Antimicrobial Polymers

www.advhealthmat.de www.MaterialsViews.com REVIEW Antimicrobial Polymers Anjali Jain, L. Sailaja Duvvuri, Shady Farah, Nurit Beyth, Abraham J. Domb,* and Wahid Khan* resistance further complicates the situation.[1,2] Hence, it is necessary to maintain these areas free from contamination. Disinfectants such as hypochlorite, hydrogen peroxide, quaternary ammonium compounds, silver salts or other reactive oxygen species were tried, but their short action duration and environmental safety limit their use.[3] At the same time, efforts were made to develop new macromolecules with antimicrobial properties and structural modification of known polymers to attain 1 desirable biological and physicochemical properties.[4] Antimicrobial polymers are materials capable of killing/inhibiting the growth of microbes on a surface or surrounding environment. They have either an inherent capacity to display antimicrobial activity such as chitosan, compounds with quaternary nitrogen groups, halamines, and poly-ε-lysine (ε-PL), or they can be a polymer acting as a backbone to incorporate small biocides and antibiotics to display their activity. Bonilla et al. provided a classification of the different antimicrobial materials in different categories: a) exhibit antimicrobial activity by themselves; b) those whose biocidal activity is conferred through their chemical modification; c) those that incorporate antimicrobial organic compounds with either low or high molecular weight (Mw); and d) those that involve the addition of active inorganic systems.[5] Timofeeva et al. have summarized the mechanism of action of selected antimicrobial polymers and non-leaching microbicidal surfaces, and 1 factors influencing their activity and toxicity.[6] Antimicrobial polymers currently being studied involve substituted/modified natural polymers, antimicrobial polymers containing several biocide units attached to the backbone, polymers with a terminal satellite biocide unit, polymer–antibiotic composite, and polymer–inorganic antimicrobial composites. This Review focuses on major classes of antimicrobial polymers, their mechanism of action, design requirements, commercial applications and clinical status. Better health is basic requirement of human being, but the rapid growth of harmful pathogens and their serious health effects pose a significant challenge to modern science. Infections by pathogenic microorganisms are of great concern in many fields such as medical devices, drugs, hospital surfaces/furniture, dental restoration, surgery equipment, health care products, and hygienic applications (e.g., water purification systems, textiles, food packaging and storage, major or domestic appliances etc.). Antimicrobial polymers are the materials having the capability to kill/inhibit the growth of microbes on their surface or surrounding environment. Recently, they gained considerable interest for both academic research and industry and were found to be better than their small molecular counterparts in terms of enhanced efficacy, reduced toxicity, minimized environmental problems, resistance, and prolonged lifetime. Hence, efforts have focused on the development of antimicrobial polymers with all desired characters for optimum activity. In this Review, an overview of different antimicrobial polymers, their mechanism of action, factors affecting antimicrobial activity, and application in various fields are given. Recent advances and the current clinical status of these polymers are also discussed. 1. Introduction Contamination by microorganisms is greatly concerns numerous human health associated sectors, such as hospitals and dental equipment, food packaging and storage, water purification systems, and household sanitation. The presence of harmful microorganisms in these areas has generated a variety of infections and diseases. Rapid development of antibiotic A. Jain, L. S. Duvvuri, Dr. W. Khan Department of Pharmaceutics National Institute of Pharmaceutical Education and Research (NIPER) Hyderabad 500037, India E-mail: wahid@niperhyd.ac.in Dr. S. Farah, Prof. A. J. Domb School of Pharmacy-Faculty of Medicine The Hebrew University of Jerusalem and Jerusalem College of Engineering (JCE) Jerusalem 91120, Israel E-mail: avid@ekmd.huji.ac.il Dr. N. Beyth Department of Prosthodontics, Faculty of Dentistry The Hebrew University-Hadassah Jerusalem 91120, Israel DOI: 10.1002/adhm.201400418 Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 2. Polymers with Inherent Antimicrobial Activity Different polymers with antimicrobial spectrum are discussed in this section in detail and the representative polymers from each category are summarized in Table 1. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1 www.advhealthmat.de REVIEW www.MaterialsViews.com 2.1. Natural Polymer 2.1.1. Chitosan Chitosan, the most widely explored polymer in the biomedical field, was discovered by Rouget in 1859. It is a linear polycationic hetero polysaccharide copolymer of β-1,4-linked D-glucosamine and N-acetyl-D-glucosamine, which is obtained by partial alkaline N-deacetylation of chitin. The number of amine groups in chitosan plays a major role to tailor physical, chemical and biological properties of the biopolymer. The amine group is the most important site for modification and provides versatility for more applications.[7–9] The broad-spectrum antibacterial activity of chitosan was first proposed by Allan.[10] Antimicrobial activity of chitosan has been demonstrated against many bacteria, filamentous fungi and yeasts. Bacteria appears to be generally less sensitive than fungi to the antimicrobial action of chitosan.[11,12] The bactericidal efficacy of chitosan depends upon polymer related factors such as positive charge density, Mw, concentration, hydrophilic/hydrophobic characteristic, chelating capacity, and the physical state of the polymer. Other factors such as ionic strength in medium, pH, temperature, reactive time and type microbe also play some role in the exertion of bactericidal efficacy of this polymer.[13] These factors are discussed in detail in other section of this Review. Different mechanisms for the anti-bacterial activity of chitosan are proposed, such as electrostatic interaction, chelating effect and hydrophobic effect (Figure 1). When the pH of the medium is less than pKa, protonation of amino groups occurs, and electrostatic interaction between the polymer and the bacterial cell wall becomes the predominant mechanism of action. When pH is higher than pKa, significant protonation is not observed; hydrobhobic interaction and chelation effects result in antimicrobial activity of chitosan. These two effects provide a reasonable explanation for a higher activity of chitosan derivatives under neutral or higher pH condition than native chitosan.[14,15] Gram negative bacteria are more sensitive to chitosan than gram positive bacteria, which can be explained by nature of their outer membrane. Gram negative bacteria possess more negative charge on the surface. These charges are stabilized by divalent metal ions[16] while gram positive bacteria contain mainly lipoteichoic acid that is polyanionic in nature and responsible for structural stability of cell walls. Gram positive bacteria display electrostatic interaction as a main mechanism. Chelation along with electrostatic interaction causes activity against gram negative bacteria. The factors described above are responsible for the initial interaction of chitosan with the bacterial cell wall. After attachment to a microbial cell, chitosan with different Mw display different mechanism of action. Low Mw water-soluble chitosan and its ultrafine nanoparticles penetrate the cell wall of bacteria and combine with DNA, which directly affects synthesis of mRNA and DNA transcription;[17] high Mw water-soluble chitosan and solid chitosan interact with the cell surface and alter cell permeability and solute transport across the cell.[18,19] Raafat et al. attempted to determine the antimicrobial activity of chitosan using a combination of approaches such as in vitro assays, killing kinetics, cellular leakage measurements, membrane 2 wileyonlinelibrary.com Anjali Jain is currently pursuing PhD from National Institute of Pharmaceutical Education and Research, Hyderabad. She worked on development of taste masked directly compressible formulations by spray drying during her master’s studies. Her area of interest include polymer and lipid based nanoformulations for transdermal delivery, nose to brain delivery, gene delivery and reformulation of traditional dosage forms. Abraham J. Domb is Professor for Medicinal Chemistry and Biopolymers at the Institute of Drug Research, School of Pharmacy-Faculty of Medicine, The Hebrew University of Jerusalem, Israel. He earned Bachelor degrees in Chemistry, Pharmacy and Law studies and PhD degree in Chemistry from Hebrew University. He did his postdoctoral training at Syntex Inc. CA, USA and MIT and Harvard Univ. Cambridge USA and was R&D manager at Nova Pharm. Co. Baltimore USA during 1988-1992. During 2007-2012 he headed the Division of Identification and Forensic Sciences of the Israel Police. His primary research interests are in biopolymers, controlled drug delivery, cancer therapy, nanoparticulate systems, and forensic sciences. Wahid Khan did his Master’s and PhD in Pharmaceutics at the National Institute of Pharmaceutical & Educational Research (NIPER) Mohali India and worked with Prof. Abraham J. Domb in The Hebrew University of Jerusalem, Israel for his post doctoral research. Currently, he is working as Assistant Professor in Department of Pharmaceutics, NIPER, Hyderabad, India. He is having experience of working in areas of drug delivery, drug targeting, nanomedicine and biodesign of implantable medical devices. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com Polymer and Structure Mechanism of action Chitosan Poly-ε-lysine (ε-PL) REVIEW Table 1. Representative polymers with inherent antimicrobial activity. Application Interaction between positively charged chitosan molecules and negatively charged microbial cell membranes leads to the leakage of protein and other intracellular constituents. Activity is function of pH, i.e., at a pH less than pKa, protonation of amino groups result in electrostatic interaction between polymer and bacterial cell wall, while at a pH higher than pKa, hydrobhobic interaction and chelation effects result antimicrobial activity of chitosan. As thickener, emulsifier and stabilizer, haemostatic and anticoagulant, fungi static and antibacterial coating for fruit, waste water treatment. Electrostatic adsorption on to the microbial cell surface followed by the stripping of the outer membrane which resulted physiological damage to cells and death of microorganism. Food preservation, drug and gene delivery, coating material for microchips, interferon inducer, dietary agent, superabsorbent, hydro gel, disinfectant and mild emulsifier. Electrostatic interaction between positively charged QAC and negatively charged bacterial membrane followed by integration of the hydrophobic tail of the QAC into the bacterial hydrophobic membrane core to denature structural proteins and enzymes. Thus cationic charge on the quaternary ammonium/phosphonium groups kill bacteria by damaging the outer membrane of gram negative/cell wall of gram positive bacteria and cytoplasmic membrane, followed by cell lysis. Preservatives in topical ointments, cosmetics, mouthwash, alcohol based hand-rubs, antifouling agents in building materials or finishing surfaces, surfactants, waste water treatment. Polyethylenimine results cell membrane rupture as a result of electrostatic interaction between cationic polyethyleneimine and negatively charged bacterial outer cell membrane. Detergents, adhesives, water treatment agents and cosmetics, liquid clarifier, immobilized carrier for enzymes, chelating agent, antimicrobial finishing of textiles. Polyguanidinium salts inhibit bacterial growth through adhesion to the negatively charged bacterial cell wall and subsequent disruption of Ca2+ salt bridges necessary for bacterial plaque adhesion or bacterial cell death. As biocide in water treatment, to prevent bio-fouling of medical equipments such as catheters, breathing tubes or stents, to impart antiseptic properties to rubber items, papers, mineral and carbon sorbents. Specific action of oxidative halogen (Cl+ or Br+) targeted at thiol groups or amino groups in proteins biological receptor upon direct contact with a cell, leading to cell inhibition or cell inactivation. Water disinfection, paints, healthcare and textiles, biocidal coatings on various dental and medical surfaces. Quaternary Ammonium Compounds (QAC) Polyethylenimine (Branched) Polyguanidines N-halamines potential estimations, electron microscopy and transcriptional response analysis. They suggest that the binding of chitosan to cell wall polymers triggers secondary cellular effects, affects membrane-bound energy generation pathways, impairs the electron transport chain, and thus forces the cells to shift to anaerobic energy production, ultimately leading to dysfunction of the whole cellular apparatus.[20] Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 2.1.2. Poly-ε-lysine Poly-ε-lysine (ε-PL) is a naturally occurring cationic homopolyamide of L-lysine (n = 25–30), having amide linkage between ε-amino and α-carboxyl groups. Its first appearance was reported in filamentous bacterium Streptomyces albulus during the screening of Dragendorff’s reagent.[21] Later, Streptomycetaceae © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 3 www.advhealthmat.de REVIEW www.MaterialsViews.com Figure 1. Mechanism of action of different antimicrobial polymers. A) Antimicrobial mechanism of chitosan, which involves- A1) electrostatic interaction, A2) chelation, A3) hydrophobic interaction. Other antimicrobial polymers such as polyethyleneimine, polyguainidine, quaternary ammonium compounds and ε-PL also acts through mechanism (A1). B) Mechanism of action of N-halamine which acts through release of active halogens. and ergot fungi species were determined to be responsible for the production of ε-PL.[22] ε-PL is a thermo-stable, biodegradable, water soluble, edible and nontoxic polymer. At alkaline pH, ε-PL in β-sheet conformation converts to antiparallel β-sheet at pH above the pKa of the α-amino group, while at acidic pH an electro statically expanded conformation is observed.[23] When compared to alpha-poly-L-lysine (n = 50), which is primarily used in gene delivery applications, ε-PL is more effective against gram-positive and gram-negative bacteria at concentrations of 1–8 µg/mL.[24] It also displays activity against spores of Bacillus coagulans, Bacillus stearothermophilus and Bacillus subtilis (B. subtilis) at concentrations of 12.5l µg/ mL, 2.5l µg/mL, and 12.5l µg/mL, respectively.[25] Antimicrobial activity of ε-PL can be explained by electrostatic adsorption on to the microbial cell surface followed by the stripping of the outer membrane, resulting in physiological damage to cells followed by death of the microorganism.[26] Kido et al. describe the role of ε-PL in the inhibition of human and porcine pancreatic lipase activity in substrate containing bile salts and phosphatidylcholine. This suggest its role to suppress dietary fat absorption from the small intestine and its use as a dietary agent for obese patients.[27] Studies show wide applicability in food preservation, drug and gene delivery, as a coating material for microchips, an interferon inducer, dietary agent, super absorbent, hydrogel, disinfectant and mild emulsifier.[28] 2.2. Nitrogen Containing Polymers 2.2.1. Linear Quaternary Ammonium Polymer Quaternary ammonium compounds (QACs) are comprised of nitrogen (N) containing compounds in which N is attached to four different groups by covalent bond. They are represented 4 wileyonlinelibrary.com by the general formula N+R1R2R3R4.X−, where R can be a hydrogen atom, a plain alkyl group or an alkyl group substituted with other functional groups, and X represents an anion. Generally, long-chain QAC with 8–18 carbon atoms possess good germicidal activity. Important representatives of this class are benzalkonium chloride, stearalkonium chloride and cetrimonium chloride.[29] The antimicrobial activity of QACs is a function of the N-alkyl chain length and hence lipophilicity. Compounds with alkyl chain length 12–14 of alkyls provide optimum antibacterial activity against gram-positive bacteria, while alkyls group with 14–16 carbon show better activity against gram-negative bacteria.[30] Initial interaction between QACs and bacterial wall results from electrostatic interaction between positively charged QACs and negatively charged bacterial membranes, followed by the integration of the hydrophobic tail of the QAC into the bacterial hydrophobic membrane core, where they denature structural proteins and enzymes. QACs also induce dose and time dependent ultrastructural changes in antibiotic resistant Escherichia coli (E. coli).[31] Cross-linked poly(ethylene glycol) based polymers are considered as benchmark protein-resistant coating materials. However, phosphonium- and ammonium functionalized polymers display higher inherent chemical stability than polyethylene glycol (PEG)-based polymers, since they are much more resistant to reduction–oxidation and acid–base reactions than oligo(ethylene oxide) groups. These properties potentially allow them to be used in medical devices that need to be proteinresistant over long period of time, or in separation systems that operate in or require chemical cleaning under harsh conditions. Results of dynamic membrane fouling experiments show that slightly cross-linked poly[trimethyl-(4-vinyl-benzyl)-phosphonium bromide] displays exceptional protein fouling resistance and better water transport properties than a representative © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com 2.2.2. Polymer with Ring Containing Nitrogen Similar to QACs, quaternary pyridinium are compounds with a heterocyclic ring containing nitrogen atom also exhibit germicidal activity. They act through a mechanism similar to QACs. Li et al. synthesized a series of insoluble pyridinium-type polymers with different compositions; they are effective against gram-positive and gram-negative bacteria and yeasts, except B. subtilis and fungi. The antibacterial activity is a function of the pyridinium group in the polymer chain; it and captures bacterial cells in a living or dead state by adsorption or adhesion.[34] These compounds display little toxicity profile with median lethal dose (LD50) of 2330 mg/kg.[35] Another family of antimicrobial polymer with aromatic/heterocyclic groups is imidazole derivatives. Imidazole, possesses the ability to form hydrogen bond with drugs and proteins while its alkylated form (imidazolium) has the ability to aggregate electro statically despite losing the hydrogen bond-forming ability of free imidazole. They are chemically stable, biocompatible and show improved biodegradability.[36] Copolymers of N-vinylimidazole and phenacyl methacrylate were synthesized; they display strong antimicrobial activity against various bacteria, fungi and yeast.[37] 2.2.3. Polyethylenimine Polyethyleneimine (PEI) is a synthetic, nonbiodegradable, cationic polymer containing primary, secondary and tertiary amino functions. It is found in both branched and linear forms that can be synthesized by acid-catalyzed polymerization of aziridine and ring opening polymerization of 2-ethyl-2-oxazoline followed by hydrolysis respectively.[38,39] Due to the abundance of reactive amino groups, PEI was tried with a wide range of chemical modifications that exhibit desirable physicochemical properties. Initially un-substituted PEIs were tested to determine its antimicrobial property by covalent attachment on glass material, but they did not show any reduction in microbial count compared with an untreated glass surface. Later, it was realized that hydrophobicity and positive charge density are primary requirements for antimicrobial activity and incorporation; alkyl groups were used to potentiate both of these effects.[40] Attempts were also made to attach N-alkyl-PEI to various organic and inorganic, natural and synthetic, macroscopic and nano scaled, monolithic and porous surface materials including commercial plastics, textiles, and glass. These immobilized surfaces resulted in almost 100% inactivation of both water borne and airborne bacteria, and fungi, including pathogenic and antibiotic-resistant strains without any report of emergence of resistance. Cell membrane rupture was reported as a main mechanism for antibacterial action. These surfaces are Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 nontoxic for mammalian (monkey kidney) cells.[41] N-alkylated PEI immobilized over different woven textiles (cotton, wool, and polyester) also exhibit strong bactericidal activity against several airborne gram-positive and gram-negative bacteria. Mw of PEI poses a significant effect on activity. High Mw exhibits excellent antimicrobial activity; low Mw PEI displays negligible activity.[42] Substituted PEIs were also used against Candida albicans (C. albicans), presenting a major challenge for the safety of prosthesis deterioration in laryngectomized patients. For this purpose dimethylaminoethyl methacrylate and PEI bonded surfaces show up to 92% reduction in bacterial growth. These are promising materials for the coating of medical devices.[43] REVIEW PEG-based polymer coating.[32] Antimicrobial polymers with only one biocide end group on polymeric backbone have been developed. These polymers were synthesized by cationic ringopening polymerization of 2-alkyl-1,3-oxazolines,terminating the macromolecule with a cationic surfactant.[33] QACs show wide applications as preservatives in topical ointments, cosmetics, mouthwash, alcohol based hand-rubs, antifouling agents in building materials, and finishing for surfaces. 2.2.4. Polyguanidines Polyguanidines and polybiguanides represent an important class of antimicrobial polymers because of their high water solubility, excellent biocidal efficiency, wide antimicrobial spectrum and non-toxicity. Acrylate monomers with pendant biguanide groups display good antimicrobial action due to electrostatic interaction with cell membranes. They display higher antibacterial activity against gram positive bacteria than gram negative bacteria. This is due to less complicated structure of gram positive bacteria which allow penetration of high Mw polymeric biocides.[44] Zhang et al. synthesized polyhexamethylene guanidine stearate and polyhexamethylene biguanidine stearate using the precipitation reaction. These polymers are heat stable and show an minimum inhibitory concentration (MIC) of less than 200 µg/mL.[45] Albert et al. synthesized a series of different oligomeric guanidines by polycondensation of guanidinium salts and four different diamines under various conditions. The compounds of these series are linear in structure and can be recognized by termination with one guanidine and one amino group (type A), two amino groups (type B), or two guanidine groups (type C), respectively. Antimicrobial activity against many microorganisms was studied. An average molecular mass of about 800 Da is necessary for efficient antimicrobial activity.[46] 2.2.5. Poly(ionic liquid)s Polymeric ionic liquids, also called poly(ionic liquid)s (PILs) were first reported by Ohno and Ito in 1998.[47] These are polymers prepared by polymerization of ionic liquid monomers; however, PILs are not liquid but solid. Ionic liquid monomers are low-melting organic salts consisting of ammonium, phosphonium, imidazolium functionality.[48] PILs have emerged as a new class of functional polymer materials with unique properties of molecular ionic liquids and specific properties of polymers, such as film formation and processibility. The antimicrobial behavior is an important characteristic of PILs, especially; imidazolium, pyridinium and quaternary ammonium based ionic liquids have shown significant activities against gram-positive, gram-negative bacteria, fungi and algae. The biological properties of ionic liquids can be easily altered by varying the cationic and anionic components.[49] Qian et al. designed high-density PIL brushes based on imidazolium salts and grafted them to TiO2 surface. The coating thickness was 80 nm and these PIL brushes were found to © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 5 www.advhealthmat.de REVIEW www.MaterialsViews.com resist adhesion of Chlorella spores. The effect of counter-anions on antimicrobial activity of PIL brushes was also studied and PILs containing hexafluorophosphate anion showed excellent anti-bacterial properties against E. coli and Staphylococcus aureus (S. aureus) as compared to pristine TiO2 nanoparticles.[50] Alberto et al. synthesized imidazolium ionic liquids containing selenium and found them effective against algae.[51] Similarly, PILs with 1-alkyl-3-methylimidazolium chloride were found to display broad spectrum antibimicrobial activity.[52] 2.3. Halogen-Containing Compounds 2.3.1. Halogen Attached to Nitrogen Atom N-halamine compounds contain one or more nitrogen–halogen covalent bonds that are usually formed by halogenation of imide, amide, or amine groups, which providing stability and slow release free active halogen species into the environment.[53] These compounds were introduced by Kovacic and coworkers in 1969.[54] The most common halogen used in these compounds is chlorine, but the activity of other halogens like bromine and iodine has also been reported. These oxidizing halogens promote the direct transfer of an active element to the biological target site or through dissociation to free halogen in aqueous media. These reactive free halogens lead to inhibition or inactivation of a microbial cell (Figure 1).[55] N-halamines display long-term stability in both aqueous solution and under dry conditions; this is preferable to inorganic halogens (e.g., chlorine or bromine). They are effective against a broad spectrum of microorganisms and are environmentally friendly and safe to human health. N-halalmine antibacterials have been synthesized by the covalent binding of N-halamine precursors onto target polymers, which are converted to an N-halamine structure upon halogenation and provide potent antimicrobial activity against a broad range of microorganisms.[56,57] Most common precursors used for this purpose are hydantoin (imidazolidine-2,4-dione) and dimethylhydantoin. The unique property of N-halamines is a renewable nature, which allows them to be charged repeatedly by reaction with chlorine or bromine donor compounds such as sodium hypochlorite, sodium hypobromite, trichloroisocyanuric acid or sodium dichlorocyanurate. Sun et al. synthesized rechargeable N-halamine polymeric biocides containing Imidazolidin-4-one derivatives. These derivatives were provided with regular chlorine bleach treatment to exhibit antibacterial properties. The material showed excellent properties against E. coli.[58] N-halamine biocidal coated onto cotton fabric via a layer-by-layer assembly technique has also been evaluated. Biocidal activity was introduced by applying household bleach treatment. This coating is stable against washing and exposure to UVA light and within 15 min results in complete inactivation of S. aureus and E. coli.[59] N-halamines can be used in many fields such as water disinfection,[60] paints,[61] healthcare,[62] textiles,[63] and biocidal coatings.[64] 2.3.2. Halogen Atom Attached to Other Atoms Halogen containing polymers constitute a large category of antimicrobial compounds. Among them fluorine-containing 6 wileyonlinelibrary.com polymers are of particularly interest due to their low polarizability, strong electro-negativity, high chemical, thermal and weather resistance, and water/oil repellency as well as low dielectric constant and extremely low surface energy. Caillier et al. synthesized polymerizable semi-fluorinated gemini surfactants, with quaternary ammonium groups such as polar heads and an acrylic function as the polymerizable moiety. Their antibacterial and antifungal properties have been evaluated against Pseudomonas aeruginosa (P. aeruginosa), S. aureus, C. albicans, and Aspergillus niger and results suggest significant antibacterial activity against both gram positive and gram negative bacteria.[65] Similarly, poly(acrylated quinolone) bearing a fluorine atom displays remarkable antimicrobial activity against E. coli, S. aureus, B. subtilis and Micrococcus luteus.[66] 3. Chemically Modified Polymer to Induce Antimicrobial Activity These are polymers possessing negligible or no antibacterial activity on their own, but they are modified by attachment of active groups or compounds to induce antimicrobial activity. These polymers are described under the headings of polymers containing active pendent groups and polymers attached with a) inorganic antimicrobial agents or b) organic antimicrobial agents. 3.1. Polymer-Containing Active Pendent Groups 3.1.1. Quaternary Ammonium as Pendent Group Most of the known cationic quaternary polyelectrolytes employed as antimicrobial polymers are acrylic or methacrylic derivatives, and a large number of them are synthesized from commercial methacrylic monomers such as 2(dimethylamino) ethyl methacrylate. These polymers provide wide structural versatility by the alteration of hydrophobicity, Mw, surface charge and other parameters.[67] Kuroda et al. synthesized several series of amphiphilic copolymers containing polymethacrylate and polymethacrylamide platforms with hydrophobic, cationic side chains. The researchers performed systematic research to obtain anon-hemolytic antimicrobial polymer by varying the nature of the hydrophobic groups, polymer composition and length. Primary, tertiary amine or quaternary ammonium groups in the side chains were used as the source of cationic charge in each copolymer series. This research shows that the nature of amine side chains as well as the hydrophobic nature of polymers are key determining factors in optimal antimicrobial activity and reversible protonation of the amine groups.[68,69] Another important class of polymers is polysiloxanes, the linear polymers of silicon oxide. These polymers offer specific advantages of high flexibility and amphiphilicity, and hence they have attracted considerable attention as antimicrobial polymers when attached to quaternary ammonium salt groups. Flexibility helps in better interaction between quaternary groups and the microorganism, while amphiphilic nature augments the concentration of the quaternary groups in the vicinity of © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com 3.1.2. Hydroxyl Group-Containing Organic Acid as Pendent Group Benzoic acid, phenol and p-hydroxy benzoate esters are among the most widely used disinfectants and preservatives. As monomers these compounds have already established their antimicrobial activity. Attempts have been made to incorporate them with some polymer backbone to synthesize new antimicrobial polymers with enhanced activity. In a comparative study of p-hydroxyphenyl acrylate, allyl p-hydroxyphenyl acetate, and p-2-propenoxyphenol for their antimicrobial action against both bacteria and fungi, p-hydroxyphenyl acrylate has been shown to be the most effective.[72] Amphiphilic polymethacrylates such as copolymer of N-(tert-butoxycarbonyl) amino ethyl methacrylate and butyl methacrylate, antimicrobial and hemolytic activities are dependent on the content of hydrophobic groups and Mw, which provide versatility for structural modification.[69] Another important compound of this class is “benzaldehyde,” known for its bactericidal, fungicidal and algaecide activities. Benzaldehyde containing methyl methacrylate polymers have been synthesized and tested against Bacillus macroides, P. aeruginosa and Dunaliella tertiolecta. Polymers show fivefold inhibition of algae growth compared to acid-glass control surfaces.[73] 3.1.3. Phospho and Sulpho as Pendent Group Antimicrobial polymers bearing quaternary phosphonium or sulfonium compounds display mechanisms similar to the quaternary ammonium group containing compounds. In terms of antimicrobial activity, phosphonium containing polycationic biocides are more effective than quaternary ammonium salt polymers. Studies carried out on water soluble thermosensitive copolymer NIPAAm and methacryloyloxyethyl trialkyl phosphonium chlorides indicate that the antimicrobial activity increases with an increase in length of the alkyl chain and phosphonium units in the polymer.[74] Anderson et al. investigated the potential of poly(sodium 4-styrene sulfonate) as an inhibitor of sperm function and as a preventive agent for conception and the transmission of sexually transmitted diseases. The polymer is an irreversible inhibitor of hyaluronidase and acrosin with half maximal inhibitory concentration (IC50) values 5.7 µg/mL and 0.5 µg/mL, respectively. When tested against human immunodeficiency (HIV-1), herpes simplex (HSV-1) viruses and Neisseria gonorrhoeae, it Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 REVIEW the microorganism cell wall. Sauvet et al. synthesized statistical and block siloxane copolymers containing quaternary ammonium salt groups as a lateral substituent; this research shows high antibacterial activity against both E. coli and S. aureus. However, no difference in activity was observed in block type polymers and statistical copolymers.[70] Mizerska et al. compared biocidal activity of polysiloxanes containing quaternary ammonium salt groups with polysiloxanes containing pendant N,N-dialkylimidazolium salt. These compounds show similar activity against Enterococcus hirae, Proteus vulgaris, E. coli, and P. aeruginosa; this was observed with polysiloxanes containing quaternary ammonium salt. In terms of thermal stability these compounds are superior to quaternary ammonium group containing polysiloxanes.[71] shows 3-log reduction in growth of these pathogens at a concentration of 7 µg/mL, 3 µg/mL, and 15 µg/mL, respectively. Almost 90% inhibition of Chlamydia trachomatis is observed at a concentration of 1 mg/mL. Polymers with high Mw are safe and superior in activity.[75,76] 3.2. Polymers Attached with Inorganic Antimicrobial Agents This section concerns polymers that present antimicrobial activity in combination with antimicrobial inorganic systems. Silver nanoparticles are probably the most widely used metal particles as an antimicrobial agent in polymeric nanocomposites. They exhibit broad antimicrobial spectrum against bacteria, virus and fungi. Generally, they work by producing highly reactive Ag+ ions in the presence of moisture or other favorable conditions for bacteria growth. These silver ions can bind to proteins causing structural changes in the cell wall and also in nuclear membranes resulting cell death. Ag+ ions can interfere in the replication of micro-organisms by forming complexes with nitrogenous bases in DNA and RNA. However, their complete mechanism is not fully understood.[77,78] Copper (Cu) particles, although relatively less studied than silver, are also known for their antimicrobial activity. Polypropylene nanocomposites containing different amounts of Cu nanoparticles were prepared by melt mixed method, and results indicate that composites with only 1% (v/v) of Cu are able to kill 99.9% of bacteria after 4 h of contact.[79] Similarly, due to the remarkable antimicrobial activity of titanium dioxide (TiO2), Huppmann et al. developed photo activated nano titanium dioxide polymer composites with antimicrobial properties for medical and sanitary applications. Generally, TiO2 is used as a thin film on surfaces to incorporate an antimicrobial character. The application of TiO2 nanoparticles incorporated into a medical grade polypropylene matrix results in impact resistant surface characteristics with superior photocatalytic and antibacterial properties of TiO2.[80] 3.3. Polymers Attached with Organic Antimicrobial Agents This class comprises polymers that display antimicrobial behavior due to the presence of organic antimicrobial agents such as antibiotics. One of the most widely used antimicrobial agents is triclosan. In experiments, solutions of triclosan were mixed with water-based styrene-acrylate emulsion; the resultant systems were tested against Enterococcus faecalis (E. faecalis). Based upon an agar diffusion test, it was demonstrated that the release of triclosan depends on the solvent, being almost inexistent or very slow in water and very rapid in n-heptane.[81] In another experiment triclosan was incorporated in water-dispersable PVA nanoparticles that shows greater antibacterial activity toward Corynebacterium than the organic/aqueous solutions of triclosan.[82] PEI polymers are also used for the incorporation of antibiotics. Very mild antimicrobial activity has been observed with PEI alone, which is significantly enhanced in combination with antibiotics due to their synergistic effects. PEI increases the permeability of bacterial cell walls and sensitizes them towards the © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 7 www.advhealthmat.de REVIEW www.MaterialsViews.com lytic action of detergent sodium dodecyl sulphonate (SDS) and Triton X-100. PEI also improves the susceptibility of test species to hydrophobic antibiotics[83] This synergistic effect was studied by Khalil and coworkers using more than 10 families of antimicrobial agents. They report that concentration of 250 nM, PEI (10 kDa) does not show any direct bactericidal or bacteriostatic effect, but at the same concentration it produced a 1.5-fold to 56-fold reduction in the MICs of antibiotics such as novobiocin, ceftazidime, ampicillin, ticarcillin, carbenicillin, piperacillin, cefotaxime, chloramphenicol, rifampin, and norfloxacin.[84] Acrylate polymers containing 5-chloro-8-hydroxy-quinoline were studied at physiological, acidic and basic pH for their hydrolytic behavior. Hydrolysis occurs by autocatalysis and is potentiated by pH, temperature and the content of hydrophilic polymers. Copolymerization of this polymer with N-vinyl pyrrolidone reduces the rate of hydrolysis due to steric hindrance.[85] 4. Protein-Mimicking Polymers Antimicrobial polymers are supposed to act against harmful pathogenic bacteria; thus, the design of antimicrobial polymers should meet the requirements of greater binding affinity towards bacterial cell walls. The outer membrane of bacteria is characterized by net negative charge, presence of teichoic/ lipoteichoic acid (gram-positive bacteria), lipopolysaccharides and phospholipids (gram-negative bacteria), and a semi-permeable nature. Based on the features of the bacterial cell, antimicrobial polymers with cationic charge were initially considered essential for this activity.[3,86] Later, however, it was realized that a cationic charged biocide repeat unit in a main or side chain is not the only requirement for a polymer to display antimicrobial characteristics. Other factors must also be taken into consideration.[87] This idea is based upon natural antimicrobial peptides, such as magainin and defensin, which display excellent antimicrobial properties due to their characteristic structural features. These polymers possess a highly rigid backbone. Their side groups are organized to provide one hydrophobic side and one side with a cationic net charge. These molecules are highly efficient in disrupting a microbial cell membrane by being inserted in a membrane with the whole backbone. This intrusion is highly destructive to the membrane and rips it apart, resulting in rapid cell death.[88,89] These findings led to the development of polymeric mimics for antimicrobial peptides. Poly(phenylene ethynylene)-based conjugated polymers with amino side groups and also other polymers with stiff backbones and cationic side groups have been developed and show high antimicrobial activity with low toxicity.[90] Zhou et al. synthesized peptides via ring opening polymerization of α-amino acid N-carboxyanhydride (NCA) monomers using lysine (K) as the hydrophilic amino acid and alanine (A), phenylalanine (F), and leucine (L) as hydrophobic amino acids. They varied the content of hydrophobic from 0 to 100% and obtained five series of co-peptides [i.e., P(KA), P(KL),P(KF), P(KAL), and P(KFL)]. MIC values determination against E. coli, P. aeruginosa, Serratia marcescens and C. albicans demonstrate that the P(KF) copeptides have broader antimicrobial activity and are more efficient than the P(KL) and P(KA) series. Similarly, the P(KFL) series is more effective than the P(KAL) 8 wileyonlinelibrary.com series.[91] Gabriel et al. attempted to bridge the research areas of natural host defense peptides (HDPs), a component of the innate immune system, and biocidal cationic polymers. This is perspective on HDPs, in the development of permanently antibacterial surfaces.[92] 5. Miscellenous 5.1. Organometallic Polymers Organometallic polymers contain metals either in the backbone chain or in the pendant group, bonded to the polymer by Π-bonds to carbon, coordination bonds to elements containing free electron pairs, or by ρ/Π-bonds to other elements. Carraher et al. synthesized organo tin polyamine ethers containing acyclovir in their backbone. Many such compounds were synthesized by varying alkyl group (methyl, ethyl, butyl, octyl, cyclohexyl, and phenyl) and tested against herpes simplex virus-1 (HSV-1) and Varicella zoster virus (VZV). The MIC determination shows the following trend of organo tin compounds containing acyclovir in the backbone against HSV-1: dibutyltin>diethyltin>diphenyltin = dioctyltin>acyclovir >dicyclohexyltin. While against VZV following order was found: die thyltin>dibutyltin>dioctyltin>diphenyl>dicyclohexyltin> acyclovir. These polymers present a good inhibition of both RNA and DNA viruses.[93] 5.2. Inclusion Complex β-cyclodextrin is a widely used complexing agent in pharmaceutical research. An inclusion compound between β-cyclodextrin and triclosan that was subsequently embedded into films of PCL or nylon was reported. This system offers protection of the antimicrobial agent against processing at higher temperatures with the retention of similar activity as triclosan embedded polymer without complexation. Further, microparticles of poly(lactide-co-glycolic acid) containing chlorhexidrine, with or without cyclodextrin complexation, were also tested against Porphyromonas gingivalis and Bacteroides forsythus bacteria. Results suggest that both the encapsulation and release of antimicrobial agent are modulated by complexation with cyclodextrin.[94] 5.3. Cationic Conjugated Polyelectrolytes Cationic conjugated polyelectrolytes (CPEs) are another category of antimicrobial quaternized polymers; they are less explored due to more complicated preparation. Whitten and co-workers performed thorough studies on the antimicrobial properties of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes. They synthesized different photomodulated PPEs with pendant quaternary ammonium or alkyl pyridinium groups, which are effective in white light, while presenting moderate efficiency in the dark. This photo activation can be attributed to the ability of PPEs to generate singlet O2 upon exposure to UV-visible light. These polymers inhibit the growth of gram-negative and gram-positive bacteria in solution and immobilized state.[95,96] © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com 6.1. Dendrimers Dendrimers are novel symmetrical, highly branched threedimensional macromolecules that diverge from a central core, which can be tailored to generate uniform or discrete functionalities and possess tunable inner cavities, surface moieties, sizes, molecular weights, and solvent interactions.[97] There are several classes of dendrimers that have been explored for various applications. However, poly(amidoamine) (PAMAM) and poly(propyleneimine) (PPI) dendrimers are most widely used for development of antimicrobial polymers. PAMAM dendrimer displays antimicrobial potential without any biocidal agent. This is attributed to its positive charge, which can electrostatically bind to bacterial cell membranes. This charge, however, also presents toxicity problems. PEGylation of dendrimers render them less toxic and also reduce their biocidal effect due to covering of surface amine groups. In addition, optimization of PEG content was carried out; 6% PEGylation on G3 dendrimer greatly reduced cytotoxicity towards human corneal epithelial cells while maintaining high potency against P. aeruginosa.[98] Biocides immobilized on dendrimer were also explored as antimicrobial agents. They were designed by functionalizing end groups of dendrimers with quaternary ammonium salts or other antimicrobial agents. They are reportedly more effective for targeting the cell wall and /or cell membrane. Once diffused through cell walls these agents act on the cell membrane and disrupt it. This is followed by release of electrolytes, destruction of DNA/RNA and cell death. Dendritic cationic biocides possess the ability to displace calcium and magnesium ions bound on the membranes, thus destabilizing the bacterial membrane. Dendrimer biocides offer greater activity than their small molecular counterpart due to high local density of active groups, narrow polydispersity, well defined Mw, target organ localization, increased duration of action and minimal toxicity. Chen et al. performed a systematic study to understand the mechanism of action of dendrimer biocides by interaction behavior of PPI dendrimers and bacterial membranes. The study was performed on both gram positive and gram negative bacteria. On contact with these antimicrobial agents, there is an increase in the release of a substance with an absorption maxima of 260 nm, which reaches a plateau with E. coli (gram negative bacteria).while releasing 260 nm of absorbent materials from S. aureus (gram positive bacteria), increasing monotonically with the concentration. This behavior is due to the difference in cell walls of both types of bacteria. Generation dependent biocidal potential of dendrimers against E. coli was also investigated. Fifth generation dendrimers are most effective; third generation dendrimers are least effective. This fact was correlated with the surface functional activity of higher generation dendrimers. The theoretical Mw of the dendrimer biocides ranged from 2000 to 2.8 × 104, which can easily cross through a bacterial cell wall.[99,100] The structure of quaternary compounds attached to dendrimers also affects the biocidal activity of dendrimers. A parabolic relation was observed for the hydrophobic chain length of quaternary groups and biocidal activity. Dendritic biocides with C-10 chains are most effective, followed by C-8 and C-12 Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 REVIEW 6. Delivery Systems for Antimicrobial Polymers chains; C-14 and C-16 chains are the least active. The reason for the parabolic relationship between antibacterial properties and alkyl chain length can be explained on the basis of dual binding sites on the surface which differ in their relative binding affinities for long and short alkyl substituent and different aggregation behavior for long and short hydrophobic moieties.[101] Metal-dendrimer complexes were also explored for their antimicrobial potential. Silver complexes of PAMAM dendrimers and silver-PAMAM dendrimer nanocomposite were tested in vitro against S. aureus, P. aeruginosa, and E. coli bacteria, using the standard agar overlay method. Both PAMAM silver salts and nanocomposites display considerable antimicrobial activity with retaining solubility and biocidal activity.[102] 6.2. Nanoparticles Nanoparticles offer multiple advantages due to their small size and properties which are effective in this particular size. Thus, attempts were made to incorporate metallic nanoparticles like silver, copper, titanium oxide nanoparticles into polymeric material to introduce antibacterial property with the added advantage of nanosize. Apart from metallic nanoparticles, polymeric nanoparticles were also examined for their antimicrobial potential in many health care areas. Dental hygiene is one such area with this, dental restoration materials have gained extensive attention in the past few years; the clinical survival is considered an important criterion for their success. Materials which were used for this purpose suffer from secondary caries, hence they require timely replacement.[103] To solve this problem, nanoparticles synthesized from cross-linked quaternary PEI incorporated into resin were introduced. These nanoparticles were optimized for particle size, positive charge, oxidative, thermal stability and antibacterial activity.[104] This system is effective against S. aureus, Staphylococcus epidermidis, E. faecalis, P. aeruginosa and E. coli. Different levels of loading of nanoparticles on resin (1% and 2%) affect antimicrobial activity with 2% loading complete inhibition; at 1% there is complete inhibition of S. aureus and E. faecalis. Some growth reduction of others was observed. These particles are completely biocompatible. However, nanoparticles loaded in resin are unable to diffuse in agar plate.[105,106] PEI nanoparticles loaded composite resins were also prepared. This system offers antibacterial activity, eliminates formation of bacterial plaque and also protects the surface of composite resin from roughness, which further prevents formation of secondary carries.[107] Quaternary ammonium PEI nanoparticles with N-octyl dimethyl residues also demonstrate good antibacterial effects.[108] Silica particles functionalized with quaternary ammonium groups were also synthesized by interpenetrating PEI into silica particles and crosslinking with diiodopentane, followed by octyliodide alkylation and methyliodide quaternization (S-QAPEI). These particles display a size range of 2–3 µm, zeta potential of +50–60 mV and strong antibacterial activity.[109] 6.3. Polymeric Micelles Polymeric micelles, being amphiphilic in nature, exert the property to self assemble and hence can be used to act © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 9 www.advhealthmat.de REVIEW www.MaterialsViews.com as antimicrobial polymers without incorporation of quaternary groups or antibiotics in a polymer chain. Yuan et al. synthesized amphiphilic ABC triblock copolymers of poly(ethyleneoxide)- block -poly( ε -caprolactone)- block -poly[(2- tert -butylami noethyl)methacrylate] (PEO-b-PCL-b-PTA) that was designed to self-assembled into water-dispersible and biodegradable polymer micelles. Biodegradable PCL was engineered to drive the copolymers into micelle structures, where PTA facilitates better interaction with the microbial wall/membrane. PEO was incorporated to provide better biocompatibility and colloidal stability to micelles in aqueous solution. The unique core/corona assembly of the micelles was expected to enable more efficient interaction with the cell membrane than individual polymers by increasing local mass and cationic charges of a self-assembled nanostructure. This is important for the disintegration of the cell membrane through electroporation. Two different types of polymers were produced by varying the content of PTA (polymer-1 contained 20 PTA units and polymer-2 contained 30 PTA units). Micelles from polymer-1 resulted in minimum bactericidal concentration (MBC) values of 0.30 and 0.15 mM, while polymer-2 showed MBCs of 0.20 and 0.08 mM against E. coli and S. aureus, respectively. Thus, increased content of PTA provides better antimicrobial properties.[110] 7. Factor Affecting Activity of Antimicrobial Polymers 10 7.2. Charge Density Positive charge density provides better electrostatic interaction of polymers with bacterial cells. In case of chitosan, charge density increases with the increasing degree of deacetylation (DD), which also enhances electrostatic interaction and thus antimicrobial activity. Takahashi et al. report higher antibacterial activity of chitosan towards S. aureus at higher DD.[112] Modification in chitosan structure to incorporate groups with higher charge density, such as asparagine N-conjugated chitosan oligosaccharide[113] and guanidinylated chitosan,[114] result in higher antimicrobial activity, while N-carboxyethyl chitosan fails to show any antimicrobial activity due to lack of a free amino group.[115] 7.3. Hydrophilicity Hydrophilicity is an important requirement for activity of any antimicrobial agent. Amphiphilic polymethacrylate derivatives tailored by alternating the content of hydrophobic groups and Mw display better antimicrobial activities.[69] Similarly, water soluble chitosan derivatives synthesized by saccharization, alkylation, acylation, quaternization and metallization display higher antimicrobial effect than in their original form.[116,117] 7.4. Counter Ions The activity of antimicrobial polymers is considered as a function of balance between multiple factors. These could be polymer related factors such as Mw, charge density, alkyl chain length, hydrophilicity, as well as environmental factors such as pH, temperature, etc. Some major factors affecting antimicrobial activity are described below. The effect of counter ions has been observed for quaternary ammonium/phosphonium compounds. Counter ions with strong binding affinity towards quaternary compound cause less antibacterial activity due to slow and less release of free ions in the medium. For quaternary ammonium compounds, bromide and chloride exert the highest antimicrobial activity.[101] 7.1. Molecular Weight and Alkyl Chain Length 7.5. pH Molecular weight (Mw) plays an important role in modulating physicochemical properties of polymers. In the case of the antimicrobial activity of polyacrylates and polymethyl acrylates with side-chain biguanide groups, Mw is the main factor to controlling bactericidal activity. The optimum range of Mw has been reported from 5 × 104 and 1.2 × 105 Da, while above and below this range significant reduction in activity occurs.[44] Likewise, poly (tributyl 4-vinylbenzyl phosphonium chloride) also shows optimum antimicrobial effect within Mw range of 1.6 × 104 to 9.4 × 104 Da.[111] However, for chitosan, the role of Mw is conflicting, and different research groups report different findings. These contradictory effects have been correlated with bacterial strains selected for study. Generally, gram negative bacteria, compared with gram positive bacteria, possess a greater challenge in diffusion of antimicrobial substance due to the presence of cell walls.[4,13] In the case of ε-PL, tuning of alkyl chain length shows significant effects on activity; polymers with a chain length of 9 L-lysine residues are optimum for inhibition of microbial growth.[24] The pH effect for chitosan and polymers with amphoteric nature has been observed. Chitosan displays pH dependent antimicrobial activity, which is at a maximum at acidic pH due to its better solubility as well as formation of polycation. However, there are no reports showing its antimicrobial effect at basic pH.[118] wileyonlinelibrary.com 8. Application 8.1. Fibers and Textiles Textile goods made from natural sources like cotton, keratinous fibers have been recognized as media to support growth of unwanted microorganisms during their use and long term storage, resulting in detrimental effects due to susceptibility for microbial growth. Textiles generated by a final finishing of polymers that protects them from these microbial attack constitute a substantial market for antimicrobial textile products.[4] © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com 8.2. Self-Sterilizing Surfaces Bacterial contamination of medical device surfaces (catheters, implants, etc.) is one of the major leading causes for infections acquired in hospital. This process starts with adherence of bacteria onto the surface followed by implantation and development into a biofilm highly resistant to antibiotics and the host’s immune system. One strategy used to overcome this problem is to develop antimicrobial materials by the addition of a biocide like quaternary ammonium compounds, silver, etc. that leaches into the surrounding environment, killing the microorganism. Such materials that were impregnated with an antimicrobial agent pose a problem of environmental contamination and short shelf life due to rapid leaching of the agent in initial stages of use. Another alternative to overcome this limitation is non-leaching biocide materials or covalent attachment of these biocides onto the surface of glass, metals, etc.[121] Tiller et al., covalently attached poly(4-vinyl-N-alkylpyridinium bromide) to glass slides, and its antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of cells remaining viable. Amino glass slides were acylated with acryloyl chloride, copolymerized with 4-vinylpyridine. A surface alternatively created by attaching poly(4-vinylpyridine) to a glass slide and alkylating it with hexyl bromide killed 97 ± 3% of the deposited S. aureus cells. A 100 fold drop in bacterial colonies was achieved with hexyl-poly vinyl pyrrolidone (PVP) slides compared with the original amino slides.[122] Materials capable of resisting long-term biofilm formation in complex media while maintaining non-fouling properties are highly desirable for many applications, but their development is very challenging. Cheng et al. investigated the potential of ultra-low fouling zwitter ionic poly(carboxybetaine methacrylate) (pCBMA) grafted from glass surfaces for resistance to long-term biofilm formation. Results show that pCBMA coatings reduce long-term biofilm formation of P. aeruginosa up to Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 REVIEW Numerous antimicrobial textile products have been launched on the market by leading manufacturers. N-halamine precursor, m-aminophenylhydantoin (m-APH) and butanetetracarboxylic acid (BTCA) are used to coat cotton fabric. Antimicrobial efficacy of butanetetracarboxylic acid/m-aminophenylhydantointreated cotton fabric against Gram-positive and Gram-negative bacteria shows a 6 log reduction within 1 min of contact time. Durability and recharge ability of these fabrics with an initial chlorine loading of about >1.0 [Cl+]%, retaining up to ten washing cycles make them a special class for the fibers and textile industries[119] Chitosan is an excellent candidate for an eco-friendly textile industry. However, the major problems associated with chitosan are its poor adhesion to fabrics and loss of the antimicrobial activity under alkaline conditions. The three water-soluble chitosan derivatives bearing double functional groups were synthesized with 2,3-epoxypropyltrimethylammonium chloride and benzaldehyde and applied to cotton fabrics together with citric acid as the crosslinking agent. The finished fabrics show strong antimicrobial activities and fairly good durability. The antibacterial efficiency of this fabric is more than 99% and 96% against S. aureus and E. coli respectively.[120] 240 h by 95% at 25 °C and for 64 h by 93% at 37 °C, and suppress Pseudomonas putida biofilm accumulation up to 192 h by 95% at 30 °C, with respect to the uncoated glass reference. The ability of pCBMA coatings to resist non-specific protein adsorption and significantly retard bacterial biofilm formation is be promising for biomedical and industrial applications.[123] Ye et al. developed self-sterilizing surfaces using a singlestep solvent less grafting method. The process was conducted by vapor deposition of a crosslinked poly(dimethylaminomethyl styrene-coethylene glycol diacrylate) (P(DMAMS-coEGDA)) prime layer, followed by in situ grafting of poly(dimethylaminomethyl styrene) (PDMAMS) from the reactive sites of the prime layer. The hybrid grafted coating of P(DMAMS-co-EGDA)-g PDMAMS showed more than 99% bacterial killing against both gram-negative E. coli and grampositive Bacillus subtilis. The grafted coating exhibited durable bactericidal efficacy after continuous washing.[124] Stainless steel implants are extensively used in orthopedic surgery, but their susceptibility for adherence of microbes is the main limitation which can create undesired health complications. Coating the stainless steel surface with a protein anti-adhesive polymer containing negatively charged or neutral hydrophilic groups can suppress interaction between solid substrates and proteins by electrostatic repulsion and reducing hydrophobic interactions. Ignatova et al. developed a two-step “grafting from” method based on the electrografting of polyacrylate chains containing an initiator for the atom transfer radical polymerization of 2-(tert-butylamino)- ethyl methacrylate (TBAEMA), copolymerization of TBAEMA with either monomethyl ether of poly(ethylene oxide) methacrylate (PEOMA), acrylic acid (AA), or styrene. A 2–3 fold decrease in fibrinogen adsorption occurs when TBAEMA is copolymerized with either PEOMA or AA, rather than homo polymerized or copolymerized with styrene. Compared with the bare stainless steel surface, brushes of polyTBAEMA, poly(TBAEMA-co-PEOMA) and poly(TBAEMA-co-AA) decrease bacteria adhesion by 3 to 4 orders of magnitude as indicated by S. aureus adhesion tests. The chemisorption of this type of polymer brushes onto stainless steel surfaces display potential in orthopedic surgery.[125] 8.3. Medical Composites Overcoming microbial resistance by antibiotics has become the prime requirement of current advancing medical technology. However, monocomponent antibacterial agents are far from meeting requirements for special conditions like catheter induced infections. Integrating the properties of organic and inorganic composites into thin films has recently been a subject of intense study. This has led to search regarding antimicrobial composites, wherein polymers form the base for loading silver or other antimicrobial metals. Such assemblies have recently gained significant attention in biomaterials and have created a demand for biocompatible and antimicrobial thin films as potential coatings for biomedical implants. A novel dual action antibacterial material composed of a cationic polymer poly(4-vinyl-N-hexylpyridinium bromide) and embedded silver bromide nanoparticles has been synthesized. The composites are capable of killing both gram-positive bacteria such as © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 11 www.advhealthmat.de REVIEW www.MaterialsViews.com Bacillus cereus, S. aureus and gram-negative bacteria such as E. coli and P. aeruginosa on surfaces and in solution. Additionally, the composites give a sustained release of biocidal silver ion and bactericidal effect for about 17 days without any loss of activity. They also inhibit biofilm formation and retain antibacterial activity after exposure to mammalian fluids.[126] The potential of novel ternary electrospun nanofibrous mats composed of quaternized chitosan (HTCC)–organic rectorite (OREC /polyvinyl alcohol (PVA) solutions in the field of food packaging and biomedical applications was proposed by Deng. Themorphology, intercalated structure, and antibacterial activity of the spun mats were investigated. X-ray diffraction results confirm the intercalation structure in nanofibrous mats wherein HTCC and PVA chains intercalate into the interlayer of OREC. The antibacterial activity of the electrospun mats is enhanced when the amount of the OREC is increased.[127] 8.4. Medical Coatings Adopting new approaches for the development of polymer conjugates used to coat implantable devices provides an opportunity to apply antimicrobial agents directly to the device surface, thus preventing bacterial colonization of the implant and inhibiting implant-associated infection. Polyacrylate derivates are one the most investigated due to their availability, low toxicity, wide variation of functionalized monomers, and easy processing. Polydimethylsiloxanes and 2-hydroxyethylacrylate/ acrylic acid have been photopolymerized to give nano phase amphiphilic coatings which are covalently attached to glass and loaded with antimicrobial surfactant cetyltrimethylammonium chloride (CTAC). This CTAC-loaded coatings acts like contactactive surfaces which do not kill microbes in the surrounding solution but only on their surface.[128] Liang et al. studied the potential of various N-halamine siloxane and quaternary ammonium salt siloxane copolymers for use in biocidal coatings. The copolymers were coated onto cotton swatches and evaluated for biocidal efficacy against S. aureus and E. coli. Both N-halamine and quaternary functional groups prove effective against S. aureus, but only the N-halamine units are effective against E. coli.[129] Polymers antibiotics composites were also investigated for their bactericidal potential. An amorphous aliphatic PE-PU polymer made from poly(lactic acid) diol (DLLA), poly(caprolactone) diol and 1,6-hexamethylene diisocyanate was developed and blended with levofloxacin. This polymer displays a constant release pattern which reaches to plateau. Preparations with a high proportion of DLLA, inhibits growth of S. aureus for 40–66 days, while preparations with a lower proportion of DLLA maintain antimicrobial activity for only 12–26 days. This polymer shows potential to prevent infection of implants in an intra-operative contamination model for at least 20 to 30 days post-implantation.[130] 8.5. Water Filtration Systems Antimicrobial polymers have wide application in water filtration systems. Chlorination is considered a classic and critical 12 wileyonlinelibrary.com step in the disinfection of drinking water and waste water treatment. However, these water soluble disinfectants suffer from the limitation of emergence of chlorine resistant microbe species, short-term stability in aqueous solution and residual toxicity of harmful degradation byproducts produced during the chlorination process, such as carcinogenic trichloromethanes and chloroacetic acids. This has raised concern over the safety issues of such disinfectants and led to development of alternate, novel and safe disinfectants. Onnis-Hayden et al. explored the use of polymeric disinfectants for water disinfection by covalently attaching N,N-hexyl, methyl- PEI onto sand surface and using this antimicrobial sand filter for water filtration and disinfection. These polymers show capability to be regenerated by simple washing steps. They are particularly useful for chlorine resistant species.[131] Some research groups propose the use of water insoluble matrices that may inactivate, kill or remove them by mere contact without releasing any reactive agents to the bulk phase to be disinfected. These matrices are intended to be combined with filtration systems.[132] Polystyrene copolymer bead supported dendrimers was synthesized and investigated for its application as a water treatment system. Macroporous crosslinked polystyrene copolymer beads were synthesized using suspension polymerization. Dendritic structure composed of di(chloroethyl)amine-type end group functionality was formed on the polystyrene copolymer beads. The polymer bound dendrimers were tested for antibacterial action against both grampositive and gram negative bacteria. The activity against both types of organisms increases with an increase in the nitrogen atoms in the polymer backbone. The dendritic structure containing both amino and di(chloroethyl) groups shows significant reduction in the bacterial count when kept in 20 mL autoclaved water with bacterial cultures having an initial count in the range of 12–83 × 106 CFU/mL.[133] N-halamine polymers in the form of highly cross-linked porous beads have been explored for use in drinking water disinfection. Beads were prepared by suspension copolymerization of styrene with vinyl hydantoin monomers like 3-allyl-5,5-dimethylhydantoin and 3-(4’-vinylbenzyl)-5,5-dimethylhydantoin with the addition of a cross-linker, DVB. After chlorination the hydantoin structures in the copolymers were transformed into N-halamines and provided the samples with powerful, and durable antimicrobial activities against E. coli and S. aureus.[57] Polyurethane (PU) is a polymer composed of a chain of organic units joined by carbamate (urethane) linkage. The bactericidal effect of silver nanoparticles coated on PU foams as a drinking water filter was investigated by Jain et al. Nanoparticles were stabilized and bound to PU by interaction with nitrogen atoms. Online tests conducted with a prototypical water filter show no presence of bacterium in output water. This finding introduces a cost effective new technology for domestic use.[134] Aviv et al. prepared iodinated polyurethane (IPU) sponges by immersing sponges in aqueous/organic solutions of iodine or exposing sponges to iodine vapors. Ethylene vinyl acetate (EVA) coating was applied on iodine loaded IPU sponges to release iodine in a controlled rate. An active carbon cartridge for removal of iodine residues after the microbial inactivation was also attached to the system. Results are impressive, at all testing points no bacteria were detected in the outlet achieving more © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com 8.6. Surfactants and Flocculants Both cationic surfactants and polymers with the quaternary ammonium moiety have many applications in conditioners, shampoo, hair mousse, hair spray, hair dye, and contact lens solutions. Lenoir et al. prepared antibacterial surfactants by the quaternization of the amino groups of poly(ethylene-cobutylene)-b-poly[2-(dimethylamino)ethylmethacrylate] (PEBb-PDMAEMA) diblock copolymers by octyl bromide. The antibacterial activity of PEB-b-PDMAEMA quaternized by octyl bromide has been assessed against bacteria and is comparable to the activity of benzalkonium chloride.[136] Chitosan and its derivatives have also been investigated for this purpose. Chitosan interacts with the adsorbed surfactant to form interfacial complexes that improved emulsion stability. The relatively thick and highly charged double layered interfaces increase electrostatic and stearic repulsion between droplets and reduce their likelihood to aggregate. Mun et al. established optimum conditions for preparing stable oil-inwater emulsions containing droplets surrounded by surfactantchitosan layers and concluded that that stable emulsions can be formed above critical chitosan concentration. Emulsions stabilized by surfactant-chitosan layers possess good stability to pH, ionic strength, thermal processing, and freezing. Emulsions stabilized by surfactant-chitosan layers possess good stability to pH, ionic strength, thermal processing, and freezing.[137] However, their low degree of hydrophobic substitution resulted in weakened stability of the micelle. A method for improvement of chitosan based amphiphilic compounds having more densely packed hydrophobic substituent was attempted by reductive N-alkylation of chitosan with 3-O-dodecyl-D-glucose.[138] 8.7. Food Packaging In recent years antimicrobial packaging has acquired significant attention from the food industry because of the increase in consumer demand for minimally processed, preservativefree products. Many natural polymer based coating have been used to control common food-borne microorganisms, and new antimicrobial packaging materials are continually being developed. Jiang and Li investigated the potential of chitosan coating in extending post-harvest life and maintaining the quality of fruit during storage at a low temperature. Parameters such as changes in respiration rate, polyphenol oxidase activity, color, eating quality, and weight loss have been measured with time. Chitosan coating shows better preservation potential which increases with rising content of chitosan.[139] Further, Caner et al. studied the effects of acid concentrations, plasticizer concentrations, and storage time on the mechanical and permeation properties of chitosan films.[140] These works indicate greater potential of chitosan films in food protective coating. However, these coatings are ineffective against lactobacilli bacteria.[141] Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 REVIEW than 7.1 to 8 log reductions as calculated upon inlet concentration. These iodinated PU systems can be used as an effective means of water purification.[135] 9. Recent Advancements 9.1. Stimuli Sensitive on Demand Coatings Antimicrobial releasing biomaterial coatings are in high demand in the fixation of orthopedic joint prostheses and central venous catheters. Generally, antimicrobial agents loaded in catheters display a rapid release profile and reach their antimicrobially effective concentrations within the first few days after implantation. This results in rapid exhaust of antimicocial agents and renders them unavailable for later stages more susceptible to microbial infection. Keeping in mind ‘on demand antimicrobial releasing polymers’ were developed and programmed for temperature sensitive triggered release of antimicrobial agents. Copolymers of styrene and n-butyl (meth) acrylate have been used as thermosentive polymers loaded with chlorhexidine. This copolymer releases drug when the temperature is raised above its glass transition temperature. Chlorhexidine concentrations are observed during 60–80 days compared with 16 days with ad libitum release from commercially-purchased catheters.[142] 9.2. Polymer to Avoid Antibiotic Resistance Even though many antimicrobial polymers provide a better bactericidal activity against a wide spectrum of bacteria, sooner or later they suffer emergence of microbial resistance. Active efforts are being made, and a couple of examples are given below. Biodegradable cationic polycarbonates containing propyl and hexyl side chains quaternized with various nitrogen-containing heterocycles, such as imidazoles and pyridines, were synthesized as new class of antimicrobial polymer. These polymers demonstrate a wide spectrum of activity against S. aureus, E. coli, P. aeruginosa and C. albicans. They have a high selectivity towards tested microbes over mammalian (rat) red blood cells by hemolysis testing. These polymers act through membrane-lytic mechanisms, hence they eliminate the chance of emergence of resistance.[143] A naturally functionalized bacterial polyhydroxyalkanoate (PHACOS) was developed to further control the emergence of antimicrobial resistance which selectively and efficiently inhibits the growth of methicillin-resistant S. aureus (MRSA) under both in vitro and in vivo conditions. Its activity is attributed to functionalized side chains containing thio-ester groups. Significantly less (3.2-fold) biofilm formation of S. aureus was detected with PHACOS compared with control [poly(3-hydroxyoctanoate-co-hydroxyhexanoate) and poly(ethylene terephthalate)]. However, no significant reduction is observed in bacterial adhesion. Moreover, PHACOS displays contact active surface killing properties.[144] 10. Clinical Trials Table 2 describing clinical trials for antimicrobial polymers 11. Conclusion Antimicrobial polymers offer a wide range of classes and applications in the areas of fibers, textile water filtration systems, © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 13 www.advhealthmat.de REVIEW www.MaterialsViews.com Table 2. Clinical trials for antimicrobial polymers. SN Clinical trial title Condition Delivery system Atopic dermatitis Biofunctional textile Coronary Angiography Comments NCT no. Phase Status Purpose is to study the use of biofunctional textile coated with chitosan. Improves quality of life and diminishes skin colonization with Staphylococcus aureus and skin moulds like Malassezia. NCT01597817 2 Ongoing HemCon pad, a bandage made of chitosan HemCon pad was tested after diagnostic percutaneous coronary angiography as an adjunct to manual compression to better control vascular access site bleeding and reduce time-to-hemostasis. NCT00716365 4 Complete Surgical Incision Closure BioWeld1: a novel medical device that consists of Chitosan film and BioWeld1 plasma ejecting device Purpose is to assess the safety and performance of the BioWeld1 system procedure for surgical incision closure of the skin in women scheduled for elective C-section procedure. NCT01709240 2,3 Ongoing Epistaxis Chitosan-coated nasal packing (ChitoFlex used in conjunction with the HemCon Nasal Plug) Purpose is to evaluate applicability of sealant in management of difficult spontaneous epistaxis and its healing effect on nasal mucosa. CHITOSAN 1. Efficacy and Safety of a Biofunctional Textile in the Management of Atopic Dermatitis 2. USF Hemostasis: Usage of HemCon for Femoral Hemostasisafter Percutaneous Procedures 3. Evaluation of the BioWeld1 System as a Method for Surgical Incision Closure 4. Trial of a Novel chitosan Hemostatic Sealant in the Management of Complicated Epistaxis Any non-desirable effects of chitosan on the nasal cavity, such as the production of fibrosis and foreign body reaction were studied NCT00863356 Complete Not started POLYETHYLENEIMINE 14 5. The Effects of a Polyethyleneimine-coated Membrane (oXiris) for Hemofiltration Versus Polymyxin B- Immobilized Fibre Column (Toraymyxin) for Hemoperfusion on Endotoxin Activity and Inflammatory Conditions in Septic Shock- A Randomized Controlled Pilot Study 6. A Clinical Study: the Antibacterial Effect of Insoluble Antibacterial Nanoparticles (IABN) Incorporated in Dental Materials for Root Canal Treatment wileyonlinelibrary.com Septic shock oXiris filter, a surface treated AN69 membrane with polyethyleneimine Hypothesis behind the study is that positively charged inner surface of the membrane allows absorbing negatively charged bacterial products such as endotoxin that leads to activation of pro- and antiinflammatory mediators at the early phase of sepsis NCT01948778 Endodontic Treatment Insoluble alkylated polyethylenimine nanoparticles The effect of antibacterial nanoparticles, incorporated in root canal sealer material and in provisional restoration to be examined. NCT01167985 Irreversible Pulpitis Health Pulp Infected Pulp © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2 Recruiting Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com SN Clinical trial title Condition Delivery system Comments NCT no. Phase Status REVIEW Table 2. Continued ACRYLATE DERIVATIVES 7. Effect of Provisional-Crown Surface Coating on Biofilm Formation Dental plaque Coating of a dental restoration material (polymethylmethacrylate) with liquid polish resin1q245r The effect of liquid polish coating or resin bonding coating on biofilm formation on poly methyl methacrylate provisional restorations (PMMA PRs) was studied and in vivo early biofilm formation on PMMA PRs with and without resin coatings was measured. NCT00254345 1 Complete 8. Bioactive Glass Composite Implants in Cranial Bone Reconstruction Bone substitute Composite Implant Purpose is to study composites of bioactive glass and methylmetacrylate with glass fibre reinforcement in cranial bone defect reconstruction. NCT01202838 0 Unknown 9. Evaluate the Effectiveness of an Experimental Urethane Dimethacrylate Resin Based Dental Composite Material Dental Caries Restorative Material Dentsply Caulk : urethane dimethacrylate resin based composite resin The purpose of study is to compare the clinical success of two tooth colored resin composite dental filling materials TPH3 and an experimental urethane dimethacrylate resin based composite resin for wear resistance staining and marginal seal using modified Ryge criteria to evaluate the posterior restorations for 24 months in duration NCT02018822 – Ongoing food packaging, surfactants and detergents, and the surgical and pharmaceuticals industries. Especially in biomedical field, these polymers reduce the suffering of people and offer them a better life. These antimicrobial polymers offer prolonged antimicrobial activity with negligible toxicity, compared with small molecular antimicrobial agents that display short term activity and environmental toxicity. The emergence of resistant species is one of the major problems with small molecular antibiotics due to their specific targets of action, whereas antimicrobial polymers physically destroy cell membranes of the organism which prevent development of drug-resistance microbes. Due to these advantages provided by antimicrobial polymers, efforts have been made to apply these polymers as contact surfaces for medical devices, fibers, and textiles, render them antimicrobial. Several modified composite polymers have also been developed to meet surface requirements. These modifications, on one hand provide a great versatility to these polymers to be applied for various fields, and on the other hand open enormous opportunities for research. It is crucial, however, to achieve an innocuous material which is non-toxic, environment friendly with potent and broad range of antimicrobial activity, long-last response and even reusable to maintain the activity. Advanced quality research, dedicated efforts, successful application and commercialization of antimicrobial polymer will help fulfill the Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 need of better hygienic conditions and improve the quality of life. Received: July 17, 2014 Revised: October 3, 2014 Published online: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] H. M. Lode, Clinical Microbiol. Infection 2009, 15, 212. G. McDonnell, A. D. Russell, Clinical Microbiol. Rev. 1999, 12, 147. F. Siedenbiedel, J. C. Tiller, Polymers 2012, 4, 46. E. R. Kenawy, S. D. Worley, R. Broughton, Biomacromolecules 2007, 8, 1359. A. Muñoz-Bonilla, M. Fernández-García, Prog. Polym. Sci. 2012, 37, 281. L. Timofeeva, N. Kleshcheva, Appl. Microbiol. Biotechnol. 2011, 89, 475. T. Jiang, M. Deng, R. James, L. S. Nair, C. T. Laurencin, Acta Biomater. 2014, 10, 1632. C. T. Laurencin, T. Jiang, S. G. Kumbar, L. S. Nair, Curr. Topics Med. Chem. 2008, 8, 354. R. A. A. Muzzarelli, J. Boudrant, D. Meyer, N. Manno, M. DeMarchis, M. G. Paoletti, Carbohydr. Polym. 2012, 87, 995. C. R. Allan, L. A. Hadwiger, Exp. Mycol. 1979, 3, 285. S. Hirano, N. Nagao, Agricultural Biol. Chem. 1989, 53, 3065. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 15 www.advhealthmat.de REVIEW www.MaterialsViews.com [12] D. F. Kendra, L. A. Hadwiger, Exp. Mycol. 1984, 8, 276. [13] M. Kong, X. G. Chen, K. Xing, H. J. Park, Int. JFood Microbiol. 2010, 144, 51. [14] Y. Hu, Y. Du, J. Yang, Y. Tang, J. Li, X. Wang, Polymer 2007, 48, 3098. [15] M. Kong, X. G. Chen, C. S. Liu, C. G. Liu, X. H. Meng, L. J. Yu, Colloids Surf. B: Biointerfaces 2008, 65, 197. [16] Y. C. Chung, Y. P. Su, C. C. Chen, G. Jia, H. l. Wang, J. C. G. Wu, J. G. Lin, Acta Pharmacol. Sin. 2004, 25, 932. [17] N. R. Sudarshan, D. G. Hoover, D. Knorr, Food Biotechnol. 1992, 6, 257. [18] B. K. Choi, K. Y. Kim, Y. J. Yoo, S. J. Oh, J. H. Choi, C. Y. Kim, Int. J. Antimicrob. Agents 2001, 18, 553. [19] P. Eaton, J. C. Fernandes, E. Pereira, M. E. Pintado, F. Xavier Malcata, Ultramicroscopy 2008, 108, 1128. [20] D. Raafat, K. Von Bargen, A. Haas, H. G. Sahl, Appl. Environ. Microbiol. 2008, 74, 3764. [21] S. Shima, Agric. Biol. Chem. 1977, 41, 1807. [22] M. Nishikawa, K. Ogawa, Appl. Environ. Microbiol. 2002, 68, 3575. [23] S. Maeda, K. K. Kunimoto, C. Sasaki, A. Kuwae, K. Hanai, J. Mol. Structure 2003, 655, 149. [24] S. Shima, H. Matsuoka, T. Iwamoto, H. Sakai, J. Antibiotics 1984, 37, 1449. [25] J. Hiraki, J. Antibacter. Antifungal Agents 1995, 23, 349. [26] S. Shima, Y. Fukuhara, H. Sakai, Agricultural Biol. Chem. 1982, 46, 1917. [27] Y. Kido, S. Hiramoto, M. Murao, Y. Horio, T. Miyazaki, T. Kodama, Y. Nakabou, J. Nutrition 2003, 133, 1887. [28] I. L. Shih, M. H. Shen, Y. T. Van, Bioresource Technol. 2006, 97, 1148. [29] O. Rahn, W. P. Van Eseltine, Ann. Rev Microbiol 1947, 1, 173. [30] P. Gilbert, L. E. Moore, J. Appl. Microbiol. 2005, 99, 703. [31] C. J. Ioannou, G. W. Hanlon, S. P. Denyer, Antimicrob. Agents Chemother. 2007, 51, 296. [32] E. S. Hatakeyama, H. Ju, C. J. Gabriel, J. L. Lohr, J. E. Bara, R. D. Noble, B. D. Freeman, D. L. Gin, J. Membrane Sci. 2009, 330, 104. [33] C. J. Waschinski, J. C. Tiller, Biomacromolecules 2005, 6, 235. [34] G. Li, J. Shen, J. Appl. Polym. Sci. 2000, 78, 676. [35] G. Li, J. Shen, Y. Zhu, J. Appl. Polym. Sci. 1998, 67, 1761. [36] E. B. Anderson, T. E. Long, Polymer 2010, 51, 2447. [37] C. Soykan, R. Coskun, A. Delibas, Journal of Macromolecular Science, Part A 2005, 42, 1603. [38] B. Brissault, A. Kichler, C. Guis, C. Leborgne, O. Danos, H. Cheradame, Bioconj. Chem. 2003, 14, 581. [39] S. K. Samal, M. Dash, S. Van Vlierberghe, D. L. Kaplan, E. Chiellini, C. Van Blitterswijk, L. Moroni, P. Dubruel, Chem. Soc. Rev. 2012, 41, 7147. [40] J. Lin, S. Qiu, K. Lewis, A. M. Klibanov, Biotechnol. Prog. 2002, 18, 1082. [41] N. M. Milovic, J. Wang, K. Lewis, A. M. Klibanov, Biotechnol. Bioeng. 2005, 90, 715. [42] J. Lin, S. Qiu, K. Lewis, A. M. Klibanov, Biotechnol. Bioeng. 2003, 83, 168. [43] K. De Prijck, N. De Smet, T. Coenye, E. Schacht, H. J. Nelis, Mycopathologia 2010, 170, 213. [44] T. Ikeda, H. Yamaguchi, S. Tazuke, Antimicrob. Agents Chemother. 1984, 26, 139. [45] Y. Zhang, J. Jiang, Y. Chen, Polymer 1999, 40, 6189. [46] M. Albert, P. Feiertag, G. Hayn, R. Saf, H. Honig, Biomacromolecules 2003, 4, 1811. [47] H. Ohno, K. Ito, Chem. Lett. 1998, 27, 751. [48] J. P. Hallett, T. Welton, Chem. Rev. 2011, 111, 3508. [49] A. Latala, P. Stepnowski, M. Nedzi, W. Mrozik, Aquat. Toxicol. 2005, 73, 91. 16 wileyonlinelibrary.com [50] Q. Ye, T. Gao, F. Wan, B. Yu, X. Pei, F. Zhou, Q. Xue, J. Mater. Chem. 2012, 22, 13123. [51] E. E. Alberto, L. L. Rossato, S. H. Alves, D. Alves, A. L. Braga, Org. Biomol. Chem. 2011, 9, 1001. [52] L. Carson, P. K. W. Chau, M. J. Earle, M. A. Gilea, B. F. Gilmore, S. P. Gorman, M. T. McCann, K. R. Seddon, Green Chem. 2009, 11, 492. [53] F. Hui, C. Debiemme Chouvy, Biomacromolecules 2013, 14, 585. [54] P. Kovacic, M. K. Lowery, J. Org. Chem. 1969, 34, 911. [55] S. P. Denyer, G. Stewart, Int. Biodeterioration Biodegradation 1998, 41, 261. [56] Y. Chen, S. D. Worley, J. Kim, C. I. Wei, T. Y. Chen, J. I. Santiago, J. F. Williams, G. Sun, Industrial Eng. Chem. Res. 2003, 42, 280. [57] Y. Sun, G. Sun, Macromolecules 2002, 35, 8909. [58] Y. Sun, T. Y. Chen, S. D. Worley, G. Sun, J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 3073. [59] I. Cerkez, H. B. Kocer, S. D. Worley, R. M. Broughton, T. S. Huang, Langmuir 2011, 27, 4091. [60] G. Sun, L. C. Allen, E. P. Luckie, W. B. Wheatley, S. D. Worley, Industrial Eng. Chem. Res. 1995, 34, 4106. [61] Z. Cao, Y. Sun, ACS Appl. Mater. Interfaces 2009, 1, 494. [62] K. Vasilev, J. Cook, H. J. Griesser, Expert Rev. Med. Devices 2009, 6, 553. [63] J. Liang, Y. Chen, X. Ren, R. Wu, K. Barnes, S. D. Worley, R. M. Broughton, U. Cho, H. Kocer, T. S. Huang, Industrial Eng. Chem. Res. 2007, 46, 6425. [64] J. Liang, R. Wu, J. W. Wang, K. Barnes, S. D. Worley, U. Cho, J. Lee, R. M. Broughton, T. S. Huang, J. Industrial Microbiol. Biotechnol. 2007, 34, 157. [65] L. Caillier, E. Taffin de Givenchy, R. Levy, Y. Vandenberghe, S. Geribaldi, F. Guittard, J. Colloid Interface Sci. 2009, 332, 201. [66] W. S. Moon, J. Chul Kim, K. H. Chung, E. S. Park, M. N. Kim, J. S. Yoon, J. Appl. Polym. Sci. 2003, 90, 1797. [67] A. Munoz Bonilla, M. Fernandez Garcia, Prog. Polym. Sci. 2012, 37, 281. [68] E. F. Palermo, K. Kuroda, Biomacromolecules 2009, 10, 1416. [69] K. Kuroda, W. F. DeGrado, J. Am. Chem. Soc. 2005, 127, 4128. [70] G. Sauvet, W. Fortuniak, K. Kazmierski, J. Chojnowski, J. Polym. Sci. Part A: Polym. Chem. 2003, 41, 2939. [71] U. Mizerska, W. Fortuniak, J. Chojnowski, R. HaÅasa, A. Konopacka, W. Werel, Eur. Polym. J. 2009, 45, 779. [72] E. S. Park, W. S. Moon, M. J. Song, M. N. Kim, K. H. Chung, J. S. Yoon, Int. Biodeterioration Biodegradation 2001, 47, 209. [73] E. Subramanyam, S. Mohandoss, H. W. Shin, J. Appl. Polym. Sci. 2009, 112, 2741. [74] T. Nonaka, L. Hua, T. Ogata, S. Kurihara, J. Appl. Polym. Sci. 2003, 87, 386. [75] R. A. Anderson, K. Feathergill, X. Diao, M. Cooper, R. Kirkpatrick, P. Spear, D. P. Waller, C. Chany, G. F. Doncel, B. Herold, J. Androl. 2000, 21, 862. [76] L. J. D. Zaneveld, D. P. Waller, R. A. Anderson, C. Chany, W. F. Rencher, K. Feathergill, X. H. Diao, G. F. Doncel, B. Herold, M. Cooper, Biol. Reproduction 2002, 66, 886. [77] W. R. Li, X. B. Xie, Q. S. Shi, H. Y. Zeng, O. U. Y. You Sheng, Y. B. Chen, Appl. Microbiol. Biotechnol. 2010, 85, 1115. [78] M. Rai, A. Yadav, A. Gade, Biotechnol. Adv. 2009, 27, 76. [79] H. Palza, S. Gutierrez, K. Delgado, O. Salazar, V. Fuenzalida, J. I. Avila, G. Figueroa, R. Quijada, Macromol. Rapid Commun. 2013, 31, 563. [80] T. Huppmann, S. Yatsenko, S. Leonhardt, E. Krampe, I. Radovanovic, M. Bastian, E. Wintermantel, “Antimicrobial polymers-The antibacterial effect of photoactivated nano titanium dioxide polymer composites”, presented at Proc. of PPS-29: The 29th International Conference of the Polymer Processing Society-Conference Papers, Nuremberg, Germany 2014. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 www.advhealthmat.de www.MaterialsViews.com Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400418 [113] Y. J. Jeon, P. J. Park, S. K. Kim, Carbohydr. Polym. 2001, 44, 71. [114] Y. Hu, Y. Du, J. Yang, J. F. Kennedy, X. Wang, L. Wang, Carbohydr. Polym. 2007, 67, 66. [115] E. Yancheva, D. Paneva, V. Maximova, L. Mespouille, P. Dubois, N. Manolova, I. Rashkov, Biomacromolecules 2007, 8, 976. [116] Y. Xie, X. Liu, Q. Chen, Carbohydr. Polym. 2007, 69, 142. [117] M. Ignatova, N. Manolova, I. Rashkov, Eur. Polym. J. 2007, 43, 1112. [118] S.-H. Lim, S. M. Hudson, Carbohydr. Res. 2004, 339, 313. [119] J. Lee, R. M. Broughton, A. Akdag, S. Worley, T.-S. Huang, Textile Res. J. 2007, 77, 604. [120] X. Fu, Y. Shen, X. Jiang, D. Huang, Y. Yan, Carbohydr. Polym. 2011, 85, 221. [121] A. E. Madkour, J. M. Dabkowski, K. Nüsslein, G. N. Tew, Langmuir 2008, 25, 1060. [122] J. C. Tiller, C.-J. Liao, K. Lewis, A. M. Klibanov, Proc. Natl. Acad. Sci. 2001, 98, 5981. [123] G. Cheng, G. Li, H. Xue, S. Chen, J. D. Bryers, S. Jiang, Biomaterials 2009, 30, 5234. [124] Y. Ye, Q. Song, Y. Mao, J. Mater. Chem. 2011, 21, 13188. [125] M. Ignatova, S. Voccia, B. Gilbert, N. Markova, D. Cossement, R. Gouttebaron, R. Jérôme, C. Jérôme, Langmuir 2006, 22, 255. [126] V. Sambhy, M. M. MacBride, B. R. Peterson, A. Sen, J. Am. Chem. Soc. 2006, 128, 9798. [127] H. Deng, P. Lin, S. Xin, R. Huang, W. Li, Y. Du, X. Zhou, J. Yang, Carbohydr. Polym. 2012, 89, 307. [128] J. Tiller, C. Sprich, L. Hartmann, J. Controlled Release 2005, 103, 355. [129] J. Liang, Y. Chen, K. Barnes, R. Wu, S. Worley, T.-S. Huang, Biomaterials 2006, 27, 2495. [130] E. Hart, K. Azzopardi, H. Taing, F. Graichen, J. Jeffery, R. Mayadunne, M. Wickramaratna, M. O’Shea, B. Nijagal, R. Watkinson, J. Antimicrob. Chemother. 2010, 65, 974. [131] A. Onnis-Hayden, B. B. Hsu, A. M. Klibanov, A. Z. Gu, Water Sci. Technol. 2011, 63, 1997. [132] E.-R. Kenawy, S. Worley, R. Broughton, Biomacromolecules 2007, 8, 1359. [133] D. Gangadharan, N. Dhandhala, D. Dixit, R. S. Thakur, K. M. Popat, P. Anand, J. Appl. Polym. Sci. 2012, 124, 1384. [134] P. Jain, T. Pradeep, Biotechnol. Bioeng. 2005, 90, 59. [135] O. Aviv, N. Laout, S. Ratner, O. Harik, K. R. Kunduru, A. J. Domb, J. Controlled Release 2013, 172, 634. [136] S. Lenoir, C. Pagnoulle, C. Detrembleur, M. Galleni, R. Jérôme, J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 1214. [137] S. Mun, E. A. Decker, D. J. McClements, Langmuir 2005, 21, 6228. [138] J. Ngimhuang, J.-i. Furukawa, T. Satoh, T. Furuike, N. Sakairi, Polymer 2004, 45, 837. [139] Y. Jiang, Y. Li, Food Chem. 2001, 73, 139. [140] C. Caner, P. J. Vergano, J. L. Wiles, J. Food Sci. 1998, 63, 1049. [141] D. S. Cha, M. S. Chinnan, Crit. Rev. Food Sci. Nutrition 2004, 44, 223. [142] J. Sjollema, R. J. B. Dijkstra, C. Abeln, H. C. van der Mei, D. van Asseldonk, H. J. Busscher, J. Controlled Release 2014, 188, 61. [143] V. W. L. Ng, J. P. K. Tan, J. Leong, Z. X. Voo, J. L. Hedrick, Y. Y. Yang, Macromolecules 2014, 47, 1285. [144] N. Dinjaski, M. Fernandez Gutierrez, S. Selvam, F. J. Parra Ruiz, S. M. Lehman, J. San Roman, E. Garcia, J. L. Garcia, A. J. Garcia, M. A. Prieto, Biomaterials 2014, 35, 14. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com REVIEW [81] D. Chung, S. E. Papadakis, K. L. Yam, Int. J. Food Sci. Technol. 2003, 38, 165. [82] H. Zhang, D. Wang, R. Butler, N. L. Campbell, J. Long, B. Tan, D. J. Duncalf, A. J. Foster, A. Hopkinson, D. Taylor, Nat. Nanotechnol. 2008, 3, 506. [83] I. M. Helander, H. L. Alakomi, K. Latva Kala, P. Koski, Microbiology 1997, 143, 3193. [84] H. Khalil, T. Chen, R. Riffon, R. Wang, Z. Wang, Antimicrob. Agents Chemother. 2008, 52, 1635. [85] M. Bankova, N. Manolova, N. Markova, T. Radoucheva, K. Dilova, I. Rashkov, J. Bioactive Compatible Polym. 1997, 12, 294. [86] M. A. Gelman, B. Weisblum, D. M. Lynn, S. H. Gellman, Org. Lett. 2004, 6, 557. [87] G. N. Tew, R. W. Scott, M. L. Klein, W. F. DeGrado, Acc. Chem. Res. 2009, 43, 30. [88] M. Zasloff, Nature 2002, 415, 389. [89] Y. Shai, Biochim. Biophys. Acta 1999, 1462, 55. [90] B. P. Mowery, S. E. Lee, D. A. Kissounko, R. F. Epand, R. M. Epand, B. Weisblum, S. S. Stahl, S. H. Gellman, J. Am. Chem. Soc. 2007, 129, 15474. [91] C. Zhou, X. Qi, P. Li, W. N. Chen, L. Mouad, M. W. Chang, S. S. J. Leong, M. B. Chan-Park, Biomacromolecules 2009, 11, 60. [92] G. J. Gabriel, A. Som, A. E. Madkour, T. Eren, G. N. Tew, Mater. Sci. Eng. R. Rep. 2007, 57, 28. [93] C. E. Carraher Jr., T. S. Sabir, M. R. Roner, K. Shahi, R. E. Bleicher, J. L. Roehr, K. D. Bassett, J. Inorg. Organometal. Polym. Mater. 2006, 16, 249. [94] I. C. Yue, J. Poff, M. E. Cortes, R. D. Sinisterra, C. B. Faris, P. Hildgen, R. Langer, V. P. Shastri, Biomaterials 2004, 25, 3743. [95] S. Chemburu, T. S. Corbitt, L. K. Ista, E. Ji, J. Fulghum, G. P. Lopez, K. Ogawa, K. S. Schanze, D. G. Whitten, Langmuir 2008, 24, 11053. [96] L. Lu, F. H. Rininsland, S. K. Wittenburg, K. E. Achyuthan, D. W. McBranch, D. G. Whitten, Langmuir 2005, 21, 10154. [97] R. Duncan, L. Izzo, Advanced drug delivery reviews 2005, 57, 2215. [98] A. I. Lopez, R. Y. Reins, A. M. McDermott, B. W. Trautner, C. Cai, Mol. BioSyst. 2009, 5, 1148. [99] C. Z. Chen, S. L. Cooper, Biomaterials 2002, 23, 3359. [100] C. Z. Chen, S. L. Cooper, N. C. B. Tan, Chem. Commun. 1999, 1585. [101] C. Z. Chen, N. C. Beck Tan, P. Dhurjati, T. K. van Dyk, R. A. LaRossa, S. L. Cooper, Biomacromolecules 2000, 1, 473. [102] L. Balogh, D. R. Swanson, D. A. Tomalia, G. L. Hagnauer, A. T. McManus, Nano Lett. 2001, 1, 18. [103] N. Beyth, S. Farah, A. J. Domb, E. I. Weiss, Reactive Funct. Polym. 2014, 75, 81. [104] S. Farah, W. Khan, I. Farber, D. Kesler Shvero, N. Beyth, E. I. Weiss, A. J. Domb, Polym. Adv. Technol.24, 446. [105] N. Beyth, I. Yudovin Farber, R. Bahir, A. J. Domb, E. I. Weiss, Biomaterials 2006, 27, 3995. [106] N. Beyth, Y. Houri Haddad, L. Baraness Hadar, I. Yudovin Farber, A. J. Domb, E. I. Weiss, Biomaterials 2008, 29, 4157. [107] N. Beyth, I. Yudovin Fearber, A. J. Domb, E. I. Weiss, Quintessence Int. 2010, 41, 827. [108] A. J. Domb, N. Beyth, S. Farah, “Quaternary Ammonium Antimicrobial Polymers”, presented at MRS Proc. 2013. [109] S. Farah, O. Aviv, N. Laout, S. Ratner, N. Beyth, A. J. Domb, Polym. Adv. Technol. 2014, 25, 689. [110] W. Yuan, J. Wei, H. Lu, L. Fan, J. Du, Chem. Commun. 2012, 48, 6857. [111] A. Kanazawa, T. Ikeda, T. Endo, J. Polym. Sci. Part A: Polym. Chem. 1993, 31, 1467. [112] T. Takahashi, M. Imai, I. Suzuki, J. Sawai, Biochem. Eng. J. 2008, 40, 485. 17