Durable and rechargeable antimicrobial cotton driven by enhanced UV stability and real-time detection of biocidal factors.

In this study, graphene oxide/N-halamine nanocomposite was synthesized through Pickering miniemulsion polymerization, which was then coated on cotton surface. The modified cotton exhibited excellent superhydrophobicity, which could effectively prevent microbial infestation and reduce the probability of hydrolysis of active chlorine, with virtually no active chlorine released in water after 72 h. Deposition of reduced graphene oxide nanosheets endowed cotton with ultraviolet-blocking properties, attributing to enhanced UV adsorption and long UV paths. Moreover, encapsulation of polymeric N-halamine resulted in improved UV stability, thus extending the life of N-halamine-based agents. After 24 h of irradiation, 85 % of original biocidal component (active chlorine content) was retained, and approximately 97 % of initial chlorine could be regenerated. Modified cotton has been proven to be an effective oxidizing material against organic pollutants and a potential antimicrobial substance. Inoculated bacteria were completely killed after 1 and 10 min of contact time, respectively. An innovative and simple scheme for determination of active chlorine content was also devised, and real-time inspection of bactericidal activity could be achieved to assure antimicrobial sustainability. Moreover, this method could be utilized to evaluate hazard classification of microbial contamination in different locations, thus broadening the application scope of N-halamine-based cotton fabrics.

Long-lasting renewable antibacterial graphene/N-halamine-coated cotton fabrics benefitting from enhanced UV stability and quantitative tracking of bactericidal factors.

In this study, anionic GO aqueous dispersion and cationic QAS aqueous solution with specific concentrations were applied for the fabrication of modified cotton fabrics (MCFs) through the layer-by-layer self-assembly method. The chlorinated cotton fabrics with optimized protocol possessed excellent ultraviolet-blocking properties, with a UPF value of 323.08. Moreover, graphene greatly improved the UV stability of N-halamine, which could also be proved in the UV aging test of MCFs. In addition, the modification procedure also endowed cotton fabrics with superhydrophobic properties, thus broadening the application range of cotton fabric. The obtained GQC10 possessed excellent antibacterial activity, with all inoculated S. aureus and E. coli O157:H7 being completely killed within 5 min and 1 min of contact time, respectively. Indicated by the quantitative function relation between the active chlorine content (ACC) and the surface sheet resistance (SSR) of the MCFs, a novel and simple method for the determination of ACC was established. This method could be used to monitor the antimicrobial efficacy to ensure its sustainability. Furthermore, according to the variation frequency of SSR, the risk level of bacterial hazards in different places could be evaluated, thus broadening the application range of N-halamine-based antibacterial cotton fabrics.

Novel porous chitosan/N-halamine structure with efficient antibacterial and hemostatic properties.

In this work, a novel chitosan based structure (CS/EVC) with low density, high porosity, three-dimensional porous structure and great adsorption capability has been prepared by using 1,2-epoxy-4-vinyl cyclohexane (EVC) as a cross-linker. After immersing CS/EVC in N-halamine 1-chloro-2,2,5,5-tetramethyl-4-imidazolinone (MC) solution, antibacterial CS/EVC/MC compounds were obtained. Compared with chitosan and CS/EVC controls, CS/EVC/MC showed excellent antimicrobial activities, which could inactivate both more than 6 logs (×1/1,000,000) of Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8099) within 30 and 10 min, respectively. Moreover, the relatively low blood clotting index of CS/EVC/MC and the activation of platelets adhering to the surfaces indicated that the CS/EVC/MC sample is potential to promote the agglutination abilities of blood cells and simultaneously control wound bleeding. In addition, in vitro cytotoxicity test showed that the CS/EVC/MC had no cytotoxicity. The material might thus have a great potential for biomedical applications.

Three-dimensionally printed polylactic acid/cellulose acetate scaffolds with antimicrobial effect.

This study aimed to develop novel, biodegradable, antiseptic-loaded and low-cost scaffolds using a direct ink writing (DIW) technique for antibacterial applications. Polylactic acid/cellulose acetate (PLA/CA) mixtures with different composition ratios were prepared, and the effect of CA content on the rheological behaviors of the inks was investigated. The printability of the prepared DIW inks was improved with the addition of the appropriate amount of CA, since the formation of hydrogen bonding 3D network between PLA and CA. As a result, a liquid form ink consisting of majority of PLA and minority of CA which was prepared and printed for the first time through DIW technique. Afterwards, the antimicrobial agent, 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC) was incorporated into the inks for preventing bacterial infections, which showed excellent stability and effective antibacterial activity against S. aureus and E. coli O157:H7 in a short time. Owning the ease of fabrication and the biocidal property, our 3D printed scaffolds will have a wide range of potential applications in the field of food packaging, communal facilities, medical equipments, and biomedical materials.

Graphene oxide as a polymeric N-halamine carrier and release platform: Highly-efficient, sustained-release antibacterial property and great storage stability.

N-halamine compounds have been applied as antibacterial agents owing to the oxidative chlorine. In this work, graphene oxide (GO) as carrier was used to load N-halamine compounds for the sustained-release of chlorine in order to maintain long-term biocidal efficacies. 3­(3'­Acrylic acid propylester)­5,5­dimethylhydantoin (APDMH) was synthesized using 5,5­dimethylhydantoin as a heterocyclic precursor and attached on the surface of GO nanosheets via in-situ polymerization. The modified GO composites were characterized by Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The chlorinated GO nanosheets modified with polymerized APDMH (PAPDMH) were very stable and possessed long-term antibacterial properties. The GO-PAPDMH-Cl composites exhibited good antimicrobial efficacies against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli O157:H7) with log reductions of 7.20 and 7.06 within 30 min of contact time, respectively.

The dominant role of surface functionalization in carbon dots' photo-activated antibacterial activity.

Background: Carbon dots (CDots) have recently been demonstrated their effective visible light-activated antimicrobial activities toward bacteria. This study was to evaluate and understand the roles of the surface functionalities in governing the antimicrobial activity of CDots. Methods: Using the laboratory model bacteria Bacillus subtilis, the photo-activated antimicrobial activities of three groups of CDots with specifically selected different surface functionalization moieties were evaluated and compared. The first group consisting of CDots with surface functionalization by 2,2-(ethylenedioxy)bis(ethylamine) (EDA) vs. 3-ethoxypropylamine (EPA), was evaluated to determine the effect of different terminal groups/charges on their photo-activated antibacterial activities. The second group consisting of CDots functionalized with oligomeric polyethylenimine (PEI) and those prepared by the carbonization of PEI - citric acid mixture, was to evaluate the effects of dot surface charges vs. fluorescent quantum yields on their antimicrobial activities. The third group consisting of CDots functionalized with PEI of 1,200 vs. 600 in average molecular weight was evaluated for the effect of molecular weight of surface passivation molecular on their antimicrobial activities. Results: The results indicated the EDA-CDots in the first group was more effective and was attributed to the positive charges from the protonation of the amino groups (-NH2) being more favorable to interactions with bacterial cells. The evaluation of the second group CDots suggested the same surface charge effect dominating the antibacterial performance over the fluorescent quantum yields. The evaluation of the third group CDots functionalized with PEI of 1,200 vs. 600 in average molecular weight, indicated the latter was significantly more effective. Conclusions: The results from this study highlighted the dominant role of surface functionalities in governing CDots' light activated antimicrobial activity and should have significant implications to the further design and development of CDots as a new class of visible light-activated antibacterial agents.

Synergistic photoactivated antimicrobial effects of carbon dots combined with dye photosensitizers.

BACKGROUND: Carbon quantum dots (CDots) have recently been reported as a new class of visible light activated antimicrobial nanomaterials. This study reports the synergistic photoactivated antimicrobial interactions of CDots with photosensitizers on bacterial cells. METHODS: The antimicrobial effects of the CDots with surface passivation molecules 2,2'-(ethylenedioxy)bis(ethylamine) in combination with photosensitizer methylene blue (MB) or toluidine blue (TB) at various concentrations were evaluated against Escherichia coli cells with and without 1-hour visible light illumination. The broth microdilution checkerboard method and isobologram analysis were used for determining if synergistic effect existed between CDots and MB or TB. RESULTS: The results showed that CDots alone at a concentration of 5 µg/mL did not display antimicrobial effects, 1 µg/mL MB alone only decreased 1.86 log of viable cell numbers, but the combination treatment with 5 µg/mL CDots combined with 1 µg/mL MB completely inhibited bacteria growth, resulted in 6.2 log viable cell number reduction, suggesting synergistic interaction between the two. The antimicrobial effects of CDots/TB combination exhibited similarly synergistic effects on E. coli cells. These synergistic effects between CDots and MB or TB were further confirmed using the checkerboard microdilution methods, where the fractional inhibitory concentration index value (0.5) and the isobologram analyses. The synergistic interactions were also correlated to the increased generation of intracellular reactive oxygen species in E. coli cells upon the combination treatments of CDots/MB or CDots/TB. CONCLUSION: The study demonstrated the synergistic photoactivated antimicrobial effects of CDots in combination with other photosensitizers. Such synergistic effect may open new strategies for developing highly effective antimicrobial methods.