Low intensity electric field inactivation of Gram-positive and Gram-negative bacteria via metal-free polymeric composite

Pulsed electric field at resonance frequency combat Klebsiella pneumonia biofilms

Healtcare-associated infections have increased due to the development of antimicrobial resistance (AMR) of Gram-negative pathogens (GNPs) and the development of outbreacks over the past two decades. In this work, we investigated how exposure to positive electric pulses affects the growth characteristics of Klebsiella pneumonia (K. pneumonia), a common cause of pneumonia. We explored the impact of varying exposure frequencies (0.2-2 Hz) and time (15-90 min, at resonance frequency) on bioelectric signals produced during cell division, biofilm formation, and bacterial antibiotic susceptibility. Our research found that an extremely low-frequency pulsed electric field (ELF-PEF) significantly inhibited K. pneumonia growth. Specifically, exposure to 0.8 Hz for one hour increased the antibiotic susceptibility of K. pneumonia to inhibitors of cell wall formation, proteins, β-lactamase, DNA, and other substances. We also noticed a notable decrease in K. pneumonia biofilm development exposed to ELF-PEF. Our results suggest that the interaction of K. pneumonia cells with ELF-PEF at the specified frequency and time alters cellular activity and bacterial structure. This technique may be used in the future to treat K. pneumonia infections both in vitro and in vivo.

Electrical Stimulating Redox Membrane Incorporated with PVA/Gelatin Nanofiber for Diabetic Wound Healing

Chronic wounds adversely affect the quality of life. Although electrical stimulation has been utilized to treat chronic wounds, there are still limitations to practicing it due to the complicated power system. Herein, an electrostimulating membrane incorporated with electrospun nanofiber (M-sheet) to treat diabetic wounds is developed. Through the screen printing method, the various alternate patterns of both Zn and AgCl on a polyurethane substrate, generating redox-mediated electrical fields are introduced. The antibacterial ability of the patterned membrane against both E. coli and S. aureus is confirmed. Furthermore, the poly(vinyl alcohol) (PVA)/gelatin electrospun fiber is incorporated into the patterned membrane to enhance biocompatibility and maintain the wet condition in the wound environment. The M-sheet can improve cell proliferation and migration in vitro and has an immune regulatory effect by inducing the polarization of macrophage to the M2 phenotype. Finally, when applied to a diabetic skin wound model, the M-sheet displays an accelerated wound healing rate and enhances re-epithelialization, collagen synthesis, and angiogenesis. It suggests that the M-sheet is a simple and portable system for the spontaneous generation of electrical stimulation and has great potential to be used in the practical wound and other tissue engineering applications.

Analysis of Carbon Materials with Infrared Photoacoustic Spectroscopy

Measurement of infrared spectroscopy has emerged as a significant challenge for carbon materials due to the sampling problem. To overcome this issue, in this work, we performed measurements of IR spectra for carbon materials including C60, C70, diamond powders, graphene, and carbon nanotubes (CNTs) using the photoacoustic spectroscopy (PAS) technique; for comparison, the vibrational patterns of these materials were also studied with a conventional transmission method, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, or Raman spectroscopy. We found that the IR photoacoustic spectroscopy (IR-PAS) scheme worked successfully for these carbon materials, offering advantages in sampling. Interestingly, the profiles of IR-PAS spectra for graphene and CNTs exhibit negative bands using carbon black as the reference; the negative spectral information may provide valuable knowledge about the storage energy, production, structure, defect, or impurity of graphene and CNTs. Thus, this approach may open a new avenue for analyzing carbon materials.

Enhancing the antibacterial effect of iron oxide and silver nanoparticles by extremely low frequency electric fields (ELF-EF) against S. aureus

Staphylococcus aureus is the cause of many infectious and inflammatory diseases and a lot of studies aim to discover alternative ways for infection control and treatment rather than antibiotics. This work attempts to reduce bacterial activity and growth characteristics of Staphylococcus aureus using nanoparticles (iron oxide nanoparticles and silver nanoparticles) and extremely low frequency electric fields (ELF-EF). Bacterial suspensions of Staphylococcus aureus were used to prepare the samples, which were evenly divided into groups. Control group, 10 groups were exposed to ELF-EF in the frequency range (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 Hz), iron oxide NPs treated group, iron oxide NPs exposed to 0.8 Hz treated group, silver NPs treated group and the last group was treated with silver NPs and 0.8 Hz. Antibiotic sensitivity testing, dielectric relaxation, and biofilm development for the living microbe were used to evaluate morphological and molecular alterations. Results showed that combination of nanoparticles with ELF-EF at 0.8 Hz enhanced the bacterial inhibition efficiency, which may be due to structural changes. These were supported by the dielectric measurement results which indicated the differences in the dielectric increment and electrical conductivity for the treated samples compared with control samples. This was also confirmed by biofilm formation measurements obtained. We may conclude that the exposure of Staphylococcus aureus bacteria to ELF-EF and NPs affected its cellular activity and structure. This technique is nondestructive, safe and fast and could be considered as a mean to reduce the use of antibiotics.

Anti-Infective and Toxicity Properties of Carbon Based Materials: Graphene and Functionalized Carbon Nanotubes

Recently, antimicrobial activities of various carbon-based nanomaterials against specific pathogens have become one of the most significant research interests in this field. Carbon nanotubes (CNTs) are promising multidisciplinary nanostructures in biomedicine, drug delivery, genetic engineering, biosensors, and artificial implants. However, the biomedical administration of CNTs is dependent on their solubility, toxicity, and biocompatibility, as well as novel drug-delivery applications through optimization of the drug's loading capacity, cellular absorption, and continuous release within the target cell. The usage of CNTs and Graphene materials as antimicrobial agents and nanocarriers for antibiotics delivery would possibly improve their bioavailability and facilitate better anti-infective therapy. However, it is worth mentioning that CNTs' antimicrobial activity and toxicity are highly dependent on their preparation and synthesis method. Various types of research have confirmed that diameter, length, residual catalyst, metal content, surface coating, electronic structure, and dispersibility would affect CNTs' toxicity toward bacteria and human cells. In this review article, a general study was performed on the antimicrobial properties of carbon-based nanomaterials, as well as their toxicity and applications in confronting different microorganisms. This study could be useful for researchers who are looking for new and effective drug delivery methods in the field of microbial resistance.

Advances in the Sensing and Treatment of Wound Biofilms

Wound biofilms represent a particularly challenging problem in modern medicine. They are increasingly antibiotic resistant and can prevent the healing of chronic wounds. However, current treatment and diagnostic options are hampered by the complexity of the biofilm environment. In this review, we present new chemical avenues in biofilm sensors and new materials to treat wound biofilms, offering promise for better detection, chemical specificity, and biocompatibility. We briefly discuss existing methods for biofilm detection and focus on novel, sensor-based approaches that show promise for early, accurate detection of biofilm formation on wound sites and that can be translated to point-of-care settings. We then discuss technologies inspired by new materials for efficient biofilm eradication. We focus on ultrasound-induced microbubbles and nanomaterials that can both penetrate the biofilm and simultaneously carry active antimicrobials and discuss the benefits of those approaches in comparison to conventional methods.

Advances in the Sensing and Treatment of Wound Biofilms

Wound biofilms represent a particularly challenging problem in modern medicine. They are increasingly antibiotic resistant and can prevent the healing of chronic wounds. However, current treatment and diagnostic options are hampered by the complexity of the biofilm environment. In this review, we present new chemical avenues in biofilm sensors and new materials to treat wound biofilms, offering promise for better detection, chemical specificity, and biocompatibility. We briefly discuss existing methods for biofilm detection and focus on novel, sensor-based approaches that show promise for early, accurate detection of biofilm formation on wound sites and that can be translated to point-of-care settings. We then discuss technologies inspired by new materials for efficient biofilm eradication. We focus on ultrasound-induced microbubbles and nanomaterials that can both penetrate the biofilm and simultaneously carry active antimicrobials and discuss the benefits of those approaches in comparison to conventional methods.

Sterilization of sealed PVDF pouches containing decellularized scaffold by electrical stimulation

A terminal sterilization process for tissue engineering products, such as allografts and biomaterials is necessary to ensure complete removal of pathogenic microorganisms such as the bacteria, fungi and viruses. However, it can be difficult to sterilize allografts and artificial tissue models packaged in wet conditions without deformation. In this study, we investigated the sterilization effects of electrical stimulation (ES) and assessed its suitability by evaluating sterility assurance levels in pouches at a constant current. Stability of polyvinylidene fluoride pouches was determined by a sterility test performed after exposure to five microorganisms (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans) for 5 days; the sterility test was also performed with decellularized human dermal tissues inoculated with the five microorganisms. Sterilization using ES inactivated microorganisms both inside and outside of sealed pouches and caused no damage to the packaged tissue. Our results support the development of a novel system that involves ES sterilization for packaging of implantable biomaterials and human derived materials. This article is protected by copyright. All rights reserved.

Antimicrobial and anti-adhesive properties of carbon nanotube-based surfaces for medical applications: a systematic review

Although high-performance carbon materials are widely used in surface engineering, with emphasis on carbon nanotubes (CNTs), the application of CNT nanocomposites on medical surfaces is poorly documented. In this study, we aimed to evaluate the antimicrobial and anti-adhesive properties of CNT-based surfaces. For this purpose, a PRISMA-oriented systematic review was conducted based on predefined criteria and 59 studies were selected for the qualitative analysis. Results from the analyzed studies suggest that surfaces containing modified CNTs, and specially CNTs conjugated with different polymers, exhibited strong antimicrobial and anti-adhesive activities. These composites seem to preserve the CNT toxicity to microorganisms and promote CNT-cell interactions, as well as to protect them from nonspecific protein adsorption. However, CNTs cannot yet compete with the conventional strategies to fight biofilms as their toxicity profile on the human body has not been thoroughly addressed. This review can be helpful for the development of new engineered medical surfaces.

Electroceutical Silk-Silver Gel to Eradicate Bacterial Infection

With more than 50% of bacteria resistant to standard antibiotics, new strategies to treat bacterial infection and colonization are needed. Based on the concept of targeting the bacteria synergistically on various fronts, it is hypothesized that an electrical insult associated with antibacterial materials may be a highly effective means of killing bacteria. In this work, an injectable conductive gel based on silk fibroin (SF) and silver nanoparticles (Ag-NPs) is synthesized, capable of coating a zone of injury, allowing the application of a low electrical current to decrease bacterial contamination. With a high conductivity of 1.5 S cm^-1 , SF/Ag-NPs gels killed 80% of Escherichia coli in 1 min, no toxicity toward Chinese hamster ovary cells is observed. The mechanism of an electrical composite gel combined with electrical wound therapy is associated with silver ion (Ag⁺ ) release, and reactive oxygen species (ROS) production. The findings in the present study show a similar Ag⁺ release for treatment with gels and the combined effect, whereas ROS generation is 50% higher when a small electrical current is applied leading to a broad bactericidal effect.

Electroactive 3D Printed Scaffolds Based on Percolated Composites of Polycaprolactone With Thermally Reduced Graphene Oxide for Antibacterial and Tissue Engineering Applications

Applying electrical stimulation (ES) could affect different cellular mechanisms, thereby producing a bactericidal effect and an increase in human cell viability. Despite its relevance, this bioelectric effect has been barely reported in percolated conductive biopolymers. In this context, electroactive polycaprolactone (PCL) scaffolds with conductive Thermally Reduced Graphene Oxide (TrGO) nanoparticles were obtained by a 3D printing method. Under direct current (DC) along the percolated scaffolds, a strong antibacterial effect was observed, which completely eradicated S. aureus on the surface of scaffolds. Notably, the same ES regime also produced a four-fold increase in the viability of human mesenchymal stem cells attached to the 3D conductive PCL/TrGO scaffold compared with the pure PCL scaffold. These results have widened the design of novel electroactive composite polymers that could both eliminate the bacteria adhered to the scaffold and increase human cell viability, which have great potential in tissue engineering applications.