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Description  |
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The present invention relates to polymeric bacteriocidal compositions
comprising a thermoplastic polyurethane which is complexed with iodine,
for use in antibacterial applications, and more particularly to such
compositions which are used in connection with medical appliances.
BACKGROUND OF THE INVENTION
The incidence of bacterial infection caused by bacterial contamination of
medical appliances has never been reduced to a satisfactory level. This is
particularly true in connection with medical appliances which cannot
normally be sterilized in autoclaves or which when in use encounter
bacteria containing environments. For example, sutures, catheters,
surgical tape, tubings, sponges, gloves, pads, surgical covers and certain
medical instruments cannot be autoclaved to insure sterility but often
must be used in areas where pathogenic bacteria are encountered.
Accordingly, for such medical appliances, the art has long sought means
and methods of rendering those medical appliances antibacterial and,
hopefully, self-sterilizing. The general approach in the art has been that
of coating the medical appliance, or a surface thereof, with a
bacteriocide. However, since most bacteriocides are partly water soluble,
or at least require sufficient solubilization for effective antibacterial
action, simple coatings of the bacteriocides have been proven unreliable.
For this reason, the art has further sought to incorporate the
bacteriocides into the medical appliance or at least provide a stabilized
coating thereon.
The art has taken many different directions in attempting to solve this
problem, but finding the combination of effective bacteriocides and means
of retaining that bacteriocide in or on the medical appliance has either
eluded the art in regard to some applications, or the art has not found
totally satisfactory solutions in regard to other applications. For
example, many of the medical appliances which encounter the above noted
problem are made of non-metallic materials, such as plastics, cat gut, and
gelatin. Since these materials cannot be adequately autoclaved, at least
in connection with the environment of use, these types of medical
appliances present the problem in its most difficult form and the problem
has never been solved. One of the earlier attempts to solve this problem
is discussed in U.S. Pat. No. 1,006,854, wherein cat gut, for suture
purposes, is treated with iodine to disinfect the suture material.
However, since the iodine is not tightly bound to the cat gut it is
rapidly released during use and quickly inactivated.
With the increased use of polymeric materials for construction of medical
appliances, such as catheters, artificial blood vessels, injection tubing,
surgical tape and the like, the problem of a self sterilizing polymer has
become more important. The art, therefore, sought combinations of plastics
and antibacterial agents wherein the antibacterial agent could be fixedly
attached to or incorporated in the plastic so that the combination thereof
could be used for the manufacture of these plastic medical appliances.
This relatively recent effort in the art has taken a myriad of different
approaches. For example, U.S. Pat. No. 3,401,005, discloses that a
combination of polyvinylpyrrolidone and iodine could be applied to cotton
gauze and the like and when dried would have a germicidal characteristic.
In a similar effort, a combination of polyvinylpyrrolidone and iodine was
placed in absorbable, gelatin foams to produce surgical sponges. It was
also found that iodine could actually be complexed with
polyvinylpyrrolidone and the complexed composition would slowly release
iodine under use conditions. Solid polyvinylpyrrolidone complexed with
iodine is disclosed in U.S. Pat. No. 3,898,326 as useful as a disinfectant
material and U.S. Pat. No. 4,017,407 extends that composition to include
other ingredients such as detergents.
Improved polyvinylpyrrolidone/iodine complexes are disclosed in U.S. Pat.
No. 4,094,967, for coating dressing materials and the like, but the art
has not been successful in using polyvinylpyrrolidone/iodine complex as a
material of construction for producing medical appliances. U.S. Pat. No.
4,113,851, suggests complexing iodine with a preformed polymer of
2-pyrrolidone and then treating with an emulsion of a polyacrylic acid to
impregnate the polyvinylpyrrolidone/iodine complex with the acid.
The lack of success of producing medical appliances with complexed
polyvinylpyrrolidone and iodine led the art toward other approaches and
U.S. Pat. No. 4,010,259 suggests complexing iodine with polysaccharide,
such as starch, dextran or cellulose, but here again, these materials are
not suitable for materials of construction of most medical appliances.
In yet another approach, U.S. Pat. No. 3,598,127 suggests infusing an
antibacterial substance, such as neomycin and the like, into a
polysiloxane rubber, while U.S. Pat. No. 4,186,745 suggests a similar
approach with microporous polyethylene, polypropylene, or polyflurocarbon
polymers. These approaches are merely mixtures and the bacteriocidal agent
is not chemically combined to the plastic and slowly released.
In an approach somewhat similar to the above, antibiotics and germicides,
e.g. penicillin and cetylpyridinium chloride, are infused into a
hydrophilic polymer for coating medical appliances such as catheters,
according to the disclosure of U.S. Pat. No. 3,566,874. Such antibiotic
approaches have other limitations in that the antibiotic is not effective
against all organisms.
In another approach, multifilament suture strands are impregnated with a
water soluble antimicrobial agent, such as penicillin, and then coated
with polyurethane polymer so as to maintain the antimicrobial agents. A
similar approach is disclosed in U.S. Pat. No. 3,987,797, where a surgical
suture is coated with a copolymer of polyquaternary polyurethane and a
polyanionic polymer, such as heparin and then treated with an
antimicrobial compound, such as penicillin. There have also been efforts
to incorporate bacteriocides, in gross, in polymers simply by mixing with
the polymer, and U.S. Pat. No. 2,947,282, is representative thereof.
Polyurethane would be most useful in producing medical appliances of the
present nature, and efforts along the above lines have also been made to
render those polyurethane appliances self-sterilizing. For example, U.S.
Pat. No. 3,235,446, prepares a polyurethane foam by the reaction between a
liquid polyfunctional hydroxyl terminated polyether or polyester and a
liquid polyfunctional organic di-isocyanate, with subsequent exposure to
water so that a foam results. The resulting plastic is a thermoset. The
foam is then treated with an iodine solution. This approach is successful
in producing a prefoamed polyurethane complexed with iodine, but materials
prepared in this manner are not thereafter convertible into other medical
appliances since they are not thermoplastic but thermosetting. Few or no
medical devices are manufactured with thermosetting plastic resins. In
addition, the diisocyanate used in the manufacture is a toxic substance
and difficult to handle.
U.S. Pat. No. 3,897,797 relates specifically to thermosetting polyurethanes
which are different from the thermoplastic polyurethanes which we have
investigated. Shelenski, Mills and Levenson have chosen a special
situation in thermosetting polyurethane resins by reacting isocyanetes
with relatively high molecular weight (M.W. 1000) compounds having
terminal hydroxal groups and containing not less than 30% ethylene oxide.
Yet, short chain polyalcohols are often used in mixtures to provide for
sparse cross-linking and these sparsely cross-linked compounds can be
thermoplastic. Although such cross-linked thermoplastic resins have high
tear resistance, steric hindrance renders the
##STR1##
urethane linkages which complex with iodine inaccessible in highly
cross-linked plastics. This factor may have discouraged the investigation
of the possibility of complexing iodine onto thermoplastic polyurethanes
which are only sparsely cross-linked.
As can thus be appreciated, considerable effort has been expended, yet
success in the art has been elusive. This is particularly true in
connection with the manufacture of medical appliances, such as catheters
and the like which should not only be sterile, but have good tensile
properties and yet be relatively inexpensively manufactured. In this
latter regard, such medical appliances are normally shaped, e.g. by
molding or extruding a thermoplastic material, which thermoplastic
material, inherently, has the tensile properties required for the
particular medical appliance. This means of manufacture is relatively
inexpensive, as is required, and can be accurately controlled for size,
shape, uniformity and reliability. Thus, any practical solution to the
above problem must also include the ability for the medical appliance to
be molded into the particular shape required by the medical appliance.
It would therefore be of substantial advantage to the art to provide a
shapeable polymeric composition which is also bacteriocidal and which, in
addition, has the required tensile properties for allowing formation
thereof into practical and usual medical appliances of a relatively
inexpensive nature.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a polymeric,
bacteriocidal composition which is thermoplastic in nature and can be
shaped into usual medical appliances in an inexpensive manner. It is a
further object of the invention to provide such composition which is also
bacteriocidal. It is a further object of the invention to provide a shaped
form of that composition, particularly forms which are in the shape of
usual medical appliances, such as sutures, catheters, tape, tubing, etc.
It is another object of the invention to provide a method of producing
such medical appliances. Other objects will be apparent from the following
description and claims.
BRIEF DESCRIPTION OF THE INVENTION
The invention is based on three primary considerations. Firstly, as can be
appreciated from the above, a number of different polymers have been used
in the art for making medical appliances of the present nature. Each of
these polymers has its own set of advantages and disadvantages. While
polyurethane polymers have been known for making medical appliances, e.g.
the foams of U.S. Pat. No. 3,235,446, discussed above, polyurethanes have
not found wide acceptability for such appliances. As is known,
polyurethanes may be made in an essentially uncross-linked or in an
essentially cross-linked state. The uncross-linked polyurethanes have
relatively weak tensile properties and while they may be made into
relatively fragile films and the like, they are not acceptable for
appliances which require more exacting physical properties. Polymers on
the other hand, while the fully cross-linked polyurethanes have
exceptionally good physical properties, they are not thermoplastic and
cannot be transformed into molded or extruded structures. For example, the
foams of U.S. Pat. No. 3,235,446, discussed above, are not thermoplastic
in the nature required for accurate molding of medical appliances. Thus,
the art has looked to other more conventional thermoplastic materials, as
discussed above, for producing medical appliances of the present nature.
Thermoplastic compounds are chemically and structurally different from the
thermosetting polyesters and polyethers mentioned in U.S. Pat. No.
3,987,797. Frequently they are sparsely cross-linked with polyamines
rather than alcohols to yield urea type linkage
##STR2##
Our investigations reveal that this type of linkage complexes with free
iodine to an even greater extent than does the urethane linkage. Because
the different linkages have varying accessibility and varying degrees of
chemical binding with the iodine the dissociation free iodine from bound
iodine will vary considerably at water plastic interface depending on the
extent of iodinization. If the polyurethane is treated with dilute iodine
solutions, those groups with the greatest avidity for iodine will react
first and will be the least dissociable into free iodine. By increasing
concentrations of iodine used in treating the thermoplastic polyurethane,
bonds which are easily broken will be complexed at higher concentrations.
These bonds will yield their iodine more readily and will produce higher
concentrations of free iodine at an aqueous interface with the plastic
surface. It is the free iodine which is responsible for the bacteriocidal
properties. Concentrations of iodine as low as 0.5 ppm have been shown to
kill staphylococcus aureus and other pathogens in 50-60 seconds. (Am Jr.
Public Health 60:535 1970; Soap Sanit Chem 28:149 1952). The ability to
render extruded and injection molded products biocidal would make
self-sterilizing medical products a practical reality since the majority
of useful medical devices cannot be fabricated with thermosetting urethane
plastics, but can be extruded or injection molded.
However, it has been discovered that a relatively narrow group of
polyurethane polymers have a unique combination of properties in that they
are sufficiently thermoplastic to be molded in conventional molding and
extrusion apparatuses, while at the same time they present physical
properties quite sufficient for the usual medical appliances. In addition,
it has also now been found that these polymers are also capable of
complexing with iodine and retaining that complexed iodine in an
advantageously releaseable form. This relatively narrow group of
polyurethane polymers is referred to in the art as sparingly (or
partially) cross-linked polyurethanes. The cross-linking is sufficient
that at room temperature or thereabouts, the polymers have quite
acceptable physical properties, but at higher temperatures, e.g. at
molding temperatures, the cross-linking is insufficient to prevent
deformation and those polymers may, indeed, be molded. Polymers of this
nature can be made by a variety of processes and with a number of
different starting materials. However, these polymers will have an average
molecular weight of between 35,000 and 50,000, an ultimate elongation of
between 200 and 800% and a Shore A scale hardness of 60-95. Thus, the
polymers useful in the present invention may be characterized by their
physical properties, as aforenoted.
The second major consideration which resulted in the present invention is
the discovery that even though these polyurethane materials are sparingly
cross-linked, the degree of steric hindrance does not prevent the reactive
groups from adequately complexing with iodine. There are sufficient
linkages at the surface of the polymer that can complex with iodine and
slowly release the iodine to create a bacteriocidal environment. Thus, the
complexed iodine is slowly dissociable from the polyurethane in sufficient
concentrations to create a germ free zone around the plastic and to kill
the bacteria on contact. For example, when the iodine complexed
polyurethane of the present invention is in a gaseous atmosphere, such as
air, sublimation of the iodine is quite low and the iodine complexed
polyurethane retains its bacteriocidal properties for prolonged periods of
time. However, when in an aqueous environment, the dissociation of the
iodine is increased and sufficient free iodine is liberated to render the
surface concentration of iodine bacteriocidal and thus keep the surface of
the plastic sterile. This liberation is not so rapid that the iodine is so
quickly removed from the polyurethane as to injure or kill normal tissues.
The polyurethane becomes a true iodophor.
The third major consideration, is that these polyurethane polymers may be
preformed into the medical appliances desired, and the iodine can be
successfully incorporated into those preformed shapes, even though the
preformed shape is not open or porous in the nature of foam or the like,
but closed and impervious, in the nature of a solid tube or the like. This
renders it unnecessary to treat the plastic prior to extrusion or
injection molding.
Thus, briefly stated, the present invention provides a polymeric
bacteriocidal composition. That composition contains a thermoplastic,
sparingly cross-linked polyurethane having --O--(CO)--NH-- urethane
linkages and iodine complexed with a sufficient number of said linkages to
provide bacteriocidal properties to the composition. The polyurethane of
the composition has an average molecular weight of between 35,000 and
50,000, an ultimate elongation of 200 to 800% and a Shore A scale hardness
of 60-95.
That composition may be rendered into a shaped form by conventional
thermoplastic molding techniques, e.g. compression molding, transfer
molding, injection molding, extrusion, casting and the like, and more
particularly, may be formed into medical or hospital appliances, such as
sutures, catheters, tape, tubing, sponges, gloves, instruments and the
like.
Within the constraints of the polyurethanes useful with the invention, as
stated above, the polyurethane can range from a semi-rigid to a flexible
composition, or may be foamed with the aid of a blowing agent or the like.
The shaped form may be prepared by shaping the composition into a preformed
shape and contacting the preformed shape with a solution of iodine, e.g. a
tincture and or aqueous solution of iodine.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, polyurethane polymers can have an exceedingly wide range of
properties. These properties can range from a very weak film, suitable
only for paints and the like, to an essentially rigid structure, quite
suitable for a building material, e.g. rigid urethane foams. In between
these extremes, the polyurethane polymers may be relatively soft and have
low ultimate elongations, e.g. 100% or less or may be quite tough, but not
thermoformable. This range of properties induced in polyurethane polymers
is a result, primarily, of the molecular weight of the polymer and the
degree of cross-linking, or absence of cross-linking. Thus, there is
almost an infinite variety of properties which can be achieved with
polyurethane polymers.
According to the present invention, it was discovered that a relative
narrow group of polyurethane polymers has the unique combination of
properties which make it suitable for medical appliances, i.e.
mechanically strong, relatively elastic, resistant to common solvents,
and, more importantly, can be shaped and will complex an adequate amount
of iodine in an advantageously releasable fashion. To achieve this unique
set of properties, the polyurethane must have an average molecular weight
of between 35,000 and 50,000 and it must be sparingly cross-linked.
In this latter regard, the term "sparingly cross-linked" has reference to
the relative number of cross-linked bonds in the polyurethane polymer. For
example, the polyurethane polymer may be prepared with relatively short
chain polyalcohols and toluene diisocyanate which will give a relatively
high density of potential cross-linking sites. However, when the
cross-linking is controlled so that there are only a small number of
cross-linked sites, the resultant polymer will be only sparingly
cross-linked. Such a "sparingly cross-linked" polyurethane polymer has a
sufficient number of NCO grouped on the surface to complex iodine. On the
other hand, for example, with long chain compounds containing only a
single terminal alcohol group, the degree of cross-linking is almost nil
since cross-linking occurs by the reaction of an alcohol with a isocyanate
group and at least two alcohol groups are required for cross-linking. The
length of the chain for the number of alcohols will determine the degree
of cross-linking. When all cross-linkable sites are cross-linked, but the
total degree of cross-linking for any polymer is still low owing to the
limited number of cross-linkable sites, the polymer is regarded as
"sparingly cross-linked". Thus, it is not the particular composition of
the polyurethane which is important in determining its thermoplastic
properties, but the degree of cross-linking or cross-link density in the
polyurethane polymer. This degree of cross-linking will determine the
polymer's molecular size and though physical properties of the
polyurethane are modified by its chemical composition, the tear resistance
and many of the physical properties are determined by the degree of
cross-linking in the polymer. Accordingly, some "sparingly cross-linked"
polyurethane polymers have an ultimate elongation of 200 to 800%, a Shore
A scale hardness of 60-95 and are thermoplastic. In this latter regard,
the term "thermoplastic" means that the polymer is shapeable in
conventional shaping machines, e.g. extruders and molders, at temperatures
less than 400.degree. F. On the other hand, it also means that the polymer
is not meltable at temperatures less than 200.degree. F.
While the foregoing describes sparingly cross-linked polyurethane polymers,
it is preferred that the ultimate elongation be between 200 and 400% and
the hardness be between 70 and 90. It is also preferred, for convenience
of manufacture and source of materials, that the polyurethane polymer be a
sparingly cross-linked form of a polyurethane made from a polyether or
polyester, the technology and connection with which is well known to the
art and will not be described herein for sake of conciseness.
The polyurethane polymer of the above nature has been found to readily
accept iodine solutions for complexing the iodine with the urethane
linkages. It has also been found that such complexed iodine is releasable
from the polyurethane in advantageous amounts and rates. The release is
neither too slow nor too fast for practical use in aqueous environments,
but is of a rate that the surface of a shaped form will have an ample
supply of released iodine for bacteriocidal purposes, but will not release
the iodine at such a rate that the shaped form will rapidly be depleted of
the iodine and injure normal tissue. In addition, it has been found that
these polyurethane polymers retain the iodine in a non-aqueous atmosphere
for prolonged periods, so that sublimation of the iodine, e.g. in an air
atmosphere, is considerably reduced and the iodine will be retained in
that atmosphere for long periods of time, e.g. during normal shelf storage
and the like.
The duration of release of iodine is roughly proportional to the amount of
iodine complexed with the polyurethane. Sufficient iodine is released to
be in equilibrium with a free iodine content in the immediate environment
of between 5 to 25 parts per million. As the iodine is bound in the
tissues or carried away by the blood stream or lymphatic circulation, more
is released. For example, if the complexing is carried out for an extended
period of time, saturation of complexed iodine will take place.
Equilibrium will be established with this pool. The amount of iodine at
the surface is essentially a sterilizing amount of iodine. Saturation
amounts can easily be determined by following the uptake of iodine during
the complexing process, as described in detail below. On the other hand,
small amounts of iodine can be complexed with the polyurethane, but in
this case, self-sterilizing conditions of the surface will not normally be
achieved, although improved bacteriocidal properties will be achieved.
Minimum iodine complexing can also be controlled during processing
thereof, as explained more in detail below, by following the uptake of
iodine during the complexing step.
The polymeric composition may be molded into a shaped form in any manner
desired, but primarily for purposes of the present invention that shaped
form will be a medical or hospital appliance, although the shaped form may
be configured as a packaging film or a package, particular for hospital
supplies and the like. Typical medical appliances are sutures, catheters,
surgical tape and tubing, sponges, surgical gloves, surgical pads, patient
bed or instrument covers and instruments themselves, e.g. infusion tubes
and the like. Alternately, the composition may be in the form of a
coating. For example, the medical appliance may be a sanitary appliance,
e.g. a bed pan, having a coating of the bacteriocidal composition thereon.
While that coated composition will have the properties as described above,
especially the moldable properties, that composition may be applied as a
paint or lacquer via a solvent carrier. Molding and coating techniques for
producing such appliances are well known in the art and need not be
described herein for sake of conciseness.
Since it is only the surface of the medical appliance where bacterial
contamination takes place, the iodine will normally be complexed into the
preformed shape on or near at least a part of the surface of the preformed
shape, consistent with placing sufficient iodine on or near the surface to
provide bacteriocidal properties for an extended period of time. It is not
necessary that the iodine be complexed throughout the preformed shape and
the complexing is carried out with this purpose in mind.
In regard to the method of making the medical appliance, the polyurethane
polymer is shaped into a preformed shape, of desired configuration. That
preformed shape is then contacted with a solution of iodine. The
temperature of the solution is not critical and can be from as low as near
the freezing point thereof, to near the boiling point thereof, but room
temperature or above is preferred, e.g. 20.degree. C. to 60.degree. C. The
amount of iodine in the solution can also vary as desired, but
concentrations of as little as 1% up to 15% are quite satisfactory.
However, in practice, where the uptake of iodine is to be more carefully
controlled, concentrations of about 2 to 4%, e.g. 3% of iodine are
preferred, since lower concentrations still provide a relatively rapid
uptake of iodine, but at a predictable and controllable rate. The iodine
may be advantageously an aqueous solution, a tincture or a combination
thereof, e.g. a 50% alcoholic solvent and, if desired, containing 1%
potassium iodide. Indeed, the iodine solutions disclosed in the U.S.
patents, noted above, dealing with polyvinylpyrrolidone are quite
acceptable for the present invention and further details will not be given
herein for the sake of conciseness.
The amount of iodine uptake will be dependent upon the concentration of the
iodine in the solution, the solvent of the iodine solution, the
temperature of the solution, and the time of contact with the iodine
solution. However, generally speaking, the period of contact will be for
at least 5 minutes and more usually at least an hour. While the contact
time can be up to 48 hours or more, the uptake of iodine after about 10 to
12 hours markedly decreases, and these extended times do not produce
substantially greater amounts of complexed iodine in the polyurethane
polymer.
More importantly than either the particular contact time, concentration, or
temperature of the solution, is the ultimate uptake of iodine by the
preformed shape. This can be measured directly by conventional methods for
determining the iodine content of the polymer or it may be measured
indirectly by analyzing the decrease of iodine concentration in the
contacting solution. Irrespective of the method of measurement, a graph of
iodine uptake versus contact time for any iodine solution, at a given
temperature, can be established and can be used for very accurately
controlling the iodine uptake.
The iodine solution may contact the preformed shape by immersing the
preformed shape into the solution, or the solution may be sprayed or
otherwise dispersed thereon. It is only necessary that the solution be in
intimate contact and uniformly dispersed about the preformed shape. For
convenience, the preformed shape is simply immersed in the iodine
solution, although for larger objects, spraying of the iodine solution may
be utilized.
After the required contact with the iodine solution, the preformed shape
will normally be washed to remove excess iodine solution from the surface
thereof. While any wash may be used, in this regard, the liberal use of
water for 48 hours has proven adequate to remove all free uncomplexed
iodine.
As an alternative process, to the process described above, the contacting
with the iodine solution may be under elevated pressures. In certain
medical appliances, it is necessary to have a porous or microporous
structure. In these cases it may be difficult to contact all of the porous
or microporous interstices with the iodine solution, particularly with
smaller pores in the porous material and higher surface tensions of the
iodine solutions. In these special cases, the preformed shape in the
iodine solution may be subjected to elevated pressures, e.g. 1 to 50
atmospheres in order to force the iodine solution into the porous
structure. After such treatment, while not necessary, a similar elevated
pressure wash may be utilized, with or without a vacuum withdrawing of
iodine and wash solution.
The invention will now be illustrated by the following examples, although
it is to be understood that the invention is not restricted thereto, but
extends to the breadth of the foregoing specification and the following
claims. In the examples, as well as in the specification and claims, all
percentages and parts are by weight unless otherwise specified.
EXAMPLE 1
Sparingly cross-linked polyurethane polymer (Estane-58271, manufactured by
B. F. Goodrich Co.) was tested and found to have an elongation of
approximately 400% and a Shore A scale hardness of 86. The polymer was
compounded with a blowing agent (sodium bicarbonate) and heated to a
flowable state, i.e. a temperature of approximately 350.degree. F.,
whereby the polymer was foamed. The gross foam was cut into sections of
approximately 1/2" in diameter and 1/8" thick. Solutions of iodine in a
50% aqueous/alcohol solvent were prepared. The iodine concentration in the
solutions were 0.125%, 0.25%, 0.5%, 1% and 2%. The cut sections were
immersed in the iodine solutions for a period of 5 minutes. Thus, the
uptake of iodine in each of the different solution concentrations would be
essentially proportional to the concentration of iodine in the solutions.
After removal from the iodine solutions, the cut sections were washed with
alcoholic potassium iodide.
Agar plates, containing Hank's solution, were prepared and into these agar
plates were placed the cut sections of the foam which had been complexed
with iodine in the different iodine concentration contacting solutions.
One plate was inoculated with S. aureus and another plate was inoculated
with Proteus vulgaris. The plates contained a dye for revealing the
absence of bacterial growth.
After 48 hours of incubation at 30.degree. C., the plates were examined for
bacterial growth. The determination was that of measuring the diameter of
absence of bacterial growth around each circular cut section and comparing
that diameter, as a ratio, with the diameter of the cut section. Thus,
where no bacterial growth inhibition takes place, the ratio is 1:1. The
results were as follows:
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% I Solution Diameters Ratio
Organism
______________________________________
0.125 1:1 S. aureus
0.25 1.05:1 "
0.50 1.1:1 "
1.0 1.5:1 "
2.0 2.5:1 "
0.125 1:1 Proteus vulgaris
0.25 1.05:1 "
0.50 1.15:1 "
1.0 1.5:1 "
2.0 2.6:1 "
______________________________________
As can be seen from the above data, very effective antibacterial properties
can be provided to the polyurethane and the degree of the antibacterial
properties can be controlled, as desired. This is an important feature of
the invention, since the liberation of iodine in controlled amounts is of
utmost importance in medical appliances, particularly appliances applied
within the body. As can be easily appreciated, too little release of
iodine will be ineffective, while too great a release of iodine would be
quite undesirable.
EXAMPLE 2
A sparingly cross-linked polyurethane, (Estane-58300, manufactured by the
B. F. Goodrich Co.) was tested and found to have an elongation of
approximately 300% and Shore A hardness of 90. The polymer was placed in a
conventional, single screw, heated barrel extruder with the die
temperature controlled at 390.degree. F. The die plate had a conventional
spider die for extruding | | |
