Silicone materials having antimicrobial efficiency

Abstract

Disclosed are antimicrobial silicone substances, which are obtained by using multifunctional cellulose/silver and silicon matrix nanocomposites. Using environmentally friendly, simple deposition techniques, Ag particles were deposited on cellulose. Silicone was filled with the obtained composites of cellulose and silver particles. The created modified cellulose/silver and silicone composite is characterized by good physical and chemical properties, as well as strong antimicrobial effect on both Gram- positive and Gram-negative bacteria.

Claims

1. A composite of a cellulose/silver nanocomposite and a polymer matrix comprising: (a) silver nanoparticles in an amount of 0.1 to 7% by weight of the total mass of the composite; (b) the cellulose/silver nanocomposite in an amount of 1-50% by weight of the total mass of the composite, wherein the cellulose/silver nanocomposite is oxidized, and wherein the silver nanoparticles are deposited on the cellulose/silver nanocomposite; and (c) the polymer matrix, wherein the cellulose/silver nanocomposite is dispersed in the polymer matrix thereby providing a diffusion system, wherein the composite has strong and long-lasting antimicrobial activity on both Gram-positive and Gram-negative bacteria, and wherein the composite is in solid form.

2. The composite according to claim 1, wherein the cellulose in the cellulose/silver nanocomposite comprises a microcrystalline cellulose of cellulose crystals and cellulose fibers.

3. The composite according to claim 2, wherein the size of particles of microcrystalline cellulose is in the range from 20 to 60 μm.

4. The composite according to claim 1, wherein the polymer matrix is selected from the group consisting of siloxane, polydimethylsiloxane, polyurethane, latex, polyvinyl chloride, rubbers.

5. The composite according to claim 1, wherein the tensile strength of the said composite is improved 75% as compared to the tensile strength of the polymer matrix without the cellulose/silver nanocomposite.

6. A method of production of a composite of a cellulose/silver nanocomposite and a polymer matrix comprising: (a) preparing silver nanoparticles, cellulose comprising cellulose fibers, and a silicon matrix; (b) depositing the silver nanoparticles on the cellulose fibers by exposing a solution of the silver nanoparticles and the cellulose fibers to microwaves of 450 W for 2 minutes; (c) oxidizing the cellulose/silver nanocomposite; (d) introducing the oxidized cellulose/silver nanocomposite into the polymer matrix by mixing the components; (e) solidifying the mixture of the cellulose/silver nanocomposite and the polymer matrix to form the composite, wherein migration of the silver nanoparticles from the solidified composite is avoided.

7. A method of synthesizing a composite of a cellulose/silver nanocomposite and a polymer matrix comprising: (a) preparing silver nanoparticles, cellulose comprising cellulose fibers, and the polymer matrix; (b) depositing the silver nanoparticles on the cellulose fiber using a cetylmethylammonium bromide solution to create a cellulose/silver nanocomposite; (c) oxidizing the cellulose/silver nanocomposite; (d) introducing the oxidized cellulose/silver nanocomposite into the polymer matrix by mixing the components; (e) solidifying the mixture of the cellulose/silver nanocomposite and the polymer matrix to form the composite, wherein migration of the silver nanoparticles from the solidified composite is avoided.

8. The method according to claim 7, wherein the cellulose used in step (a) consists of a microcrystalline cellulose of cellulose crystals and the cellulose fibers.

9. The method according to claim 7, wherein in step (a) the silver nanoparticles are obtained from a silver salt selected from the group consisting of AgNO.sub.3, Ag.sub.2CO.sub.3, Ag.sub.3PO.sub.4, Ag.sub.2SO.sub.4, Ag.sub.2SO.sub.3, silver zirconium, organic silver salts, silver acetate, silver lactate and combinations or mixtures thereof.

10. The method according to claim 7, wherein the solidifying step (e) is carried out at a temperature from 30 to 120° C.

11. The method according to claim 7, wherein the polymer matrix is a silicone matrix and the silver nanoparticles are deposited is an amount such that the silver nanoparticles constitute 0.1-7% by weight of the total mass of the composite.

12. The method according to claim 11, wherein polymer matrix used in step (a) is selected from the group consisting of siloxanes, phenyl dimethicone, phenyl trimethicone, fluorine silicone, amino silicone.

13. A silver/cellulose and matrix composite for the manufacture of antimicrobial substances comprising the composite of claim 1.

14. The composite according to claim 2, wherein the size of particles of microcrystalline cellulose is in the range from 20 to 60 μm.

15. The composite according to claim 2, wherein tensile strength of the said silver/cellulose and matrix composite is up to 75%.

16. The composite according to claim 3, wherein tensile strength of the said silver/cellulose and matrix composite is up to 75%.

17. The method according to claim 12, wherein the cellulose used in step (a) consists of a microcrystalline cellulose of cellulose crystals and the cellulose fibers.

18. The method according to claim 8, wherein in step (a) the silver nanoparticles are obtained from a silver salt selected from the group consisting of AgNO.sub.3, Ag.sub.2CO.sub.3, Ag.sub.3PO.sub.4, Ag.sub.2SO.sub.4, Ag.sub.2SO.sub.3, silver zirconium, organic silver salts, silver acetate, silver lactate and combinations or mixtures thereof.

19. The method according to claim 8, wherein the solidifying step (e) is carried out at a temperature from 30 to 120° C.

20. The method according to claim 7, wherein the silver nanoparticles are deposited in an amount such that the silver nanoparticles constitute 5% by weight, of the total mass of the composite.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The above description of the preferred embodiments is provided in order to illustrate and describe the present invention. This is not an exhaustive or limiting description, seeking to determine the exact form or embodiment. The above description should be considered more like an illustration, rather than a limitation. It is evident that numerous modifications and variations may be obvious to the persons skilled in the art. Embodiment is chosen and described so that the persons skilled in the art in the best way clarify the principles of this invention and the best practical application for various embodiments with various modifications suitable for a particular use or application of the embodiment. It is intended that the scope of the invention is defined in the claim appended thereto and its equivalents, where all of the said terms have meaning within the widest range, unless indicated otherwise.

(2) The Materials Used and Their Characteristics

(3) Silicone Matrix

(4) A polydimethylsiloxane (PDMS) of a linear structure with terminal vinyl groups was used. This is a two-component A/B silicone, which is solidified by a platinum complex according to the mechanism presented as following:

(5) ##STR00001##

(6) The main characteristics of PDMS used are presented in Table 1.

(7) TABLE-US-00001 TABLE 1 The main characteristics of PDMS Characteristic Value Viscosity of mixture A:B = 1:1, Pa .Math. s 350 (T = 25° C.) Specific density, kg/cm.sup.3 1.02 (T = 25° C.) Curing duration 120° C./15 min Durability, h 16 (T = 25° C.) Thermal conductivity, W/mK 0.2 Shore hardness A, relative units 35 Dielectric permittivity, kV/mm 27 Volumetric resistance, Ωcm 2.2 × 10.sup.14 Dielectric constant 4.5 (T = 25° C., 100 kHz) Dissipation factor 0.002 (T = 25° C., 100 kHz)
Microcrystalline Cellulose of Fibrillar Structure

(8) Microcrystalline cellulose (MCC), the main characteristics of which are presented in Table 2, was used as PDMS filler. MCC is obtained when mineral acids partially depolymerize amorphous areas of α-cellulose derived from fibrous plant matter. After hydrolysis of cellulose, predominantly crystalline microfibrils remain.

(9) TABLE-US-00002 TABLE 2 Main characteristics of microcrystalline cellulose Characteristic Value Particle size, μm 18-22 pH 5-7 (11 wt. %) Density, g/mL 0.5 (T = 25° C.) Moisture content, % ≤5.0
Silver Nanoparticles

(10) Silver nanoparticles (AgNPs) were synthesized by two different chemical methods. Chemical reagents used for the synthesis of silver nanoparticles are presented in Table 3.

(11) TABLE-US-00003 TABLE 3 Chemical reagents used for the synthesis of silver nanoparticles Chemical Reagent formula Purpose Manufacturer Synthesis of AgNPs (1) Silver nitrate AgNO.sub.3 Precursor Sigma-Adrich Morpholine C.sub.4H.sub.9NO Medium Sigma-Adrich Oleic acid C.sub.18H.sub.34O.sub.2 Stabilizer Avsista Hydrazine hydrate N.sub.2H.sub.4•H.sub.2O Reducer Sigma-Adrich Chloroform CHCl.sub.3 Medium Sigma-Adrich Distilled water H.sub.2O Medium KTU Synthesis of AgNPs (2) Silver nitrate AgNO.sub.3 Precursor Sigma-Adrich Polyvinylpyrrolidone (C.sub.6H.sub.9NO).sub.n Reducer, Reducer, anticoagulant, anticoagulant, stabilizer stabilizer Distilled water H.sub.2O Medium KTU
Methods of Synthesis of Silver Nanoparticles
1. Synthesis of Ag NPs (2) by Chemical Reduction in Chloroform Medium

(12) At room temperature, 10 ml of morpholine and 2 g of oleic acid is slowly poured into 20 ml of 0.05 M AgNO.sub.3 solution. This solution is stirred and, after it reaches the desired temperature (25-100° C.), 3 ml of hydrazine hydrate is slowly added dropwise. The solution is stirred further until it gets yellow and becomes brown, a lot of foam is formed (it can be counteracted by pouring distilled H.sub.2O). Reaction mixture is then stirred for an additional 3 min. at 25-100° C. After cooling, the solution is diluted 1:2 with acetone and centrifuged for 5 minutes 2 times to wash the precipitates. The obtained precipitates are dried in a ventilated electric furnace for ˜15 minutes at 20-120° C. Dry powder is dispersed in 50 ml of chloroform. The resulting solution is allowed to settle for 24 hours at room temperature.

(13) 2. Synthesis of Ag NPs Colloid by Chemical Reduction in Ethanol Medium

(14) At room temperature, 10 g of polyvinylpyrrolidone (PVP) is dissolved in 80 ml of ethyl alcohol (when the particles are poorly soluble the solution can be heated up to 30-40° C.). Then, 2 g of silver nitrate (AgNO.sub.3) dissolved in 10 ml of distilled H.sub.2O is admixed into the resulting solution. The total amount of the mixture is increased to 100 ml by adding alcohol. The resulting solution is allowed to settle for 24 hours at room temperature. CA.sub.g=12 mg/ml.

(15) Production of MCC/AgNPs Composite

(16) Before the synthesis of the MCC/AgNPs composites, cellulose was treated with KOH in order to remove lignin.

(17) Treatment of cellulose with KOH or NaOH. 1.2 g of KOH (or NaOH) is dissolved in 200 ml of distilled H.sub.2O and stirred for ˜30 min. until the substance is completely dissolved. 10 g of cellulose is added into the obtained solution and stirred for another hour. The resulting cellulose is washed with 2 liters of distilled H.sub.2O.

(18) Further treated cellulose and silver particle composites were obtained applying the two chemical synthesis methods. Chemical reagents used for the synthesis of composites are given in Table 4.

(19) TABLE-US-00004 TABLE 4 Chemical reagents used for the synthesis of MCC/AgNPs composite Chemical Reagent formula Purpose Manufacturer Synthesis of MCC/AgNPs (1) Cellulose (C.sub.6H.sub.10O.sub.5).sub.n Filler Sigma-Adrich Silver nitrate AgNO.sub.3 Precursor Sigma-Adrich Cetyltrimethylammonium C.sub.19H.sub.42BrN Reducer Sigma-Adrich bromide Sodium borohydride NaBH.sub.4 Reducer Sigma-Adrich Distilled water H.sub.2O Medium KTU Synthesis of MCC/AgNPs (2) Cellulose (C.sub.6H.sub.10O.sub.5)n Filler Sigma-Adrich Silver nitrate AgNO.sub.3 Precursor Sigma-Adrich Ethylene glycol C.sub.2H.sub.6O.sub.2 Medium Eurochemicals
Methods for Synthesis of MCC/AgNPs Composites
(1) Synthesis of MCC/AgNPs Composite

(20) Three separate solutions are prepared: Solution A: 0.98 g of cetylmethylammonium bromide (CTAB) is dissolved in 100 ml of distilled H.sub.2O. Solution B: 0.34 g of AgNO.sub.3 is dissolved in 50 ml of distilled H.sub.2O. Solution C: 0.16 g of NaBH.sub.4 is dissolved in 50 ml of distilled H.sub.2O. A and B solutions were mixed. 10 g of cellulose treated with KOH is poured into the resulting clear homogeneous solution and stirred for 60 minutes. Solution C is slowly dripped into to the suspension and everything stirred for further 2 hours. The resulting cellulose and Ag composite is washed with 1 liter of distilled H.sub.2O and dried in the electric furnace at 20-100±1° C. for 2 hours.
(2) Preparation of MCC/AgNPs Composite

(21) 0.34 g of AgNO.sub.3 is dissolved in 100 ml of ethylene glycol. Vigorously stirring 2 g of PVP is poured into the solution. 10 g of cellulose is added to the obtained solution and dispersed ultrasonically for 5 minutes. The suspension is placed in a microwave and exposed to 450 W microwaves for 2 minutes.

(22) After the preparation of MCC/AgNPs (1) and MCC/AgNPs (2) composites, they are oxidized in order to increase their antimicrobial effectiveness. Chemical reagents used for oxidation are given in Table 5.

(23) TABLE-US-00005 TABLE 5 Chemical reagents used for oxidation of MCC/AgNPs Reagent Chemical formula Purpose Manufacturer Potassium KMnO.sub.4 Oxidizer Valentis permanganate Distilled water H.sub.2O Medium KTU

(24) Oxidation of MCC/AgNPs composite was carried out according to the given methodology. 2 g of KMnO.sub.4 was dissolved in 250 ml of distilled H.sub.2O. The resulting solution was stirred and heated to 60° C. for 1 hour. Then, the resulting solution is poured into 20 g of CMC/Ag and stirred for another 60 minutes. After cooling, the resulting suspension is rinsed with acetone.

(25) Depending on the MCC/AgNPs composite (1) or (2) is used, the PDMS-MCC/AgNPs composite (1) or (2) was obtained respectively. A stronger antimicrobial activity is obtained introducing also AgNPs. Only by using these two ways of synthesis PDMS becomes fully solid.

(26) (1) Production of PDMS-MCC/AgNPs Composite

(27) The composite is obtained by adding various amounts of oxidized (1) MCC/AgNPs composite (5-30% by weight) to PDMS A:B=1:1. In order to ensure an even distribution of particles of the composite MCC/AgNPs (1) in bi-component PDMS medium, the selected amount of the composite is mixed with 10 ml of chloroform at room temperature and the resulting suspension is dispersed with an ultrasonic probe UP200S with a security box for 30 minutes. Then the homogeneous system is slowly poured into PDMS component A, particles AgNPs (1) (3-7% by weight) are also poured in and the mixture is stirred with a magnetic stirrer at a temperature of 30±10° C. for 2 hours. PDMS component B is added into the obtained homogeneous mixture and continues to mix it intensively for 15 minutes. The resulting composite is poured into the mold and the excess air that got into the mixture during mixing is removed by vacuuming at 0.06 MPa for 60 minutes. Composite-filled molds were placed in a ventilated low-temperature electric furnace SNOL 58/350 (UABMORIS Technology, Lithuania) and heated at 70±20° C. for 30 minutes until PDMS-MCC/AgNPs becomes completely solid (curing).

(28) (2) Preparation of PDMS-MCC/AgNPs Composite

(29) The composite is obtained by adding various amounts of oxidized (2) MCC/AgNPs filler (5-30% by weight) to PDMS A:B=1:1. In order to ensure an even distribution of particles of the composite MCC/AgNPs (2) in bi-component PDMS medium, the selected amount of the filler is mixed with 10 ml of chloroform at room temperature and the resulting suspension is dispersed with an ultrasonic probe UP200S with a security box for 30 minutes. Then the homogeneous system is slowly poured into PDMS component A, particles AgNPs (2) (3-7% by weight) are also poured in and the mixture is stirred with a magnetic stirrer at a temperature of 30±10° C. for 2 hours. PDMS component B is added into the obtained homogeneous mixture and continues to mix it intensively for 15 minutes. The resulting composite is poured into the mold and the excess air that got into the mixture during mixing is removed by vacuuming at 0.06 MPa for 60 minutes. Composite-filled molds were placed in a ventilated low-temperature electric furnace SNOL 58/350 (UAB MORIS Technology, Lithuania) and heated at 70±20° C. for 30 minutes until the silicone becomes completely solid (curing).