Cellulose nanocrystals (CNCs) have emerged as a sustainable nanomaterial for several environmental applications, including the development of novel antimicrobial agents. Although previous studies have reported antibacterial activity for CNCs, their toxicity mechanism to bacterial cells is still unknown. Here, we investigate the toxicity of CNCs dispersed in water and coated surfaces against Escherichia coli cells. CNC-coated surfaces were able to inactivate approximately 90% of the attached E. coli cells, confirming potential of CNCs to be applied as a sustainable and cost-effective antibiofouling nanomaterial. The toxicity of CNCs in a suspension was concentration-dependent, and an inhibitory concentration (IC50%) of 200 μg/mL was found. Glutathione and 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFA) assays were conducted to evaluate the role of oxidative stress in the CNC toxicity mechanism. Our findings showed that oxidative stress has no significant effect on the antimicrobial activity of CNC. In contrast, scanning electron microscopy (SEM) images and a leakage assay performed with dye-encapsulated phospholipid vesicles indicated that CNCs inactivate bacteria by physically damaging their cell membrane. CNC interaction with dye-encapsulated vesicles resulted in a dye leakage corresponding to 43% of the maximum value, thus confirming that contact-mediated membrane stress is the mechanism governing the toxicity of CNCs to bacteria cells.

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Cellulose nanocrystals (CNCs) and nanofibrils (CNFs) are sustainable candidates for designing nanocomposites and all-nanocellulose systems for a myriad of advanced applications, such as protective coatings, packaging materials, and hydrogels. The role of nanocellulose in such different applications is mainly determined by its morphological and physicochemical properties. Although these properties have been studied at length by a consistent and growing number of publications, there is still a lack of a comprehensive study of the relationships between structure, properties, and functions of different nanocelluloses. Here, we thoroughly investigated the combined effect of distinct production methods and anatomical origins of non-wood cellulose on the structure−property relationships of CNCs and CNFs. These nanoparticles were obtained by the most established production approaches, that is, sulfuric acid hydrolysis or TEMPO-mediated oxidation/fibrillation of elephant grass leaves or stems, that is, two different parts of a unique biosource. We were able to prepare CNCs and CNFs with modulated morphological features and degrees of polymerization, which implied major effects on the mechanical and rheological behaviors of nanocellulose films and dispersions, respectively. Additionally, tailoring lignin and ionizable group contents as well as the color, transparency, and stability of nanocellulose dispersions could provide important implications for the shelf life of nanocellulose formulations, as well as for their application as nanocomposite additives with UV-protection and antioxidant abilities. Therefore, the assembly of results presented here can work as a tool to guide decision-making for both (1) the selection of methods and/or plant anatomical parts to produce nanocelluloses with tailored properties and (2) the prospects of combining different cellulose nanostructures to design advanced materials.

In this study, we were able to impart antimicrobial properties onto the surface of a commercial thin-film composite (TFC) membrane using sustainably derived cellulose nanocrystals (CNC) extracted from elephant grass (Pennisetum purpureum) leaves. Carboxylic acid-containing CNC were chemically bound to the amine-terminated polyamide active layer of TFC membranes using a cross-linking reaction. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy were conducted to confirm the presence of CNC on the membrane surface. TFC membranes functionalized with needle-like and antimicrobial CNC nanoparticles showed robust toxicity to bacteria, inactivating ∼89% of attached Escherichia coli cells under contact. These findings establish that functionalization with CNC is a promising approach for mitigating biofouling on TFC membranes and substantiates the application of sustainable materials for the design of the next-generation membranes for water purification.

Green nanocomposites combining cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs), and lignin nanoparticles (LNPs) were designed and applied for the first time as ternary protective coatings on cellulosic materials, i.e., substrates mainly composed of cellulose. All the nanostructures were obtained from elephant grass biomass. CNFs and CNCs are less than 10 nm thick and present a filament-like morphology, while LNPs are spheres with an average diameter of less than 100 nm. The use of water-based nanoparticle dispersions is a facile and greener alternative to synthetic varnishes usually based on toxic organic solvents. Moreover, the coatings from renewable sources were chemically stable; showed high compatibility with wood, paper, and fabric; and preserved the roughness and surface morphology of the substrates after application. Moist-heat accelerated aging and UV-shielding assays revealed that the nanocellulose/nanolignin coatings were able to protect the coated cellulosic substrates against degradation. The wettability of nanocomposite-coated substrates could be tailored and reduced to produce hydrophobic surfaces by applying additional layers of water-based carnauba wax nanoparticles, which are also sustainable. Additionally, two-dimensional infrared spectroscopy mapping confirmed the reversibility of the coating application, as the nanocomposite layers could be easily removed from the cellulosic substrates by water-loaded cleaning hydrogels. Therefore, the functional protective coating introduced here represents an environmentally friendly and nontoxic approach for the conservation of cellulosic artifacts in general, including cultural heritage objects based on paper, wood, and fabric.

The development of high-performance anti-biofouling surfaces is paramount for controlling bacterial attachment and biofilm growth in biomedical devices, food packing, and filtration membranes. Cellulose nanocrystals (CNCs), a carbon-nanotubelike nanomaterial, have emerged as renewable and sustainable antimicrobial agents. However, CNCs inactivate bacteria under contact-mediated mechanisms, limiting its antimicrobial property mostly to the attached bacteria. This study describes the combination of CNCs with silver nanoparticles (CNC/Ag) as a strategy to increase their toxicity and anti-biofouling performance. CNC/Ag-coated surfaces inactivated over 99% of the attached Escherichia coli and Bacillus subtilis cells compared to 66.9 and 32.9% reduction shown by the pristine CNC, respectively. CNC/Ag was also very toxic to planktonic cells, displaying minimal inhibitory of 25 and 100 μg/mL against B. subtilis and E. coli, respectively. CNC/Ag seems to inactivate bacteria through an "attacking−attacking" mechanism where CNCs and silver nanoparticles play different roles. CNCs can kill bacteria by piercing the cell membrane. This physical membrane stress-mediated mechanism is demonstrated as lipid vesicles release their encapsulated dye upon contact with CNCs. Once the cell membrane is punctured, silver ions can enter the cell passively and compromise the integrity of DNA and other organelles. Inside the cells, Ag + may damage the cell membrane by selectively interacting with sulfur and nitrogen groups of enzymes and proteins or by harming DNA via accumulation of reactive oxygen species. Therefore, CNC/Ag toxicity seems to combine the puncturing effect of the needle-like CNC and the silver's ability to impair the cell membrane and DNA functionalities.

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