Shape- and nitric oxide flux-dependent bactericidal activity of nitric oxide-releasing silica nanorods

Enhanced Nitric Oxide Delivery Through Self-Assembling Nanoparticles for Eradicating Gram-Negative Bacteria

In the current battle against antibiotic resistance, the resilience of Gram-negative bacteria against traditional antibiotics is due not only to their protective outer membranes but also to mechanisms like efflux pumps and enzymatic degradation of drugs, underscores the urgent need for innovative antimicrobial tactics. Herein, this study presents an innovative method involving the synthesis of three furoxan derivatives engineered to self-assemble into nitric oxide (NO) donor nanoparticles (FuNPs). These FuNPs, notably supplied together with polymyxin B (PMB), achieve markedly enhanced bactericidal efficacy against a wide spectrum of bacterial phenotypes at considerably lower NO concentrations (0.1-2.8 µg mL-1), which is at least ten times lower than the reported data for NO donors (≥200 µg mL-1). The bactericidal mechanism is elucidated using confocal, scanning, and transmission electron microscopy techniques. Neutron reflectometry confirms that FuNPs initiate membrane disruption by specifically engaging with the polysaccharides on bacterial surfaces, causing structural perturbations. Subsequently, PMB binds to lipid A on the outer membrane, enhancing permeability and resulting in a synergistic bactericidal action with FuNPs. This pioneering strategy underscores the utility of self-assembly in NO delivery as a groundbreaking paradigm to circumvent traditional antibiotic resistance barriers, marking a significant leap forward in the development of next-generation antimicrobial agents.

Nitric Oxide as an Efficient Antimicrobial Treatment for Second-Degree Burn Wounds

INTRODUCTION

Nitric oxide (NO) is a lipophilic gas with potent antimicrobial activity. Several in vitro and in vivo studies have demonstrated the broad-spectrum antimicrobial activity of NO-releasing compounds against bacteria, viruses, and parasites. The objective of this study was to assess the efficacy of topical NO formations with sustained release on microbial reduction in wounds.

MATERIALS AND METHODS

Swine was used as the preclinical animal model because of the similarities of porcine skin to human skin. Second-degree burn wounds were created in 3 pigs and then inoculated with Methicillin-resistant Staphylococcus aureus, Acinetobacter baumannii, or Candida albicans and covered with polyurethane film dressings to create biofilms. After 48 hours, wounds were then treated daily and then recovered for the bacterial burden assessments. Statistical analysis was performed using IBM SPSS statistics 27 using one-way ANOVA.

RESULTS

All treatments significantly reduced (P ≤ .05) the bacterial counts between assessment days 4 and 7. Wounds treated with the NVN4000 (1.8%) exhibited greater than 99.7% bacterial reduction on days 4 and 7. Significant differences (P ≤ .05) were observed in wounds treated with NVN4000 (1.8%) compared to silver sulfadiazine.

CONCLUSIONS

These studies demonstrate that topical NO-releasing formulations effectively reduce the microbial burden of several microorganisms and exhibit superior antimicrobial efficacy compared to silver sulfadiazine in the porcine wound model.

Essential-Oils-Loaded Biopolymeric Nanoparticles as Strategies for Microbial and Biofilm Control: A Current Status

The emergence of bacterial strains displaying resistance to the currently available antibiotics is a critical global concern. These resilient bacteria can form biofilms that play a pivotal role in the failure of bacterial infection treatments as antibiotics struggle to penetrate all biofilm regions. Consequently, eradicating bacteria residing within biofilms becomes considerably more challenging than their planktonic counterparts, leading to persistent and chronic infections. Among various approaches explored, essential oils loaded in nanoparticles based on biopolymers have emerged, promising strategies that enhance bioavailability and biological activities, minimize side effects, and control release through regulated pharmacokinetics. Different available reviews analyze nanosystems and essential oils; however, usually, their main goal is the analysis of their antimicrobial properties, and progress in biofilm combat is rarely discussed, or it is not the primary objective. This review aims to provide a global vision of biofilm conformation and describes mechanisms of action attributed to each EO. Furthermore, we present a comprehensive overview of the latest developments in biopolymeric nanoparticles research, especially in chitosan- and zein-based nanosystems, targeting multidrug-resistant bacteria in both their sessile and biofilm forms, which will help to design precise strategies for combating biofilms.

New Weapons to Fight against Staphylococcus aureus Skin Infections

The treatment of Staphylococcus aureus skin and soft tissue infections faces several challenges, such as the increased incidence of antibiotic-resistant strains and the fact that the antibiotics available to treat methicillin-resistant S. aureus present low bioavailability, are not easily metabolized, and cause severe secondary effects. Moreover, besides the susceptibility pattern of the S. aureus isolates detected in vitro, during patient treatment, the antibiotics may never encounter the bacteria because S. aureus hides within biofilms or inside eukaryotic cells. In addition, vascular compromise as well as other comorbidities of the patient may impede proper arrival to the skin when the antibiotic is given parenterally. In this manuscript, we revise some of the more promising strategies to improve antibiotic sensitivity, bioavailability, and delivery, including the combination of antibiotics with bactericidal nanomaterials, chemical inhibitors, antisense oligonucleotides, and lytic enzymes, among others. In addition, alternative non-antibiotic-based experimental therapies, including the delivery of antimicrobial peptides, bioactive glass nanoparticles or nanocrystalline cellulose, phototherapies, and hyperthermia, are also reviewed.

Powering mesoporous silica nanoparticles into bioactive nanoplatforms for antibacterial therapies: strategies and challenges

Bacterial infection has been a major threat to worldwide human health, in particular with the ever-increasing level of antimicrobial resistance. Given the complex microenvironment of bacterial infections, conventional use of antibiotics typically renders a low efficacy in infection control, thus calling for novel strategies for effective antibacterial therapies. As an excellent candidate for antibiotics delivery, mesoporous silica nanoparticles (MSNs) demonstrate unique physicochemical advantages in antibacterial therapies. Beyond the delivery capability, extensive efforts have been devoted in engineering MSNs to be bioactive to further synergize the therapeutic effect in infection control. In this review, we critically reviewed the essential properties of MSNs that benefit their antibacterial application, followed by a themed summary of strategies in manipulating MSNs into bioactive nanoplatforms for enhanced antibacterial therapies. The chemically functionalized platform, photo-synergized platform, physical antibacterial platform and targeting-directed platform are introduced in details, where the clinical translation challenges of these MSNs-based antibacterial nanoplatforms are briefly discussed afterwards. This review provides critical information of the emerging trend in turning bioinert MSNs into bioactive antibacterial agents, paving the way to inspire and translate novel MSNs-based nanotherapies in combating bacterial infection diseases.

Antibacterial and antifungal action of CTAB-containing silica nanoparticles against human pathogens

New antibiotic agents are urgently needed worldwide to combat the increasing tolerance and resistance of pathogenic fungi and bacteria to current antimicrobials. Here, we looked at the antibacterial and antifungal effects of minor quantities of cetyltrimethylammonium bromide (CTAB), ca. 93.8 mg g^-1, on silica nanoparticles (MPSi-CTAB). Our results show that MPSi-CTAB exhibits antimicrobial activity against Methicillin-resistant Staphylococcus aureus strain (S. aureus ATCC 700698) with MIC and MBC of 0.625 mg mL^-1 and 1.25 mg mL^-1, respectively. Additionally, for Staphylococcus epidermidis ATCC 35984, MPSi-CTAB reduces MIC and MBC by 99.99% of viable cells on the biofilm. Furthermore, when combined with ampicillin or tetracycline, MPSi-CTAB exhibits reduced MIC values by 32- and 16-folds, respectively. MPSi-CTAB also exhibited in vitro antifungal activity against reference strains of Candida, with MIC values ranging from 0.0625 to 0.5 mg mL^-1. This nanomaterial has low cytotoxicity in human fibroblasts, where over 80% of cells remained viable at 0.31 mg mL^-1 of MPSi-CTAB. Finally, we developed a gel formulation of MPSi-CTAB, which inhibited in vitro the growth of Staphylococcus and Candida strains. Overall, these results support the efficacy of MPSi-CTAB with potential application in the treatment and/or prevention of infections caused by methicillin-resistant Staphylococcus and/or Candida species.

The biofilm inhibition activity of a NO donor nanosilica with enhanced antibiotics action

Nitric oxide (NO) has emerged as a promising antibacterial agent, where NO donor compounds have been explored. Here, we investigated the role of a silica nanoparticle containing nitroprusside (MPSi-NP) as a NO donor agent against methicillin-sensitive (ATCC 25,923 and ATCC 12228) and methicillin-resistant (ATCC 700,698 and ATCC 35984) Staphylococcus strains. Biofilm inhibition was studied along with antibiotic activity in combination with standard antibiotics (ampicillin and tetracycline). MPSi-NP exhibited thermal release of 63% of NO within 24 h, while free nitroprusside released only 18% during a dialysis assay, indicating an assisted release of NO mediated by the nanoparticles. This nanomaterial showed only a moderate activity in blocking biofilm production, but exhibited a significant decrease in the number of viable bacterial cells (over 600-fold for Staphylococcus aureus ATCC 700,698 and Staphylococcus epidermidis ATCC 35984). Remarkably, even using MPSi-NP at concentrations below any antibacterial action, its combination with ampicillin promoted a significant decrease in MIC for resistant strains of S. aureus ATCC 700,698 (2-fold) and S. epidermidis ATCC 35,984 (4-fold). A carbopol-based gel formulation with MPSi-NP (0.5% w/w) was prepared and showed a zone of inhibition of 7.7 ± 0.6 mm for S. epidermidis ATCC 35984. Topical use of MPSi-NP in combination with antibiotics might be a manageable strategy to prevent and eventually treat complicated resistant bacterial infections.

Recent advances in the development of nitric oxide-releasing biomaterials and their application potentials in chronic wound healing

Chronic wounds, such as pressure ulcers, vascular ulcers and diabetic foot ulcers (DFUs), often stay in a state of pathological inflammation and suffer from persistent infection, excess inflammation, and hypoxia, thus they are difficult to be healed. Nitric oxide (NO) plays a critical role in the regulation of various wound healing processes, including inflammatory response, cell proliferation, collagen formation, antimicrobial action and angiogenesis. The important role of NO in wound healing attracts intensive research focus on NO-based wound healing therapy. However, the application of NO gas therapy needs to resolve the intrinsic shortcomings of gas therapy, such as short storage and release times as well as temporal and spatial uncontrollability of the release mode. So far, various types of NO donors, including organic nitrates (RONO2), nitrites (RONO), S-nitrosothiols (RSNOs), nitrosamines, N-diazeniumdiolates (NONOates), and metal-NO complexes, have been developed to solidify gaseous NO and they were further encapsulated in or conjugated onto a variety of biomaterial vectors to develop NO delivery systems. NO synthetic enzyme mimics to catalyze the production and release of NO from l-arginine have also been developed. This paper reviews recent advances of NO donors, biomaterial vectors, thus-formed NO delivery systems, as well as recently emerged NO synthetic enzyme mimics. Furthermore, this review also summarizes the functions of NO releasing biomaterials that would benefit chronic wound healing, including antibacterial properties and the promotion of angiogenesis, as well as the convenient combination of light/thermal induced NO release with light/thermal therapies, and the prospects for future developing trends in this area.

Diatom-inspired 2D nitric oxide releasing anti-infective porous nanofrustules

Two-dimensional (2D) nanomaterials (NM) have emerged as promising platforms for antibacterial applications. However, the inherent "flatness" of 2D NM often limits the loading of antimicrobial components needed for synergistic bactericidal actions. Here, inspired by the highly ornamented siliceous frustules of diatoms, we prepared 2D ultrathin (<20 nm) and rigid "nanofrustule" plates via the out-of-plane growth of cetyltrimethylammonium bromide (CTAB) directed silica mesostructures on the surfaces of 2D graphene oxide nanosheets. The nanofrustules were characterized by the presence of mesoporous channels with a pore size of 3 nm and a high specific surface area of 674 m2 g-1. S-nitrosothiol-modification on the silica surfaces enables the development of a novel anti-infective nitric oxide (NO) releasing NO-nanofrustule system. The cage-like mesoporous silica architecture enabled a controlled and sustainable release of NO from the NO-nanofrustules under physiological conditions. The NO-nanofrustules displayed broad antibacterial effects against Staphylococcus aureus and Escherichia coli with a minimum inhibitory concentration of 250 μg ml-1. Mechanistic studies revealed that the antibacterial property of NO-nanofrustules was attained via a unique "capture-and-release" mode-of-action. The first step entailed the capture of the bacteria by the NO-nanofrustules to form micro-aggregates. This was followed by the release of high levels of NO to the captured bacteria to elicit a potent anti-infective effect. In combination with the lack of cytotoxicity in human dermal cells, the 2D hybrid NO-nanofrustules may be utilized to combat wound infections in clinical settings.

Polyester Mesh Functionalization with Nitric Oxide-Releasing Silica Nanoparticles Reduces Early Methicillin-Resistant Staphylococcus aureus Contamination

Background: Infected hernia mesh is a cause of post-operative morbidity. Nitric oxide (NO) plays a key role in the endogenous immune response to infection. We sought to study the efficacy of a NO-releasing mesh against methicillin-resistant Staphylococcus aureus (MRSA). We hypothesized that a NO-releasing polyester mesh would decrease MRSA colonization and proliferation. Materials and Methods: A composite polyester mesh functionalized with N-diazeniumdiolate silica nanoparticles was synthesized and characterized. N-diazeniumdiolate silica parietex composite (NOSi) was inoculated with 10⁴,10⁶, or 10⁸ colony forming units (CFUs) of MRSA and a dose response was quantified in a soy tryptic broth assay. Utilizing a rat model of contaminated hernia repair, implanted mesh was inoculated with MRSA, recovered, and CFUs were quantified. Clinical metrics of erythema, mesh contracture, and adhesion severity were then characterized. Results: Methicillin-resistant Staphylococcus aureus CFUs demonstrated a dose-dependent response to NOSi in vitro. In vivo, quantified CFUs showed a dose-dependent response to NOSi-PCO. Treated rats had fewer severe adhesions, less erythema, and reduced mesh contracture. Conclusions: We demonstrate the efficacy of a NO-releasing mesh to treat MRSA in vitro and in vivo. Creation of a novel class of antimicrobial prosthetics offers new strategies for reconstructing contaminated abdominal wall defects and other procedures that benefit from deploying synthetic prostheses in contaminated environments.

Metal-organic frameworks for therapeutic gas delivery

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) are gaseous signaling molecules (gasotransmitters) that regulate both physiological and pathological processes and offer therapeutic potential for the treatment of many diseases, such as cancer, cardiovascular disease, renal disease, bacterial and viral infections. However, the inherent labile nature of therapeutic gases results in difficulties in direct gases administration and their controlled delivery at clinically relevant ranges. Metal-organic frameworks (MOFs) with highly porous, stable, and easy-to-tailor properties have shown promising therapeutic gas delivery potential. Herein, we highlight the recent advances of MOF-based platforms for therapeutic gas delivery, either by endogenous (i.e., direct transfer of gases to targets) or exogenous (i.e., stimulating triggered release of gases) means. Reports that involve in vitro and/or in vivo studies are highlighted due to their high potential for clinical translation. Current challenges for clinical requirements and possible future innovative designs to meet variable healthcare needs are discussed.

NIR-II light triggered nitric oxide release nanoplatform combined chemo-photothermal therapy for overcoming multidrug resistant cancer

The overexpression of P-glycoprotein (P-gp) in multidrug resistance (MDR) cancer cells increases the efflux of anticancer drugs thereby causing the failure of clinical chemotherapy. To address this obstacle, in this study, we rationally designed a near-infrared (NIR) light-responsive nitric oxide (NO) delivery nanoplatform for targeting the MDR tumors based on core-shell structured nanocomposites. The mesoporous silica shell provided abundant sites for modification of the NO donor, N-diazeniumdiolate, and tumor-targeting molecule, folic acid (FA), and enabled high encapsulation capacity for doxorubicin (DOX) loading. Under NIR light irradiation, the generation of NO gas can efficiently augment chemotherapeutic effects via the inhibition of P-gp expression. Simultaneously, the photothermal conversion agents of the Cu_2-xSe core produce a large amount of heat for photothermal therapy (PTT). Finally, this combinational gas/chemo/PTT not only displays a superior and synergistic effect for overcoming MDR cancer, but also provides an efficient strategy to construct a multifunctional nano-drug delivery system with diversified therapeutic modalities.

Specialty Tough Hydrogels and Their Biomedical Applications

Hydrogels have long been explored as attractive materials for biomedical applications given their outstanding biocompatibility, high water content, and versatile fabrication platforms into materials with different physiochemical properties and geometries. Nonetheless, conventional hydrogels suffer from weak mechanical properties, restricting their use in persistent load-bearing applications often required of materials used in medical settings. Thus, the fabrication of mechanically robust hydrogels that can prolong the lifetime of clinically suitable materials under uncompromising in vivo conditions is of great interest. This review focuses on design considerations and strategies to construct such tough hydrogels. Several promising advances in the proposed use of specialty tough hydrogels for soft actuators, drug delivery vehicles, adhesives, coatings, and in tissue engineering settings are highlighted. While challenges remain before these specialty tough hydrogels will be deemed translationally acceptable for clinical applications, promising preliminary results undoubtedly spur great hope in the potential impact this embryonic research field can have on the biomedical community.

Mesoporous silica nanoparticles for tissue-engineering applications

Mesoporous silica nanoparticles (MSNs) have been widely investigated as a nanocarrier for the delivery of various cargoes in nanomedicine. The application of MSNs in tissue engineering is a relatively newly emerged field that has gained much research interest. In this review, the recent advances in the tissue-engineering application of MSNs are summarized. The controlled synthesis of MSNs is delineated first in terms of tuning the morphology, pore size of MSNs, and its surface chemistry, as well as biodegradability. Then, the different roles of MSNs in tissue engineering are successively introduced, which mainly comprise the delivery of bioactive factors, the inherent bioactivity of MSNs, stem cells labelling, and the impacts of incorporated MSNs on scaffolds. Furthermore, the recent progress in the applications of MSNs for tissue engineering, particularly bone tissue engineering, is summarized in detail. Finally, the challenges or potential trends for the further applications of MSNs in tissue engineering are also discussed. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Developing regulatory property of gelatin-tannic acid multilayer films for coating-based nitric oxide gas delivery system

To utilize potentials of nitric oxide (NO) gas in anti-bacterial, anticancer, wound healing applications, numerous studies have been conducted to develop a NO delivery system in the past few decades. Even though a coating method and film types are essential to apply in biomedical device coating from previous NO delivery systems, release control from the coating system is still challenging. In this study, we introduced a multilayered polymeric coating system to overcome the uncontrollable NO release kinetics of film systems. We used biocompatible gelatin and tannic acid to construct a rough, porous structured film based on the layer-by-layer self-assembly method. The multilayered polymeric structure facilitated the controlled amount of NO release from (Gel/TA)n film and showed burst release in early period owing to their large surface area from the rough, porous structure. We synthesized the proton-responsive NO donor, N-diazeniumdiolate (NONOates), into the (Gel/TA)n film through a chemical reaction under high pressure NO gas. NO release profile was analyzed by a real-time NO analysis machine (NOA 280i). Then, the NO-releasing (Gel/TA)n film was tested its toxicity against human dermal fibroblast cells and bactericidal effects against Staphylococcus aureus.

Nitric Oxide Therapy for Diabetic Wound Healing

Nitric oxide (NO) represents a potential wound therapeutic agent due to its ability to regulate inflammation and eradicate bacterial infections. Two broad strategies exist to utilize NO for wound healing; liberating NO from endogenous reservoirs, and supplementing NO from exogenous sources. This progress report examines the efficacy of a variety of NO-based methods to improve wound outcomes, with particular attention given to diabetes-associated chronic wounds.

Gas-Generating Nanoplatforms: Material Chemistry, Multifunctionality, and Gas Therapy

The fast advances of theranostic nanomedicine enable the rational design and construction of diverse functional nanoplatforms for versatile biomedical applications, among which gas-generating nanoplatforms (GGNs) have emerged very recently as unique theranostic nanoplatforms for broad gas therapies. Here, the recent developments of the rational design and chemical construction of versatile GGNs for efficient gas therapies by either exogenous physical triggers or endogenous disease-environment responsiveness are reviewed. These gases involve some therapeutic gases that can directly change disease status, such as oxygen (O₂ ), nitric oxide (NO), carbon monoxide (CO), hydrogen (H₂ ), hydrogen sulfide (H₂ S) and sulfur dioxide (SO₂ ), and other gases such as carbon dioxide (CO₂ ), dl-menthol (DLM), and gaseous perfluorocarbon (PFC) for supplementary assistance of the theranostic process. Abundant nanocarriers have been adopted for gas delivery into lesions, including poly(d,l-lactic-co-glycolic acid), micelles, silica/mesoporous silica, organosilica, MnO₂ , graphene, Bi₂ Se₃ , upconversion nanoparticles, CaCO₃ , etc. Especially, these GGNs have been successfully developed for versatile biomedical applications, including diagnostic imaging and therapeutic use. The biosafety issue, challenges faced, and future developments on the rational construction of GGNs are also discussed for further promotion of their clinical translation to benefit patients.

Nitric Oxide-Releasing Macromolecular Scaffolds for Antibacterial Applications

Exogenous nitric oxide (NO) represents an attractive antibacterial agent because of its ability to both disperse and directly kill bacterial biofilms while avoiding resistance. Due to the challenges associated with administering gaseous NO, NO-releasing macromolecular scaffolds are developed to facilitate NO delivery. This progress report describes the rational design and application of NO-releasing macromolecular scaffolds as antibacterial therapeutics. Special consideration is given to the role of the physicochemical properties of the NO storage vehicles on antibacterial or anti-biofilm activity.

Progress and Promise of Nitric Oxide-Releasing Platforms

Nitric oxide (NO) is a highly potent radical with a wide spectrum of physiological activities. Depending on the concentration, it can enhance endothelial cell proliferation in a growth factor-free medium, mediate angiogenesis, accelerate wound healing, but may also lead to tumor progression or induce inflammation. Due to its multifaceted role, NO must be administered at a right dose and at the specific site. Many efforts have focused on developing NO-releasing biomaterials; however, NO short half-life in human tissues only allows this molecule to diffuse over short distances, and significant challenges remain before the full potential of NO can be realized. Here, an overview of platforms that are engineered to release NO via catalytic or noncatalytic approaches is presented, with a specific emphasis on progress reported in the past five years. A number of NO donors, natural enzymes, and enzyme mimics are highlighted, and recent promising developments of NO-releasing scaffolds, particles, and films are presented. In particular, key parameters of NO delivery are discussed: 1) NO payload, 2) maximum NO flux, 3) NO release half-life, 4) time required to reach maximum flux, and 5) duration of NO release. Advantages and drawbacks are reviewed, and possible further developments are suggested.

Use of gasotransmitters for the controlled release of polymer-based nitric oxide carriers in medical applications

Nitric Oxide (NO) is a small molecule gasotransmitter synthesized by nitric oxide synthase in almost all types of mammalian cells. NO is synthesized by NO synthase by conversion of l-arginine to l-citrulline in the human body. NO then stimulates soluble guanylate cyclase, from which various physiological functions are mediated in a concentration-dependent manner. High concentrations of NO induce apoptosis or antibacterial responses whereas low NO circulation leads to angiogenesis. The bidirectional effect of NO has attracted considerable attention, and efforts to deliver NO in a controlled manner, especially through polymeric carriers, has been the topic of much research. This naturally produced signaling molecule has stood out as a potentially more potent therapeutic agent compared to exogenously synthesized drugs. In this review, we will focus on past efforts of using the controlled release of NO via polymer-based materials to derive specific therapeutic results. We have also added studies and our future suggestions on co-delivery methods with other gasotransmitters as a step towards developing multifunctional carriers.

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.

Nitric Oxide-Releasing Alginates

Low and high molecular weight alginate biopolymers were chemically modified to store and release potentially therapeutic levels of nitric oxide (NO). Carbodiimide chemistry was first used to modify carboxylic acid functional groups with a series of small molecule alkyl amines. The resulting secondary amines were subsequently converted to N-diazeniumdiolate NO donors via reaction with NO gas under basic conditions. NO donor-modified alginates stored between 0.4-0.6 μmol NO·mg-1. In aqueous solution, the NO-release kinetics were diverse (0.3-13 h half-lives), dependent on the precursor amine structure. The liberated NO showed bactericidal activity against Pseudomonas aeruginosa and Staphylococcus aureus with pathogen eradication efficiency dependent on both molecular weight and NO-release kinetics. The combination of lower molecular weight (∼5 kDa) alginates with moderate NO-release durations (half-life of ∼4 h) resulted in enhanced killing of both planktonic and biofilm-based bacteria. Toxicity against human respiratory epithelial (A549) cells proved negligible at NO-releasing alginate concentrations required to achieve a 5-log reduction in viability in the biofilm eradication assay.

Nanoengineered hollow mesoporous silica nanoparticles for the delivery of antimicrobial proteins into biofilms

The delivery of bactericidal proteins into biofilms is challenging. Hollow mesoporous silica nanoparticles with large cone-shaped pores were synthesized to deliver antimicrobial proteins into biofilms and showed enhanced antimicrobial activities.

Mesoporous Silica and Organosilica Nanoparticles: Physical Chemistry, Biosafety, Delivery Strategies, and Biomedical Applications

Predetermining the physico-chemical properties, biosafety, and stimuli-responsiveness of nanomaterials in biological environments is essential for safe and effective biomedical applications. At the forefront of biomedical research, mesoporous silica nanoparticles and mesoporous organosilica nanoparticles are increasingly investigated to predict their biological outcome by materials design. In this review, it is first chronicled that how the nanomaterial design of pure silica, partially hybridized organosilica, and fully hybridized organosilica (periodic mesoporous organosilicas) governs not only the physico-chemical properties but also the biosafety of the nanoparticles. The impact of the hybridization on the biocompatibility, protein corona, biodistribution, biodegradability, and clearance of the silica-based particles is described. Then, the influence of the surface engineering, the framework hybridization, as well as the morphology of the particles, on the ability to load and controllably deliver drugs under internal biological stimuli (e.g., pH, redox, enzymes) and external noninvasive stimuli (e.g., light, magnetic, ultrasound) are presented. To conclude, trends in the biomedical applications of silica and organosilica nanovectors are delineated, such as unconventional bioimaging techniques, large cargo delivery, combination therapy, gaseous molecule delivery, antimicrobial protection, and Alzheimer's disease therapy.

Study of Crystal Formation and Nitric Oxide (NO) Release Mechanism from S-Nitroso-N-acetylpenicillamine (SNAP)-Doped CarboSil Polymer Composites for Potential Antimicrobial Applications

Stable and long-term nitric oxide (NO) releasing polymeric materials have many potential biomedical applications. Herein, we report the real-time observation of the crystallization process of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), within a thermoplastic silicone-polycarbonate-urethane biomedical polymer, CarboSil 20 80A. It is demonstrated that the NO release rate from this composite material is directly correlated with the surface area that the CarboSil polymer film is exposed to when in contact with aqueous solution. The decomposition of SNAP in solution (e.g. PBS, ethanol, THF, etc.) is a pseudo-first-order reaction proportional to the SNAP concentration. Further, catheters fabricated with this novel NO releasing composite material are shown to exhibit significant effects on preventing biofilm formation on catheter surface by Pseudomonas aeruginosa and Proteus mirabilis grown in CDC bioreactor over 14 days, with a 2 and 3 log-unit reduction in number of live bacteria on their surfaces, respectively. Therefore, the SNAP-CarboSil composite is a promising new material to develop antimicrobial catheters, as well as other biomedical devices.

Nanoantibiotics: a new paradigm for the treatment of surgical infection

Infections following orthopedic device implantations often impose a substantial health burden and result in high medical costs. Currently, preventative methods are often employed following an orthopedic implant to reduce risk of infection; however, contamination of the surgical site can still occur. Although antibiotics have demonstrated a substantial reduction in bacterial growth and maintenance, biofilm formation around the implant can often minimize efficacy of the antibiotic. Recently, nanotechnology has garnered significant interest, resulting in the development of several antibiotic delivery strategies that exhibit extended release and increased efficacy. In this review, treatment methods of orthopedic-device-related infections will be discussed and an overview of antimicrobial-based nanotechnologies will be provided. Specifically, nonmetal-, metal- and oxide-based nanotechnologies, incorporating antibacterial strategies, will be discussed.

Recent advances in thromboresistant and antimicrobial polymers for biomedical applications: just say yes to nitric oxide (NO)

Biomedical devices are essential for patient diagnosis and treatment; however, when blood comes in contact with foreign surfaces or homeostasis is disrupted, complications including thrombus formation and bacterial infections can interrupt device functionality, causing false readings and/or shorten device lifetime. Here, we review some of the current approaches for developing antithrombotic and antibacterial materials for biomedical applications. Special emphasis is given to materials that release or generate low levels of nitric oxide (NO). Nitric oxide is an endogenous gas molecule that can inhibit platelet activation as well as bacterial proliferation and adhesion. Various NO delivery vehicles have been developed to improve NO's therapeutic potential. In this review, we provide a summary of the NO releasing and NO generating polymeric materials developed to date, with a focus on the chemistry of different NO donors, the polymer preparation processes, and in vitro and in vivo applications of the two most promising types of NO donors studied thus far, N-diazeniumdiolates (NONOates) and S-nitrosothiols (RSNOs).

Reprint of: Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72 h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72 h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

Co-delivery of nitric oxide and antibiotic using polymeric nanoparticles

The rise of hospital-acquired infections, also known as nosocomial infections, is a growing concern in intensive healthcare, causing the death of hundreds of thousands of patients and costing billions of dollars worldwide every year. In addition, a decrease in the effectiveness of antibiotics caused by the emergence of drug resistance in pathogens living in biofilm communities poses a significant threat to our health system. The development of new therapeutic agents is urgently needed to overcome this challenge. We have developed new dual action polymeric nanoparticles capable of storing nitric oxide, which can provoke dispersal of biofilms into an antibiotic susceptible planktonic form, together with the aminoglycoside gentamicin, capable of killing the bacteria. The novelty of this work lies in the attachment of NO-releasing moiety to an existing clinically used drug, gentamicin. The nanoparticles were found to release both agents simultaneously and demonstrated synergistic effects, reducing the viability of Pseudomonas aeruginosa biofilm and planktonic cultures by more than 90% and 95%, respectively, while treatments with antibiotic or nitric oxide alone resulted in less than 20% decrease in biofilm viability.

Functionalized Mesoporous Silica via an Aminosilane Surfactant Ion Exchange Reaction: Controlled Scaffold Design and Nitric Oxide Release

Nitric oxide-releasing mesoporous silica nanoparticles (MSNs) were prepared using an aminosilane-template surfactant ion exchange reaction. Initially, bare silica particles were synthesized under basic conditions in the presence of cetyltrimethylammonium bromide (CTAB). These particles were functionalized with nitric oxide (NO) donor precursors (i.e., secondary amines) via the addition of aminosilane directly to the particle sol and a commensurate ion exchange reaction between the cationic aminosilanes and CTAB. N-Diazeniumdiolate NO donors were formed at the secondary amines to yield NO-releasing MSNs. Tuning of the ion exchange-based MSN modification approach allowed for the preparation of monodisperse particles ranging from 30 to 1100 nm. Regardless of size, the MSNs stored appreciable levels of NO (0.4-1.5 μmol mg(-1)) with tunable NO release durations (1-33 h) dependent on the aminosilane modification. Independent control of NO release properties and particle size was achieved, demonstrating the flexibility of this novel MSN synthesis over conventional co-condensation and surface grafting strategies.

Anti-biofilm action of nitric oxide-releasing alkyl-modified poly(amidoamine) dendrimers against Streptococcus mutans

The effect of nitric oxide (NO)-releasing dendrimer hydrophobicity on Streptococcus mutans killing and biofilm disruption was examined at pH 7.4 and 6.4, the latter relevant to dental caries. Generation 1 (G1) poly(amidoamine) (PAMAM) dendrimers were modified with alkyl epoxides to generate propyl-, butyl-, hexyl-, octyl-, and dodecyl-functionalized dendrimers. The resulting secondary amines were reacted with NO to form N-diazeniumdiolate NO donor-modified dendrimer scaffolds (total NO ∼1μmol/mg). The bactericidal action of the NO-releasing dendrimers against both planktonic and biofilm-based S. mutans proved greatest with increasing alkyl chain length and at lower pH. Improved bactericidal efficacy at pH 6.4 was attributed to increased scaffold surface charge that enhanced dendrimer-bacteria association and ensuing membrane damage. For shorter alkyl chain (i.e., propyl and butyl) dendrimer modifications, increased antibacterial action at pH 6.4 was due to faster NO-release kinetics from proton-labile N-diazeniumdiolate NO donors. Octyl- and dodecyl-modified PAMAM dendrimers proved most effective for eradicating S. mutans biofilms with NO release mitigating dendrimer scaffold cytotoxicity.

STATEMENT OF SIGNIFICANCE

We report the antibacterial and anti-biofilm efficacy of dual-action nitric oxide (NO)-releasing dendrimers against S. mutans, an etiological agent in dental caries. This work was undertaken to enhance the anti-biofilm action of these scaffolds by employing various alkyl chain modifications. Furthermore, we evaluated the ability of NO to eradicate cariogenic biofilms. We found that at the lower pH associated with dental caries (pH ∼6.4), NO has a more pronounced antibacterial effect for alkyl modifications less capable of biofilm penetration and membrane disruption. Of greatest significance, we introduce dendrimers as a new macromolecular antibacterial agent against the cariogenic bacteria S. mutans.

S-Nitrosothiol-modified hyperbranched polyesters

S-Nitrosothiol-modified hyperbranched polyesters as a novel biodegradable nitric oxide-releasing scaffold.

Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

Evaluation of experimental methods for nitric oxide release from cardiovascular implants; bypass grafts as an exemplar

BACKGROUND

There is a great potential for nitric oxide (NO) eluting biomaterials in biomedical applications. These include the development of cardiovascular implants, wound healing products, or applications in cancer and respiratory therapy. While the potential of these materials as a therapy is becoming clearer, the real-time monitoring of NO is not easy and the success in the development of such materials depends on the accurate quantification of NO release.

METHOD

To emphasize on the importance of a measurement technique on the outcome of an experiment, we compared total NO released from S-nitroso-N-acetyl-d-penicillamine (SNAP) incorporated nanocomposite polymer in the form of bypass grafts under simulated physiological conditions using amperometric and chemiluminescence techniques.

RESULTS

We found that the total amount of NO measured by the amperometric technique was 35.8% of the theoretical amount. Similarly, on measuring NO release from the bypass grafts, we demonstrated that the chemiluminesence technique detected NO at a relatively higher level.

CONCLUSIONS

The results of this study clearly demonstrate the relative difference between analysis techniques for accurate NO detection that can be applied to distinct experimental models associated with NO-eluting cardiovascular implants.

Kinetic-dependent Killing of Oral Pathogens with Nitric Oxide

Nitric oxide (NO)-releasing silica nanoparticles were synthesized via the co-condensation of tetramethyl orthosilicate with aminosilanes and subsequent conversion of secondary amines to N-diazeniumdiolate NO donors. A series of ~150 nm NO-releasing particles with different NO totals and release kinetics (i.e., half-lives) were achieved by altering both the identity and mol% composition of the aminosilane precursors. Independent of identical 2 h NO-release totals, enhanced antibacterial action was observed against the periodontopathogens Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis with extended NO-release kinetics at pH 7.4. Negligible bactericidal effect was observed against cariogenic Streptococcus mutans at pH 7.4, even when using NO-releasing silica particles with greater NO-release totals. However, antibacterial activity was observed against S. mutans at lower pH (6.4). This result was attributed to more rapid proton-initiated decomposition of the N-diazeniumdiolate NO donors and greater NO-release payloads. The data suggest a differential sensitivity to NO between cariogenic and periodontopathogenic bacteria with implications for the future development of NO-releasing oral care therapeutics.

S-Nitroso-N-acetylpenicillamine (SNAP) Impregnated Silicone Foley Catheters: A Potential Biomaterial/Device To Prevent Catheter-Associated Urinary Tract Infections

Urinary Foley catheters are utilized for management of hospitalized patients and are associated with high rates of urinary tract infections (UTIs). Nitric oxide (NO) potently inhibits microbial biofilm formation, which is the primary cause of catheter associated UTIs (CAUTIs). Herein, commercial silicone Foley catheters are impregnated via a solvent swelling method with S-nitroso-N-acetyl-D-penicillamine (SNAP), a synthetic NO donor that exhibits long-term NO release and stability when incorporated into low water-uptake polymers. The proposed catheters generate NO surface-fluxes >0.7 × 10^–10 mol min^–1 cm^–2 for over one month under physiological conditions, with minimal SNAP leaching. These biomedical devices are demonstrated to significantly decrease formation of biofilm on the surface of the catheter tubings over 3, 7, and 14 day periods by microbial species (Staphylococcus epidermidis and Proteus mirabilis) commonly causing CAUTIs. Toxicity assessment demonstrates that the SNAP-impregnated catheters are fully biocompatible, as extracts of the catheter tubings score 0 on a 3-point grading scale using an accepted mouse fibroblast cell-line toxicity model. Consequently, SNAP-impregnated silicone Foley catheters can likely provide an efficient strategy to greatly reduce the occurrence of nosocomial CAUTIs.

Nitric oxide-releasing poly(lactic-co-glycolic acid)-polyethylenimine nanoparticles for prolonged nitric oxide release, antibacterial efficacy, and in vivo wound healing activity

Nitric oxide (NO)-releasing nanoparticles (NPs) have emerged as a wound healing enhancer and a novel antibacterial agent that can circumvent antibiotic resistance. However, the NO release from NPs over extended periods of time is still inadequate for clinical application. In this study, we developed NO-releasing poly(lactic-co-glycolic acid)-polyethylenimine (PEI) NPs (NO/PPNPs) composed of poly(lactic-co-glycolic acid) and PEI/diazeniumdiolate (PEI/NONOate) for prolonged NO release, antibacterial efficacy, and wound healing activity. Successful preparation of PEI/NONOate was confirmed by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and ultraviolet/visible spectrophotometry. NO/PPNPs were characterized by particle size, surface charge, and NO loading. The NO/PPNPs showed a prolonged NO release profile over 6 days without any burst release. The NO/PPNPs exhibited potent bactericidal efficacy against methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa concentration-dependently and showed the ability to bind on the surface of the bacteria. We also found that the NO released from the NO/PPNPs mediates bactericidal efficacy and is not toxic to healthy fibroblast cells. Furthermore, NO/PPNPs accelerated wound healing and epithelialization in a mouse model of a MRSA-infected wound. Therefore, our results suggest that the NO/PPNPs presented in this study could be a suitable approach for treating wounds and various skin infections.

S-Nitrosothiol-modified nitric oxide-releasing chitosan oligosaccharides as antibacterial agents

S-Nitrosothiol-modified chitosan oligosaccharides were synthesized by reaction with 2-iminothiolane hydrochloride and 3-acetamido-4,4-dimethylthietan-2-one, followed by thiol nitrosation. The resulting nitric oxide (NO)-releasing chitosan oligosaccharides stored ∼0.3μmol NO mg(-1) chitosan. Both the chemical structure of the nitrosothiol (i.e. primary and tertiary) and the use of ascorbic acid as a trigger for NO donor decomposition were used to control the NO-release kinetics. With ascorbic acid, the S-nitrosothiol-modified chitosan oligosaccharides elicited a 4-log reduction in Pseudomonas aeruginosa viability. Confocal microscopy indicated that the primary S-nitrosothiol-modified chitosan oligosaccharides associated more with the bacteria relative to the tertiary S-nitrosothiol system. The primary S-nitrosothiol-modified chitosan oligosaccharides elicited minimal toxicity towards L929 mouse fibroblast cells at the concentration necessary for a 4-log reduction in bacterial viability, further demonstrating the potential of S-nitrosothiol-modified chitosan oligosaccharides as NO-release therapeutics.

Preparation of a mitochondria-targeted and NO-releasing nanoplatform and its enhanced pro-apoptotic effect on cancer cells

The therapeutic applications of exogenous nitric oxide are usually limited by its short half-life and its vulnerability to many biological substances, thus straightforward and precise spatiotemporal control of NO delivery may be critical to its therapeutic effects. Herein, the mitochondria-targeted and photoresponsive NO-releasing nanosystem is demonstrated as a new approach for cancer treatment. The nanosystem is fabricated by covalently incorporating a NO photo-donor and a mitochondria targeting ligand onto carbon-dots; accordingly, multi-functionalities (mitochondria-targeting, light-enhanced efficient NO-releasing, and cell imaging) are achieved. The in vitro NO release profiles for the nanosystem show that the duration of NO release from the present C-dot-based nanosystem containing immobilized SNO can be extended up to 8 hours or more. Upon cellular internalization, the nanosystem can target mitochondria and release NO. The action of the nanosystem on three cancer cell lines is evaluated; it is found that the targeted NO-releasing system can cause high cytotoxicity towards the cancer cells by specifically damaging their mitochondria. Additionally, light irradiation can amplify the cell apoptosis by enhancing NO release. These observations demonstrate that incorporating mitochondria-targeting ligand onto a NO-releasing system can enhance its pro-apoptosis action, thereby providing new insights for exploiting NO in cancer therapy.

One-step template-directed synthesis of walnut-kernel- and tremella-like silica spheres composed of U-shaped mesoporous structures based on pH-induced colloid aggregation

WKSS and TSS composed of U-shaped mesoporous structures were fabricated by a pH-induced colloid aggregation method with mixtures of CTAB and SDS used as templates.