coatings of the invention may
comprise a single hydrolyzed form (in terms of % hydrolysis) and
molecular weight range, or may comprise a mixture of two or more
PVA types (% hydrolysis and molecular weight ranges). The
concentration of PVA in the antimicrobial coating formulations of
the invention typically ranges between 0.1 and 1000 g/L. In a
currently preferred embodiment, the concentration of PVA having
87-89% hydrolysis, and a molecular weight range of 124,000 to
186,000 is 50 g/L.
[0028] The cross-linking agents for the PVA based antimicrobial
coatings of the present invention include a mono- or dialdehyde
monomer or a diol. Examples of aldehyde cross-linking agents
include, but are not limited to, formaldehyde, paraformaldehyde,
glyoxal, or glutaraldehyde. The crosslinking agent may be added to
the hydrophilic polymer in the form of a solution. In one
embodiment, the cross-linking solution is maintained at an acidic
pH. In a currently preferred embodiment, the cross-linking agent
comprises 3% formaldehyde and 1% glyoxal in a solution of 1%
hydrochloric acid. In another embodiment, chemical cross-linking is
accomplished in partially or completely dried coatings on a
substrate surface obtained from the antimicrobial coating
formulations of the invention comprising PVA and a solubilized
substantially water-insoluble antimicrobial metallic material on a
substrate, drying the coating for an appropriate amount of time and
reacting it in a chemical cross-linking step using a suitable
aldehyde by contacting the PVA coating to a solution containing the
aldehyde cross-linking agent. Cross-link density in the hydrogel
matrix forming the antimicrobial coatings of the invention may be
controlled or pre-determined by varying the concentration of the
cross-linking reaction, by appropriately varying the reaction time
of the cross-linking process, by varying the time between
application of the coating and cross-linking agents, and/or
reaction temperature of the cross-linking reaction. In a currently
preferred embodiment, the cross-linking agent comprises a solution
containing 3% formaldehyde and 1% glyoxal in a solution of 1%
Hydrochloric acid.
[0029] The bioactive agent in the antimicrobial coatings of the
invention comprises a substantially water-insoluble antimicrobial
water-insoluble material including an antimicrobial metal, metal
alloy, metal salt, metal or metal complex that is maintained in a
solubilized form in the hydrogel layer of the antimicrobial
coating, and optionally, combined with a non-metallic antimicrobial
or antibiotic compound. Such substantially water-insoluble
antimicrobial metallic materials include, but are not limited to
antimicrobial metal salts and metal complexes of silver, copper and
zinc. In a preferred embodiment, the substantially water-insoluble
antimicrobial metallic material is a substantially water insoluble
antimicrobial silver compounds including, but not limited to,
silver halides, silver sulfazines, silver sulfadiazines, silver
sulfonamides and silver sulfonylureas. In a currently preferred
embodiment the substantially water-insoluble antimicrobial metallic
compound is silver sufladiazine, (AgSD).
[0030] In a preferred embodiment, the antimicrobial coating
formulations of the invention comprises AgSD in a range from about
1 mg/L to about 100 g/L. In a currently preferred embodiment, the
concentration of AgSD is about 20 g/L. In a second preferred
embodiment the concentration is 30 g/L. These concentrations of
AgSD in the coating formulations of the invention enable the
formation of relatively thin coatings that comprise high AgSD
loading and reservoir capacity that provides bactericidal levels of
Ag.sup.+ ions and sulfadiazine into the contacting environment. For
example, a 15 .mu.m thick coating obtained from a antimicrobial
coating formulation having an AgSD concentration of 20 g/L,
provides approximately 70 .mu.g/cm.sup.2 of solubilized AgSD in the
resulting coating that provides bactericidal levels of Ag.sup.+
ions and sulfadiazine into the contacting environment. The
antimicrobial coatings of the invention which provide high
concentrations of AgSD per unit area of coating for very thin
coatings (<100 .mu.M) due to the solubilization of AgSD within
the coating, therefore overcome a major limiting factor that exist
in the conventional method of utilizing of micronized AgSD. Based
on the substantially low solubility of AgSD in aqueous solutions
(.about.6.times.10.sup.-4 moles/L AgSD equivalent to .about.0.22
grams/L AgSD) a coating containing micronized AgSD would have to be
about 2.5 mm thick in order to produce a similar loading of about
70 .mu.g/cm.sup.2. Coatings containing micronized AgSD in the
absence of other water-soluble antibacterial agents are therefore,
not only impractical for coating medical devices with small
dimensions, but also result in coatings that have defects and poor
mechanical properties. The advantages of the coatings of the
present invention comprising solubilized AgSD and the deficiencies
of a similar coating on a stainless steel piercing containing
micronized AgSD are shown in FIG. 1. As seen in FIG. 1(a), a
hydrophilic PVA coating containing micronized AgSD is relatively
thick, opaque and has considerable defects in terms of both coating
uniformity and coating integrity, whereas the PVA coating of the
present invention comprising solubilized AgSD shown in FIG. 1(b) is
highly uniform, thin and transparent with good coating
integrity.
[0031] The antimicrobial coatings and coating formulations of the
invention additionally comprises a stabilizing compound that
maintains the substantially water-insoluble antimicrobial metallic
material in a solubilized form within the coating hydrogel layer.
The presence of a stabilizing compound, for example an antioxidant
such as TiO.sub.2, imparts a protective effect to the antimicrobial
coatings of the invention against discoloration of the coating
during exposure to light, thereby rendering the coatings to be
photostable.
[0032] Without wishing to be bound by theory, it is believed that
the presence of a stabilizing compound in the antimicrobial
coatings of the invention, such as an antioxidant, photostabilizer
or free-radical scavenger in the coating is believed to impart a
protective effect that prevents the reduction of AgSD and the
diffusing Ag.sup.+ ions from ionized AgSD diffusing from within the
coating to particulate metallic silver (Ag.sup.0) that is
antimicrobially inert, thereby maintaining the AgSD in an
antibacterially active solubilized form that provides bactericidal
amounts of Ag.sup.+ ions into the contacting environment.
[0033] In one embodiment, the antimicrobial coating composition
additionally comprises a stabilizer compound such as an
antioxidant, photostabilizer or free-radical scavenger compound or
mixtures thereof. Any suitable antioxidant may be used.
Antioxidants include, but are not limited to, lactones, phenolics,
phosphites, thioesters, hindered phenolics such as, for example,
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,-
6-(1H,3H,5H)-trione (Cyanox.RTM. 1790), hindered amines such as,
for example,
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-pi-
peridyl)imino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]]
(Cyasorb.RTM.UV-3346), and hindered benozoates such as, for
example, 3,5-di-t-butyl-4-hydroxybenzoic acid, hexadecyl ester
(Cyasorb.RTM.UV-2908). Cyanox.RTM.1790, Cyasorb.RTM.UV-3346 and
Cyasorb.RTM.UV-2908 are distributed by Cytec Industries Inc., West
Paterson, N.J. Vitamin E (alpha-tocopherol), TPGS (alpha-tocopherol
polyetheylene glycol succinate), BHT (alpha-lipoic acid, butylated
hydroxy toluene) and ascorbate (sodium ascorbate) may also be
suitable antioxidants, particularly in a water soluble form.
Photostabilizing compounds include, but are not limited to,
benzoates, benzophenone, benzotriazole, cyanoacrylate, organo
nickel and organo zinc and compounds such as magnesium silicate.
Stabilizers include, but are not limited to titanium dioxide
(TiO.sub.2) and tungsten trioxide (WO.sub.3) in any of their
polymorphic forms. In one embodiment, the antioxidant is
TiO.sub.2.
[0034] In a preferred embodiment, the concentration of titanium
dioxide (TiO.sub.2) in the antimicrobial coating formulation ranges
from ranges between 0.1 g/L and 10.0 g/L. In a currently preferred
embodiment, the concentration of TiO.sub.2 is about 2 g/L. The
TiO.sub.2 is preferably micronized by standard methods, such as for
example, using a jet milling process, to have an average particle
size ranging between 0.1 to 20 .mu.m. In a currently preferred
embodiment, the average particle size of the micronized TiO.sub.2
is about 1 .mu.m. In another currently preferred embodiment, a
commercial grade, sub-micron particulate TiO.sub.2 with an average
particle diameter of <45 nanometers (nm) is used as an
antioxidant stabilizer compound in the antimicrobial coating
formulations of the invention.
[0035] The presence of a stabilizer compound in the antimicrobial
coatings of the present invention maintain the AgSD in a
solubilized form and inhibit the reduction of AgSD and the Ag.sup.+
ions generated from the AgSD (including photoreduction) to metallic
silver that is antimicrobially inactive, and therefore, maintains
high coating antimicrobial efficacy, and provides relatively
faster, and longer kill rates in comparison to coatings without a
stabilizer compound. The presence of TiO.sub.2 as a stabilizer
compound in the antimicrobial coatings of the invention containing
solubilized AgSD, for example, results in improved antimicrobial
efficacy demonstrated by faster kill rates relative to coatings
containing solubilized AgSD alone.
[0036] The effect of a stabilizer compound on the activity of
solubilized AgSD was confirmed by an in-vitro antimicrobial assay
in aqueous solutions containing 0.5 .mu.g/mL of dissolved AgSD (to
simulate solubilized AgSD in the coatings of the invention) with
and without added TiO.sub.2 (0.3 .mu.g/mL) that were challenged
with .about.10.sup.4 cfu/mL of staph. epidermidis for 60 minutes.
The test results (summarized in Table 1 below) show that AgSD
solution containing TiO.sub.2 exhibits faster kill rates in 60
minutes (100%) compared to the AgSD solution without TiO.sub.2
(40%) relative to control, while a TiO.sub.2 containing solution
without AgSD is not antibacterial, thereby substantiating the
stabilizing influence of TiO.sub.2 in maintaining the AgSD in a
soluble form and preventing the reduction to metallic silver.
TABLE-US-00001 TABLE 1 Effect of stabilizer compound (TiO2) on the
antimicrobial efficacy of PVA-solubilized AgSD coating at t = 60
minutes. % Reduction % Reduction % Reduction % Reduction Control
AgSD AgSD + TiO.sub.2 TiO.sub.2 0 ~40 100 0
[0037] In yet another embodiment, the bioactive agent in the
antimicrobial coatings of the invention comprises one or more
antibacterial or antibiotic agents in addition to the solubilized,
substantially water-insoluble metallic material. These include
antibiotics such as but not limited to rifampin, gentamicin,
vancomycin, neomycin, soframycin, bacitracin, polymycin, synthetic
antibiotics including ofloxacin, levofloxacin and ciprofloxacin,
antbacterials including biguanides such as chlorhexidine and their
salts, alkyl ammonium halides such as benzalkonium chloride
cetrimide, domiphen bromide and phenolics such as triclosan.
[0038] The antimicrobial coating formulation of the present
invention comprise coating solutions that include at least one
hydrophilic polymer that is dissolved in an appropriate solvent,
and a bioactive agent comprising a substantially water-insoluble
antimicrobial metallic material that is solubilized in the coating
solution so as to form a homogeneous phase or a substantially
homogeneous phase with the hydrophilic polymer. The coating
solutions of the invention comprise one or more water-soluble
hydrophilic polymers having polyfunctional groups, including but
not limited to polyvinyl alcohol, polyvinylpyrrolidone,
polyethyleneimine, polyacrylic acid, polyhydroxyethylmethacrylate,
and copolymers and mixtures thereof. In a currently preferred
embodiment, the coating solutions of the invention comprise an
aqueous solution of polyvinyl alcohol (PVA). The substantially
water-insoluble antimicrobial metallic material is chosen from, but
not limited to, antimicrobial metal salts and metal complexes of
silver, copper and zinc. In a preferred embodiment, the
substantially water-insoluble antimicrobial metallic material is a
substantially water insoluble antimicrobial silver compounds
including, but not limited to, silver halides, silver sulfazines,
silver sulfadiazines, silver sulfonamides and silver sulfonylureas.
In a currently preferred embodiment the substantially
water-insoluble antimicrobial metallic compound is silver
sufladiazine, (AgSD).
[0039] In another preferred embodiment, antimicrobial coating
formulations of the present invention additionally comprise a
stabilizer compound that maintains the substantially
water-insoluble antimicrobial metallic material, which is
solubilized in the coating formulation, in a solubilized form in
coatings obtained from the coating formulations. Examples of such
stabilizer compounds include antioxidant, photostabilizer or
free-radical scavenger compounds, or mixtures thereof. Stabilizer
compounds include, but are not limited to TiO.sub.2 and WO.sub.3 in
any of their polymorphic forms. Photostabilizing compounds include
compounds such as magnesium silicate. In a currently preferred
embodiment, the stabilizer compound is TiO.sub.2.
[0040] The substantially water-insoluble antimicrobial metallic
material is dissolved in an aqueous acidic solution at an elevated
temperature so as to effect complete dissolution of the metallic
material. The acidic solution containing the dissolved
antimicrobial metallic material is then mixed with an aqueous
solution of the hydrophilic polymer so as to maintain the
antimicrobial metallic material in a solubilized form in the
solution mixture in a homogeneous or substantially homogeneous
aqueous phase, wherein the antimicrobial metallic material and the
hydrophilic polymer are homogeneously dispersed in the aqueous
coating solution.
[0041] In a currently preferred embodiment, a pre-determined amount
of silver sulfadiazine is added to an aqueous solution of heated
dilute nitric acid to bring the desired concentration of AgSD into
solution. The heated AgSD/nitric acid solution is stirred and
heated between about 65.degree. to about 70.degree. C. Following
the complete dissolution of the AgSD, a predetermined amount of PVA
having the desired percent hydrolysis and molecular weight range is
added with stirring. The PVA/AgSD/nitric acid solution is stirred
and heated until all components are dissolved. The viscosity of the
resulting coating solution comprising the PVA and solubilized AgSD
ranges from about 10 to about 30 centipoises (cP), depending on the
characteristics of the PVA used. In a particularly preferred
embodiment, the viscosity of the coating formulation is about 20
cP, the nitric acid concentration is about 1 Molar, and the
temperature of dissolution is about 70.degree. C. In another
embodiment, the AgSD solution in aqueous nitric acid is further
mixed with buffer solution, such as for example, a phosphate
buffer, prior to addition of PVA.
[0042] In another preferred embodiment of the invention, the
coating formulation of the invention comprises a coating solution
containing a hydrophilic polymer dissolved therein, a bioactive
agent comprising a antimicrobial metallic material that is
solubilized in the coating solution, and at least one stabilizer
compound that is either dissolved in the coating solution to form a
homogeneous phase, or suspended in the coating solution as a
microparticulate dispersion. In a currently preferred embodiment,
the stabilizer compound is an inorganic oxide antioxidant compound,
namely TiO.sub.2, which is suspended as a microparticular
dispersion in the coating formulation. In a currently preferred
embodiment, micronized TiO.sub.2 is mixed with dry PVA to obtain a
dry powder mixture that is added to a stirred solution of aqueous
acidic AgSD solution while maintaining an elevated temperature,
preferably between 75.degree. and 80.degree. C. to obtain a coating
formulation suspension containing PVA, solubilized AgSD in which
the TiO.sub.2 is evenly dispersed. The resulting coating solution
containing PVA, solubilized AgSD and the TiO.sub.2 suspension is
mixed additionally for 1 to 5 hours. Alternatively, the TiO.sub.2
is added to an aqueous solution of PVA to obtain a suspension, and
PVA/TiO.sub.2 suspension is then added to a stirred aqueous acidic
AgSD solution while maintaining an elevated temperature, preferably
between 75.degree. and 80.degree. C.
[0043] The coating formulations of the invention is applied on a
substrate surface using any of the standard coating methods known
in the art such as dipping, spraying, rolling, etc. In a preferred
embodiment, the coating formulations are applied on substrate
materials using a dipping process. In a one embodiment, the
substrate is dipped into the coating material at a temperature
ranging from 35 about to about 41.degree. C., preferably at
38.degree. C., for about 1 to 60 seconds. The substrate is then
mechanically withdrawn from the coating material such that a
uniform coat is achieved. The antimicrobial coatings of the
invention comprising a bioactive agent that includes a solubilized
antimicrobial metallic material and optionally, a stabilizer
compound of are obtained by applying the antimicrobial coating
formulations of the invention on a substrate material, subjecting
the coating to either a partial or complete drying step, followed
by reacting the coatings formed thereby to a cross-linking step.
The coatings of the invention may be produced on substrate
materials either in their unfinished form (sheet, granules, pellets
etc.) or a finished product such as a medical device or healthcare
product. When the substrate to be coated contains a lumen, a vacuum
or positive pressure may be applied to during the coating process
to ensure that all parts of the substrate are contacted with the
coating formulation. The substrate material is optionally subjected
to a spin step to aid in vertical and radial consistency of the
resulting coating when utilizing a dip process during the
withdrawal of the substrate material from the coating formulation.
In one embodiment the spin rate during coated substrate material
withdrawal is maintained between 0-25 rpm. In one embodiment, the
withdrawal speed ranges between about 0.25 to about 10 mm/sec, and
preferably, about 5.0 mm/sec.
[0044] In another embodiment, the antimicrobial coating
formulations of the invention comprising coating solutions are
applied to the surface of a substrate material by a spray coat
method. The antimicrobial coating formulations is sprayed on the
substrate material surface using standard spraying equipment and
methods known in the art. Suitable spraying equipment include, but
are not limited to, sprayers using pressurized air, and sprayers
using an ultrasonic spray head, both of which aerosolize the
coating solutions. PVA molecular weight range, weight percentage,
and percent hydrolysis are appropriately chosen so as to maximally
aerosolize the coating solution. In a currently preferred
embodiment, a PVA with molecular weight range of 89,000 to 98,000
and 99+% hydrolysis is combined with PVA with a molecular weight
range of 31,000 to 50,000 and 87-89% hydrolysis in a ratio of 2:5
or 100 and 250 g/L respectively.
[0045] In another embodiment, the antimicrobial coating of the
present invention comprises a plurality of individual coating
layers or "coats" that is obtained by a series of coating
formulation application and drying steps performed simultaneously
and optionally, including an additional cross-linking step after
one or more drying steps, thereby enabling the control of elution
kinetics as well as the concentration of the
antibacterial/antimicrobial compound. For example, by overlaying
two coating layers of approximately the same thickness, the
effective concentration of AgSD released per cm.sup.2 of the coated
substrate is effectively doubled. Other variations include
excluding the cross-linking step in the inner layers of with a
multiple-layer coating, and limiting the cross-linking to the
outermost coating layer.
[0046] The coating layer formed on substrate material surface by
any of the methods described hereinabove is then dried by a
suitable drying process that include, but not limited to,
air-drying, infrared radiation, convection or radiation drying
(e.g. a drying oven), or warm forced air (e.g. heat gun). The
drying step is performed both before and after contacting the
coating with a cross-linking agent. In the case of multi-layer
coatings, the drying step may be performed after formation of each
of the inner layers without contacting a cross-linking agent, while
it is performed on the outermost layer after contacting the
cross-linking agent. The drying time and drying temperature alter
the elution kinetics of the antimicrobial coatings of the
invention. Longer drying times at a given temperature produces less
cross-linking and therefore, result in relatively faster drug
release profiles. Typically, drying of the coated substrate
materials is accomplished by means of a "heating iris" or plenum,
which the substrate is withdrawn through, that is located
proximally (approximately two inches) from the surface of the
coating formulation which the substrate material or finished
product is being dipped, or alternatively, from the surface of the
coated substrate material of finished product when the coating is
applied by a spray method. Heating of the coated substrate material
is accomplished for example, with a hot air blower that provides a
temperature of about 60.degree. to about 70.degree. C. and airflow
of several liters per minute to the plenum. Such an airflow is
usually directed circumferentially around the part during
withdrawal and spin process of the substrate material from the
coating formulations. Cross-linking of the coating layer to obtain
the hydrogel network in the antimicrobial coatings of the invention
is accomplished by contacting a partially or completely dry coating
layer on the substrate material with a cross-linking agent by
immersion of the coated substrate material or finished product into
a solution comprising the cross-linking agent either prior to after
the drying step following which the coating is subjected to
additional drying at elevated temperature for a pre-determined time
to induce cross-linking. Alternatively, the cross-linking agent may
also be applied to the substrate by spray coating the substrate
first with coating material, and secondly with a solution
containing the cross-linking agent(s). In a currently preferred
embodiment the cross-linking solution contains 1% glyoxal, 3%
formaldehyde, and 1% HCl.
[0047] The coating formulations of the invention may be applied to
a variety of substrate materials, including but not limited to
synthetic and naturally occurring organic and inorganic polymers
such as polyethylene, polypropylene, polyacrylates, polycarbonate,
polyamides, polyurethane, polyvinylchloride (PVC), polyetherketone
(PEEK), polytetrafluroethylene (PTFE), cellulose, silicone and
rubber (polyisoprene), plastics, metals, glass, and ceramics. While
the coating formulations of the invention may applied either
directly on materials with a hydrophilic surface such as metals,
glass and cellulose or optionally on top of a primer undercoat,
materials with hydrophobic surfaces such as silicone and PTFE are
subject to a surface pre-treatment step prior to application of the
coating.
[0048] Substrates that are not wettable by the coating formulations
of the invention, particularly hydrophobic substrates such as
silicone, polytetrafluoroethylene (PTFE) etc., are surface
pre-treated prior to coating. The surface pre-treatment process
involves either coating the hydrophobic substrate with a primer
layer on which the antimicrobial coatings of the invention are
deposited, or a surface modification step wherein the surface of
the substrate material is subjected to an oxidation process that is
optionally followed by a chemical grafting reaction to render the
surface hydrophilic, and compatible with the coating formulations
of the invention. In one embodiment, the surface pre-treatment of
the substrate material involves a plasma oxidation process under
reduced pressure, followed by chemical grafting of an aliphatic
alcohol. In a currently preferred embodiment, the aliphatic alcohol
is allyl alcohol. The power settings, gas flow rates, times, and
pressures are maintained optimally during the surface oxidation
process, and during grafting of alcohol The coating thickness of
the antimicrobial coatings of the invention are controllable by
optimal choice of substrate withdrawal speed from the coating
formulations after immersion, coating solution viscosity, coating
solution temperature, number of coats applied, and substrate
material spin speed. The coating thickness can be pre-determined by
controlling the temperature of the PVA/AgSD during the dip process,
the viscosity of the coating formulation during immersion of the
substrate material or finished product, e.g. a medical device or
healthcare product, withdrawal speed and technique (spinning,
etc.), coating method (e.g. spray instead of dip), number of
dip/spray cycles and immersion/spray time. In one embodiment, a
coating with thickness of about 10-20 .mu.m is obtained by
maintaining the withdrawal speed at 5 mm/sec, the coating viscosity
at 20 cP, and the coating solution temperature at 38.degree. C. and
substrate material spin rate at 5 rpm. In another preferred
embodiment, the withdrawal speed of the substrate is varied as the
part is withdrawn to account for the time variation of immersion
time from the bottom to the top of the length of the substrate. The
withdrawal speed (rate of withdrawal) the substrate material or
finished product from the coating formulation is either maintained
at a constant value, or is varied during the withdrawal process. In
a currently preferred embodiment, the withdrawal speed is
maintained initially at 5 mm/sec, and subsequently changed to 6
mm/sec after about 1/3 of the of the substrate material or finished
product (e.g. length if the product has a linear configuration,
such as for example, a catheter) has been withdrawn from the
coating formulation, and further changed to 7 mm/sec after
withdrawal of 2/3 of the substrate material or finished product.
The coating thickness of the antimicrobial coatings of the
invention can be used to effectively control the amount and
duration of bioactive agent release in a contacting environment.
The coating thickness of the antimicrobial coatings of the
invention ranges between 5 .mu.m to 100 .mu.m, while bioactive
agent loading in dry coatings range between 10 to 300
.mu.M/cm.sup.2 of coated surface area.
[0049] Release of bioactive agent, in particular, the solubilized
antimicrobial metallic material is measured in an elution assay.
Both static and dynamic elution assay methods described herein may
be used to estimate the released bioactive agent. Typical static
and dynamic elution profiles for AgSD as a function of coating
cross-link density in the antimicrobial coatings of the invention
are shown in FIG. 2A and 2B, respectively, which measure the total
AgSD released from the coating. As seen in FIG. 3, the elution
profiles for AgSD antimicrobial coatings of the invention indicate
that higher concentrations of sulfadiazine (SD) and correspondingly
a higher level of Ag.sup.+ ions are released into the contacting
aqueous environment at a fairly constant rate at lower coating
cross-link densities (e.g. 1.5% glyoxal), and a substantially
constant rate at relatively higher cross-link densities (e.g. 5%
glyoxal) over a period of over 400 hours. In contrast, a previously
known hydrophobic coating micronized AgSD provides substantially
lower levels of SD and Ag.sup.+ ions under similar conditions (FIG.
3). The hydrophilic antimicrobial coatings of the present invention
therefore, offer the advantage of conferring coated surfaces with
higher antimicrobial efficacy towards inhibition of bacterial
adhesion and biofilm formation on coated substrate materials and
finished products such as medical devices and healthcare products
over a long duration of time, compared with hydrophobic coatings
containing micronized AgSD.
[0050] The antimicrobial coatings of the present invention are
effective in preventing bacterial adhesion and subsequent biofilm
formation on coated surfaces. FIG. 4 shows scanning electron
micrographs of a coated and uncoated outlet housing component of a
medical device that were maintained in contact with S. epidermidis,
which is a bacteria that is responsible for colonizing the surface
of implanted medical device such as catheters that results in
biofilm formation. As seen in FIG. 4, the uncoated housing
(control) shows well developed biofilm formation resulting from
bacterial adhesion and proliferation on the component surface (FIG.
4A), while the housing component coated with the antimicrobial
coating of the present invention shows virtually no bacterial
adhesion or biofilm formation (FIG. 4B).
[0051] Further, the antimicrobial coatings of the invention are
also stable in physiologic environments such as urine, blood,
plasma, and are stable to commonly used terminal stabilization
methods for medical devices. The antimicrobial coatings of the
present invention can be obtained on a variety of substrate
materials, including those commonly used in the manufacture of
medical devices and healthcare products and on the finished
products themselves. Examples of medical devices or healthcare
products that are coated with the antimicrobial coatings and
coating formulations of the invention to obtain antimicrobial
coatings that inhibit bacterial adhesion and biofilm formation
include, but are not limited to, a urological catheters, central
venous catheters, wound drains, orthopedic implants, dental
implants, feeding tubes, tracheal tubes, and medication delivery
products (e.g. needle-less connectors and/or IV products).
[0052] The methods of manufacturing the coatings and coating
compositions of the invention and their analysis are described in
the following examples which are not intended to be limiting in any
way.
EXAMPLES
Example 1
Coating Formulation Containing Solubilized Silver Sulfadiazine
(AgSD)
[0053] A coating formulation comprising AgSD (20 g/L) was prepared
as follows. Nitric acid (64 mL, 70%) was added to 800 mL H.sub.2O.
The resulting nitric acid solution was then heated to 70.degree. C.
using a double boiler. AgSD (20 g) was added to the nitric acid
solution with stirring using and overhead stirrer with a dissolving
stirring shaft. The AgSD was dissolved in a couple minutes. The
final volume of the AgSD solution was brought to 1.0 L with
H.sub.2O.
[0054] Additional coating ingredients may be added when the AgSD
(20 g/L) coating formulation is complete. Higher concentrations of
AgSD such as 30 g/L may be prepared using analogous procedures.
Example 2
Coating Formulation Preparation
[0055] A liter of coating formulation comprising AgSD (20.0 g) and
PVA (50.0 g, MW=124,000 to 186,000, 87-89% hydrolysis) was prepared
as follows.
[0056] In an appropriate sized temperature controlled mixing vessel
set at moderate mixing, Nitric acid (64 mL, 70%) was added to
purified H.sub.2O and diluted to 800 mL. The temperature of the
circulating heater with oil & pump was set between 65.degree.
C. and 70.degree. C. The variable speed overhead mixer with
dissolving stirrer attachment was set at 500 rpm. AgSD 20.0 g was
added slowly to the mixing water and acid mixture. The solution was
mixed for a minimum of 15 minutes. The dissolution was confirmed by
turning off the mixer and observing that no solid particles settle
out after 60 seconds. The temperature of the circulating heater was
set to 80.degree. C. and the stirrer was turned back on. The
temperature in temperature controlled vessel containing the
drug/acid mixture was allowed to reach at least 75.degree. C.
before proceeding.
[0057] While maintaining the temperature between 75.degree. C. and
80.degree. C., 50.0 g of polyvinylalcohol was added to the
acid/water AgSD solution with stirring at 500 rpm. The solution was
mixed for an additional 3 hours at 500 rpm. The resulting PVA
coating formulation was a light yellow color and had a smooth
appearance in about an hour after the last component was added. The
final volume of coating was brought up to 1.0 L with purified
water.
[0058] The PVA coating formulation may be stored at room temperate
in a covered/sealed container until it is used. The PVA coating
formulations are stable for about 5 days after preparation at
ambient temperature, and about 3 months at about 38.degree. C. The
PVA coating formulation may normally be used at 38.degree. C.
Alternatively, the PVA coating formulation may stored at room
temperature, and heated to its application temperature, with
mixing, for about 24 hours prior to use ensuring that all
components are in solution and well mixed. The PVA coating
formulation may be additionally screened through the 20.times.20
stainless steel screen before being stored or used in the coating
processes.
Example 3
Coating Formulation Preparation with TiO.sub.2
[0059] A liter of coating formulation comprising AgSD (20.0 g), PVA
(50.0 g, MW=124,000 to 186,000, 87-89% hydrolysis) and TiO.sub.2
(2.0 g) was prepared as follows.
[0060] In an appropriate sized temperature controlled mixing vessel
set at moderate mixing, Nitric acid (64 mL, 70%) was added to
purified H.sub.2O and diluted to 800 mL. The temperature of the
circulating heater with oil & pump was set between 65.degree.
C. and 70.degree. C. The variable speed overhead mixer with
dissolving stirrer attachment was set at 500 rpm. AgSD 20.0 g was
added slowly to the mixing water and acid mixture. The solution was
mixed for a minimum of 15 minutes. The dissolution was confirmed by
turning off the mixer and observing that no solid particles settle
out after 60 seconds. The temperature of the circulating heater was
set to 80.degree. C. and the stirrer was turned back on. The
temperature in temperature controlled vessel containing the
drug/acid mixture was allowed to reach at least 75.degree. C.
before proceeding.
[0061] Micronized Titanium dioxide (2.0 g) was added to 50.0 g of
dry PVA powder. The two powders are well mixed with each other,
before being added together to the AgSD solution. While maintaining
the temperature between 75.degree. C. and 80.degree. C., the PVA
Titanium Dioxide mixture was added to the acid/water AgSD solution
with stirring at 500 rpm. The solution was mixed for an additional
3 hours at 500 rpm. The resulting PVA coating formulation was a
light yellow color and had a smooth appearance in about an hour
after the last component was added. The final volume was brought to
1.0 L with purified water.
[0062] The PVA coating formulation may be stored at room temperate
in a covered/sealed container until use. The PVA coating
formulation may have a shelf life of about 5 days from the date of
manufacture at room temperature and a shelf life of about 90 days
at about 38.degree. C. The PVA coating formulation may normally be
used at 38.degree. C. The PVA coating formulation may be heated to
its application temperature, with mixing, for 24 hours before use
ensuring that all components are in solution and well mixed. The
PVA coating formulation may be screened through the 20.times.20
stainless steel screen before being stored or used for dipping or
spray or other coating processes.
Example 4
Coating Formulation for Spray Coating
[0063] A liter of coating formulation comprising AgSD (30.0 g), PVA
(41.7 g, MW=31,000 to 50,000, 87-89% hydrolysis), PVA (16.7 g,
MW=89,000 to 98,000, 99+% hydrolysis) and TiO.sub.2 (2.0 g) was
prepared in accordance with the following procedure.
[0064] In an appropriate sized temperature controlled mixing vessel
set at moderate mixing, Nitric acid (64 mL, 70%) was added to
purified H.sub.2O and diluted to 800 mL. The temperature of the
circulating heater with oil & pump was set between 65.degree.
C. and 70.degree. C. The variable speed overhead mixer with
dissolving stirrer attachment was set at 500 rpm. AgSD 30.0 g was
added slowly to the mixing water and acid mixture. The solution was
mixed for a minimum of 3 hours. The dissolution was confirmed by
turning off the mixer and observing that no solid particles settle
out after 60 seconds. The temperature of the circulating heater was
set to 80.degree. C. and the stirrer was turned back on. The
temperature in temperature controlled vessel containing the
drug/acid mixture was allowed to reach at least 75.degree. C.
before proceeding.
[0065] Micronized Titanium dioxide (2.0 g) was added to 58.4 g of
dry PVA powder. The two powders are well mixed with each other,
before being added together to the AgSD solution. While maintaining
the temperature between 75.degree. C. and 80.degree. C., the PVA
Titanium Dioxide mixture was added to the acid/water AgSD solution
with stirring at 500 rpm. The solution was mixed for an additional
3 hours at 500 rpm. The resulting PVA coating formulation was a
light yellow color and had a smooth appearance in about an hour
after the last component was added. The final volume was brought to
1.0 L with purified water.
[0066] The PVA coating formulation may be stored at room temperate
in a covered/sealed container until use. The PVA coating
formulation may have a shelf life of about 5 days from the date of
manufacture at room temperature and a shelf life of about 90 days
at about 38.degree. C. The PVA coating formulation may normally be
used at 38.degree. C. The PVA coating formulation may be heated to
its application temperature, with mixing, for 24 hours before use
ensuring that all components are in solution and well mixed. The
PVA coating formulation may be screened through the 20.times.20
stainless steel screen before being stored or used for dipping or
spray or other coating processes.
Example 5
Cross-Linking Formulation
[0067] A liter of cross-linking solution is prepared by measuring
867 mL of purified water and adding while stirring: 27 mL 37% HCl.
The solution is stirred for a minimum of 3 minutes before
proceeding. Next, 25 mL 40% glyoxal, and 81 mL 37% formaldehyde are
added sequentially, with 3 minutes of stirring after each addition.
Cross-linker is stored at room temperature in a covered container
until it is used. The shelf-life is 90 days from the date of
manufacture.
Example 6
Coating Method
[0068] A catheter to be coated was dipped into the coating material
at a temperature of approximately 38.degree. C. for 30 seconds. The
catheter was spun at 2 rpm during the immersion. The catheter was
then mechanically withdrawn from the coating material at a speed
that varied from 5 to 7 mm/second, while spinning the part at 5
rpm. The catheter was then dried for 10 minutes at 83.degree. F.,
and followed by a cross-linking step. The cross-linking step
consists of submerging the coated and dried catheter into a
solution containing the cross-linking formulation for 40 seconds,
while spinning at 5 rpm. The catheter is removed from the
cross-linking solution at 25 mm/sec and 5 rpm. Additional drying of
10 minutes at 83.degree. F. allows removal of excess crosslinking
agent, and ensures consistent coatings.
Example 7
Multiple Coating Method
[0069] The catheter of Example 4 was dipped into the coating
mixture twice, and a cross-linking solution once at the end of the
cycle. During coating, the first dip sat in the coating for 30
seconds to allow the temperature of the catheter to equilibrate
with the coating. It was withdrawn through the drying plenum, and
held for about 60 seconds before dipping a second time. The
catheter was completely submerged for 5 seconds before beginning
withdrawal through the drying plenum. Following a drying step, the
coated catheter was then combined with a solution containing a
crosslinking agent as above.
Example 8
Coating Pretreatment Method
[0070] A catheter was pretreated prior to coating. Contaminants on
the surface of the catheter, such as oil and mold release agents,
were removed by pumping down the pressure to 25 mTorr. The oxygen
cleaning and etching step was performed by setting the power of a
plasma apparatus at 495 Watts and increasing the pressure to 120
mTorr. The allyl alcohol functionalization step was performed using
a flow rate=0.25 mL of alcohol/mm for 8 minutes with 3% argon as a
carrier gas at a pressure of approximately 50 mTorr. The allyl
alcohol addition can also be done with 3% argon and 5% oxygen as
the carrier gases.
[0071] The presence of alcohol functional groups on the pretreated
catheter, was detected by soaking the sample in a solution
containing a fluorescent probe, such as
5-(4,6-dichlorotrazinyl)aminofluoroscein (DTAF) overnight and a
using a fluorometer to detect the DTAF signal on the surface of the
catheter. The presence of alcohol functional groups was
alternatively detected by dipping the catheter into 10 mg/L
methylene blue solution for 5 minutes. Samples with alcohol groups
on the surface come out medium blue, while those without the turn
out only slightly blue.
Example 9
Cross-Linking Procedure
[0072] The coating was cross-linked using a dip process which is
carried out using similar tank, mixing conditions, temperature
control and drying systems as described in Examples 4 and 5. The
catheter was dipped for 40 seconds into a tank containing a
cross-linking agent (1% glyoxal, 3% formaldehyde, 1% HCl) and
withdrawn at 25 mm/sec through the drying plenum with airflow at
several liters/mm and a temperature of 70.degree. C.
Example 10
Measurement of Coating Thickness & Estimation of AgSD
Concentration
[0073] Coating thickness was measured using standard techniques.
The catheter was cut using a scalpel forming a cross-sectional
segment having a thickness of to about 1 mm. The coating thickness
was measured utilizing an optical microscope using standard
techniques.
[0074] Loading calculations were based on the percent loading rate
(wet=2%) and loss on drying (.about.70%). The total loading
therefore increases to 6.7% by weight. The weight of the catheter
was measured before and after the application of the coating, and
the total mass of dried coating was multiplied by 6.7% to obtain
the total AgSD concentration. An analogous procedure was used for
TiO.sub.2. TiO.sub.2 was estimated to be 0.2% by weight wet.
Example 11
[0075] Dynamic Biofilm Assay
[0076] The bacterial inoculum level was maintained at a consistent
level. The inoculum was obtained by serially diluting an overnight
batch of bacterial culture of an appropriate organism. These
serially diluted batch cultures were then used to inoculate
syringes containing an appropriate diluent. Inoculum controls were
monitored daily to maintain uniform bacterial concentrations for
coated material sections. Controls were prepared in duplicate and
were plated at t=0 hours and t=24 hours.
[0077] A protein soak was performed prior to contacting the coated
material with the inoculum for the purposes of mediating bacterial
attachment. The protein soak was typically performed for a time
period of about 5 minutes utilizing either human urine or serum.
Following the protein soak, the coated material was transferred to
a flow cell and the inoculated syringes were placed onto syringe
pumps and attached to the flow cells. Length measurements were
calculated to correspond to an overall surface area of 100
mm.sup.2. Throughout the duration of the assay, the flow of
inoculum was maintained at a constant flow rate (0.007 mL/min).
[0078] At 24 hour intervals, a sample of the coated material was
removed from its flow cell and rinsed by immersing the coated
material 10 times each in 4 subsequent rinse stations, which
contained either Phosphate Buffered Saline or Nanopure Water,
thereby removing planktonic cells and leaving only adhered
bacterial cells. Following the rinse, the coated material was
transferred into an appropriate neutralizing solution, which was
specific to the coated materials' anti-infective coating.
[0079] The coated material and neutralizing solution were then
aseptically transferred to a sterile petri dish, wherein the
biofilm was removed from the coated material utilizing a sterile
scalpel. The neutralizing solution and biofilm were passed through
a pipette tip approximately 10 times to break up the biofilm. The
coated material and neutralizing solution containing the biofilm
were then transferred into a test tube and pulse sonicated for 30
seconds, thereby breaking up any remaining large groups of biofilm.
Following the sonication, the biofilm was evenly distributed in the
neutralizing solution by subjecting the test tube to vortex (30
seconds). The biofilm/neutralizing solution was serially diluted,
followed by drop plate enumeration of the dilutions.
Example 12
Static Biofilm Assay
[0080] The bacterial inoculum level was maintained at a consistent
level. The inoculum was obtained by serially diluting an overnight
batch of bacterial culture of an appropriate organism. These
serially diluted batch cultures were then used to inoculate test
tubes containing an appropriate diluent. Inoculum controls were
monitored daily to maintain uniform bacterial concentrations for
coated material sections. Controls were prepared in duplicate and
were plated at t=0 hours and t=24 hours.
[0081] Length measurements of samples to be analyzed were
calculated to correspond to an overall surface area of 100
mm.sup.2. A protein soak was performed prior to contacting the
coated material with inoculum for the purpose of mediating
bacterial attachment. The protein soak was typically performed for
a time period of about 5 minutes utilizing either human urine or
serum. Following the protein soak, the coated material was then
transferred to a sterile vile containing an appropriate diluent,
which had been inoculated with desired concentration of the
microbial organism.
[0082] Test tubes containing the coated material were placed onto
test tube rockers for 24 hours. Following the designated number of
24 hour contact cycles, the coated material to be processed was
removed from the system. Coated materials that were to continue to
endure bacterial contact were kept separate from the samples used
for quantifying adhesion. Each remaining test tube was additionally
inoculated with the microbial organism at 24 hour intervals.
[0083] The coated material was rinsed by immersing the coated
material 10 times each in 4 subsequent rinse solutions comprising
either Phosphate Buffered Saline or Nanopure Water, facilitating
the removal of planktonic cells and leaving only adhered bacterial
cells. Following the rinse, the coated material was transferred
into an appropriate neutralizing solution.
[0084] The coated material and neutralizing solution were then
aseptically transferred to a sterile petri dish, wherein the
biofilm was removed utilizing a sterile scalpel. The neutralizing
solution and biofilm were passed through a pipette tip
approximately 10 times to break up the biofilm.
[0085] The coated material and neutralizing solution containing the
biofilm were then transferred into a test tube and pulse sonicated
for 30 seconds, thereby breaking up any remaining large groups of
biofilm. Following the sonication, the biofilm was evenly
distributed in the neutralizing solution by subjecting the test
tube to vortex (30 seconds). The biofilm/neutralizing solution was
serially diluted and was followed by drop plate enumeration of the
dilutions
[0086] All patents, patent applications, and published references
cited herein are hereby incorporated by reference in their
entirety. While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
Example 13
Spray Coating Process
[0087] A PVA based spray coating was applied to polycarbonate
needle-less connectors. The PVA material used consisted of that
prepared as in Example 4, above. Two separate ultrasonic sprayers
were utilized to atomize the PVA material and the cross-linking
solutions. A rotary part holder was used to sequentially move the
parts through a series of spray and cross-linking cycles consisting
of: coating spray 16 .mu.L, 7.5 Watts, 5 seconds of spray; 3
minutes of drying at 80.degree. F.; cross-linking spray 16 .mu.L,
4.0 Watts, 5 seconds of spray; 3 minutes of drying; coating spray
16 .mu.L, 7.5 Watts, 5 seconds of spray; 3 minutes of drying at
80.degree. F.; cross-linking spray 16 .mu.L, 4.0 Watts, 5 seconds
of spray; drying time of 5 minutes at 80.degree. F. The spray
volumes and times varied based on the surface area of the part to
be sprayed, while all other parameters were held constant.
[0088] All patents, patent applications, and published references
cited herein are hereby incorporated by reference in their
entirety. While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
spirit and scope of the invention encompassed by the appended
claims.
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