Silver-nanoparticles-modified biomaterial surface resistant to staphylococcus: new insight into the antimicrobial action of silver

Silver-doped laser-induced graphene for potent surface antibacterial activity and anti-biofilm action

Silver nanoparticles embedded in laser-induced graphene surfaces were generated in a one step process, resulting in highly antibacterial surfaces.

Facile Synthesis of Silver Nanoparticles with High Antibacterial Activity

We report on a reverse microemulsion method for the synthesis of silver nanocrystals and examine their antibacterial activities. As the molar ratio of water to sodium bis(2-ethylhexyl) sulfosuccinate (AOT) increases to 25, a morphology transition from a sphere-like nanocrystal to a wire-like one was observed. For both the gram-negative and gram-positive bacteria, the wire-like silver nanocrystal showed higher antibacterial activities. We conclude that the morphology of silver nanocrystals dominates their antibacterial activity.

Biologically produced silver chloride nanoparticles from B. megaterium modulate interleukin secretion by human adipose stem cell spheroids

Stem cell tissue constructs are likely to come into contact with silver-based nanoparticles-such as silver chloride nanoparticles (AgCl-NPs)-used as microbicidals at the implant site or in cosmetics. However, the effect of silver-based nanoparticles on 3D cell cultures with potential for tissue engineering has received little attention. Here, we examined the effect of sub-lethal doses (5, 10 and 25 µg/mL, for 1, 7 and 21 days) of AgCl-NPs produced by 'green' bacterial-based synthesis on spheroid 3D cultures of human adipose tissue stem cells (ASCs). Light microscopy analysis revealed that the shape and diameter of ASC spheroids remained largely unchanged after AgCl-NP treatment. Flow cytometry analysis with 7-AAD and 2',7'-dichlorofluorescein diacetate revealed no statistically significant differences in cell death but showed an increase of ROS levels for the untreated group and significant differences for the groups treated with 5 and 10 µg/mL at day 7 (p = 0.0395, p = 0.0266, respectively). Electron microscopy analysis showed limited cell damage in the periphery of AgCl-NP-treated spheroids. However, treatment with AgCl-NP had statistically significant effects on the secretion of IL-6, IL-8, IL-1β and IL-10 by spheroids, at specific treatment periods and concentrations, and particularly for IL-6, IL-8 and IL-1β. TGF-β1 and -β2 secretion also changed significantly throughout the treatment period. Our results indicate that, despite having little effect on cell viability and morphology, sub-lethal AgCL-NP doses modulate ROS production at day 7 for the groups treated with 5 and 10 µg/mL and also modulate the secretory profile of ASC spheroids. Thus, the use of skin implants or products containing Ag-NPs may promote long-term disturbances in subcutaneous adipose tissue homeostasis.

Bioengineering of Functional Nanosilver Nanogels for Smart Healthcare Systems

Functional designing of nanogels has become an attractive domain of biomedical engineering to develop bioactive materials with innovative features for the human healthcare system. Nanosilver has attracted enormous attention due to its wide antimicrobial spectrum and ability to kill almost all types of bacteria in its vicinity. However, the most crucial challenge for bioscientists is the lack of binding ability of nanosilver with the material surfaces that allow nanosilver to leach out to the surrounding tissue and exert toxicity while the biomaterial is in contact with the living system. Designing nanosilver within a nanogel confinement offers enormous possibilities to develop functional bioactive nanoparticles that may be bonded to any biomaterial surface via the nanogel functionality. This approach requires the proper combination of material science with nanotechnology and biotechnology to innovate interesting domain of functional nanogels with unique features. This work aims at providing a critical review on the current progress, approaches, and vision in designing nanosilver-entrapped nanogel particles with diverse functionality, and their bioactivity against microorganisms for human healthcare devices.

Uniform Generation of Sub-nanometer Silver Clusters in Zeolite Cages Exhibiting High Photocatalytic Activity under Visible Light

Sub-nanometer silver clusters that exhibit discrete electronic structure with molecular-like properties are highly desirable in various technologies. However, the methods for their preparation suffer from limitations related with the reproducibility and particles uniformity and/or the possibility of the scale-up. Another critical drawback is that free sub-nanometer silver clusters tend to aggregate into larger particles. In this work, a new approach that successfully overcomes the above limitations is developed. It allows, for the first time, an ultrafast preparation of sub-nanometer silver particles with high abundance, uniformity (7 Å), and stability into the cages of nanosized zeolite crystals. The new method consists of UV excitation of a water suspension of nanozeolite containing photoactive vanadate clusters in the presence of ethanol (as an electron donor) and silver precursor. The characteristic features of sub-nanometer silver particles are presented, and the mechanism of their formation is discussed. Sub-nanometer Ag clusters exhibit exceptional photocatalytic activity and selectivity in the reforming of formic acid to H₂ and CO₂ under visible light.

Effects of Local Application of Nano-silver on Osteomyelitis and Soft Tissue Infections: An Experimental Study in Rats

Purpose: Bone and soft tissue infections are among the least desired complications after orthopaedic surgery. This study analysed the in vivo effects of the local application of nano-silver particles (AgNPs) [1nm = 1 billionth of a meter] in soft tissue infections. Materials-Method: An experimental osteomyelitis model was formed by inoculating both tibias of 24 rats with methicillin-resistant Staphylococcus aureus. The rats were followed without treatment for 21 days. Blood samples and tibial x-rays at day 21 confirmed the development of infection. Then, the rats were divided randomly into two groups. One group (12 rats) underwent surgical debridement and received 21 days of teicoplanin therapy. The second group had the same treatment, with the addition of local nano-silver. All of the rats were sacrificed at day 42. Blood and wound swab samples were taken and the culture results were analysed. Results: No differences were observed between the groups in healing values at pathological examination, or in changes in the number of colonies at days 21 and 42. No differences in white blood cell count (WBC) were observed between the groups before and after the treatment. Conclusion: Although in vitro studies suggest the effectiveness of AgNPs on pathogens, we found that the application of nano-silver did not make any difference when used in addition to the classical osteomyelitis treatment with antibiotics and local surgical debridement. We believe that additional in vivo studies using repeated nano-silver application could be beneficial.

Evaluation of the temporary effect of physical vapor deposition silver coating on resistance to infection in transdermal skin and bone integrated pylon with deep porosity

Periprosthetic infection via skin-implant interface is a leading cause of failures and revisions in direct skeletal attachment of limb prostheses. Implants with deep porosity fabricated with skin and bone integrated pylons (SBIP) technology allow for skin ingrowth through the implant's structure creating natural barrier against infection. However, until the skin cells remodel in all pores of the implant, additional care is required to prevent from entering bacteria to the still nonoccupied pores. Temporary silver coating was evaluated in this work as a means to provide protection from infection immediately after implantation followed by dissolution of silver layer in few weeks. A sputtering coating with 1 µm thickness was selected to be sufficient for fighting infection until the deep ingrowth of skin in the porous structure of the pylon is completed. In vitro study showed less bacterial (Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa) growth on silver coated tablets compared to the control group. Analysis of cellular density of MG-63 cells, fibroblasts, and mesenchymal stem cells (MSCs) showed that silver coating did not inhibit the cell growth on the implants and did not affect cellular functional activity. The in vivo study did not show any postoperative complications during the 6-month observation period in the model of above-knee amputation in rabbits when SBIP implants, either silver-coated or untreated were inserted into the bone residuum. Three-phase scintigraphy demonstrated angiogenesis in the pores of the pylons. The findings suggest that a silver coating with well-chosen specifications can increase the safety of porous implants for direct skeletal attachment. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 169-177, 2019.

Synthesis of Metal Nanoparticles in Metal-Phenolic Networks: Catalytic and Antimicrobial Applications of Coated Textiles

The synthesis of metal nanoparticle (NP)-coated textiles (nanotextiles) is achieved by a dipping process in water without toxic chemicals or complicated synthetic procedures. By taking advantage of the unique nature of tannic acid, metal-phenolic network-coated textiles serve as reducing and stabilizing sites for the generation of metal nanoparticles of controllable size. The textiles can be decorated with various metal nanoparticles, including palladium, silver, or gold, and exhibit properties derived from the presence of the metal nanoparticles, for example, catalytic activity in water (>96% over five cycles using palladium nanoparticles) and antibacterial activity against Gram-negative bacteria (inhibition of Escherichia coli using silver nanoparticles) that outperforms a commercial bandage. The reported strategy offers opportunities for the development of hybrid nanomaterials that may have application in fields outside of catalysis and antimicrobials, such as sensing and smart clothing.

Emerging Nanomedicine Therapies to Counter the Rise of Methicillin-Resistant Staphylococcus aureus

In a recent report, the World Health Organisation (WHO) classified antibiotic resistance as one of the greatest threats to global health, food security, and development. Methicillin-resistant Staphylococcus aureus (MRSA) remains at the core of this threat, with persistent and resilient strains detectable in up to 90% of S. aureus infections. Unfortunately, there is a lack of novel antibiotics reaching the clinic to address the significant morbidity and mortality that MRSA is responsible for. Recently, nanomedicine strategies have emerged as a promising therapy to combat the rise of MRSA. However, these approaches have been wide-ranging in design, with few attempts to compare studies across scientific and clinical disciplines. This review seeks to reconcile this discrepancy in the literature, with specific focus on the mechanisms of MRSA infection and how they can be exploited by bioactive molecules that are delivered by nanomedicines, in addition to utilisation of the nanomaterials themselves as antibacterial agents. Finally, we discuss targeting MRSA biofilms using nano-patterning technologies and comment on future opportunities and challenges for MRSA treatment using nanomedicine.

Modification of a conventional polyurethane composition provides significant anti-biofilm activity against Escherichia coli

Tecoflex-NH₃⁺ exhibited a contact-killing mechanism and showed excellent anti-biofilm properties against E. coli even after 5 days.

Minocycline hydrochloride loaded on titanium by graphene oxide: an excellent antibacterial platform with the synergistic effect of contact-killing and release-killing

Graphene oxide loaded with minocycline hydrochloride as an excellent antibacterial platform with the synergistic effect of contact-killing and release-killing.

Enhanced Anti-Infective Efficacy of ZnO Nanoreservoirs through a Combination of Intrinsic Anti-Biofilm Activity and Reinforced Innate Defense

The increasing prevalence of implant-associated infections (IAIs) imposes a heavy burden on patients and medical providers. Bacterial biofilms are recalcitrant to antiseptic drugs and local immune defense and can attenuate host proinflammatory response to interfere with bacterial clearance. Zinc oxide nanoparticles (ZnO NPs) play a dual role in antibacterial and immunomodulatory activities but compromise the cytocompatibility because of their intracellular uptake. Here, ZnO NPs were immobilized on titanium to form homogeneous nanofilms (from discontinuous to continuous) through magnetron sputtering, and the possible antimicrobial activity and immunomodulatory effect of nano-ZnO films were investigated. Nano-ZnO films were found to prohibit sessile bacteria more than planktonic bacteria in vitro, and the antibacterial effect occurred in a dose-dependent manner. Using a novel mouse soft tissue IAI model, the in vivo results revealed that nano-ZnO films possessed outstanding antimicrobial efficacy, which could not be ascribed solely to the intrinsic anti-infective activity of nano-ZnO films observed in vitro. Macrophages and polymorphonuclear leukocytes (PMNs), two important factors in innate immune response, were cocultured with nano-ZnO and bacteria/lipopolysaccharide in vitro, and the nano-ZnO films could enhance the antimicrobial efficacy of macrophages and PMNs through promoting phagocytosis and secretion of inflammatory cytokines. This study provides insights into the anti-infective activity and mechanism of ZnO and consolidates the theoretical basis for future clinical applications of ZnO.

Staphylococcal biofilm gene expression on biomaterials - A methodological study

The combination of increased healthcare access, universal aging, and infallible therapy demands, synergistically drive the need for the development of biomaterial technologies that mitigate the challenge of biomaterial-associated infections (BAI). Staphylococcus epidermidis and Staphylococcus aureus account for the majority of BAI due to their ability to accumulate in adherent multilayered biofilm. This investigation details the development of gene expression assays to evaluate the genetic processes of attachment, accumulation, maturation, and dispersal phases of biofilms on biomaterials in vitro, while abiding by the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines. The biofilm formation of S. epidermidis on polyurethane (PU) central venous catheters and S. aureus on machined titanium (Ti) was examined in terms of gene expression at early and late time points. The results provided insight into how each stage of biofilm formation is orchestrated over time on these biomaterials in vitro. Furthermore, the results suggested that mechanical RNA extraction, organic solvents, elimination of genomic DNA, and preamplification are advisable strategies to implement for biofilm gene expression analysis. It is concluded that this method can be employed for the assessment of biofilm-biomaterial interactions at the molecular level. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3400-3412, 2017.

Layer-Number Dependent Antibacterial and Osteogenic Behaviors of Graphene Oxide Electrophoretic Deposited on Titanium

Graphene oxide has attracted widespread attention in the biomedical fields due to its excellent biocompatibility. Herein we investigated the layer-number dependent antibacterial and osteogenic behaviors of graphene oxide in biointerfaces. Graphene oxide with different layer numbers was deposited on the titanium surfaces by cathodal electrophoretic deposition with varied deposition voltages. The initial cell adhesion and spreading, cell proliferation, and osteogenic differentiation were observed from all the samples using rat bone mesenchymal stem cells. Both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were used to investigate the antibacterial effect of the modified titanium surfaces. Cocultures of human gingival fibroblasts (HGF) cells with Escherichia coli and Staphylococcus aureus were conducted to simulate the conditions of the clinical practice. The results show that the titanium surfaces with graphene oxide exhibited excellent antibacterial and osteogenic effects. Increasing the layer-number of graphene oxide resulted in the augment of reactive oxygen species levels and the wrinkling, which led to the antibacterial and osteogenic effects, respectively. Compared to pure titanium surface in the cells-bacteria coculture process, the modified titanium surfaces with graphene oxide exhibited higher surface coverage percentage of cells.

Local and Systemic Changes Associated with Long-term, Percutaneous, Static Implantation of Titanium Alloys in Rhesus Macaques (Macaca mulatta)

Metal alloys are frequently used as implant materials in veterinary medicine. Recent studies suggest that many alloys induce both local and systemic inflammatory responses. In this study, 37 rhesus macaques with long-term skull-anchored percutaneous titanium alloy implants (duration, 0 to 14 y) were evaluated for changes in their hematology, coagulation, and serum chemistry profiles. Negative controls (n = 28) did not have implants. Macaques with implants had higher plasma D-dimer and lower antithrombin III concentrations than nonimplanted animals. In addition, animals with implants had higher globulin and lower albumin and calcium concentrations compared with nonimplanted macaques. Many of these changes were positively correlated with duration of implantation and the number of implants. Chronic bacterial infection of the skin was present around many of the implant sites and within deeper tissues. Representative histopathology around the implant site of 2 macaques revealed chronic suppurative to pyogranulomatous inflammation extending from the skin to the dura mater. X-ray fluorescence microscopy of tissue biopsies from the implant site of the same 2 animals revealed significantly higher levels of free metal ions in the tissue, including titanium and iron. The higher levels of free metal ions persisted in the tissues for as long as 6 mo after explantation. These results suggest that long-term skull-anchored percutaneous titanium alloy implants can be associated with localized inflammation, chronic infection, and leaching of metal ions into local tissues.