Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
1997-12-23
2001-03-06
Azpuru, Carlos A. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C424S404000, C424S405000, C424S409000
Reexamination Certificate
active
06197322
ABSTRACT:
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—)
n
and repels the hydrophilic segments (—NH
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—)
n
of the polyacrylic acid stay on the surface and at the same time repels the hydrophilic segmen
Bevernitz Kurt James
Dutkiewicz Jacek
Huard Linda Susan
Qin Jian
Ramaswami Wallajapet Palani Raj
Azpuru Carlos A.
Croft Gregory E.
Kimberly--Clark Worldwide, Inc.
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