Thermoplastic polyurethane article treated with iodine for antibacterial use

There is provided a polymeric bacteriocidal composition comprising a thermoplastic, partially cross-linked polyurethane having --NH--(C.dbd.O)--O-- urethane linkages and/or urea linkages --NH--(C.dbd.O)--NH-- and iodine complexed with a sufficient number of these linkages to provide bacteriocidal properties to said composition. The polyurethane has an average molecular weight between 35,000 and 50,000, an ultimate elongation of 200 to 800% and a Shore A scale hardness of 60 to 95. The composition is shaped into a conventional medical appliance form, e.g. a catheter.

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: 
______________________________________ 
% 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 a tubular shape and the extruded polyurethane 
polymer, at room temperature, was in the form of semi-rigid, but yet 
bendable or flexible tube. Sections of the tube so extruded were cut and 
immersed in the 2% iodine solution of Example 1. After a dwell period of 1 
hour, the tubes were washed with the same solvent as that of Example 1 and 
dried. The uptake of iodine produced a brown color in the tube and the 
intensity of that brown color is directly proportional to the iodine 
content in the tube. 
The tube was placed at room temperature in a covered container, but opened 
to the atmosphere, whereby sublimation of the iodine could take place. 
After three months, the intensity of the brown color of the tube was 
compared to the intensity of the brown color of a freshly prepared tube, 
i.e. prepared in the identical manner. The intensity of the brown color of 
the test tube was only slightly less than the intensity of the brown color 
of the freshly prepared tube, demonstrating that no significant amount of 
the iodine had sublimated during the test. 
Accordingly, it will be seen from the above that the objects of the 
invention have been achieved. It will also be appreciated that 
modifications of the invention, as specifically described above, will be 
apparent to those skilled in the art. Thus, it is intended that those 
apparent modifications be embraced by the spirit and scope of the annexed 
claims.