Patent Publication Number: US-2011060070-A1

Title: Coating composition comprising an antimicrobial cross-linker

Description:
The invention relates to a coating composition comprising an antimicrobial cross-linker, the use of said coating composition in medical applications and, in particular in a medical device and to a medical device comprising the coating composition. 
     Infections that arise as a result of temporary or permanent implants are some of the most serious and frequent sources of complications that arise from the use of invasive medical devices. During the implantation or insertion procedure of medical articles like hip and knee implants, pacemaker leads, meshes, catheters and vascular devices the mucosal or endothelial or indeed any biological counter surface is often damaged, resulting in microbial infections. Thus in the drive to minimise microbial infections it is important to provide a medical device with antimicrobial properties. 
     Medical devices, such as medical implants, are often provided with hydrophilic coatings, as such coatings feature low absorption of cellular species. Hydrophilic coatings are often formed using a cross-linkable coating composition to avoid the dissolution of the coating components, such as polymers, under wet conditions, e.g. in body fluids. Such release of coating components into the body fluids would be unacceptable. In addition, the mechanical properties of the coatings may be lost, or demolished, due to the high water uptake. 
     Medical devices can be provided with antimicrobial properties by adding antimicrobial agents, as disclosed in several publications. Usually antimicrobial agents, such as silver, quaternary ammonium compounds etc. are added as separate (low molecular) compounds. A disadvantage of this approach is that the antimicrobial agent is not fixed in the medical device and can leach out to the surface of the device, whereby the antimicrobial properties of the device get deteriorate. 
     The aim of the invention is therefore to provide a medical device, in particular a coating on a medical device, comprising a antimicrobial agent that does not leach out to the surface of the device, or at least leaches out to a lesser extent. 
     This can be achieved according to the present invention by providing a coating composition comprising a cross-linker that comprises at least one antimicrobial group, in particular a quaternary ammonium group. Examples of antimicrobial cross-linkers comprised in a coating composition according to the invention are given below. 
     1. Antimicrobial cross-linker formed from di(meth)acrylamide and a primary amine. The primary amine can react with two double bonds: 
     
       
         
         
             
             
         
       
     
     wherein Z represents H or CH 3 ; Y represents CHR 1 , R 1  being H or a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms or derivatives thereof; R, R′ independently represent a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms, preferably a C1-C20 hydrocarbon, more preferably a C1-C20 alkyl or aryl; X represents Cl, Br, or I; W represents N or O; A represents H or a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms, preferably a C1-C20 hydrocarbon, more preferably a C1-C20 alkyl; and n is an integer having a value of at least 1. 
     The primary amine used above is preferably a monoamine, in order to prevent cross-linking during the reaction of the di(meth)acrylamide and the primary amine. 
     2. Antimicrobial cross-linker formed from di(meth)acrylate and a difunctional secondary amine. 
     
       
         
         
             
             
         
       
     
     wherein Z represents H or CH 3 ; Y represents CHR 1 , R 1  being H or a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms or derivatives thereof; P, R, R′, and R″ independently represent a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms, preferably a C1-C20 hydrocarbon, more preferably a C1-C20 alkyl; X represents Cl, Br, or I; W represents N or O; A represents H or a group selected from substituted and unsubstituted hydrocarbons which optionally contain one or more heteroatoms, preferably a C1-C20 hydrocarbon, more preferably a C1-C20 alkyl; and n is an integer having a value of at least 1. 
     In both types of cross-linker n is an integer preferably having a value of 2-100. 
     P. Ferruti et al. (Biomacromolecules, 2001, 2, 1023-1028) have shown that poly(amido amines) are very suitable hydrophilic polymers for medical applications. The synthesis allows the preparation of polymers with polymerizable end groups, which makes them suitable as cross-linker. Another advantage of these polymers is that they are already in the clinical stage. An interesting peculiarity of these polymers is that they have many tertiary amines in their polymer backbone, which can probably be converted into quaternary ammonium groups. This offers a versatile method to make series of antibacterial cross-linkers and/or polymers systems and particularly suitable for hydrophilic applications. 
     Primary and secondary amines that can be used to prepare the antimicrobial cross-linkers are for example primary amine such as methyl amine, ethyl amine, butyl amine, dodecyl amine, 2-hydroxy ethyl amine, allyl amine, 2-mercapto ethyl amine, amino acids such as glycin, alanine, leucine, aspargine, histidine, tyrosine, cystein, secondary amines such as piperazine, 2-methyl piperazine, 2-carboxy piperazine, 1,2-N,N diethyl ethylene diamine, 1,4-N,N dimethyl butyl diamine. 
     The coating composition according to the invention comprises the antimicrobial cross-linker. Preferably, the coating composition further comprises a hydrophilic polymer. 
     In particular, the coating composition may be used for medical applications, more in particular in the manufacture of a coating composition to reduce the risk of infections, for example catheter associated infections, such as catheter associated urinary tract infections and catheter associated blood stream infections, or for the treatment of a disorder selected from the group consisting of complications of the urinary tract, complications of a cardiovascular vessel, kidney infections, blood infections (septicaemia), urethral injury, skin breakdown, bladder stones and hematuria or to prevent infections. 
     The invention further relates to the use of a coating composition according to the invention or a coating obtainable by curing a coating composition according to the invention to reduce bacterial adhesion or to act as an antimicrobial agent. The coating composition or coating may be used in vitro or in vivo. 
     The term “polymer” is used herein for a molecule comprising two or more repeating units. In particular it may be composed of two or more monomers which may be the same or different. As used herein, the term includes oligomers and prepolymers. Usually polymers have a number average weight of about 500 g/mol or more, in particular of about 1000 g/mol or more, although the molar mass may be lower in case the polymer is composed of relatively small monomeric units and/or the number of units is relatively low. The term polymer includes oligomers. A polymer is considered an oligomer if it has properties which do vary significantly with the removal of one or a few of the units. 
     The term “to cure” includes any way of treating the coating composition such that it forms a firm or solid coating. In particular, the term includes a treatment whereby the hydrophilic polymer further polymerises, is provided with grafts such that it forms a graft polymer and/or is cross-linked, such that it forms a cross-linked polymer. 
     In line with common practice, when referred to “a” moiety or “the” moiety (e.g. a compound for instance a (hydrophilic) polymer, a polyelectrolyte, an initiator) this is meant to refer to one or more species of said moiety. 
     Within the context of the invention a coating on the (outer) surface of a medical device, such as a catheter, is considered lubricious if (when wetted) it can be inserted into the intended body part without leading to injuries and/or causing unacceptable levels of pain to the subject. In particular, a coating is considered lubricious if it has a friction as measured on a Harland FTS Friction Tester of 20 g or less at a clamp-force of 300 g and a pull speed of 1 cm/s, preferably of 15 g or less. 
     The term “wetted” is generally known in the art and—in a broad sense—means “containing water”. In particular the term is used herein to describe a coating that contains sufficient water to be lubricious. In terms of the water concentration, usually a wetted coating contains at least 10 wt. % of water, based on the dry weight of the coating, preferably at least 50 wt. %, based on the dry weight of the coating, more preferably at least 100 wt. % based on the dry weight of the coating. For instance, in a particular embodiment of the invention a water uptake of about 300-500 wt. % water is feasible. 
     Within the context of the invention, the dry-out time is the duration of the coating remaining lubricious after the device has been taken out of the wetting fluid wherein it has been stored/wetted. Dry-out time can be determined by measuring the friction in gram as a function of time the catheter had been exposed to air (22° C., 35% RH) on the Harland Friction tester. The dry-out time is the point in time wherein the friction reaches a value of 20 g or higher, or in a stricter test 15 g or higher. 
     The inventors have realised that providing a coating making use of a photo-initiator is advantageous in that it allows the coating of articles comprising a material that is not sufficiently thermally stable to allow thermal curing and/or drying at an elevated temperature. 
     The inventors further contemplate that also for coating an article which is thermally stable, thermal curing/drying may be disadvantageous. It is contemplated that as a result of the heating, one or more additives in the article—in particular one or more plasticizers may migrate to the surface of the article, possibly even into or through the coating, thereby affecting a property of the coating and/or leading to medical complications, in case the article is inside a patient&#39;s body or in contact therewith. For instance, blooming may occur as a result of migration of a plasticizer to the surface of the article. As a coating composition may also be used to provide a coating without needing elevated temperature, such risk is avoided or at least reduced in a method of the invention. 
     It is further contemplated that the photo-curing provides an advantageous polymer network, in particular such network comprising grafts and/or cross-links, with good lubricity and/or wear resistance. 
     The coating composition according to the invention therefore preferably further comprises an initiator, more preferably a photo-initiator. As a photo-initiator, in principle any photo-initiator can be used that is suitable to cure the coating composition in the presence of electromagnetic radiation, in particular UV, visible or IR light. 
     Particularly suitable is a photo-initiator that is soluble in a carrier liquid that is used in the coating composition according to the invention, at the concentration wherein the initiator is present in the coating composition. 
     Particularly suitable is a photo-initiator, capable of performing a photochemical homolytic bond cleavage, such as a Norrish type I cleavage reaction, or a heterolytic bond cleavage, in particular a Norrish type II cleavage. 
     Norrish Type I photo-initiators cause homolytic cleavage of the chromophore directly to generate radicals that initiate polymerization. Norrish Type II photo-initiators generate radicals indirectly by hydrogen abstraction from a suitable synergist, e.g. a tertiary amine. More in detail: free-radical photo-initiators are generally divided into two classes according to the process by which the initiating radicals are formed. Compounds that undergo unimolecular bond cleavage upon irradiation are termed Norrish Type I or homolytic photo-initiators, as shown by formula (1): 
     
       
         
         
             
             
         
       
     
     Depending on the nature of the functional group and its location in the molecule relative to the carbonyl group, the fragmentation can take place at a bond adjacent to the carbonyl group (α-cleavage), at a bond in the β-position (β-cleavage) or, in the case of particularly weak bonds (like C—S bonds or O—O bonds), elsewhere at a remote position. The most important fragmentation in photopinitiator molecules is the α-cleavage of the carbon-carbon bond between the carbonyl group and the alkyl residue in alkyl aryl ketones, which is known as the Norrish Type I reaction. 
     If the excited state photo-initiator interacts with a second molecule (a co-initiator COI) to generate radicals in a bimolecular reaction as shown by formula (2), the initiating system is termed a Type II photo-initiator. In general, the two main reaction pathways for Type II photo-initiators are hydrogen abstraction by the excited initiator or photo-induced electron transfer, followed by fragmentation. Bimolecular hydrogen abstraction is a typical reaction of diaryl ketones. Photo-induced electron transfer is a more general process, which is not limited to a certain class of compounds. 
     
       
         
         
             
             
         
       
     
     Examples of suitable Type I or cleavage free-radical photo-initiators are benzoin derivatives, methylolbenzoin and 4-benzoyl-1,3-dioxolane derivatives, benzylketals, α,α-dialkoxyacetophenones, α-hydroxy alkylphenones, α-aminoalkylphenones, acylphosphine oxides, bisacylphosphine oxides, acylphosphine sulphides, halogenated acetophenone derivatives, and the like. Commercial examples of suitable Type I photo-initiators are Irgacure 2959 (2-hydroxy-4′-(2-hydroxyethoxy)-2-methyl propiophenone), Irgacure 651 (benzildimethyl ketal or 2,2-dimethoxy-1,2-diphenylethanone, Ciba-Geigy), Irgacure 184 (1-hydroxy-cyclohexyl-phenyl ketone as the active component, Ciba-Geigy), Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one as the active component, Ciba-Geigy), Irgacure 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one, Ciba-Geigy), Irgacure 369 (2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one as the active component, Ciba-Geigy), Esacure KIP 150 (poly {2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one}, Fratelli Lamberti), Esacure KIP 100 F (blend of poly {2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one} and 2-hydroxy-2-methyl-1-phenyl-propan-1-one, Fratelli Lamberti), Esacure KTO 46 (blend of poly {2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one}, 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and methylbenzophenone derivatives, Fratelli Lamberti), acylphosphine oxides such as Lucirin TPO (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, BASF), Irgacure 819 (bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine-oxide, Ciba-Geigy), Irgacure 1700 (25:75% blend of bis(2,6-dimethoxybenzoyl)2,4,4-trimethyl-pentyl phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one, Ciba-Geigy), and the like. Also mixtures of type I photo-initiators can be used. For colored (e.g. pigmented) systems, phosphine oxide type photo-initiators and Irgacure 907 are preferred. 
     Preferred photo-initiators are soluble in the carrier liquid or can be adjusted to become soluble in the carrier liquid. Also preferred photo-initiators are polymeric or polymerizable photo-initiators. 
     Good results have been achieved with a Norrish type II initiator. Particular good results have been achieved with benzophenone. Other examples of suitable initiators include hydroxymethylphenylpropanone, dimethoxyphenylacetophenone, 2-methyl-1-4-(methylthio)-phenyl-2-morpholino-propanone-1,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 1-(4-dodecyl-phenyl)-2-hydroxy-2-methylpropan-1-one, diethoxyphenyl acetophenone, and the like. Phosphine oxide photoinitator types (e.g., Lucirin TPO by BASF) such as benzoyl diaryl phosphine oxide photo-initiators may be used. 
     The concentration of the photo-initiator can be determined based upon the efficiency of the initiator, the desired degree of polymerization and the amount of polymer (i.e. the hydrophilic polymer, if present the cross-linker and if present the polymeric polyelectrolyte). 
     Usually, the total initiator concentration is up to 10 wt. %, based on the total weight of the polymer. In particular in case a high dry-out time and/or high lubricity are desired, preferably a relatively low amount of photo-initiator is used, in particular an amount of up to 5 wt. %, more in particular of up to 4 wt. %. Particularly good results have been achieved with an amount of about 2 wt. % or less, for instance about 1 wt. %. 
     Usually the concentration is at least 0.1 wt. %, based on the weight of the polymer. For improved adhesion to the surface of the article and/or for a low amount of extractables, a relatively high concentration may be desired, in particular of at least 0.5 wt. %, more in particular of at least 1.0 wt. %, based on the weight of the polymer. 
     Preferably, in the case of an application as a hydrophilic coating, the coating composition according to the invention further comprises a hydrophilic polymer. As such hydrophilic polymer in principle any polymer may be used that is suitable to provide a lubricious hydrophilic coating. In particular, suitable is such a polymer that is polymerisable, graftable and/or cross-linkable in the presence of a photo initiator. 
     Generally such hydrophilic polymer may have a number average molar mass in the range of about 1 000-5 000 000 g/mol. Preferably, the molar mass is at least, 20 000, more preferably at least 100 000. Advantageously, the molar mass is up to 2 000 000, in particular up to 1 300 000 g/mol. The molar mass is the value as determined by light scattering. 
     The polymer may for instance be a prepolymer, i.e. a polymer comprising one or more polymerisable groups, in particular one or more radically polymerisable groups such as one or more vinyl groups. 
     For providing a cross-linked network, a prepolymer having an average number of reactive groups per molecule of more than 1 is in particular suitable. Preferably, the average number of reactive groups is at least 1.2, more preferably at least 1.5, in particular at least 2.0. Preferably the average number of groups is up to 64, more preferably in the range of up to 15, in particular in the range of up to 8, more in particular up to 7. 
     However, also a polymer which is free of such polymerisable groups may be cured in the presence of a photo-initiator, in particular by the formation of grafts when the coating composition is exposed to light. 
     In preferred embodiment, the coating composition comprises at least one hydrophilic polymer selected from the group consisting of poly(lactams), in particular polyvinylpyrrolidones; polyurethanes; homo- and copolymers of acrylic and methacrylic acid; polyvinyl alcohols; polyvinylethers; maleic anhydride based copolymers; polyesters; vinylamines; polyethyleneimines; polyethylene oxides; poly(carboxylic acids); polyamides; polyanhydrides; polyphosphazenes; cellulosics, in particular methyl cellulose, carboxymethyl cellulose, hydroxymethylcellulose, hydroxypropylcellulose and other polysaccharides, in particular chitosans, hyaluronic acids, alginates, gelatins, chitins, heparins, dextrans; chondroitin sulphates; (poly)peptides/proteins, in particular collagens, fibrins, elastins, albumin; polyesters, in particular polylactides, polyglycolides, polycaprolactones; and polynucleotides. Preferably, the coating composition comprises at least one polymer selected from polyvinylpyrrolidone, polyethylene oxide (PEO/PEG) and polypropylene oxide. 
     In particular for polyvinylpyrrolidone (PVP) and polymers of the same class, a polymer having a molar mass corresponding to at least K15, more in particular K30, even more in particular K80 is preferred. Particular good results have been achieved with a polymer having a molar mass corresponding to at least K90. Regarding the upper limit, a K120 or less, in particular a K100 is preferred. The K-value is the value as determinable by the Method W1307, Revision 5/2001 of the Viscotek Y501 automated relative viscometer. This manual may be found at www.ispcorp.com/products/hairscin/index — 3.html. 
     The concentration of the hydrophilic polymer in the (dry) coating is usually at least 1 wt. %, in particular at least 2 wt. %, preferably at least 10 wt. %, based upon the total weight of the dry coating. Usually the concentration is up to 90 wt. % although its concentration may be higher. Preferably, the concentration is up to 80 wt. %, in particular up to 70 wt. %, up to 60 wt. % or up to 50 wt. %. 
     In the coating, the presence of a polyelectrolyte (which may be a further hydrophilic polymer) is preferred for its beneficial effect on the dry-out time. The use of a compound capable of forming a radical upon radiation has in particular been found advantageous in improving the lubriciousness/dry-out time of a coating comprising a polyelectrolyte, in particular a coating comprising both a polyelectrolyte and a hydrophilic polymer mentioned above. 
     Herein a polyelectrolyte is defined as a polymer, which may be linear, branched or cross-linked, composed of macromolecules comprising constitutional units, in which between 5 and 100% of the constitutional units contain ionic or ionisable groups, or both. A constitutional unit may be a repeating unit, e.g. a monomer. 
     The polyelectrolyte preferably has a number average molar mass in the range of 1 000 to 5 000 000 g/mol, as determined by light scattering. 
     Examples of ionic or ionisable groups that may be present include amine groups, ammonium groups, phosphonium groups, sulphonium groups, carboxylic acid groups, carboxylate groups, sulphonic acid groups, sulphate groups, sulphinic acid groups, phosphonic acid groups, phosphinic acid groups and phosphate groups. 
     Preferably a polyelectrolyte is selected from the group consisting of (salts of) homopolymers and copolymers of acrylic acid, methacrylic acid, acrylamide, maleic acid, sulfonic acid, styrenic acid, fumaric acid, quaternary ammonium salts and mixtures and/or derivatives thereof. 
     If present, the concentration of the polyelectrolyte is usually in the range of 1 to 90 wt. %. Preferably it is at least 5 wt. %, in particular at least 10 wt. %. Preferably the concentration is up to 50 wt. %, more preferably up to 30 wt. %. The weight percentages are based upon the dry weight of the coating. 
     The polyelectrolyte is preferably present in combination with a hydrophilic polymer that is essentially free of ionic groups; such as PVP or another non-ionic/ionisable hydrophilic polymer mentioned above. Herein the other polymer may serve as a hydrophilic supporting network for the polyelectrolyte. An advantage thereof is an increased stability of the coating. In particular the tendency of the polyelectrolyte to leak out of the coating is thus reduced. Further, a combination of two or more of such polymers is advantageous with respect to both lubricity (in particular smoothness) and dry-out time. 
     The weight to weight ratio of polyelectrolyte to other hydrophilic polymer is preferably in the range of 1:90 to 9:1, more preferably 1:30 to 1:1, even more preferably 1:10 to 1:5. 
     Optionally one or more additives may be present in a coating composition respectively coating of the invention. Such additives may in particular be selected from antioxidants, surfactants, UV-blockers, stabilisers such as anti-sagging agents, discolourants, lubricants, plasticizers, organic antimicrobial compounds, pigments, and dyes. Such components may be selected from those known in the art, e.g. the prior art identified above. If present, the total concentration of such additives is usually less than 10 wt. % based on dry weight, in particular 5 wt. % or less. 
     Suitable antioxidants in particular include anti-oxidative vitamins (such as vitamin C and vitamin E) and phenolic antioxidants. 
     The surfactant may be an ionic (anionic/cationic), non-ionic or amphoteric surfactant. Examples of ionic surfactants include alkyl sulphates (such as sodium dodecylsulphates), sodium cholate, bis(2-ethylhexyl)sulphosuccinate sodium salt, quaternary ammonium compounds, such as cetyltrimethylammonium bromide or chloride, lauryldimethylamine oxide, N-lauroylsarcosine sodium salt and sodium deoxycholate. Examples of non-ionic surfactants include alkylpolyglucosides, branched secondary alcohol ethoxylates, octylphenol ethoxylates. If present, the surfactant concentration is usually 0.001-1 wt. %, preferably 0.05-0.5 wt. % of the liquid phase. 
     The coating composition further comprises a carrier liquid in a sufficient amount to disperse or dissolve the other components of the coating composition. The carrier liquid concentration is usually at least 68 wt. %, preferably at least 75 wt. %, more preferably at least 80 wt. %, even more preferably at least 85 wt. % of the total weight of the composition. In view of handling properties (low viscosity) and/or in order to facilitate the application of the composition such that a coating with the desired thickness is obtained, the amount of solvent in the composition is preferably relatively high. For that reason the total solids content is preferably 20 wt. % or less. 
     The carrier liquid may be a single solvent or a mixture. It is chosen such that the polymers can be dissolved or at least dispersed therein. In particular for dissolving or dispersing the hydrophilic polymer well, it is preferred that the carrier liquid is a polar liquid. In particular, a liquid is considered polar if it is soluble in water. Preferably it comprises water and/or an organic liquid soluble in water, preferably an alcohol, more preferably a C1-C4 alcohol, in particular methanol and/or ethanol. In case of a mixture, the ratio water to organic solvent, in particular one or more alcohols, may be in the range of about 25:75 to 75:25, in particular 40:60 to 60:40, more in particular 45:55 to 55:45. 
     As described above, the invention further relates to a method for coating an article and to a coated article. In principle, the coating composition can be used to provide any article with an antimicrobial coating. In particular, the coating composition may be used to coat an article and the article is a medical device. More in particular, the article may be intended for use in an orifice of a subject, such as the ear, the mouth, the nose or the urethral tract. 
     Preferred coated articles of the invention include catheters, endoscopes, laryngoscopes, tubes for feeding or drainage or endotracheal use or oesophageal use, guide wires, condoms, gloves, wound dressings, contact lenses, implants, extracorporeal blood conduits, bone screws, membranes (e.g. for dialysis, blood filters, devices for circulatory assistance), sutures, fibers, filaments and meshes. 
     The antimicrobial coating may be present on an inner surface (in case of a hollow article, such as a tube) and/or an outer surface. In view of providing an antimicrobial function, it is preferred that at least the surface or surfaces which are intended to be in direct contact with a body tissue and/or a body fluid are provided with the antimicrobial lubricious coating comprising the antimicrobial cross-linker according to the invention. 
     The surface to be coated can in principle be composed of any material, in particular of any polymer having satisfactory properties for the purpose of the article. Suitable polymers in particular include PVC, polytetrafluorethylene (PTFE, e.g. Teflon®), latex, silicone polymers, polyesters, polyurethanes, polyamides, polycarbonates, polyolefines, in particular ultra high molecular weight polyethylene, and the like. 
     If desired, the surface can be pre-treated in order to improve adherence of the antimicrobial coating, for instance a chemical and/or physical pre-treatment. Suitable pre-treatments are known in the art for specific combinations of materials for the surface of the article and the hydrophilic polymer. Examples of pre-treatments include plasma treatment, corona treatment, gamma irradiation, light irradiation, chemical washing, polarising and oxidating. 
     In an embodiment, the surface of the article is first provided with a primer layer, upon which the antimicrobial coating is applied to provide a coated article according to the invention. For instance, a primer layer as described in WO 06/056482, of which the contents with respect to the primer layer are incorporated herein by reference. 
     Application of the coating composition of the invention may be done in a manner per se. Curing conditions can be determined, based on known curing conditions for the photo-initiator and polymer or routinely be determined. 
     In general, curing may be carried out at ambient temperature (about 25° C.) or below, although in principle it is possible to cure at an elevated temperature (for instance up to 100° C., up to 200° C. or up to 300° C.) as long as the mechanical properties or another property of the article and the coating are not adversely affected to an unacceptable extent. A reason for curing at an elevated temperature may be an improved adherence of the coating to the surface of the article. 
     Intensity and wavelength of the electromagnetic radiation can routinely be chosen based on the photo-initiator of choice. In particular, a suitable wavelength in the UV, visible or IR part of the spectrum may be used. 
     The invention will now be illustrated by the following examples. 
    
    
     EXAMPLE 
     Preparation of an Antimicrobial Cross-Linker According to the Invention 
     2,2′-bis(acrylamino) acetic acid sodium salt (22.0 g, 0.1 mol) was dissolved in 50 ml water. The solution was purged with nitrogen. 2-methylpiperazine (2.5 g, 25 mmol) was added and the mixture was flushed once more with nitrogen. The reaction mixture was kept at 25° C. and left for 5 days. 
     Subsequently, the mixture was diluted with water and the product was purified by dialysis and finally recovered by freeze drying. 
     The polymer (5 g) and 0.5 g of methyl bromide were dissolved in 25 ml dimethyl formamide (DMF) and heated to 80° C. for 1 hour. After cooling down the mixture to room temperature the solution was extracted three times with 25 ml of diethyl ether to remove the excess of methyl bromide. To this DMF solution 40 g of poly(vinyl pyrolidone) (Mw 1.3×10 6  g/mol) and 1 wt % of benzophenone with respect to the solid content was added, and this mixture was applied on polyurethane test samples of 5×5 cm, in a 25 μm thick layer. The layer was cured under UV light for 5 minutes. 
     The cured test samples were evaluated in the JIS Z2801 antibacterial test and it was shown that no bacterial growth was observed.