Packaging plays a critical role in ensuring food safety and shelf life by protecting against e.g., moisture, gases, and light. Polyethylene (PE) is widely used in food packaging, but it is mainly produced from non-renewable resources and it is an inefficient oxygen and light barrier. In this study, the layer-by-layer (LbL) assembly of a sustainably produced lignin-based polymer (EH) with polyethylenimine (PEI) or chitosan (CH) was used to fabricate (partially or fully) bio-based coatings with the aim of improving barrier properties of PE films. The charge density of EH was calculated using a polyelectrolyte titration method and the hydrodynamic diameters of EH, PEI and CH were determined by Dynamic Light Scattering (DLS). LbL assembly was monitored in situ via Quartz Crystal Microbalance with Dissipation (QCM-D) and Stagnation Point Adsorption Reflectometry (SPAR). PE films were coated with a variable number of PEI/EH or CH/EH bilayers (BL) using an immersive LbL assembly method. Coated films were studied in terms of light-blocking ability, wettability, thermal behaviour, surface structure, as well as oxygen and water vapor barrier properties. QCM-D and SPAR data showed a stepwise multilayer formation and strong interactions between the oppositely charged polymers, with PEI/EH coating having a greater amount of deposited polymer compared to CH/EH coating at the same number of BL. Overall, light barrier properties and wettability of the coated films increased with the number of deposited bilayers. Coated PE films maintained the overall thermal behaviour of PE. A number of BL of 20 was found to be the most promising based on the studied properties. Selected samples showed improved oxygen and water vapor barrier properties, with PEI/EH coating performing better than CH/EH coating. Taken altogether, we demonstrated that a novel and sustainable lignin-based polymer can be combined with PEI or CH to fabricate (partially or fully) bio-based coatings for food packaging.

Cancer represents a significant global public health challenge and ranks as the second mostcommon cause of death in the United States. The onset of cancer entails an initial phasewhere cells lose their polarity and disconnect from the normal basement membrane, allowingthem to form distinct three-dimensional (3D) configurations that interact with adjacent cellsand the surrounding microenvironment. Cells grown in 2D monolayers demonstrate differentgene expression patterns and different activation of signaling pathways compared to cellscultivated within the natural structure of tumor tissue of the same cell type. Multicellulartumor spheroids (MCTS) are extensively investigated as a well-studied model of organotypiccancer. These spheroids are formed by tumor cells, either alone or in combination with othercell types, and they can be created with or without the application of supportive scaffolds.The MCTSs are also considered promising models for preclinical assessments of chemosensitivity.However, the creation of these tumor spheroids presents challenges, as not alltumor cell lines can consistently form regular spheroids.Cellulose nanofibrils (CNF) have become essential as a sustainable and environmentallyfriendly material. For example, thin films, with inherent mechanical properties, and flexibility,offer versatility across various applications. Also known for its biocompatibility and non-toxicnature, native CNF is a natural option to use. Its fibrous structure closely mimics the collagenmatrix in human tissue, showing potential as an effective scaffold for 3D cell culture. In thisregard, an innovative Layer-by-Layer (LbL) coating technique using CNF-polyelectrolytebilayers was investigated to generate spheroids. This method constructs bilayers of CNFand polyelectrolytes and can coat various surfaces. In this thesis, the first focus was ondemonstrating the spheroid formation capability using low molecular weight polyelectrolytesin LbL assembly. Secondly, an investigation was conducted involving embedding of LbLgrownspheroids in a decellularized extracellular matrix (ECM) aiming to determine howECM, possessing suitable mechanical characteristics, could influence the cancer stem celltraits in spheroids. Thirdly, the thesis demonstrated the utilization of LbL for capturing andreleasing of circulating tumor cells. Lastly, the shift from using low molecular weightpolyelectrolytes in the LbL assembly to high molecular weight counterparts and analyzingthe differences in spheroid formation abilities to assess the underlying differences inmolecular weights of the polyelectrolytes was explored. All-in-all, employing the CNF-basedLbL surface coating strategy explored in the thesis has proven to be promising for thedevelopment of spheroid models closely resembling in vivo conditions and holds significantpotential for applications in drug development.

Central nervous system (CNS) injuries such as stroke or trauma can lead to long-lasting disability, and there is no currently accepted treatment to regenerate functional CNS tissue after injury. Hydrogels can mimic the neural extracellular matrix by providing a suitable 3D structure and mechanical properties and have shown great promise in CNS tissue regeneration. Here we present successful synthesis of a thermosensitive hyaluronic acid-RADA 16 (Puramatrix (TM)) peptide interpenetrating network (IPN) that can be applied in situ by injection. Thermosensitive hyaluronic acid (HA) was first synthesized by combining HA with poly(N-isopropylacrylamide). Then, the Puramatrix (TM) self-assembled peptide was combined with the thermosensitive HA to produce a series of injectable thermoresponsive IPNs. The HA-Puramatrix (TM) IPNs formed hydrogels successfully at physiological temperature. Characterization by SEM, rheological measurements, enzymatic degradation and swelling tests was performed to select the IPN optimized for neurologic use. SEM images of the optimized dry IPNs demonstrated an aligned porous structure, and the rheological measurements showed that the hydrogels were elastic, with an elastic modulus of approximately 500 Pa, similar to that of brain tissue. An evaluation of the cell-material interactions also showed that the IPN had biological characteristics required for tissue engineering, strongly suggesting that the IPN hydrogel possessed properties beneficial for regeneration of brain tissue.

Three-dimensional (3D) tumor spheroids are regarded as promising models for utilization as preclinical assessments of chemo-sensitivity. However, the creation of these tumor spheroids presents challenges, given that not all tumor cell lines are able to form consistent and regular spheroids. In this context, we have developed a novel layer-by-layer coating of cellulose nanofibril–polyelectrolyte bilayers for the generation of spheroids. This technique builds bilayers of cellulose nanofibrils and polyelectrolytes and is used here to coat two distinct 96-well plate types: nontreated/non-sterilized and Nunclon Delta. In this work, we optimized the protocol aimed at generating and characterizing spheroids on difficult-to-grow pancreatic tumor cell lines. Here, diverse parameters were explored, encompassing the bilayer count (five and ten) and multiple cell-seeding concentrations (10, 100, 200, 500, and 1000 cells per well), using four pancreatic tumor cell lines—KPCT, PANC-1, MiaPaCa-2, and CFPAC-I. The evaluation includes the quantification (number of spheroids, size, and morphology) and proliferation of the produced spheroids, as well as an assessment of their viability. Notably, our findings reveal a significant influence from both the number of bilayers and the plate type used on the successful formation of spheroids. The novel and simple layer-by-layer-based coating method has the potential to offer the large-scale production of spheroids across a spectrum of tumor cell lines.

Three-dimensional multicellular spheroids (MCSs) are complex structure of cellular aggregates and cell-to-matrix interaction that emulates the in-vivo microenvironment. This research field has grown to develop and improve spheroid generation techniques. Here, we present a new platform for spheroid generation using Layer-by-Layer (LbL) technology. Layer-by-Layer (LbL) containing cellulose nanofibrils (CNF) assemble on a standard 96 well plate. Various bi-layer numbers, multiple cell seeding concentration, and two tumor cell lines (HEK 293 T, HCT 116) are utilized to generate and characterize spheroids. The number and proliferation of generated spheroids, the viability, and the response to the anti-cancer drug are examined. The spheroids are formed and proliferated on the LbL-CNF coated wells with no significant difference in connection to the number of LbL-CNF bi-layers; however, the number of formed spheroids correlates positively with the cell seeding concentration (122 ± 17) and (42 ± 8) for HCT 116 and HEK 293T respectively at 700 cells ml−1. The spheroids proliferate progressively up to (309, 663) µm of HCT 116 and HEK 293T respectively on 5 bi-layers coated wells with maintaining viability. The (HCT 116) spheroids react to the anti-cancer drug. We demonstrate a new (LbL-CNF) coating strategy for spheroids generation, with high performance and efficiency to test anti-cancer drugs.

Electrochemical anodized titanium dioxide (TiO2) nanotubes are of immense significance as electrochemical energy storage devices owing to their fast electron transfer by reducing the diffusion path and paving way to fabricating binder-free and carbon-free electrodes. Besides these advantages, when nitrogen is doped into its lattice, doubles its electrochemical activity due to enhanced charge transfer induced by oxygen vacancy. Herein, we synthesized nitrogen-doped TiO2 (N-TiO2) and studied its electrochemical performances in supercapacitor and as anode for a lithium-ion battery (LIB). Nitrogen doping into TiO2 was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical performance of N-TiO2 nanotubes was outstanding with a specific capacitance of 835 mu F cm(-2) at 100 mV s(-1) scan rate as a supercapacitor electrode, and it delivered an areal discharge capacity of 975 mu A h cm(-2) as an anode material for LIB which is far superior to bare TiO2 nanotubes (505 mu F cm(-2) and 86 mu A h cm(-2), respectively). This tailor-made nitrogen-doped nanostructured electrode offers great promise as next-generation energy storage electrode material.

This paper presents an experimental characterization of the prebreakdown phenomena in liquid/solid interfaces. The characterization is devoted to the 2nd mode positive streamers initiated and propagated along interfaces of mineral-oil and solids with different chemical composition and physical properties. Polymers of low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF) and papers made of kraft paper and a kraft fibril paper (made from cellulosic micro and nano fibrils), lignin-free paper and paper with high lignin content (referred to as k107 kraft paper) are used as the solid to study their influence on the streamer inception and propagation. The streamers are initiated at the interface by applying steps of voltage to a point-plane electrode arrangement with a solid (dielectric barrier) into the gap. The solid is placed diagonal to the oil gap and near to the point electrode. Shadowgraphs, charge and light intensity recordings are obtained during the inception and propagation of the streamers. Thus, estimations of the streamer length, velocity, current and average charge, are also presented. A time delay has been observed before the initiation of the streamer. This delay is probably correlated to the initiation process and formation of the gaseous phase of the streamer near to the interface. The threshold propagation voltage of the 2nd mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. However, the inception voltage is highly influenced by the interface. Additionally, the observed characteristics of streamers propagation (e.g. current, length, velocity, etc) along the tested interfaces cannot be fully explained by a capacitive coupling effect (permittivity mismatch). This open a discussion for the possibility that properties of the solid such as chemical composition, wettability and surface roughness can influence the streamer propagation.

The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.

Fundamental research plays a pivotal role in the development of sustainable solutions that benefit both our environment and everyday lives. Cellulose, as an abundant and renewable resource, holds immense potential for sustainable applications. However, navigating the complexities of molecular and supramolecular structure of cellulose poses significant challenges in harnessing its full potential. By delving into fundamental research, we aim to uncover the underlying mechanisms governing cellulose interactions, paving the way for innovative advancements in sustainable material development.This thesis uncovers the intricate relationship between fundamental research and applied methodologies by showing how molecular contact and structure at the interface of cellulose-rich materials will control the development of the macroscopic mechanical properties of networks from cellulose-rich fibres. The study encompasses various facets, ranging from the development of model materials for studying interfacial interactions to the preparation of fibrous networks with tailored properties.In the initial part of the work the research delves into the development of model materials to investigate interactions at smooth interfaces of regenerated cellulose. The study reveals the crucial role of the making and breaking of cellulose interface, or sometimes interphase, in the development of adhesive joints. Experimental findings demonstrate how chemical additives influence the interactions between cellulose surfaces, thereby modulating the structural and adhesive properties at the interface. Furthermore, by utilizing model materials, insights are gained into fibre-fibre interactions and the influence of surface treatments on network formation and mechanical performance. Lastly, the research focused on investigating the preparation of fibrous networks at different densities and amount of adsorbed additives, providing a comprehensive understanding of how network density and composition affect mechanical properties of the networks.This work not only exemplifies a synergistic approach, where fundamental insights into molecular contacts and interface structures are translated into practical applications for enhancing macroscopic properties but also highlights the importance of integrating fundamental and applied methodologies in molecular engineering, offering novel strategies for advancing sustainable paper production practices and contributing to the attainment of sustainable development goals.

Despite extensive research on biobased and fiber-basedmaterials, fundamental questions regarding the molecular processesgoverning fiber−fiber interactions remain unanswered. In this study, weintroduce a method to examine and clarify molecular interactions withinfiber−fiber joints using precisely characterized model materials, i.e.,regenerated cellulose gel beads with nanometer-smooth surfaces. Byphysically modifying these materials and drying them together to createmodel joints, we can investigate the mechanisms responsible for joiningcellulose surfaces and how this affects adhesion in both dry and wet statesthrough precise separation measurements. The findings reveal a subtlebalance in the joint formation, influencing the development ofnanometer-sized structures at the contact zone and likely inducingbuilt-in stresses in the interphase. This research illustrates how model materials can be tailored to control interactions betweencellulose-rich surfaces, laying the groundwork for future high-resolution studies aimed at creating stiff, ductile, and/or tough jointsbetween cellulose surfaces and to allow for the design of high-performance biobased materials.

Achieving a sustainable foam production requires a complete substitution of synthetic components with natural and renewable alternatives, as well as development of an environment-friendly production process. This work demonstrates a synergetic combination of heat-treated beta-lactoglobulin proteins and cellulose nanofibrils (CNFs) to create fully bio-based and highly-stable wet foams. Furthermore, a gradual reduction in the pH, enabled oven-drying of the wet foams without any major structural collapse of the foam, resulting in the preparation of lightweight solid foams with the density of 10.2 kg.m(-3). First, the foaming behavior of heat-treated beta-lactoglobulin systems (HBSs) containing amyloid nanofibrils (ANFs) and non-converted peptides was investigated at different pHs. Subsequently, the HBS foams were stabilized using CNFs, followed by a gradual acidification of the system to a final pH of 4.5. To gain a deeper understanding of the stabilization mechanism of the foam, the interactions between the foam's components, their positioning in the foam structure, and the viscoelasticity of the fibrillar network were investigated using quartz crystal microgravimetry, confocal microscopy and rheology. The analysis of the obtained data suggests that the stability of the foams was associated with the accumulation of CNFs and ANFs at the air-water interface, and that the concomitant formation of an intertwined network surrounding the air bubbles. This together resulted in a significant decrease in drainage rate of the liquid in the foam lamellae, bubble coarsening and bubble coalescence within the foams. The results also show that the major surface-active component participating in the creation of the foam is the free peptide left in solution after the formation of the ANFs. A slow reduction in pH to 4.5 lead to further gelation of the fibrillar network and an improved storage modulus of the foam lamellae. This resulted in a strong coherent structure that could withstand oven-drying without collapse. The density, porosity, microstructure and compressive mechanical properties of such prepared dry foams were assessed. Overall, the results demonstrate the potential of HBSs to replace synthetic surfactants and outlines a sustainable preparation protocol for the preparation of light-weight porous composite structures of ANFs and CNFs.

Cellulose nanofibril-based aerogels have promising applicability in various fields; however, developing an effi-cient technique to functionalize and tune their surface properties is challenging. In this study, physically and covalently crosslinked cellulose nanofibril-based aerogel-like structures were prepared and modified by a mo-lecular layer-by-layer (m-LBL) deposition method. Following three m-LBL depositions, an ultrathin polyamide layer was formed throughout the aerogel and its structure and chemical composition was studied in detail. Analysis of model cellulose surfaces showed that the thickness of the deposited layer after three m-LBLs was approximately 1 nm. Although the deposited layer was extremely thin, it led to a 2.6-fold increase in the wet specific modulus, improved the acid-base resistance, and changed the aerogels from hydrophilic to hydrophobic making them suitable materials for oil absorption with the absorption capacity of 16-36 g/g. Thus, demon-strating m-LBL assembly is a powerful technique for tailoring surface properties and functionality of cellulose substrates.

Healthy material alternatives based on renewable resources and sustainable technologies have the potential to disrupt the environmentally damaging production and consumption practices established throughout the modern industrial era. In this study, a mycelium–nanocellulose biocomposite with hybrid properties is produced by the agitated liquid culture of a white-rot fungus (Trametes ochracea) with nanocellulose (NC) comprised as part of the culture media. Mycelial development proceeds via the formation of pellets, where NC is enriched in the pellets and depleted from the surrounding liquid media. Micrometer-scale NC elements become engulfed in mycelium, whereas it is hypothesized that the nanometer-scale fraction becomes integrated within the hyphal cell wall, such that all NC in the system is essentially surface-modified by mycelium. The NC confers mechanical strength to films processed from the biocomposite, whereas the mycelium screens typical cellulose–water interactions, giving fibrous slurries that dewater faster and films that exhibit significantly improved wet resistance in comparison to pure NC films. The mycelium–nanocellulose biocomposites are processable in the ways familiar to papermaking and are suggested for diverse applications, including packaging, filtration, and hygiene products.

Composites of biopolymers and conducting polymers are emerging as promising candidates for a green technological future and are actively being explored in various applications, such as in energy storage, bioelectronics, and thermoelectrics. While the device characteristics of these composites have been actively investigated, there is limited knowledge concerning the fundamental intracomponent interactions and the modes of molecular structuring. Here, by use of cellulose and poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), it is shown that the chemical and structural makeup of the surfaces of the composite components are critical factors that determine the materials organization at relevant dimensions. AFM, TEM, and GIVVAXS measurements show that when mixed with cellulose nanofibrils, PEDOT:PSS organizes into continuous nanosized beadlike structures with an average diameter of 13 nm on the nanofibrils. In contrast, when PEDOT:PSS is blended with molecular cellulose, a phase-segregated conducting network morphology is reached, with a distinctly relatively lower electric conductivity. These results provide insight into the mechanisms of PEDOT:PSS crystallization and may have significant implications for the design of conducting biopolymer composites for a vast array of applications.

Due to climate change and plastic pollution, there is an increasing demand for bio-based materials with similar properties to those of common plastics yet biodegradable. In this respect, cellulose is a strong candidate that is already being refined on a large industrial scale, but the properties differ significantly from those of common plastics in terms of shapeability and water-resilience.

This thesis investigates how supramolecular interactions can be used to tailor the properties of cellulose-based materials by modifying cellulose surfaces or control the assembly of cellulose nanofibrils (CNFs). Most of the work is a fundamental study on interactions in aqueous environments, but some material concepts are presented and potential applications are discussed.

The first part deals with the modification of cellulose by the spontaneous adsorption of xyloglucan or polyelectrolytes. The results indicate that xyloglucan adsorbs to cellulose due to the increased entropy of water released from the surfaces, which is similar to the increased entropy of released counter-ions that drives polyelectrolyte adsorption. The polyelectrolyte adsorption depends on the charge of the cellulose up to a limit after which the charge density affects only the first adsorbed layer in a multilayer formation.

Latex nanoparticles with polyelectrolyte coronas can be adsorbed onto cellulose in order to prepare hydrophobic cellulose surfaces with strong and ductile wet adhesion, provided the glass transition of the core is below the ambient temperature.

The second part of the thesis seeks to explain the interactions between different types of cellulose nanofibrils in the presence of different ions, using a model consisting of ion-ion correlation and specific ion effects, which can be employed to rationally design water-resilient and transparent nanocellulose films. The addition of small amounts of alginate also creates interpenetrating double networks, and these networks lead to a synergy which improves both the stiffness and the ductility of the films in water.

A network model has been developed to understand these materials, with the aim to explain the properties of fibril networks, based on parameters such as the aspect ratio of the fibrils, the solidity of the network, and the ion-induced interactions that increase the friction between fibrils. With the help of this network model and the model for ion-induced interactions, we have created films with wet-strengths surpassing those of common plastics, or a ductility suitable for hygroplastic forming into water-resilient and biodegradable packages. Due to their transparency, water content, and the biocompatibility of cellulose, these materials are also suitable for biomaterial or bioelectronics applications. 

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

Ion-induced assemblies of highly anisotropic nanoparticles can be explained by a model consisting of ion-ion correlation and specific ion effects: dispersion interactions, metal-ligand complexes, and local acidic environments. Films of cellulose nanofibrils and montmorillonite clay were treated with different ions, and their subsequent equilibrium swelling in water was related to important parameters of the model in order to investigate the relative importance of the mechanisms. Ion-ion correlation was shown to be the fundamental attraction, supplemented by dispersion interaction for polarizable ions such as Ca2+ and Ba2+, or metal-ligand complexes for ions such as Cu2+, Al3+ and Fe3+. Ions that form strong complexes induce local acidic environments that also contribute to the assembly. These findings are summarized in a comprehensive semi-quantitative model and are important for the design of nanomaterials and for understanding biological systems where specific ions are involved.

Cellulose nanofibrils (CNFs) assemble into water-resilient materials in the presence of multivalent counter-ions. The essential mechanisms behind these assemblies are ion-ion correlation and specific ion effects. A network model shows that the interfibril attraction indirectly influences the wet modulus by a fourth power relationship to the solidity of the network (E-w proportional to phi(4)). Ions that induce both ion-ion correlation and specific ion effects significantly reduce the swelling of the films, and due to the nonlinear relationship dramatically increase the wet modulus. Herein, this network model is used to explain the elastoplastic behavior of wet films of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized, carboxymethylated, and phosphorylated CNFs in the presence of different counter-ions. The main findings are that the aspect ratio of the CNFs influences the ductility of the assemblies, that the bivalency of phosphorylate ligands probably limits the formation of interfibril complexes with divalent ions, and that a higher charge density increases the friction between fibrils by increasing the short-range attraction from ion-ion correlation and specific ion effects. These findings can be used to rationally design CNF materials for a variety of applications where wet strength, ductility, and transparency are important, such as biomaterials or substrates for bioelectronics.

The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only −1 V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of ≈700 water molecules per electron–ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7 MPa (1.4 MPa vs dry) and a work density of ≈150 kJ m−3 (2 MJ m−3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems.

A process has been developed to create self-supporting hydrogels with low solids content (down to 0.5 wt %) and anisotropic aerogels with a low density (down to 5 kg/m(3)) from cellulose nanofibrils (CNFs). The CNF networks were formed by vacuum filtration of dilute dispersions (0.2 wt %) of 90% CNFs and 10% alginate. We call this process "the dynamic CNF network approach" since the solids content of these hydrogels can be tuned in the range of 0.5-3 wt % by reswelling the filter cakes in a medium with a controlled osmotic pressure. These hydrogels are significantly stronger than the 1-2 wt % CNF gels typically used to prepare hydrogels and aerogels because the dynamic CNF networks are formed below their arrested state threshold (ca. 0.5 wt %) and are thus homogeneous. The vacuum filtration leads to a directional reswelling vertical to the plane of the filter cake, and this is crucial in order to turn a two-dimensional (2D) shape, cut from the filter cake, into a 3D hydrogel without distorting the 2D shape. The anisotropic swelling was used to create intricate 3D-shaped hydrogels and solved some of the issues involved in the degassing and molding of high-viscosity CNF gels. Multivalent ions were used to lock the CNF and alginate networks at the desired solids content and 3D shape, and resulted in an increase by an order of magnitude in storage modulus. Moreover, the self-supporting nature of the hydrogels allowed us to freeze-cast them into anisotropic aerogels with the same 3D shape without using any container. The 5 kg/m(3) aerogel had a specific modulus of 43 kN m/kg and an anisotropy index of 12, which are impressive properties in relation to earlier experiences. The process can be used for applications where a precise control of density and shape is critical.

With the increasing global demand for net-zero carbon emissions, actions to address climate change have gained momentum among policymakers and the public. The urgent need for a sustainable economy is underscored by the mounting waste crisis in landfills and oceans. However, the proliferation of distributed electronic devices poses a significant challenge due to the resulting electronic waste. To combat this issue, the development of sustainable and environmentally friendly materials for these devices is imperative. Cellulose, an abundant and CO2-neutral substance with a long history of diverse applications, holds great potential. By integrating electrically interactive components with cellulosic materials, innovative biobased composites have been created, enabling the fabrication of bulk electroactive paper and the establishment of new, potentially more sustainable manufacturing processes for electronic devices. This review explores recent advances in bulk electroactive paper, including the fundamental interactions between its constituents, manufacturing techniques, and large-scale applications in the field of electronics. Furthermore, it addresses the importance and challenges of scaling up production of electroactive paper, highlighting the need for further research and development.

The need for achieving sustainable technologies has encouraged research on renewable and biodegradable materials for novel products that are clean, green, and environmentally friendly. Nanocellulose (NC) has many attractive properties such as high mechanical strength and flexibility, large specific surface area, in addition to possessing good wet stability and resistance to tough chemical environments. NC has also been shown to easily integrate with other materials to form composites. By combining it with conductive and electroactive materials, many of the advantageous properties of NC can be transferred to the resulting composites. Conductive polymers, in particular poly(3,4-ethylenedioxythiophene:poly(styrene sulfonate) (PEDOT:PSS), have been successfully combined with cellulose derivatives where suspensions of NC particles and colloids of PEDOT:PSS are made to interact at a molecular level. Alternatively, different polymerization techniques have been used to coat the cellulose fibrils. When processed in liquid form, the resulting mixture can be used as a conductive ink. This review outlines the preparation of NC/PEDOT:PSS composites and their fabrication in the form of electronic nanopapers, filaments, and conductive aerogels. We also discuss the molecular interaction between NC and PEDOT:PSS and the factors that affect the bonding properties. Finally, we address their potential applications in energy storage and harvesting, sensors, actuators, and bioelectronics. 

In the context of three-dimensional (3D) cell culture and tissue engineering, 3D printing is a powerful tool for customizing in vitro 3D cell culture models that are critical for understanding the cell-matrix and cell-cell interactions. Cellulose nanofibril (CNF) hydrogels are emerging in constructing scaffolds able to imitate tissue in a microenvironment. A direct modification of the methacryloyl (MA) group onto CNF is an appealing approach to synthesize photocross-linkable building blocks in formulating CNF-based bioinks for light-assisted 3D printing; however, it faces the challenge of the low efficiency of heterogenous surface modification. Here, a multistep approach yields CNF methacrylate (CNF-MA) with a decent degree of substitution while maintaining a highly dispersible CNF hydrogel, and CNF-MA is further formulated and copolymerized with monomeric acrylamide (AA) to form a super transparent hydrogel with tuneable mechanical strength (compression modulus, approximately 5-15 kPa). The resulting photocurable hydrogel shows good printability in direct ink writing and good cytocompatibility with HeLa and human dermal fibroblast cell lines. Moreover, the hydrogel reswells in water and expands to all directions to restore its original dimension after being air-dried, with further enhanced mechanical properties, for example, Young’s modulus of a 1.1% CNF-MA/1% PAA hydrogel after reswelling in water increases to 10.3 kPa from 5.5 kPa.

To model complex biological tissue in vitro, a specific layout for the position and numbers of each cell type isnecessary. Establishing such a layout requires manual cell placement in three dimensions (3D) with micrometricprecision, which is complicated and time-consuming. Moreover, 3D printed materials used in compartmentalizedmicrofluidic models are opaque or autofluorescent, hindering parallel optical readout and forcing serial charac-terization methods, such as patch-clamp probing. To address these limitations, we introduce a multi-level co-culture model realized using a parallel cell seeding strategy of human neurons and astrocytes on 3D structuresprinted with a commercially available non-autofluorescent resin at micrometer resolution. Using a two-stepstrategy based on probabilistic cell seeding, we demonstrate a human neuronal monoculture that forms net-works on the 3D printed structure and can establish cell-projection contacts with an astrocytic-neuronal co-cultureseeded on the glass substrate. The transparent and non-autofluorescent printed platform allows fluorescence-based immunocytochemistry and calcium imaging. This approach provides facile multi-level compartmentaliza-tion of different cell types and routes for pre-designed cell projection contacts, instrumental in studying complextissue, such as the human brain.

Organic mixed ionic-electronic conductors are promising materials for interfacing and monitoring biological systems, with the aim of overcoming current challenges based on the mismatch between biological materials and convectional inorganic conductors. The conjugated polymer/polyelectrolyte complex poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT/PSS) is, up to date, the most widely used polymer for in vitro or in vivo measurements in the field of organic bioelectronics. However, PEDOT/PSS organic electrochemical transistors (OECTs) are limited by depletion mode operation and lack chemical groups that enable synthetic modifications for biointerfacing. Recently introduced thiophene-based polymers with oligoether side chains can operate in accumulation mode, and their chemical structure can be tuned during synthesis, for example, by the introduction of hydroxylated side chains. Here, we introduce a new thiophene-based conjugated polymer, p(g42T-T)-8% OH, where 8% of the glycol side chains are functionalized with a hydroxyl group. We report for the first time the compatibility of conjugated polymers containing ethylene glycol side chains in direct contact with cells. The additional hydroxyl group allows covalent modification of the surface of polymer films, enabling fine-tuning of the surface interaction properties of p(g42T-T)-8% OH with biological materials, either hindering or promoting cell adhesion. We further use p(g42T-T)-8% OH to fabricate the OECTs and demonstrate for the first time the monitoring of epithelial barrier formation of Caco-2 cells in vitro using accumulation mode OECTs. The conjugated polymer p(g42T-T)-8% OH allows organic-electronic-based materials to be easily modified and optimized to interface and monitor biological systems.

A contact-active antibacterial approach based on the physical adsorption of a cationic polyelectrolyte onto the surface of a cellulose material is today regarded as an environment-friendly way of creating antibacterial surfaces and materials. In this approach, the electrostatic charge of the treated surfaces is considered to be an important factor for the level of bacteria adsorption and deactivation/killing of the bacteria. In order to clarify the influence of surface charge density of the cellulose on bacteria adsorption as well as on their viability, bacteria were adsorbed onto cellulose model surfaces, which were modified by physically adsorbed cationic polyelectrolytes to create surfaces with different positive charge densities. The surface charge was altered by the layer-by-layer (LbL) assembly of cationic polyvinylamine (PVAm)/anionic cellulose nanofibril/PVAm onto the initially differently charged cellulose model surfaces. After exposing the LbL-treated surfaces to Escherichia coli in aqueous media, a positive correlation was found between the adsorption of bacteria as well as the ratio of nonviable/viable bacteria and the surface charge of the LbL-modified cellulose. By careful colloidal probe atomic force microscopy measurements, it was estimated, due to the difference in surface charges, that interaction forces at least 50 nN between the treated surfaces and a bacterium could be achieved for the surfaces with the highest surface charge, and it is suggested that these considerable interaction forces are sufficient to disrupt the bacterial cell wall and hence kill the bacteria.

While strong water association with cellulose in plant cell walls and man-made materials is well-established, its molecular scale aspects are not fully understood. The thermodynamic consequences of having water molecules located at the microfibril-microfibril interfaces in cellulose fibril aggregates are therefore analyzed by molecular dynamics simulations. We find that a thin layer of water molecules at those interfaces can be in a state of thermal equilibrium with water surrounding the fibril aggregates because such an arrangement lowers the free energy of the total system. The main reason is enthalpic: water at the microfibril- microfibril interfaces enables the cellulose surface hydroxyls to experience a more favorable electrostatic environment. This enthalpic gain overcomes the entropic penalty from strong immobilization of water molecules. Hence, those particular water molecules stabilize the cellulose fibril aggregates, akin to the role of water in some proteins. Structural and functional hypotheses related to this finding are presented.

Designing materials for electrochemical energy storage with short charging times and high charge capacities is a longstanding challenge. The fundamental difficulty lies in incorporating a high density of redox couples into a stable material that can efficiently conduct both ions and electrons. We report all-organic, fused aromatic materials that store up to 310 mAh g−1 and charge in as little as 33 s. This performance stems from abundant quinone/imine functionalities that decorate an extended aromatic backbone, act as redox-active sites, engage in hydrogen bonding, and enable a delocalized high-rate energy storage with stability upon cycling. The extended conjugation and hydrogen-bonding-assisted bulk charge storage contrast with the surface-confined or hydration-dependent behavior of traditional inorganic electrodes.

We reveal here the construction of Ni-based metal-organic frameworks (MOFs) and conjugated coordination polymers (CCPs) with different structural dimensionalities, including closely pi-stacked 1D chains (Ni-1D), aggregated 2D layers (Ni-2D), and a 3D framework (Ni-3D), based on 2,3,5,6-tetraamino-1,4-hydroquinone (TAHQ) and its various oxidized forms. These materials have the same metal-ligand composition but exhibit distinct electronic properties caused by different dimensionalities and supramolecular interactions between SBUs, ligands, and structural motifs. The electrical conductivity of these materials spans nearly 8 orders of magnitude, approaching 0.3 S/cm.

Nucleic Acid Amplification Tests (NAATs) with PCR technology to amplify DNA, are the golden standard for infectious disease diagnostics, but they require benchtop instruments and trained users to be performed. For this reason, we all had to send PCR test to centralized laboratories during the Covid-19 pandemic. A year into the pandemic, home-based antigen paper-based tests became available for Covid, but these were not as sensitive, so PCR tests had to be used still. This development emphasized the need for technologies that enable NAATs with superior sensitivity to be performed at home. There are three technological advanced that could make such tests possible: 1)  Paper based devices, called paper microfluidics, have been developed to enable more advanced steps of testing without laboratory equipment. These paper-based system incorporate advanced functionality and multiple reaction steps. 2) New DNA amplification techniques, called isothermal amplification, have been developed which, contrary to PCR, can be run without a thermocycler, enabling DNA amplification to be carried out even inside a paper.  3) Several methods to detect DNA have been shown using paper.

One step that is still largely unsolved in NAATs is the sample preparation step, hindering the development of fully paper-based NAATs. In sample preparation, nucleic acids are extracted from bacteria or virus, usually using reagents harmful to DNA amplification. These steps are thereofore complicated and require several washing steps and heating, and are therefore difficult to integrate into paper.

In this thesis, we used a simple, cost-effective, and scalable method to incorporate sample preparation in paper, thus taking NAATs towards point of care. We solve this problem by immobilizing enzymes that are used for sample preparation on nitrocellulose paper. The immobilized enzymes remain functional and can be used for biochemical reactions, while they are strongly bound to the paper. This method enables the separation of these enzymes from the sample, protecting downstream sensitive reactions of DNA amplification and eliminates the need for high temperature deactivation or washing steps. Specifically, we show that the enzyme achromopeptidase can do cell lysis from the Staphylococcus epidermidis bacteria, a common pathogenic gram-positive bacterium, and use its DNA in further reaction to perform a sample-to-answer paper-based NAAT. These NAATs employed a low temperature amplification step called Recombinase Polymerase Amplification (RPA) and DNA detection with a lateral flow strip.

We further show the enzyme proteinase K, also immobilized on paper, can digest RNase in saliva samples, an enzyme that breaks down RNA leading to false-negative results. This results enabled an easy sample preparation step towards saliva viral DNA self-testing.

Finally, in this work we developed a paper microfluidic system that can carry out an enzyme-linked oligonucleotide assay, which demonstrated much higher sensitivity in detecting amplified DNA than conventional lateral flow assays. In summary, these results provide solutions towards high-performing, affordable and instrument-free paper-based NAATs home-testing.

Enzymes are the cornerstone of modern biotechnology. Achromopeptidase (ACP) is a well-known enzyme that hydrolyzes a number of proteins, notably proteins on the surface of Gram-positive bacteria. It is therefore used for sample preparation in nucleic acid tests. However, ACP inhibits DNA amplification which makes its integration difficult. Heat is commonly used to inactivate ACP, but it can be challenging to integrate heating into point-of-care devices. Here, we use recombinase polymerase amplification (RPA) together with ACP, and show that when ACP is immobilized on nitrocellulose paper, it retains its enzymatic function and can easily and rapidly be activated using agitation. The nitrocellulose-bound ACP does, however, not leak into the solution, preventing the need for deactivation through heat or by other means. Nitrocellulose-bound ACP thus opens new possibilities for paper-based Point-of-Care (POC) devices.

Abstract: Industrial production of low-charge microfibrillated cellulose (MFC) typically results in wide fibril size distributions. This polydispersity influences viscosity, overall colloidal stability, and rheological properties of MFC suspensions and gels in aqueous systems. In this work, a systematic rheological analysis is performed for industrially prepared MFC and fractions of different size distributions. Gel formation and flow characteristics (e.g., shear-thinning) of each fraction are examined under neutral and acidic conditions and compared with the unfractionated MFC suspension. The effects of size, aspect ratio, and surface charge on the rheology of semi-dilute MFC suspensions are discussed. The results demonstrate that particle size and aspect ratio distribution control the viscoelasticity and shear-thinning properties of MFC suspensions. An increased fraction of small diameter nanofibrils, by ex situ addition of the fine particles with high aspect ratio or removal of the coarsest particles (with lower aspect ratio) by fractionation, significantly enhances the storage modulus and the yield stress of the complex mixture, compared to the properties of the coarser fractions. New insights are also reported on the tailoring of the rheology of highly polydisperse fibrillar mixtures, where the rheological contributions of each fraction are discussed. Graphic abstract: [Figure not available: see fulltext.].

In the field of polymer reinforcement, it is important to understand the interactions involved between the polymer matrix and the reinforcing component. This paper is a contribution to the fundamental understanding of the adhesion mechanisms involved in natural fibre reinforced composites. We report on the use of the colloidal probe technique for the assessment of the adhesion behaviour between poly(lactic acid) microspheres and embedded cross-sections of regenerated lignocellulosic fibres. These fibres consisted of tailored mixtures of cellulose, lignin and xylan, the amount of which was determined beforehand. The influence of the chemical composition of the fibres on the adhesion behaviour was studied in ambient air and in dry atmosphere. In ambient air, capillary forces resulted in larger adhesion between the sphere and the fibres. Changing the ambient medium to a dry nitrogen atmosphere allowed reducing the capillary forces, leading to a drop in the adhesion forces. Differences between fibres of distinct chemical compositions could be measured only on freshly cut surfaces. Moreover, the surface energy of the fibres was assessed by inverse gas chromatography. Compared to fibres containing solely cellulose, the presence of lignin and/or hemicellulose led to higher adhesion and lower surface energy, suggesting that these chemicals could serve as natural coupling agents between hydrophobic and hydrophilic components.

The development of sustainable and renewable materials is paramount in today’s society. As the most abundant biopolymer on Earth, cellulose from cellulose-rich fibres is an excellent alternative for advanced and innovative material solutions. Nonetheless, competing with the impressive material properties and the low manufacturing costs of fossil-based plastics imposes great challenges. To increase the potential of cellulose fibres in a broader set of applications, the material properties of cellulose need to be tuned depending on the application. An in-depth study of the fibre structure and the application of different tailoring techniques is required to induce tailoring of the physical and chemical properties of the cellulose fibre materials. 

This thesis focuses on the structure-property relationship of fibrillar hydrogel networks as model structures for the delignified wet-fibre wall. First, a mathematical framework was developed to describe the characteristics of the swelling and mechanical behaviour of anisotropic fibrillar structures, considering the fibril aspect ratio, surface chemistry of the fibrils, and electrolyte concentration in the system. A chemical functionalisation was then introduced to the fibrillar structure, which provided the CNFs with colloidal stability and the ability to participate in free radical polymerisation with monomers and telechelic oligomers. As a result, fibrillar networks were crosslinked with flexible polymer links that provided the network with different mechanical and chemical properties. Additionally, by tailoring the molecular weight of the crosslinks, the ionic strength of the solution, and even the aspect ratio of the fibrils, the mechanical properties of the network were tuned to be either stiffer or more ductile. 

Finally, an innovative and more sustainable approach was developed to introduce charge and alkene functionality to the fibres. Following the lessons learned from the CNF model investigations, a polymerisation approach was developed in the presence of functionalised fibres. The polymers were grown from the fibre wall, followed by radical crosslinking to create strong Fibre reinforced hydrogel structures. Depending on the application, the method can be easily applied to introduce other types of molecules and functionalities to the fibres and tailor the properties of the fibres to suit a wide range of applications.

The high structural anisotropy and colloidal stability of cellulose nanofibrils' enable the creation of self-standing fibrillar hydrogel networks at very low solid contents. Adding methacrylate moieties on the surface of TEMPO oxidized CNFs allows the formation of more robust covalently crosslinked networks by free radical polymerization of acrylic monomers, exploiting the mechanical properties of these networks more efficiently. This technique yields strong and elastic networks but with an undefined network structure. In this work, we use acrylate-capped telechelic polymers derived from the step-growth polymerization of PEG diacrylate and dithiothreitol to crosslink methacrylated TEMPO-oxidized cellulose nanofibrils (MATO CNF). This combination resulted in flexible and strong hydrogels, as observed through rheological studies, compression and tensile loading. The structure and mechanical properties of these hydrogel networks were found to depend on the dimensions of the CNFs and polymer crosslinkers. The structure of the networks and the role of individual components were evaluated with SAXS (Small-Angle X-ray Scattering) and photo-rheology. A thorough understanding of hybrid CNF/polymer networks and how to best exploit the capacity of these networks enable further advancement of cellulose-based materials for applications in packaging, soft robotics, and biomedical engineering.