Structure Formation by 3D-Printing of Cellulose from Cellulose-NMMO-Water Solutions: Analysis of Extrusion, Regeneration, and Drying Stages.

Processing cellulose from 4-methyl morpholine n-oxide (NMMO)-water solutions is a completely circular route that produces biodegradable cellulose fibers or films while recovering reusable NMMO [Guo, Y.; Cai, J.; Sun, T.; Xing, L.; Cheng, C.; Chi, K.; Xu, J.; Li, T. The purification process and side reactions in the N-methylmorpholine-N-oxide (NMMO) recovery system. Cellulose 2021, 28(12), 7609-7617]. Despite proven success in two-dimensional applications, challenges in transitioning to three-dimensional objects arise from the critical changes that cellulose undergoes during deposition, regeneration, and postregeneration stages. While emphasizing the critical diffusion-driven precipitation during regeneration, this investigation explores the influence of extrusion temperature, printing alignment, regeneration, and drying processes on interfilament fusion, bonding, shape integrity, and mechanical properties. Three distinct drying processes: ambient, vacuum, and freeze-drying were investigated. Tensile and flexural bending tests provided insight into the delamination of dried specimens. Ambient and vacuum drying enhanced the properties of specimens, while freeze-drying resulted in a more stable shape. The findings contribute to advancing the understanding of 3D-printing cellulose from NMMO solutions, addressing crucial aspects of the extrusion, regeneration, and drying stages for enhanced applications in sustainable manufacturing.

The Effects of High Pressure and High Temperature in Semidilute Aqueous Cellulose Nanocrystal Suspensions.

A semidilute cellulose nanocrystal suspension was tested for pressure, volume, temperature dependencies of its viscosity and density. The compression of a 2.0 wt % cellulose nanocrystal suspension under 5.0 MPa at room temperature resulted in morphological changes from istotropic to nematic form. However, at high temperature, high-pressure treatment caused desulfation and gelation. Those results have significant applications, not only as additives in drilling and fracturing fluids but also for the preparation of hydrogels.

Cationic poly(2-aminoethylmethacrylate) and poly(N-(2-aminoethylmethacrylamide) modified cellulose nanocrystals: synthesis, characterization, and cytotoxicity.

Cellulose nanocrystals (CNCs) continue to gain increasing attention in the materials community as sustainable nanoparticles with unique chemical and mechanical properties. Their nanoscale dimensions, biocompatibility, biodegradability, large surface area, and low toxicity make them promising materials for biomedical applications. Here, we disclose a facile synthesis of poly(2-aminoethylmethacrylate) (poly(AEM)) and poly(N-(2-aminoethylmethacrylamide) (poly(AEMA)) CNC brushes via the surface-initiated single-electron-transfer living radical polymerization technique. The resulting modified CNCs were characterized for their chemical and morphological features using a combination of analytical, spectroscopic, and microscopic techniques. Zeta potential measurements indicated a positive surface charge, and further proof of the cationic nature was confirmed by gold deposition as evidenced by electron microscopy. The cytotoxicity of these cationic modified CNCs was evaluated utilizing a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in two different cell lines, J774A1 (mouse monocyte cells) and MCF-7 (human breast adenocarcinoma cells). The results indicated that none of the cationic modified CNCs decreased cell viability at low concentrations, which could be suitable for biomedical applications.

The impact of cellulose nanocrystals on the aggregation and initial adhesion of Pseudomonas fluorescens bacteria.

Deposition on silica surfaces of two Pseudomonas fluorescens strains (CHA0 and CHA19-WS) having different extracellular polymeric substance (EPS) producing capacities was studied in the absence and presence of cellulose nanocrystals (CNCs). Batch (batch soaking) and continuous flow (quartz crystal microbalance with dissipation) methods were used to evaluate the impact of CNCs on bacterial initial adhesion. This study demonstrated that bacterial initial adhesion to solid surfaces can be significantly hindered by CNCs using both methods. In the presence of CNCs, it was observed that bacteria with more EPS aggregated more significantly compared to bacteria with less EPS, and that bacterial deposition under this condition decreased to a greater extent. The classic DLVO theory failed to predict bacterial adhesion behavior in this study. A detailed discussion is provided regarding potential antibacterial adhesion mechanisms of CNCs.

Double crosslinked hyaluronic acid and collagen as a potential bioink for cartilage tissue engineering.

The avascular nature of hyaline cartilage results in limited spontaneous self-repair and regenerative capabilities when damaged. Recent advances in three-dimensional bioprinting have enabled the precise dispensing of cell-laden biomaterials, commonly referred to as 'bioinks', which are emerging as promising solutions for tissue regeneration. An effective bioink for cartilage tissue engineering needs to create a micro-environment that promotes cell differentiation and supports neocartilage tissue formation. In this study, we introduced an innovative bioink composed of photocurable acrylated type I collagen (COLMA), thiol-modified hyaluronic acid (THA), and poly(ethylene glycol) diacrylate (PEGDA) for 3D bioprinting cartilage grafts using human nasal chondrocytes. Both collagen and hyaluronic acid, being key components of the extracellular matrix (ECM) in the human body, provide essential biological cues for tissue regeneration. We evaluated three formulations - COLMA, COLMA+THA, and COLMA+THA+PEGDA - for their printability, cell viability, structural integrity, and capabilities in forming cartilage-like ECM. The addition of THA and PEGDA significantly enhanced these properties, showcasing the potential of this bioink in advancing applications in cartilage repair and reconstructive surgery.

Dispersions of nanocrystalline cellulose in aqueous polymer solutions: structure formation of colloidal rods.

The steady-state shear and linear viscoelastic deformations of semidilute suspensions of rod-shaped nanocrystalline cellulose (NCC) particles in 1.0% hydroxyethyl cellulose and carboxymethyl cellulose solutions were investigated. Addition of NCC at the onset of semidilute suspension concentration significantly altered the rheological and linear viscoelastic properties of semidilute polymer solutions. The low-shear viscosity values of polymers solutions were increased 20-490 times (depending on polymer molecular weight and functional groups) by the presence of NCC. NCC suspensions in polymer solutions exhibited yield stresses up to 7.12 Pa. Viscoelasticity measurements also showed that NCC suspended polymer solutions had higher linear elastic moduli than the loss moduli. All of those results revealed the gel formation of NCC particles and presence of internal structures. The formation of a weak gel structure was due to the nonadsorbing macromolecules which caused the depletion-induced interaction among NCC particles. A simple interaction energy model was used to show successfully the flocculation of NCC particles in the presence of nonadsorbing polymers. The model is based on the incorporation of the depletion interaction term between two parallel plates into the DLVO theory for cubic prismatic rod shaped NCC particles.

Recent advances and future perspective on nanocellulose-based materials in diverse water treatment applications.

Over the past few years, nanocellulose and its derivatives have drawn attention as promising bio-based materials for water treatment applications due to their high surface area, high strength, and renewable, biocompatible nature. The abundance of hydroxyl functional groups on the surfaces of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) enables a broad range of surface modifications which results in propitious nanocomposites with tunable characteristics. In this context, this review describes the continuously developing applications of nanocellulose-based materials in the areas of adsorption, catalysis, filtration, and flocculation, with a special emphasis on the removal of contaminants such as heavy metals, dyes, and pharmaceutical compounds from diverse water systems. Recent progresses in the diverse forms of application of nanocellulose adsorbents (suspension, hydrogel, aerogel, and membrane) are also highlighted. Finally, challenges and future perspectives on emerging nanocellulose-based materials and their possible industrial applications are presented and discussed.

Release of Cellulose Nanocrystal Particles from Natural Rubber Latex Composites into Immersed Aqueous Media.

In the current study, we focused on the preparation of nanocomposite films of natural rubber latex-cellulose nanocrystals (NR/CNCs) and investigated the release of CNCs from those materials into aqueous solutions. The obtained nanocomposite films were well characterized for further understanding of the release mechanism; as the intermolecular interactions between the two components were studied by Fourier-transform infrared spectroscopy, the morphology was studied with scanning electron microscopy, and nanostructures were analyzed by tensile and dynamic mechanical testing. The release behavior of CNCs from the NR/CNCs nanocomposite films was studied by a fluorescent labeling technique, and the release process in various media was modeled by first-order kinetics. Higher contents of CNCs in the nanocomposite films and a relatively acidic or alkaline medium facilitated the release process, while higher ionic strength of the media could hamper the release of CNCs from the nanocomposite films. In this study, our objective was to transport CNC particles from NR/CNC composites into immersed media to be used beneficially in biomedical applications. Nevertheless, in other surroundings, the release of CNCs or any other nanoparticles from composite materials may not be desirable. Hence, this study also provides a protocol to investigate the release of nanoparticles from a host matrix into the surrounding media and also promotes a rethinking of the nanoparticle release issue from composites to the environment.

Plant celluloses, hemicelluloses, lignins, and volatile oils for the synthesis of nanoparticles and nanostructured materials.

A huge variety of plants are harvested worldwide and their different constituents can be converted into a broad range of bionanomaterials. In parallel, much research effort in materials science and engineering is focused on the formation of nanoparticles and nanostructured materials originating from agricultural residues. Cellulose (40-50%), hemicellulose (20-40%), and lignin (20-30%) represent major plant ingredients and many techniques have been described that separate the main plant components for the synthesis of nanocelluloses, nano-hemicelluloses, and nanolignins with divergent and controllable properties. The minor components, such as essential oils, could also be used to produce non-toxic metal and metal oxide nanoparticles with high bioavailability, biocompatibility, and/or bioactivity. This review describes the chemical structure, the physical and chemical properties of plant cell constituents, different techniques for the synthesis of nanocelluloses, nanohemicelluloses, and nanolignins from various lignocellulose sources and agricultural residues, and the extraction of volatile oils from plants as well as their use in metal and metal oxide nanoparticle production and emulsion preparation. Furthermore, details about the formation of activated carbon nanomaterials by thermal treatment of lignocellulose materials, a few examples of mineral extraction from agriculture waste for nanoparticle fabrication, and the emerging applications of plant-based nanomaterials in different fields, such as biotechnology and medicine, environment protection, environmental remediation, or energy production and storage, are also included. This review also briefly discusses the recent developments and challenges of obtaining nanomaterials from plant residues, and the issues surrounding toxicity and regulation.

Mechanisms of the immune response cause by cationic and anionic surface functionalized cellulose nanocrystals using cell-based assays.

The interest in functionalized cellulose nanocrystals (CNCs) for multiple biomedical application has been increasing in recent years. CNCs are suitable to functionalization with an array of polymers, generating chemically related nanomaterials with different morphologies, surface charges that can affect bioreactivity, including immune response. In this study, we sought to understand the mechanistic differences regarding immunological responses evoked by functionalized CNCs and whether surface charges play a role in this effect. We investigated the effect of a cationic, CNCs-poly(APMA), and an anionic, CNCs-poly(NIPAAm) derivatives on the secretion of inflammatory cytokines, mitochondria-derived ROS and mitochondrial function and antioxidant response as well as on endoplasmic reticulum (ER) stress, in human and murine inflammatory cells. The cationic CNCs-poly(APMA) evoked a more robust immunological response in murine cell line, while the anionic CNCs-poly(NIPAAm) showed a significant NLRP3 inflammasome-dependent and independent immunological response in human monocytes. Moreover, CNCs-poly(NIPAAm) induced greater formation of acidic vesicular organelles, mitochondrial ROS in non-stimulated cells while CNCs-poly(APMA) mainly affected mitochondrial function by decreasing the intracellular ATP. The differences on the biological responses may be related to the surface charges of CNCs, and their likely interactions with intra and extracellular biomolecules.

The impact of cellulose nanocrystals on the aggregation and initial adhesion to a solid surface of Escherichia coli K12: Role of solution chemistry.

Aggregation of bacteria and their initial adhesion to silica surfaces are affected greatly by solution chemistry, particularly pH and ionic strength (IS). The effects of pH and IS on the aggregation and deposition of Escherichia coli K12 on silica surfaces were investigated in NaCl solutions at variable pH and IS, and in the absence and presence of cellulose nanocrystals (CNC). In the presence of CNC, bacterial aggregation was generally enhanced as the pH was increased from 3.5 to neutral at a given IS (10mM). At a given pH (7.2), bacterial aggregation was highest at 10mM as the IS was increased from 1mM to 50mM. The contribution of DLVO interaction and depletion interaction to bacterial aggregation in the bacteria and CNC system was compared. The results indicate that at pH ranging from 5.2 to 7.2 and IS ranging from 10mM to 50mM conditions, depletion attraction is the dominant mechanism for CNC induced bacterial aggregation. The lower bacterial deposition rates observed at 10mM IS and pH 7.2 compared with other conditions were mainly attributed to the aggregation of bacteria which could result in decreased convective-diffusive transport to the silica surface.

Electrolyte effect on gelation behavior of oppositely charged nanocrystalline cellulose and polyelectrolyte.

The electrolyte (NaCl) influences on the sol-gel transition of the complex solution composed of oppositely charged nanocrystalline cellulose (NCC) and polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) were investigated by the rheological means in the present paper. Winter and Chambon theory was applicable to describe the sol-gel transition, and the critical gel points have been successfully determined. When increasing the NaCl concentration, more NCC were needed to form a critical gel due to the screening of the electrostatic interaction, and the larger loss tangent and relaxation exponent (n) values at the gel point demonstrated a less elastic nature of the complex solution with more NaCl. The results indicated the gel network was composed of entanglements and association of QHEC (as polymer network), as well as the electrostatic adsorption interaction between QHEC chains and NCC rods (as cross-linking). With the addition of NaCl, the screening effect led to the enhancement of the entanglements and weakening of the electrostatic adsorption, however, the gel strength decreased with increasing the NaCl amount, suggesting the electrostatic adsorption interaction played a more dominant role than the entanglements when the gel was formed. Moreover, the exponents of the scaling law η0∝ɛ(-γ) and Ge∝ɛ(z) of the QHEC/NCC/NaCl solution revealed that the scaling law n=z/(z+γ) between n, γ, and z was only feasible at the highest NaCl concentration, as a result of that the intermolecular electrostatic interaction was completely screened, indicating the scaling law was only feasible when intermolecular interaction was small enough to be neglected.

Investigation of the scaling law on gelation of oppositely charged nanocrystalline cellulose and polyelectrolyte.

The sol-gel transition in the mixture system of oppositely charged polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) and nanocrystalline cellulose (NCC) induced by electrostatic adsorption interaction was investigated by rheological means. Winter and Chambon theory was validated to be applicable for the critical gel point determination, and critical gel point have been successfully determined. With QHEC concentration increasing, more NCC were needed to form a critical gel, and smaller loss tangent and relaxation exponent (n) values at the gel point were observed, indicating the elastic nature of mixture was enhanced with QHEC increase. Gel strength behaved as a function of both QHEC and NCC concentrations, suggesting the gel network at the critical point was composed of entanglements and association of QHEC macromolecular chains, as well as the electrostatic adsorption interaction between QHEC chains and NCC rods. The calculated number of NCC rods per junction decreased from 0.30 to 0.01 when the QHEC concentration increased from 1.0wt% to 3.0wt%, indicating the electrostatic adsorption interaction between the NCC rods and QHEC chains was less significant to gel formation at higher QHEC concentrations. Therefore, the exponents of scaling law η0∝ϵ(-γ) and Ge∝ϵ (z) for the QHEC/NCC mixtures revealed that the scaling law n=z/(z+γ) between n, γ, and z was only feasible at highest QHEC concentration, since the intermolecular interaction (electrostatic adsorption interaction in this article) was so weak that can be neglected and the critical gel network was dominated by QHEC chain entanglements and association.

Structure of poly(N-isopropylacrylamide) brushes and steric stability of their grafted cellulose nanocrystal dispersions.

Thermo-responsive poly(N-isopropylacrylamide) (poly(NIPAAm)) brushes were grafted from the surface of cellulose nanocrystals (CNC) via living radical polymerization (LRP) using different initiator and monomer concentrations. The dry film thickness of the poly(NIPAAm) layer around CNC was calculated based on Scanning Electron Microscopy (SEM) and dynamic light scattering (DLS) measurements. The wet film thicknesses of grafted poly(NIPAAm) brushes in water were calculated to be 15 and 9nm for NIPAAm-CNC-1 and NIPAAm-CNC-2, respectively. Grafted chain densities and wet film thicknesses at below and above the critical temperature (T=34°C) of polyNIPAAm were calculated by applying mean-field analytical theory. The non-ionic poly(NIPAAm) brushes screened the surface charges of CNC particles, leading to a significant decrease in the absolute zeta potential values for the poly(NIPAAm) grafted CNCs compared to the unmodified and initiator modified CNC samples. Nevertheless, the colloidal stability of poly(NIPAAm) grafted CNC particles were still maintained by steric stabilization below the critical temperature On the other side, hydrophobic attractions among poly(NIPAAm) grafted CNC rods above 34°C lead to coagulation and phase separation. While both poly(NIPAAm) grafted CNC samples showed thermo-responsive behavior, the reversibility of this temperature triggered property was dependent on grafting density.