In this study, silver nanoparticles (Ag NPs) coated with catechol-conjugated chitosan (CSS) were prepared using green methods. Interestingly, we uncovered that CSS-coated Ag NPs (CSS-Ag NPs) exhibited a higher toxicity against gram-negative Escherichia coli (E. coli) bacteria than against gram-positive Staphylococcus aureus (S. aureus) bacteria. The differences revealed that the CSS-Ag NPs killed gram bacteria with distinct, species-specific mechanisms. The aim of this study is to further investigate these underlying mechanisms through a series of analyses. The ultrastructure and morphology of the bacteria before and after treatment with CSS-Ag NPs were observed. The results demonstrated the CSS-Ag NPs killed gram-positive bacteria through a disorganization of the cell wall and leakage of cytoplasmic content. In contrast, the primary mechanism of action on gram-negative bacteria was a change in membrane permeability, induced by adsorption of CSS-Ag NPs. The species-specific mechanisms are caused by structural differences in the cell walls of gram bacteria. Gram-positive bacteria are protected from CSS-Ag NPs by a thicker cell wall, while gram-negatives are more easily killed due to an interaction between a special outer membrane and the nanoparticles. Our study offers an in-depth understanding of the antibacterial behaviors of CSS-Ag NPs and provides insights into ultimately optimizing the design of Ag NPs for treatment of bacterial infections.

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Conductive hydrogels have attracted a myriad of interest due to their potential applications for human motion monitoring, personal healthcare diagnosis and so forth. However, fabrication of hydrogel-based strain sensors integrating with ultrastretchability, adhesiveness, strain sensitivity, biocompatibility, and self-cleaning function is still a challenge. Herein, a new type of semiinterpenetrating multifunctional hydrogels, which integrated all above practical features magically were prepared via a facile one-pot in-situ radical copolymerization method. Thereinto, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) and acrylamide (AAm) copolymers cross-linked by N,N 0-Methylenebisacrylamide (MBAA) served as the soft and functional matrix, whereas alginate was employed as the enhanced component. The transparent zwitterionic hydrogels had a max elongation and ionic conductivity of 1353% and 0.15 S/m, respectively. They could adhere onto various surfaces, including steel, glass, skin, and rubber. The repeatable adhesiveness, linear strain sensitivity within 0%-250% tensile strain and 0%-30% compressive strain provided remarkable working range and using stability. What's more notable was that the biocompatibility and self-cleaning function tested by MTT, live/ dead assay, allergy patch tests, and plate colony-counting method imparted great possibility of practical application for strain sensors to hydrogels from a biological point of view.

A new kind of chitosan-based sponge with sustained silver release was prepared by loading CCS-AgNPs into chitosan matrix through interaction between catechol and chitosan, which is considered as a potential candidate for wound healing dressings.

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