Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Matrices
Reexamination Certificate
2000-07-05
2002-04-30
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Matrices
C424S486000, C424S426000, C514S772700, C514S777000, C514S944000
Reexamination Certificate
active
06379702
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of poly(N-vinyl lactam)-chitosan gels and more particularly to gels which are absorbent and may be skin adhering, which are flexible and contour-conforming, and which can be used for a variety of applications. The gels of the present invention have K values of below 60.
Chitosan is a deacetylated chitin, and is a linear polysaccharide of deacetylated N-acetyl-D-glucosamine. Chitosan has been used to absorb heavy metals from water and industrial waste streams, and as a dyeing assistant in photographic emulsions. Chitosan derivatives have also been used in cosmetics and conditioning agents, in hair setting lotions and shampoos as, for example, in U.S. Pat. Nos. 4,134,412 and 4,202,881, when neutralized with acids.
Poly(N-vinyl lactam) s such as polyvinylpyrrolidone (PVP) have been used, for example, in pharmaceuticals, in certain types of films and in some cosmetic products.
It has been known that polyvinylpyrrolidone forms complexes with polyurethanes to yield hydrophilic blends or alloys. U.S. Pat. No. 4,642,267 describes hydrophilic polymer blends of polyurethane and hydrophilic poly(N-vinyl lactam) prepared in solvent solution to provide slippery coatings when wet and which are water insoluble to some extent once cured by drying.
European Patent Application 107,376 describes tacky PVP gels which require the use of ionizing radiation for cross-linking. U.S. Pat. No. 4,646,730 describes a PVP/Silver Sulfadiazine hydrogel dressing in which electron beam radiation is required to cross-link the PVP and form a gel. In addition, magnesium trisilicate, hydrogen peroxide and/or polyacrylic acid are added for color stabilization. It is apparent that there would be an advantage in making skin-adhering gels in the absence of expensive equipment and/or processing.
U.S. Pat. No. 5,420,197 describes poly (N-vinyl lactum)-chitosan gels wherein the K values are at least 60.
Ring opening of pyrrolidone groups on PVP was described by H. P. Frank, “The Lactam-Amino Acid Equilibria for Ethylpyrrolidone and Polyvinylpyrrolidone”, Journal of Polymer Science 12, 565-576 (1954), and A. Conix and G. Smets, “Ring Opening in Lactam Polymers”, J. Poly. Chem.13, 221-229 (1955). The concept of ring-opened pyrrolidone groups is made use of in this invention to unexpectedly attain absorbent gels.
It is therefore an object of the invention to provide dermatologically-compatible gels having a hydrophilic absorbent property and K values of less than 60.
It is a further object to produce gels with K values of less than 60 without a need for expensive equipment and/or processing.
It is another object to provide gels of poly(N-vinyl lactam) and chitosan derivatives with K values of less than 60 which can be used in a variety of products such as cavity dressings, drug delivery patches, face masks, wound dressings and prostheses.
SUMMARY OF THE INVENTION
Accordingly, there is provided a stable, hydrophilic gel which comprises a blend of acid-neutralized chitosan and a poly(N-vinyl lactam), with or without a plasticizer, the poly(N-vinyl lactam) having a K value of less than about 60 and mole equivalents of acid groups of at least about 1.4. The gel may be formed into a wound packing or cavity dressing where, unlike hydrocolloid dressings, it is able to absorb exudate without losing its gel structure. It can also be utilized as a drug carrier for transdermal devices and for use in dry skin masks to deliver moisturizers to the skin. It can also be used in prosthetic devices such as breast implants.
The poly(N-vinyl lactam) is preferably a polyvinylpyrrolidone having mole equivalents of acid groups of at least about 1.4 formed by ring opening of pyrrolidone groups.
The gel is prepared by mixing aqueous poly(N-vinyl lactam) solution and acidneutralized chitosan in aqueous solution at a poly(N-vinyl lactam)/chitosan weight ratio of from about 12/1 to about 1/1, preferably from about 10/1 to about 5/1, to form a blend at about 5 wt. % to 40 wt. % total polymer concentration, preferably from about 12.5 wt. % to about 25 wt. % polymer concentration, and allowing the blend to cure until a gel is formed.
The gel preferably includes at least one additional ingredient which may be releasable from the gel. Preferably the releasable ingredient is a moisturizer, drug or other bio-effecting or body-treating material.
Preferred products for which the gel can be used are cavity-filling wound dressings, other wound and burn dressings, drug delivery systems, cosmetic masks, prostheses and wraps.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, and its scope will be pointed out in the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that poly(N-vinyl lactam) such as polyvinylpyrrolidone (PVP), with a degree of ring-opened pyrrolidone groups, forms hydrophilic gels with chitosans. The gels are flexible and transparent or translucent and may be used alone or with various additives. The gels can be used for wound packing, wound and burn dressings, drug delivery systems, prostheses, cosmetic face and nail wraps, and other applications where the high absorption capacity of the gel and the high heat capacity and transport capacity of water as part of the hydrophilic gel can be utilized. These gels may have either a tacky quality or a non-tacky quality.
Chitosan, a natural product, is derived from chitin. Chitin is an unbranched linear polysaccharide of N-acetyl-D-glucosamine units linked by &bgr;-1,4 bonds. It is a polymer of glucose in which the hydroxyl group on C-2 is replaced by the N-acetylamino group —NHCOCH
3
. In chitosan, the acetyl group is absent. Therefore, chitosan is a deacetylated chitin. Chitosan contains approximately 7% nitrogen and is structurally similar to cellulose. Chitin occurs in nature in the exoskeletons of arthropods such as crabs, lobsters and shrimp. Chitin can be obtained from these sources as an amorphous powder after dissolution of the calcium carbonate with mineral acids and removal of the proteins. It is also found in some fungi, algae and yeast.
Chitosan becomes soluble in water when protonated with acids. The polymer thus formed is positively charged and thus more likely to interact with negatively charged surfaces like skin and hair.
Chitosan derivatives are commercially available as, for example, chitosan neutralized with pyrrolidone carboxylic acid available as Kytamer PCA from Amerchol Corporation; carboxymethyl sodium salt of chitosan available as Chitisol from Muto Corporation; chitosan neutralized with glutamic acid available as Seacure+210 from Protan Corporation; N,O-carboxymethyl chitosan available from Nova Chem Ltd., Canada; and un-neutralized chitosan available from Tokyo Kasei Inc. Suitable chitosan derivatives for this invention are the dermatologically-compatible salts of chitosan such as those with pyrrolidone carboxylic acid, glutamic acid, acetate, etc., and also N,O-carboxymethyl chitosan.
Suitable poly(N-vinyl lactams) have a K value of less than about 60, preferably less than about 45, most preferably from about 25 to about 35, and optimally about 30. The K value represents kinematic viscosity. It is a measure of the resistive flow of a fluid under the influence of gravity. The K value is derived from viscosity measurements and is calculated according to Eikentscher's formula described by Kline, G. M., “Polyvinylpyrrolidone”, Modern Plastics p 157 (November 1945) and is also described in General Aniline & Film Corporation Technical Bulletin 7583-033. The K value is a function of molecular weight. At the same K value or molecular weight, the level of ring-opened poly(N-vinyl lactam) is an important consideration in determining whether a gel forms.
In the invention, poly N-vinyl lactams containing above certain levels of ring-opened pyrrolidone groups, when mixed with certain solutions of neutralized chitosans, form gels which may be mildly tacky. The term tacky is intended to mean having the p
Lee Connie C.
Lorenz Donald H.
Fubara Blessing
Hoffman & Baron LLP
Hydromer, Inc.
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