WO2020255079A1

WO2020255079A1 - Improved medical tubing and method for producing said tubing

Info

Publication number: WO2020255079A1
Application number: PCT/IB2020/055806
Authority: WO
Inventors: Aharon Gedanken; Ilana Perelshtein; Nina Perkas; Ehud Banin; Michal NATAN
Original assignee: Bar-Ilan University
Priority date: 2019-06-21
Filing date: 2020-06-19
Publication date: 2020-12-24

Abstract

Methods, devices, and systems relating to applying an antimicrobial coating on a substrate, such as, for instance, medical tubing, and to applying a protective coating on top of the antimicrobial coating, thereby shielding the antimicrobial coating from exposure to fluids, including, but not limited to, natural or artificial bodily fluids such as urine. In embodiments of the present invention, the antimicrobial coating inhibits growth of various microbes, including, but not limited to, bacteria, and further exhibits antifouling properties. In embodiments of the present invention, the protective coating is inert to acidic and basic pH environments, as well as inert to natural or artificial bodily fluids, as well as nonreactive with proteins occurring in the natural or artificial bodily fluids. The antimicrobial coating may further comprise at least one metal oxide nanoparticle. The protective coating may further comprise carbon and/or silica.

Description

IMPROVED MEDICAL TUBING AND METHOD FOR PRODUCING SAID TUBING

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 62/864,826, filed June 21, 2019, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates in general to improvements in medical tubing and medical devices and in particular to catheters, and to new methods for producing said catheters.

BACKGROUND

Catheters are medical devices comprising of thin soft tubing made from medical grade materials, such as polyurethane, polyimides, latex, polytetrafluoroethylene, polyethylene terephthalate (PET) and silicone rubber. The device is inserted into a body cavity, duct or vessel to allow drainage or administration of fluids or gases or access of surgical instruments. As such, the material used for the catheter must be inert and unreactive to body fluids, such as urine, and a range of medical fluids with which it might come into contact. Silicone rubber has been a common material for catheters in the past, but it is weak mechanically and a number of fractures in silicone rubber catheters have been reported.

It is also critical for the catheters to be sterile and inhibit microbial growth, including, for instance, bacterial growth, during their use. For example, urinary catheters are primarily used for draining urine after surgeries and for urinary incontinence. Bacterial growth on the catheter can allow bacteria to travel up to the bladder and cause infection. A major cause of catheter- associated urinary tract infection is attributed to the use of non-ideal materials in the fabrication of urinary catheters. The ideal urinary catheter is made out of materials that are biocompatible, antimicrobial, and antifouling. Although much research has been conducted in this area, the ideal biomaterial has yet to be developed.

Biofilms, also called biofouling, are another major problem faced by urinary catheter patients because of the inherent property of urine to deposit minerals once infection by any microbe has occurred. Free-floating bacteria come across a surface submerged in the fluid and within minutes become attached. These attached bacteria produce slimy, extracellular polymeric substances that colonize the surface and form the biofilm. Urease-producing bacteria colonize the catheter with the help of these biofilms and the urease produced by the bacteria breaks down urinary urea to release ammonia, increasing its pH. The alkalinity of urine causes precipitation of salt crystals that are deposited on the catheter and cause blockage.

Thus, it is important to limit any microbial growth on the catheter, in particular urinary catheters. Antimicrobial coatings are often applied to the tubing, such as a silver coating, with low concentrations of silver ions being sufficient to kill microbes. The silver (Ag) ion releasing coatings can be designed in the form of Ag alloy (with gold, palladium), Ag-containing polymers and Ag nanoparticles (NPs). The use of alloys and nanoparticles enables the fast release of the Ag ions to be controlled and sustained. The large surface-to-volume ratio of NPs gives them an edge in antimicrobial efficacy. Furthermore, the efficacy of Ag-NPs is its tight incorporation with the catheter material to prevent fast and excessive release of ions which could prove cytotoxic to patients.

Alternative antimicrobial coatings for catheters include nanoparticles of CuO, or ZnO or Cu doped ZnO nanocomposites, such as Cuo_.89Zno_.11. The Applicant’s earlier Patent Publication No. WO 2014/181329 A1 discusses such compositions for coating medical devices and other articles. While these nanoparticles were satisfactorily coated on the catheter and provided good antimicrobial properties, the nanoparticles were dissolved upon treatment with artificial urine. It is therefore essential to improve the alloy nanoparticle coating on the catheter in order to prevent its removal by urine with which it will come into contact during use.

It is an object of the present invention to provide an improved coating for a catheter that aims to overcome, or at least alleviate, the above-mentioned drawbacks. A further objection of the present invention to provide an improved method for coating a catheter.

SUMMARY OF THE INVENTION

These and other objects are accomplished in the protective coating methods and systems of the subject invention.

The present invention in its various embodiments comprises a method of protecting a substrate, the method comprising applying the substrate with an antimicrobial coating, and applying a protective coating to the antimicrobial coating. The antimicrobial coating prevents, or retards, the growth of various microbes, including, but not limited to, bacteria. In at least one embodiment, the antimicrobial coating additionally has antifouling properties, i.e., the coating prevents, or retards, the growth of living organisms (biofouling) and/or non-living organic or inorganic substances.

The antimicrobial coating may comprise one or more elements, chemicals, and/or compounds that have antimicrobial properties, such as, for example, one or more metals ( e.g ., silver), one or more metal oxides, and one or more organic antimicrobial compounds (e.g., amylase). In at least one embodiment, one or more nanoparticles may be embedded in the antimicrobial coating. Thus, the antimicrobial coating in at least one embodiment comprises at least one metal oxide nanoparticle.

The protective coating is layered on top of the antimicrobial coating is, in at least some embodiments, inert to acid or alkali and therefore stable in both acidic and basic pH

environments. The word“inert,” at least as used herein, refers to being chemically stable and unreactive under the specified condition. Thus, the protective coating being inert to acid or alkali means that the protective coating is chemically stable and unreactive in both acidic and alkaline conditions.

In various embodiments, the protective coating does not react with proteins occurring in bodily fluids, including, but not limited to, proteins in urine, proteins in blood, and proteins in sweat.

Preferably, the protective coating is inert with respect to natural or artificial bodily fluids, such as plasma, artificial urine, urine, sweat. The term“natural bodily fluid,” at least as used herein, refers to a fluid or a secretion that naturally occurs in the human body. The term “artificial bodily fluid,” at least as used herein, refers to a fluid that does not naturally occur in the human body but mimics the chemical, biological, and/or physical properties of a natural bodily fluid.

More preferably, the protective coating comprises at least one of carbon or silica.

Additionally, in at least one embodiment of the present invention, a complete layer of the protective coating is applied over the antimicrobial coating.

In a further aspect, the present invention comprises a substrate coated with at least one layer of the antimicrobial coating, the at least one layer being at least partially coated with an inert protective coating, preferably a carbon or silica protective coating or mixture thereof.

Preferably, the antimicrobial coating is applied to the substrate by ultrasonic radiation. The protective coating is preferably applied to this coating by spray coating or by electron beam physical vapour deposition.

The protective coating may be applied to the antimicrobial coating to a thickness of anywhere from 50 nm to 1 micron. Preferably, the protective coating is applied to a minimum thickness of 50 nm, preferably at least lOOnm. More preferably, the thickness of the protective coating is 150-200 nm.

In one or more embodiments of the invention, the antimicrobial coating comprises at least one metal oxide, which may be selected from the group consisting of ZnO, CuO, ZnO doped with Cu⁺² ions, CuO doped with Zn⁺² ions, and mixtures thereof. The nanoparticles are preferably pristine ZnO or CuO. Alternatively, the nanoparticle may be CuO doped with Zn⁺² nanoparticles or ZnO doped with Cu⁺² nanoparticles but other metal precursors may be used to provide other metal oxide doped nanoparticles. In a preferred embodiment, Cuo_.89Zno_.11O nanoparticles are applied to the substrate.

The substrate coated with the protective coating is preferably a substrate that requires protection from urine, such as, for instance, medical devices, including, but not limited to, urinary catheters, which come into contact with urine. Accordingly, the present invention in its various embodiments further comprises a substrate coated with an antimicrobial coating comprising at least one metal oxide nanoparticle, said antimicrobial coating being at least partially coated with a protective coating that is inert to natural or artificial bodily fluids. The protective coating on the substrate may comprise, for instance, a carbon, a silica, and mixtures thereof. In at least one embodiment, the at least one metal oxide is selected from the group consisting of ZnO, CuO, ZnO doped with Cu⁺² ions, CuO doped with Zn⁺² ions, and mixtures thereof. In further embodiments, the protective coating is applied to a minimum thickness of 50 nm, or to a minimum thickness of 100 nm, or to a minimum thickness of 150-300 nm. In at least one embodiment, the protective coating is applied to a maximum thickness of 1 micron.

Additional embodiments of the present invention comprise a medical tubing, such as, for example, a catheter tubing, coated with at least one layer of an antimicrobial coating, such as, for instance, an antimicrobial coating with a ZnO nanoparticle, said at least one layer having at least a partial coating of a protective coating that is stable at acidic and basic pH levels, that is inert to natural or artificial bodily fluids, and/or that does not react with proteins occurring in such natural or artificial bodily fluids. In at least one embodiment, the protective coating preferably comprises carbon and/or silica. In at least one embodiment, the antimicrobial coating comprises a ZnO nanoparticle layer, optionally doped with Cu²⁺ ions.

The present invention in further embodiments also comprise a protective coating for use in maintaining the antibacterial activity of a substrate at least partially coated with an

antimicrobial coating that provides such antibacterial activity. In various embodiments, the antimicrobial coating may comprise at least one metal oxide nanoparticle, and the protective coating is inert to natural or artificial bodily fluids and preferably comprises at least one of a silica or carbon.

Therefore, based on the foregoing and continuing description, the subject invention in its various embodiments may comprise one or more of the following features in any non-mutually- exclusive combination:

• A method of protecting a substrate, said method comprising applying an

antimicrobial coating to the substrate, and applying a protective coating to the protective coating, wherein the protective coating is inert to acid or alkali;

• A protective coating for the substrate, the protective coating being inert to acid or alkali;

• A protective coating for the substrate, the protective coating being inert with respect to natural or artificial bodily fluids;

• A protective coating for the substrate, the protective coating being unreactive with proteins present in bodily fluids;

• The protective coating being inert with respect to bodily fluids, the bodily fluids comprising plasma, urine, blood, and/or sweat;

• The protective coating being unreactive with proteins present in bodily fluids, the bodily fluids comprising plasma, urine, blood, and/or sweat;

• An antimicrobial coating for the substrate, the antimicrobial coating inhibiting fouling on the substrate;

• An antimicrobial coating for the substrate, the antimicrobial coating comprising at least one metal, at least one metal oxide, and/or at least one organic antimicrobial compound;

• An antimicrobial coating for the substrate, the antimicrobial coating comprising at least one metal oxide nanoparticle;

• A protective coating for the substrate, the protective coating comprising carbon and/or silica;

• Applying the antimicrobial coating to the substrate by ultrasonic radiation;

• Applying the protective coating to the antimicrobial coating by spray coating or by electron beam physical vapour deposition;

• Applying a complete layer of the protective coating over the antimicrobial

coating;

• The protective coating having a minimum thickness of at least 50 nm;

• The protective coating having a maximum thickness of 1 micron;

• The protective coating having a thickness of between 50 nm and 1 micron;

• The protective coating having a thickness of 150-300 nm;

• The protective coating having a thickness of between 50-300 nm;

• The antimicrobial coating comprising at least one metal oxide, the at least one metal oxide being selected from the group consisting of ZnO, CuO, ZnO doped with Cu⁺² ions, CuO doped with Zn⁺² ions, and mixtures thereof;

• A method of protecting a substrate coated with an antimicrobial coating, the method comprising applying a protective coating to the substrate, wherein the protective coating is inert to acid or alkali;

• A protective coating for the substrate, the protective coating being chemically inert in both natural urine and artificial urine;

• A substrate coated with an antimicrobial coating and a protective coating that at least partially covers the antimicrobial coating, the protective coating being inert to natural or artificial bodily fluids;

• A protective coating for the substrate, the protective coating comprising carbon, silica, or a mixture thereof;

• The protective coating comprising carbon, silica, or combinations thereof;

• The substrate being a medical device that comes into contact with urine;

• The substrate being a catheter;

• A medical tubing coated with at least one layer of an antimicrobial coating and a protective coating that at least partially covers the at least one layer, the protective coating being inert to naturally-occurring bodily fluids; • The at least one layer of the antimicrobial coating being a ZnO nanoparticle layer;

• The ZnO nanoparticle layer being doped with Cu2+ ions;

• Adhering the at least one layer of the antimicrobial coating to the medical tubing via ultrasonic radiation;

• Adhering the protective coating to the at least one layer of the antimicrobial coating via either spray coating or electron beam physical vapour deposition;

• The medical tubing being a urinary catheter;

• A protective layer for use in maintaining antimicrobial activity of a substrate coated with an antimicrobial coating, the protective layer being inert to natural or artificial bodily fluids, and the protective coating being inert in acidic and basic pH environments;

• The protective layer being applied on top of the antimicrobial coating;

• The protective layer comprising carbon and/or silica;

• A protective layer for use in shielding a coated substrate from natural or artificial bodily fluids, the protective layer being inert in acidic and basic pH environments;

• The coated substrate having antimicrobial and/or antifouling properties;

• The protective layer being applied to a thickness of between 50-300 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 A is HRSEM of a ZnO coated catheter without a protective layer.

Figure IB is a HRSEM of a ZnO coated catheter with a carbon protective layer according to an embodiment of the present invention.

Figure 1C is a HRSEM of a ZnO coated catheter with a silica protective layer according to an embodiment of the present invention.

Figure 2A is a HRSEM of the ZnO coated catheter of Figure 1A after exposure to artificial urine for 14 days.

Figure 2B is a HRSEM of the ZnO-carbon coated catheter of Figure IB after exposure to artificial urine for 14 days, together with an EDS of the catheter.

Figure 2C is a HRSEM of the ZnO-silica coated catheter of Figure 1C after exposure to artificial urine for 14 days, together with an EDS of the catheter.

Figure 3 is a graph demonstrating anti-bacterial activity against S. aureus for a control and the ZnO coated catheter, ZnO-carbon coated catheter and ZnO-silica coated catheter before and after exposure to artificial urine.

Figure 4 depicts four different catheters, each with a different coating, specifically, from left to right, silicone, ZnO alone, ZnO and carbon, and ZnO and silica (S1O2).

Figure 5 is a graph demonstrating measured bacterial activity for four types of catheters (specifically, a control catheter, a catheter coated with an antimicrobial (ZnO) coating, a catheter coated with the antimicrobial coating plus an additional protective coating comprising carbon, and a catheter coated with the antimicrobial coating plus an additional protective coating comprising silica) before exposure to artificial urine.

Figure 6 is a graph demonstrating measured bacterial activity for the four types of catheters from Figure 5 after exposure to artificial urine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following includes solutions to the problems of bacterial and other microbial growth, and the growth of biofilms, on medical devices, including, but not limited to, medical tubing and urinary catheters.

It is known to coat catheters or other substrates with a CuO or ZnO nanoparticle coating to provide antibacterial properties, the coating being found to provide complete killing of S. aureus and a 3 -log reduction of E. coli. The coating process is done sonochemically from a water-based solution, such as the process described in the Applicant’s published application No. WO2014/181329 Al, the contents of which are incorporated herein by reference.

In an exemplary procedure, a metal precursor or a mixture of metal precursors to be coated on the catheter is dissolved in water, ethanol is added to obtain, for example a 9: 1 ethanol: water solution, the catheter is immersed in the solution and the obtained mixture is subjected to ultrasonic irradiation. The substrate is kept at constant distance of around 2 cm from the sonicator tip during the entire reaction process. The obtained coated catheter is washed twice with double-distilled water and once with ethanol, and then dried under vacuum.

In the example below, ZnO nanoparticles are used to coat the catheter but other metal oxide nanoparticles may be used, such as CuO nanoparticles and Zn-doped CuO nanoparticles.

However, while these coatings have been found to have good antibacterial properties, the coating is dissolved upon contact with artificial urine, making this type of coating unsatisfactory for urinary catheters. The present invention therefore concerns both the application of an antimicrobial coating to a substrate, such as, for instance, urinary catheters, and the application of an additional protective coating on top of the antimicrobial coating, whereby the protective coating prevents dissolution of the antimicrobial coating. In non-limiting Example 1 below, an antimicrobial coating, which comprises ZnO, is coated on a catheter and a protective coating is coated on top of the antimicrobial coating, and the protective coating prevents dissolution of the antimicrobial coating after contact between the catheter and urea. In particular, the protective coating comprises carbon or silica (S1O2). The coating of the protective layer is done by spray coating or by electron beam deposition.

EXAMPLES

Example 1 : Comparison of the anti-bacterial properties of a silicone catheter coated with ZnO alone. ZnO with a second protective layer of carbon and ZnO with a second protective layer of silica (silicon dioxide. S1O2)

A sonochemical method was applied for the deposition of ZnO nanocrystals as a coating on a silicone catheter. The preparation procedure was as follows:

A silicone catheter was placed in a 0.02M solution of Zn(Ac)2 (working volume 600 ml) in an ethanol-water solvent and also a pure water solvent. The pH was adjusted to 8 for the reaction mixture. The solution was then irradiated for 1 hour with a high intensity ultrasonic horn (Ti-horn, 20kHz, 1.5kW at 75% efficiency) under a flow of argon at a distance of 5-6 cm. The amount of ZnO coating applied to the catheter was -0.07 wt%.

These ZnO catheters were then further provided with a protective coating of carbon or silica by spray coating or by electron beam physical vapour deposition (EB-PVD). This is a technique in which a high energy electron beam is used to heat the carbon or silica which is then deposited on the surface of the ZnO-coated catheter in the molecular form under high vacuum conditions. In this example, the carbon was spray coated and the silica was applied by electron beam deposition. The thickness of the protective coating is between 150 nm to 300 nm. The morphology of the coated catheters was tested by high resolution scanning electron microscopy (HRSEM) and is presented in Figure 1A (ZnO coated catheters with no protective coating), Figure IB (ZnO coated catheter with a carbon protective coating) and Figure 1C (ZnO coated catheter with a silica protective coating). The experimental process included exposing the coated catheters to artificial urine of a pH of 6.6 +/- 0.1 in order to assess durability. In particular, the stability of the coated catheters in artificial urea was then investigated by placing 1.2 g of the coated catheter in 10 ml of artificial urine for 14 days. The components of the artificial urine, as well as the concentration of these components, are given in Table 1 below.

Table 1. Components of artificial urea for testing stability of coated catheters.

At the end of the process, the catheters were analyzed for the amount of ZnO coating, the results for which are shown in Table 2 below.

Table 2. Amount of ZnO coating on coated catheters after exposure to artificial urea.

The morphology of the catheters post-urine exposure was also tested using HRSEM and the results are presented in Figures 2A to 2C. In addition, elemental analysis (EDS) was performed which confirms the presence of Zn on the catheters protected by C and S1O2 after exposure to artificial urine.

The results demonstrated that ZnO coated catheters without any further protective coating did not withstand exposure to artificial urine. Without being bound by theory, the ZnO coating dissolved most probably due to the chemical interaction of ZnO with phosphates present in the artificial urine, according to the below reaction:

2 (NH₄)₂HP0₄ + 3 CUO A CU₃(P0₄)₂ + 3 H₂0 + 4 NH₃

The amount of coating was thus reduced tenfold for the ZnO coated catheters without any further protective coating, while in the case of carbon and silica protected ZnO catheters, the decrease in the amount of ZnO coating was small (28%).

Additionally, the antibacterial properties of the catheters were tested against the common bacteria Staphylococcus aureus (S. aureus) by soaking the catheters for 14 days in the artificial urine described above. Antibacterial properties of these catheters were evaluated both before and after exposure to the artificial urine. The results are presented in Figure 3 of the accompanying drawings, which charts the presence of S. aureus in fluid surrounding the catheter, in units of CFU/ml of fluid (CFO being a Colony -Forming Unit). The catheters were inserted in a fluid containing the S. aureus pathogen, initially in a concentration of -100,000 CFU/mL (per the control) and the fluid was tested for the presence of the pathogen after 60 minutes. The ZnO coating alone was found to have good antibacterial and antifouling activity, with a complete killing of S. aureus in 60 minutes. The additional protective coating of carbon or silica did not have a significant impact on the antibacterial properties even though the ZnO coating is covered, reducing the concentration of S. aureus from -100,000 CFU/mL to under 100 CFU/mL. After 14 days of immersion exposure to artificial urine, the antibacterial properties of ZnO-coated catheters were reduced. However, the ZnO-coated catheters coated with carbon or silica provided a complete cleaning of bacteria.

As seen in Figure 3, the ZnO catheter exhibited antibacterial properties before exposure to the artificial urine. The addition of another coating, either a carbon-based protective coating (ZnO + C) or a silica-based protective coating (ZnO + S1O2), inhibited this antibacterial effect, as might be expected since the protective coating shields the ZnO coating. However, after exposure to urine, the two catheters containing a protective coating (ZnO + C and ZnO + S1O2), respectively) had almost no bacterial growth when compared to the ZnO catheter. These results indicate that the protective coatings of carbon and silica (S1O2), respectively, shield the metal oxide coating from exposure to urine, and further ensure that the antibacterial properties of the metal oxide coating are undamaged due to such exposure. By contrast, the ZnO-coated catheter without any further protective coating lost its antibacterial properties after 14 days’ exposure to artificial urine. As stated above, such loss is likely due to dissolution of the ZnO coating from the chemical interaction of ZnO with phosphates present in the artificial urine.

Based on all of the aforementioned results, a ZnO-coated catheter that is further coated with a protective coating of carbon (C) or silica (S1O2) is preferable to a ZnO-coated catheter alone. Deposition of this protective coating may be done via sputtering or by electron beam deposition. Figure 4 illustrates catheters coated with (A) silicone, (B) ZnO alone, (C) ZnO and carbon, and (D) ZnO and silica (S1O2).

Example 2: Comparison of the anti-bacterial properties of a silicone catheter coated with an antimicrobial coating alone versus the antimicrobial coating plus a second protective coating

An antimicrobial coating (specifically, in this example, a ZnO coating) was applied to a silicone catheter as follows. As a general procedure, the silicone catheter was placed in a 0.01M solution of Zn(Ac)2 (working volume 600 ml) in a pure ethanol solvent. The pH of the solution was adjusted to 8. The solution was then irradiated for 30min with a high intensity ultrasonic horn at a distance of 1-2 cm. The amount of ZnO coating applied to the catheter was -0.04 wt%.

One of skill in the art will appreciate that variations on the above procedure are possible. For instance, the precursor solution may be, instead of zinc acetate, any source of metal ions including, for example, zinc nitrate, copper acetate, silver nitrate, and the like. Additionally, the molarity of the precursor solution may vary from, for example, 0.001M to 1M. Likewise, different solvents may be used in order to generate the precursor solution, depending on solubility of the metal ion precursor (here, zinc acetate). Irradiation can also be varied from 15 minutes to 2 hours. Distance of application of the ultrasonic horn may be varied from the 1 -2 cm recited above as well, such as, for instance, a distance of 0.5 mm to 10 cm. Finally, amount of the antimicrobial coating applied may range from 0.001 wt% to 2 wt%.

Catheters with the antimicrobial coating were then further coated in either a protective coating comprising carbon (C), or a protective coating comprising silica (SiCL). Four types of catheters were then exposed to the artificial urine in Table 1 above. These four types of catheters were: (A) a control catheter that did not have either an antimicrobial coating or a protective coating, (B) a catheter with the antimicrobial (ZnO) coating, (C) a catheter with the antimicrobial coating plus a further protective coating comprising carbon (C), and (D) a catheter with the antimicrobial coating plus a further protective coating comprising silica (SiCh). In particular, 1.2 g of the coated catheters were placed in 10 ml of artificial urine for 14 days. It should be appreciated that there are other methods of exposing coated catheters to urine, including, for instance, introducing full lengths of coated catheters into 1L of artificial urine.

Bacterial counts were ascertained for each type of catheter both before their exposure to the artificial urine and after such exposure, based on units of Colony Forming Units (CFU) per ml of fluid surrounding the catheter. These results are shown in Figure 5 and Figure 6.

Figure 5 displays the number of bacteria found for each catheter type before exposure to artificial urine. As can be seen, the control catheter, which had neither an antimicrobial coating nor a protective coating, had the most bacteria. The remaining three catheters (that is, the antimicrobial (ZnO) catheter alone, the catheter with antimicrobial coating + protective coating with carbon, and the catheter with antimicrobial coating + protective coating with silica) all displayed a reduction in the number of bacteria before exposure to artificial urine. It should be appreciated that these three catheters all have similar reduction in number of bacteria when compared to the control, and further that the three catheters have similar bacterial numbers generally (within one order of magnitude).

Figure 6 displays the number of bacteria found for each catheter type after exposure to artificial urine. Both scraping and sonication methods were used to remove the bacteria so the bacteria could be counted. As can be seen, for both the scraping and sonication methods, the catheters with protective coatings (both carbon and silica) had less bacteria than either the control catheter or the catheter with an antimicrobial (ZnO) coating alone. Indeed, it should be appreciated that the catheters with protective coatings outperformed (i.e., had lower bacteria numbers than) the catheter with a ZnO coating alone, demonstrating that the protective coatings protect and preserve the antimicrobial effect of the ZnO coating.

It should therefore be appreciated from the disclosures herein, including, but not limited to, both of the above Examples, that the protective coating not only provides additional protection to the ZnO-coated catheter, but also does not interfere with, and indeed keeps intact, the antibacterial properties of the metal oxide nanoparticles. The thickness of the protective coating, with respect to both the ZnO + carbon and the ZnO + silica coating, was 150-200 nm, although such a thickness is a non-limiting example. As stated previously herein, the thickness of the protective coating may range from anywhere between 50 nm to 1 micron. It should further be appreciated that the biocidal activity of the aforementioned two catheters was similar to that of the unprotected catheter (i.e., the catheter with only a ZnO coating) before exposure to urine.

It is to be appreciated that other types of antimicrobial coatings provide antimicrobial and/or antifouling properties in addition to the metal oxide coating described above herein. Additionally, it should be further appreciated that different types of protective coatings may be applied on top of the antimicrobial coating, which will protect the antimicrobial coating from chemical reactions / interactions with fluids such as, for instance, naturally- occurring plasma, urine, sweat, and blood, as well as artificial plasma, urine, sweat, and blood. The protective coating may additionally protect the underlying antimicrobial coating by not reacting with any proteins occurring in any of the aforementioned fluids. Further, the protective coating may be inert to acidic or alkaline environments, and thus stable at both acidic and basic pHs.

While specific preferred embodiments and examples of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications or alterations, changes, variations, substitutions and equivalents will occur to those skilled in the art without deviating from the spirit and scope of the invention, and are deemed part and parcel of the invention disclosed herein.

Further, the invention should be considered as comprising all possible combinations of every feature described in the instant specification, appended claims, and/or drawing figures which may be considered new, inventive and industrially applicable.

Multiple variations and modifications are possible in the embodiments of the invention described here. Although certain illustrative embodiments of the invention have been shown and described here, a wide range of modifications, changes and substitutions is contemplated in the foregoing disclosure. While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of one or another preferred embodiment thereof. In some instances, some features of the present invention may be employed without a corresponding use of the other features.

Accordingly, it is appropriate that the foregoing description be construed broadly and understood as being given by way of illustration and example only, the spirit and scope of the invention being limited only by the claims which ultimately issue.

Claims

CLAIMS:

1. A method of protecting a substrate, said method comprising:

applying an antimicrobial coating to the substrate; and

applying a protective coating to the protective coating, wherein the protective coating is inert to acid or alkali.

2. The method according to claim 1, wherein the protective coating is inert with respect to natural or artificial bodily fluids.

3. The method according to any of claims 1-2, wherein the protective coating does not react with proteins present in bodily fluids.

4. The method according to any of claims 2-3, wherein the bodily fluids comprise plasma, urine, blood, and/or sweat.

5. The method according to any of claims 1-4, wherein the antimicrobial coating also inhibits fouling on the substrate.

6. The method according to any of claims 1-5, wherein the antimicrobial coating comprises at least one metal, at least one metal oxide, and/or at least one organic antimicrobial compound.

7. The method according to claim 6, wherein the antimicrobial coating comprises at least one metal oxide nanoparticle.

8. The method according to any of claims 1-7, wherein the protective coating comprises carbon and/or silica.

9. The method according to claim 1, wherein the applying the antimicrobial coating step is performed by ultrasonic radiation.

10. The method according to claims 1 or 9, wherein the applying the protective coating step is performed by either spray coating or electron beam physical vapour deposition.

11. The method according to claim 1 , wherein the applying the protective coating step further comprises applying a complete layer of the protective coating over the antimicrobial coating.

12. The method according to claims 1 or 11, wherein the protective coating has a minimum thickness of at least 50 nm.

13. The method according to claims 1 or 11, wherein the protective coating has a maximum thickness of 1 micron.

14. The method according to any of claims 12-13, wherein the protective coating has a thickness of 150-300 nm.

15. The method according to any of claims 6-7, wherein the at least one metal oxide is selected from the group consisting of ZnO, CuO, ZnO doped with Cu⁺² ions, CuO doped with Zn⁺² ions, and mixtures thereof.

16. A method of protecting a substrate coated with an antimicrobial coating, said method comprising:

applying a protective coating to the substrate, wherein the protective coating is inert to acid or alkali.

17. The method according to claim 16, wherein the protective coating is inert with respect to natural or artificial bodily fluids.

18. The method according to any of claims 16-17, wherein the protective coating does not react with proteins present in bodily fluids.

19. The method according to any of claims 17-18, wherein the bodily fluids comprise plasma, urine, blood, and/or sweat.

20. The method according to any of claims 16-19, wherein the antimicrobial coating also inhibits fouling on the substrate.

21. The method according to any of claims 16-20, wherein the antimicrobial coating comprises at least one metal, at least one metal oxide, and/or at least one antimicrobial compound.

22. The method according to claim 21, wherein the antimicrobial coating comprises at least one metal oxide nanoparticle.

23. The method according to any of claims 16-22, wherein the protective coating comprises carbon and/or silica.

24. The method according to any of claims 16-22, wherein the protective coating is chemically inert in both natural urine and artificial urine.

25. A substrate coated with an antimicrobial coating and a protective coating that at least partially covers the antimicrobial coating, the protective coating being inert to natural or artificial bodily fluids.

26. The substrate as claimed in claim 25, wherein the protective coating does not react with any proteins occurring in the natural or artificial bodily fluids.

27. The substrate as claimed in any of claims 25-26, wherein the natural or artificial bodily fluids comprise plasma, urine, blood, and/or sweat.

28. The substrate as claimed in any of claims 25-27, wherein the protective coating comprises carbon, silica, or a mixture thereof.

29. The substrate as claimed in any of claims 25-28, wherein the antimicrobial coating comprises at least one metal oxide.

30. The substrate as claimed in claim 29, wherein the at least one metal oxide is selected from the group consisting of ZnO, CuO, ZnO doped with Cu⁺² ions, CuO doped with Zn⁺² ions, and mixtures thereof.

31. The substrate as claimed in any of claims 25-30, wherein the protective coating has a thickness of between 50 nm and 1 micron.

32. The substrate as claimed in claim 31, wherein the protective coating has a thickness of between 150-200 nm.

33. The substrate as claimed in any of claims 25-30, wherein the substrate is a medical device that comes into contact with urine.

34. The substrate as claimed in claim 33, wherein the substrate is a catheter.

35. A medical tubing coated with at least one layer of an antimicrobial coating and a protective coating that at least partially covers the at least one layer, the protective coating being inert to naturally- occurring bodily fluids.

36. The medical tubing as claimed in claim 35, wherein the at least one layer is a ZnO nanoparticle layer.

37. The medical tubing as claimed in any of claims 35-36, wherein the protective coating comprises carbon, silica, or combinations thereof.

38. The medical tubing as claimed in any of claims 35-37, wherein the at least one layer is adhered to the medical tubing via ultrasonic radiation.

39. The medical tubing as claimed in any of claims 35-38, wherein the protective coating is adhered to the at least one layer via either spray coating or electron beam physical vapour deposition.

40. The medical tubing as claimed in any of claims 35-37, wherein the medical tubing is a urinary catheter.

41. The medical tubing as claimed in claim 36, wherein the ZnO nanoparticle layer is doped with Cu²⁺ ions.

42. The medical tubing as claimed in any of claims 35-39, wherein the protective coating has a thickness of between 50 nm and 1 micron.

43. The medical tubing as claimed in claim 42, wherein the protective coating has a thickness of between 50-300 nm.

44. A protective layer for use in maintaining antimicrobial activity of a substrate coated with an antimicrobial coating, the protective layer being inert to natural or artificial bodily fluids, and the protective coating being inert in acidic and basic pH environments.

45. The protective layer for use according to claim 44, wherein the protective layer is applied on top of the antimicrobial coating.

46. The protective layer for use according to any of claims 44-45, wherein the protective layer comprises carbon and/or silica.

47. A protective layer for use in shielding a coated substrate from natural or artificial bodily fluids, the protective layer being inert in acidic and basic pH environments.

48. The protective layer for use according to claim 47, wherein the coated substrate has antimicrobial and/or antifouling properties.

49. The protective layer for use according to any of claims 47-48, wherein the protective layer comprises carbon and/or silica.

50. The protective layer for use according to any of claims 47-49, wherein the protective layer is applied to a thickness of between 50-300 nm.