Patent Application
20120202043
The invention relates to medical articles that include an antimicrobial coating. More particularly, the invention relates a medical device, device surface, or material surface having an applied silver nanoparticle coating.
Application of antimicrobial agents such as metal nanoparticles or antibiotic coatings to surfaces such as, for example, surfaces of medical devices or other material surfaces are typically conducted in a batch style process due to difficulty in maintaining reagent stability and coating uniformity in continuous processes. Exemplary batch style processes may include vapor deposition, direct incorporation of the antimicrobial agent in a material forming the surface, dipping of the device into a bath containing the active agent and a binder material, or a combination of the above processes. Existing methods typically cannot be adapted to continuous or in-line processes and can include the incorporation of expensive equipment, operator skill, and labor intensive steps, Also certain substrates provide a particular challenge in that they require selective application on detailed geometries or are porous and have a requirement that the application be limited as to the depth of impregnation. Currently available dipping processes for the application of coating agents are difficult to implement and generally provide coatings of insufficient concentration tolerances for the desired application herein.
A typical dip type coating can apply silver, Ag, to the surface of a material, but the process is relatively uncontrolled and variable. An example illustrating the variability of results from a dip coating process is shown in
As is evident from
Accordingly, there is a need for a coating process that can be tightly controlled to provide a relatively predictable and uniform deposition of a metal nanoparticle such as silver nanoparticle. There is also a need for a process that allows selective application of an antimicrobial nanoparticle, flexibility of delivery vehicle (meaning a variety of organic solvents can be employed depending on substrate material), and coating concentration. Moreover, there is a need for silver-containing, non-aqueous formulations that can be the basis of a coating process that is flexible and provides a controllable and relatively predictable and uniform deposition of silver nanoparticles. This need extends to materials that can be produced by such a coating process. There is a need for a fluoropolymer material having satisfactory antimicrobial properties. This need is specifically apparent because of the difficulty of applying coatings to fluoropolymer materials.
The present invention addresses the problems described above by providing an antimicrobial composite structure that includes: a microporous polymeric material, the material having a first exterior surface, a second exterior surface and an interior portion between the exterior surfaces; and nanoparticles present in interstices adjacent the first exterior surface but not in interstices adjacent the second exterior surface.
According to the invention, the microporous polymeric material may be a matrix of expanded polymer material. For example, the first exterior surface may be an expanded fluoropolymer material and may have nodes and fibrils of expanded fluoropolymer material. Desirably, the expanded fluoropolymer material may be expanded polytetrafluoroethylene.
The nanoparticles may be metal nanoparticles and desirably are silver nanoparticles. The composite structure may further include copper nanoparticles, chlorohexidine, iodine, antibiotics and combinations thereof. According to an aspect of the invention, the nanoparticles are present in the microporous polymeric material beginning at or preferably adjacent the exterior surface and are distributed into the microporous polymeric material to a predetermined depth. For example, the nanoparticles may be present in interstices of the microporous polymeric material up to a depth of about 100 micrometers. As another example, the nanoparticles may be present in interstices of the microporous polymeric material up to a depth of about 50 micrometers. As yet another example, the nanoparticles may be present in interstices of the microporous polymeric material up to a depth of about 25 micrometers. According to the invention, the nanoparticles may be present in interstices of the microporous polymeric material up to a depth of from about 5 to about 20 micrometers. For example, the nanoparticles may be present in a matrix of expanded fluoropolymer material such as expanded polytetrafluoroethylene up to a depth of about 50 micrometers. As another example, the nanoparticles may be present in a fluoropolymer material such as polytetrafluoroethylene expanded to a matrix of nodes and fibrils up to a depth of about 50 micrometers.
In an aspect of the invention, the distribution of nanoparticles into the interstices of the polymeric material (e.g., into the matrix of expanded polymeric material) to a predetermined depth help make the nanoparticles resist removal by frictional forces applied to the exterior surface of the matrix. For example, the distributing nanoparticles into the matrix to a predetermined depth help make the nanoparticles resist removal wiping.
In yet another aspect of the invention, the antimicrobial composite structure may form an area, region, portion, or dimension of a medical device, device material, packaging material or combinations thereof.
According to an aspect of the invention, such antimicrobial composite structures are produced by a process for depositing nanoparticles on a surface such as a matrix of expanded fluoropolymer material such that the nanoparticles penetrate the matrix. The process involves providing a sol composed of a volatile non-aqueous liquid and nanoparticles suspended in the non-aqueous liquid. The sol may be provided by preparing an aqueous suspension of nanoparticles and extracting the nanoparticles into a non-aqueous liquid to form a sol. For example, the sol may be prepared by forming an aqueous suspension of silver nanoparticles and extracting the silver nanoparticles into a non-aqueous liquid. Any water immiscible organic solvent may be used in the extraction process.
The sol desirably has low viscosity and is adapted to forming droplets utilizing conventional droplet forming techniques. The sol is then processed to form a plurality of droplets. These droplets are deposited on a surface of the matrix and penetrate into the matrix. Finally, the non-aqueous liquid is evaporated from the surface to leave a residue of nanoparticles. Alternatively and/or additionally to forming droplets, it is contemplated that the process may deposit the sol on a surface of the matrix by techniques selected from printing, dipping, brushing or combinations thereof.
Generally speaking, the volatile non-aqueous liquid component of the sol may be any water immiscible organic solvent that has a sufficiently low viscosity for an application process such as spraying has a high volatility to be quickly evaporated, is compatible with the nanoparticles, can be readily handled in an application process, and has surface energy that allows the sol to penetrate into a matrix of expanded fluoropolymer material. For example, the liquid may be selected from benzene, butanol, carbon tetrachloride, cyclohexane, 1,2-dichloroethane, dichloromethane, ethyl acetate, ethyl ether, iso-octane, methyl-t-butylether, methyl ethyl ketone, pentane, heptane, chloroform, toluene, and hexane and mixtures thereof. Desirably, the nanoparticle component of the sol is silver nanoparticles. The silver nanoparticles may have an effective diameter of less than 20 nanometers (nm). Even more desirably, the residue of nanoparticles (i.e., the nanoparticles deposited into the matrix of expanded fluoropolymer material) provides antimicrobial properties. It is contemplated that the sol may further include other materials having antimicrobial properties including, but not limited to, copper nanoparticles, chlorohexidine, iodine, antibiotics and combinations thereof.
The plurality of droplets may be formed by a spray process. For example, the spray process may utilize a centrifugal pressure nozzle, a solid cone nozzle, a fan spray nozzle, a sonic atomizer, a rotary atomizer, a flashing liquid jet, ultrasonic nozzles or combinations thereof. The spray process may utilize electrostatic charge. The expanded fluoropolymer material to be treated may be a particular area, region, portion, or dimension of a medical device, device material, packaging material or combinations thereof.
In an aspect of the invention, the steps of depositing the plurality of droplets on a surface and evaporating the non-aqueous liquid from the surface leaving a residue of nanoparticles in the expanded matrix of fluoropolymer material may be conducted a plurality of times. That is, the process may deposit nanoparticles on a porous surface such as an expanded matrix of fluoropolymer material that the nanoparticles penetrate the porous surface or matrix. More particularly, the process may deposit nanoparticles on a porous surface such as an expanded matrix of fluoropolymer material in such manner that the penetration of nanoparticles into the porous surface or matrix is controlled.
The present invention also encompasses an article including a surface such as an expanded matrix of fluoropolymer material containing nanoparticles deposited according to any of the above-described processes or system. Desirably, the article surface is a matrix having a first exterior surface, a second exterior surface and an interior portion between the exterior surfaces; and the nanoparticles are present in the interior portion adjacent the first exterior surface but not in the interior portion adjacent the second exterior surface.
Other objects, advantages and applications of the present disclosure will be made clear by the following detailed description.
To illustrate the invention and demonstrate its operation, various articles were prepared by applying silver nanoparticles (occasionally referred to herein as “nanosilver”) onto selective surfaces of various materials including microporous polymeric materials such as, for example, matrices of expanded polymer material. However, it is contemplated that the metal nanoparticle may be gold, platinum, indium, rhodium, palladium, copper or zinc. The nanoparticles may be in the size range of 0.1 to 100 nm. These nanoparticles may have a standard normal size distribution; however, nanoparticles less than about 20 nm have been found to work well.
The silver nanoparticles were applied or deposited onto surfaces of expanded fluoropolymer materials from a sol composed of a volatile non-aqueous liquid and nanoparticles suspended in the non-aqueous liquid. The sol may be readily provided by preparing an aqueous suspension of nanoparticles and extracting the nanoparticles into a non-aqueous liquid to form a sol. Suitable techniques may be found at, for example, U.S. Patent Application Publication No. 2007/0003603 for “Antimicrobial Silver Composition” published Jan. 4, 2007, the contents of which are incorporated herein by reference.
Generally speaking, the liquid component of the sol is any volatile water immiscible organic solvent that has a sufficiently low viscosity for the application process (e.g., spraying), has a relatively high volatility to be quickly evaporated, is compatible with the nanoparticles, and can be readily handled in an application process. For example, the liquid may be selected from benzene, butanol, carbon tetrachloride, cyclohexane, 1,2-dichloroethane, dichloromethane, ethyl acetate, ethyl ether, iso-octane, methyl-t-butylether, methyl ethyl ketone, pentane, heptane, chloroform, toluene, and hexane and mixtures thereof. Silver nanoparticles having an effective diameter of less than 20 nm have been found to work well. A silver nanoparticle sol having a viscosity of about 1 cP or less at 25° C. has been found to work well. The viscosity of the nanoparticle sol at the typical concentrations of nanoparticles (e.g., 25 to 5000 parts per million) will have a viscosity of the volatile water immiscible organic solvent. Of course, the viscosity may be determined utilizing viscometers such as a Brookfield RV DV-E Viscometer with Helipath Spindle Set (T-bar spindles). However, the viscosity may be so low that it may be only possible to determine that the viscosity is less than 1 cP with conventional viscometers.
The surface to be treated is desirably a microporous polymeric material. While various microporous polymeric materials are contemplated, it is desirable that the polymeric materials have a relatively open structure that allows nanoparticles to penetrate into to portions or areas or interstices in the material immediately adjacent the surface such that the nanoparticles are not present or exposed on top of the surface like on the surface of smooth film but are instead present predominately below the outermost surface.
For example, a microporous polymeric material may be in the form of an expanded polymeric material such as an expanded fluoropolymer (e.g., polytetrafluoroethylene), expanded polyester (e.g., polyethylene terephthalate), expanded polyethylene (e.g., ultra high molecular weight polyethylene) or the like. The expanded polymer material desirably is in the form of a porous matrix or porous structure that may be described as a node and fibril microstructure. Such microstructure is described at, for example U.S. Pat. No. 3,962,153 for Very Highly Stretched Polytetrafluoroethylene and Process Therefore issued Jun. 8, 1976 to Gore; and U.S. Pat. No. 4,187,390 for Porous Products and Process Therefore issued Feb. 5, 1980 to Gore; the contents of each of which is incorporated herein by reference.
In an aspect of the invention, the steps of depositing the plurality of droplets on a surface (e.g., an exterior surface of a matrix of expanded fluoropolymer) and allowing the plurality of droplets to penetrate into the expanded polymer matrix and evaporating the non-aqueous liquid from the surface leaving a residue of nanoparticles may be conducted a plurality of times. According to an aspect of the invention, the process may deposit nanoparticles on a porous surface (e.g., an expanded material such as expanded polytetrafluoroethylene) such that the nanoparticles penetrate into the porous surface. More particularly, the process may deposit nanoparticles on a porous surface in such manner that the penetration of nanoparticles into the porous surface is controlled. This can be important in a variety of applications where nanoparticles are desired to be present at or near a surface (e.g., beneath a surface) but not penetrated entirely through or throughout a material.
The present invention encompasses the use of a silver nanoparticle sol composed of 25 to 5000 parts per million of silver nanoparticles; and 995000 to 999975 parts per million of a non-aqueous liquid to for the droplets that are deposited on the expanded polymer surface. For purposes of the present invention, a concentration of nanoparticles in non-aqueous characterized as 1,000 parts per million (i.e., 1,000 parts nanoparticles to 1,000,000 parts non-aqueous liquid) generally correspond to 1,000 micrograms (μg) of nanoparticles per 1,000,000 grams (g) of liquid which may be expressed as (m/g). In other words, a nanoparticle concentration of 1 part per million (i.e., 1 ppm) generally corresponds to a concentration of 1 μg/g for the types of nanoparticles and non-aqueous liquids employed in the present invention. Desirably, the silver nanoparticles have an effective diameter of less than 20 nm. The silver nanoparticle sol also has a viscosity of about 1 cP or less at 25° C. The non-aqueous liquid may be benzene, butanol, carbon tetrachloride, cyclohexane, 1,2-dichloroethane, dichloromethane, ethyl acetate, ethyl ether, iso-octane, methyl-t-butylether, methyl ethyl ketone, pentane, heptane, chloroform, toluene, and hexane and mixtures thereof.
The sol desirably has low viscosity and is adapted to forming droplets utilizing conventional droplet forming techniques. The sol is then processed to form a plurality of droplets utilizing conventional spray processes or techniques. For example, a spray process may utilize a centrifugal pressure nozzle, a solid cone nozzle, a fan spray nozzle, a sonic atomizer, a rotary atomizer, a flashing liquid jet, ultrasonic nozzles or combinations thereof. The spray process may utilize electrostatic charge.
These droplets are deposited on a surface (e.g., the exterior surface of the expanded polymer matrix) and allowed to penetrate. The penetration can be controlled by varying the rate at which the droplets are applied and the amount that is applied. Alternatively and/or additionally to forming droplets, it is contemplated that the process may deposit the sol on a surface by techniques selected from printing, dipping, brushing or combinations thereof. The surface to be treated may be a particular area, region, portion, or dimension of a medical device, device material, packaging material or combinations thereof. The surface may be hydrophobic or hydrophilic. The surface (or portions of the surface) may be pretreated to modify the surface energy to enhance the application of the sol or to help repel the sol. Non-polar non-aqueous liquids such as, for example, heptanes have been found to work particularly well on hydrophobic surfaces such as, for example, polytetrafluoroethylene. Without being held to a particular theory of operation, the surface energy of the nanoparticle sol formed from non-polar, non-aqueous liquid penetrates the matrix of expanded polymer to allow deposition of nanoparticles in the matrix. This is advantageous because the nanoparticles can adhere well to the nodes and fibrils of the matrix through van der Waals interaction, chemical interactions and/or mechanical interactions. Moreover, the presence of nanoparticles such as silver nanoparticles in the matrix adjacent the first exterior surface permits the elution of ions from the nanoparticles without the hindering effects of binders or other coatings and/or fixing agents that may impede the elution of ions. The elution of ions (e.g., silver ions) is important to provide antimicrobial properties to the composite material.
After the sol is deposited on the surface, the non-aqueous liquid is evaporated from the matrix to leave a residue of nanoparticles at or, more desirably, adjacent the surface of the matrix. A spray booth or similar structure with an exhaust system is useful to provide a flow of air to help evaporate the non-aqueous liquid and to properly handle the vapor. The residue of nanoparticles adheres to the surface of the article. The steps of depositing the sol (e.g., as a plurality of droplets or by other techniques) on a surface and evaporating the non-aqueous liquid from the surface leaving a residue of nanoparticles may be conducted a plurality of times.
The residue of nanoparticles may be designed to provide antimicrobial properties. Desirably, the nanoparticles are present at only the article surface. It is contemplated that the sol may further include other antimicrobial constituents including, but not limited to, copper nanoparticles, chlorohexidine, iodine, antibiotics and combinations thereof to enhance the antimicrobial properties of the residue.
The antimicrobial composite structure may be a particular area, region, portion, or dimension of a medical device, device material, packaging material or combinations thereof.
In one example, polytetrafluoroethylene material was treated selectively on the outer dimension of a tubular structure with nanoparticles of antimicrobial silver suspended in heptane, chloroform, and toluene, or mixtures thereof, by a spray technique utilizing a spray apparatus. In other examples, the nanoparticles have been applied to the surface of polytetrafluoroethylene material by dipping, brushing, or dripping the solvent/nanosilver mixture onto the surface of the material. Other examples represent additional materials that have been imparted with nanosilver in this fashion including silicone, paper, polyethylene, polystyrene, Styrofoam, polypropylene, wood, cotton, and polycarbonate. The nanosilver used in these examples is initially generated as an aqueous suspension according to commonly assigned U.S. Patent Application Publication No. 2007/0003603 for “Antimicrobial Silver Composition” published Jan. 4, 2007, the contents of which are incorporated herein by reference. U.S. Patent Application Publication No. 2007/0003603 corresponds to PCT/US2005/027261 and PCT International Application Publication WO2006026026A2). The silver nanoparticles generated in the aqueous suspension are then subjected to an extraction step that includes the total transfer of nanosilver from the aqueous phase into the organic phase of choice (e.g., heptane, chloroform and/or toluene).
It was desired to deposit nanosilver selectively to the outside diameter of a tubular structure. A spray deposition technique was developed to deposit silver in such a manner as to uniformly apply a coating on the outside of the tubular expanded PTFE or ePTFE (expanded polytetrafluoroethylene is available from W.L. Gore & Associates) material while leaving the inside diameter completely free of silver. The ePTFE graft material treated in this example was a hollow tube with an internal diameter of 6 mm and a length of up to 44 inches. The uniform application of the nanosilver was accomplished by rotating the tubular material on a mandrel that spans the length of the tubular structure. Referring to
This equipment could also utilize multi-axis motion control to precisely control the application of nanoparticles to complex substrate geometries. The nanoparticle sol may be contained in a reservoir 20. It is contemplated that the nanoparticle sol may be fed from an external reservoir. Features including a spray pass counter 22, motor controls 24, regulators for spray control, spray head position, and the like may be included.
Referring to
The spray coating was conducted in a specially designed and fabricated spray booth that included multi-axis spraying capabilities, specialized exhaust features to remove volatile organic vapors, and an automated programmable coating counter to control the number of spray coats and the point of shut-off for the spray head.
This treatment process includes the following steps:
After the ePTFE material was coated with silver, it was tested for antimicrobial efficacy utilizing a conventional 24 hour bacterial challenge assay. In such a test, the substrates are challenged with known bacterial count while immersed in medium for 24 hours. The medium was then appropriately diluted and plated on MHA (Mueller-Hinton Agar) plates to estimate the surviving bacterial count. A log reduction of bacteria exposed to the treated substrate over a 24-hour period is a typical test to measure antimicrobial activity. A reduction of 3-logs (99.9%) of bacteria is widely considered to indicate a coating or treatment that is highly effective as an antibacterial agent. Table A demonstrates the antimicrobial nature of the deposited nanosilver against Methicillin Resistant Staphylococcus Aureus (MRSA). In Table 1, T0 is the zero time inoculum and T1 is 24 hour time survivor count. The log T0 data is included to confirm that nothing was abnormally affecting bacterial growth on the untreated plates. The data in Table A below indicate a log reduction in excess of the 3-log threshold.
Paper of various constructions, including notebook paper, cardboard, particulates, was treated with nanosilver by dripping a mixture of an organic solvent and suspended nanoparticles onto a selected surface of material. This was conducted using chloroform, toluene, and heptane as the solvent or combinations thereof and nanosilver as the nanoparticles. The volatile nature of these solvents allows the solvent to evaporate before the untreated side of the substrate is saturated and therefore allows silver to be deposited only on one side of the paper. This method was also performed on materials made with polyethylene, polystyrene, Styrofoam (using only heptanes), polypropylene, wood, cotton (such as a gauze material), and polycarbonate. The advantage of solvent based nanosilver deposition is the rapid nature of the deposition time and the selectivity of the treatment method to render materials antimicrobial.
It will be recognized that the above methods and examples can be modified as appropriate without departing from the scope of the invention. The silver deposition step may be carried out at room temperature or optionally below or above room temperature. The substrate to be coated with nanosilver can undergo identical spray, dip, or brushing steps to increase the surface concentration of nanosilver as desired. Additionally, it has been verified that the AgNP:Organic mixture can be stored in excess of 6 months, the nanosilver particles remain uniformly suspended in the mixture, and the mixture remains viable for the coating process.
An exemplary antimicrobial composite structure in the form of the expanded polytetrafluoroethylene tubing treated with a silver nanoparticle sol according to the process described in Example 1 was prepared. The tubing was treated by twenty-five (25) spray passes. Measurements for expanded polytetrafluoroethylene tubing that was treated are as follows:
Outside Diameter: 0.78 cm
Inside Diameter: 0.60 cm
Sample Length: 15 cm
Outside Surface Area: 36.76 cm2
Density: 0.742 g/cc (theoretical=2.2 g/cc)
Percent Solid: 34% (based on density)
Percent Open: 66%
Referring to
Two separate sets of tubing sections were analyzed. First, a section of tubing approximately one-half inch (˜13 mm) long was cut from approximately the center region of the tubing. This section was mounted and a series of seven (7) energy dispersive x-ray spectroscopy (EDS) analyses were performed across the length of the sample. Secondly, five sections (approximately 13 mm long) were cut one from: each end (i.e., approximately 1 inch inward towards the center from the end), each quarter point (i.e., approximately equidistant from the “end” sample and the mid-point) and the one mid-point. These samples had the EDS analysis performed at two points. The calculated silver weight percent for the high and low points for the five sections taken from along the length of the tube along with the high (average plus 1-standard deviation) and the low (average minus 1-standard deviation) of the multiple analyses on one piece are shown in
From
The overall trend that the end regions (both taken approximately 1 inch in from the end) have a lower silver intensity than the middle region is most likely a valid comparison. The size of the spread from the seven analyses that were performed along the same ˜13 mm piece suggests that the surface is far from ideal for quantitative analysis. From
Various measurements of two samples of expanded polytetrafluoroethylene tubing treated utilizing the spray process described in Example 1 are reported in Table B below. These measurements include dimensions, weights and silver concentrations based on EDS analyses.
Surface Analysis: X-ray photoelectron spectroscopy (XPS) was used to examine the chemistry on the very outer (10 nanometer) surface of the tubing. A section of tubing from near the middle of the sample was cut out and mounted for analysis. This sample had two definitive shades (darker and lighter) and each region had three areas analyzed. In a representative XPS wide scan from the treated tubing, the dominance of fluorine is seen for these analyses just like for the EDS. Table C shows the averages of the XPS analyses for the two regions.
These results show that the surface is predominantly that of the PTFE (i.e., CF2) and that the silver is found at trace levels (<1 at %) for both the darker and lighter area.
The main difference between the darker and lighter regions is the darker region has slightly more carbon, oxygen, and silicon and less fluorine than the lighter region. But it should be noted that like the EDS analysis the surface roughness will also influence the XPS results.
From a representative XPS spectrum, the carbon is represented by two peaks. The smaller peak at 284.6 eV is from aliphatic carbon (—C—H) that is most likely from residual carbonaceous material deposited during the treatment. The larger carbon peak at ˜292 eV is from the carbon that is bound to two fluorine atoms in the PTFE matrix (—CF2). Curve fitting these peaks allows the percent area of the two carbon peaks to be determined. Using the area percent and the total atomic percent for carbon the atomic percent carbon for the two functionalities can be determined. Table D shows the curve fitting results for the carbon peaks.
From this it can be seen that the aliphatic carbon is the minor component and that the darker area has approximately 1.6 times more aliphatic carbon than the lighter area. Overall, a very light coating of surface oriented silver treatment was found along the length of the tubing with the highest levels being found near the midpoint of the sample. When these results (relatively low amount of silver in the first 10 nanometers of the surface) are considered in combination with the overall weight percentage of silver, it is clear that silver nanoparticles are distributed in the expanded polymer matrix in the interior portion adjacent the first exterior surface.
A length of Teflon® polytetrafluoroethylene film approximately 0.005 inch thick and 12 inches wide and having a smooth finish (McMaster-Carr, Part No. 8569K38) was sprayed horizontally with the silver nanoparticle sol (silver nanoparticles in heptane) prepared according to Example 1. Three zones were created by varying the number of treatment passes. Referring to
After bring allowed to dry, the sample was subjected to a single wipe pass utilizing a KimTech Science™ KimWipes®—delicate task wiper, available from Kimberly-Clark Corporation, at three separate locations to assess the durability of the deposited silver nanoparticle treatment on the film. The wipe was drawn across the sample using the index finger of the tester while apply moderate pressure (about equal to the force typically used to write with a pencil or other writing instrument on paper). One wipe was used dry, one wipe was saturated with deionized water and one wiper was saturated with an aqueous solution of isopropyl alcohol (approximately 70% isopropyl alcohol and approximately 30% water).
As can be seen in
As noted above, the silver nanoparticle sol was applied to create three different treatments zones by varying the number a treatment passes: 15 passes (top); 25 passes (middle); and 30 passes (bottom). A sample from each zone and a control (i.e., untreated Teflon® polytetrafluoroethylene film) was subjected to energy dispersive x-ray spectroscopy (EDS) analyses. The results are reported in Table E below.
Even though the samples are carbon coated, the C and F values are consistent with that expected for the Teflon substrate since the carbon coating is extremely thin.
The 15× and 30× regions have similar silver loadings with the 25× region having the highest silver level.
Referring now to
A 48 mm diameter circle of the untreated film (0.005″ thick) was cut and measured. The measurements are as follows:
Weight: 0.5261+/−0.0017 g
Area: 18.096 cm2
Area per unit weight: 34.398 cm2/g
Density: 2.29 g/cc (theoretical=2.2 g/cc)
Measurements from samples of smooth polytetrafluoroethylene film treated utilizing the above-described spray process are reported in Table F below. These measurements reflect two samples per zone from each of the three separate zones created by varying the number of spray passes. Because the amount of added silver is in microgram quantities, the weight per unit area for the treated film samples was assumed to be the same as for the untreated film for sample having an area on the order of 10 cm2 or so. These measurements include dimensions, weights and silver concentrations based on EDS analyses.
The quantitative values averaged over a larger area still show some variation within each zone, but on average the amount of silver added per pass (application) is remarkably the same.
X-ray photoelectron spectroscopy (XPS) was used to examine the chemistry on the very outer (10 nanometer) surface of the film samples from each of the three separate areas of treatment (i.e., 15×, 25× and 30×). Table G shows the results of the XPS analyses for the three areas and for the antimicrobial composite structure (e.g., expanded polytetrafluoroethylene tube).
The polytetrafluoroethylene film is a solid surface substrate that essentially is coated as a two-dimensional structure. The surface analysis shows that more of the polytetrafluoroethylene surface is covered for the film as compared to the expanded polytetrafluoroethylene microstructure of the tube and this also corresponds into a higher silver concentration for the solid surface as compared to the outermost layer of the expanded polytetrafluoroethylene microstructure of the tube.
Generally speaking, the quantitative data suggests that the expanded polytetrafluoroethylene microstructure of the tube is able to retain (accept) more silver per unit area than the solid polytetrafluoroethylene film. This highlights an advantage of the antimicrobial composite material in that more nanoparticle material is able to be captured by the microstructure.
The EDS analysis suggests that the outer 1 micrometer of the expanded polytetrafluoroethylene microstructure of the tube (i.e., expanded PTFE tube) has slightly less silver than the polytetrafluoroethylene film's surface (i.e., the Teflon® Film). The
XPS analysis suggests that the outer 10 nanometers of the expanded polytetrafluoroethylene microstructure of the tube has significantly less silver than the corresponding portion of the polytetrafluoroethylene film's outer surface. This leads to a silver analysis gradient as follows:
Outer Surface (10 nanometers): Teflon® Film>expanded PTFE tube
Near Surface (1 micrometer): Teflon® Film≧expanded PTFE tube
Bulk: expanded PTFE tube>Teflon® Film
While the inventors should not be held to a particular theory of operation, this gradient analysis shows that the open structure or microstructure of the expanded PTFE tube allows for a three dimensional coating (albeit thin) that contains more silver per unit area than is achieved for the solid polytetrafluoroethylene film even for equivalent treatments (25 passes for the expanded polytetrafluoroethylene tubing and 25-30 passes for the polytetrafluoroethylene film). It should be noted that the polytetrafluoroethylene film treated with 15 spray passes had even less silver per unit area than for the expanded polytetrafluoroethylene tubing treated with 25 spray passes.
Various scanning electron microscopy images (SEM images) of the film were analyzed. These images suggest that, for the first 15 spray passes, the deposition of the silver is mainly influenced by the morphology (roughness) of the film. For higher numbers of spray passes (i.e., 25-30 spray passes) the deposition takes on the appearance of more closely resembling overlapping droplets with outer rim particulate deposition (i.e., build up at the outer rim of the droplet). Since the particles on the film's surface do not have anywhere to go, the build-up/pattern of the deposit becomes influenced by the addition of more spray treatment (i.e., more application of the silver nanoparticle sol).
SEM: Scanning electron microscopy (SEM) was performed with a Hitachi S4500 field emission scanning electron microscope (FESEM) operating at 1.2 kV. The samples were dusted onto conductive carbon tape and imaged without coating. Digital images were collected using Quartz PCI software.
EDS: Energy dispersive x-ray spectroscopy was performed using an Oxford Instruments Pentafet Si(Li) solid state EDS detector with Link™ software. A collection voltage of 20 kV was used and the samples were gold coated to mitigate charging.
XPS: Surface analysis was performed by x-ray photoelectron spectroscopy (XPS) using a Fisons M-Probe spectrometer equipped with monochromatic Al Kα x-rays. Atomic sensitivity factors, supplied with the Fisons M-Probe spectrometer, were used to establish the relative atomic concentration of the elements detected by the spectrometer. Spot size of ˜1 mm was used. Charge neutralization was accomplished using the electron flood gun/screen (FGS) method. Wide scans were performed to document the elemental composition of the surface.
While various patents have been incorporated herein by reference, to the extent there is any inconsistency between incorporated material and that of the written specification, the written specification shall control. In addition, while the disclosure has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various alterations, modifications and other changes may be made to the disclosure without departing from the spirit and scope of the present disclosure. It is therefore intended that the claims cover all such modifications, alterations and other changes encompassed by the appended claims.
This application claims the benefit of priority from U.S. Provisional Application No. 61/433,647 filed on Jan. 18, 2011, and U.S. patent application Ser. No. 13/336,193 filed on Dec. 23, 2011.
| Number | Date | Country | |
|---|---|---|---|
| 61433647 | Jan 2011 | US |
