Nitric Oxide-Releasing Polymer-Based Systems for Antibiofilm Applications

Bacterial cells are well known to embed within self-produced extracellular substance known as biofilms which protect them from most antibacterial agents. Biofilm-related infections not only cause human pain but also place a substantial economic burden on society. One approach to overcome this global challenge involves the use of the nitric oxide (NO) molecule. However, practical applications of NO donors have been hindered by their poor stability and lack of localized delivery. The utilization of polymers in nitric oxide delivery has been shown to be a promising strategy to surmount these weaknesses. This work aimed to explore polymer-based platforms for NO delivery.Firstly, synthesis of nanoparticles with two morphologies for the delivery of NO were explored. The spherical and cylindrical nanoparticles were prepared using Photo-initiated Polymerization Induced Self-Assembly and employed to encapsulate N-diazeniumdiolate in their cores. The resulting NO-releasing nanoparticles demonstrated excellent antibacterial activity at very low concentrations. Additionally, the NO release rate and biofilm dispersal were found to strongly depend on the nanoparticle morphology.In the second approach, the versatile adhesion feature of polydopamine (pDA) was used to prepare NO-releasing coatings that could prevent the formation of biofilm. A facile coating process was implemented to design a coating that possessed low-fouling properties (conferred by polyethylene glycol) and NO-releasing capabilities. The novel feature of this work was the applicability of this facile technology for a broad range of surfaces, including polymer films and inorganic surfaces (glass). The introduction of both functionalities in pDA film prevented the formation of P. aeruginosa biofilms, including a multidrug-resistant strain, on substrates and killed 99.9% of any adhered bacteria biofilm cells.The third approach included the development of an antibiofilm coating that possessed S-nitrosothiol NO donors for biofilm prevention applications. Cell culture dishes with 4 different film thicknesses were coated via plasma polymerization (PP) using a thiol monomer. The thiol functionality on the substrates was converted to S-nitrosothiol NO precursors. The plasma-modified surfaces showed 81% inhibition of P. aeruginosa bacterial attachment to the surface after 24 h exposure to the bacterial solution and presented a potential viable strategy to inhibit bacterial biofilm formation

Surface functionalization of upconversion nanoparticles using visible light-mediated polymerization

Lanthanide-doped upconversion nanoparticles (UCNPs) have unique photoluminescent properties which are useful in many biomedical applications. However, to extend their practical use prior surface modification is essential. Herein, we present a straightforward and generic visible light-mediated method for growing a polymer shell with controlled architecture from the UCNPs surfaces (i.e. "grafting from") and demonstrate an application in the delivery of nitric oxide (NO). Our approach has the advantage that no external photocatalyst or initiator is required to initiate the polymerization of the polymer chains. A silica layer was initially generated on the surfaces of the UCNPs as a platform for tethering 4-cyano-4-((dodecylsulfanylthiocarbonyl) sulfanyl) pentanoic acid (CDTPA), a chain transfer agent. The polymerization of functional monomers (glycidyl methacrylate (GMA), poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) or hydroxyethyl methacrylate (HEMA) were then initiated using CDTPA as initiator/chain transfer agent under blue (460 nm, 0.7 mW/cm2) or green (530 nm, 0.7 mW/cm2) light. The PGMA layer can be used to chemically attach various functional molecules onto the UCNPs surface without affecting the luminescence properties of the particles. The polymers also improve the colloidal stability of the UCNPs in water and biocompatibility of the UCNPs. These particles were then used to store and release NO by functionalizing their surfaces with N-diazeniumdiolates (NONOate) moieties. Using the NONOate functionalized UCNPs, relatively slow and controlled release of NO over 6 h can achieved

Recent advances in nitric oxide delivery for antimicrobial applications using polymer-based systems

The nitric oxide (NO) molecule has gained increasing attention in biological applications to combat biofilm-associated bacterial infections. However, limited NO loading, relatively short half-lives of low molecular weight NO donor compounds, and difficulties in targeted delivery of NO have hindered their practical clinical administration. To overcome these drawbacks, the combination of NO and scaffolds based on biocompatible polymers is an effective way towards realizing the practical utility of NO in biomedical applications. In this regard, the present overview highlights the recent developments in NO-releasing polymeric biomaterials for antimicrobial applications, focusing on antibiofilm treatments and the challenges that need to be overcome

Synergy between Synthetic Antimicrobial Polymer and Antibiotics:A Promising Platform to Combat Multidrug-resistant Bacteria

The failure of many antibiotics in the treatment of chronic infections caused by multidrug-resistant (MDR) bacteria necessitates the development of effective strategies to combat this global healthcare issue. Here, we report an antimicrobial platform based on the synergistic action between commercially available antibiotics and a potent synthetic antimicrobial polymer that consists of three key functionalities: low-fouling oligoethylene glycol, hydrophobic ethylhexyl, and cationic primary amine groups. Checkerboard assays with Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli demonstrated synergy between our synthetic antimicrobial polymer and two antibiotics, doxycycline and colistin. Coadministration of these compounds significantly improved the bacteriostatic efficacy especially against MDR P. aeruginosa strains PA32 and PA37, where the minimal inhibitory concentrations (MICs) of polymer and antibiotics were reduced by at least 4-fold. A synergistic killing activity was observed when the antimicrobial polymer was used in combination with doxycycline, killing >99.999% of planktonic and biofilm P. aeruginosa PAO1 upon a 20 min treatment at a polymer concentration of 128 μg mL -1 (4.6 μM) and doxycycline concentration of 64 μg mL -1 (133.1 μM). In addition, this synergistic combination reduced the rate of resistance development in P. aeruginosa compared to individual compounds and was also capable of reviving susceptibility to treatment in the resistant strains

Antibiofilm Nitric Oxide-Releasing Polydopamine Coatings

The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices

Exploiting the Versatility of Polydopamine-Coated Nanoparticles to Deliver Nitric Oxide and Combat Bacterial Biofilm

In this study, an antimicrobial platform in the form of nitric oxide (NO) gas-releasing polydopamine (PDA)-coated iron oxide nanoparticles (IONPs) is developed for combating bacterial biofilms. NO is bound to the PDA-coated IONPs via the reaction between NO and the secondary amine moieties on PDA to form N-diazeniumdiolate (NONOate) functionality. To impart colloidal stability to the nanoparticles in aqueous solutions (e.g., phosphate buffered saline (PBS) and bacteria cell culture media M9), a polymer bearing hydrophilic and amine pendant groups, P(OEGMA)-b-P(ABA), is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and is subsequently grafted onto the PDA-coated IONPs by employing the Schiff base/Michael addition reaction between o-quinone and a primary amine. These nanoparticles are able to effectively disperse Pseudomonas aeruginosa biofilms (up to 79% dispersal) at submicromolar NO concentrations. In addition, the nanoparticles demonstrate excellent bactericidal activity toward P. aeruginosa planktonic and biofilm cells (up to 5-log10 reduction)

Nitric Oxide-Loaded Antimicrobial Polymer for the Synergistic Eradication of Bacterial Biofilm

Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO)-releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 μg mL-1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a single chemical entity, instead of a cocktail physical mixture of two individual components. The excellent antimicrobial/antibiofilm activity of this dual-action polymer suggests the advantages of combination therapy in combating bacterial biofilms

Nitric Oxide-Loaded Antimicrobial Polymer for the Synergistic Eradication of Bacterial Biofilm

Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO) releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm 99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 μg mL-1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a single chemical entity, instead of a cocktail physical mixture of two individual components. The excellent antimicrobial/antibiofilm activity of this dual-action polymer suggests the advantages of combination therapy in combating bacterial biofilms

Exploiting the Versatility of Polydopamine-Coated Nanoparticles to Deliver Nitric Oxide and Combat Bacterial Biofilm

In this study, an antimicrobial platform in the form of nitric oxide (NO) gasreleasing polydopamine (PDA)-coated iron oxide nanoparticles (IONPs) is developed for combating bacterial biofilms. NO is bound to the PDA-coated IONPs via the reaction between NO and the secondary amine moieties on PDA to form N-diazeniumdiolate (NONOate) functionality. To impart colloidal stability to the nanoparticles in aqueous solutions (e.g., phosphate buffered saline (PBS) and bacteria cell culture media M9), a polymer bearing hydrophilic and amine pendant groups, P(OEGMA)-b-P(ABA), is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and is subsequently grafted onto the PDA-coated IONPs by employing the Schiff base/Michael addition reaction between o-quinone and a primary amine. These nanoparticles are able to effectively disperse Pseudomonas aeruginosa biofilms (up to 79% dispersal) at submicromolar NO concentrations. In addition, the nanoparticles demonstrate excellent bactericidal activity toward P. aeruginosa planktonic and biofilm cells (up to 5-log10 reduction)

Nitric Oxide-Loaded Antimicrobial Polymer for the Synergistic Eradication of Bacterial Biofilm

Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO)-releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 μg mL^–1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a single chemical entity, instead of a cocktail physical mixture of two individual components. The excellent antimicrobial/antibiofilm activity of this dual-action polymer suggests the advantages of combination therapy in combating bacterial biofilms