Immobilized cellulose nanospheres enable rapid antigen detection in lateral flow immunoassays.

Rapid diagnostic systems are essential in controlling the spread of viral pathogens and efficient patient management. The available technologies for low-cost viral antigen testing have several limitations, including a lack of accuracy and sensitivity. Here, we introduce a platform based on cellulose II nanoparticles (oppositely charged NPan and NPcat) for effective control of surface protein interactions, leading to rapid and sensitive antigen tests. Passivation against non-specific adsorption and augmented immobilization of sensing antibodies is achieved by adjusting the electrostatic charge of the nanoparticles. The interactions affecting the performance of the system are investigated by microgravimetry and confocal imaging. As a proof-of-concept test, SARS-CoV-2 nucleocapsid sensing was carried out by using saliva-wicking by channels that were stencil-printed on paper. We conclude that inkjet-printed NPcat elicits strong optical signals, visible after a few minutes, opening the opportunity for cost-effective and rapid diagnostic. Supplementary Information: The online version contains supplementary material available at 10.1007/s10570-022-05038-y.

Evaluation of Keratin-Cellulose Blend Fibers as Precursors for Carbon Fibers.

One main challenge to utilize cellulose-based fibers as the precursor for carbon fibers is their inherently low carbon yield. This study aims to evaluate the use of keratin in chicken feathers, a byproduct of the poultry industry generated in large quantities, as a natural charring agent to improve the yield of cellulose-derived carbon fibers. Keratin-cellulose composite fibers are prepared through direct dissolution of the pulp and feather keratin in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) and subsequent dry jet wet spinning (so-called Ioncell process). Thermogravimetric analysis reveals that there is an increase in the carbon yield by ∼53 wt % with 30 wt % keratin incorporation. This increase is comparable to the one observed for lignin-cellulose composite fibers, in which lignin acts as a carbon booster due to its higher carbon content. Keratin, however, reduces the mechanical properties of cellulose precursor fibers to a lesser extent than lignin. Keratin introduces nitrogen and induces the formation of pores in the precursor fibers and the resulting carbon fibers. Carbon materials derived from the keratin-cellulose composite fiber show potential for applications where nitrogen doping and pores or voids in the carbon are desirable, for example, for low-cost bio-based carbons for energy harvest or storage.

Carboxymethyl Cellulose (CMC) Optical Fibers for Environment Sensing and Short-Range Optical Signal Transmission.

Optical fibers are a key component in modern photonics, where conventionally used polymer materials are derived from fossil-based resources, causing heavy greenhouse emissions and raising sustainability concerns. As a potential alternative, fibers derived from cellulose-based materials offer renewability, biocompatibility, and biodegradability. In the present work, we studied the potential of carboxymethyl cellulose (CMC) to prepare optical fibers with a core-only architecture. Wet-spun CMC hydrogel filaments were cross-linked using aluminum ions to fabricate optical fibers. The transmission spectra of fibers suggest that the light transmission window for cladding-free CMC fibers was in the range of 550-1350 nm, wherein the attenuation coefficient for CMC fibers was measured to be 1.6 dB·cm-1 at 637 nm. CMC optical fibers were successfully applied in touch sensing and respiratory rate monitoring. Finally, as a proof-of-concept, we demonstrate high-speed (150 Mbit/s) short-distance signal transmission using CMC fibers (at 1310 nm) in both air and water media. Our results establish the potential of carboxymethyl cellulose-based biocompatible optical fibers for highly demanding advanced sensor applications, such as in the biomedical domain.

Bicomponent Cellulose Fibrils and Minerals Afford Wicking Channels Stencil-Printed on Paper for Rapid and Reliable Fluidic Platforms.

Flexible and easy-to-use microfluidic systems are suitable options for point-of-care diagnostics. Here, we investigate liquid transport in fluidic channels produced by stencil printing on flexible substrates as a reproducible and scalable option for diagnostics and paper-based sensing. Optimal printability and flow profiles were obtained by combining minerals with cellulose fibrils of two different characteristic dimensions, in the nano- and microscales, forming channels with ideal wettability. Biomolecular ligands were easily added by inkjet printing on the channels, which were tested for the simultaneous detection of glucose and proteins. Accurate determination of clinically relevant concentrations was possible from linear calibration, confirming the potential of the introduced paper-based diagnostics. The results indicate the promise of simple but reliable fluidic channels for drug and chemical analyses, chromatographic separation, and quality control.

Thermoresponsive Nanocellulose Films as an Optical Modulation Device: Proof-of-Concept.

Flexible optoelectronic technologies are becoming increasingly important with the advent of concepts such as smart-built environments and wearable systems, where they have found applications in displays, sensing, healthcare, and energy harvesting. Parallelly, there is also a need to make these innovations environmentally sustainable by design. In the present work, we employ nanocellulose and its excellent film-forming properties as a basis to develop a green flexible photonic device for sensing applications. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were used as matrix materials along with a black thermochromic pigment to prepare thermoresponsive hybrid films. Optical properties of nanocellulose films such as transparency and haze were tuned by varying pigment loading. Nearly 90% transparent CNF and CNC films could be tuned to reduce the transmission to as low as 4 and 17%, respectively. However, the films regained transparency to up to 60% when heated above the thermochromic transition temperature (31 °C). The thermoresponsive behavior of the prepared films was exploited to demonstrate an all-optical modulation device. Continuous infrared light (1300 nm) was modulated by using a 660 nm visible diode laser. The laser intensity was sufficient to cause a localized thermochromic transition in the films. The laser was pulsed at 0.3 Hz and a uniform cyclic modulation depth of 0.3 dB was achieved. The demonstrated application of functional nanocellulose hybrid films as a light switch (modulator) could be harnessed in various thermally stimulated sensing systems such as temperature monitoring, energy-saving, and anti-counterfeiting.

Impact of incubation conditions and post-treatment on the properties of bacterial cellulose membranes for pressure-driven filtration.

Bacterial cellulose (BC) has shown potential as a separation material. Herein, the performance of BC in pressure-driven separation is investigated as a function of incubation conditions and post-culture treatment. The pure water flux of never-dried BC (NDBC), was found to be 9 to 16 times higher than that for dried BC (DBC), in a pressure range of 0.25 to 2.5 bar. The difference in pressure response of NDBC and DBC was observed both in cross-flow filtration and capillary flow porometry experiments. DBC and NDBC were permeable to polymers with a hydrodynamic radius of ∼60 nm while protein retention was possible by introducing anionic surface charges on BC. The results of this work are expected to expand the development of BC-based filtration membranes, for instance towards the processing of biological fluids.

High-Throughput Tailoring of Nanocellulose Films: From Complex Bio-Based Materials to Defined Multifunctional Architectures.

This paper demonstrates a high-throughput approach to fabricate nanocellulose films with multifunctional performance using conventionally existing unit operations. The approach comprises cast-coating and direct interfacial atmospheric plasma-assisted gas-phase modification along with the microscale patterning technique (nanoimprint lithography, NIL), all applied in roll-to-roll mode, to introduce organic functionalities in conjunction with structural manipulation. Our strategy results in multifunctional cellulose nanofibrils (CNF) films in which the high optical transmittance (∼90%) is retained while the haze can be adjusted (2-35%). Concomitantly, the hydrophobic/hydrophilic balance can be tuned (50-21 mJ/m2 with the water contact angle ranging from ∼20 up to ∼120°), while intrinsic hygroscopicity of CNF films is not significantly compromised. Therefore, a challenge to produce multifunctional bio-based materials with properties defined by various high-performance applications conjoined to the lack of efficient processing strategies is elucidated. Overall, economically and ecologically viable strategy, which was realized by facile and upscalable unit operations using the R2R technology, is introduced to expand the properties' spaces and thus offer a vast variety of interesting applications for CNF films.

Self-Assembly of Soft Cellulose Nanospheres into Colloidal Gel Layers with Enhanced Protein Adsorption Capability for Next-Generation Immunoassays.

Soft cationic core/shell cellulose nanospheres can deform and interpenetrate allowing their self-assembly into densely packed colloidal nanogel layers. Taking advantage of their water-swelling capacity and molecular accessibility, the nanogels are proposed as a new and promising type of coating material to immobilize bioactive molecules on thin films and paper. The specific and nonspecific interactions between the cellulosic nanogel and human immunoglobulin G as well as bovine serum albumin (BSA) are investigated. Confocal microscopy, electroacoustic microgravimetry, and surface plasmon resonance are used to access information about the adsorption behavior and viscoelastic properties of self-assembled nanogels. A significant BSA adsorption capacity on nanogel layers (17 mg m-2 ) is measured, 300% higher compared to typical polymer coatings. This high protein affinity further confirms the promise of the introduced colloidal gel layer, in increasing sensitivity and advancing a new generation of substrates for a variety of applications, including immunoassays, as demonstrated in this work.

Electrically Conductive Thin Films Based on Nanofibrillated Cellulose: Interactions with Water and Applications in Humidity Sensing.

TEMPO-oxidized cellulose nanofibrils (TOCNF) and oxidized carbon nanotubes (CNT) were used as humidity-responsive films and evaluated using electroacoustic admittance (quartz crystal microbalance with impedance monitoring, QCM-I) and electrical resistivity. Water uptake and swelling phenomena were investigated in a range of relative humidity (% RH) between 30 and 60% and temperatures between 25 and 50 °C. The presence of CNT endowed fibril networks with high water accessibility, enabling fast and sensitive response to changes in humidity, with mass gains of up to 20%. The TOCNF-based sensors became viscoelastic upon water uptake, as quantified by the Martin-Granstaff model. Sensing elements were supported on glass and paper substrates and confirmed a wide window of operation in terms of cyclic % RH, bending, adhesion, and durability. The electrical resistance of the supported films increased by ∼15% with changes in % RH from 20 to 60%. The proposed system offers a great potential to monitor changes in smart packaging.

Delignification and Ionic Liquid Treatment of Wood toward Multifunctional High-Performance Structural Materials.

Wood-based multifunctional materials with excellent mechanical performance are increasingly considered for sustainable advanced applications due to their unique hierarchical structure and inherent reinforcing cellulose phase orientation. Nonetheless, a wider multipurpose utilization of wood materials is so far hampered because of constraints arising from scalable functionalization, efficient processing, facile shaping as well asnatural heterogeneity and durability. This study introduces a multifunctional all-wood material fabrication method relying on delignification, ionic liquid (IL) treatment, and pressure-assisted consolidation of wood. Structure-retaining controlled delignification of wood was performed to enable direct access to the hierarchical cellulose assembly, while preserving the highly aligned and thus beneficial wood structural directionality. As a following step, the obtained biobased scaffold with an increased porosity was infiltrated with an IL and heat-activated to partially dissolve and soften the cellulose fiber surface. Samples washed with water to remove IL exhibited pronounced isotropic flexibility, which upon combined compression and lateral shear allowed the fabrication of various 3D shapes with adjustable fiber architecture. The obtained very compact and totally additive-free all-wood materials were extensively characterized, revealing superior mechanical performance, and gained multifunctionality compared to native wood.

Author Correction: Shape fidelity and structure of 3D printed high consistency nanocellulose.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Shape fidelity and structure of 3D printed high consistency nanocellulose.

The aim of the present study was to investigate the additive manufacturing process for high consistency nanocellulose. Unlike thermoformable plastics, wood derived nanocelluloses are typically processed as aqueous dispersions because they are not melt-processable on their own. The ability to use nanocellulose directly in additive manufacturing broadens the possibilities regarding usable raw materials and achievable properties thereof. Modern additive manufacturing systems are capable of depositing nanocellulose with micrometer precision, which enables the printing of accurate three-dimensional wet structures. Typically, these wet structures are produced from dilute aqueous fibrillar dispersions. As a consequence of the high water content, the structures deform and shrink during drying unless the constructs are freeze-dried. While freeze-drying preserves the geometry, it results in high porosity which manifests as poor mechanical and barrier properties. Herein, we study an additive manufacturing process for high consistency enzymatically fibrillated cellulose nanofibers in terms of printability, shape retention, structure, and mechanical properties. Particular emphasis is placed on quantitative shape analysis based on 3D scanning, point cloud analysis, and x-ray microtomography. Despite substantial volumetric as well as anisotropic deformation, we demonstrate repeatability of the printed construct and its properties.

Two-Dimensional Antifouling Fluidic Channels on Nanopapers for Biosensing.

Two-dimensional (hydrophilic) channels were patterned on films prepared from cellulose nanofibrils (CNF) using photolithography and inkjet printing. Such processes included UV-activated thiol-yne click coupling and inkjet-printed designs with polystyrene. The microfluidic channels were characterized (SEM, wetting, and fluid flow) and applied as platforms for biosensing. Compared to results from the click method, a better feature fidelity and flow properties were achieved with the simpler inkjet-printed channels. Human immunoglobulin G (hIgG) was used as target protein after surface modification with either bovine serum albumin (BSA), fibrinogen, or block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) (PDMAEMA- block-POEGMA copolymers). Surface plasmon resonance (SPR) and AFM imaging were used to determine their antifouling effect to prevent nonspecific hIgG binding. Confocal laser scanning microscopy revealed diffusion and adsorption traces in the channels. The results confirm an effective surface passivation of the microfluidic channels (95% reduction of hIgG adsorption and binding). The inexpensive and disposable systems proposed here allow designs with space-resolved blocking efficiency that offer a great potential in biosensing.

Injection Molding of Thermoplastic Cellulose Esters and Their Compatibility with Poly(Lactic Acid) and Polyethylene.

Interest in biobased polymers from renewable resources has grown in recent years due to environmental concerns, but they still have a minimal fraction of the total global market. In this study, the injection molding of thermoplastic cellulose octanate (cellulose C8) and cellulose palmitate (cellulose C16) were studied. The mechanical properties of injection-molded test specimens were analyzed by using tensile testing, and the internal structure of injection-molded objects was studied by using a field emission scanning electron microscopy (FE-SEM). We showed that thermoplastic cellulose C8 and cellulose C16 were completely processable without the addition of a plasticizer, which is very unusual in the case of cellulose esters. The compatibility of cellulose esters with poly(lactic acid) (PLA) and biopolyethylene (bio-PE) was also tested. By compounding the cellulose esters with PLA, the elongation of PLA-based blends could be improved and the density could be reduced. The tested thermoplastic cellulose materials were fully biobased, and have good future potential to be used in injection molding applications.

Enhancing the Stability of Aqueous Dispersions and Foams Comprising Cellulose Nanofibrils (CNF) with CaCO3 Particles.

In this work, stability of dispersions and foams containing CaCO3-based pigments and cellulose nanofibrils (CNF) was evaluated with the aim to reveal the mechanisms contributing to the overall stability of the selected systems. The utmost interest lies in the recently developed hydrocolloid hybrid CaCO3 pigments and their potential to form bionanocomposite structures when incorporated with CNF. These pigments possess a polyelectrolyte layer deposited on the surface of the particle which is expected to enhance the compatibility between inorganic and organic components. Stability assessment of both dispersions and foams was conducted using turbidity profile scanning. In dispersions, CNF provides stability due to its ability to form a firm percolation network. If surface-modified pigments are introduced, the favourable surface interactions between the pigments and CNF positively influence the stability behaviour and even large macro-size pigments do not interfere with the stability of either dispersions or foams. In foams, the stability can be enhanced due to the synergistic actions brought by CNF and particles with suitable size, shape and wetting characteristics resulting in a condition where the stability mechanism is defined by the formation of a continuous plateau border incorporating a CNF network which is able to trap the inorganic particles uniformly.

Cyclodextrin-Functionalized Fiber Yarns Spun from Deep Eutectic Cellulose Solutions for Nonspecific Hormone Capture in Aqueous Matrices.

A wood based yarn platform for capturing pharmaceutical molecules from water was developed. Cellulose fiber yarns were modified with cyclodextrins, and the capture of 17α-ethinyl estradiol (EE2), a synthetic estrogen hormone used as contraceptive, from water was tested. The yarns were prepared by spinning a deep eutectic solution (DES) of cellulose in choline chloride-urea. Despite their high porosity and water sorption capacity (5 g/g), the spun fiber yarns displayed high wet strength, up to 60% of that recorded in dry condition (128 MPa with 17% strain at break). Cyclodextrin irreversible attachment on the yarns was achieved with adsorbed chitosan and the conjugation reactions and capture of EE2 by the cyclodextrin-modified cellulose were confirmed via online detection with Surface Plasmon Resonance (SPR). The facile synthesis of the bioactive yarns and EE2 binding capacity from aqueous matrices (as high as 2.5 mg/g) indicate excellent prospects for inexpensive platforms in disposable affinity filtration. The study presents a strategy to produce a wood fiber based yarn to be used as a platform for human and veterinary pharmaceutical hormone capture.

Spinning Approach for Cellulose Fiber Yarn Using a Deep Eutectic Solvent and an Inclined Channel.

We developed a spinning approach for a dope produced by treating softwood pulp with a deep eutectic solvent (DES). The DES enables formation of a sufficiently viscous spinnable gel-like suspension of fibers, which solidifies upon the removal of the DES. This solidification, however, requires a longer time compared to most conventional wet spinning processes. Consequently, the continuity of the spinning process has been constrained in previous work. Moreover, the ability to draw the incipient yarn to increase orientation has been limited. Here we present a continuous spinning approach where the fiber yarn properties and processability can be improved using an inclined channel. A combination of an air gap and an inclined ethanol stream transports and draws the incipient fiber yarn during spinning. The influence of syringe tip diameter, angle of the channel, ethanol flow rate, and twisting were studied experimentally. The improvements in the spinning process resulted in an increase in load bearing capability and ability to reduce the linear density of the fiber yarn.

Filaments with Affinity Binding and Wet Strength Can Be Achieved by Spinning Bifunctional Cellulose Nanofibrils.

We demonstrate benzophenone (BP) conjugation via amine-reactive esters onto oxidized cellulosic fibers that were used as precursors, after microfluidization, of photoactive cellulose nanofibrils (CNF). From these fibrils, cellulose I filaments were synthesized by hydrogel spinning in an antisolvent followed by fast biradical UV cross-linking. As a result, the wet BP-CNF filaments retained extensively the original dry strength (a remarkable ∼80% retention). Thus, the principal limitation of these emerging materials was overcome (the wet tensile strength is typically <0.5% of the value measured in dry conditions). Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated onto residual surface carboxyl groups, making the filaments bifunctional for their active groups and properties (wet strength and bioactivity). Optical (surface plasmon resonance) and electroacoustic (quartz crystal microgravimetry) measurements conducted with the bifunctional CNF indicated effective anti-Hb conjugation (2.4 mg m-2), endowing an excellent sensitivity toward Hb targets (1.7 ± 0.12 mg m-2) and negligible nonspecific binding. Thus, the anti-Hb biointerface was deployed on filaments that captured Hb efficiently from aqueous matrices (confocal laser microscopy of FITC-labeled antibodies). Significantly, the anti-Hb biointerface was suitable for regeneration, while its sensitivity and selectivity in affinity binding can be tailored by application of blocking copolymers. The developed bifunctional filaments based on nanocellulose offer great promise in detection and affinity binding built upon 1D systems, which can be engineered into other structures for rational use of material and space.

Control of Protein Affinity of Bioactive Nanocellulose and Passivation Using Engineered Block and Random Copolymers.

We passivated TEMPO-oxidized cellulose nanofibrils (TOCNF) toward human immunoglobulin G (hIgG) by modification with block and random copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA). The block copolymers reversibly adsorbed on TOCNF and were highly effective in preventing nonspecific interactions with hIgG, especially if short PDMAEMA blocks were used. In such cases, total protein rejection was achieved. This is in contrast to typical blocking agents, which performed poorly. When an anti-human IgG biointerface was installed onto the passivated TOCNF, remarkably high affinity antibody-antigen interactions were observed (0.90 ± 0.09 mg/m(2)). This is in contrast to the nonpassivated biointerface, which resulted in a significant false response. In addition, regeneration of the biointerface was possible by low pH aqueous wash. Protein A from Staphylococcus aureus was also utilized to successfully increase the sensitivity for human IgG recognition (1.28 ± 0.11 mg/m(2)). Overall, the developed system based on TOCNF modified with multifunctional polymers can be easily deployed as bioactive material with minimum fouling and excellent selectivity.

Effect of Molecular Architecture of PDMAEMA-POEGMA Random and Block Copolymers on Their Adsorption on Regenerated and Anionic Nanocelluloses and Evidence of Interfacial Water Expulsion.

Block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) with varying block sizes were synthesized by consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization and then exposed to cellulose substrates with different anionic charge density. The extent and dynamics of quaternized PDMAEMA-b-POEGMA adsorption on regenerated cellulose, cellulose nanofibrils (CNF), and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) was determined by using electromechanical and optical techniques, namely, quartz crystal microbalance (QCM-D) and surface plasmon resonance (SPR), respectively. PDMAEMA-b-POEGMA equilibrium adsorption increased with the anionic charge of cellulose, an indication of electrostatic interactions. Such an observation was further confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Depending on their architecture, adsorption on TOCNF of some of the PDMAEMA-b-POEGMA copolymers produced a significant reduction in QCM frequency, as expected from large mass uptake, while surprisingly, other copolymers induced the opposite effect. This latter, remarkable behavior was ascribed to coupled water expulsion from the interface upon charge neutralization of anionic surface sites with adsorbing cationic polymer segments. These observations were further investigated with SPR and QCM-D measurements using deuterium oxide solvent exchange to determine the amount of coupled water at the TOCNF-block copolymer interface. Finally, random copolymers with similar composition adsorbed to a larger extent compared to the respective block copolymers, revealing the effect of adsorbed loops and tails as well as hydration.