Precisely Structured Nitric-Oxide-Releasing Copolymer Brush Defeats Broad-Spectrum Catheter-Associated Biofilm Infections In Vivo

Macrophage-Targeted GSH-Depleting Nanocomplexes for Synergistic Chemodynamic Therapy/Gas Therapy/Immunotherapy of Intracellular Bacterial Infection

Intracellular pathogens can survive inside the macrophages to protect themselves from eradication by the innate immune system and conventional antibiotics, resulting in severe bacterial infections. In this work, an antibiotic-free nanocomplex (HA/GA-Fe@NO-DON), exhibiting macrophage-targeted synergistic gas therapy (nitric oxide, NO)/chemodynamic therapy/immunotherapy, was reported. HA/GA-Fe nanoparticles were synthesized by the strong coordination interactions among carboxyl groups of hyaluronic acid (HA), polyphenol groups of gallic acid (GA), and Fe(II) ions. The hydrophobic glutathione (GSH)-responsive NO donor (NO-DON) was encapsulated in HA/GA-Fe nanoparticles to form the final nanocomplexes (HA/GA-Fe@NO-DON). HA on the nanocomplexes guides the macrophage-specific uptake and intracellular accumulation. After the uptake, HA/GA-Fe@NO-DON nanocomplexes could not only generate highly toxic hydroxyl radicals (•OH) by the Fenton reaction and GSH depletion but also release NO when stimulated by intracellular GSH. Meanwhile, the nanocomplexes could trigger an efficient proinflammation immune response to reinforce the antibacterial activity. This work presents the development of antibiotic-free macrophage-targeted HA/GA-Fe@NO-DON nanocomplexes as an effective adjuvant nanomedicine with synergistic gas therapy/chemodynamic therapy/immunotherapy for eliminating intracellular bacterial infection.

A comprehensive status update on modification of foley catheter to combat catheter-associated urinary tract infections and microbial biofilms

Present-day healthcare employs several types of invasive devices, including urinary catheters, to improve medical wellness, the clinical outcome of disease, and the quality of patient life. Among urinary catheters, the Foley catheter is most commonly used in patients for bladder drainage and collection of urine. Although such devices are very useful for patients who cannot empty their bladder for various reasons, they also expose patients to catheter-associated urinary tract infections (CAUTIs). Catheter provides an ideal surface for bacterial colonization and biofilm formation, resulting in persistent bacterial infection and severe complications. Hence, rigorous efforts have been made to develop catheters that harbour antimicrobial and anti-fouling properties to resist colonization by bacterial pathogens. In this regard, catheter modification by surface functionalization, impregnation, blending, or coating with antibiotics, bioactive compounds, and nanoformulations have proved to be effective in controlling biofilm formation. This review attempts to illustrate the complications associated with indwelling Foley catheters, primarily focussing on challenges in fighting CAUTI, catheter colonization, and biofilm formation. In this review, we also collate scientific literature on catheter modification using antibiotics, plant bioactive components, bacteriophages, nanoparticles, and studies demonstrating their efficacy through in vitro and in vivo testing.

Urchin-like Fe3O4@Bi2S3 Nanospheres Enable the Destruction of Biofilm and Efficiently Antibacterial Activities

Biofilm-associated infections (BAIs) have been considered a major threat to public health, which induce persistent infections and serious complications. The poor penetration of antibacterial agents in biofilm significantly limits the efficiency of combating BAIs. Magnetic urchin-like core-shell nanospheres of Fe3O4@Bi2S3 were developed for physically destructing biofilm and inducing bacterial eradication via reactive oxygen species (ROS) generation and innate immunity regulation. The urchin-like magnetic nanospheres with sharp edges of Fe3O4@Bi2S3 exhibited propeller-like rotation to physically destroy biofilm under a rotating magnetic field (RMF). The mild magnetic hyperthermia improved the generation of ROS and enhanced bacterial eradication. Significantly, the urchin-like nanostructure and generated ROS could stimulate macrophage polarization toward the M1 phenotype, which could eradicate the persistent bacteria with a metabolic inactivity state through phagocytosis, thereby promoting the recovery of implant infection and inhibiting recurrence. Thus, the design of magnetic-driven sharp-shaped nanostructures of Fe3O4@Bi2S3 provided enormous potential in combating biofilm infections.

Heparin-network-mediated long-lasting coatings on intravascular catheters for adaptive antithrombosis and antibacterial infection

Bacteria-associated infections and thrombosis, particularly catheter-related bloodstream infections and catheter-related thrombosis, are life-threatening complications. Herein, we utilize a concise assembly of heparin sodium with organosilicon quaternary ammonium surfactant to fabricate a multifunctional coating complex. In contrast to conventional one-time coatings, the complex attaches to medical devices with arbitrary shapes and compositions through a facile dipping process and further forms robust coatings to treat catheter-related bloodstream infections and thrombosis simultaneously. Through their robustness and adaptively dissociation, coatings not only exhibit good stability under extreme conditions but also significantly reduce thrombus adhesion by 60%, and shows broad-spectrum antibacterial activity ( > 97%) in vitro and in vivo. Furthermore, an ex vivo rabbit model verifies that the coated catheter has the potential to prevent catheter-related bacteremia during implantation. This substrate-independent and portable long-lasting multifunctional coating can be employed to meet the increasing clinical demands for combating catheter-related bloodstream infections and thrombosis.

Biosurfactant from Nile Papyrus endophyte with potential antibiofilm activity against global clones of Acinetobacter baumannii

Acinetobacter baumannii is a leading cause of biofilm-associated infections, particularly catheter-related bloodstream infections (CRBSIs) that are mostly recalcitrant to antimicrobial therapy. One approach to reducing the burden of CRBSIs is inhibiting biofilm formation on catheters. Owing to their prodigious microbial diversity, bacterial endophytes might be a valuable source of biosurfactants, which are known for their great capacity to disperse microbial biofilms. With this in mind, our study aimed to screen bacterial endophytes from plants growing on the banks of the River Nile for the production of powerful biosurfactants capable of reducing the ability of A. baumannii to form biofilms on central venous catheters (CVCs). This was tested on multidrug- and extensive drug-resistant (M/XDR) clinical isolates of A. baumannii that belong to high-risk global clones and on a standard strain of A. baumannii ATCC 19606. The drop collapse and oil dispersion assays were employed in screening the cell-free supernatants (CFS) of all endophytes for biosurfactant activity. Of the 44 bacterial endophytes recovered from 10 plants, the CFS of Bacillus amyloliquefaciens Cp24, isolated from Cyperus papyrus, showed the highest biosurfactant activity. The crude biosurfactant extract of Cp24 showed potent antibacterial activity with minimum inhibitory concentrations (MICs) ranging from 0.78 to 1.56 mg/ml. It also showed significant antibiofilm activity (p-value<0.01). Sub-MICs of the extract could reduce biofilm formation by up to 89.59%, while up to 87.3% of the preformed biofilms were eradicated by the MIC. A significant reduction in biofilm formation on CVCs impregnated with sub-MIC of the extract was demonstrated by CV assay and further confirmed by scanning electron microscopy. This was associated with three log₁₀ reductions in adhered bacteria in the viable count assay. GC-MS analysis of the crude biosurfactant extract revealed the presence of several compounds, such as saturated, unsaturated, and epoxy fatty acids, cyclopeptides, and 3-Benzyl-hexahydro-pyrrolo [1, 2-a] pyrazine-1,4-dione, potentially implicated in the potent biosurfactant and antibiofilm activities. In the present study, we report the isolation of a B. amyloliquefaciens endophyte from the plant C. papyrus that produces a biosurfactant with potent antibiofilm activity against MDR/XDR global clones of A. baumannii. The impregnation of CVCs with the biosurfactant was demonstrated to reduce biofilms and, hence, proposed as a potential strategy for reducing CRBSIs.

Nitric Oxide-Releasing Hemodialysis Catheter Lock Solutions

In an attempt to address the significant morbidity, mortality, and economic cost associated with tunneled dialysis catheter (TDC) dysfunction, we report the development of nitric oxide-releasing dialysis catheter lock solutions. Catheter lock solutions with a range of NO payloads and release kinetics were prepared using low-molecular-weight N-diazeniumdiolate nitric oxide donors. Nitric oxide released through the catheter surface as a dissolved gas was maintained at therapeutically relevant levels for at least 72 h, supporting clinical translatability (interdialytic period). Slow, sustained NO release from the catheter surface prevented bacterial adhesion in vitro by 88.9 and 99.7% for Pseudomonas aeruginosa and Staphylococcus epidermidis, respectively, outperforming a burst NO-release profile. Furthermore, bacteria adhered to the catheter surface in vitro prior to lock solution use was reduced by 98.7 and 99.2% for P. aeruginosa and S. epidermidis, respectively, when using a slow releasing NO donor, demonstrating both preventative and treatment potential. The adhesion of proteins to the catheter surface, a process often preceding biofilm formation and thrombosis, was also lessened by 60-65% by sustained NO release. In vitro cytotoxicity of catheter extract solutions to mammalian cells was minimal, supporting the non-toxic nature of the NO-releasing lock solutions. The use of the NO-releasing lock solution in an in vivo TDC porcine model demonstrated decreased infection and thrombosis, enhanced catheter functionality, and improved outcome (i.e., likelihood of survival) as a result of catheter use.

Nanoarchitectonics of nitric oxide releasing supramolecular structures for enhanced antibacterial efficacy under visible light irradiation

Light-controlled therapies offer a promising strategy to prevent and suppress infections caused by numerous bacterial pathogens. Excitation of exogenously supplied photosensitizers (PS) at specific wavelengths elicits levels of reactive oxygen intermediates toxic to bacteria. Porphyrin-based supramolecular nanostructure frameworks (SNF) are effective PS with unique physicochemical properties that have led to their widespread use in photomedicine. Herein, we developed a nitric oxide (NO) releasing, biocompatible, and stable porphyrin-based SNF (SNF-NO), which was achieved through a confined noncovalent self-assembly process based on π-π stacking. Characterization of the SNFs via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis showed the formation of three-dimensional, well-defined octahedral structures. These SNF-NO were shown to exhibit a red shift due to the noncovalent self-assembly of porphyrins, which also show extended light absorption to broadly cover the entire visible light spectrum to enhance photodynamic therapy (PDT). Under visible light irradiation (46 J cm-2), the SNF generates high yields of singlet oxygen (1O2) radicals, hydroxyl radicals (HO), superoxide radicals (O2), and peroxynitrite (ONOO-) radicals that have shown potential to enhance antimicrobial photodynamic therapy (APDT) against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli (E. coli). The resulting SNFs also exhibit significant biofilm dispersion and a decrease in biomass production. The combination of robust photosensitizer SNFs with nitric oxide-releasing capabilities is dynamic in its ability to target pathogenic infections while remaining nontoxic to mammalian cells. The engineered SNFs have enormous potential for treating and managing microbial infections.

Brush Polymer Coatings with Hydrophilic Main-Chains for Improving Surface Antibacterial Properties

Polymer coatings with improved surface antibacterial properties are of great importance for the application and development of implantable medical devices. Herein, we report the design, preparation, and antibacterial properties of a series of brush polymers (Dex-KEs) with hydrophilic dextran main-chains and mixed-charge polypeptide (KE) side-chains. Dex-KEs showed higher bactericidal activity and antifouling and antibiofilm properties than maleic acid modified dextran (Dex-Ma), KE, Dex-Ma/KE blend coatings, and brush polymer coatings with hydrophobic main-chains (AcDex-KEs). They also showed negligible in vitro cytotoxicity toward different mammalian cells and good in vivo biocompatibility. Dex-KE-coated implants exhibited potent in vivo resistance to bacterial infection before or after implantation.

Regulable Polyelectrolyte-Surfactant Complex for Antibacterial Biomedical Catheter Coating via a Readily Scalable Route

Constructing multifunctional surfaces is one of the practical approaches to address catheter-related multiple complications but is generally time-consuming and substrate-dependent. Herein, a novel anti-adhesion, antibacterial, low friction, and robustness coating on medical catheters are developed via a universal and readily scalable method based on a regulable polyelectrolyte surfactant complex. The complex is rapidly assembled in one step by electrostatic and hydrophobic interactions between organosilicon quaternary ammonium surfactant (N⁺ _Si ) and adjustable polyelectrolyte with cross-linkable, anti-adhesive, and anionic groups. The alcohol-soluble feature of the complex is conducive to the rapid formation of coatings on any medical device with arbitrary shapes via dip coating. Different from the conventional polyelectrolyte-surfactant complex coating, the regulated complex coating with nonleaching mode could be stable in harsh conditions (high concentration salt solution, organic reagents, etc.) because of the cross-linked structure while improving the biocompatibility and reducing the adhesion of various bacteria, proteins, and blood cells. The coated catheter exhibits good antibacterial infection in vitro and in vivo, owing to the synergistic effect of N⁺ _Si and zwitterionic groups. Therefore, the rationally designed complex supplies a facile coating approach for the potential development in combating multiple complications of the medical catheter.

Antibacterial brush polypeptide coatings with anionic backbones

Preventing initial colonization of bacteria on biomaterial surfaces is crucial to address the medical device-associated infection issues. Antimicrobial peptide (AMP) or cationic polymer modified surfaces have shown promising potentials to inhibit the initial colonization of bacteria by contact killing. However, their development has been impeded because of bacterial adhesion and high cytotoxicity. Herein, we report a series of brush polypeptide coatings with anionic backbones and cationic AMP mimetic side-chains that displayed superior bactericidal activity, antibacterial adhesion property, and biocompatibility. The cationic side-chain density played an important role in the bioactivities of the brush polypeptide modified surfaces. Brush polypeptide coating with low side-chain density exhibited improved bactericidal activity and antibacterial adhesion property, ascribing to the cooperative effects of adjacent side-chains and backbones/side-chains, respectively. It also showed negligible hemolysis/cytotoxicity in vitro and potent anti-infection property (≥99.9% bactericidal efficacy) in vivo. Brush polymers with anionic backbones and cationic side-chains can be used as a promising design motif to potentiate both antibacterial property and biocompatibility of coatings for combating device-associated infections. STATEMENT OF SIGNIFICANCE: Device-associated infections (DAIs) have led to increased medical cost, pain, and even mortality of patients. Antimicrobial peptide and cationic polymer coatings provide an important strategy to combat DAIs by preventing initial colonization of bacteria on biomaterial surfaces. Nevertheless, they have suffered bacterial adhesion and cytotoxicity issues. Herein, we developed a brush polypeptide coating with anionic backbones and cationic side-chains. The brush polypeptide coating showed superior bactericidal and antibacterial adhesion properties outperforming conventional antibacterial coatings based on antimicrobial peptide (i.e., melittin), lysozyme (i.e., lysostaphin), cationic polymer, anionic polymer, and the blends of cationic/anionic polymers. It also showed good biocompatibility and potent anti-infection property, making it a promising candidate to combat the DAIs.

Emerging Strategies in Stimuli-Responsive Prodrug Nanosystems for Cancer Therapy

Prodrugs are chemically modified drug molecules that are inactive before administration. After administration, they are converted in situ to parent drugs and induce the mechanism of action. The development of prodrugs has upgraded conventional drug treatments in terms of bioavailability, targeting, and reduced side effects. Especially in cancer therapy, the application of prodrugs has achieved substantial therapeutic effects. From serendipitous discovery in the early stage to functional design with pertinence nowadays, the importance of prodrugs in drug design is self-evident. At present, studying stimuli-responsive activation mechanisms, regulating the stimuli intensity in vivo, and designing nanoscale prodrug formulations are the major strategies to promote the development of prodrugs. In this review, we provide an outlook of recent cutting-edge studies on stimuli-responsive prodrug nanosystems from these three aspects. We also discuss prospects and challenges in the future development of such prodrugs.

Strategies to prevent, curb and eliminate biofilm formation based on the characteristics of various periods in one biofilm life cycle

Biofilms are colonies of bacteria embedded inside a complicated self-generating intercellular. The formation and scatter of a biofilm is an extremely complex and progressive process in constant cycles. Once formed, it can protect the inside bacteria to exist and reproduce under hostile conditions by establishing tolerance and resistance to antibiotics as well as immunological responses. In this article, we reviewed a series of innovative studies focused on inhibiting the development of biofilm and summarized a range of corresponding therapeutic methods for biological evolving stages of biofilm. Traditionally, there are four stages in the biofilm formation, while we systematize the therapeutic strategies into three main periods precisely:(i) period of preventing biofilm formation: interfering the colony effect, mass transport, chemical bonds and signaling pathway of plankton in the initial adhesion stage; (ii) period of curbing biofilm formation:targeting several pivotal molecules, for instance, polysaccharides, proteins, and extracellular DNA (eDNA) via polysaccharide hydrolases, proteases, and DNases respectively in the second stage before developing into irreversible biofilm; (iii) period of eliminating biofilm formation: applying novel multifunctional composite drugs or nanoparticle materials cooperated with ultrasonic (US), photodynamic, photothermal and even immune therapy, such as adaptive immune activated by stimulated dendritic cells (DCs), neutrophils and even immunological memory aroused by plasmocytes. The multitargeted or combinational therapies aim to prevent it from developing to the stage of maturation and dispersion and eliminate biofilms and planktonic bacteria simultaneously.

Recent Developments in Multifunctional Antimicrobial Surfaces and Applications toward Advanced Nitric Oxide-Based Biomaterials

Implant-associated infections arising from biofilm development are known to have detrimental effects with compromised quality of life for the patients, implying a progressing issue in healthcare. It has been a struggle for more than 50 years for the biomaterials field to achieve long-term success of medical implants by discouraging bacterial and protein adhesion without adversely affecting the surrounding tissue and cell functions. However, the rate of infections associated with medical devices is continuously escalating because of the intricate nature of bacterial biofilms, antibiotic resistance, and the lack of ability of monofunctional antibacterial materials to prevent the colonization of bacteria on the device surface. For this reason, many current strategies are focused on the development of novel antibacterial surfaces with dual antimicrobial functionality. These surfaces are based on the combination of two components into one system that can eradicate attached bacteria (antibiotics, peptides, nitric oxide, ammonium salts, light, etc.) and also resist or release adhesion of bacteria (hydrophilic polymers, zwitterionic, antiadhesive, topography, bioinspired surfaces, etc.). This review aims to outline the progress made in the field of biomedical engineering and biomaterials for the development of multifunctional antibacterial biomedical devices. Additionally, principles for material design and fabrication are highlighted using characteristic examples, with a special focus on combinational nitric oxide-releasing biomedical interfaces. A brief perspective on future research directions for engineering of dual-function antibacterial surfaces is also presented.

Silicone Foley catheters impregnated with microbial indole derivatives inhibit crystalline biofilm formation by Proteus mirabilis

Proteus mirabilis is a common causative agent for catheter-associated urinary tract infections (CAUTI). The crystalline biofilm formation by P. mirabilis causes catheter encrustation and blockage leading to antibiotic treatment resistance. Thus, biofilm formation inhibition on catheters becomes a promising alternative for conventional antimicrobial-based treatment that is associated with rapid resistance development. Our previous work has demonstrated the in vitro antibiofilm activity of microbial indole derivatives against clinical isolates of P. mirabilis. Accordingly, we aim to evaluate the capacity of silicone Foley catheters (SFC) impregnated with these indole derivatives to resist biofilm formation by P. mirabilis both phenotypically and on the gene expression level. Silicon Foley catheter was impregnated with indole extract recovered from the supernatant of the rhizobacterium Enterobacter sp. Zch127 and the antibiofilm activity was determined against P. mirabilis (ATCC 12435) and clinical isolate P8 cultured in artificial urine. The indole extract at sub-minimum inhibitory concentration (sub-MIC=0.5X MIC) caused a reduction in biofilm formation as exhibited by a 60-70% reduction in biomass and three log₁₀ in adhered bacteria. Results were confirmed by visualization by scanning electron microscope. Moreover, changes in the relative gene expression of the virulence genes confirmed the antibiofilm activity of the indole extract against P. mirabilis. Differential gene expression analysis showed that extract Zch127 at its sub-MIC concentration significantly down-regulated genes associated with swarming activity: umoC, flhC, flhD, flhDC, and mrpA (p< 0.001). In addition, Zch127 extract significantly down-regulated genes associated with polyamine synthesis: speB and glnA (p< 0.001), as well as the luxS gene associated with quorum sensing. Regulatory genes for capsular polysaccharide formation; rcsB and rcsD were not significantly affected by the presence of the indole derivatives. Furthermore, the impregnated catheters and the indole extract showed minimal or no cytotoxic effect against human fibroblast cell lines indicating the safety of this intervention. Thus, the indole-impregnated catheter is proposed to act as a suitable and safe strategy for reducing P. mirabilis CAUTIs.

Dopamine Assisted Self-Cleaning, Antifouling, and Antibacterial Coating via Dynamic Covalent Interactions

The rapid accumulation of dead bacteria or protein on a bactericidal surface can reduce the effectiveness of the modified surface and alter its biocidal activity by shielding the surface biocide functional groups, promoting microbial attachment and subsequent biofilm formation. Thus, the alteration of biocidal activity due to biofilm formation can cause serious trouble including severe infection or implant or medical device failure leading to death. Therefore, developing a smart self-cleaning surface is of great interest. Ideally, such a surface can not only kill the attached microbials but also release the dead cells and foulants from the surface under a particular incitement on demand. In this project, a sugar-responsive self-cleaning coating has been developed by forming covalent boronic ester bonds between catechol groups from polydopamine and a benzoxaborole pendant from zwitterionic and cationic polymers. To incorporate antifouling properties and enhance the biocompatibility of the coating, bioinspired zwitterionic compound 2-methacryloyloxyethyl phosphorylcholine (MPC) was chosen and benzoxaborole pendant containing zwitterionic polymer poly(MPC-st-MAABO) (MAABO: 5-methacrylamido-1,2-benzoxaborole) was synthesized. Additionally to impart antibacterial properties to the surface, a quaternary ammonium containing cationic polymer poly(2-(methacryloyloxy)ethyl trimethylammonium (META)-st-MAABO)) was synthesized. These synthesized polymers were covalently grafted to a polydopamine (PDA) coated surface by forming a strong cyclic boronic ester complex with a catechol group of the PDA layer endowing the surface with bacteria contact-killing properties and capturing specific protein. After the addition of cis-diol containing competitive molecules, i.e., saccharides/sugars, this boronic ester complex with a catechol group of PDA was replaced and the attached polymer layer was cleaved from the surface, resulting in the release of both absorbed protein and live/killed bacteria electrostatically attached to the polymer layer. This dynamic self-cleaning surface can be a promising material for biomedical applications avoiding the gathering of dead cells and debris that are typically encountered on a traditional biocidal surface.

Potent, Broad-Spectrum Antimicrobial Effects of S-Nitroso-N-acetylpenicillamine-Impregnated Nitric Oxide-Releasing Latex Urinary Catheters

Although numerous prevention and intervention techniques have been developed to counteract catheter-associated urinary tract infections (CAUTIs), urinary catheters remain one of the most common sources of hospital-acquired infections. Nitric oxide (NO), a gaseous free radical responsible for regulating many physiological functions in the body, has gained immense popularity due to its potent, broad-spectrum antimicrobial activity, which is capable of combating medical device-associated infections. In this work, a straightforward solvent-swelling method was used to load the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) into commercial latex catheters (SNAP-UCs) for the first time. The effects of swelling catheters with different concentrations of SNAP solutions (25-125 mg/mL SNAP in tetrahydrofuran (THF)) were studied by measuring the NO release kinetics, SNAP loading, and SNAP leaching. SNAP-UCs impregnated with a 50 mg/mL SNAP-THF solution were found to maximize the amount of SNAP loaded into the latex (0.115 ± 0.009 mg SNAP/mg catheter) and showed physiological levels of NO release (>2 × 10^-10 mol min^-1 cm^-2) over 7 days and minimal SNAP leaching (<2%). SNAP-UCs showed impressive in vitro contact-based and diffusible antimicrobial efficacy against three CAUTI-associated pathogens, reducing the viability of adhered and planktonic Escherichia coli, Proteus mirabilis, and Staphylococcus aureus by ∼98.0 to 99.1% (adhered) and 86.3-96.3% (planktonic) compared to control latex catheters. In vitro cytotoxicity against 3T3 mouse fibroblasts using a CCK-8 assay showed that SNAP-UCs were noncytotoxic (>90% viability). In summary, SNAP-UCs show stable, noncytotoxic NO release characteristics capable of potent, broad-spectrum antimicrobial activity, demonstrating great potential for reducing the devastating effects associated with CAUTIs.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Recent Developments in Nitric Oxide Donors and Delivery for Antimicrobial and Anti-Biofilm Applications

The use of nitric oxide (NO) is emerging as a promising, novel approach for the treatment of antibiotic resistant bacteria and biofilm infections. Depending on the concentration, NO can induce biofilm dispersal, increase bacteria susceptibility to antibiotic treatment, and induce cell damage or cell death via the formation of reactive oxygen or reactive nitrogen species. The use of NO is, however, limited by its reactivity, which can affect NO delivery to its target site and result in off-target effects. To overcome these issues, and enable spatial or temporal control over NO release, various strategies for the design of NO-releasing materials, including the incorporation of photo-activable, charge-switchable, or bacteria-targeting groups, have been developed. Other strategies have focused on increased NO storage and delivery by encapsulation or conjugation of NO donors within a single polymeric framework. This review compiles recent developments in NO drugs and NO-releasing materials designed for applications in antimicrobial or anti-biofilm treatment and discusses limitations and variability in biological responses in response to the use of NO for bacterial eradiation.

A Self-defense Hierarchical Antibacterial Surface with Inherent Antifouling and Bacteria-activated Bactericidal Properties for Infection Resistance

Biomedical device-associated infection (BAI) is one of the main reasons for the function failure of implants in clinic practices. Development of high-efficiency antibacterial materials is of great significance to reduce...

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

Human health damage and economic losses due to bacterial infections are very serious worldwide. Excessive use of antibiotics has caused an increase in bacterial resistance. Fortunately, various non-antibiotic antibacterial materials...

Reduction in Foreign Body Response and Improved Antimicrobial Efficacy via Silicone-Oil-Infused Nitric-Oxide-Releasing Medical-Grade Cannulas

Foreign body response and infection are two universal complications that occur with indwelling medical devices. In response, researchers have developed different antimicrobial and antifouling surface strategies to minimize bacterial colonization and fibrous encapsulation. In this study, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and silicone oil were impregnated into silicone rubber cannulas (SR-SNAP-Si) using a solvent swelling method to improve the antimicrobial properties and decrease the foreign body response. The fabricated SR-SNAP-Si cannulas demonstrated a stable, prolonged NO release, exhibited minimal SNAP leaching, and maintained sliding angles < 15° for 21 days. SR-SNAP-Si cannulas displayed enhanced antimicrobial efficacy against Staphylococcus aureus in a 7-day biofilm bioreactor study, reducing the viability of adhered bacteria by 99.2 ± 0.2% compared to unmodified cannulas while remaining noncytotoxic toward human fibroblast cells. Finally, SR-SNAP-Si cannulas were evaluated for the first time in a 14- and 21-day subcutaneous mouse model, showing significantly enhanced biocompatibility compared to control cannulas by reducing the thickness of fibrous encapsulation by 60.9 ± 6.1 and a 60.8 ± 10.5% reduction in cell density around the implant site after 3 weeks. Thus, this work demonstrates that antifouling, NO-releasing surfaces can improve the lifetime and safety of indwelling medical devices.

Photoactivatable Nitric Oxide-Releasing Gold Nanocages for Enhanced Hyperthermia Treatment of Biofilm-Associated Infections

With the increasing clinical use of invasive medical devices, various healthcare-associated infections (HAIs) caused by bacterial biofilm colonization of biomedical devices have posed serious threats to patients. The formation of biofilms makes it much more difficult and costly to treat infections. Here, we report a nitric oxide (NO)-releasing gold nanocage (AuNC@NO) that is stimulated by near-infrared (NIR) irradiation to deliver NO and generate hyperthermia for biofilm elimination. AuNC@NO was prepared by immobilizing a temperature-responsive NO donor onto gold nanocages (AuNCs) through thiol-gold interactions. AuNC@NO possesses stable and excellent photothermal conversion efficiency, as well as the characteristics of slow NO release at physiological temperature and on-demand quick NO release under NIR irradiation. Based on these features, AuNC@NO exhibits enhanced in vitro bactericidal and antibiofilm efficacy compared with AuNCs, which could achieve 4 orders of magnitude bacterial reduction and 85.4% biofilm elimination under NIR irradiation. In addition, we constructed an implant biofilm infection model and a subcutaneous biofilm infection model to evaluate the anti-infective effect of AuNC@NO. The in vivo results indicated that after 5 min of 0.5 W cm^-2 NIR irradiation, NO release from AuNC@NO was significantly accelerated, which induced the dispersal of methicillin-resistant Staphylococcus aureus (MRSA) biofilms and synergized with photothermal therapy (PTT) to kill planktonic MRSA that had lost its biofilm protection. Meanwhile, the surrounding tissues showed little damage because of controlled photothermal temperature and toxicity. In view of the above-mentioned results, the AuNC@NO nanocomposite developed in this work reveals potential application prospects as a useful antibiofilm agent in the field of biofilm-associated infection treatment.

Host Defense Peptide-Mimicking Polymers and Polymeric-Brush-Tethered Host Defense Peptides: Recent Developments, Limitations, and Potential Success

Amphiphilic antimicrobial polymers have attracted considerable interest as structural mimics of host defense peptides (HDPs) that provide a broad spectrum of activity and do not induce bacterial-drug resistance. Likewise, surface engineered polymeric-brush-tethered HDP is considered a promising coating strategy that prevents infections and endows implantable materials and medical devices with antifouling and antibacterial properties. While each strategy takes a different approach, both aim to circumvent limitations of HDPs, enhance physicochemical properties, therapeutic performance, and enable solutions to unmet therapeutic needs. In this review, we discuss the recent advances in each approach, spotlight the fundamental principles, describe current developments with examples, discuss benefits and limitations, and highlight potential success. The review intends to summarize our knowledge in this research area and stimulate further work on antimicrobial polymers and functionalized polymeric biomaterials as strategies to fight infectious diseases.

High-Density Three-Dimensional Network of Covalently Linked Nitric Oxide Donors to Achieve Antibacterial and Antibiofilm Surfaces

Bacterial colonization on biomedical devices often leads to biofilms that are recalcitrant to antibiotic treatment and the leading cause of hospital-acquired infections. We have invented a novel pretreatment chemistry for device surfaces to produce a high-density three-dimensional (3-D) network of covalently linked S-nitrosothiol (RSNO), which is a nitric oxide (NO) donor. Poly(polyethylene glycol-hydroxyl-terminated) (i.e., PPEG-OH) brushes were grafted from an ozone-pretreated polyurethane (PU) surface. The high-density hydroxyl groups on the dangling PPEG-OH brushes then underwent condensation with a mercapto-silane (i.e., MPS, mercaptopropyl trimethoxysilane) followed by S-nitrosylation to produce a 3-D network of NO-releasing RSNO to form the PU/PPEG-OH-MPS-NO coating. This 3-D coating produces NO flux of up to 7 nmol/(cm² min), which is nearly 3 orders of magnitude higher than the picomole/(cm² min) levels of other NO-releasing biomedical implants previously reported. The covalent immobilization of RSNO avoids donor leaching and reduces the risks of cytotoxicity arising from leachable RSNO. Our coated PU surfaces display good biocompatibility and exhibit excellent antibiofilm formation activity in vitro (up to 99.99%) against a broad spectrum of Gram-positive and Gram-negative bacteria. Further, the high-density RSNO achieves nearly 99% and 99.9% in vivo reduction of Pseudomonas aeruginosa (P. aeruginosa) and methicillin-resistant Staphylococcus aureus (MRSA) in a murine subcutaneous implantation infection model. Our surface chemistry to create high NO payload without NO-donor leaching can be applied to many biomedical devices.

Universal Intraductal Surface Antifouling Coating Based on an Amphiphilic Copolymer

Surface modification on the inner wall of medical or industrial polymeric catheters with a high length/diameter ratio is highly desired. Herein, a universal and facile method based on an amphiphilic copolymer was developed to immobilize an intraductal surface antifouling coating for a variety of polymeric catheters. A fouling-repelled thin layer was formed by swelling-driven adsorption via directly perfusing an amphiphilic copolymer [polyvinylpyrrolidone-polydimethylsiloxane-polyvinylpyrrolidone (PVP-PDMS-PVP)] solution into catheters. In this copolymer, hydrophobic PDMS was embedded into a shrinking cross-linked network of catheters; also, PVP segments migrated to the surface under driving water to form a hydrophilic antifouling coating. Moreover, because of the coordination between I₂ and pyrrolidone of PVP, the copolymer-modified intraductal surface was then infused with aqueous I₂ to form the PVP-I₂ complex, endowing this coating with bactericidal activity. Notably, diverse catheters with arbitrary shapes (circular, rectangular, triangular, and hexagonal) and different components (silicone, polyurethane, and polyethylene) were also verified to work using this interfacial interpenetration strategy. The findings in this work provide a new avenue toward facile and universal fabrication of intraductal surface antifouling catheters, creating a superior option for decreasing the consumable costs in industrial production and alleviating the pain of replacing catheters for patients.

Impact of DMPEI on Biofilm Adhesion on Latex Urinary Catheter

BACKGROUND

Microorganisms can migrate from the external environment to the patient's organism through the insertion of catheters. Despite being indispensable medical device, the catheter surface can be colonized by microorganisms and become a starting point for biofilm formation. Therefore, new technologies are being developed in order to modify surfaces to prevent the adhesion and survival of microorganisms. Patents with the use of DMPEI have been filed.

OBJECTIVE

In the present work, we coated latex catheter surfaces with 2 mg mL-1 DMPEI in different solvents, evaluated the wettability of the surface and the anti- biofilm activity of the coated catheter against Escherichia coli, Staphylococcus aureus, and Candida albicans.

METHODS

We coated the inner and outer catheter surfaces with 2 mg mL-1 of DMPEI solubilized in butanol, dimethylformamide, and cyclohexanone and the surfaces were analyzed visually. Contact angle measurement allowed the analysis of the wettability of the surfaces. The CFU mL-1 count evaluated E. coli, S. aureus, and C. albicans adhesion onto the control and treated surfaces.

RESULTS

The contact angle decreased from 50.48º to 46.93º on the inner surface and from 55.83º to 50.91º on the outer surface of latex catheters coated with DMPEI. The catheter coated with DMPEI showed anti-biofilm activity of 83%, 88%, and 93% on the inner surface and 100%, 92%, and 86% on the outer surface for E. coli, S. aureus, and C. albicans, respectively.

CONCLUSION

Latex catheter coated with DMPEI efficiently impaired the biofilm formation both on the outer and inner surfaces, showing a potential antimicrobial activity along with a high anti-biofilm activity for medical devices.

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