1. Antimicrobial activity of amino-modified cellulose nanofibrils decorated with silver nanoparticlesVesna Lazić, Jovan Nedeljković, Vanja Kokol, 2024, izvirni znanstveni članek Opis: Silver nanoparticles (Ag NPs) conjugated with amino-functionalized cellulose nanofibrils (NH2−CNFs) were in situ-prepared by reducing silver ions with free amino groups from NH2−CNFs. The spectroscopy and transmission electron microscopy measurements confirmed the presence of non-agglomerated nanometer-in-size Ag NPs within micrometer-large NH2−CNFs of high (20 wt.-%) content. Although the consumption of amino groups during the formation of Ag NPs lowers the ζ-potential and surface charge of prepared inorganic–organic hybrids (from +31.3 to +19.9 mV and from 2.4 to 1.0 mmol/g at pH 7, respectively), their values are sufficiently positive to ensure electrostatic interaction with negatively charged cell walls of pathogens in acidic and slightly (up to pH ~8.5) alkaline solutions. The antimicrobial activity of hybrid microparticles against various pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) is comparable with pristine NH2−CNFs. However, a long-timescale use of hybrids ensures the slow and controlled release of Ag+ ions to surrounding media (less than 1.0 wt.-% for one month). Ključne besede: amino-modified cellulose nanofibrils, silver nanoparticles, hybrid microparticles, zeta-potential, antimicrobial activity Objavljeno v DKUM: 09.12.2024; Ogledov: 0; Prenosov: 2
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2. Dielectric and thermal conductive properties of differently structured ▫$Ti_3C_2T_x$▫ MXene-integrated nanofibrillated cellulose filmsSubramanian Lakshmanan, Vida Jurečič, Vid Bobnar, Vanja Kokol, 2024, izvirni znanstveni članek Opis: The fabrication of nanocellulose-based substrates with high dielectric permittivity and anisotropic thermal conductivity to replace synthetic thermoplastics in flexible organic electronics remains a big challenge. Herein, films were prepared from native (CNF) and carboxylated (TCNF) cellulose nanofibrils, with and without the addition of thermally conductive multi-layered Ti3C2Tx MXene, to examine the impact of polar (− OH, − COOH) surface groups on the film morphological, moisturizing, dielectric, and thermal dissipation properties. The electrostatic repulsion and hydrogen bonding interaction between the hydrophilic surface/terminal groups on CNF/TCNF and MXene was shown to render their self-assembly distribution and organization into morphologically differently structured films, and, consequently, different properties. The pristine CNF film achieved high intrinsic dielectric permittivity (ε' ~ 9), which was further increased to almost ε' ~ 14 by increasing (50 wt%) the MXene content. The well-packed and aligned structure of thinner TCNF films enables the tuning of both the composite’s dielectric permittivity (ε' ~ 6) and through-plane thermal conductivity (K ~ 2.9 W/mK), which increased strongly (ε' ~ 17) at higher MXene loading giving in-plane thermal conductivity of ~ 6.3 W/mK. The air-absorbed moisture ability of the films contributes to heat dissipation by releasing it. The dielectric losses remained below 0.1 in all the composite films, showing their potential for application in electronics. Ključne besede: nanofibrillated cellulose, Ti3C2T, Mxene, film preparation, moisture content, thermal conductivity Objavljeno v DKUM: 03.09.2024; Ogledov: 36; Prenosov: 11
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3. Antibacterial Komagataeibacter hansenii nanocellulose membranes with avocado seed bioactive compoundsKaja Kupnik, Mateja Primožič, Vanja Kokol, Željko Knez, Maja Leitgeb, 2024, izvirni znanstveni članek Ključne besede: bacterial nanocellulose membrane, avocado seed extracts, extraction, swelling, release, antibacterial activity Objavljeno v DKUM: 23.08.2024; Ogledov: 70; Prenosov: 4
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4. Slot‑die coating of cellulose nanocrystals and chitosan for improved barrier properties of paperYlenia Ruberto, Vera Vivod, Janja Juhant Grkman, Gregor Lavrič, Claudia Graiff, Vanja Kokol, 2024, izvirni znanstveni članek Opis: Cellulose nanocrystals (CNCs) and chitosan (Cht) have been studied extensively for oxygen and water vapour barrier coatings in biodegradable, compostable or recyclable paper packaging. However, rare studies have been performed by using scalable, inexpensive, and fast continuous slot-die coating processes, and none yet in combination with fast' and high-throughput near-infrared (NIR) light energy drying. In this frame, we studied the feasibility of a moderately concentrated (11 wt%) anionic CNC and (2 wt%) cationic Cht coating (both containing 20 wt% sorbitol related to the weight of CNC/Cht), by using plain and pigment pre-treated papers. The effect of coating parameters (injection speed, dry thickness settings) were investigated on coating quantity (dry weight, thickness) and homogeneity (coverage), papers' structure (thickness, grammage, density), whiteness, surface wettability, barrier (air, oxygen and water vapour) properties and adhesion (surface strength). The coating homogeneity was dependent primarily on the suspensions' viscosity, and secondarily on the applied coating parameters, whereby CNCs could be applied at 1–2 times higher injection speeds (up to 80 mL/min) and versatile coating weights, but required a relatively longer time to dry. The CNCs thus exhibited outstanding air (4.2–1.5 nm/Pa s) and oxygen (2.7–1.1 cm3 mm/m2 d kPa) barrier performance at 50% RH and 22–33 g/m2 deposition, whereas on top deposited Cht (3–4 g/m2) reduced its wetting time and improved the water vapour barrier (0.23–0.28 g mm/m2 d Pa). The balanced barrier properties were achieved due to the polar characteristic of CNCs, the hydrophobic nature of Cht and the quantity of the applied bilayer coating that can provide sustainable paper-based packaging. Ključne besede: paper, nanocellulose, chitosan, slot‑die coating, near-infrared (NIR) drying, barrier properties Objavljeno v DKUM: 06.05.2024; Ogledov: 227; Prenosov: 12
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5. Enzymatic, Antioxidant, and Antimicrobial Activities of Bioactive Compounds from Avocado (Persea americana L.) SeedsKaja Kupnik, Mateja Primožič, Vanja Kokol, Željko Knez, Maja Leitgeb, 2023, izvirni znanstveni članek Ključne besede: avocado seed, Persea Americana, HPLC, phenolic compounds, enzymatic activity, phytochemistry, antioxidant, antimicrobial activity Objavljeno v DKUM: 10.04.2024; Ogledov: 351; Prenosov: 337
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6. Effect of nozzle diameter and cross-linking on the micro-structure, compressive and biodegradation properties of 3D printed gelatin/collagen/hydroxyapatite hydrogelYasir Beeran Potta Thara, Vanja Kokol, 2023, izvirni znanstveni članek Ključne besede: 3D printing, gelatin, collagen, hydroxyapatite, microstructure, compression Objavljeno v DKUM: 09.04.2024; Ogledov: 201; Prenosov: 16
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7. Cationised fibre-based cellulose multi-layer membranes for sterile and high-flow bacteria retention and inactivationVanja Kokol, Monika Kos, Vera Vivod, Nina Gunde-Cimerman, 2023, izvirni znanstveni članek Opis: Low-cost, readily available, or even disposable membranes in water purification or downstream biopharma processes are becoming attractive alternatives to expensive polymeric columns or filters. In this article, the potential of microfiltration membranes prepared from differently orientated viscose fibre slivers, infused with ultrafine quaternised (qCNF) and amino-hydrophobised (aCNF) cellulose nanofibrils, were investigated for capturing and deactivating the bacteria from water during vacuum filtration. The morphology and capturing mechanism of the single- and multi-layer structured membranes were evaluated using microscopic imaging and colloidal particles. They were assessed for antibacterial efficacy and the retention of selected bacterial species (Escherichia coli, Staphylococcus aureus, Micrococcus luteus), differing in the cell envelope structure, hydrodynamic biovolume (shape and size) and their clustering. The aCNF increased biocidal efficacy significantly when compared to qCNF-integrated membrane, although the latter retained bacteria equally effectively by a thicker multi-layer structured membrane. The retention of bacterial cells occurred through electrostatic and hydrophobic interactions, as well as via interfibrous pore diffusion, depending on their physicochemical properties. For all bacterial strains, the highest retention (up to 100% or log 6 reduction) at >50 L/h∗bar∗m2 flow rate was achieved with a 4-layer gradient-structured membrane containing different aCNF content, thereby matching the performance of industrial polymeric filters used for removing bacteria. Ključne besede: fibrous membrane, cationised cellulose nanofibrils, amino-hydrophobised cellulose nanofibrils, antibacterial activity, multi-layer structure, flux, bacteria retention Objavljeno v DKUM: 28.03.2024; Ogledov: 220; Prenosov: 6
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8. Phosphonate-modified cellulose nanocrystals potentiate the Th1 polarising capacity of monocyte-derived dendritic cells via GABA-B receptorMarina Bekić, Miloš Vasiljević, Dušica Stojanović, Vanja Kokol, Dušan Mihajlović, Dragana Vučević, Petar S. Uskoković, Miodrag Čolić, Sergej Tomić, 2022, izvirni znanstveni članek Opis: Purpose:
Phosphonates, like 3-AminoPropylphosphonic Acid (ApA), possess a great potential for the therapy of bone tumours, and their delivery via cellulose nanocrystals (CNCs) seems a promising approach for their increased efficacy in target tissues. However, the immunological effects of CNC-phosphonates have not been investigated thoroughly. The main aim was to examine how the modification of CNCs with phosphonate affects their immunomodulatory properties in human cells.
Methods:
Wood-based native (n) CNCs were modified via oxidation (ox-CNCs) and subsequent conjugation with ApA (ApA-CNCs). CNCs were characterised by atomic force microscopy (AFM) and nanoindentation. Cytotoxicity and immunomodulatory potential of CNCs were investigated in cultures of human peripheral blood mononuclear cells (PBMCs) and monocyte-derived dendritic cells (MoDCs)/T cells co-cultures by monitoring phenotype, cytokines production, allostimulatory and Th/Treg polarisation capacity.
Results:
AFM showed an increase in CNCs’ thickens, elasticity modulus and hardness during the modification with ApA. When applied at non-toxic doses, nCNCs showed a tolerogenic potential upon internalisation by MoDCs, as judged by their increased capacity to up-regulate tolerogenic markers and induce regulatory T cells (Treg), especially when present during the differentiation of MoDCs. In contrast, ox- and ApA-CNCs induced oxidative stress and autophagy in MoDCs, which correlated with their stimulatory effect on the maturation of MoDCs, but also inhibition of MoDCs differentiation. ApA-CNC-treated MoDCs displayed the highest allostimulatory and Th1/CTL polarising activity in co-cultures with T cells. These effects of ApA-CNCs were mediated via GABA-B receptor-induced lowering of cAMP levels in MoDCs, and they could be blocked by GABA-B receptor inhibitor. Moreover, the Th1 polarising and allostimulatory capacity of MoDCs differentiated with ApA-CNC were largely preserved upon the maturation of MoDCs, whereas nCNC- and ox-CNC-differentiated MoDCs displayed an increased tolerogenic potential.
Conclusion:
The delivery of ApA via CNCs induces potent DC-mediated Th1 polarisation, which could be beneficial in their potential application in tumour therapy. Ključne besede: cellulose nanocrystals, phosphonates, dendritic cells, regulatory T-cell subsets, immunomodulation, GABA-B receptor Objavljeno v DKUM: 17.08.2023; Ogledov: 328; Prenosov: 28
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9. Synergistic effect of screen-printed Al(OH)[sub]3 nanoparticles and phosphorylated cellulose nanofibrils on the thermophysiological comfort and high-intensive heat protection properties of flame-retardant fabricTjaša Kolar, Jelka Geršak, Nataša Knez, Vanja Kokol, 2022, izvirni znanstveni članek Opis: Al(OH)3 nanoparticles (ATH NPs) and phosphorylated cellulose nanofibrils (PCNFs) were used as user-friendly and comfortable coating components on flame-retardant fabric to improve its thermophysiological comfort and high-intensive heat protection properties. The effect of the PCNF imprinting and its attachment after the post-printing of a hydrophobic polyacrylate (AP) on the same (back side) or the other (front) side of the fabric, with and without the addition of ATH NPs, was considered, to maintain the front side (facing the wearer) as hydrophilic while keeping the back side (facing the outside) hydrophobic. The amount of coatings applied and their patterning were studied, varied with the ATH NPs’ concentration (1.7, 3.3 and 6.7 wt%) and screen mesh size used (60 and 135), based on the coating’ mass, fabric’s air permeability, thickness and microstructure. The reduced moisture build-up (55%), increased the water vapour (13%) and heat (12%) transfer from the skin, were assessed by applying PCNF under the AP, being more pronounced in the case of using a 135 mesh-sized screen, given the smaller, more densely distributed, thinner and imprinted pattern coatings. These effects were further improved by the addition of nanoporous ATH NPs, which allowed more homogeneous spreading of the moisture and its faster transport. Such a treatment also shifted the fabric’s degradation temperature towards higher values (up to 15°C), retained up to 30% of high-heat flux (21 kW/m2), prolonged the time to ignition by 11 s and reduced the total heat released by up to 60%, thereby providing better protection when exposed to the heat, due to the presence of the phosphorous (PCNF) promoted generation of an Al2O3 char acting as a barrier layer, while also reducing the production of heat and generation of smoke by 75%. Ključne besede: tekstilna tehnologija, ognjevaren tekstil, Al(OH)3 nanodelci, celulozni nanofibrili, tiskanje tekstilij, optične lastnosti, termofiziološko udobje, toplotna zaščita, flame-retardant textile, Al(OH)3 nanoparticles, phosphorylated cellulose nanofibrils, screen-printing, thermophysiological comfort, heat protection Objavljeno v DKUM: 12.07.2023; Ogledov: 455; Prenosov: 14
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10. Using different surface energy models to assess the interactions between antiviral coating films and phi6 model virusZdenka Peršin Fratnik, Olivija Plohl, Vanja Kokol, Lidija Fras Zemljič, 2023, izvirni znanstveni članek Opis: High molecular weight chitosan (HMWCh), quaternised cellulose nanofibrils (qCNF), and their mixture showed antiviral potential in liquid phase, while this effect decreased when applied to facial masks, as studied in our recent work. To gain more insight into material antiviral activity, spin-coated thin films were prepared from each suspension (HMWCh, qCNF) and their mixture with a 1:1 ratio. To understand their mechanism of action, the interactions between these model films with various polar and nonpolar liquids and bacteriophage phi6 (in liquid phase) as a viral surrogate were studied. Surface free energy (SFE) estimates were used as a tool to evaluate the potential adhesion of different polar liquid phases to these films by contact angle measurements (CA) using the sessile drop method. The Fowkes, Owens–Wendt–Rabel–Kealble (OWRK), Wu, and van Oss–Chaudhury–Good (vOGC) mathematical models were used to estimate surface free energy and its polar and dispersive contributions, as well as the Lewis acid and Lewis base contributions. In addition, the surface tension SFT of liquids was also determined. The adhesion and cohesion forces in wetting processes were also observed. The estimated SFE of spin-coated films varied between mathematical models (26–31 mJ/m2) depending on the polarity of the solvents tested, but the correlation between models clearly indicated a significant dominance of the dispersion components that hinder wettability. The poor wettability was also supported by the fact that the cohesive forces in the liquid phase were stronger than the adhesion to the contact surface. In addition, the dispersive (hydrophobic) component dominated in the phi6 dispersion, and since this was also the case in the spin-coated films, it can be assumed that weak physical van der Waals forces (dispersion forces) and hydrophobic interactions occurred between phi6 and the polysaccharide films, resulting in the virus not being in sufficient contact with the tested material during antiviral testing of the material to be inactivated by the active coatings of the polysaccharides used. Regarding the contact killing mechanism, this is a disadvantage that can be overcome by changing the previous material surface (activation). In this way, HMWCh, qCNF, and their mixture can attach to the material surface with better adhesion, thickness, and different shape and orientation, resulting in a more dominant polar fraction of SFE and thus enabling the interactions within the polar part of phi6 dispersion. Ključne besede: films, surface free energy, SFE mathematical models, phi6, wettability, spreading, interactions Objavljeno v DKUM: 21.04.2023; Ogledov: 555; Prenosov: 38
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