U.S. patent application number 14/464897 was filed with the patent office on 2014-12-18 for reinforced, laminated, impregnated, and composite-like materials as crosslinked polyvinyl alcohol hydrogel structures.
The applicant listed for this patent is Nedeljko Vladimira Gvozdic. Invention is credited to Nedeljko Vladimira Gvozdic.
Application Number | 20140370075 14/464897 |
Document ID | / |
Family ID | 41400591 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140370075 |
Kind Code |
A1 |
Gvozdic; Nedeljko
Vladimira |
December 18, 2014 |
REINFORCED, LAMINATED, IMPREGNATED, AND COMPOSITE-LIKE MATERIALS AS
CROSSLINKED POLYVINYL ALCOHOL HYDROGEL STRUCTURES
Abstract
Reinforced, laminated, impregnated, and materials with composite
properties as cross linked polyvinyl alcohol hydrogel structures in
bulk or cellular matrix forms that can take essentially any
physical shape, or can have essentially any size, degree of
porosity and surface texture. They have a wide range of physical
properties, unusual and unique combinations of physical properties
and unique responses to stress fields, which allows for their use
in many end use applications.
Inventors: |
Gvozdic; Nedeljko Vladimira;
(Gainesville, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gvozdic; Nedeljko Vladimira |
Gainesville |
FL |
US |
|
|
Family ID: |
41400591 |
Appl. No.: |
14/464897 |
Filed: |
August 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12462829 |
Aug 10, 2009 |
8840989 |
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14464897 |
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10963053 |
Oct 12, 2004 |
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12462829 |
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10020785 |
Oct 29, 2001 |
6855743 |
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10963053 |
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Current U.S.
Class: |
424/447 ;
424/78.06; 521/141; 524/557 |
Current CPC
Class: |
A61L 15/42 20130101;
C08J 5/045 20130101; Y10T 428/31855 20150401; C08J 2201/024
20130101; C08J 3/24 20130101; C08K 3/20 20130101; Y10T 428/249921
20150401; C08J 2205/022 20130101; A61L 15/24 20130101; C08J 3/075
20130101; Y10T 428/249953 20150401; C08J 9/26 20130101; Y10T
428/31913 20150401; Y10T 428/249992 20150401; C08J 2329/04
20130101 |
Class at
Publication: |
424/447 ;
521/141; 424/78.06; 524/557 |
International
Class: |
C08J 3/075 20060101
C08J003/075; C08K 3/20 20060101 C08K003/20; A61L 15/24 20060101
A61L015/24; A61L 15/42 20060101 A61L015/42; C08J 3/24 20060101
C08J003/24; C08J 9/26 20060101 C08J009/26 |
Claims
1. (canceled)
2. A laminated polyvinyl alcohol structure, said structure having:
(A) a physically cross linked polyvinyl alcohol based matrix
derived from a bulk physically crosslinkable polyvinyl alcohol
hydrogel laminated with (B) a solid material.
3. A polyvinyl alcohol impregnated structure comprising: (A) a
solid structure, said structure being impregnated with (B) a
physically crosslinkable polyvinyl alcohol based matrix derived
from a bulk physically crosslinkable polyvinyl alcohol
hydrogel.
4.-7. (canceled)
8. A composite structure comprising two or more physically cross
linked polyvinyl alcohol based matrices each derived from a bulk
physically crosslinkable polyvinyl alcohol hydrogel.
9. A reinforced polyvinyl alcohol structure, said structure having
a polyvinyl alcohol based material with composite properties as a
matrix as claimed in claim 8 and a reinforcing material capable of
reinforcing said matrix.
10. A laminated polyvinyl alcohol structure, said structure having:
a polyvinyl alcohol based material with composite properties as a
matrix as claimed in claim 8 laminated with a solid material.
11. (canceled)
12. A composite structure comprising two or more physically cross
linked polyvinyl alcohol based matrices each derived from a
cellular physically cross linkable polyvinyl alcohol hydrogel.
13. A reinforced polyvinyl alcohol structure, said structure having
a polyvinyl alcohol based material with composite properties as a
matrix as claimed in claim 12 and a reinforcing material capable of
reinforcing said matrix.
14.-23. (canceled)
24. A composite structure comprising at least one physically cross
linked polyvinyl alcohol based matrix derived from a bulk
physically cross linkable polyvinyl alcohol hydrogel and at least
one physically cross linked polyvinyl alcohol based matrix derived
from a cellular physically cross linkable polyvinyl alcohol
hydrogel.
25. A reinforced polyvinyl alcohol structure, said structure having
a polyvinyl alcohol based material with composite properties as a
matrix as claimed in claim 24 and a reinforcing material capable of
reinforcing said matrix.
26.-66. (canceled)
67. A polyvinyl alcohol structure, said structure having: a
physically cross linked polyvinyl alcohol based matrix derived from
a combined cellular and bulk physically cross linkable polyvinyl
alcohol hydrogel and wherein the combined cellular and bulk
physically cross linkable polyvinyl alcohol based matrix has been
prepared by the method comprising the steps of: (I) providing a
polyvinyl alcohol polymer capable of being physically crosslinked;
(II) dissolving said polyvinyl alcohol polymer in a material
selected from the group consisting essentially of: (i) a single
solvent for the polyvinyl alcohol polymer and, (ii) a mixture of
solvents for the polyvinyl alcohol polymer, to form a solution,
(III) mixing the solution from (II) with a material selected from
the group consisting of: (a) a surface active agent and, (b) a
mixture of surface active agents and frothing said mixture; (IV)
combining the froth formed in (III) with polyvinyl alcohol polymer
solution: (V) providing conditions for a material with composite
properties for the mixture from (IV) at which the polymer will
undergo physical cross linking; (VI) bringing the mixture to about
room temperature.
68. A polyvinyl alcohol structure as claimed in claim 67 that is
reinforced.
69. (canceled)
70. A polyvinyl alcohol structure as claimed in claim 67 that is a
material with composite properties.
71. (canceled)
72. A polyvinyl alcohol structure, said structure having: a
physically cross linked polyvinyl alcohol based matrix derived from
a combined cellular and a bulk physically cross linkable polyvinyl
alcohol hydrogel and wherein the combined cellular and a bulk
physically cross linkable polyvinyl alcohol based matrix has been
prepared by the method comprising the steps of: (I) providing a
polyvinyl alcohol polymer capable of being physically cross linked;
(II) dissolving said polyvinyl alcohol polymer in a material
selected from the group consisting essentially of: (i) a single
solvent for the polyvinyl alcohol polymer and, (ii) a mixture of
solvents for the polyvinyl alcohol polymer, to form a solution;
(III) mixing the solution formed in (II) with a pore forming
material; (IV) combining the mixture of (III) with polyvinyl
alcohol polymer solution; (V) providing conditions for a material
with composite properties for the mixture from (IV) at which the
polymer will undergo physical cross linking; (VI) bringing the
mixture to about room temperature; (VII) removing the pore forming
material by a means which does not significantly affect the cross
linking.
73. A polyvinyl alcohol structure as claimed in claim 72 that is
reinforced.
74. (canceled)
75. A polyvinyl alcohol structure as claimed in claim 72 that is a
material with composite properties.
76.-91. (canceled)
92. A reinforced polyvinyl alcohol structure, said structure
having: a physically cross linked polyvinyl alcohol based matrix
derived from a cellular physically cross linicable polyvinyl
alcohol hydrogel wherein the cellular physically cross linkable
polyvinyl alcohol based matrix is a hydrogol sponge having
collapsed walls which has been prepared by the method comprising
the steps of: (I) providing a polyvinyl alcohol polymer capable of
being physically cross linked; (II) dissolving said polyvinyl
alcohol polymer in a material selected from the group consisting
essentially of: (i) a single solvent for the polyvinyl alcohol
polymer and, (ii) a mixture of solvents for the polyvinyl alcohol
polymer, to form a solution; (III) mixing the solution formed in
(II) with a pore-forming material; (IV) providing conditions for
the mixture of (III) in which the polyvinyl alcohol polymer will
undergo physical cross linking; (V) bringing the mixture from (IV)
to about room temperature; (VI) removing all of the solvents by a
means which does not significantly affect the cross linking or pore
forming material; (VII) heating the material at an elevated
temperature for a period of time of ten seconds to eight hours, and
(VIII) cooling the minute from (VII) to about room temperature and
removing the pore forming material by a means which does not
significantly affect the cross linking.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/462,829, filed Aug. 10, 2009, currently
pending, which is a continuation-in-part application of U.S. patent
application Ser. No. 10/963,053, filed Oct. 12, 2004, now
abandoned, which is a divisional application of U.S. Ser. No.
10/020,785, filed on Oct. 29, 2001, issued as U.S. Pat. No.
6,855,743 on Feb. 15, 2005, from which priority is claimed.
[0002] The invention disclosed herein deals with reinforced,
laminated, impregnated and composite-like materials as cross linked
polyvinyl alcohol hydrogel structures in bulk (non-cellular) or
cellular matrix forms that can take essentially any physical shape,
or can have essentially any size, degree of porosity and surface
texture. They have a wide range of physical properties, unusual and
unique combinations of physical properties and unique responses to
stress fields, which allows for their use in many end use
applications.
BACKGROUND OF THE INVENTION
[0003] Polyvinyl alcohol and its hydrogel forms have a relatively
long history of use in a wide variety of applications. Polyvinyl
alcohol in the form of fibers and covalently cross linked polyvinyl
alcohol sponges and foams have already established themselves as
very useful materials in numerous applications such as in
packaging, thermal and acoustic insulation, construction,
furniture, transportation aerospace, food industry, household,
textile, medical, cosmetics, and a number of other areas. For
example, polyvinyl alcohol sponges are used commercially as filters
for water, air filters in intakes of compressors, engines, and air
conditioners, oil filters, and the like. Large numbers of uses of
polyvinyl alcohol sponges are based on their ability to readily
absorb and hold water such as, household sponges, absorbent cloths,
industrial dehydrating rollers, paint rollers, acoustic filters,
and the like. Polyvinyl alcohol in the form of fibers is also used
in a wide variety of applications.
[0004] The use of polyvinyl alcohol hydrogels in the medical field
is especially important because of the physico-chemical properties
of the hydrogels. When the hydrogels are physically cross linked,
they have exceptional compatibility with human and animal tissue.
Some of the unique properties of physically cross linked hydrogels
is that they are imperviousness to attack by body fluids, blood,
urine and other bodily secretions. They are non-sticking and
non-adherent to tissue, essentially they do not have an affinity
for sticking to proteins and they do not have cell adsorption. They
are non-thrombogenic and have exceptional biocompatibility.
[0005] There are basically two families of methods for the
preparation of bulk and cellular hydrogels, that is, one method
which relies on covalent cross linking and the other method which
requires physical cross linking of the polyvinyl alcohol
molecules.
[0006] Thus, covalent cross linking, also known as chemical cross
linking, includes the use of multi-functional reactive chemical
molecules such as aldehydes, maleic acid, dimethyl urea,
di-isocyanates, boric acid, and the like, and also the use of
ionizing radiation, ultraviolet light, and the like, while physical
cross linking methods, also known as reversible cross linking,
includes cross linking through crystallites, hydrogen bonding and
complexing agents such as titanium, aluminum, manganese, and
copper, to name a few. Physical cross linking through formation of
crystallites in polyvinyl alcohols has been reported, using for
example, partial freeze-drying, repeated freezing and thawing, low
temperature crystallization, physical cross linking induced by the
presence of aqueous solutions of organic compounds, salts, acids
and bases and the like.
[0007] Porous (cellular) polyvinyl alcohol materials have been
prepared by frothing methods and the only method known to the
inventor herein is the preparation of cellular polyvinyl alcohol
hydrogels using covalently cross linked polyvinyl alcohol matrices.
Physical cross linking methods have been reported only for the
preparation of bulk polyvinyl alcohol hydrogels.
[0008] The preparation of cellular polyvinyl alcohol hydrogels
having open pores by reacting polyvinyl alcohol with formaldehyde
in an aqueous solution has been known for a long time. The earliest
disclosure of a method can be found in U.S. Pat. No. 2,609,347,
which issued to Wilson in 1952, that teaches the preparation of
porous polyvinyl alcohol hydrogels by cross linking the hydrogels
with formaldehyde at temperatures between 20.degree. C. and
60.degree. C. in the presence of an acid catalyst, such as sulfuric
acid. Porous structures are created by entrapping gas bubbles in
the polyvinyl alcohol solution in the presence of wetting agents
that stabilize the bubbles and help to disperse the bubbles
uniformly throughout the polyvinyl alcohol phase. The first step in
the preparation of those hydrogels is the preparation of a solution
of the polyvinyl alcohol or its copolymers in appropriate solvent,
typically water. Then the entrapment of the air bubbles in the
polyvinyl alcohol solution in the presence of a surfactant is
carried out and finally, the polyvinyl alcohol is cross linked by
reacting it with a multi-functional cross linker.
[0009] The cross linking agents used in the prior art processes
render the polyvinyl alcohol sponges insoluble in any solvent due
to formation of the covalent bonds between the molecules.
Typically, cross linking agents for the hydrogels are selected from
the aldehyde family such as for example, formaldehyde, glyoxal,
gluteraldehyde and others that leads to the formation of highly
acetalized cellular networks.
[0010] The only method for the preparation of cellular polyvinyl
alcohol hydrogels by a pore forming method is that based on
chemically cross linked matrices. The inventor herein is not aware
of any reported method for the preparation of physically cross
linked cellular polyvinyl alcohol hydrogels using pore forming
methods.
[0011] Bulk polyvinyl hydrogels can be prepared by a number of
methods. These methods teach gelling of the hydrogels from their
solutions, by, for example, cooling the solution, or by addition of
gelling agents such as, for example, phenol, naphtol, Congo Red or
amino or metallic compounds. Initially, only aqueous solutions were
used and were gelled by cooling to room temperature or below
0.degree. C. Such hydrogels are invariably fragile, weak, sticky
and unstable in water. A number of methods have also been reported
to enhance the properties of such hydrogels. Almost every time, it
was attempted by inducing additional chemical cross links using
aldehydes, boric acid, radiation and coordination bonding. However,
none of the methods that generate chemical bonds was successful in
sufficiently enhancing the physical properties of the
hydrogels.
[0012] A major improvement in the performance characteristics of
the hydrogels is disclosed in U.S. Pat. No. 4,663,358 that issued
to Hyon in 1987. This patent discloses a method of manufacturing
polyvinyl alcohol hydrogels by cooling a solution of the polyvinyl
alcohols to below 0.degree. C. in a mixed solvent consisting of
water and a water-miscible organic solvent. The preferred solvent
is a mixture of water and dimethylsulfoxide, with the water
concentration being in the range of from 10 to 90 weight percent.
The hydrogels prepared from mixed solvents are transparent whereas
hydrogels prepared from the solution in either water or
dimethylsulfoxide as the only solvent, are opaque.
[0013] U.S. Pat. No. 4,851,168 that issued in 1989 to Graiver
teaches a method of preparation of hydrogels and in particular
polyvinyl alcohol fibers, by cooling a non-aqueous solution of
polyvinyl alcohol to below -10.degree. C., wherein the solvent is a
mixture of monohydric alcohols containing 1 to 4 carbon atoms and
dimethylsulfoxide. The preferred concentration of mixed organic
solvents is about 10 to 30 weight percent of a monohydric alcohol
and the rest being dimethylsulfoxide.
[0014] A review of the prior art has disclosed only two patents
which cover the method of preparation and the composition of matter
for reinforcement of physically cross linked bulk polyvinyl alcohol
hydrogels with short polyvinyl alcohol fibers. No references were
found for laminated structures or for a structures with composite
or composite-like properties, or for impregnated structures of
physically cross linked bulk polyvinyl alcohol hydrogels.
[0015] Two patents, U.S. Pat. No. 5,336,551 that issued to Graiver
in 1995, and U.S. Pat. No. 5,422,050 that issued to Graiver in
1994, teach the composition of matter and the method to reinforce
bulk polyvinyl alcohol hydrogels with short polyvinyl alcohol
fibrils.
[0016] The reinforcement is accomplished by uniformly dispersing a
plurality of fibrils made from highly oriented crystalline
polyvinyl alcohol, wherein the diameter of the fibrils is less than
1 mm and the aspect ratio of the fibrils is from 2:1 to 1000:1. The
key feature of a reinforced hydrogel material made according to
this invention is that it has a gradual transition in the degree of
the crystallinity at the interface between the matrix and the
fibrils.
[0017] As opposed to the prior art structures, the structures of
the invention disclosed herein require no prior treatment of the
polyvinyl alcohol fiber to establish strong interfaces between the
fibers and the hydrogel matrix. This leads to cohesive failure as
the only failure mechanism of the reinforced polyvinyl alcohol
hydrogels. Also, the present invention requires no pretreatment of
a number of other fibers or structures used to reinforce and/or
laminate such hydrogels, such as, silk, wool, cellulose, acrylates,
carbon, graphite, and the like. The simple addition of these fibers
or structures to the polyvinyl alcohol solution prior to gellation
or crystallization will provide sufficiently strong interfaces with
the hydrogel and thus, ensure no adhesive failures of the
structures set forth herein.
[0018] By the invention herein, there is provided methods by which
a material with composite-like structures can be obtained by
combining physically cross linked bulk or cellular polyvinyl
alcohol hydrogels with other materials and their structures. One
can also combine physically cross linked bulk or cellular polyvinyl
alcohol hydrogels with covalently cross linked polyvinyl alcohol
hydrogels and arrive at unique unitary structures capable of
providing adhesive strength. Such adhesive resistance, wherein any
failure is due to cohesive failure, indicates that the interfacial
bonding strength is higher than the strength of the polyvinyl
alcohol hydrogel itself.
[0019] Thus, in summary, the prior art found that is related to
reinforced, laminated, composite, and impregnated structures of
physically cross linked, bulk and cellular polyvinyl alcohol
hydrogels teach the use of polyvinyl alcohol fibrils to reinforce
bulk polyvinyl alcohol hydrogels. The method of the prior art
requires heating the fibrils in a solvent for a certain time
periods to soften and partially dissolve the surfaces of the
fibrils that is necessary to impart strong interfaces between the
fibrils and the hydrogel. This method is cumbersome and is
difficult to use because of the difficulties in defining the exact
time necessary to soften the fibrils without over-softening them.
Furthermore, any upset in the process parameters, especially an
increase in the solvent treatment temperature, or exposure to the
solvent for too long a period of time, will lead to excessive or
even complete dissolution of the fibrils.
THE INVENTION
[0020] The invention disclosed and claimed herein deals with
reinforced, laminated, impregnated, and materials with composite or
composite-like properties as physically cross linked, bulk and
cellular polyvinyl alcohol hydrogels. The structures disclosed
herein are highly resilient without breaking or tearing, are
hydrophilic, not affected by common organic solvents, not affected
by changes in pH, or extremes of pH, are resistant to microbial
attack, are highly biocompatible, are non-toxic, are lint free, and
are free of any foreign leachable or covalently bonded
materials.
[0021] It is an object of this invention to provide a method for
the preparation of reinforced, or laminated, or materials with
composite-like properties, or impregnated, unitary articles or
structures that are composed of combinations of physically cross
linked bulk and/or cellular polyvinyl alcohol hydrogels having
different physical properties either alone or in combination with
reinforcement and/or lamination and/or materials with composite or
composite-like properties, and/or impregnated structures.
[0022] It is another object of this invention to provide
reinforcement and/or lamination and/or materials with composite or
composite-like properties, and/or impregnated structures which can
be combined with polyvinyl alcohol hydrogels to produce systems
having a wide variety of physical properties such as, desirable
modulus, porosity, water content, water uptake ability, and the
like, that can result in articles having almost any desired
combination of physical properties and performance
characteristics.
[0023] Yet another object of this invention is to provide processes
to tailor physical properties of reinforced and/or laminated and/or
materials with composite or composite-like properties and/or
impregnated polyvinyl hydrogel compositions by selecting proper
molecular parameters of polyvinyl alcohol polymers and solvents,
porosity, texture, water content, water uptake ability, and the
like, of cellular and bulk polyvinyl alcohol hydrogels and,
selecting the proper type of reinforcing agents and/or laminating
structures, and/or a material with composite properties structures,
and/or impregnated structures, and/or mixtures of polyvinyl alcohol
hydrogels with other more or less hydrophilic materials, and by
selecting processing conditions for solvent treatment and heat
treatment to provide articles of exceptional character and physical
properties.
[0024] Still another object of this invention is to provide methods
of coloring and/or making polyvinyl alcohol hydrogel compositions
and articles Radio opaque and to provide methods of complexing such
polyvinyl alcohol matrices with iodine and/or other germicidal
agents or disinfectants that can be fashioned into useful articles
or structures.
[0025] The physical properties of the structures of this invention
can be widely varied and precisely tailored to the needs of the
particular end use application by controlling the molecular and
processing parameters, choosing the appropriate type of hydrogel,
i.e. cellular, bulk, or a combination of these, and the nature and
the form of reinforcing agents, laminating agents, a material with
composite or composite-like properties, and impregnating agents and
structures, and the like. The hydrogel structures have an unusual
combination of physical properties as well as an unusual response
to compressive and extensional stress fields, low to exceptionally
high water holding capacity, slow to nearly instantaneous water
wicking abilities, low to exceptionally high compressibility and
expandability, weak and delicate in one dimension to exceptionally
strong in another dimension in the same object, weak and delicate
in one dimension while having high modulus and tear resistance in
another dimension in the same object, non-abrasive and very
slippery, to significantly abrasive and rugged exteriors.
[0026] The hydrogel structures of this invention can be colored or
dyed, can be made Radio opaque or complexed with iodine and other
germicides and disinfectants.
[0027] The hydrogel structures of this invention can be subjected
to a solvent treatment and/or heat treatment subsequent to
gellation in order to modify and further tailor their physical
properties.
[0028] The term "bulk polyvinyl alcohol hydrogel" as used herein
means polyvinyl alcohol hydrogels that have a certain size, shape
and volume, and are recognizable as one, two or three-dimensional
bodies, i.e. fiber-like, sheet-like or three-dimensional objects
that are non-cellular, that is, being macroscopically non-porous
bodies.
[0029] "Hydrogel" as used herein means bulk (i.e. macroscopically
non-cellular) or cellular (i.e. sponge or foam-like) polyvinyl
alcohol hydrogels that contain water but are not soluble in water
at temperatures below 40.degree. C.
[0030] "Composite" as used herein means both composites and
structures having composite properties.
[0031] The polyvinyl alcohol hydrogels of the present invention can
be designed to have exceptionally wide ranges of physical
properties and can have unusual combinations of properties within
the same unitary structure or article. This can be accomplished
according to this invention by selecting and controlling molecular
and processing parameters, selecting the nature and the form of
reinforcing and/or laminating and/or a material with composite
properties, and/or impregnated structures, selecting and combining
hydrogels having certain desirable modulus, porosity, surface
texture skin or lack thereof, water content, water uptake ability
and the like.
[0032] For example, unitary structures or article or blocks of
materials can have a multitude of properties such as the following.
They can be prepared by combining into one unitary structure,
polyvinyl alcohol hydrogels having different physical properties
such as, porosities and/or Modulii and/or responses to stress
fields, water content, water uptake abilities, and the like. One
section of a structure, or article may contain some reinforcement
and or lamination and another section of the same article may not.
For example, one section or one side of a structure can be bulk
polyvinyl alcohol hydrogel having one set of desired physical
properties while the other section or side can be cellular
polyvinyl alcohol hydrogel having another set of desired physical
properties. One section or one side of a structure may consist of
cellular polyvinyl alcohol hydrogel having one type and degree of
porosity and one set of physical properties while the other side or
section may have a different type and/or degree of porosity and the
same or different set of physical properties. Each side may or may
not have a skin. One dimension/direction/surface of an article can
be soft, delicate, slippery, while another
dimension/direction/surface can be hard, tough, rugged, abrasive,
high modulus, tear resistant, and the like. One can have a surface
or section of an article reinforced and/or laminated and/or
combined with other types of materials into materials with
composite properties while the other surface or section of that
article can be bulk or cellular polyvinyl alcohol. One can have one
surface or section of an article with a polyvinyl alcohol of one
modulus while another surface or section may have a widely
differing modulus.
[0033] One can curl, twist, bend, ripple, or warp, or change shape
in a reproducible and controlled manner induced by a loss or gain
of water or other hydrophilic liquids. The extent and direction of
curling, twisting, rippling, warping, and bending of an article can
be controlled by imbedding single or multiple, high modulus or
elastomeric fibers, sheets, laminates, or any other such desired
structure, or by combining a neat polyvinyl alcohol hydrogel on one
side with reinforced or laminated polyvinyl alcohol hydrogel on the
other side. Also, the article can be composed of two or more
different hydrogels placed on different sides of the article. One
side can be neat polyvinyl alcohol hydrogel while the other side of
the article can be a combination i.e. a mixture of polyvinyl
alcohol hydrogels with super absorbers such as sodium acrylate or
sodium alginate and the like, or components which reduce water
uptake ability of the hydrogel such as, poly(vinyl pyrrolidone),
and the like.
[0034] The hydrogel structures of the present invention can also be
colored, dyed, or rendered radio opaque and/or impregnated with
disinfectant dyes and or complexed with iodine and/or other
germicides.
[0035] These materials can be incorporated into the hydrogels
either by homogeneously or heterogeneously dispersing them therein.
They are useful during surgery. The radiopacity permits a surgeon
to easily locate the bulk or cellular material that has been placed
into a body cavity, visually, or by X-Ray. Radio opaque-containing
materials can also be placed at certain designated locations in a
device to assist in visual guidance and positioning of a device,
such as in the case of an aneurysm treatment.
[0036] Typical Radioopaque materials are those having high electron
density and include, but are not limited to barium sulfate, bismuth
suboxide, gold, and the like. Radioopaque materials are added in
various amounts to the hydrogels, usually at the level of from
about 1 to about 35 weight percent based on the total weight of the
additive and the hydrogel.
[0037] The hydrogels of this invention can be plasticized and thus
can be made permanently flexible. This can be accomplished by
incorporating suitable plasticizers, such as, but not limited to,
polyhydric alcohols having 2 to 6 carbon atoms and 2 to 3 hydroxyl
groups, particularly alkane diols and triols, diglycols,
triglycols, polyethylene and polypropylene glycols of various
molecular weights and mixtures thereof The use of triethylene
glycol is especially preferred for plasticization of the hydrogel
matrices when the articles are intended to be used for topical
human applications, and glycerin is generally used when the
plasticizer needs to have low cytotoxicity.
[0038] Physical properties of bulk and cellular physically cross
linked hydrogels can be significantly improved by reinforcing
and/or laminating agents and/or impregnating agents or structures
through the formation of sufficiently strong interfaces between the
hydrogel matrix and reinforcing and/or laminating and/or
impregnating agents or structures and/or materials with composite
properties so that preferentially adhesive failure is eliminated in
such a system, or, through the formation of sufficiently strong
mechanical interlocking between the hydrogel matrix and reinforcing
agents and/or laminate structures and/or materials with composite
structures, and/or impregnated structures, or through a combination
of these methods, which provide significant improvement in
mechanical properties of the overall systems.
[0039] Unitary articles composed of polyvinyl alcohol hydrogel
sections/sides having different compositions, modulii, porosity,
surface texture, water content, water uptake ability, and the like,
can be prepared generally in the following manner, with the details
of such methods being set forth infra.
[0040] For example, one can prepare different concentrations of
solutions of the polyvinyl alcohol or use different molecular
weights of polyvinyl alcohols for preparation of solutions,
provided that each solution can generate hydrogels having different
but desirable physical properties such as, water content, water
uptake ability, and the like, and then combine them in a mold, or
in some other method, simultaneously or sequentially, or combine
them with covalently cross linked polyvinyl alcohol
bulk/sponge/foam hydrogels.
[0041] One can prepare cellular polyvinyl alcohol hydrogels by
either pore forming methods or frothing methods either
simultaneously or sequentially and combine them with bulk
physically cross linked polyvinyl alcohol hydrogels or with
covalently cross linked polyvinyl alcohols to create portions of an
article having different porosities, different physical properties,
which may have skin or no skin, and the like.
[0042] One can coat or cover, in any desired manner, reinforced
and/or laminated and/or impregnated and/or materials with composite
properties, covalently cross linked polyvinyl alcohol structures
with either neat polyvinyl alcohol solution or with any desired
mixture of polyvinyl alcohol with other materials and subject such
systems to conditions which will induce formation of physical cross
linking sites in the polyvinyl alcohol matrix.
[0043] One can prepare a block of material having desirable
dimensions, shape and composition, and then machine the final
article out of that block material, either at room temperature or
by first freezing the whole block of material and then machining an
article from the frozen block.
[0044] One can prepare a polyvinyl alcohol solution by mixing the
polyvinyl alcohol with superabsorbing materials or materials which
reduce the ability of the materials to absorb water, and make bulk
and/or cellular polyvinyl alcohol hydrogels and use them to make
any combinations or articles described above.
[0045] Following is a general outline of the steps required to make
the structures and articles of this invention.
[0046] A. The polyvinyl alcohol polymers are first dissolved in
single or mixed solvents.
[0047] B. The appropriate conditions for preparation of the
polyvinyl alcohol hydrogels are then selected according to the
desired modulus and/or degree of porosity, water content, water
uptake ability, and other physical properties of cellular and/or
bulk polyvinyl alcohol hydrogel matrices and/or mixtures of
polyvinyl alcohols with other more or less hydrophilic
materials.
[0048] C. Mixing or otherwise combining the desired polyvinyl
alcohol solution with reinforcing agents and/or laminating and/or
impregnating structures and/or colorant and/or disinfectant dyes
and/or any other adjuvants desired for making hydrophilic materials
and/or any other adjuvant for making a particular type of bulk or
cellular polyvinyl alcohol hydrogel matrix and/or coating or
covering desired structures with the hydrogel solutions or hydrogel
mixtures.
[0049] D. Combining the material obtained in C with one or more
neat polyvinyl alcohol hydrogels having desired physical
properties, or mixture of such hydrogels with any ingredient listed
in C, including mixtures of polyvinyl alcohol with other
superabsorbing hydrogels or components which can increase or reduce
water uptake ability of the hydrogels.
[0050] E. Generating physical cross linking in the hydrogel matrix
by using any of the known methods that lead to formation of
crystallites and/or hydrogen bonding of the molecules leading to
gellation and/or coagulation of the polyvinyl alcohol matrix.
[0051] F. Removing substantially all of the solvent used to make B
or C by either evaporation, extraction or by any other means which
does not substantially affect the polyvinyl alcohol cross linking
sites or the components of the mixture of B and C
[0052] G. Solvent treating or heat-treating the article or
material, when desired, at elevated temperatures for a certain
period of time in a non-oxidizing environment.
[0053] H. Washing the hydrogel with water when necessary and
re-hydrating the hydrogel.
[0054] When the articles are prepared that contain cellular
polyvinyl alcohol hydrogels, it is typically desirable to follow
all of the steps from A to H. However, when bulk polyvinyl alcohol
hydrogels are a component of an article, the steps F and G are
typically omitted because the properties of these hydrogels can be
or are better tailored in other ways such as, by selecting proper
polyvinyl alcohol concentrations, molecular and processing
parameters, and the like, that are known in the art of physically
cross linked polyvinyl alcohol bulk hydrogels.
[0055] The instant invention also includes a combination of bulk
and cellular physically cross linked polyvinyl alcohol hydrogels
with covalently cross linked polyvinyl alcohol hydrogels and their
combinations with reinforcing and/or laminating and/or materials
with composite properties and/or impregnated structures into
articles having desirable compositions and physical properties.
[0056] Thus, the first step in the preparation of polyvinyl alcohol
hydrogels according to the present invention, is the preparation of
the appropriate polyvinyl alcohol solutions by dissolving polyvinyl
alcohol polymers in a single or mixed solvent, such as, water,
non-aqueous organic solvents, mixed organic solvents, or aqueous
solutions of salts, acids or bases.
[0057] The preferred average degree of polymerization of polyvinyl
alcohol polymer is above 500. Typically, the higher the degree of
polymerization of polyvinyl alcohol polymer, the more desirable are
the mechanical properties of the hydrogels. Polyvinyl alcohol
polymers with degrees of polymerization lower than 500 can also be
used to make cellular hydrogels according to this invention,
however, such hydrogels may not have sufficiently good mechanical
properties, especially at low polymer concentrations, unless they
are subjected to a post treatment, such as solvent or heat
treatment. The preferred degree of hydrolysis of the polyvinyl
alcohol is eighty-eight percent or higher. If the hydrogels having
high strength, high tear resistance and stability to hydrophilic
solvents are desired, then a preferred degree of hydrolysis is
greater than ninety-five percent, and most preferred is fully
hydrolyzed polyvinyl alcohol. The preferred degree of branching of
the polymers is no branching at all, or a minimum of branching.
[0058] The concentration of the polyvinyl alcohol in solution, for
purposes of this invention, is preferred to be between 0.5 and 50
weight percent, but it is not so limited. The preferred
concentration will depend on the degree of polymerization, degree
of hydrolysis, desired properties of the resulting hydrogels, the
nature of the method used to induce physical cross linking, the
nature and the extent of post treatment and the like.
[0059] The bulk and cellular hydrogels of the present invention can
be reinforced with short or long fibers, woven and non-woven, one
dimensional, two-dimensional or three-dimensional fibrous or
non-fibrous structures. These hydrogels can also be laminated with
and/or can impregnate or coat the same variety of materials and
structures as in the case of reinforcement, and lamination. Also,
the hydrogels having widely different modulii, porosity, water
content, water uptake ability, and the like can be combined into a
unitary article by combining their solutions in any desired manner,
either in a one step or a multiple step method, simultaneously or
in a sequence. Furthermore, reinforced and/or laminated, and/or a
material with composite properties hydrogels, or articles
impregnated with such hydrogels having different physical
properties can be combined into a unitary article either in one, or
two or more steps. Still further, any of the above-mentioned
hydrogels can be further combined with other hydrogels and
materials of any shape, size or structural complexity to make
articles having even more complex, but desirable combinations of
properties.
[0060] Non-polar surfaces can also generate reasonably strong
interfaces provided that their surfaces have been modified or
functionalized so that they can have sufficiently strong
interaction with the polyvinyl alcohol hydrogel. An example would
be a modified surface of a polyolefin polymer such as Vectra.RTM.
fibers available from Hoechst Celanese Corporation of Charlotte,
N.C., USA. Surface modification of non-polar substrates is
typically done by discharge treatments (corona, and glow
discharge), flame, ozone, radiation, or wet treatment. The wet
treatment of fiber surfaces requires the use of reactive chemical
agents such as those used to make primers, coatings,
electrodeposition, grafting, and the like. The laminate and the
reinforcement and impregnating material can also be based on
naturally occurring or man made fibers, non-woven fabrics of
naturally occurring or man made fibers, strands of naturally
occurring and man made fibers, knitted structures of naturally
occurring or man made fiber, and the like.
[0061] High strength and high modulus polyvinyl alcohol hydrogel
composites, and/or reinforced and/or laminated, and/or impregnated
articles are obtained especially when long fibers are woven or
knitted into two-dimensional or three dimensional structures which
are subsequently encapsulated and/or impregnated with polyvinyl
alcohol hydrogels. Mechanical strength of such structures will be
the function of fiber orientation, number of fibers per cross
sectional area and the extent to which the fibers are stretched or
aligned in the structure. Mechanical properties of such hydrogel
structures can be conveniently tailored by using appropriately
oriented fibrous structures and by choosing the appropriate type of
weaving, knitting, or braiding which will define the direction of
the mechanical reinforcement. Fibers used to weave or knit or braid
the fabrics can be of the same kind or blended fibers of different
kinds and origins. In the cases of an extensional force field, the
fibers and structures are actually load bearing while the hydrogel
matrix holds the fiber/fibrous structures together and provides a
means to maintain form and shape of an article. When such
composites are subjected to compression, the response of the
material with composite properties will typically be that of the
hydrogel matrix itself Typically, the contribution of the fibrous
structure in compression is not that significant. Fibers useful
herein can be naturally occurring or man made fibers, polymer
foams, metals, ceramics, polymers, and the like. All of the
reinforcing, laminating and impregnating fabrics and structures
typically have an intra-fabric void ratio between 20 and 90 percent
by volume.
[0062] Fibers useful herein include, but are not limited to,
synthetic fibers such as polyethylene terephthalate (PET),
polyethylene (PE), polypropylene (PP), nylon,
polytetrafluoroethylene (PTFE), polyurethane (PU), polyvinyl
alcohol (PVA), polyacrylates, rayon (regenerated cellulose fibers)
and the like. Natural fibers can be for example, collagen, chitin,
choitosan, and the like. Biodegradable fibers are, for example,
PGA, i.e. poly(glycolic acid), PLA, i.e. poly(lactic acid), PLG,
i.e. poly(lactic-co-glyclide) copolymers, PGL, i.e.
poly(glycolide-co-lactide) copolymers, polydioxanone, and the like.
Inorganic fibers include, for example, carbon fibers, ceramic
fibers, hydroxyapatite, polysiloxane fibers, and the like.
[0063] The laminate or the mechanical support for the hydrogels can
be made from woven or non-woven fabrics or films having plain,
twilled, leno, and the like, weaving. The preferred laminate
material has a porous, screen-like, fibrous or mesh structure. The
most suitable supports for laminates are typically made from long
fibers and include woven fabrics, non-woven fabrics, strands,
strands of interconnected/knitted structures, or other
interconnected fibrous structures, all either naturally occurring
or man made.
[0064] Yet another embodiment of this invention is the provision of
materials with composite properties from polyvinyl hydrogel
structures having the capability of performing as semi-permeable
membranes which are useful, for example, in ultrafiltration and
high-pressure separation processes. The semi-permeable membrane is
composed of a porous support layer made from woven or non-woven
fabrics. The fabric serves as reinforcement, a portion of a
laminate, or an impregnating structure and is covered with a layer
of the polyvinyl alcohol hydrogel resulting in an impregnated
microporous membrane. Pre-sizing of the membrane openings can be a
function of the polyvinyl alcohol hydrogel itself, or the size can
be generated by a method of extraction of a pore forming material.
In order to improve the interfacial strength between the polyvinyl
hydrogel and the fabric, it is sometimes desirable to modify, for
example, by corona treatment, the surface of the fibers used to
make the fabric.
[0065] Another embodiment of the present invention is to prepare
reinforced and laminated high strength, high modulus polyvinyl
alcohol hydrogels and articles made from them, having exceptional
dimensional stability in tension, but in compression, having
properties essentially the same as those characteristics of bulk or
cellular polyvinyl alcohol hydrogel itself The reinforcement or
lamination is accomplished by incorporating reinforcing or
laminating agents or structures into polyvinyl alcohol hydrogels
such as, knitted, woven or non-woven fabrics where fabrics were
knitted or woven in three-dimensional networks which are
subsequently impregnated or encapsulated with bulk or cellular
polyvinyl alcohol hydrogels. The fibers of the three dimensional
fabrics can be of natural, organic, inorganic or of man made
origin. When three-dimensional weaving is done by tri-axial
weaving, it can lead to the formation of tubular woven or knitted
structures that can be impregnated or laminated with the bulk or
cellular hydrogels. Such impregnated or laminated structures are
useful as artificial blood vessels, catheters, hoses, tubes, and
are especially useful to make articles and devices that are in
contact with blood or other body fluids because of exceptional
anti-thrombogenic and other biocompatibility properties of the
hydrogels. Another application of impregnated and laminated three
dimensionally woven structures is the use as an artificial
ligament, especially when it is made in the form of a cord.
[0066] Another embodiment of the present invention is when the
reinforcement or laminate is inserted through the axis of a
cylinder or through different symmetry axes of an geometrical
article or through any direction of a three dimensional or a two
dimensional article made from a bulk or cellular polyvinyl alcohol
hydrogel. One can use filaments, ropes, roving, non-woven or woven
long fibers in one dimension or two dimensions or even three
dimensions to control the expansion of the impregnated polyvinyl
alcohol hydrogel-based article. This provides directional stability
and control of directional expansion, curling, twisting, bending,
warping, and the like. This is possible because fibers have either
sufficiently good interfacial strength with the hydrogel or are
sufficiently well mechanically interlocked with the hydrogel, to
prevent, reduce, or control completely, or partially, or
differentially, the extent of expansion of the hydrogel in the
desired direction upon loss or gain of liquids, such as water, or
hydrophilic liquids, or, when the hydrogel is exposed to a stress
field.
[0067] Yet another embodiment of the present invention is to
produce hydrophilic cellular polyvinyl alcohol hydrogel matrices
free of any reactive additives and any dangling, non-reacted
functional groups belonging to covalent type cross linkers or
surface modifiers. These materials are obtained by physically cross
linking through crystallites and hydrogen bonding, wherein
crystallites may also serve as reinforcing agents. These structures
provide exceptional mechanical properties, environmentally
degradable, lint free, even when cut and used abrasively, flexible,
compressible and resilient, properties. They have a remarkable
ability to retain their original shape and volume after a force has
been removed that has been applied to them that has been used to
drain the free water from the pores thereof They are useful in a
wide variety of applications including household, cosmetic,
transportation, biomedical and numerous other applications. Since
the polyvinyl alcohol hydrogel matrices of this invention are
physically cross linked, they can be dissolved at or near the
boiling point of water or in other appropriate solvents for the
polyvinyl alcohol, and provide desirable routes for disposal and
recycling of the articles having bulk and cellular polyvinyl
hydrogels as their matrix.
[0068] The cross linking of the polyvinyl alcohol solutions leading
to bulk or cellular hydrogels can be accomplished by subjecting the
solutions or mixture to any of the following: [0069] Simple cooling
below 130.degree. C., or [0070] single freezing and thawing, or
[0071] repeated freeing and thawing in cycles, or [0072] freezing
and then partial or complete freeze drying, or [0073] applying
conditions that induce physical cross linking such as the use of
aqueous solutions of salts, acids or bases, or solutions of organic
compounds, and the like.
[0074] Since some of these methods may produce relatively weak
hydrogel matrices or hydrolytically unstable cross linking sites,
it is advantageous to subject these hydrogels to a post treatment
to improve the physical properties especially in the case of
cellular hydrogels. However, when the hydrogels are dissolved in
mixed solvents, such as those based on dimethylsulfoxide and water
or dimethylsulfoxide and alcohol, the simple holding of the
solutions at temperatures below about 130.degree. C., or cooling
the mixture to temperatures near or even below 0.degree. C., tend
to create remarkably strong physically cross linked hydrogel
matrices. Post treatment of such hydrogel matrices is often not
necessary except when it is desired to have hydrogel matrices
having anisotropic physical properties or when the hydrogel matrix
having exceptionally high mechanical strength, tear resistance,
controlled elongation or collapsed cell walls are desired.
Typically, in the case of cellular hydrogel matrices, the
improvement of physical properties through the post treatment is
often very desirable.
[0075] The present invention includes methods to tailor the
physical properties of reinforced and/or laminated and/or a
material with composite properties and/or impregnated structures
made from them. All physical properties of these hydrogels can be
varied widely by selecting appropriate processing conditions and
molecular parameters of the polyvinyl alcohol and processing aids
and desired post treatment.
[0076] For example, soft and delicate hydrogel matrices can be
obtained by selecting polyvinyl alcohol polymers having lower
molecular weight and/or lower degrees of hydrolysis and/or lower
polyvinyl alcohol concentrations in solution. Solvent treatment is
desirable when moderate improvement of physical properties of the
whole article or the segment composed of only polyvinyl alcohol
hydrogel matrix is desired. However, when physical properties of
the hydrogels need to be significantly improved, such as, strength
and tear resistance, the post treatment of the hydrogels, such as
heat treatment is particularly desirable. The duration of heat
treatment depends on the selected temperature and the nature of the
media in which heat treatment is carried out. Typically, duration
of the heat treatment is between 5 minutes to 12 hours or longer.
The higher the heat treatment temperature, the shorter the heat
treatment time. The higher the heat treatment temperature, and the
longer the duration of the heat treatment, the stronger the
hydrogel.
[0077] Mechanical drawing, i.e. molecular orientation of hydrated
hydrogels can also significantly improve mechanical strength,
modulus, tear resistance, and the like, of the hydrogel. This kind
of treatment is typically most desirable when geometry of the
object permits drawing such as in the case of fibers, rods, and
films, and the like.
[0078] Some of the reinforced and/or laminated polyvinyl alcohol
hydrogel matrices of the present invention, that are obtained
immediately after the polyvinyl alcohol matrix has been physically
cross linked are relatively weak, especially when prepared from
solutions having extremely low polyvinyl alcohol concentrations or
using polyvinyl alcohols having a low degree of polymerization
and/or low degree of hydrolysis. This is often the case with
cellular polyvinyl alcohol hydrogels. Mechanical properties of such
hydrogels can be improved by the treatment of the hydrogels by
solvents. Solvents used to prepare the polyvinyl alcohol gel need
to be removed by extraction or evaporation, or any other convenient
means. The solvent extraction and the solvent treatment are
typically done simultaneously by simply placing the hydrogel into a
desired low boiling solvent such as, methanol, or ethanol, or
acetone, to extract all of the solvents used to prepare the
solution. In order to accelerate solvent removal, the use of
Soxhlet-like extractors is preferred. Upon extraction of all
original solvents used to prepare the hydrogel, the gel becomes
significantly stronger. It was also found that a simple drying of
the extracted gel at room temperature typically further improves
the mechanical properties of the hydrogel upon re-hydration.
[0079] Once the original solvents that have been used to prepare
the polyvinyl alcohol solution are removed and the hydrogel matrix
has been dried, the mechanical properties of the hydrogels can be
further dramatically improved by subsequent heat treatment at
elevated temperatures. The present invention requires that in order
to maximize the improvement of physical properties by heat
treatment of the hydrogel matrix, substantially all of the solvents
must be removed. The heat treatment is believed by the inventor
herein to be an "annealing" process that causes an increase in
crystallinity of the polyvinyl alcohol, but the inventor should not
be held to such a theory. The increase in crystallinity reduces the
ability of the hydrogels to hydrate and expand making such hydrogel
matrices significantly more firm, rugged, and abrasive, leading to
significant increases in mechanical strength.
[0080] The preferred heat treatment of the hydrogel matrix is
carried out at temperatures between 40 and 180.degree. C.,
preferably in a vacuum or non-oxidizing atmosphere such as nitrogen
or non-oxidizing liquids such as silicone oils, organic solvents,
solutions of salts, or the like. Heat treatment may also be carried
out in air, but oxygen from the air may cause undesirable oxidative
degradation of the polyvinyl alcohol at elevated temperatures. It
is critical that the heat treatment temperatures be lower than the
melting temperature or degradation temperature of selected
polyvinyl alcohol and that all ingredients such as reinforcement,
laminating and impregnating materials, colorants, radioopaque
materials, and the like, are also stable at the selected heat
treatment temperatures. The duration of the heat treatment depends
on the selected temperature and the nature of the media in which
the heat treatment is carried out. Typically, the duration of a
heat treatment is between 5 minutes to 12 hours or longer.
[0081] The structures of the instant invention have substantial
biocompatibility. They are not toxic, they will not cause
inflammation of tissue, and they will not irritate tissue or
encourage tissue growth into them. They will not adhere to a human
tissue nor require adhesion prevention ointments such as petroleum
jelly, which in itself could produce a foreign body reaction of the
tissue.
[0082] These materials are capable of allowing water and water
soluble, low molecular weight compounds to pass through them. Such
compounds are, for example, ammonia, common salts, uric acid, urea,
creatinine, glucose, lactic acid and antibiotics. However, the
passing of bacteria, yeasts and molds cannot take place through
them. Therefore, in the event that sterile polyvinyl alcohol
hydrogel matrices are exposed to non-aseptic environment, the
contamination of the polyvinyl hydrogel matrix is only limited to
the surface of the hydrogel. The hydrogel can be made aseptic again
by sterilizing the surface by using ultraviolet light or ethylene
oxide, propylene oxide, ozone, hydrogen peroxide, aldehydes, ethyl
alcohol, isopropyl alcohol, or chlorohexidine, or the like,
followed by washing with sterile water or saline.
[0083] The biocompatibility of these hydrogel systems provides that
they have a wide range of applications in the biomedical field.
They can easily be made to contain very low to very high water
content and thus can easily match the water content of various
tissues. They can be used externally or internally, such as, but
not limited to, bandages applied to wounds, trauma treatment such
as thermal and chemical burns, or as application to ulcers, lesions
and surgical sites, or sanitary napkins, swabs, surgical aids,
various implants, such as cardiovascular, orthopedic,
reconstructive and cosmetic surgeries. As surgical aids, these
hydrogels can be used to remove body fluids such as blood, serum,
plasma, lymph fluid, spinal fluids, urine, sweat, bile juices,
digestive fluids, blotters for incisions, and the like. They can be
used to separate organs and absorb blood and other body fluids
during internal surgery. The smooth surfaces provide little or no
abrasion to even the most delicate tissues, such as the brain,
while maintaining an anti-thrombic character. Separation of organs
can be done using these systems that are in the form of films and
sheets, which can be reinforced or laminated, impregnated, or in
the form of a material with composite properties, to maintain the
desired form and shape.
[0084] The polyvinyl alcohol structures of the present invention
are also useful in alkaline and acidic environments because they
have good resistance to these materials. These polyvinyl alcohol
structures can also act as superabsorbents.
[0085] Another embodiment of this invention is the impregnation of
microcellular polyester and polyether based cellular urethane foams
and the like with the bulk or cellular polyvinyl alcohol hydrogels
with the result that unique materials with composite properties and
structures are obtained that retain the physical properties of the
support material, but exhibit the biocompatibility of the hydrogel.
Other base materials that can be used are, for example, cellophane,
cellulose acetate, ethyl acetate copolymers, polyurethane,
plasticized vinyl acetate-vinyl chloride copolymers, ethylene-vinyl
acetate copolymers, polyester elastomers, polyether block
copolymers, polyacrylates, ethylene-acrylate copolymers,
polyesters, ionomer resins, nylon, polyethylene, polypropylene and
their copolymers, polyvinyl chloride, paper, cloth, aluminum foil,
and the like.
[0086] The polyvinyl alcohol structures of the present invention
can have uses in endovascular, thoracic, gastrological and
urological prosthesis applications. Such structures can be made by
impregnating tubular, woven, three-dimensional fabrics, or crossed
helical wire mesh structures, and the like. The tubular fabric can
be woven in a tight manner providing no expansion, or can be woven
in a manner that provides an ability to change the shape as a
response to any stress field imposed on the impregnated tube and
which can also act as a reinforcement that prevents the bursting of
the tube. When the fabric is loosely woven and impregnated with the
hydrogel, it can be used as an inflatable balloon. These structures
can be used as stents, vascular grafts, catheters, expansion
balloons, drainage tubes for body fluids, internal tubes that
provide inner body secretions to flow from organs where they are
produced to the desired organs, audio and pulmonary tubular
structures, bandages and topical patches for wounds, burns, ulcers,
lesions, trauma or surgical sites, transdermal films which can have
the ability to release active agents into the body by targeting,
triggering and modulating mechanisms of controlled release,
suppositories which can have the ability for controlled release of
active agents, and gauze-like pads.
[0087] The polyvinyl alcohol structures of the present invention
can be used as substrates and/or scaffolding structures for tissue
engineering. The substrates and scaffolding can be either made from
neat bulk or cellular polyvinyl alcohol hydrogels or from the
corresponding reinforced, laminated and/or impregnated and/or
materials with composite properties in the form of one, two, or
three-dimensional objects. They can be used as neat hydrogels or
may contain any of the desirable bioactive agents that can be
released in a controlled manner to induce, promote, guide, and the
like, of tissue growth. These substrates and/or scaffolding
structures made from polyvinyl alcohol hydrogels in addition to
crystallite cross linking sites, may contain ionic cross linking
sites that can be selectively removed leaving crystallite physical
sites intact when desired. The selective removal of ionic cross
linking sites is possible because of their hydrolytic instability
in certain environments.
[0088] These structures also have application in non-surgical uses,
for example, hydrogel sponges by themselves, or reinforced and/or
laminated sponges with other, different materials, can be used in
cosmetics and in health care application as absorbents and packing,
and these sponges and laminated and reinforced sponges can be used
in tissue protective applications such as catamenial pads,
cardioplegic blankets, neurological sponges, bandages, dressing for
wounds, and the like.
[0089] The polyvinyl alcohol structures of this invention can also
bind disinfectants such as disinfectant dyes, such as methylene
blue, gentian violet, acridine orange, brilliant green, acridine
yellow, quinacrine, trypan blue, and trypan red, and the like.
[0090] The polyvinyl alcohol hydrogels can be used to modify the
surfaces of other materials to provide structures having
hydrophilic surfaces, biocompatibility, softness, slipperiness, and
the like. These materials are especially useful for treating blood
handling and blood testing equipment to prevent the adhesion of
blood or blood components to the equipment, thus eliminating
thrombogenic process that may cause false test results or make
blood unsafe for patients to use.
[0091] The structures of this invention are useful as self-sealing
gaskets and seals in applications that require special shapes,
forms and performance characteristics, such as, for example, for
handling water, or polar and non-polar solvents.
[0092] The technology of this invention is also useful in the
manufacture of fishing lures, especially at the dockside, or in a
boat, where the lures can be manufactured for the immediate need.
These structures can also be formed into toys that have unique
changes in shapes and sizes that are induced by the loss or gain of
water.
[0093] They can take the form of films, tubes, rods, bulk pieces,
which can be obtained by common methods such as extrusion, molding,
casting, coating, machining, and the like. They can be co-extruded,
co-molded, and co-cast, as well.
[0094] The fact that the hydrogels of the present invention can be
produced by physical cross linking of the polyvinyl alcohol matrix
and that the physical properties of the hydrogels can be modified
and improved without the use of chemical means such as
multi-functional cross linker or radiation or any other additives
to create covalent cross linking sites, is a very desirable feature
particularly when the hydrogels are used in biomedical application.
Just as in the case of neat bulk and cellular hydrogels, the
materials and the articles of the present invention, which include
the reinforced, laminated, materials with composite properties, and
impregnated articles from the hydrogels, possess all the desirable
and unique properties of neat hydrogels plus some additional unique
properties.
[0095] The ability to be reinforced and/or laminated, and/or make a
material with composite properties, or make impregnated articles
from bulk and cellular polyvinyl alcohol hydrogels having different
modulus, response to stress field, porosity, water content, water,
uptake ability, and the like is very important for a variety of
applications. For example, such materials with composite properties
can be very desirable to produce articles useful in medical
applications, such as, wound and burn dressing, surgical aids,
articles useful in dentistry, cosmetics and other applications as
desired, wherein the unique hydrogel structures and articles are
critical for the performance of the same.
[0096] Turning now to the methods by which the structures of the
present invention are prepared, starting with the preparation
methods for the polyvinyl alcohol solutions and hydrogels, one such
method is the preparation of a cellular, physically cross linked
polyvinyl alcohol structure, wherein the structure has a cross
linked polyvinyl alcohol based matrix derived from a cellular cross
linkable polyvinyl alcohol hydrogel wherein the cellular cross
linkable polyvinyl alcohol based matrix is a hydrogel sponge having
collapsed walls which have been prepared by a method comprising the
steps of providing a polymer capable of being physically cross
linked and then dissolving the polymer in a material selected from
the group consisting essentially of a single solvent for the
polyvinyl alcohol, or a mixture of solvents for the polyvinyl
alcohol, to form a solution. The solution is then mixed with a
pore-forming material. Then, the polymer is physically cross linked
and this solution of cross linked polymer is brought to about room
temperature and then essentially all of the solvents are removed by
a method which does not significantly affect the cross linking or
pore forming material. Thereafter, the mixture is heated at an
elevated temperature for a period of from ten seconds to about
eight hours and then cooled to about room temperature again and
then the pore forming material is removed by a means which does not
significantly affect the cross linking.
[0097] Yet another method is based on providing a physically cross
linked polyvinyl alcohol based matrix derived from a cellular
physically cross linkable polyvinyl alcohol hydrogel wherein the
cellular physically cross linkable polyvinyl alcohol based matrix
is a hydrogel sponge having expanded walls which has been prepared
by the method comprising the steps of providing a polyvinyl alcohol
polymer capable of being physically cross linked and dissolving the
polymer in a material selected from the group consisting
essentially of a single solvent for the polyvinyl alcohol or a
mixture of solvents for the polyvinyl alcohol, to form a solution.
This solution is then mixed with a pore-forming material and then
physically cross linked. This material is then brought to about
room temperature and the pore forming material is removed by a
means which does not significantly affect the cross linking or pore
forming material.
[0098] Still another method comprises providing a physically cross
linked polyvinyl alcohol based matrix derived from a cellular
physically cross linkable polyvinyl alcohol hydrogel wherein the
cellular physically cross linkable polyvinyl alcohol based matrix
has been prepared by the method comprising the steps of providing a
polyvinyl alcohol polymer capable of being physically cross linked
and dissolving the polymer in a material selected from the group
consisting essentially of a single solvent for the polyvinyl
alcohol or a mixture of solvents for the polyvinyl alcohol to form
a solution. The solution thus formed is mixed with a pore-forming
material capable of partially dissolving in the solution. There is
then provided conditions at which the polymer will undergo physical
cross linking caused by the presence of the partially dissolved
pore forming material. The mixture is then brought to about room
temperature and the pore forming material is removed by a means
which does not significantly affect the cross linking or pore
forming material.
[0099] In addition, there is another method which requires
providing a physically cross linked polyvinyl alcohol based matrix
derived from a cellular physically cross linkable polyvinyl alcohol
hydrogel wherein the cellular physically cross linkable polyvinyl
alcohol based matrix has been prepared by the method comprising the
steps of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polyvinyl alcohol
polymer in a material selected from the group consisting
essentially of a single solvent for the polyvinyl alcohol or a
mixture of solvents for the polyvinyl alcohol to form a solution
and then mixing the solution with a pore-forming material capable
of partially dissolving in the solution. Then, providing conditions
at which the polymer will undergo physical cross linking caused by
the presence of the partially dissolved pore forming material and
then bringing the mixture to about room temperature. Thereafter,
all of the solvents are removed by a means which does not
significantly affect the cross linking or pore forming material.
Then heating the material at an elevated temperature for a period
of time of ten seconds to about eight hours, and then cooling the
mixture to about room temperature and removing the pore forming
material by a means which does not significantly affect the cross
linking.
[0100] A further method requires that there is provided a
physically cross linked polyvinyl alcohol based matrix derived from
a cellular physically cross linkable polyvinyl alcohol hydrogel
wherein the cellular physically cross linkable polyvinyl alcohol
based matrix has been prepared by a method comprising the steps of
providing a polyvinyl alcohol polymer capable of being physically
cross linked and dissolving said polymer in a material selected
from the group consisting essentially of a single solvent for the
polyvinyl alcohol or a mixture of solvents for the polyvinyl
alcohol to form a solution and then mixing the solution with a
pore-forming material. The mixture is then submersed in a bath
consisting of a material selected from the group consisting
essentially of a non-solvent for the polyvinyl alcohol polymer, or
is a low temperature non-solvent for the polyvinyl alcohol polymer
or, a poor solvent for the polyvinyl alcohol polymer, or an aqueous
solution of a material selected from the group consisting
essentially of a salt, or an acid at a low temperature, or, a base,
to induce physical crosslinking such as crystallization, gellation,
coagulation, or a mixture of crystallization, gellation, or
coagulation, of the polyvinyl alcohol polymer. The solution is then
brought to about room temperature and essentially all of the pore
forming materials are removed by means which does not significantly
affect the cross linking.
[0101] Going to still another method there is provided a physically
cross linked polyvinyl alcohol based matrix derived from a cellular
physically crosslinkable polyvinyl alcohol hydrogel in combination
with a reinforcing material capable of reinforcing said matrix
wherein the cellular physically cross linkable polyvinyl alcohol
based matrix has been prepared by the method comprising the steps
of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polymer in a material
selected from the group consisting essentially of a single solvent
for the polyvinyl alcohol or a mixture of solvents for the
polyvinyl alcohol to form a solution. The solution is mixed with a
pore-forming material and reinforcing material and then submersed
in a bath consisting of a material selected from the group
consisting essentially of a non-solvent for the polyvinyl alcohol
polymer at low temperature or, a non-solvent for the polyvinyl
alcohol polymer, or a poor solvent, to induce crystallization,
gellation, coagulation, or a mixture of crystallization, gellation,
or coagulation, of the polyvinyl alcohol polymer.
[0102] The mixture is then brought to about room temperature and
all of the pore forming materials are removed by a means which does
not significantly affect the cross linking.
[0103] There is additionally provided a method that requires
providing a physically cross linked polyvinyl alcohol based matrix
derived from a cellular physically cross linkable polyvinyl alcohol
hydrogel in combination with a reinforcing material capable of
reinforcing said matrix wherein the cellular physically cross
sinkable polyvinyl alcohol based matrix has been prepared by the
method comprising the steps of providing a polyvinyl alcohol
polymer capable of being physically cross linked and dissolving the
polymer in a material selected from the group consisting
essentially of a single solvent for the polyvinyl alcohol or, a
mixture of solvents for the polyvinyl alcohol to form a solution.
The solution is then mixed with a pore-forming material and
reinforcing material and then submersed in a bath consisting of a
solution of a material selected from the group consisting
essentially of a salt, or an acid at a low temperature or, a base
to induce physical crosslinking such as crystallization, gellation,
coagulation, or a mixture of crystallization, gellation, or
coagulation, of the polyvinyl alcohol polymer. The mixture is then
brought to about room temperature and essentially all of the pore
forming materials are removed by a means which does not
significantly affect the cross linking.
[0104] Yet another method requires providing a physically cross
linked polyvinyl alcohol based matrix derived from a cellular
physically cross linkable polyvinyl alcohol hydrogel in combination
with a reinforcing material capable of reinforcing the matrix
wherein the cellular physically cross linkable polyvinyl alcohol
based matrix has been prepared by the method comprising the steps
of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polymer in a material
selected from the group consisting essentially of a single solvent
for the polyvinyl alcohol or, a mixture of solvents for the
polyvinyl alcohol to form a solution. Thereafter, mixing the
solution with a material selected from the group consisting
essentially of a surface active agent or a mixture of surface
active agents and frothing the mixture. Thereafter, mixing the
froth with the reinforced material and cooling the frothed mixture
to a temperature at which the polymer will undergo physical cross
linking and then essentially removing any solvent present in the
frothed mixture by a means which does not significantly affect the
cross linking and then bringing the mixture to an elevated
temperature for a period of time and then cooling the mixture to
about room temperature.
[0105] Going on, there is provided still another method wherein
there is provided a physically cross linked polyvinyl alcohol based
matrix derived from a cellular physically cross linkable polyvinyl
alcohol hydrogel in combination with a reinforcing material capable
of reinforcing the matrix wherein the cellular physically cross
linkable polyvinyl alcohol based matrix has been prepared by the
method comprising the steps of providing a polyvinyl alcohol
polymer capable of being physically cross linked and dissolving the
polymer in a material selected from the group consisting
essentially of a single solvent for the polyvinyl alcohol or, a
mixture of solvents for the polyvinyl alcohol to form a solution.
The solution is then mixed with a material selected from the group
consisting essentially of a surface active agent or, a mixture of
surface active agents and frothing the mixture. Thereafter mixing
the froth with the reinforcing material and cooling the mixture to
a temperature at which the polymer will undergo physical cross
linking and then bringing the mixture to about room
temperature.
[0106] Going to another method, the method requires that there is
provided a physically cross linked polyvinyl alcohol based matrix
derived from a cellular physically cross linkable polyvinyl alcohol
hydrogel in combination with a reinforcing material capable of
reinforcing said matrix wherein the cellular physically cross
linkable polyvinyl alcohol based matrix has been prepared by the
method comprising the steps of providing a polyvinyl alcohol
polymer capable of being physically cross linked and dissolving
said polymer in a material selected from the group consisting
essentially of a single solvent for the polyvinyl alcohol or, a
mixture of solvents for the polyvinyl alcohol to form a solution.
Thereafter, mixing the solution with a material selected from the
group consisting essentially of a surface active agent or, a
mixture of surface active agents and frothing the mixture.
Thereafter, mixing the froth with the reinforcing material and
cooling the frothed mixture to a temperature at which the polymer
will undergo physical cross linking and thereafter, submersing the
mixture in a bath consisting essentially of a material selected
from the group consisting of a non-solvent at low temperature for
the polyvinyl alcohol or, a non-solvent for the polyvinyl alcohol
or, a poor solvent for the polyvinyl alcohol or, an aqueous
solution of a salt or, an aqueous solution of an acid at low
temperature or, an aqueous solution of a base to induce
crystallization, gellation, coagulation, or a mixture of
crystallization, gellation, or coagulation of said polymer.
[0107] Still another method is that wherein there is provided a
physically cross linked polyvinyl alcohol based matrix derived from
a cellular physically cross linkable polyvinyl alcohol hydrogel in
combination with a reinforcing material capable of reinforcing the
matrix wherein the cellular physically cross linkable polyvinyl
alcohol based matrix has been prepared by the method comprising the
steps of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polymer in a material
selected from the group consisting essentially of a single solvent
for the polyvinyl alcohol or, a mixture of the solvents for the
polyvinyl alcohol to form a solution. Thereafter, mixing the
solution with a material selected from the group consisting
essentially of a surface active agent or, a mixture of surface
active agents and frothing said mixture. Thereafter, mixing the
froth with the reinforcing material and cooling the mixture to a
temperature at which the polymer will undergo physical cross
linking and thereafter, submersing the mixture in a bath consisting
of an aqueous solution of a material selected from the groups
consisting essentially of a salt or, an acid at low temperature or,
a base to induce crystallization, gellation, coagulation or a
mixture of crystallization, gellation or coagulation of said
polymer.
[0108] There is also a method which requires providing a physically
cross linked polyvinyl alcohol based matrix derived from a cellular
physically cross linkable polyvinyl alcohol hydrogel in combination
with a reinforcing material capable of reinforcing the matrix
wherein the cellular physically cross linkable polyvinyl alcohol
based matrix has been prepared by the method comprising the steps
of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polymer in a material
selected from the group consisting essentially of a single solvent
for the polyvinyl alcohol or, a mixture of solvents for the
polyvinyl alcohol to form a solution and thereafter, mixing the
solution with a material selected from the group consisting of a
surface active agent or, a mixture of surface active agents and
frothing the mixture and thereafter, combining the froth with the
solution of polyvinyl alcohol containing a pore forming material
and the reinforcing material into a unitary object of a desired
shape and producing a material with composite properties.
Thereafter, submersing the resulting a material with composite
properties material in a bath consisting of a material selected
from the group consisting essentially of a non-solvent for the
polyvinyl alcohol or, a poor solvent for the polyvinyl alcohol and
thereafter, providing conditions at which the polymer will undergo
physical cross linking. Then bringing the mixture to about room
temperature and removing the pore forming material by a means which
does not significantly affect the cross linking.
[0109] Finally there is a method which requires providing a
physically cross linked polyvinyl alcohol based matrix derived from
a cellular physically cross linkable polyvinyl alcohol hydrogel in
combination with a reinforcing material capable of reinforcing said
matrix wherein the cellular physically cross linkable polyvinyl
alcohol based matrix has been prepared by the method comprising the
steps of providing a polyvinyl alcohol polymer capable of being
physically cross linked and dissolving the polymer in a material
selected from the group consisting essentially of a single solvent
for the polyvinyl alcohol or, a mixture of solvents for the
polyvinyl alcohol to form a solution. Thereafter, mixing the
solution with material selected from the group consisting of a
surface active agent or, a mixture of surface active agents and
frothing the mixture and thereafter, combining the froth with a
polyvinyl alcohol solution containing pore forming material and the
reinforcing material. The combination is then submersed in a bath
consisting essentially of a non-solvent for the polyvinyl alcohol
or, a poor solvent for the polyvinyl alcohol and then providing
conditions at which the polymer will undergo physical cross
linking. Thereafter, the mixture is brought to about room
temperature and the solvents are removed by a means which does not
significantly affect the cross linking or pore forming material.
Thereafter, heating the material at an elevated temperature for a
period of time from ten seconds to about eight hours, and then
cooling the mixture to about room temperature and removing the pore
forming material by a means which does not significantly affect the
cross linking. This method produces reinforced a material with
composite properties objects consisting of two different cellular
structures having collapsed walls.
[0110] It will be obvious to one skilled in the art upon reading
this specification, to envision the possibility of variations,
combinations and all of the possibilities of processing of the
hydrogels and the reinforcement, lamination and impregnation of any
object having a simple or complex composition, consisting of bulk
and cellular polyvinyl alcohol hydrogel materials, once the
essentials of this specification and the examples presented below
have been studied.
[0111] For example, one can create the objects based on the
enclosed teaching in the following general ways: making each
section or segment of the object separately and independently of
the other sections or segments, such that one section or segment is
produced at a time, but in a continuous sequence of steps; making
each section or segment of the object separately and independently
of the other sections or segments, that is, one section segment at
a time, and then assembling them later on and making them adhere to
each other using, for example, warm or hot polyvinyl alcohol
solutions, or tackifying the surfaces with solvents or using a
cyanoacrylate types of glue or similar adhesives or, making all the
sections or segments of the object simultaneously, i.e. at the same
time by co-extrusion, co-molding, co-deposition, or using a process
similar to ink-jet dispensing mechanisms for custom building of
complex or intricate three-dimensional devices or objects, i.e.
rapid prototyping or rapid stereo object production, relying on
computer aided manufacturing.
[0112] The pore forming materials and surface active agents useful
in this invention are those pore forming materials and surface
active agents that are well-known to those skilled in the art,
representative examples of which are set forth in the following
examples.
EXAMPLES
Example 1
[0113] A polyvinyl alcohol polymer having a high degree of
polymerization and having a viscosity of about 66 cps for a 4
weight percent aqueous polyvinyl alcohol solution at 20.degree. C.,
and a high degree of hydrolysis of about 99.3% was dissolved in an
80/20 dimethylsulfoxide and water solution with the polyvinyl
alcohol concentration at about 25 weight %. Dissolution was carried
out at 120.degree. C. under a nitrogen atmosphere while
continuously stirring for three hours. Cotton gauze was placed on
the entire bottom surface of a rectangular mold with the depth of
the mold being about 4 mm. Then the solution, which had been kept
at about 95.degree. C., was poured on top of the gauze in the mold
to completely fill the mold. Additional rectangular molds were used
and the molds were filled with the solution to about half of the
depth of the mold. Then, cotton gauze was placed on the top of the
solution in the mold and an additional solution was poured into the
mold to fill it. In both cases, the molds containing cotton gauze,
together with the solution were placed into a freezer at a
temperature of -18.degree. C. for 8 hours. The molds were then
taken out of the freezer and the reinforced matrices removed and
submersed in a water bath to extract the dimethylsulfoxide. The
water in the bath was changed four times every 6 hours. The
resulting product contained no detectable dimethylsulfoxide. This
hydrogel system had a high modulus, tensile strength and tear
resistance along the plane of the cotton gauze, while perpendicular
to the plane of the cotton gauze, the mechanical properties were
those characteristic of the hydrogel itself Upon a small loss of
water, the hydrogel having gauze on only one of its surfaces curled
uniformly onto itself The hydrogel having gauze in the middle
shrank uniformly upon controlled loss of water. When these
reinforced and laminate samples were exposed to tensile or shear
forces, they failed exclusively through cohesive mechanisms
indicating that the interfacial strength between cotton gauze and
the polyvinyl alcohol hydrogel matrix is at least as high as the
strength of the polyvinyl alcohol hydrogel matrix itself.
Example 2
[0114] The same procedure was used as in example 1 except that the
concentration of the hydrogel in the solution was five weight % and
knitted wool cloth was used for the reinforcement. The surfaces of
the reinforced hydrogel in this case were very soft and delicate to
the touch. However, modulus, tensile strength and tear resistance
in the plane of the reinforcement corresponded to the knitted wool
cloth, while perpendicular to the plane of the knitted wool cloth
the mechanical properties were those characteristic of the hydrogel
itself. Similar phenomena, as described in example 1 were observed
in both of these samples when the samples lost water. When these
reinforced and laminate samples were exposed to tensile or shear
forces, they failed exclusively through cohesive mechanism
indicating that the interfacial strength between wool cloth and the
polyvinyl alcohol hydrogel matrix is at least as high as the
strength of the polyvinyl alcohol hydrogel matrix itself.
Example 3
[0115] A similar procedure was used as in example 1 except that the
polyvinyl alcohol had a low degree of polymerization, having a
viscosity of about 4 cps for a 4 weight % solution at 20.degree.
C., and a degree of hydrolysis of about 98% was dissolved in a
70/30 dimethylsulfoxide/ethanol solution with the concentration of
the hydrogel being about 30 weight %. In this case, knitted acrylic
fiber cloth was used for the reinforcement. The mechanical
properties of the polyvinyl alcohol matrix were further improved by
using heat treatment procedures by holding the sample in a vacuum
at 90.degree. C. for two hours.
[0116] The modulus, tensile strength and tear resistance of these
samples in the plane of the knitted acrylic fiber cloth were those
characteristic of the acrylic fiber cloth reinforcing material
while perpendicular to the plane of the knitted wool cloth the
mechanical properties were those characteristic of the hydrogel
itself Similar phenomena were observed again with the samples when
they lost water, as in the Examples above. When these reinforced
and laminated samples were exposed to tensile or shear forces, they
failed exclusively through cohesive mechanism indicating that the
interfacial strength between knitted acrylic fiber cloth and
polyvinyl alcohol hydrogel matrix is at least as high as the
strength of the polyvinyl alcohol hydrogel matrix itself.
Example 4
[0117] Using the procedure of example 1, a polyvinyl alcohol having
a medium high degree of polymerization, having a viscosity of about
50 cps for a 4 weight % aqueous solution at 20.degree. C., and a
degree of hydrolysis of about 88%, was dissolved in a 80/20
dimethylsulfoxide/ethanol solution with a hydrogel concentration of
about 30 weight %. A cloth of carbon fibers provided the
reinforcement. The hydrogel of this example was not completely
stable when submersed into water at room temperature for an
extended period of time. The resulting a material with composite
properties was very soft and delicate to the touch. The stability
of the hydrogel was significantly improved by a heat treatment at
180.degree. C. in a vacuum for 1 minute. After this heat treatment,
the sample typically showed a weight loss of about 25 to 30 weight
% in water at room temperature, but after losing that weight, the
hydrogel samples became stable in the water for an extended period
of time and showed nor further loss of weight. The modulus, tensile
strength and tear resistance of these reinforced hydrogels in the
plane of the carbon fiber cloth was that characteristic of the
carbon fiber cloth while, perpendicular to the plane of the carbon
fiber cloth, the mechanical properties were those characteristic of
the hydrogel itself Similar phenomena were observed again with both
of these samples when the samples lost water as described in
Example 1. When these reinforced and laminated samples were exposed
to tensile or shear forces, they failed exclusively through
cohesive mechanisms indicating that the interfacial strength
between the carbon fiber cloth and the polyvinyl alcohol hydrogel
matrix is at least as high as the strength of the polyvinyl alcohol
hydrogel matrix itself.
Example 5
[0118] Similar procedures as was used in example 2 were used herein
except that extrusion was used to create 7 mm diameter rods having
imbedded in them continuous Vectra(r) fibers along their length.
The polyvinyl alcohol hydrogel rods were extruded so that the fiber
or fibers in each rod were positioned in different fashions. Sample
(a) contained a single fiber in the middle of the rod. Sample (b)
contained a single fiber along the outer surface in a straight
fashion. Sample (c) had fiber wound as a spiral around the outside
surface of the rod and sample (d) contained multiple fibers
parallel to the axis of the rod. After physical cross linking and
extraction of the solvent, as described in example 1, these samples
underwent unique changes in the shape after a small loss of water
and after the extraction of the solvent. Sample (a) was randomly
warped, sample (b) was randomly twisted, while sample (c) had
regular twisting, that is, a spiraling shape. Sample (d) behaved
similarly as (a) except it was less warped and had a higher tensile
strength since it contained more of the fibers in its cross
section. All of these samples, as expected, in the direction of the
fibers had modulus, tensile strength and tear resistance
characteristic of the fibers. However, these rods were soft and
delicate to the touch in a direction perpendicular to the axis of
the rods, exhibiting properties typical for high water content
polyvinyl alcohol hydrogels. When these reinforced and laminated
samples were exposed to tensile or shear forces, they failed
exclusively through cohesive mechanisms indicating that the
interfacial strength between the fibers and the polyvinyl alcohol
hydrogel matrix is at least as high as the strength of the
polyvinyl alcohol hydrogel matrix itself.
Example 6
[0119] Similar procedures were used herein as described in Example
1 except that the polyvinyl alcohol concentration in the solution
was 11 weight % and instead of using neat solution as in example 1,
polyvinyl alcohol solution was first loaded with coarse sugar as a
pore forming material wherein the sugar had an average particle
size of about 0.8 mm. In this case, woven cloth made from natural
silk was used for reinforcement. After the physical cross linking,
and after water extraction of the sugar, the resulting material was
soft, delicate and opaque. However, as expected, modulus, tensile
strength and tear resistance of the samples were characteristic of
the natural silk cloth, while perpendicular to the plane of the
natural silk cloth, the mechanical properties were those
characteristic of the hydrogel itself Similar phenomena with shape
as observed in Example 1 was observed with both of the samples as
the samples were losing water, but less pronounced. When these
reinforced and laminated samples were exposed to tensile or shear
forces, they failed exclusively through cohesive mechanisms
indicating that the interfacial strength between natural silk cloth
and the polyvinyl alcohol hydrogel matrix is at least as high as
the strength of the polyvinyl alcohol hydrogel matrix itself.
Example 7
[0120] Similar procedures were used as in Example 6 except that the
hydrogel samples were reinforced with polyvinyl alcohol fiber cloth
and were heat treated at 120.degree. C. for 90 minutes. After the
heat treatment the hydrogel matrix had collapsed cell walls, having
exceptional tensile strength and tear resistance and
compressibility and being somewhat abrasive to the touch. The
hydrogel samples have modulus, tensile strength and tear resistance
in the plane equivalent to those expected for polyvinyl alcohol
fiber cloth, while perpendicular to the plane of the polyvinyl
alcohol fiber cloth, the mechanical properties were those
characteristic of the hydrogel itself The change of shape upon
partial water loss or gain was less pronounced in these samples
after they were subjected to heat treatment as compared to those
without the heat treatment. When these reinforced and laminate
samples were exposed to tensile or shear forces, they failed
exclusively through cohesive mechanism indicating that the
interfacial strength between the polyvinyl alcohol fiber cloth and
the polyvinyl alcohol hydrogel matrix is at least as high as the
strength of the poly vinyl alcohol hydrogel matrix itself.
Example 8
[0121] Similar procedures were used as in example 6 except that the
hydrogel samples were molded into rods having natural silk
filaments imbedded in the middle of the rod. After they had been
physically cross linked at low temperature and all solvents had
been removed, the rod was heat treated at 120.degree. C. for 90
minutes. After the heat treatment, the pore forming material was
removed and the result was a rod having collapsed cell walls. The
rods had good tensile strength and tear resistance, and had
exceptional compressibility and were somewhat abrasive to the
touch. The silk filament reinforced hydrogel rods had modulus,
tensile strength and tear resistance equivalent to those expected
of silk filaments. However, these rods were exceptionally soft and
delicate to the touch in a direction perpendicular to the long axis
of the rods. When these reinforced and laminated samples were
exposed to tensile or shear forces, they failed exclusively through
cohesive mechanisms indicating that the interfacial strength
between natural silk filaments and the polyvinyl alcohol hydrogel
matrix is at least as high as the strength of the polyvinyl alcohol
hydrogel matrix itself.
Example 9
[0122] Similar procedures were used as in Examples 6 and 7 except
that the polyvinyl alcohol concentration in solution was 1 weight %
and polyvinyl alcohol fiber cloth were used for reinforcement.
After heat treatment at 120.degree. C. for 90 minutes, very fluffy
reinforced polyvinyl alcohol sponges were obtained. The sponges
were very soft, and had reasonably good strength and had good tear
resistance, were somewhat abrasive and had exceptional
compressibility. The mechanical properties of the materials with
composite properties in the plane of the polyvinyl alcohol fiber
cloth were equivalent to those of the polyvinyl fiber cloth itself.
The catastrophic failure of the sample takes place through the
cohesive failure mechanism as indicated in earlier examples.
Example 10
[0123] Similar procedures were used as in Example 1, 4, and 6
except that the following colorants were added to the polyvinyl
alcohol solution in separate molds: methylene blue, Bonney's blue
and various food colorants. Another separate sample was also made
containing homogeneously dispersed barium sulfate as a radio opaque
material. The observations of physical properties were essentially
the same as described in the corresponding examples except that the
samples were colored.
Example 11
[0124] Similar procedures were used as in Example 6 except the
following: before granular sugar was loaded into the polyvinyl
alcohol solution, in one sample, short natural silk fibers and in
the second sample, short polyvinyl alcohol fibers, having average
lengths of 5 mm, were added to the solutions at ten weight % as
compared to the hydrogel weight fraction. Short silk and short
polyvinyl alcohol fibers were homogeneously dispersed throughout
the hydrogel sample. The rest of the sample preparation procedures
were the same as described in Example 6. After physical cross
linking and after extraction of the sugar with water, the short
fiber reinforced cellular polyvinyl alcohol hydrogel was relatively
soft, having improved tensile strength and tear resistance as
compared to cellular polyvinyl alcohol hydrogel matrices not
reinforced with the fibers as expected for short fiber reinforced
hydrogel matrices. The catastrophic failure of the sample takes
place through the cohesive failure mechanism as indicated by the
samples supra.
Example 12
[0125] Polyvinyl alcohol having a high degree of polymerization and
having a viscosity of about 66 cps for a 4% aqueous solution at
20.degree. C., and a high degree of hydrolysis of 99.3%, was
dissolved in dimethylsulfoxide solution with a polyvinyl alcohol
concentration of about 10 weight %. Dissolution was carried out at
120.degree. C., under nitrogen atmosphere, while continuously
stirring for 2 hours. Then, 20 grams of distilled water was poured
into 400 ml beakers together with 0.74 grams of sodium laurel
sulfate and 0.90 grams of DC-194 surfactant (Dow Corning
Corporation, Midland, Mich.), while nitrogen bubbled through the
solution. The aqueous solution was vigorously mixed at room
temperature for 5 minutes using a high speed stirrer equipped with
blender blades. This produced a froth having about 15 times higher
volume as compared to the initial water volume. Then, 20 grams of
the polyvinyl alcohol solution in dimethylsulfoxide was added
slowly while maintaining the high speed mixing with the final
polyvinyl alcohol concentration in the froth being about 5 weight
%. The froth was slowly cooled to about 15.degree. C. that resulted
in a stable froth that was then poured into molds. In one case, the
mold contained jute cloth placed on the entire bottom surface of
the rectangular mold with the depth of the mold being 4 mm. Then,
polyvinyl alcohol froth, still kept at about 15.degree. C., was
poured onto the cloth to completely fill the mold. In the case of a
second rectangular mold, polyvinyl froth was poured into the mold
to fill only the half of its depth and then linen cloth was placed
on the top of that polyvinyl forth layer. Additional polyvinyl
alcohol froth was added to the mold to fill the rest of the mold.
In both cases, the molds containing the cloth were placed into a
freezer at a temperature of -18.degree. C. and kept at that
temperature for 8 hours. Molds were then taken out of the freezer
and the cellular polyvinyl alcohol hydrogels were allowed to thaw.
The cellular hydrogels were very soft, delicate and had low tensile
strengths and low tear strengths. However, modulus, tensile
strength and tear resistance of the over-all a material with
composite properties in the direction of the plane of the sample
were those of the corresponding cloths. The catastrophic failure of
the sample takes place through the cohesive failure mechanism as
indicated in the examples, supra. The cellular polyvinyl alcohol
hydrogel was unstable in water and collapsed to a large extent when
placed in a water bath.
Example 13
[0126] Similar procedures were used as in Example 12, except that
after the a material with composite properties had been physically
cross linked at low temperature, it was immediately place into
acetone to extract the dimethylsulfoxide and water. Extraction was
carried out by holding the samples in an acetone bath for 8 hours
and then fresh acetone was used to replenish every 8 hours during
the next 24 hours of extraction time. At the end of the 24 hours,
the samples were taken out of the acetone and placed in a hood
overnight to completely remove acetone. While the reinforced
cellular polyvinyl alcohol structure was still holding acetone it
was quite strong and firm. After the acetone was completely
removed, the cellular structure became a semi-solid, porous
structure. Finally, after this solvent treatment, the dry cellular
structure was fully re-hydrated with water and it became
appreciably stronger and more stable in water than the original
sample of Example 12. The catastrophic failure of the sample takes
place through the cohesive failure mechanism as indicated in
earlier examples.
Example 14
[0127] Similar procedures as was used in Example 13 were used
herein except that once all of the acetone was removed from the
materials with composite properties; it was placed into a vacuum
oven and evacuated for 30 minutes. Then it was heat treated to
130.degree. C. for 120 minutes and allowed to cool to room
temperature while still under vacuum. Heat-treated samples were
placed into a water bath to re-hydrate, which resulted in a very
fine, soft, open celled hydrogel sponge supported with cloth. This
cellular hydrogel had very thin cell walls, that is, collapsed cell
walls. The hydrogel itself is strong, tough and has reasonable tear
resistance and has exceptional dimensional stability. The modulus,
tensile strength and tear resistance of the overall a material with
composite properties in the plane of the cloth was that of the
corresponding cloth. The catastrophic failure of the sample takes
place through the cohesive failure mechanism as indicated in the
examples, supra.
Example 15
[0128] Similar procedures were followed as in Examples 12, 13, and
14, except that polyvinyl alcohol fibers having an average length
of about 1.5 mm were added to the solution and then the solution
was frothed. Polyvinyl alcohol fibers were added at a 15 weight %
level as compared to the weight of the polyvinyl alcohol and no
cloth was used for additional reinforcement. The cellular structure
was solvent and heat-treated. The hydrogel had significantly
increased tensile strength and tear resistance as compared to
corresponding hydrogels without the addition of fibers.
Example 16
[0129] Similar procedures were followed as in examples 12, 13 and
14, except that frothed polyvinyl alcohol was extruded into shapes
of 5 mm diameter rods having continuous polyvinyl alcohol filaments
imbedded parallel to the long axis of the rod. Physical properties
in a transversal direction were those of corresponding cellular
polyvinyl alcohol hydrogels. However, modulus, tensile strength and
tear resistance in the direction of the continuous polyvinyl
alcohol filaments was that characteristic of the polyvinyl alcohol
filaments. The catastrophic failure of the sample takes place
through the cohesive failure mechanism as indicated in the
examples, supra.
Example 17
[0130] Similar procedures as used in Examples 2 was used herein
except that the polyvinyl alcohol solution was cast onto an
assembly analogous to Band Aid.RTM. strips. Polyvinyl alcohol
solution was poured onto the cotton gauze surface of the strips to
create a hydrogel having a thickness of about 1 mm. The hydrogel
was complexed with iodine by submersing the hydrogel into a
solution of iodine. This article can be used in wound and burn
healing applications providing the ability to dispense disinfectant
in a controlled manner, provide protection for the injured skin,
provide a non-adhering surface, and maintain moisture in a healing
tissue.
Example 18
[0131] The same procedure was used herein as was used in Example 17
except that the polyvinyl alcohol solution had a concentration of
two weight %. A small amount of polyvinyl alcohol solution was
poured onto an assembly analogous to the Band Aid strips of Example
17 and the excess polyvinyl alcohol solution was allowed to run off
creating a coated or impregnated cotton gauze structure. The volume
of the solution that was poured onto the cotton gauze surface of
the strip was sufficient to completely coat the surface of the
cotton fibers and create a thin hydrogel coating only on the fiber
network without creating a continuous hydrogel surface or film
supported by the structure. This approach allowed the complete
surface modification of the cotton gauze and also allowed it to
complex a sufficient amount of iodine by submersing the coated
cotton gauze into a solution of iodine. This article can be used in
wound and burn healing applications providing the ability to
dispense disinfectant in a controlled manner, provide protection
for the injured skin, maintain moisture, provide a non-adhering
surface to a healing tissue and allow air accessibility when
necessary.
Example 19
[0132] Similar procedures as was used in Example 6 were used herein
except that the polyvinyl alcohol solution loaded with granular
sugar was cast onto the assembly analogous to the Band Aid strips
of Example 17. The polyvinyl alcohol solution was loaded with
granular sugar and was placed onto the cotton gauze surface of the
strip to create a cellular polyvinyl alcohol hydrogel on the
surface of the cotton gauze having a height of about 2 mm. The
hydrogel on the strip was obtained by cooling the assembly to about
-15.degree. C. for 8 hours. Then, after extraction of the sugar,
the hydrogel was complexed with iodine in the usual manner. This
article can be used in wound and burn healing as well.
Example 20
[0133] Similar procedures as was used in Example 2 were used herein
except that the polyvinyl alcohol solution was poured onto the
surface of hard polystyrene into which cellulose fibers had been
previously imbedded. In this case, cellulose fibers were imbedded
into a polystyrene surface in the following manner: first, the
surface of the polystyrene was softened and partially dissolved
with hydrocarbon solvents such as acetone, toluene and the like,
and then, cellulose fibers were partially imbedded into the
softened polystyrene surface, and finally the solvent was allowed
to evaporate to lock a portion of the cellulose fibers into the
polystyrene surface. This produces an article having a dual surface
where one surface is hard polystyrene and the other surface is that
of a chosen type and in the nature of a hard, soft and/or delicate
polyvinyl alcohol hydrogel.
Example 21
[0134] Similar procedures as was used in Example 20 were used
herein except that the polyvinyl alcohol solution was poured onto
the surface of a poly(dimethyl siloxane) cured film into which
polyvinyl alcohol fibers had been previously partially imbedded. In
this case, polyvinyl alcohol fibers were partially imbedded into
the surface of the siloxane film by first casting a curable
poly(dimethyl siloxane) material, then partially imbedding into it
the polyvinyl alcohol fibers and then curing the siloxane material.
This produced an article having a dual surface wherein one surface
is hydrophobic, liquid water impermeable, water vapor highly
permeable and the other surface is that of a chosen type and in the
nature of a hard, soft, and/or delicate, hydrophilic polyvinyl
alcohol hydrogel.
Example 22
[0135] Similar procedures were used herein as in Example 21 except
that cellular polyvinyl alcohol hydrogel was created on the surface
of the poly(dimethyl siloxane) film. This was accomplished by first
partially imbedding the polyvinyl alcohol fibers into a cured
poly(dimethyl siloxane) film and then placing polyvinyl alcohol
solution loaded with salt particles on the film. In the second
case, cotton gauze was imbedded into the surface of the siloxane
film. Cotton gauze was imbedded into the polydimethysiloxane film
by first extruding curable siloxane film and then placing cotton
gauze onto the surface of the uncured film, and finally allowing
the film to cure. This produces an article having a dual surface
wherein one surface is hydrophobic, liquid water impermeable, water
vapor highly permeable and the other surface is that of a chosen
type and in the nature of a hydrophilic hydrogel.
Example 23
[0136] Two polyvinyl alcohol solutions from the same polyvinyl
alcohol polymer, having different concentrations, were prepared.
One solution contained polyvinyl alcohol polymer having a high
degree of polymerization and having a viscosity of about 66 cps for
a 4% aqueous solution at 20.degree. C., and a high degree of
hydrolysis of 99.3%. It was dissolved in an 80/20 mixture of
dimethylsulfoxide and water with a concentration of about 25 weight
%. The second solution had a concentration of 5 weight percent.
These two solutions were cast sequentially (a) into a mold to form
a slab having a 2 mm thickness and (b) into a mold to form an 8 mm
diameter rod having 50 mm long section of one solution and 50 mm
long section of the second solution. In another sample, these
solutions were co-extruded into rods and 4 mm thick sheets. In both
cases, samples were then placed into a freezer at -18.degree. C.
for 8 hours and the solvent was extracted with water. The samples
resulted in two sections with widely differing physical properties
one having low tear strength, high water content and the other
having high tear strength, low water content. The catastrophic
failure of this sample takes place through the cohesive failure
mechanism.
Example 24
[0137] The same solutions of polyvinyl alcohol as described in
example 23 were used to make cubes consisting of complex structures
obtained by combining two polyvinyl alcohol solutions
simultaneously, resulting in a unitary cube having the two
polyvinyl alcohol bulk hydrogels interlocking and intertwining
throughout the body of the cube. The simultaneous combining of both
solutions in a mold in a certain pattern was carried out using two
syringes that are capable of being moved freely in a plane above
the mold surface. Once the cube mold is completely filled with
polyvinyl alcohol solutions, it was cooled at -18.degree. C. for
eight hours and washed with water to remove solvents. The resulting
polyvinyl alcohol hydrogel cube has a complex response to tensile
and compressive forces as the result of the complex composition.
The catastrophic failure of this sample takes place through the
cohesive failure mechanism.
Example 25
[0138] The same polyvinyl alcohol solutions that were used in
example 23 were used except that the object having the complex
structure consisting of the interlocking polyvinyl alcohol bulk
hydrogels was built without the mold, that is, they were freely
laid out on the platform in a mode similar to ink-jet dispensing.
Two polyvinyl alcohol solutions were dispensed in this controlled
manner creating a desired pattern using syringes that can move
freely in the plain parallel to the surface of the platform. The
platform is located and partially submersed in the bath that
contains a gelling media such as a solution of a salt or
non-solvent. As the object is being built, the platform submerges,
causing the submerged portions of polyvinyl alcohol solutions to
gel, creating continuously and simultaneously the unitary object
having the desired intricate, complex, intertwining and
interlocking composition consisting of the polyvinyl alcohol bulk
hydrogels. The catastrophic failure of the sample takes place
through the cohesive failure mechanism.
Example 26
[0139] Polyvinyl alcohol having a high degree of polymerization and
having a viscosity of about 66 cps for a 4% aqueous solution at
20.degree. C., and a high degree of hydrolysis of 99.3% was
dissolved in an 80/20 mixture of dimethylsulfoxide and water with a
concentration of about 10 weight %. This solution was poured into a
rectangular mold measuring 20 mm.times.20 mm.times.10 mm and then
it was loaded with salt particles and placed into a freezer to form
a hydrogel. After the salt was extracted with water, the
rectangular cellular polyvinyl alcohol hydrogel was obtained. This
sample was then encapsulated with bulk hydrogel made from the same
polyvinyl alcohol solution by pouring a small portion of the
hydrogel solution into a larger rectangular having a measurement of
30 mm.times.30 mm.times.20 mm and the first rectangular cellular
hydrogel that had been prepared was placed into the larger mold and
additional polyvinyl alcohol solution that was prepared secondly
was poured around and on the top to completely encapsulate the
cellular hydrogel. It was then placed in a freezer to make the
second hydrogel. This a material with composite properties
structure has a soft interior because it contains sponge and
significantly higher modulus at or near walls of the object
originating from the continuous bulk polyvinyl alcohol hydrogel
envelope, i.e. walls, of the a material with composite properties
object. The catastrophic failure of this sample takes place only
through the cohesive failure mechanism.
Example 27
[0140] Similar to the example 24, frothed polyvinyl alcohol
solution was combined with bulk polyvinyl alcohol hydrogel
resulting in a complex structure composed of intertwining cellular
and bulk polyvinyl alcohol hydrogels in a co-continuous or
semi-continuous fashion. The catastrophic failure of this sample
took place through a cohesive failure mechanism.
Example 28
[0141] Similar to the example 24, frothed polyvinyl alcohol
solution was combined with polyvinyl alcohol solution containing a
pore forming material. After gelling the polyvinyl alcohol cellular
matrices and extraction of the pore forming material, the resulting
structures had a complex structure composed of two intertwining,
different types of cellular polyvinyl alcohol hydrogels in a
co-continuous or semi-continuous fashion. The catastrophic failure
of this sample took place through a cohesive failure mechanism. The
examples that have been provided herein are some of the typical
possibilities of the making of structures according to this
invention. These examples are not intended to limit the scope of
the invention.
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