Synergism of Water Shock and a Biocompatible Block Copolymer Potentiates the Antibacterial Activity of Graphene Oxide

Herbal Medicine-Inspired Carbon Quantum Dots with Antibiosis and Hemostasis Effects for Promoting Wound Healing

Bleeding and bacterial infections are crucial factors affecting wound healing. The usage of herbal medicine-derived materials holds great potential for promoting wound healing. However, the uncertain intrinsic effective ingredients and unclear mechanism of action remain great concerns. Herein, inspired by the herbal medicine Ligusticum wallichii, we reported the synthesis of tetramethylpyrazine-derived carbon quantum dots (TMP-CQDs) for promoting wound healing. Of note, the use of TMP as the precursor instead of L. wallichii ensured the repeatability and homogeneity of the obtained products. Furthermore, TMP-CQDs exhibited high antibacterial activity. Mechanically, TMP-CQDs inhibited the DNA repair, biosynthesis, and quorum sensing of the bacteria and induced intracellular reactive oxygen species (ROS). Moreover, TMP-CQDs could accelerate blood coagulation through activating factor VIII and promoting platelet aggregation. Effective wound healing was achieved by using TMP-CQDs in the Staphylococcus aureus-infected mouse skin wound model. This study sheds light on the development of herbal medicine-inspired materials as effective therapeutic drugs.

Functionalization of graphene oxide with amphiphilic block copolymer to enhance antibacterial activity

Functionalization of GO with an amphiphilic block copolymer is designed with an aim to enhance its biocompatibility, however, long copolymer chains can screen the blade effect of GO to sacrifice its antimicrobial activities. To solve this problem, low molecular weight of poly(ethylene glycol) (PEG), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and their block copolymer were respectively introduced onto GO via an isophorone diisocyanate modified GO as a intermediate, followed by a solvent evaporation of an oil-in-water emulsion treatment (SE treatment) to induce block copolymer into polymer micelle via phase separation to refresh the sharp edges of GO. Block copolymer modified GO possessed similar dispersibility and stability to PEG modified GO, and even higher loading capacity of the hydrophobic drug than PHBV modified GO, illustrating its superior properties to homopolymer. PEG, PHBV and their block copolymer modified GO were nontoxic towards ATDC5 cells while cultured for 3 days and compatible with erythrocytes within 8 h. SE treatment enhanced greatly the loading capacity of the hydrophobic drug and the accumulative release reached 91.3% within 24 h. The inhibition zone of the block copolymer modified GO was 14.1 mm and 14.8 mm against E. coli and S. aureus, comparable to that of PEG modified GO. The bacterial reduction rate of the copolymer micelle modified GO was 87.1% and 82.7% towards E. coli and S. aureus, much greater than that of PEG, PHBV and their block copolymer modified GO at a concentration of 1 mg/mL. The antibiofilm capacity of the copolymer micelle modified GO were equal to that of PEG modified, demonstrating its great promise in tissue engineering application for repair of infected tissue defects.

Ni Nanocrystals Supported on Graphene Oxide: Antibacterial Agents for Synergistic Treatment of Bacterial Infections

The effects of antibiotics on bacterial infections are gradually weakened, leading to the wide development of nanoparticle-based antibacterial agents with unique physical and chemical properties and antibacterial mechanisms different from antibiotics. In this study, we fabricated the uniform and stable graphene oxide (GO)/Ni colloidal nanocrystal cluster (NCNC) nanocomposite by electrostatic self-assembly and investigated its synergistic antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in vitro. The GO/NCNC nanocomposite was shown to possess higher inhibition efficiency than a pure NCNC or GO suspension, with 99.5 and 100% inhibition against S. aureus and E. coli at a 125 μg/mL concentration, respectively. Antibacterial mechanism analysis revealed that (i) NCNCs decorated on GO can further enhance the antibacterial properties of GO by binding and capturing bacteria, (ii) the leaching of Ni²⁺ was detected during the interaction of GO/NCNCs and bacteria, resulting in a decrease in the number of bacteria, and (iii) the GO/NCNC nanocomposite can synergistically destroy the bacterial membrane through physical action and induce the reactive oxygen species generation, so as to further damage the cell membrane and affect ATPase, leakage of intercellular contents, and ultimately bacterial growth inhibition. Meanwhile, cell culture experiments demonstrated no adverse effect of GO/NCNCs on cell growth. These preliminary results indicate the high antibacterial efficiency of the GO/NCNC nanocomposite, suggesting the possibility to develop it into an effective antibacterial agent in the future against bacterial infections.

GO-based antibacterial composites: Application and design strategies

Graphene oxide (GO), for its unique structure with high biocompatibility and designability, is widely used in the antibacterial field. Various strategies have been designed to fabricate GO-based composites with antibacterial properties. This review summarized these strategies, divided them into three types and interpreted their antibacterial mechanisms: (i) "GO*/non-GO" type in which GO acts as the single antibacterial core, (ii) "GO*/non-GO*" type in which GO and non-GO components function synergistically as dual antibacterial cores, (iii) "GO/non-GO*" type in which non-GO acts as the single antibacterial core, while GO component plays a supportive, not a dominant role in antibiosis. Besides, the fields suiting their applications and factors influencing their antibacterial properties were analyzed. Finally, the limitations and prospects in the current researches were discussed. In summary, GO-based composites have revolutionized antibacterial strategies. This review may serve as a reference to inspire further research on GO-based antibacterial composites.

Graphene-Based Biomaterials for Bone Regenerative Engineering: A Comprehensive Review of the Field and Considerations Regarding Biocompatibility and Biodegradation

Graphene and its derivatives have continued to garner worldwide interest due to their unique characteristics. Having expanded into biomedical applications, there have been efforts to employ their exceptional properties for the regeneration of different tissues, particularly bone. This article presents a comprehensive review on the usage of graphene-based materials for bone regenerative engineering. The graphene family of materials (GFMs) are used either alone or in combination with other biomaterials in the form of fillers in composites, coatings for both scaffolds and implants, or vehicles for the delivery of various signaling and therapeutic agents. The applications of the GFMs in each of these diverse areas are discussed and emphasis is placed on the characteristics of the GFMs that have implications in this regard. In tandem and of importance, this article evaluates the safety and biocompatibility of the GFMs and carefully elucidates how various factors influence the biocompatibility and biodegradability of this new class of nanomaterials. In conclusion, the challenges and opportunities regarding the use of the GFMs in regenerative engineering applications are discussed, and future perspectives for the developments in this field are proposed.

Synthesis, Characterization, and Toxicity Assessment of Pluronic F127-Functionalized Graphene Oxide on the Embryonic Development of Zebrafish (Danio rerio)

BACKGROUND

In the current literature, there are ongoing debates on the toxicity of graphene oxide (GO) that demonstrate contradictory findings regarding its toxicity profile. As a potential drug carrier, these findings are very concerning due to the safety concerns in humans, as well as the dramatic rise of GO being excreted into the environment. Therefore, there is an imperative need to mitigate the potential toxicity of GO to allow for a safer application in the future.

PURPOSE

The present study aims to address this issue by functionalizing GO with Pluronic F127 (PF) as a means to mitigate toxicity and resolve the biocompatibility of GO. Although results from previous studies generally indicated that Pluronic functionalized GO exhibits relatively low toxicity to living organisms, reports that emphasize on its toxicity, particularly during embryonic developmental stage, are still scarce.

METHODS

In the present study, two different sizes of native GO samples, GO and NanoGO, as well as PF-functionalized GO, GO-PF and NanoGO-PF, were prepared and characterized using DLS, UV-Vis, Raman spectroscopy, FTIR, and FESEM analyses. Toxicological assessment of all GO samples (0-100 µg/mL) on zebrafish embryonic developmental stages (survival, hatching and heart rates, and morphological changes) was recorded daily for up to 96 hours post-fertilization (hpf).

RESULTS

The toxicity effects of each GO sample were observed to be higher at increasing concentrations and upon prolonged exposure. NanoGO demonstrated lower toxicity effects compared to GO. GO-PF and NanoGO-PF were also found to have lower toxicity effects compared to native GO samples. GO-PF showed the lowest toxicity response on zebrafish embryo.

CONCLUSION

These findings highlight that toxicity is dependent on the concentration, size, and exposure period of GO. Functionalization of GO with PF through surface coating could potentially mitigate the toxicity effects of GO in embryonic developmental stages, but further investigation is warranted for broader future applications.

Wound therapy via a photo-responsively antibacterial nano-graphene quantum dots conjugate

Common bacterial pathogens have become resistant to traditional antibiotics, representing an indispensable public health crisis. Photodynamic therapy (PDT), especially when common visible light sources are used as photodynamic power, is a promising bactericidal method. Based on the special photodynamic properties triggered by commonly available light emitting diode (LED) lamps, a kind of graphene quantum dots (GQDs) based composite system (termed GQDs@hMSN(EM)) was prepared through loading both GQDs and erythromycin (EM) into the hollow mesoporous silica nanoparticle (hMSN), aiming to achieve joint antimicrobial effect. Bacterial density experiments confirmed that GQDs@hMSN(EM) had combined antimicrobial effects from photodynamic effect and drug release on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). In animal models, the healing degree of wounds infected by bacteria also confirmed that GQDs@hMSN(EM) group had the best therapeutic effect, with the significantly reduced inflammatory factors in blood. Different from traditional GQDs synthesized by solvothermal method, the as-prepared GQDs@hMSN can produce singlet oxygen (¹O₂) under light exposure to destroy the structure of bacteria, thus achieving highly efficient antimicrobial effect. The GQDs@hMSN(EM) in this work possesses good antimicrobial activity, sufficient drug loading, and controllable drug release ability, which provides a new opportunity for GQDs-based nanoplatform to enhance antimicrobial effect and reduce their drug resistance.

Reusable magnetic Ag/Fe, N-TiO2/Fe3O4@SiO2 composite for simultaneous photocatalytic disinfection of E. coli and degradation of bisphenol A in sewage under visible light

A visible-light-driven and magnetic photocatalyst Ag/Fe,N-TiO₂/Fe₃O₄@SiO₂ (AgFeNTFS) was synthesized through a multi-step method. AgFeNTFS was tested for the photocatalytic disinfection of Escherichia coli (E. coli) and degradation of bisphenol A (BPA) under visible light irradiation, separately and simultaneously. The results showed that a 6.3-log reduction in cell density of E. coli was achieved and BPA (2 mg/L) was completely removed by AgFeNTFS in the separated photocatalytic processes within 120 min. In the simultaneous process, the photocatalytic disinfection of E. coli was not influenced in the presence of BPA, but the efficiency of BPA degradation was dropped by 10%. This was likely due to the competition for the same dominant reactive species of O₂^- and H₂O₂ between E. coli and BPA in the simultaneous process, as evidenced by the scavenger study and the interactions between the pollutants and AgFeNTFS. Moreover, the simultaneous photocatalytic activity of E. coli disinfection and BPA degradation by AgFeNTFS was investigated in the sewage obtained from a local wastewater treatment plant. The photocatalysis treated sewage could meet with the local disinfection discharge standard with a 3-log reduction of E. coli after 90 min, and a complete removal of BPA was achieved simultaneously after 360 min. Moreover, AgFeNTFS showed high magnetic separation efficiency and had a good reusability over three cycles for the simultaneous photocatalytic disinfection and degradation of BPA in both synthetic water and sewage. This study provides insights on the application of a reusable magnetic photocatalyst for simultaneous disinfection and degradation of BPA in sewage.

Antimicrobial graphene materials: the interplay of complex materials characteristics and competing mechanisms

Graphene materials (GMs) exhibit attractive antimicrobial activities promising for biomedical and environmental applications. However, we still lack full control over their behaviour and performance mainly due to the complications arising from the coexistence and interplay of multiple factors. Therefore, in this minireview, we attempt to illustrate the structure-property-activity relationships of GMs' antimicrobial activity. We first examine the chemical/physical complexity of GMs focusing on five aspects of their materials characteristics: (i) chemical composition, (ii) impurities and imperfections, (iii) lateral dimension, (iv) self-association (e.g., restacking), and (v) composite/hybrid formation. Next, we briefly summarise the current understanding of their antimicrobial mechanisms. Then, we assign the outlined materials characteristics of GMs to the proposed antimicrobial mechanisms. Lastly, we share our vision regarding the future of research and development in this fast-emerging field.

Graphene Materials in Antimicrobial Nanomedicine: Current Status and Future Perspectives

Graphene materials (GMs), such as graphene, graphene oxide (GO), reduced GO (rGO), and graphene quantum dots (GQDs), are rapidly emerging as a new class of broad-spectrum antimicrobial agents. This report describes their state-of-the-art and potential future covering both fundamental aspects and biomedical applications. First, the current understanding of the antimicrobial mechanisms of GMs is illustrated, and the complex picture of underlying structure-property-activity relationships is sketched. Next, the different modes of utilization of antimicrobial GMs are explained, which include their use as colloidal dispersions, surface coatings, and photothermal/photodynamic therapy agents. Due to their practical relevance, the examples where GMs function as synergistic agents or release platforms for metal ions and/or antibiotic drugs are also discussed. Later, the applicability of GMs in the design of wound dressings, infection-protective coatings, and antibiotic-like formulations ("nanoantibiotics") is assessed. Notably, to support our assessments, the existing clinical applications of conventional carbon materials are also evaluated. Finally, the key hurdles of the field are highlighted, and several possible directions for future investigations are proposed. We hope that the roadmap provided here will encourage researchers to tackle remaining challenges toward clinical translation of promising research findings and help realize the potential of GMs in antimicrobial nanomedicine.

Bactericidal Effects of Silver Nanoparticles on Lactobacilli and the Underlying Mechanism

While the antibacterial properties of silver nanoparticles (AgNPs) have been demonstrated across a spectrum of bacterial pathogens, the effects of AgNPs on the beneficial bacteria are less clear. To address this issue, we compared the antibacterial activity of AgNPs against two beneficial lactobacilli ( Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus casei) and two common opportunistic pathogens ( Escherichia coli and Staphylococcus aureus). Our results demonstrate that those lactobacilli are highly susceptible to AgNPs, while the opportunistic pathogens are not. Acidic environment caused by the lactobacilli is associated with the bactericidal effects of AgNPs. Our mechanistic study suggests that the acidic growth environment of lactobacilli promotes AgNP dissolution and hydroxyl radical (•OH) overproduction. Furthermore, increases in silver ions (Ag⁺) and •OH deplete the glutathione pool inside the cell, which is associated with the increase in cellular reactive oxygen species (ROS). High levels of ROS may further induce DNA damage and lead to cell death. When E. coli and S. aureus are placed in a similar acidic environment, they also become more susceptible to AgNPs. This study provides a mechanistic description of a pH-Ag⁺-•OH bactericidal pathway and will contribute to the responsible development of products containing AgNPs.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Synthesis, Characterization, and Bactericidal Evaluation of Chitosan/Guanidine Functionalized Graphene Oxide Composites

In response to the wide spread of microbial contamination induced by bacterial pathogens, the development of novel materials with excellent antibacterial activity is of great interest. In this study, novel antibacterial chitosan (CS) and polyhexamethylene guanidine hydrochloride (PHGC) dual-polymer-functionalized graphene oxide (GO) (GO-CS-PHGC) composites were designed and easily fabricated. The as-prepared materials were characterized by Fourier transform infrared (FTIR), X-ray photoelectron spectrometer (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy. Their antibacterial capability towards bacterial strains was also studied by incubating both Gram-negative bacteria and Gram-positive bacteria in their presence. More significantly, the synergistic antibacterial action of the three components was assayed, and the findings implied that the as-prepared GO-CS-PHGC shows enhanced antibacterial activity when compared to its single components (GO, CS, PHGC or CS-PHGC) and the mixture of individual components. Not only Gram-negative bacteria but also Gram-positive bacteria are greatly inhibited by GO-CS-PHGC composites. The minimum inhibitory concentration (MIC) value of GO-CS-PHGC against E. coli was 32 μg/mL. With the powerful antibacterial activity as well as its low cost and facile preparation, GO-CS-PHGC has potential applications as a novel antibacterial agent in a wide range of biomedical uses.

Bacterial physiology is a key modulator of the antibacterial activity of graphene oxide

Carbon-based nanomaterials have a great potential as novel antibacterial agents; however, their interactions with bacteria are not fully understood. This study demonstrates that the antibacterial activity of graphene oxide (GO) depends on the physiological state of cells for both Gram-negative and -positive bacteria. GO susceptibility of bacteria is the highest in the exponential growth phase, which are in growing physiology, and stationary-phase (non-growing) cells are quite resistant against GO. Importantly, the order of GO susceptibility of E. coli with respect to the growth phases (exponential ≫ decline > stationary) correlates well with the changes in the envelope ultrastructures of the cells. Our findings are not only fundamentally important but also particularly critical for practical antimicrobial applications of carbon-based nanomaterials.

Antibacterial activity of graphene-based materials

Complications related to infectious diseases have significantly decreased due to the availability and use of a wide variety of antibiotics and antimicrobial agents. However, excessive use of antibiotics and antimicrobial agents over years has increased the number of drug resistant pathogens. Microbial multidrug resistance poses serious risks and consequently research attention has refocused on finding alternatives for antimicrobial treatment. Among the various approaches, the use of engineered nanostructures is currently the most promising strategy to overcome microbial drug resistance by improving the remedial efficiency due to their high surface-to-volume ratio and their intrinsic or chemically incorporated antibacterial activity. Graphene, a two-dimensional ultra-thin nanomaterial, possesses excellent biocompatibility, putting it in the forefront for different applications in biosensing, drug delivery, biomedical device development, diagnostics and therapeutics. Graphene-based nanostructures also hold great promise for combating microbial infections. Yet, several questions remain unanswered such as the mechanism of action with the microbial entities, the importance of size and chemical composition in the inhibition of bacterial proliferation and adhesion, cytotoxicity, and other issues when considering future clinical implementation. This review summarizes the current efforts in the formulation of graphene-based nanocomposites with antimicrobial and antibiofilm activities as new tools to tackle the current challenges in fighting against bacterial targets. Furthermore, the review describes the features of graphene-bacterial interactions, with the hope to shed light on the range of possible mode of actions, serving the goal to develop a better understanding of the antibacterial capabilities of graphene-based nanostructures.