EP2126146B1

EP2126146B1 - Method of manufacturing silver nanoparticles, cellulosic fibers and nanofibers containing silver nanoparticles and uses thereof in bactericidal yarns and tissues

Info

Publication number: EP2126146B1
Application number: EP07709262.5A
Authority: EP
Inventors: Ryszard Kozlowski; Bogumil Laszkiewicz; Piotr Kulpinski; Malgorzata Muzyczek; Piotr Czarnecki; Marcin Rubacha; Barbara Niekraszewicz; Jolanta Jedrzejczak; Bogdan Peczek
Original assignee: Institute of Natural Fibres and Medicinal Plants
Current assignee: INSTITUTE OF NATURAL FIBRES AND MEDICINAL PLANTS
Priority date: 2007-02-13
Filing date: 2007-02-13
Publication date: 2015-07-15
Anticipated expiration: 2027-02-13
Also published as: WO2008100163A1; EP2126146A1

Description

The subjects of the invention are a method of manufacturing silver nanoparticles, a method of manufacturing cellulose fibers that contain silver nanoparticles, cellulosic fibers containing silver nanoparticles, the use of silver nanoparticles to the manufacture of cellulosic fibers and nanofibers and a wound dressing that contains silver nanoparticles. Silver nanoparticles are characterized by a considerable and selective biological activity due to which they are bactericidal, bacteriostatic and fungicidal. Advantages of nanoparticle-sized silver are its very large active surface that enables its use at very low concentrations, no risk of increasing susceptibility to mycosis and non-causing potentially hazardous mutations of bacteria. According to the invention presented, silver nanoparticles can be employed directly in the form of spinning solution of cellulose for the manufacture of cellulosic fibers and nanofibers of bactericidal properties.
Nanotechnological processes make possible to perform structural modifications of many substances, both simple and complex ones, thus enabling their transformations into submicroscopic objects. Relatively recently, it was found that submicroscopic fragments of the matter are characterized by unusual biochemical properties. Metallic nanoparticles usually contain from several dozen to several thousand atoms. Most of nanoparticle-sized substances used in pharmacy are in the form of colloids, where nanoparticles make the dispersed phase and water is the dispersion medium. [M.J. Pike-Biegunski, Nanotechnology in medicine and pharmacy. Lek w Polsce (in Polish) vol. 15 nr 9'05 (207)].
Silver is a recognized therapeutic agent since antiquity. In the XIX century, the first inorganic and organic silver compounds, such as nitrate (lunar caustic), bromide, lactate, acetate and formate, were synthesized.
Silver nitrate has been applied to the treatment of burns since 1935. Although the mechanism of silver role in biology of burn wound still requires a better recognition, three basic properties of silver, that are of importance to wound treatment, have been established: antimicrobial, anti-inflammatory and wound-healing stimulation [Demling R. H.; (2001) The beneficial effects of silver on the bum wound (basic concepts). The Role of Silver in Burn Wound. Management. Official Satellite Symposium of the 9th Congress of the European Burns Association, Lyon, 13.15 Sep. 2001]. At concentrations of 0.5 - 1%, the drug affects Gram-positive and Gram-negative bacteria, does not trigger allergies and pain complaints, however, it does not permeate through necrotic scab, it colors skin and clothing brown. It should be mentioned, however, that vehicles applied can bring about a number of undesired effects resulting from the interaction of the above compound with living tissue, particularly with mucous membranes. However, colloidal silver in the form of nanoparticles does not cause a damage to mucosa.
The mechanism of antimicrobial action of silver ions consists in blocking of breathing cycle of a host at the cell level. Silver ions, after being bound to DNA of a bacterial cell, exert cytotoxic action by blocking electron transfer inside the cell. Such a mechanism causes that, in practice, no resistance of bacteria to the action of silver ions is observed and the range of silver ion activity includes many Gram-positive and Gram-negative bacteria and fungi. At the same time, silver ions are not toxic to human cells, therefore they are a relatively safe drug, and reported undesired effects result from vehicles used in pharmaceutical preparations. Since several dozen of years, classical silver-containing preparations contained silver nitrate and sulfadiazine silver salt [Monafo W. W., Bessey P. Q.: Wound care, [in:] Herndon D. N. (ed.) Total bum care. W. B. Saunders Company Ltd., London (1996), pp. 88.97].
Recently, studies started on evaluation of preparations in the form of nanoparticles from the point of view of their bactericidal and fungicidal activities. Preparations in the form of silver and copper nanoparticles are characterized by unique biocidal properties that result from their particular structure, biochemical activity, unique atomic structures and unusually large active surfaces. An additional advantage of these preparations is the fact that they can be produced directly in solutions, gases and liquefied cryogenic gases. Results of measurements carried out by Pike-Biegunski show that size reduction from pulverized silver to the form of nanoparticles brings about the increase in surface area by at least 1000000 times [M.J. Pike-Biegunski, Nanotechnology in medicine and pharmacy. Lek w Polsce (in Polish), vol. 15 nr 9'05 (207)].
Destructive effect of silver nanoparticles on pathogens comes down to three recently found mechanisms. In the case of fungi, the presence of silver results in a disordering their water balance. In the case of bacteria, the destructive effect of nanoparticles consists in causing a disturbance of electric potentials of cell membrane (the latter determine the transfer of substances and energy appropriate to life of bacteria), flagellae (locomotor serving for mechanical generation of transport of substances present in the aqueous habitat of bacteria), nucleus and mitochondria. The destructive effect on viruses consists in depriving them of ability to catalytic decomposition of lipid-protein substrate and to receiving lipid-protein material from a carrier. In normal conditions, the decomposition results in virus development that is accompanied by the degradation of protein structure of cells and tissues.
Metallic silver in the form of nanoparticles is characterized by very high electric conduction, which causes that when it adheres to bacterial cell membrane, naturally occurring electric potential gradient, generated by living cell membrane of bacteria, becomes disturbed. This, in turn, brings about a significant disorder of living functions of cytoplasma membrane, resulting in disruption of the transfer of energy and substances. In the presence of silver, bacteria cease to feed and excrete products of metabolism, thus being killed by toxins of their own. Silver, when contacted with flagellum immobilizes it, and when permeates to the interior, it causes disorder of mitochondria and cell nucleus. Bacteria are unable to create an effective defense mechanism against such an action. [M.J. Pike-Biegunski, Nanotechnology in medicine and pharmacy. Lek w Polsce (in Polish), vol. 15 nr 9'05 (207)].
Nanoparticles destroy fungi by causing disorder of water balance, bacteria - by disturbing cell electric potentials, and viruses - by depriving of catalytic activity for the decomposition of lipid-protein substrate of a carrier.
The method of the preparation of silver nanoparticles, described in Colloid Journal [v. 67 no.1, 2005 pup.7984], consists in dissolving silver nitrate in water and adding this solution to a solution containing tannin as a reducing agent, as well as gelatin, sodium carbonate, or poly(vinyl alcohol). Vigorous stirring of these solutions results in obtaining a stable aqueous suspension of silver nanoparticles sized 200- 800 nm. Nanoparticles prepared by such a method are dispersed in a solution containing tannin, sodium carbonate or poly(vinyl alcohol), which limits the application of suspension of nanoparticles prepared in the such a way, because of their contamination with components of the mixture.
In the patent application US No 2005/0008861 (published on January 13, 2005 ), a method was described of the preparation of silver-containing nanoparticles that consists in dissolving silver nitrate (AgNO₃) in a mixture of water and isopropyl alcohol, followed by introducing the above solution, in the form of aerosol, to a plasma reactor at 3000 K, where solvents evaporate in the presence of oxygen and after cooling down, silver nanoparticles smaller than 1 micrometer (below 100 nm in particular) are obtained.
In the patent application US2006/00065075 (published on March 30, 2006 ), a method was presented of obtaining silver nanoparticles by reduction of silver trifluoroacetate with tributylamine in acetone solution.
In the patent application US2006/0045916 (published on March 2, 2006 ) a method was described of producing silver nanoparticles, according to which aqueous solutions of starch in the presence of phosphene amino acids are employed. This method enables to obtain silver nanoparticles in the system that contains organo-phosphorus compounds, which limits the application of silver nanoparticles of such a type, because of toxicity of organo-phosphorus compounds.
In the patent US6,979,491 (published on December 27, 2005 ), a method was disclosed of manufacturing antimicrobial yarns and textiles from cotton, flax, silk and fiber blends containing man-made fibers, that consists in impregnation of these products with silver nitrate solution, followed by reduction of silver nitrate deposited on them to metallic nanosilver by using aqueous solution of glucose, vitamin C or hydrazine hydrate.
In the patent WO2004/081267 A1 (published on September 23, 2004 ), a method of making modified cellulose fibers from cellulose solution in N-methylmorpholine-N-oxide, which involves mixing cellulose with aqueous N-methylmorpholine-N-oxide, evaporation and filtration of the spinning solution subsequently forced through the holes in the spinning nozzle into the aqueous spinning bath, finally rinsing, drying and conditioning, is described by the fact that modifying substances such as ceramic oxides, metal oxides or their mixtures, if necessary containing additional surfactants, carbon, if necessary modified with silver, bactericidal agents, acid-base indicators, thermo chromic dyes in the shape of molecules above 1nm in diameter are added into the cellulose, the solvent or the spinning solution.
In the patent application PL20010333996 (published on January 2, 2001 ), a method was disclosed of imparting electroconductive, bactericidal and fungicidal properties to no nitryl group-containing man-made fibers, particularly to polyester and polyamide fibers, where bactericidal and fungicidal properties are desirable, in addition to electroconductive ones. The above method consists in subjecting fibers to a bath that contains copper- and silver salts as well as 0.2 - 7% of water-soluble zinc salts in relation to fiber mass; the process is performed at pH 7,5 - 2, at temperature of-60-130°C for 60 - 270 minutes, and cyano groups are introduced with dyes by means of one of well-known dyeing methods.
In the patent application KR20040085132 (published on October 7, 2004 ), functional soap containing pearl powder with skin soothing and sterilizing activities and silver nanoparticles and preparation method thereof were presented. The functional soap contains pearl powder and silver nanoparticles. The pearl powder and silver nanoparticles are contained in amount of 0.02 - 0.5 g and 0.001 - 0.01 g per 100 g of the soap base, respectively. The method for preparing the functional soap comprises the steps of (a) introducing pearl powder and silver nanoparticles into a soap base and mixing them with stirring; (b) curing the soap composition prepared from step (a); and (c) ageing the cured functional soap for a predetermined time, while controlling water content of the soap.
In the patent application KR20040058866 (published on July 5, 2004 ), a silver-containing dentifrice was presented. In the dentifrice containing base material and foaming agent, it is characterized by being added with silver-nanoparticles characteristically showing antibacterial activity. The particle size of the silver-nanoparticle ranges from several micrometers to several dozen nanometers.
In the patent application KR100588763 (published on June 3, 2006 ), a method for the preparation of silver nanoparticles-containing antimicrobial fiber and antimicrobial fiber obtained thereby were presented.
In the patent application US2006202382 (published on September 14, 2006 ), a method was disclosed of producing nanosilver fibers. According to the above patent, an organic solution of a dispersant is prepared. Then, a silver salt and a reductant are added into the organic solution. The organic solution is stirred to let the silver salt and the reductant react to form silver nanoparticles dispersed in the organic solution uniformly. Next, a spinnable polymer resin is dissolved in the organic solution to form a spinning solution. A wet spinning method is performed to let the spinning solution form nanosilver fibers.
In the patent CN1759962 (published on April 19, 2006 ), a method for preparing nanosilver sol was presented. A process for preparing nano-Ag sol includes such steps as preparing the reverse-phase microemulsion from glucolipide-type surfactant, mixing the microemulsion containing reducer with the microemulsion containing silver nitrate, while high-speed stirring, preparing Ag nanoparticles, demulsifying, separating, washing, and distributing them in nonpolar solvent. Its advantages are high stability and high antibacterial effect.
In the patent application WO2006070130 (published on July 6, 2006 ), a method for preparing nanoparticles of a metal or a metal alloy, dispersed on a substrate, by chemical vapor deposition were presented. The invention concerns a method for depositing nanoparticles of a metal or of an alloy of said metal, the metal being selected among the metals of columns VIIIB and IB of the periodic table, dispersed on a substrate, by chemical vapor deposition (CVD), from one or more precursors, wherein the deposition is carried out in the presence of a gas comprising over 50 vol. % of an oxidizing reactive gas. The invention also concerns a substrate comprising at least one surface whereon are dispersed nanoparticles of metal or metal alloy, for example, of silver or a silver alloy. The invention further concerns the use of the substrate for catalyzing a chemical reaction.
In the patent application JP2006118010 (published on May 11, 2006 ), Ag nanoparticles, method for producing the same and dispersed solution of Ag nanoparticles were presented. The goal of the invention was to provide Ag nanoparticles easily redispersed even if a dispersed solution of Ag nanoparticles is dried and hardened or is made into a state close thereto by a method of concentration or the like, and from which a dispersing agent can be removed by a simple operation, and to obtain a dispersed solution comprising the Ag nanoparticles. The Ag nanoparticles with a particle diameter of 1 to 20 nm comprising the ammino complex of silver nitrate as a dispersing agent can be obtained by mixing silver nitrate, a reducing agent which does not show reducibility in an organic solvent and alkylamine in an organic solvent.
In the patent application WO2005077329 (published on August 25, 2005 ) silver/polymer composite nanospheres obtained by depositing silver nanoparticles on the surface of polymeric support and a process for preparation thereof were presented. The silver/polymer composite nanospheres according to the invention may not cause general discoloration and cohesion by colloidal silver and thereby can be used as a preservative having strong antimicrobial activity. In addition, the silver/polymer composite nanospheres can preserve cosmetics during a long period, not using conventional preservatives. Accordingly, the invention relates to silver/polymer composite nanospheres to be used as a cosmetic preservative and to cosmetic compositions containing the same. A process for preparing silver/polymer composite nanospheres, which comprises the following steps of (1) dissolving monomer, crosslinking agent and initiator in a solvent to give a monomer solution; (2) emulsifying said monomer solution in the presence of dispersion stabilizer to give an emulsion ; (3) polymerizing said emulsion and then removing the solvent to collect porous polymer particles; and (4) depositing silver nanoparticles formed by reducing silver salts with a reducing agent, on the surface of the porous polymer particles collected in step (3).
Despite the above described research on the preparation of silver micro- and nanoparticles as well as fibers and wound dressings showing bactericidal properties, there is still a need for finding more efficient solutions making possible to create effective systems that do not trigger skin allergy, whose bactericidal effect is long-lasting and do not result in increased susceptibility to mycosis and do not induce hazardous mutations of bacteria.
The presented invention is aimed at delivering means for the development of a method of manufacturing metallic silver in the form of nanoparticles generated directly in an organic solvent that serves at the same time as an excellent solvent of cellulose and other polymers which could be used for obtaining bactericidal cellulosic fibers containing silver nanoparticles of long-lasting bactericidal effect and bactericidal activity being unchanged after multiple washings.
The realization of such a stated goal and solving problems described in the state of art concerning the production of stable silver nanoparticles and their use for manufacturing bactericidal cellulosic fibers, that are very active bactericidal and fungicidal agents, applied directly in the form of cellulose spinning solution for producing cellulosic fibers and nanofibers of bactericidal properties have all been achieved in the present invention.
The subject of the present invention is a method of manufacturing silver nanoparticles as a result of reduction of water-soluble silver salts, characterized in that the aqueous solution of silver nitrate is subjected to a reaction with aqueous solution of N-methylmorpholine N-oxide at a molar ratio of silver to N-methylmorpholine oxide ranging from 10^-6 to 0.5, at 0 - 130°C, for 5 seconds to 10 minutes, followed by the cooling of the reaction mixture containing nanoparticles of silver and separating the precipitate of silver nanoparticles from the Reaction mixture..
Preferentially silver nanoparticles of 1 - 350 nm in size are obtained.
The next subject of invention is a method of manufacturing cellulose fibers that contain silver nanoparticles, characterized in that the aqueous solution of silver nitrate is subjected to a reaction with an aqueous solution of N-methylmorpholine N-oxide at a molar ratio of silver to N-methylmorpholine oxide from 10^-6 to 0.5, at a temperature of 0 - 130°C, for 5 seconds to 10 minutes, followed by the cooling of the reaction mixture containing nanoparticles of silver and using the mixture directly as a solvent for cellulose in the process of the manufacture of bactericidal cellulosic fibers. Preferentially, the solution of N-methylmorpholine N-oxide is supplemented by cellulose, a cellulose mass stabilizer and possibly substances applied as fiber modifiers, wherein the temperature range is from 0 - 130'C, followed by a direct formation of cellulose fibers, after evaporating a portion of the water from the mixture, performed in such a way that the cellulose content of the mixture exceeds 5%, by using spinneret. Preferentially, the cellulose fibers containing silver nanoparticles sized from 1 to 350 nm are obtained.
The next subject of invention are cellulose fibers, obtained by the method of claim 4 characterized in that they contain evenly distributed silver nanoparticles of 1-350 nm in size and their content falls in the range from 0.001 to 10%, and the above fibers are bacteriostatic, bactericidal and fungicidal and exhibit a bacteriostatic activity of 0.0 - 5.2 and bactericidal activity of 0.0 - 3.3 against Gram-positive bacteria, and bacteriostatic activity of 0.5 - 6.9 and bactericidal activity of 0.0 - 3.9 against Gram-negative bacteria and they are further characterized by tenacity falling in the range of 15-33 cN/tex and ultimate elongation at break falling in the range of 6-11%. Preferentially, the cellulose content in silver nanoparticle-containing spinning solution contains colloidal silver.
The next subject of invention is a method of manufacturing silver nanoparticle-containing cellulose nanofibers, characterized in that an aqueous solution of silver nitrate is subjected to the reaction with aqueous solution of N-methylmorpholine N-oxide at the mole ratio of silver to N-methylmorpholine oxide from 10^-6 to 0.5, at temperature of 0 - 130'C, for 5 seconds to 10 minutes, followed by cooling the reaction mixture that contains nanoparticles of silver and using the mixture directly as a cellulose solvent in the process of the manufacture of bactericidal cellulose nanofibers. Preferentially, the the solution of N-methylmorpholine N-oxide is supplemented by cellulose, cellulose mass stabilizer and possibly substances applied as fiber modifiers, wherein the temperature range is from 0 - 130°C, followed by a direct formation of cellulose nanofibers after the evaporation of a portion of the water from the mixture, performed in such a way that cellulose content in the mixture is below 5%. Preferentially, the cellulose fibers containing silver nanoparticles sized from 1 to 350 run are obtained.
The next subject of invention is an use of silver nanoparticles formed as a result of reduction of silver salts soluble in aqueous solution of N-methylmorpholine N-oxide, where the aqueous solution of silver nitrate is subjected to a reaction with an aqueous solution of N-methylmorpholine N-oxide, preferentially at a concentration of 50-60%, supplemented by cellulose, a cellulose mass stabilizer and possibly substances applied as fiber modifiers, at molar ratio of silver to N-methylmorpholine oxide from 10^-6 to 0.5, at temperature of 0 - 130°C; excess water is evaporated off under a reduced pressure for 60 to 80 minutes and the NMMO-water-cellulose-silver mixture obtained in such a way is used for the manufacture of bactericidal cellulose fibers and nanofibers. Preferentially, the reaction mixture that contains the silver nanoparticles, after the evaporation of a portion of the water from the above mixture, is used for the direct formation of bactericidal cellulose fibers when the cellulose content in the mixture is above 5% or bactericidal cellulose nanofibers when the cellulose content in the said solution is below 5%.
The next subject of invention is a wound dressing for external use, made of silver nanoparticle-containing cellulose fibers and/or nanofibers as defined in claim 6 or obtained by the method of claims 3, 4, 8, 9 characterized in that the dressing consists of cellulose fibers and/or nanofibers of a width of up to 10 cm, in which the cellulose content is at least 5% and silver nanoparticles are 1 - 350 nm in size and their content is in the range of 0.001 do 10%, wherein also the dressing is bacteriostatic, bactericidal and fungicidal.
Below examples are given if the invention described.

Example 1

To 50 g of 50% aqueous solution of N-methylmorpholine-N-oxide (NMMO) of temperature of 90°C, 5 ml of 3.36 M aqueous solution of silver nitrate (AgNO₃) were added. The mole ratio of NMMO to silver was 13:1. Right away after the addition of AgNO₃, a black precipitate was formed and silver mirror appeared on walls of the reaction flask. The reaction mixture was heated at 90°C for about 30 minutes and then it was cooled down and silver precipitate was centrifuged. The supernatant solution was investigated by means of mass spectroscopy, and silver obtained was examined by wide-angle X-ray diffraction. Silver crystallites of 21 nm in size have been obtained..

Example 2

To 50 g of 50% aqueous solution of NMMO of temperature of 90°C, 6.6 ml of 3.36 M aqueous solution of AgNO₃ were added. The mole ratio of NMMO to silver was 6:1. Right away after the addition of AgNO₃, a black precipitate was formed and silver mirror appeared on walls of the reaction flask. The reaction mixture was heated at 90°C for about 30 minutes and then it was cooled down and precipitated silver was centrifuged. The supernatant solution and silver obtained were studied as in example 1.
Silver crystallites of 18 nm in size have been obtained.

Example 3

To 50 g of 50% aqueous solution of NMMO of temperature of 5°C, 5 ml of 3.36 M aqueous solution of AgNO₃ were added. The mole ratio of NMMO to silver was 13:1. After the addition of AgNO₃, a precipitate was formed that was initially light yellow colored and then grew dark to eventually become black The precipitate formed was centrifuged. The supernatant solution and silver obtained were studied as in example 1.
Silver crystallites of 15 nm in size have been obtained.

Example 4

To 50 g of 50% aqueous solution of NMMO of temperature of 5°C, 6.6 ml of 3.36 M aqueous solution of AgNO₃ were added. The mole ratio of NMMO to silver was 6:1. After the addition of AgNO₃, a precipitate was formed that was initially light yellow colored and then grew dark to eventually become black The precipitate formed was centrifuged. The supernatant solution and silver obtained were studied as in example 1.
Silver crystallites of 13 nm in size have been obtained.

Example 5

To 342 g of 50% aqueous solution of NMMO, 31 g were added of finely divided spruce cellulose of DP 800, α-cellulose content of 95.4%, moisture content of 5% and 0.1% (in relation to α-cellulose mass) of free radical stabilizer of trade name Tenox PG. The mixture was heated under a reduced pressure with vigorous stirring. The excess of water was removed during heating. When temperature of the reaction mixture has reached 100°C, 1 ml of 0.25 M aqueous solution of AgNO₃ was added. A homogeneous NMMO-water-cellulose-silver mixture, containing silver particles of 4 nm in size, was obtained. The size of silver particles was determines as in example 1.
After evaporating water from the obtained mixture, fibers were formed from the residue at 120°C using an 18-orifice spinneret The fibers formed have shown bacteriostatic activity of 6.3 and bactericidal activity of 3.7 against E. coli and bacteriostatic activity of 5.2 and bactericidal activity of 3.3 against S. aureus. Moreover, the fibers were characterized by tenacity of 31 cN/tex and ultimate elongation at break of 8%.

Example 6

To 342 g of 50% aqueous solution of NMMO, 1 ml of 0.5 M aqueous solution of AgNO₃ was added, followed by introducing 31 g of finely divided spruce cellulose of properties as in example 5 and 0.1% (in relation to α-cellulose mass) of Tenox PG stabilizer. The mixture was heated at120°C for 60 minutes under a reduced pressure with vigorous stirring and removal of the excess of water. After that time, a homogeneous NMMO-water-cellulose-silver mixture, containing silver particles of 7 nm in size, was obtained. The size of silver particles was determines as in example 1.
From the obtained solution, fibers were formed at 120°C using an 18-orifice spinneret. The fibers have shown bacteriostatic activity of 6.9 and bactericidal activity of 3.9 against E. coli and bacteriostatic activity of 2.6 and bactericidal activity of 0.85 against S. aureus. Moreover, the fibers were characterized by tenacity of 30 cN/tex and ultimate elongation at break of 7%.

Example 7

11,6 g of finely divided spruce cellulose of properties as in example 5 was mixed with 336 g of NMMO monohydrate and 0.1% (in relation to α-cellulose mass) of Tenox PG stabilizer. The mixture was heated to 90°C during 60 minutes with vigorous stirring. Then 0.5 ml of 0.1 M aqueous solution of AgNO₃ was added drop by drop.
A NMMO-water-cellulose-silver mixture, containing silver particles of 2 nm in size, was obtained. The size of silver particles was determines as in example 1.
The obtained mixture was heated at 105°C and used for the formation at voltage of 15 kV of nanofibers of 120 nm in diameter that characterized by water retention of 1250%. The fibers have shown bacteriostatic activity of 2.1 and bactericidal activity of 0.72 against E. coli.

Example 8

To 342 g of 50% aqueous solution of NMMO, 31 g of finely divided spruce cellulose of properties as in example 5 and 0.1% (in relation to α-cellulose mass) of Tenox PG stabilizer were added. The mixture was heated under a reduced pressure with vigorous stirring and removal of water excess from the system. When reactor temperature has reached 100°C, 1ml of 0.5 M aqueous solution of AgNO₃ was added drop by drop to the mixture, so that the final concentration of silver was 0.1% in relation to α-cellulose, and 5 ml of 30% colloidal silica solution LUDOX SM-30.
After evaporation of appropriate amount of water, a clear NMMO-water-cellulose-silver nanoparticles nanosilica mixture was obtained from which nanofibers were formed at 120°C using an 18-orifice spinneret.
The obtained fibers were characterized by tenacity of 29 cN/tex and ultimate elongation at break of 10%. They have shown bacteriostatic activity of 6.3 and bactericidal activity of 3.7 against E. coli and bacteriostatic activity of 5.2 and bactericidal activity of 3.3 against S. aureus.

Example 9

To 342 g of 50% aqueous solution of NMMO, 1 ml of 0.25 M aqueous solution of AgNO₃, 5 ml of 30% colloidal silica solution LUDOX PW, 31 g of finely divided spruce cellulose of properties as in example 5 and 0.1% (in relation to α-cellulose mass) of Tenox PG stabilizer were added. The mixture was heated under a reduced pressure with vigorous stirring and removal of water excess from the system. After evaporation of appropriate amount of water, a clear NMMO-cellulose-silver nanoparticles-nanosilica mixture was obtained from which fibers were formed at 117°C using an 18-orifice spinneret.
The obtained fibers were characterized by tenacity of 28 cN/tex and ultimate elongation at break of 11%. They have shown bacteriostatic activity of 6.8 and bactericidal activity of 3.7 against E. coli and bacteriostatic activity of 2.9 and bactericidal activity of 1.9 against S. aureus.

Example 10

342 g of 50% aqueous solution of NMMO were mixed with 31 g of finely divided spruce cellulose of properties as in example 5 and 0.1% (in relation to α-cellulose mass) of Tenox PG stabilizer and 5 ml of 30% colloidal silica solution LUDOX AM. The mixture was heated under a reduced pressure with vigorous stirring and removal of water excess from the system. When the reactor temperature has reached 100°C, 1ml of 0.125 M aqueous solution of AgNO₃ was added drop by drop. After evaporation of appropriate amount of water, a clear NMMO-cellulose-silver nanoparticles-nanosilica mixture was obtained from which nanofibers were formed at 117°C using an 18-orifice spinneret.
The obtained fibers were characterized by tenacity of 32 cN/tex and ultimate elongation at break of 11 %. They have shown bacteriostatic activity of 6.2 and bactericidal activity of 2.9 against E. coli and bacteriostatic activity of 2.4 and bactericidal activity of 1.4 against S. aureus.

Claims

A method of manufacturing silver nanoparticles as a result of reduction of water-soluble silver salts, characterized in that the aqueous solution of silver nitrate is subjected to a reaction with aqueous solution of N-methylmorpholine N-oxide at a molar ratio of silver to N-methylmorpholine oxide ranging from 10^-6 to 0.5, at 0-130°C, for 5 seconds to 10 minutes, followed by the cooling of the reaction mixture containing nanoparticles of silver and separating the precipitate of silver nanoparticles from the reaction mixture.
A method according to Claim 1, characterized in that silver nanoparticles of 1 - 350 nm in size are obtained.
A method of manufacturing cellulose fibers that contain silver nanoparticles, characterized in that the aqueous solution of silver nitrate is subjected to a reaction with an aqueous solution of N-methylmorpholine N-oxide at a molar ratio of silver to N-methylmorpholine oxide from 10^-6 to 0.5, at a temperature of 0 - 130°C, for 5 seconds to 10 minutes, followed by the cooling of the reaction mixture containing nanoparticles of silver and using the mixture directly as a solvent for cellulose in the process of the manufacture of bactericidal cellulosic fibers.
A method according to Claim 4-3, characterized in that the solution of N-methylmorpholine N-oxide is supplemented by cellulose, a cellulose mass stabilizer and possibly substances applied as fiber modifiers, wherein the temperature range is from 0 - 130°C, followed by a direct formation of cellulose fibers, after evaporating a portion of the water from the mixture, performed in such a way that the cellulose content of the mixture exceeds 5%, by using spinneret.
A method according to Claim 3 or 4, characterized in that the cellulose fibers containing silver nanoparticles sized from 1 to 350 nm are obtained.
Cellulose fibers, obtained by the method of claim 4 characterized in that they contain evenly distributed silver nanoparticles of 1 - 350 nm in size and their content falls in the range from 0.001 to 10%, and the above fibers are bacteriostatic, bactericidal and fungicidal and exhibit a bacteriostatic activity of 0.0 - 5.2 and bactericidal activity of 0.0 - 3.3 against Gram-positive bacteria, and bacteriostatic activity of 0.5 - 6.9 and bactericidal activity of 0.0 - 3.9 against Gram-negative bacteria and they are further characterized by tenacity falling in the range of 15-33 cN/tex and ultimate elongation at break falling in the range of 6-11%.
Cellulose fibers according to Claim 6, characterized in that the silver nanoparticle-containing spinning solution contains colloidal silica.
A method of manufacturing silver nanoparticle-containing cellulose nanofibers according to claim 3, characterized in that an aqueous solution of silver nitrate is subjected to the reaction with aqueous solution of N-methylmorpholine N-oxide at the mole ratio of silver to N-methylmorpholine oxide from 10^-6 to 0.5, at temperature of 0-130°C, for 5 seconds to 10 minutes, followed by cooling the reaction mixture that contains nanoparticles of silver and using the mixture directly as a cellulose solvent in the process of the manufacture of bactericidal cellulose nanofibers.
A method according to Claim 8, characterized in that the solution of N-methylmorpholine N-oxide is supplemented by cellulose, cellulose mass stabilizer and possibly substances applied as fiber modifiers, wherein the temperature range is from 0 - 130°C, followed by a direct formation of cellulose nanofibers after the evaporation of a portion of the water from the mixture, performed in such a way that cellulose content in the mixture is below 5%.
A method according to Claims 8 or 9, characterized in that the cellulose fibers containing silver nanoparticles sized from 1 to 350 nm are obtained.
A wound dressing for external use, made of silver nanoparticle-containing cellulose fibers and/or nanofibers as defined in claim 6 or obtained by the method of claims 3, 4, 8, 9 characterized in that the dressing consists of cellulose fibers and/or nanofibers of a width of up to 10 cm, in which the cellulose content is at least 5% and silver nanoparticles are 1 - 350 nm in size and their content is in the range of 0.001 do 10%, wherein also the dressing is bacteriostatic, bactericidal and fungicidal.