Carbon nanotubes as anti-bacterial agents

Advances in dual functional antimicrobial and osteoinductive biomaterials for orthopaedic applications

A vast growing problem in orthopaedic medicine is the increase of clinical cases with antibiotic resistant pathogenic microbes, which is predicted to cause higher mortality than all cancers combined by 2050. Bone infectious diseases limit the healing ability of tissues and increase the risk of future injuries due to pathologic tissue remodelling. The traditional treatment for bone infections has several drawbacks and limitations, such as lengthy antibiotic treatment, extensive surgical interventions, and removal of orthopaedic implants and/or prosthesis, all of these resulting in long-term rehabilitation. This is a huge burden to the public health system resulting in increased healthcare costs. Current technologies e.g. co-delivery systems, where antibacterial and osteoinductive agents are delivered encounter challenges such as site-specific delivery, sustained and prolonged release, and biocompatibility. In this review, these aspects are highlighted to promote the invention of the next generation biomaterials to prevent and/or treat bone infections and promote tissue regeneration.

Nanomaterials as Delivery Vehicles and Components of New Strategies to Combat Bacterial Infections: Advantages and Limitations

Life-threatening bacterial infections have been well-controlled by antibiotic therapies and this approach has greatly improved the health and lifespan of human beings. However, the rapid and worldwide emergence of multidrug resistant (MDR) bacteria has forced researchers to find alternative treatments for MDR infections as MDR bacteria can sometimes resist all the present day antibiotic therapies. In this respect, nanomaterials have emerged as innovative antimicrobial agents that can be a potential solution against MDR bacteria. The present review discusses the advantages of nanomaterials as potential medical means and carriers of antibacterial activity, the types of nanomaterials used for antibacterial agents, strategies to tackle toxicity of nanomaterials for clinical applications, and limitations which need extensive studies to overcome. The current progress of using different types of nanomaterials, including new emerging strategies for the single purpose of combating bacterial infections, is also discussed in detail.

Initial Bacterial Adhesion Properties of Anodically Oxidized Ti6Al4V

This paper reports about the initial interaction of bacteria with anodically oxidized Ti6Al4V for the use as dental implant abutment surfaces. Ti6Al4V samples are anodically oxidized in hydrofluoric acid using different voltages. The resulting nanotopographies are characterized by atomic force microscopy, scanning electron microscopy and contact angle measurements. The topographies reach from micro-porous structures with small nanoporosities on top to fully hexagonally aligned nanotubes. For initial bacterial adhesion tests, Escherichia coli and Staphylococcus aureus are used. Samples are incubated for 2 h and afterwards non-adherent cells are washed off. The results of live/dead staining and cell counts are presented. Gram-negative and Gram-positive strains show different behavior in respect to total number of initially adherent cells on different micro/nanotopographies. The observed reduction of adhered microorganisms is mainly based on underlying microporous topographies.

Prospects for the Use of New Technologies to Combat Multidrug-Resistant Bacteria

The increasing use of antibiotics is being driven by factors such as the aging of the population, increased occurrence of infections, and greater prevalence of chronic diseases that require antimicrobial treatment. The excessive and unnecessary use of antibiotics in humans has led to the emergence of bacteria resistant to the antibiotics currently available, as well as to the selective development of other microorganisms, hence contributing to the widespread dissemination of resistance genes at the environmental level. Due to this, attempts are being made to develop new techniques to combat resistant bacteria, among them the use of strictly lytic bacteriophage particles, CRISPR-Cas, and nanotechnology. The use of these technologies, alone or in combination, is promising for solving a problem that humanity faces today and that could lead to human extinction: the domination of pathogenic bacteria resistant to artificial drugs. This prospective paper discusses the potential of bacteriophage particles, CRISPR-Cas, and nanotechnology for use in combating human (bacterial) infections.

Antimicrobial photodynamic activity of toluidine blue-carbon nanotube conjugate against Pseudomonas aeruginosa and Staphylococcus aureus - Understanding the mechanism of action

BACKGROUND

The emergence of drug-resistant bacterial strains has raised the need to develop alternative treatment modalities to combat infectious diseases. Antimicrobial photodynamic therapy (aPDT) is an alternative to conventional treatment modalities. aPDT integrates a photosensitizer, which, after exposure to light of an appropriate wavelength, leads to the generation of cytotoxic reactive oxygen species (ROS).

METHODS

The aim of the present study was to synthesize a toluidine blue/multiwalled carbon nanotube conjugate (TBCNT) for enhanced photoinactivation of Pseudomonas aeruginosa and Staphylococcus aureus. Synthesized TBCNT conjugate was characterized and its antibacterial and antibiofilm activity was determined.

RESULTS

During TBCNT synthesis, dye loading, and entrapment efficiency of the CNT were 12.04 ± 0.55% and 48.99 ± 2.33%, respectively. The photo-destruction of planktonic cells of the test bacteria was performed by exposure to a 125 mW red laser with a wavelength of 670 nm (radiant exposure of 58.49 J/cm²) for 3 min. Photoinactivation using TBCNT resulted in a 4.91- and 5.47-log10 reduction in P. aeruginosa and S. aureus, respectively. The mechanism of this aPDT was studied by measuring intracellular ROS generation, protein leakage, and lipid peroxidation in the test bacteria after light irradiation. The antibiofilm activity of TBCNT after light exposure was 69.94% and 75.54% for P. aeruginosa and S. aureus, respectively. Photoinactivation of test bacteria treated with TBCNT reduced cell viability and exopolysaccharide production. Confocal laser-scanning microscopy revealed a significant biofilm inhibition efficacy of the TBCNT conjugate.

CONCLUSION

Therefore, TBCNT conjugates may be used for the eradication of P. aeruginosa and S. aureus biofilms.

Treatment of boar sperm with nanoparticles for improved fertility

Continuous progress in nanoscience has allowed the synthesis of various nanoscale particles, known as nanoparticles or nanomaterials which, by harnessing unique physico-chemical properties, are crucial for multiple bio-applications. Despite the revealed toxicity (nanotoxicity) of nanoparticles in various in vitro and in vivo studies, their careful design for biocompatibility and effective interactions with single-celled and multi-cellular organisms has permitted their use in several fields of research and biomedicine. The various nanoparticles synthesized and applied in the veterinary sciences, including reproductive biology, have shown potential to influence routine practices in animal production systems. These include post-collection manipulation of semen and the protection of high-quality spermatozoa to extend their preservation, and to improve sperm-related biotechnologies such as sperm-mediated gene transfer, sperm sorting, sex-sorting, and cryopreservation. Therefore, the application of nanotechnology-based tools to semen may enhance assisted reproductive technologies for biomedical applications and improve economic productivity for farmers. Here, we review the efficacy of available techniques and emerging tools of nanotechnology that might be useful for further selection of high quality boar spermatozoa and productivity improvement.

Nanocarbon materials in water disinfection: state-of-the-art and future directions

Water disinfection practices are critical for supplying safe drinking water. Existing water disinfection methods come with various drawbacks, calling for alternative or complementary solutions. Nanocarbon materials (NCMs) offer unique advantages for water disinfection owing to their high antimicrobial activity, often low environmental/human toxicity, and tunable physicochemical properties. Nevertheless, it is a challenge to assess the research progress made so far due to the structure and property diversity in NCMs as well as their different targeted applications. Because of these, here we provide a broad outline of this emerging field in three parts. First, we introduce the antimicrobial activities of the different types of NCMs, including fullerenes, nanodiamonds, carbon (nano)dots, carbon nanotubes, and graphene-family materials. Next, we discuss the current status in applying these NCMs for different water disinfection problems, especially as hydrogel filters, filtration membranes, recyclable aggregates, and electrochemical devices. We also introduce the use of NCMs in photocatalysts for photocatalytic water disinfection. Lastly, we put forward the key hurdles of the field that hamper the realization of the practical applications and propose possible directions for future investigations to address those. We hope that this minireview will encourage researchers to tackle these challenges and innovate NCM-based water disinfection platforms in the near future.

Nanotechnology in metastatic cancer treatment: Current Achievements and Future Research Trends

The systemic spread of malignant cells from a primary site, a process termed metastasis represents a global challenge in cancer treatment. There is a real need to develop novel therapy strategies and nanomedicine may have remarkable and valuable contribution through specific and selective delivery of chemotherapeutic agents, through its intrinsic cytotoxic activity or through imaging applications, appealing also in the context of cancer personalized therapy. This review is focused on the applications of nanoparticles in the treatment of metastatic cancer, particularly on the possible effect on cell stabilization, growth inhibition, eventual interaction with adhesion molecules and antiangiogenic effect.

Synthesis and antimicrobial photodynamic effect of methylene blue conjugated carbon nanotubes on E. coli and S. aureus

The methylene blue and CNT nanoconjugate effectively produced singlet oxygen via photoactivation using a diode laser. It was employed for aPDT against pathogenic bacteria.

Antimicrobial photodynamic activity of rose bengal conjugated multi walled carbon nanotubes against planktonic cells and biofilm of Escherichia coli

BACKGROUND

The global threat of antimicrobial resistance especially due to the bacterial biofilms has engaged researchers in the search of new treatment modalities. Antimicrobial photodynamic inactivation (aPDI) is one of the alternative treatment modalities which kills bacteria by generating endogenous reactive oxygen species (ROS). In this work authors evaluated the antibacterial and antibiofilm efficacy of rose Bengal (RB) conjugated to CNT against E. coli.

METHODS

The interaction of anionic dye to the CNT was studied using UV-vis spectroscopy, HRTEM, FTIR and spectrofluorometry. Phototoxicity of RBCNT conjugate against E. coli was studied using a green light of 50 mW and radiant exposure of 1674.7 J/ cm² for 10 min. The antibiofilm activity and mechanism of action of RBCNT conjugate in presence of light was evaluated.

RESULTS

The loading and encapsulation was found to be 15.46 ± 1.05 and 61.85 ± 4.23% respectively. The photodynamic inactivation of planktonic cells of E. coli was found to 5.46 and 3.56 log₁₀ CFU/ml reduction on treatment with RBCNT and RB respectively. The conjugate also exhibited efficient and enhanced antibiofilm activity against E. coli. The study of mechanism of action has confirmed cell membrane and DNA damage were the two main targets of aPDI.

CONCLUSION

This report has concluded the efficient photodynamic inactivation occurred in Gram negative bacteria E. coli due to the increased production of ROS inside the bacterial cells. Hence, the newly synthesized RBCNT conjugate can be efficiently utilized to control infections caused by E. coli.

Cytotoxicity, cytokine release and ER stress-autophagy gene expression in endothelial cells and alveolar-endothelial co-culture exposed to pristine and carboxylated multi-walled carbon nanotubes

Recently we found that direct exposure of human umbilical vein endothelial cells (HUVECs) to multi-walled carbon nanotubes (MWCNTs) might induce toxicological responses through the modulation of ER stress gene expression, but whether this signal could be transferred from other cells to endothelial cells (ECs) is unknown. This study investigated the toxicity of pristine and carboxylated MWCNTs to HUVECs and alveolar-endothelial co-culture, the later of which could mimic the possible signaling communications between ECs and MWCNT exposed alveolar cells. The results showed that direct contact with high levels of MWCNTs induced cytotoxicity and modulated expression of genes associated with ER stress (HSPA5, DDIT3 and XBP-1s) and autophagy (BECN1 and ATG12) both in A549-THP-1 macrophages cultured in the upper chambers as well as HUVECs. However, most of these responses were minimal or negligible in HUVECs cultured in the lower chambers. Moreover, significantly increased cytokine release (interleukin-6 and soluble vascular cell adhesion molecule-1) was only observed in MWCNT exposed HUVECs (p < 0.01) but not HUVECs cultured in the lower chambers (p > 0.05). The minimal or even absent response was likely due to relatively low translocation of MWCNTs from upper chambers to lower chambers, whereas A549-macrophages cultured in the upper chambers internalized large amount MWCNTs. The results indicated that ER stress-autophagy signaling might not be able to transfer from alveolar cells to endothelial cells unless sufficient MWCNTs are translocated.

Mechanistic Insight into the Light-Irradiated Carbon Capsules as an Antibacterial Agent

Infections caused by bacteria are a growing global challenge for public health as bacteria develop resistance, which will cause the failure of anti-infective treatment eventually. An effective alternative strategy to traditional antibacterial therapy is utilizing reactive oxygen species (ROS) to kill bacteria. Here, we report a simple route to prepare PEGylated nitrogen-doped carbon capsules (PEG-N-CCs) as an antibacterial agent. The PEG-N-CCs can translate near-infrared light (NIR) into heat and produce a high concentration of ROS triggered by NIR irradiation. Both heating and ROS are critical to destroy the outer membranes and rupture cell bodies, causing DNA fragmentation and glutathione oxidation both in Gram-negative Escherichia coli, Gram-positive Staphylococcus aureus, and their multidrug-resistant strains. Moreover, PEG-N-CCs plus NIR irradiation can efficiently scavenge the existing biofilms and prevent the formation of new biofilms, killing planktonic bacteria as well as those within the biofilm. Our studies prove that the PEG-N-CCs plus NIR irradiation can provide a simple and effective platform for combating bacteria, employing carbon nanomaterials as an antibacterial alternative for treatment of infectious diseases.

High Aspect Ratio Nanostructures Kill Bacteria via Storage and Release of Mechanical Energy

The threat of a global rise in the number of untreatable infections caused by antibiotic-resistant bacteria calls for the design and fabrication of a new generation of bactericidal materials. Here, we report a concept for the design of antibacterial surfaces, whereby cell death results from the ability of the nanofeatures to deflect when in contact with attaching cells. We show, using three-dimensional transmission electron microscopy, that the exceptionally high aspect ratio (100-3000) of vertically aligned carbon nanotubes (VACNTs) imparts extreme flexibility, which enhances the elastic energy storage in CNTs as they bend in contact with bacteria. Our experimental and theoretical analyses demonstrate that, for high aspect ratio structures, the bending energy stored in the CNTs is a substantial factor for the physical rupturing of both Gram-positive and Gram-negative bacteria. The highest bactericidal rates (99.3% for Pseudomonas aeruginosa and 84.9% for Staphylococcus aureus) were obtained by modifying the length of the VACNTs, allowing us to identify the optimal substratum properties to kill different types of bacteria efficiently. This work highlights that the bactericidal activity of high aspect ratio nanofeatures can outperform both natural bactericidal surfaces and other synthetic nanostructured multifunctional surfaces reported in previous studies. The present systems exhibit the highest bactericidal activity of a CNT-based substratum against a Gram-negative bacterium reported to date, suggesting the possibility of achieving close to 100% bacterial inactivation on VACNT-based substrata.

Review on the Antimicrobial Properties of Carbon Nanostructures

Swift developments in nanotechnology have prominently encouraged innovative discoveries across many fields. Carbon-based nanomaterials have emerged as promising platforms for a broad range of applications due to their unique mechanical, electronic, and biological properties. Carbon nanostructures (CNSs) such as fullerene, carbon nanotubes (CNTs), graphene and diamond-like carbon (DLC) have been demonstrated to have potent broad-spectrum antibacterial activities toward pathogens. In order to ensure the safe and effective integration of these structures as antibacterial agents into biomaterials, the specific mechanisms that govern the antibacterial activity of CNSs need to be understood, yet it is challenging to decouple individual and synergistic contributions of physical, chemical and electrical effects of CNSs on cells. In this article, recent progress in this area is reviewed, with a focus on the interaction between different families of carbon nanostructures and microorganisms to evaluate their bactericidal performance.