Silver alginate foam compositions

Details Silver alginate foam compositions Silver alginate foam compositions

2001-07-26

2004-02-24

Page, Thurman K. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Web, sheet or filament bases; compositions of bandages; or...

C424S444000, C424S445000, C424S446000, C424S447000, C424S448000

Reexamination Certificate

active

06696077

ABSTRACT:

DESCRIPTION OF THE PRIOR ART
The effect of various metals on biological processes has generally been referred to as an “oligodynamic” action. A detailed discussion of the history of such oligodynamic action with particular emphasis on the use of silver is contained in Chapters 24 and 28 of the monograph by Lawrence and Block,
Disinfection, Sterilization, and Preservation
, Lea and Febiger, Philadelphia, 1968. Consequently, Chapters 24 and 28 of Lawrence and Block's treatise on disinfection are cited herein by reference in their entirety.
Goodman and Gilman (1943) reported that the toxic effects of silver compounds on microorganisms is probably due to the silver ions which precipitate the protein of bacterial protoplasm. It is very well known that soluble silver salts such as silver nitrate will quickly precipitate protein and oxidize to a dark brown or black precipitate. The silver protein complex so formed contributes to a sustained antiseptic action by slowly liberating small amounts of silver ions. Goodman and Gilman felt it probable that in the use of simple salts of silver as antiseptics, some metallic silver is obtained by reduction and that its oligodynamic action contributes to the anti-bacterial effect.
Studies examining the mechanism of action by silver in demonstrating antimicrobial activity led various workers to conclude that the surface area of silver ions was more important that the amount of silver nor the time that the substrate containing microbes was exposed to the silver. The silver was prepared in the form of a spongy metallic form or by coating various products which contain large surfaces such as sand. Thus Süpfle and Werner (1951) were able to show that
E. coli
placed in flasks having counts of 18,000
E. coli
per ml of water. When such counts were exposed to flasks containing sand coated with silver at a concentration of 10% silver of the amount of sand, would result in a sterile environment in four hours. Even counts as high as 120,000
E. coli
per ml of solution, resulted in sterility in 24 hours.
Clinical studies utilized a silver powder prepared by Rochat and Uzdins (1947) showed that particles of silver of a size of 2 microns to {fraction (1/100)} of a micron, when prepared in the form of a paste could be used to treat dental root canals, in the form of a spray to treat tonsillitis, or in the form of a powder in water suspension to treat abrasions and burns. Such silver compounds were successful for the treatment of severe burns, carbuncles and infected wounds. As such, the silver preparations promoted tissue granulation, suppressed fecal odors of wounds, accelerated healing, as well as prevented keloid formulation.
Kreidl and Kreidl (U.S. Pat. No. 2,396,514) prepared a cloth or gauze by treating the material with a solution of a silver compound, such as silver nitrate, followed by a soluble halide such as sodium chloride and after a period of time, which resulted in an insoluble silver chloride precipitate being impregnated into the cloth, they washed off the excess of silver chloride that was not absorbed onto the material, so resulting in an impregnated material which had antiseptic properties. The dressing containing silver chloride as prepared by Kreidl and Kreidl would have exerted minimal antimicrobial activity because, as is well-known in the profession, silver chloride is a highly insoluble chemical and is insoluble in water or other aqueous solutions to the extent of 0.000089
10
parts per 100 ml of water.
Schwartz (U.S. Pat. No. 2,459,896) impregnated fibers such as nylon fibers with colloidal silver and then reduced the silver by treating the preparation with alkylamines. These fibers were then shown to have antimicrobial activity. Here also in the Schwartz patent nylon fibers which are not soluble in aqueous solutions or tissue exudate, would be expected to have very low antimicrobial activity, because the only colloidal silver that would be available to act on microorganisms are those colloidal silver particles on the very surface of the nylon fiber and they would essentially be few and far between and fixed in situ of the nylon. In addition, such a preparation of a colloidal silver-impregnated nylon fiber would not have the characteristics that have been shown to be important in utilizing silver as an antimicrobial agent, in that the total silver surface area of silver ions available to the tissue exudate would be minimal, because colloidal silver is silver in the non-ionic state.
In a subsequent patent (U.S. Pat. No. 2,459,897) Schwartz also produced fibers that were impregnated with silver and reducing agents of silver in which the reduction of the silver was achieved with heterocyclic secondary amines such as piperidine or pyrrolidine. These fibers thereby developed antimicrobial activity. In this patent of Schwartz (U.S. Pat. No. 2,459,897), Schwartz recognized the necessity to reduce the free silver to silver ions and thereby incorporated secondary amines which acted as reducing agents which were also impregnated into the nylon fibers in order to procure antimicrobial activity. Here also, however, the only antimicrobial activity that would be available to a tissue exudate would be those on the very surface of the fiber and all of the reduced silver ions present inside the nylon fiber would not be available to the tissue exudate, therefore, the antimicrobial activity would be diminished.
Goetz, in his U.S. Pat. No. 2,521,713 formed silver complexes which were antimicrobial by utilizing a finely divided silver oxide sludge and finely divided zinc oxide to react for a short period of time. The mixture was then dried and made into granules or pellets. These complexes in the form of a paste could be used as germicides for the treatment of burns, wounds, or skin infections. In this patent by Goetz, the silver oxide sludge so prepared would be expected to have minimal antimicrobial activity, because silver oxide in the form of Ag
2
O is soluble in aqueous solutions (and therefore tissue exudates) to the extent of 0.0013
20
parts per hundred. The oxide of silver as silver oxide Ag
2
O is essentially considered insoluble in water. Because of the highly insoluble nature of the silver oxides, ionization of the silver oxides would be minimal and therefore antimicrobial activity also would be significantly diminished.
In a patent by Wilhelm Dieck and Sally Schiff (U.S. Pat. No. 2,008,131) the inventors relied exclusively on oxides of silver to procure antimicrobial activity. Thus even when a solution of silver permanganate utilized by the inventors was reduced, the inventors indicate the possible production of a silver oxide-manganite compound, which compound may (emphasis added) be a silver manganite compound having the composition of Ag
2
O
2
MnO
2
.
Consequently, the remarks we have made above stipulating the high degree of insolubility of the silver oxide compounds are germane to the Dieck & Schiff patent. Further, even if the hypothetical compound, such as the silver manganite formula postulated by the authors was correct, there are no experiments cited to determine whether any antimicrobial activity is due to the highly insoluble silver oxides or to the presumed manganese oxide which the authors set forth in a number of the claims of their invention.
In the patent by Conconi (U.S. Pat. No. 2,283,883) the inventor claims that pure silver, when impregnated into a clay or related porous candle, will act as a filter to inactivate microorganisms present in solutions that are passed through such a filter. The invention of Conconi claims that the oligodynamic effect is highest when the metallic agent consists of pure silver. However, Conconi prepares his presumable silver clay matrix in the form of a candle by starting with silver nitrate and then reducing the silver nitrate with reducing agents to form metallic silver. Nowhere in Conconi's invention is it shown that 100% of the silver nitrate has been so reduced to metallic silver since even very dilute solutions of silver nitrate are well known in the profession to be high

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