Antimicrobial structures

Certain antimicrobial agents, particularly chitosan- or chitin-based polymers, exhibit increased antimicrobial activity when coated onto the surface of a hydrophobic material such as polypropylene. When applied to the surface of a polypropylene nonwoven fabric, for example, the resulting material can be used for diaper liners to reduce odors and promote skin wellness.

BACKGROUND OF THE INVENTION
 The use of antimicrobial agents to prevent or retard the growth of bacteria
 finds applicability in a wide variety of applications in the medical and
 personal care fields. Some of these applications involve combining an
 antimicrobial agent with a solid surface. In such cases, it is necessary
 to attach an antimicrobial agent to the solid surface while maintaining
 the antimicrobial activity of the antimicrobial agent. Unfortunately, in
 so doing the antimicrobial activity of the antimicrobial agent can be
 reduced in the process, rendering the resulting material insufficiently
 effective.
 Hence there is a need for a coated antimicrobial material which exhibits
 high antimicrobial activity. Such materials could be useful for certain
 components of personal care articles, such as diaper liners and the like.
 SUMMARY OF THE INVENTION
 It has now been discovered that certain antimicrobial agents, such as
 chitosan and other chitin-based materials, when thinly coated onto a
 substrate having a hydrophobic surface, exhibit antimicrobial activity
 which is even greater than the activity of the antimicrobial agent alone.
 In general, the increase in microbial activity can be about 10 percent or
 greater, more specifically about 50 percent or greater, still more
 specifically about 100 percent or greater, still more specifically about
 200 percent or greater, and most specifically from about 10 to about 500
 percent. As used herein, the term "antimicrobial" includes sequestering or
 immobilizing microorganisms such that their numbers within a suspension
 medium are reduced, even though the microorganisms may not be killed.
 Hence, in one aspect the invention resides in a method for making an
 antimicrobial structure comprising coating a hydrophobic surface of a
 solid substrate with a chitosan material, wherein the amount of the
 chitosan material is from about 0.0005 to about 2.5 grams per square meter
 on a solids basis. More specifically, the method can include the steps of
 (1) preparing a solution or suspension containing the chitosan material;
 (2) coating the solution or suspension onto a hydrophobic surface of a
 solid substrate; (3) drying the coated substrate; and (4) optionally
 post-treating the dried structure to insolubilize the chitosan material.
 In another aspect, the invention resides in an anitmicrobial structure
 comprising a solid substrate having a hydrophobic surface, said
 hydrophobic surface having a coating of a chitosan material of from about
 0.0005 to about 2.5 grams per square meter.
 In another aspect, the invention resides in a personal care garment, such
 as a diaper, incontinent garment, feminine pad and the like, comprising a
 body-side liner, a liquid impervious backsheet, and an absorbent core in
 between, wherein the body-side liner comprises a polypropylene nonwoven
 fabric having a coating of a chitosan material of from about 0.0005 to
 about 2.5 grams per square meter.
 The antimicrobial effectiveness of the coated antimicrobial structure
 appears to be at least partly dependent upon the hydrophobicity of the
 surface of the substrate and the thickness or amount of the coating. In
 general, as the hydrophobicity of the surface of the base polymer
 increases and the thickness of the coating decreases, the effectiveness of
 the antimicrobial structure is increased. While not wishing to be bound to
 any particular theory, it is believed that when coating a chitosan
 material onto a hydrophobic surface of a substrate such as polypropylene,
 for example, the hydrophobic surface of the polymer attracts the
 hydrophobic segments (--C--C--).sub.n and repels the hydrophilic segments
 (--NH.sub.2) of the chitosan material. This results in a structure in
 which most of the hydrophobic segments of the coated chitosan material
 (which are also the non-functional segments in terms of antimicrobial
 properties) are aligned towards the interface between the chitosan
 material coating and the polymeric substrate. At the same time, most of
 the hydrophilic segments of the coated chitosan material (which are also
 the functional segments in terms of antimicrobial properties) are
 outwardly aligned at the surface of the structure. Such a structure, which
 has most of the functional groups exposed on the surface, has enhanced
 antimicrobial properties. The optimal structure would have 100 percent of
 the functional segments on the outer surface of the coating. Since only
 the surface portion of the coating contributes to the antimicrobial
 properties of the composite structure, thinner coatings are more
 effective. As the coating thickness increases, the interaction between the
 hydrophobic segments of the chitosan material and the hydrophobic
 substrate decreases, thereby decreasing the otherwise preferential outward
 orientation of the hydrophilic segments.
 For purposes herein, the term "hydrophobic" means a material having a
 contact angle of water in air of 90 degrees or greater. In contrast, the
 term "hydrophilic" refers to a material having a contact angle of water in
 air of less than 90 degrees. For purposes of this application, contact
 angle measurements are determined as set forth in "Surface and Colloid
 Science--Experimental Methods", Vol. II, Robert J. Good and Robert J.
 Stromberg, Ed. (Plenum Press, 1979).
 For purposes herein, the term "chitosan material" means chitosans, modified
 chitosans (i.e., carboxymethyl chitins/chitosans) and chitosan salts. Such
 materials can have a wide range of molecular weights. In general, chitosan
 materials having very high molecular weights and high charge densities
 have a high viscosity, which may prohibit the formation of the desired
 thin and even coating layer on the base material, or which may require
 high dilution with an appropriate solvent in order to process them, either
 of which situations may be not economical on a commercial scale. On the
 other hand, if the molecular weight of the chitosan material is too low,
 it may be difficult to retain the chitosan material on the surface of the
 substrate, at least in those instances where a water soluble chitosan
 material is used. To balance desirability of low cost and high substrate
 retention (low washability), it is suggested that the weight average
 molecular weight of the chitosan material be from about 1,000 to about
 10,000,000, more specifically from about 2,000 to about 1,000,000, still
 more specifically from about 3,000 to about 800,000, and most specifically
 from about 5,000 to about 500,000.
 A suitable amount of the chitosan material, for purposes of this invention,
 can be from about 0.0005 to about 2.5 grams per square meter, more
 specifically from about 0.001 to about 1 gram per square meter, and still
 more specifically from about 0.005 to about 0.01 gram per square meter.
 Alternatively, the amount of the chitosan material can be expressed as a
 dry weight percent of the substrate to which it is applied. Such amounts
 can be from about 0.01 to about 10 weight percent, more specifically from
 about 0.1 to about 5 weight percent, and still more specifically from
 about 1 to about 5 weight percent.
 Suitable solid substrates include, but are not limited to, particulates,
 filaments, films, foams, fibers, agglomerates, nonwovens and fabrics of
 various polymers. Generally, the physical form having the larger surface
 area is preferred if possible. Suitable polymers include hydrophobic
 polymers such as polyethylene, polypropylene, polyester, polyvinyl
 chloride, polyvinylidene chloride, polystyrene, polyesters, polyamides,
 polyimides, and copolymers and mixtures of the same. However, even
 hydrophilic polymers can form a hydrophobic surface if specially treated.
 For example, polyacrylic acid is a hydrophilic polymer due to the presence
 of carboxylic acid groups (--COOH). However, the surface of the
 polyacrylic acid can be very hydrophobic if the solution of the polymer is
 dried in hot air. That is because the hot air in nature is hydrophobic
 relative to water which attracts, in the drying process, the hydrophobic
 segments (--C--C--).sub.n of the polyacrylic acid stay on the surface and
 at the same time repels the hydrophilic segments (--COOH) of the polymer
 away from the surface.
 In preparing to coat the substrate using a coating solution or suspension
 comprising the chitosan material(s), water is generally the preferred
 solvent or carrier due to its low cost and non-hazardous nature. The
 concentration of the chitosan material can be from about 0.1 to about 60
 weight percent, more specificaly from about 0.5 to about 50 weight
 percent, and more specifically from about 1 to about 30 weight percent.
 Particular product applications may require the use of one or more
 co-solvents, which can include, but are not limited to, methanol, ethanol,
 acetone, isopropyl alcohol, ethylene glycol, glycerol, and the like.
 When the chitosan material is not soluble in the solvent, it can be made as
 a suspension for coating. In such a situation, the chitosan material must
 be first prepared into a form which possesses a huge surface area in order
 to deliver the desired antimicrobial properties. One example of such a
 form is, but is not limited to, a chitosan micron powder having a particle
 diameter of from about 0.1 to about 80 microns. Besides having
 antimicrobial properties, another benefit of using a large surface area
 micron powder is to enhance the adhesion of the chitosan material to the
 substrate.
 If the adhesion of the chitosan material to the substrate is a concern,
 additional adhesive material can be added into either the solution or the
 suspension. Such adhesive material should not be reactive to but
 compatible with the chitosan material so that it does not have any
 significant effect of reducing the antimicrobial properties.
 In some end-use applications, the coated materials of this invention may
 have to be exposed to an aqueous solution multiple times. One such example
 is the use of the coated material as a top layer (close to the skin) in a
 diaper. Since multiple urine insults are expected, it is important to
 prevent the chitosan material from being washed away from the top layer.
 One way to reduce washability of the coating agent is to use one or more
 crosslinking agents to insolubilize or bind the chitosan material to the
 substrate. Crosslinking agents suitable for use in the present invention
 are generally soluble in the solvent used for dissolving the chitosan
 material and do not substantially reduce the antimicrobial properties. One
 suitable crosslinking agent is an organic compound having at least two
 functional groups or functionalities capable of reacting with active
 groups located on the chitosan materials. Examples of such active groups
 include, but are not limited to, carboxyl (--COO.sup.-), carboxylic acid
 (--COOH), amino (--NH.sub.2), or hydroxyl (--OH) groups. Examples of such
 suitable crosslinking agents include, but are not limited to, diamines,
 polyamines, diols, polyols, polycarboxylic acids, polyoxides, and the
 like.
 One way to introduce a crosslinking agent into the chitosan material
 solutions is to mix the crosslinking agent with the chitosan material
 during preparation of the solution. Another suitable crosslinking agent
 comprises a metal ion with more than two positive charges, such as
 Al.sup.3+, Fe.sup.3+, Ce.sup.3+, Ce.sup.4+, Ti.sup.4+, Zr.sup.4+ and
 Cr.sup.3+. In the case of cationic polymers, polyanionic substances are
 also suitable crosslinking agents. Examples are sodium polyacrylate,
 carboxymethylcellulose, polyphosphate, and the like. Since the cations on
 the chitosan material possess antimicrobial properties, it is not
 preferred to use a crosslinking agent reactive to the cations unless no
 alternative crosslinking agent is available.
 When using crosslinking agents for purposes of this invention, a suitable
 amount of crosslinking agent is from about 0.001 to about 30 weight
 percent based on the dry weight of the chitosan material, more
 specifically from about 0.02 to about 20 weight percent, more specifically
 from about 0.05 to about 10 weight percent, and still more specifically
 from about 0.1 to about 5 weight percent.
 After the coating step, a drying process may be necessary to remove any
 solvent used to dissolve or disperse the chitosan material. The drying
 temperature is important because hot air is hydrophobic and may reduce the
 number of functional segments on the surface of the coating layer. In
 general, a relatively low drying temperature is preferred. Suitable
 temperatures can be from about 40.degree. C. to about 150.degree. C., more
 specifically from about 40.degree. C. to about 100.degree. C., and still
 more specifically from about 40.degree. C. to about 80.degree. C. If a
 high temperature is needed and the hydrophobicity of the hot air is a
 concern, humidified air can be used. The relative humidity of the hot and
 humidified air can be from about 30 to about 90 percent, more specifically
 from about 40 to about 80 percent, more specifically from about 40 to
 about 70 percent, and still more specifically from about 40 to about 60
 percent.
 As stated previously, a post treatment may be necessary to induce a
 crosslinking reaction to occur when a latent crosslinking agent is used.
 Suitable post treatments include, but are not limited to, heat curing
 (&gt;40.degree. C.), ultra-violet light exposure, microwave treatment,
 electron beam radiation, steam or high pressure treatment, organic solvent
 or humidity treatment, etc.

EXAMPLES
 Twelve different samples were prepared in order to illustrate the
 effectiveness of the chitosan materials of this invention. These samples
 are summarized below:

Sample 2% chitosan-HCl solution, VNS-608,
 #1 Mw = 11,000,000, Degree of Acetylation = 0.14
 Sample 35% Na-polyacrylate solution, Mw = 60,000,
 #2 Degree of Neutralization = 50%
 Sample 2% chitosan acetate solution, VNS-608, Mw = 11,000,000,
 #3 Degree of Acetylation = 0.14
 Sample 2% carboxymethyl cellulose solution, Aqualon CMC-7H3SXF,
 #4 DS = 0.7, Mw = 1,000,000
 Sample 20% polydiallydimethylammonium chloride solution
 #5
 Sample Chitosan acetate film (0.3 mm thickness), casting film from
 #6 Sample #3
 Sample Chitosan sulfate film (0.3 mm thickness), Sample #6 treated with
 #7 1% H.sub.2 SO.sub.4, washed/dried
 Sample Chitosan film (0.3 mm thickness), Sample #6 treated with 1%
 #8 NaOH, washed/dried
 Sample Polypropylene (PP) spunbond liner (0.50 ounces per square yard;
 #9 denier of 2 dpf) w/3 wt % chitosan acetate
 coating (Sample #3 solution)
 Sample PP spunbond liner w/3 wt % chitosan sulfate coating, Sample #9
 #10 treated with 1% H.sub.2 SO.sub.4, washed/dried
 Sample PP spunbond liner w/3 wt % chitosan coating, Sample #9 treated
 #11 with 1% NaOH, washed/dried
 Sample PP spunbond liner wo/coating (control)
 #12
 SAMPLE PREATION
 The various samples were prepared as follows:
 Sample 1: 18 grams of chitosan (VNS-608 from Vanson Chemical Company Inc.,
 Redmond, Wash.; molecular weight of 11,000,000; degree of acetylation of
 0.14) were dispersed in 544 grams of distilled water. To this mixture was
 added 6.4 milliliters of an aqueous solution of hydrochloric acid having a
 concentration of 37 percent. The resultant mixture was stirred until the
 chitosan was dissolved. To this solution was added 37 milliliters of
 distilled water. The solution was stirred again for 30 minutes and
 filtered through a Buchner funnel using a polypropylene filter fabric.
 Sample 2: 35 grams of sodium polyacrylate (molecular weight of 60,000 and
 degree of neutralization of 50 percent) were dissolved in 65 grams of
 distilled water by stirring the mixture until the solution was clear.
 Sample 3: 4.5 grams of chitosan (same as that of Sample 1) were dispersed
 in 185.5 grams of distilled water. To this mixture were added 1.5
 milliliters of glacial acetic acid and the resultant mixture was stirred
 until the chitosan was dissolved. 33.5 milliliters of distilled water was
 added to the solution and the solution was stirred again for 30 minutes
 and filtered through a Buchner funnel using a polypropylene filter fabric.
 Sample 4: 2 grams of carboxymethylcellulose (CMC-7H3SXF from Aqualon Oil
 Field Chemicals, Division of Hercules Incorporated, Houston, Tex.;
 molecular weight of 1,000,000 and degree of substitution of 0.7) was
 dissolved in 98 grams of distilled water by stirring the mixture until the
 solution was clear.
 Sample 5: About 68 milliliters of 60 percent by weight aqueous solution of
 diallyldimethylammonium chloride monomer was added to a 500 milliliter
 conical flask. To this about 132 milliliters of distilled water was added
 to make a 20 percent solution of diallyidimethylammonium chloride in
 water. The solution was purged with nitrogen gas for 20 minutes and placed
 in a shaker water bath maintained at 60.degree. C. After the temperature
 of the monomer solution reached 60.degree. C., 0.072 grams of potassium
 persulfate and 0.28 grams of sodium bisulfite was dissolved into the
 monomer solution to initiate polymerization. The reaction was continued
 for 24 hours by maintaining the solution at 60.degree. C. After completion
 of the reaction, the viscous polymer solution was added to 1 liter of
 acetone to precipitate the polymer. The precipitated polymer was
 redissolved in 200 milliliters of distilled water and reprecipitated in
 1000 milliliters of acetone. The dissolution and precipitation was
 repeated three times and the recovered polymer was dried at 40.degree. C.
 About 20 grams of the dried polymer was then dissolved in 80 milliliters
 of distilled water to make the 20 percent solution of
 polydiallyidimethylammonium chloride in water.
 Sample 6: 10 grams of a chitosan material (VSN-608 from Vanson having a
 viscosity of 11,400 cps for a 1% solution in 1% acetic acid) was suspended
 in 2 liters of distilled water and mixed with acetic acid with a molar
 ratio of chitosan to acetic acid of about 0.9 to 1. After more than 15
 hours of mixing time, the chitosan material was completely dissolved.
 (This solution (0.5% concentration) was used in film casting and nonwoven
 coating treatments to prepare several of the samples described below). The
 solution was poured onto a surface treated (non sticky) pan and air dried
 at room temperature for two days. The dried film was further heat treated
 at 80.degree. C. for 30 minutes.
 Sample 7: The film of Sample 6 was immersed in a large amount of a 1%
 aqueous sulfuric acid solution for at least 4 hours, washed thoroughly
 with distilled water and dried at 60.degree. C.
 Sample 8: The film of Sample 6 was immersed in a large amount of a 1%
 aqueous sodium hydroxide solution for at least 4 hours, washed thoroughly
 with distilled water and dried at 60.degree. C.
 Sample 9: Commercial polypropylene spunbond liner taken from a HUGGIES.RTM.
 diaper manufactured by Kimberly-Clark Corporation was dipped into the 0.5%
 chitosan acetate of solution described in the preparation of Sample 6 and
 dried at room temperature (most of the chitosan acetate solution on the
 surface of the liner was removed to achieve an even coating). The dried
 liner was heat treated at 80.degree. C. for 30 minutes. About 5.5 dry
 weight percent of the chitosan acetate was estimated to be coated onto the
 surface of the liner using the weight difference before and after the
 treatment.
 Sample 10: The treated liner of Sample 9 was immersed in a large amount of
 a 1% aqueous sulfuric acid solution for at least 2 hours, washed
 thoroughly with distilled water and dried at 60.degree. C.
 Sample 11: The treated liner of Sample 9 was immersed in a large amount of
 a 1% aqueous sodium hydroxide solution for at least 2 hours, washed
 thoroughly with distilled water and dried at 60.degree. C.
 Sample 12: Untreated commercial polypropylene spunbond liner.
 ANTIMICROBIAL TESTING OF THE SAMPLES
 Examples 1-4
 For solution samples(#1-#4): The test is performed by mixing the test
 solutions with the challenge organisms (E. coli, S. aureus, P. aeruginosa,
 C. albicans, A. niger), incubating at room temperature for 24 hours (up to
 48 hours for yeast, and 7 days for molds), and periodically sampling the
 mixture to determine the number of viable organisms remaining in the test
 sample. Enumeration of remaining organism in the sampling solution mixture
 enabled quantitative measurement of antimicrobial activity, as measured by
 Colony Forming Units (CFUs).
 Example 5
 For solution sample (#5): For the 20% polydiallydimethylammonium chloride
 solution, the test was performed by inoculating the test solutions
 separately with the challenge organisms (E. coli, S. aureus and C.
 albicans) and incubating at 31.degree. C. Serial dilutions were performed
 at time points 0, 6, 30 and 54 hours. E. coli and S. aureus were
 enumerated on duplicate plates of 1% tripticase soy agar (TSA) and C.
 albicans was enumerated on duplicate plates of sabouraud dextrose agar.
 Examples 6-8
 For film samples(#6-#8): Test material was cut in 3 sample weights of 25
 mg, 50 mg and 100 mg, and placed in individual wells of 6-well FALCON
 tissue culture plates. S. aureus inoculum was prepared in physiological
 saline such that the bacterial concentration was fixed at approximately
 5.times.10.sup.6 CFU/ml. Inoculum volumes added to pre-weighed samples
 were: 10 ml for sample #6 (due to the absorbent nature of the material),
 and 5 ml for samples #7 and #8. Inoculated samples were covered and
 incubated on a rotating platform set at 100 rpms. Serial dilutions of
 samples were prepared in letheen neutralizing broth at time points of
 zero, two and four hours. Viable S. aureus recovery was determined by
 plating the dilutions onto nutrient agar. Controls of straight inoculum (5
 ml) were simultaneously evaluated at the designated time points.
 Antimicrobial activity was determined by sample recovery relative to
 control recovery. Note: only S. aureus was assayed with this method.
 Examples 9-12
 For coated samples(#9-#12): Test material was cut with a calibrated die
 cutter into 11/8 inch disks and weighed prior to analysis. Each test
 organism (S. aureus, E. coli, C. albicans) was washed and resuspended in
 pH 5 acetate buffer. Organisms were applied to the test material in a
 volume of 2 .mu.m of inoculum per milligram of material. Inoculated
 organisms were allowed contact incubation times of zero, 3 and 6 hours.
 The zero time point samples were processed immediately, and the 3 and 6
 hour samples were incubated in a sterile, humidified, enclosed 31.degree.
 C. chamber (approximate skin surface temperature). Samples were processed
 by placing inoculated disks into 25 milliliters of letheen neutralizing
 solution and vortexing vigorously for 30 seconds to remove adhering
 organisms into the surrounding fluid. Serial dilutions of this solution
 were spread plated onto nutrient agar to recover viable test organisms.
 Enumeration of organism recovery of samples relative to controls enabled
 quantitative measurement of antimicrobial activity.
 The results of the antimicrobial testing are summarized in the tables which
 follow:
 TABLE 1
 Solutions
 Sample CFU's @ CFU's @ CFU's @
 # Organism t = 0 hr t = 24 hrs t = 30 hrs
 #1 S. aureus 1.9 .times. 10.sup.7 0
 P. aeruginosa 4.9 .times. 10.sup.6 1.4 .times. 10.sup.5
 E. coli 2.1 .times. 10.sup.5 0
 C. albicans 0 0
 A. niger 2.2 .times. 10.sup.5 2.4 .times. 10.sup.6
 #2 S. aureus 6.3 .times. 10.sup.7 4.1 .times. 10.sup.7
 P. aeruginosa 6.4 .times. 10.sup.6 0
 E. coli 1.4 .times. 10.sup.7 0
 C. albicans 6.3 .times. 10.sup.5 1.6 .times. 10.sup.4
 A. niger 4.7 .times. 10.sup.5 1.3 .times. 10.sup.6
 #3 S. aureus 1.7 .times. 10.sup.8 1.7 .times. 10.sup.7
 P. aeruginosa 4.0 .times. 10.sup.5 0
 E. coli 3.8 .times. 10.sup.5 6.4 .times. 10.sup.3
 C. albicans 0 0
 A. niger 7.7 .times. 10.sup.4 4.6 .times. 10.sup.5
 #4 S. aureus 7.2 .times. 10.sup.7 1.8 .times. 10.sup.8
 P. aeruginosa 5.0 .times. 10.sup.7 6.5 .times. 10.sup.8
 E. coli 4.2 .times. 10.sup.7 6.4 .times. 10.sup.8
 C. albicans 5.5 .times. 10.sup.5 9.4 .times. 10.sup.6
 A. niger 8.5 .times. 10.sup.5 8.4 .times. 10.sup.5
 #5 E. coli 1.64 .times. 10.sup.5 0
 S. aureus 1.37 .times. 10.sup.5 0
 C. albicans 1.88 .times. 10.sup.5 0
 Conclusion: Chitosan hydrochloride (Sample 1) and chitosan acetate (Sample
 3) exhibited significantly higher antimicrobial activity than sodium
 polyacrylate (Sample 2) and carboxymethylcellulose (Sample 4).
 Polydiallyldimethylammonium chloride (Sample 5) also exhibited high
 antimicrobial activity.
 TABLE 2
 Chitosan Films
 (S. aureus inoculum 5.9 .times. 10.sup.6)
 Sample Wt Time (hrs) Sample #6 Sample #7 Sample #8 Control
 25 mg 0 3.9 .times. 10.sup.6 6.1 .times. 10.sup.6 7.7
 .times. 10.sup.6 7.9 .times. 10.sup.6
 2 1.3 .times. 10.sup.4 6.4 .times. 10.sup.6 5.2
 .times. 10.sup.6 1.2 .times. 10.sup.6
 4 6.9 .times. 10.sup.4 7.9 .times. 10.sup.8 2.2
 .times. 10.sup.6 1.7 .times. 10.sup.5
 50 mg 0 5.0 .times. 10.sup.6 5.9 .times. 10.sup.6 4.9
 .times. 10.sup.6 7.9 .times. 10.sup.8
 2 7.1 .times. 10.sup.3 5.1 .times. 10.sup.6 3.6
 .times. 10.sup.6 1.2 .times. 10.sup.6
 4 1.4 .times. 10.sup.3 5.4 .times. 10.sup.6 3.5
 .times. 10.sup.6 1.7 .times. 10.sup.5
 100 mg 0 n/e 5.5 .times. 10.sup.6 6.4 .times. 10.sup.6 7.9
 .times. 10.sup.6
 2 n/e 9.6 .times. 10.sup.6 2.4 .times. 10.sup.6
 1.2 .times. 10.sup.6
 4 n/e 7.0 .times. 10.sup.6 2.9 .times. 10.sup.5
 1.7 .times. 10.sup.5
 TABLE 3
 Chitosan Coated on Polypropylene Liner
 Time Sample Sample Sample Sample
 Organism (hrs) #9 #10 #11 #12
 S. aureus 0 8.1 .times. 10.sup.6 7.6 .times. 10.sup.6 5.7
 .times. 10.sup.6 8.2 .times. 10.sup.6
 (Inoc. 7.3 .times. 10.sup.8) 3 5.6 .times. 10.sup.3 8.6 .times.
 10.sup.5 2.3 .times. 10.sup.3 7.3 .times. 10.sup.6
 6 3.0 .times. 10.sup.3 4.3 .times. 10.sup.5 &lt;100
 2.8 .times. 10.sup.5
 E. coli 0 3.0 .times. 10.sup.6 4.0 .times. 10.sup.6 3.7
 .times. 10.sup.6 3.7 .times. 10.sup.6
 (Inoc. 4.1 .times. 10.sup.6) 3 &lt;100 4.6 .times. 10.sup.4 2.5
 .times. 10.sup.3 6.8 .times. 10.sup.5
 6 &lt;100 7.9 .times. 10.sup.3 &lt;100 5.8 .times.
 10.sup.5
 C. albicans 0 3.9 .times. 10.sup.4 8.1 .times. 10.sup.4 8.1
 .times. 10.sup.4 6.3 .times. 10.sup.4
 (Inoc. 5.0 .times. 10.sup.4) 3 7.0 .times. 10.sup.3 5.2 .times.
 10.sup.4 1.0 .times. 10.sup.4 4.8 .times. 10.sup.4
 6 3.0 .times. 10.sup.3 1.3 .times. 10.sup.4 &lt;100
 1.7 .times. 10.sup.4
 Conclusion:
 The chitosan acetate (Sample #9), chitosan sulfate (Sample #10) and
 chitosan (Sample #11) coated on a hydrophobic surface demonstrate
 antimicrobial activities compared to the control material (Sample #12)
 Comparing the antimicrobial activity of Samples 6 vs 9, Samples 7 vs 10 and
 Samples 8 vs 11, it is surprisingly shown that with respect to S. aureus,
 the antimicrobial activity of the structures of this invention (chitosan
 coated onto a polypropylene nonwoven fabric) is greater than the
 antimicrobial activity of the chitosan films alone.
 The foregoing examples, given for purposes of illustration, are not to be
 construed as limiting the scope of this invention, which is defined by the
 following claims and all equivalents thereto.