Silver. I: Its antibacterial properties and mechanism of action

A review of the recent advances in antimicrobial coatings for urinary catheters

More than 75% of hospital-acquired or nosocomial urinary tract infections are initiated by urinary catheters, which are used during the treatment of 15-25% of hospitalized patients. Among other purposes, urinary catheters are primarily used for draining urine after surgeries and for urinary incontinence. During catheter-associated urinary tract infections, bacteria travel up to the bladder and cause infection. A major cause of catheter-associated urinary tract infection is attributed to the use of non-ideal materials in the fabrication of urinary catheters. Such materials allow for the colonization of microorganisms, leading to bacteriuria and infection, depending on the severity of symptoms. The ideal urinary catheter is made out of materials that are biocompatible, antimicrobial, and antifouling. Although an abundance of research has been conducted over the last forty-five years on the subject, the ideal biomaterial, especially for long-term catheterization of more than a month, has yet to be developed. The aim of this review is to highlight the recent advances (over the past 10years) in developing antimicrobial materials for urinary catheters and to outline future requirements and prospects that guide catheter materials selection and design.

STATEMENT OF SIGNIFICANCE

This review article intends to provide an expansive insight into the various antimicrobial agents currently being researched for urinary catheter coatings. According to CDC, approximately 75% of urinary tract infections are caused by urinary catheters and 15-25% of hospitalized patients undergo catheterization. In addition to these alarming statistics, the increasing cost and health related complications associated with catheter associated UTIs make the research for antimicrobial urinary catheter coatings even more pertinent. This review provides a comprehensive summary of the history, the latest progress in development of the coatings and a brief conjecture on what the future entails for each of the antimicrobial agents discussed.

Synthesis, structures and biomolecular interactions of new silver(i) 5,5-diethylbarbiturate complexes of monophosphines targeting Gram-positive bacteria and breast cancer cells

New silver(i) 5,5-diethylbarbiturate complexes exhibit very high antimicrobial activity against Gram-positive bacteria and kill MCF-7 cells, damaging mitochondria and DNA.

A chemosensor for micro- to nano-molar detection of Ag+ and Hg2+ ions in pure aqueous media and its applications in cell imaging

The synthesis and characterization of a simple thiourea-based Ag⁺ and Hg²⁺ sensor is reported.

Luminescent Silver-Purine Double Helicate: Synthesis, Self-Assembly and Antibacterial Action

The synthesis, self-assembly and antibacterial activity of a luminescent silver-purine double helicate is reported. The structure of the newly synthesized silver-supported helicate [C₃₆ H₂₄ N₁₆ O₄ Cl₅ Ag₁ ] was unambiguously characterized by single-crystal X-ray crystallography. It exhibited a bright bluish-green emission (λ_max =460 nm), when excited with 380 nm light. Microscopic investigations showed that the complex has a propensity to self-assemble into nanospheres. The antibacterial activity of this silver-containing helicate was studied against both Gram-positive and Gram-negative bacteria. MIC (minimal inhibitory concentration) values showed that the complex is very active against Gram-negative bacteria. Further internalization of the silver complex into E. coli bacteria was mapped with the help of microscopic techniques. These results are significant as silver was recently found to enhance antibiotic action against Gram-negative bacteria, raising hope in countering severe bacterial infections.

Composite Porous Silicon-Silver Nanoparticles as Theranostic Antibacterial Agents

A theranostic nanoparticle with biochemically triggered antibacterial activity is demonstrated. Metallic silver is deposited onto porous silicon nanoparticles (pSiNPs) by galvanic displacement. When aqueous diaminesilver ([Ag(NH₃)₂]⁺) is used as a silver source, the pSiNPs template the crystalline silver as small (mean diameter 13 nm) and well-dispersed nanoparticles embedded within and on the larger (100 nm) pSiNPs. The silver nanoparticles (AgNPs) quench intrinsic photoluminescence (PL) from the porous silicon (pSi) matrix. When exposed to an aqueous oxidant, the AgNPs are preferentially etched, Ag⁺ is released into solution, and PL from the pSi carrier is recovered. The released Ag⁺ results in 90% killing of (Gram-negative) Pseudomonas aeruginosa and (Gram-positive) Staphylococcus aureus within 3 h. When conjugated with the TAT peptide (sequence RKKRRQRRR), the silver-deposited porous silicon (pSi-Ag) nanocomposite shows distinct targeting toward S. aureus bacteria in vitro. Intravenously injected TAT-conjugated pSi-Ag nanoparticles accumulate in the liver, spleen, and lungs of mice, and the in vivo release of Ag⁺ and recovery of PL from pSi are demonstrated by the subsequent intraperitoneal administration of a hexacyanoferrate solution. The released Ag⁺ leads to a significant bacterial count reduction in liver tissue relative to the control. The data demonstrate the feasibility of the targeted and triggered delivery of antibacterial Ag⁺ ion in vivo, using a self-reporting and nontoxic nanocarrier.

Drug Delivery Approaches for the Treatment of Cervical Cancer

Cervical cancer is a highly prevalent cancer that affects women around the world. With the availability of new technologies, researchers have increased their efforts to develop new drug delivery systems in cervical cancer chemotherapy. In this review, we summarized some of the recent research in systematic and localized drug delivery systems and compared the advantages and disadvantages of these methods.

Thermal Characterizations of Silver-containing Bioactive Glass-coated Sutures

This study utilized and compared a number of thermal analysis methods to characterize the thermal properties of commercial sutures with and without antimicrobial coatings of silver-doped bioactive glass (AgBG) interlocking particulates. The effect of a slurry dipping technique used to coat resorbable Vicryl® (polyglactin 910) and non-resorbable Mersilk® surgical sutures with AgBG was investigated using conventional differential scanning calorimetry (DSC), high speed calorimetry (or HYPERDSC™), and modulated temperature DSC (MTDSC). These methods were compared in terms of their ability to resolve the thermal transitions of the types of suture materials. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used to verify the thermal degradation temperatures of these materials and to quantify the AgBG coatings on the sutures.

The use of complementary thermal analysis techniques enabled the understanding of the effect of the AgBG coating technique on the morphological properties of the sutures. The slurry dipping technique had no significant effect on the thermal transitions of both types of materials. The use of high speed calorimetry through DSC offered better resolution for the transitions that appeared to be weak through conventional heating regimes, and was able to separate broad double transitions. Furthermore, it was shown not to compromise either the melting temperature or the enthalpy of melting. Therefore this method allows for the accurate determination of thermal transitions through much shorter experimental times thus allowing for an increased sample throughput. The combined DTA and TGA indicated that a greater AgBG coating was obtained in the case of the Mersilk® sutures.

Recurring Wounds in a Diabetic with Multiple Medical Problems: Lower Extremity Wound Care

Acute trauma leading to open wounds in the lower extremity of a patient with diabetes mellitus can be life threatening. Diabetes mellitus complicates and compromises wound care and tissue repair for several reasons. This case report describes the successful wound care treatment modalities used in the care of a 53-year-old male who presented with diabetes and a full-thickness lower leg wound.

Silver containing hydrofiber dressing promotes wound healing in paediatric patients with partial thickness burns

INTRODUCTION

Burn injury is one of the most common reasons for admission in paediatric population. There is currently no international consensus on the best wound dressing material. Aquacel Ag, a new silver containing hydrofiber dressing material has been reported to produce good clinical results. Yet, only a limited number of studies exist in the paediatric population. This study aims to review our experience of burn management over the past 5 years and to evaluate the effectiveness of Aquacel Ag in the management of partial thickness burns.

METHODS

A retrospective review of all patients admitted for burn injury between January 2010 and December 2014 was conducted. Patients' demographics, mechanism of injury, body surface areas involved, treatment applied, and clinical outcomes were analyzed. Patients with superficial injury, full thickness burns that required surgical debridement, burn area less than 2 % or more than 25 % of total body surface area, or incomplete clinical data were excluded from the comparative study.

RESULTS

A total of 119 patients were identified. 114 (96 %) was due to domestic injury, of which 108 (91 %) was food-related. The most commonly affected areas were limbs (n = 89, 74.8 %), followed by trunk (n = 62, 74.8). 84 patients fulfilled the inclusion criteria and were recruited into the study. 31 patients received Aquacel Ag dressing and 53 patients received standard paraffin gauze dressing. The two groups showed no statistical difference in age, sex, percentage of total body surface area involved, and infection rate. Outcomes of patients treated with Aquacel Ag were compared with patients treated with standard dressing. The mean hospital stay was significantly shorter for the Aquacel Ag group (14.26 vs 23.45, p = 0.045). Aquacel Ag group required much less frequent dressing change (5.67 vs 20.59, p = 0.002). 5 patients in standard dressing group developed hypertrophic scar and required prolonged pressure garment, whereas only one hypertrophic scar was observed in the Aquacel Ag group.

CONCLUSION

Aquacel Ag appears to promote early burn wound healing with less hypertrophic scar formation.

In Vitro Assessment of the Antibacterial Potential of Silver Nano-Coatings on Cotton Gauzes for Prevention of Wound Infections

Multidrug-resistant organisms are increasingly implicated in acute and chronic wound infections, thus compromising the chance of therapeutic options. The resistance to conventional antibiotics demonstrated by some bacterial strains has encouraged new approaches for the prevention of infections in wounds and burns, among them the use of silver compounds and nanocrystalline silver. Recently, silver wound dressings have become widely accepted in wound healing centers and are commercially available. In this work, novel antibacterial wound dressings have been developed through a silver deposition technology based on the photochemical synthesis of silver nanoparticles. The devices obtained are completely natural and the silver coatings are characterized by an excellent adhesion without the use of any binder. The silver-treated cotton gauzes were characterized through scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA) in order to verify the distribution and the dimension of the silver particles on the cotton fibers. The effectiveness of the silver-treated gauzes in reducing the bacterial growth and biofilm proliferation has been demonstrated through agar diffusion tests, bacterial enumeration test, biofilm quantification tests, fluorescence and SEM microscopy. Moreover, potential cytotoxicity of the silver coating was evaluated through 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide colorimetric assay (MTT) and the extract method on fibroblasts and keratinocytes. Inductively coupled plasma mass spectrometry (ICP-MS) was performed in order to determine the silver release in different media and to relate the results to the biological characterization. All the results obtained were compared with plain gauzes as a negative control, as well as gauzes treated with a higher silver percentage as a positive control.

Essential oils and metal ions as alternative antimicrobial agents: a focus on tea tree oil and silver

The increasing occurrence of hospital-acquired infections and the emerging problems posed by antibiotic-resistant microbial strains have both contributed to the escalating cost of treatment. The presence of infection at the wound site can potentially stall the healing process at the inflammatory stage, leading to the development of a chronic wound. Traditional wound treatment regimes can no longer cope with the complications posed by antibiotic-resistant strains; hence, there is a need to explore the use of alternative antimicrobial agents. Pre-antibiotic compounds, including heavy metal ions and essential oils, have been re-investigated for their potential use as effective antimicrobial agents. Essential oils have potent antimicrobial, antifungal, antiviral, anti-inflammatory, antioxidant and other beneficial therapeutic properties. Similarly, heavy metal ions have also been used as disinfecting agents because of their broad spectrum activities. Both of these alternative antimicrobials interact with many different intracellular components, thereby resulting in the disruption of vital cell functions and eventually cell death. This review will discuss the application of essential oils and heavy metal ions, particularly tea tree oil and silver ions, as alternative antimicrobial agents for the treatment of chronic, infected wounds.

Proteomic Analysis to Elucidate the Antibacterial Action of Silver Ions Against Bovine Mastitis Pathogens

Silver ions act as a powerful, broad-spectrum antimicrobial agent and are known to kill over 650 different kinds of pathogens. We investigated the protein expression pattern and identity after silver ion treatment in Escherichia coli and Staphylococcus aureus, which are primarily responsible for the majority of bovine mastitis cases using proteomics. Two-dimensional electrophoresis showed that silver ion treatment significantly reduced 5 spot's density in E. coli and S. aureus, respectively. We identified 10 proteins (alkyl hydroperoxide reductase C22 subunit, phosphoglucomutase, fructose-1-phosphate kinase, putative carbamoyl transferase, alpha-galactosidase, carbamate kinase, ornithine transcarbamoylase, fumarate hydratase class II, alcohol dehydrogenase, and conserved hypothetical protein) by matrix-assisted laser desorption ionization time of flight (MALDI-TOF). These results demonstrated that silver ions have bactericidal effects through energy deprivation, inhibition of DNA replication, and accumulation of oxidants in bovine mastitis pathogens and suggested that silver ions can be applied for the treatment of bovine mastitis.

Nanoparticle-Based Therapies for Wound Biofilm Infection: Opportunities and Challenges

Clinical data from human chronic wounds implicates biofilm formation with the onset of wound chronicity. Despite the development of novel antimicrobial agents, the cost and complexity of treating chronic wound infections associated with biofilms remain a serious challenge, which necessitates the development of new and alternative approaches for effective anti-biofilm treatment. Recent advancement in nanotechnology for developing a new class of nanoparticles that exhibit unique chemical and physical properties holds promise for the treatment of biofilm infections. Over the last decade, nanoparticle-based approaches against wound biofilm infection have been directed toward developing nanoparticles with intrinsic antimicrobial properties, utilizing nanoparticles for controlled antimicrobials delivery, and applying nanoparticles for antibacterial hyperthermia therapy. In addition, a strategy to functionalize nanoparticles towards enhanced penetration through the biofilm matrix has been receiving considerable interest recently by means of achieving an efficient targeting to the bacterial cells within biofilm matrix. This review summarizes and highlights the recent development of these nanoparticle-based approaches as potential therapeutics for controlling wound biofilm infection, along with current challenges that need to be overcome for their successful clinical translation.

Ionically Crosslinked Chitosan Hydrogels for the Controlled Release of Antimicrobial Essential Oils and Metal Ions for Wound Management Applications

The emerging problems posed by antibiotic resistance complicate the treatment regime required for wound infections and are driving the need to develop more effective methods of wound management. There is growing interest in the use of alternative, broad spectrum, pre-antibiotic antimicrobial agents such as essential oils (e.g., tea tree oil, TTO) and metal ions (e.g., silver, Ag⁺). Both TTO and Ag⁺ have broad spectrum antimicrobial activity and act on multiple target sites, hence reducing the likelihood of developing resistance. Combining such agents with responsive, controlled release delivery systems such as hydrogels may enhance microbiocidal activity and promote wound healing. The advantages of using chitosan to formulate the hydrogels include its biocompatible, mucoadhesive and controlled release properties. In this study, hydrogels loaded with TTO and Ag⁺ exhibited antimicrobial activity against P. aeruginosa, S. aureus and C. albicans. Combining TTO and Ag⁺ into the hydrogel further improved antimicrobial activity by lowering the effective concentrations required, respectively. This has obvious advantages for reducing the potential toxic effects on the healthy tissues surrounding the wound. These studies highlight the feasibility of delivering lower effective concentrations of antimicrobial agents such as TTO and Ag⁺ in ionically crosslinked chitosan hydrogels to treat common wound-infecting pathogens.

Gingival Mesenchymal Stem Cell (GMSC) Delivery System Based on RGD-Coupled Alginate Hydrogel with Antimicrobial Properties: A Novel Treatment Modality for Peri-Implantitis

PURPOSE

Peri-implantitis is one of the most common inflammatory complications in dental implantology. Similar to periodontitis, in peri-implantitis, destructive inflammatory changes take place in the tissues surrounding a dental implant. Bacterial flora at the failing implant sites resemble the pathogens in periodontal disease and consist of Gram-negative anaerobic bacteria including Aggregatibacter actinomycetemcomitans (Aa). Here we demonstrate the effectiveness of a silver lactate (SL)-containing RGD-coupled alginate hydrogel scaffold as a promising stem cell delivery vehicle with antimicrobial properties.

MATERIALS AND METHODS

Gingival mesenchymal stem cells (GMSCs) or human bone marrow mesenchymal stem cells (hBMMSCs) were encapsulated in SL-loaded alginate hydrogel microspheres. Stem cell viability, proliferation, and osteo-differentiation capacity were analyzed.

RESULTS

Our results showed that SL exhibited antimicrobial properties against Aa in a dose-dependent manner, with 0.50 mg/ml showing the greatest antimicrobial properties while still maintaining cell viability. At this concentration, SL-containing alginate hydrogel was able to inhibit Aa growth on the surface of Ti discs and significantly reduce the bacterial load in Aa suspensions. Silver ions were effectively released from the SL-loaded alginate microspheres for up to 2 weeks. Osteogenic differentiation of GMSCs and hBMMSCs encapsulated in the SL-loaded alginate microspheres were confirmed by the intense mineral matrix deposition and high expression of osteogenesis-related genes.

CONCLUSION

Taken together, our findings confirm that GMSCs encapsulated in RGD-modified alginate hydrogel containing SL show promise for bone tissue engineering with antimicrobial properties against Aa bacteria in vitro.

Growth of Ag-nanoparticles in an aqueous solution and their antimicrobial activities against Gram positive, Gram negative bacterial strains and Candida fungus

Silver nanoparticles (AgNPs) were synthesized using Ocimum sanctum (Tulsi) leaves aqueous extract as reducing as well as a capping agent in absence and presence of cetyltrimethylammonium bromide (CTAB). The resulting nanomaterials were characterized by UV-visible spectrophotometer, and transmission electron microscope. The UV-Vis spectroscopy revealed the formation of AgNPs at 400-450 nm. TEM photographs indicate that the truncated triangular silver nanoplates and/or spherical morphology of the AgNPs with an average diameter of 25 nm have been distorted markedly in presence of CTAB. The AgNPs were almost mono disperse in nature. Antimicrobial activities of AgNPs were determined by using two bacteria (Gram positive Staphylococcus aureus MTCC-3160), Gram negative Escherichia coli MTCC-450) and one species of Candida fungus (Candida albicans ATCC 90030) with Kirby-Bauer or disc diffusion method. The zone of inhibition seems extremely good showing a relatively large zone of inhibition in both Staphylococcus aureus, Escherichia coli, and Candida albicans strains.

Antimicrobial Properties and Cytocompatibility of PLGA/Ag Nanocomposites

The purpose of this study was to investigate the antimicrobial properties of multifunctional nanocomposites based on poly(dl-Lactide-co-Glycolide) (PLGA) and increasing concentration of silver (Ag) nanoparticles and their effects on cell viability for biomedical applications. PLGA nanocomposite films, produced by solvent casting with 1 wt%, 3 wt% and 7 wt% of Ag nanoparticles were investigated and surface properties were characterized by atomic force microscopy and contact angle measurements. Antibacterial tests were performed using an Escherichia coli RB and Staphylococcus aureus 8325-4 strains. The cell viability and morphology were performed with a murine fibroblast cell line (L929) and a human osteosarcoma cell line (SAOS-2) by cell viability assay and electron microscopy observations. Matrix protein secretion and deposition were also quantified by enzyme-linked immunosorbent assay (ELISA). The results suggest that the PLGA film morphology can be modified introducing a small percentage of silver nanoparticles, which induce the onset of porous round-like microstructures and also affect the wettability. The PLGA/Ag films having silver nanoparticles of more than 3 wt% showed antibacterial effects against E. coli and S. aureus. Furthermore, silver-containing PLGA films displayed also a good cytocompatibility when assayed with L929 and SAOS-2 cells; indicating the PLGA/3Ag nanocomposite film as a promising candidate for tissue engineering applications.

Choosing a Wound Dressing Based on Common Wound Characteristics

Significance: Chronic wounds are a major healthcare burden.The practitioner should have an appropriate understanding of both the etiology of the wound as well as the optimal type of dressings to use. Fundamental wound characteristics may be used to guide the practitioner's choice of dressings. The identification of optimal dressings to use for a particular wound type is an important element in facilitating wound healing. Recent Advances: Researchers have sought to design wound dressings that aim to optimize each stage in the healing process. In addition, dressings have been designed to target and kill infection-causing bacteria, with the incorporation of antimicrobial agents. Critical Issues: Chronic wounds are frequently dynamic in presentation, and the numerous wound dressings available make dressing selection challenging for the practitioner. Choosing the correct dressing decreases time to healing, provides cost-effective care, and improves patient quality of life. Future Directions: Research into the mechanisms of wound healing has enhanced our ability to heal chronic wounds at a faster rate through the use of moisture-retentive dressings. Newer dressings are incorporating the use of nanotechnology by incorporating miniature electrical sensors into the dressing. These dressings are engineered to detect changes in a wound environment and alert the patient or practitioner by altering the color of the dressing or sending a message to a smartphone. Additional investigations are underway that incorporate biologic material such as stem cells into dressings.

Tuning of azine derivatives for selective recognition of Ag+ with the in vitro tracking of endophytic bacteria in rice root tissue

X-ray structurally characterized probes to track Ag⁺ in in vitro endophytic bacteria at rice root tissue and human breast cancer cells (MCF7).

Silver nanoparticles in aquatic environments: Physiochemical behavior and antimicrobial mechanisms

Nanosilver (silver nanoparticles or AgNPs) has unique physiochemical properties and strong antimicrobial activities. This paper provides a comprehensive review of the physicochemical behavior (e.g., dissolution and aggregation) and antimicrobial mechanisms of nanosilver in aquatic environments. The inconsistency in calculating the Gibbs free energy of formation of nanosilver [ΔGf(AgNPs)] in aquatic environments highlights the research needed to carefully determine the thermodynamic stability of nanosilver. The dissolutive release of silver ion (Ag(+)) in the literature is often described using a pseudo-first-order kinetics, but the fit is generally poor. This paper proposes a two-stage model that could better predict silver ion release kinetics. The theoretical analysis suggests that nanosilver dissolution could occur under anoxic conditions and that nanosilver may be sulfidized to form silver sulfide (Ag2S) under strict anaerobic conditions, but more investigation with carefully-designed experiments is required to confirm the analysis. Although silver ion release is likely the main antimicrobial mechanism of nanosilver, the contributions of (ion-free) AgNPs and reactive oxygen species (ROS) generation to the overall toxicity of nanosilver must not be neglected. Several research directions are proposed to better understand the dissolution kinetics of nanosilver and its antimicrobial mechanisms under various aquatic environmental conditions.

Green synthesis of silver nanoparticles with enhanced antibacterial activity using holocellulose as a substrate and reducing agent

The silver nanoparticles with uniform size and well-defined structure have been synthesized by using a hydrothermal method with holocellulose as substrate and reducing agent for silver ions, which exhibited good cytocompatibility and highly toxic.

Escherichia coli under Ionic Silver Stress: An Integrative Approach to Explore Transcriptional, Physiological and Biochemical Responses

For a better understanding of the systemic effect of sub-lethal micromolar concentrations of ionic silver on Escherichia coli, we performed a multi-level characterization of cells under Ag⁺-mediated stress using an integrative biology approach combining physiological, biochemical and transcriptomic data. Physiological parameters, namely bacterial growth and survival after Ag⁺ exposure, were first quantified and related to the accumulation of intracellular silver, probed for the first time by nano secondary ion mass spectroscopy at sub-micrometer lateral resolution. Modifications in E. coli biochemical composition were evaluated under Ag⁺-mediated stress by in situ synchrotron Fourier-transform infrared microspectroscopy and a comprehensive transcriptome response was also determined. Using multivariate statistics, correlations between the physiological parameters, the extracellular concentration of AgNO₃ and the intracellular silver content, gene expression profiles and micro-spectroscopic data were investigated. We identified Ag⁺-dependent regulation of gene expression required for growth (e.g. transporter genes, transcriptional regulators, ribosomal proteins), for ionic silver transport and detoxification (e.g. copA, cueO, mgtA, nhaR) and for coping with various types of stress (dnaK, pspA, metA,R, oxidoreductase genes). The silver-induced shortening of the acyl chain of fatty acids, mostly encountered in cell membrane, was highlighted by microspectroscopy and correlated with the down-regulated expression of genes involved in fatty acid transport (fadL) and synthesis/modification of lipid A (lpxA and arnA). The increase in the disordered secondary structure of proteins in the presence of Ag⁺ was assessed through the conformational shift shown for amides I and II, and further correlated with the up-regulated expression of peptidase (hfq) and chaperone (dnaJ), and regulation of transpeptidase expression (ycfS and ycbB). Interestingly, as these transpeptidases act on the structural integrity of the cell wall, regulation of their expression may explain the morphological damage reported under Ag⁺-mediated stress. This result clearly demonstrates that the cell membrane is a key target of ionic silver.

Antibacterial Plasma Polymer Films Conjugated with Phospholipid Encapsulated Silver Nanoparticles

Medical device associated infections are a persistent medical problem which has not found a comprehensive solution yet. Over the last decades, there have been intense research efforts toward developing antibacterial coatings that could potentially improve medical outcomes. Silver nanoparticles have attracted a great deal of attention as a potent alternative to conventional antibiotics. Herein, we present a biologically inspired approach to synthesize phospholipid encapsulated silver nanoparticles and their surface immobilization to a functional plasma polymer interlayer to generate antibacterial coatings. The antibacterial efficacy of the coatings was evaluated against three medically relevant pathogens including the Gram-positive Staphylococcus aureus and Staphylococcus epidermidis, and the Gram-negative Pseudomonas aeruginosa. The innate immune response to the coatings was assessed in vitro using primary bone marrow derived macrophages (BMDM). Any potential cytotoxicity was studied with primary human dermal fibroblasts (HDFs). Overall, the coatings had excellent inhibition of bacterial growth. We also observed reduced expression of pro-inflammatory cytokines from BMDM which suggests a reduced inflammatory response. The combined properties of coatings developed in this study may make them a good candidate for application on medical devices such as catheters and wound dressings.

Development of shampoo, soap and ointment formulated by green synthesised silver nanoparticles functionalised with antimicrobial plants oils in veterinary dermatology: treatment and prevention strategies

Many scientists have focused their research on the role of nanotechnology for the control of human pathogens, but there are also many topical pathogens present in animals, which infect animals and transfer to humans. Topical therapy is extremely important for the management of dermatological condition in animals. Therefore, the present study aims to evaluate the efficacy of biogenic silver nanoparticles (AgNPs) in combination with herbal oils against animal skin infections which may be responsible for causing infections in human beings. Here, the authors synthesised and characterised the AgNPs from Azadirachta indica. The oils were extracted from medicinal plants including Cymbopogon citratus, Cymbopogon martini, Eucalyptus globules, A. indica and Ocimum sanctum and the antifungal and antibacterial activity of plant oils along with AgNPs were evaluated. An excision wound model was used for the study of wound healing activity in rabbits. AgNPs functionalised oil has demonstrated remarkable antimicrobial activity against pathogens present on the skin of animals. The nano-functionalised antimicrobial oils were used in the formulation of shampoo, soap and ointment for veterinary dermatology. Antimicrobial products of plant origin with AgNPs are valuable, safe and have a specific role in controlling diseases. The authors believe that this approach will be a good alternative therapy to solve the continuous antibiotic resistance developed by many bacterial pathogens and will be utilised in various animal contacting areas in medicine.

Characterization of silver nanoparticle-infused tissue adhesive for ophthalmic use

In this work, we demonstrate the successful enhancement of breaking strength, adhesive strength, and antibacterial efficacy of ophthalmic tissue adhesive (2-octyl cyanoacrylate) by doping with silver nanoparticles, and investigate the effects of nanoparticle size and concentration. Recent work has shown that silver nanoparticles are a viable antibacterial additive to many compounds, but their efficacy in tissue adhesives was heretofore untested. Our results indicate that doping the adhesive with silver nanoparticles reduced bacterial growth by an order of magnitude or more; nanoparticle size and concentration had minimal influence in the range tested. Tensile breaking strength of polymerized adhesive samples and adhesive strength between a T-shaped support and excised porcine sclera were measured using a universal testing machine according to ASTM (formerly American Society for Testing and Materials) standard techniques. Both tests showed significant improvement with the addition of silver nanoparticles. The enhanced mechanical strength and antibacterial efficacy of the doped adhesive supports the use of tissue adhesives as a viable supplement or alternative to sutures.

Injectable and Self-Healing Dynamic Hydrogels Based on Metal(I)-Thiolate/Disulfide Exchange as Biomaterials with Tunable Mechanical Properties

Despite numerous strategies involving dynamic covalent bonds to produce self-healing hydrogels with similar frequency-dependent stiffness to native tissues, it remains challenging to use biologically relevant thiol/disulfide exchange to confer such properties to polymeric networks. Herein, we report a new method based on Metal(I) [Au(I) or Ag(I)] capping to protect thiolates from aerial oxidation without preventing thiolate/disulfide exchange. Dynamic hydrogels were readily prepared by injecting simultaneously aqueous solutions of commercially available HAuCl4 and 4-arm thiol-terminated polyethylene glycol [(PEGSH)4], resulting in a network containing a mixture of Au(I)-thiolate (Au-S) and disulfide bonds (SS). While the dynamic properties of the hydrogel were closely dependent on the pH, the mechanical properties could be easily tuned by adjusting (PEGSH)4 concentration and amount of Au-S, as judged by dynamic rheology studies. Permanent Au-S/SS exchange at physiological pH conferred self-healing behavior and frequency-dependent stiffness to the hydrogel. In addition, in vitro studies confirmed that Au-based dynamic material was not cytotoxic to human dermal fibroblasts, demonstrating its potential use as a medical device. Dynamic hydrogels obtained using Ag(I) ions demonstrated that the exchange reaction was not affected by the nature of the Metal(I) capping. Finally, this efficient thiolate capping strategy offers a simple way to produce injectable and self-healing dynamic hydrogels from virtually any thiol-containing polymers.

Design and construction of a silver(I)-loaded cellulose-based wound dressing: trackable and sustained release of silver for controlled therapeutic delivery to wound sites

Although application of silver nitrate and silver sulfadiazine have been shown to be effective in thwarting infections at burn sites, optimization of the delivery of bioactive silver (Ag(+)) remains as an obstacle due to rapid precipitation and/or insolubility of the silver sources. To circumvent these shortcomings, we have designed a silver(I) complex [Ag(ImD)2]ClO4 (ImD = dansyl imidazole) that effectively increases the bioavailability of Ag(+) and exhibits MIC values of 2.3 and 4.7 μg/mL against E. coli and S. aureus, respectively. This fluorescent silver complex has been incorporated within a robust hydrogel derived from carboxymethyl cellulose that allows slow release of silver. A complete occlusive dressing has finally been constructed with the Ag(ImD)CMC (1% Ag loaded) pad sealed between a sterile mesh gauze (as bottom layer) and a rayon-based surgical tape (as the top layer). Such construction has afforded a dressing that displays sustained delivery of silver onto a skin and soft tissue infection model and causes effective eradication of bacterial loads within 24 h. The transfer of the bioactive silver complex is readily visualized by the observed fluorescence that overlays precisely with the kill zone. The latter feature introduces a unique feature of therapeutic trackability to this silver-donating occlusive dressing.

Curbing Inflammation in Skin Wound Healing: A Review

Wound healing is a complex regulated process that results in skin scar formation in postnatal mammals. Chronic wounds are major medical problems that can confer devastating consequences. Currently, there are no treatments to prevent scarring. In the early fetus wounds heal without scarring and the healing process is characterized by relatively less inflammation compared to adults; therefore, research aimed at reducing the inflammatory process related to wound healing might speed healing and improve the final scar appearance.

The Anti-Inflammatory and Antibacterial Action of Nanocrystalline Silver and Manuka Honey on the Molecular Alternation of Diabetic Foot Ulcer: A Comprehensive Literature Review

Honey and silver have been used since ancient times for treating wounds. Their widespread clinical application has attracted attention in light of the increasing prevalence of antibiotic-resistant bacteria. While there have been a number of studies exploring the anti-inflammatory and antibacterial effects of manuka honey and nanocrystalline silver, their advantages and limitations with regard to the treatment of chronic wounds remain a subject of debate. The aim of this paper is to examine the evidence on the use of nanocrystalline silver and manuka honey for treating diabetic foot ulcers through a critical and comprehensive review of in vitro studies, animal studies, and in vivo studies. The findings from the in vitro and animal studies suggest that both agents have effective antibacterial actions. Their anti-inflammatory action and related impact on wound healing are unclear. Besides, there is no evidence to suggest that any topical agent is more effective for use in treating diabetic foot ulcer. Overall, high-quality, clinical human studies supported by findings from the molecular science on the use of manuka honey or nanocrystalline silver are lacking. There is a need for rigorously designed human clinical studies on the subject to fill this knowledge gap and guide clinical practice.

Anti-tumor activity of lipophilic imidazolium salts on select NSCLC cell lines

The anti-tumor activity of imidazolium salts is highly dependent upon the substituents on the nitrogen atoms of the imidazolium cation. We have synthesized and characterized a series of naphthalene-substituted imidazolium salts and tested them against a variety of non-smallcell lung cancer cell lines. Several of these complexes displayed anticancer activity comparable to cisplatin. These compounds induced apoptosis in the NCI-H460 cell line as determined by Annexin V staining, caspase-3, and PARP cleavage. These results strongly suggest that this class of compounds can serve as potent chemotherapeutic agents.

Negative-pressure wound therapy for management of diabetic foot wounds: a review of the mechanism of action, clinical applications, and recent developments

Negative-pressure wound therapy (NPWT) plays an important role in the treatment of complex wounds. Its effect on limb salvage in the management of the diabetic foot is well described in the literature. However, a successful outcome in this subgroup of diabetic patients requires a multidisciplinary approach with careful patient selection, appropriate surgical debridement, targeted antibiotic therapy, and optimization of healing markers. Evolving NPWT technology including instillation therapy, nanocrystalline adjuncts, and portable systems can further improve results if used with correct indications. This review article summarizes current knowledge about the role of NPWT in the management of the diabetic foot and its mode of action, clinical applications, and recent developments.

Silver in medicine: a brief history BC 335 to present

Silver is a naturally occurring element. Similar to other metals, the ionized form of silver (Ag(+1)) has known antimicrobial properties. A number of wound dressings incorporating silver ion or silver compounds have recently been developed and marketed. In addition, the antimicrobial effects of silver are currently being promoted in consumer products such as clothing and household appliances. The present use of silver in medical and consumer products has prompted concerns for potential toxicity and ecological effects, including induction of microbial resistance to antibiotics. These concerns ignore the fact that silver has been used for medicinal purposes for several thousand years. A historical review of the uses of silver in medicine is presented.

Silver in medicine: the basic science

Silver compounds are increasingly used in medical applications and consumer products. Confusion exists over the benefits and hazards associated with silver compounds. In this article, the biochemistry and physiology of silver are reviewed with emphasis on the use of silver for wound care.

Adsorption of Silver Nanoparticles onto Different Surface Structures of Chitin/Chitosan and Correlations with Antimicrobial Activities

Size-controlled spherical silver nanoparticles (Ag NPs) can be simply prepared by autoclaving mixtures of glass powder containing silver with glucose. Moreover, chitins with varying degrees of deacetylation (DDAc < 30%) and chitosan powders and sheets (DDAc > 75%) with varying surface structure properties have been evaluated as Ag NP carriers. Chitin/chitosan-Ag NP composites in powder or sheet form were prepared by mixing Ag NP suspensions with each of the chitin/chitosan-based material at pH 7.3, leading to homogenous dispersion and stable adsorption of Ag NPs onto chitin carriers with nanoscale fiber-like surface structures, and chitosan carriers with nanoscale porous surface structures. Although these chitins exhibited mild antiviral, bactericidal, and antifungal activities, chitin powders with flat/smooth film-like surface structures had limited antimicrobial activities and Ag NP adsorption. The antimicrobial activities of chitin/chitosan-Ag NP composites increased with increasing amounts of adsorbed Ag NPs, suggesting that the surface structures of chitin/chitosan carriers strongly influence adsorption of Ag NPs and antimicrobial activities. These observations indicate that chitin/chitosan-Ag NPs with nanoscale surface structures have potential as antimicrobial biomaterials and anti-infectious wound dressings.