Hannes Orelma

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.

High velocity dry spinning of nanofibrillated cellulose (CNF) filaments on an adhesion controlled surface with low friction

A new process for preparing thin cellulose nanofibril (CNF) filaments (thickness of 16xa0µm) was investigated by utilizing the dry spinning approach. In the process, CNF hydrogel was extruded through a fine nozzle onto an adhesion controlled capstan (drum) with low friction (slippery surface) at a speed of up to 11xa0m/s. The utilized capstan enables excellent line speed control when the slippery surface is applied, and prevents drying shrinkage of the spun filaments. The mechanical properties of prepared filaments can be optimized with the stretch ratio, the ratio of the speed of the drum surface, and the CNF jet flow. The developed method allows for manufacturing thin CNF filaments with an elevated spinning rate in a more controlled manner.

Retention of lysozyme activity by physical immobilization in nanocellulose aerogels and antibacterial effects

Aerogels prepared from aqueous dispersions of anionic and cationic cellulose nanofibrils (CNFs) were investigated as solid supports for enzymes and silver nanoparticles and to elicit a sustained antibacterial effect. The imparted stabilization in dry conditions was studied with aerogels that were cast after mixing the enzymes with CNFs followed by dehydration (freeze-drying). The activity of lysozyme immobilized in the given CNF system was analyzed upon storage in liquid and air media. In contrast with aqueous solutions of free, unbound enzyme, which lost activity after the first day, the enzyme immobilized physically in unmodified and cationic CNF presented better stability (activity for a longer time). However, the enzyme activity was reduced in the case of anionic CNF, which was prepared by TEMPO-mediated oxidation (TO-CNF). Both humidity and temperature reduced the stability of the enzyme immobilized in the respective CNF aerogel. The antibacterial activity of CNF aerogels carrying lysozyme was also tested against gram-negative and gram-positive bacteria. The results were compared with those obtained from CNF systems loaded with silver nanoparticles (AgNP) after in situ synthesis via UV reduction. Storage in cold or dry conditions preserved the activity and antibacterial performance of enzyme-loaded CNF aerogels. As expected, the lysozyme-containing aerogels showed lower inhibition than the AgNP-containing aerogel. In this latter case, the antibacterial activity depended on the concentration and size of the nanoparticles. Compared to unmodified CNF and TO-CNF, the aerogels prepared with cationic CNF, loaded with either lysozyme or AgNPs, showed remarkably better antibacterial activity. Similar experiments were conducted with horseradish peroxidase, which confirmed, to different degrees, the observations derived from the lysozyme systems. Overall, the results indicate that non-toxic and biodegradable CNF is a suitable support for bio-active materials and is effective in protecting and retaining enzymatic and antibacterial activities.

Mechanically ground softwood fines as a raw material for cellulosic applications

Utilization of mechanically manufactured lignocellulosic fines (LCNFs) was investigated in making filaments and films. The LCNFs particles were prepared by using a mechanical grinding method with a w-profile grinding stone that produces mostly fines with dimensions in the micrometer scale. The chemical and elemental composition of the w-stone ground LCNFs particles was investigated. It was found that the mechanically manufactured material exhibited the chemical structure of native wood. The LCNFs particles had an anionic surface charge making them colloidally semi-stable in water. The short length of the fines particles prevents their effective mechanical entanglement, which sets some limitations on preparation of filaments and films. Filament manufacturing required the use of a composite approach with carboxymethyl cellulose (CMC) as a binder polymer. The filament was manufactured by using dry-jet wet spinning with aluminium sulfate crosslinking. The chemical composition, crosslinking mechanism, and mechanical properties of the composite filaments were investigated. The composite approach with CMC was also used to prepare composite films with good mechanical performance. The investigated LCNFs material could be utilized in all-lignocomposite applications with cellulose derivatives, where biodegradability and biobased characteristics are desired properties.

Understanding the interactions of cellulose fibres and deep eutectic solvent of choline chloride and urea

A deep eutectic solvent composed of choline chloride (ChCl) and urea has been recently introduced as a promising cellulose compatible medium that enables e.g. fibre spinning. This paper clarifies the influence of such a solvent system on the structure and chemical composition of the cellulosic pulp fibres. Special emphasis was placed on the probable alterations of the chemical composition due to the dissolution of the fibre components and/or due to the chemical derivatisation taking place during the DES treatment. Possible changes in fibre morphology were studied with atomic force microscopy and scanning electron microscopy. Chemical compositions of pulp fibres were determined from the carbohydrate content, and by analysing the elemental content. Detailed structural characterisation of the fibres was carried out using spectroscopic methods; namely X-Ray Photoelectron Spectroscopy, solid state Nuclear Magnetic Resonance and Raman Spectroscopy. No changes with respect to fibre morphology were revealed and negligible changes in the carbohydrate composition were noted. The most significant change was related to the nitrogen content of the pulp after the DES treatment. Comprehensive examination using spectroscopic methods revealed that the nitrogen originated from strongly bound ChCl residuals that could not be removed with a mild ethanol washing procedure. According to Raman spectroscopic data and methylene blue adsorption tests, the cationic groups of ChCl seems to be attached to the anionic groups of pulp by electrostatic forces. These findings will facilitate the efficient utilisation of DES as a cellulose compatible medium without significantly affecting the native fibre structure.

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.

Improving the mechanical properties of CNF films by NMMO partial dissolution with hot calender activation

Reinforcing of cellulose nanofibril (CNF) films by partial dissolution with N-methylmorpholine-N-oxide (NMMO) was investigated. The method investigated is composed of impregnation of CNF film with liquid solution of NMMO followed by dry heat activation. The heat activation of the impregnated film was carried out using a heated calendering nip, which enabled simultaneous heating and compression. The partial dissolution of cellulose by NMMO caused a significant increase in the transparency of CNF film due to the decrease of film porosity and increased surface smoothness. The dry strength of the reinforced film was increased from 122 up to 195xa0MPa. Furthermore, the wet strength of the reinforced film was up to 70% greater than the dry strength of pure CNF film. The changes in the fibrillar structure were investigated with topographical imaging (SEM and AFM) and spectroscopically using NMR and FTIR. No significant changes in the fibril structure or cellulose morphology were observed. Moreover, the treated film resisted significant water pressure, highlighting CNF film’s permanent water resistance. The partial dissolution process with NMMO was also capable of reinforcing a CNF composite film with macro scale structural elements (lyocell short-cut fibres). The strategy investigated is a robust and fast method to improve the mechanical properties of fibrillary cellulose films, allowing them utilization in applications where improved water resistance and fully cellulosic character are required properties.

Keratin-reinforced cellulose filaments from ionic liquid solutions

Cellulose-based filaments produced with ionic liquid-based processes have high application potential in textiles and composites to replace cotton fibres. These filaments already have unique properties that could be further improved with the addition of proteins. Keratin from poultry feathers is currently a low-value material that has potential as a renewable feedstock in material applications. In this study, cellulose filaments with chicken feather keratin were prepared by wet-spinning from an ionic liquid solution. Both keratin and cellulose were dissolved in [EMIM]AcO and spun into ethanol to regenerate cellulose and keratin and wash out the ionic liquid. The effect of keratin addition on the filament properties was investigated by microscopic, spectroscopic and strength analyses. It was observed that a small keratin addition into the cellulosic filaments improved the mechanical properties remarkably, whereas high keratin additions resulted in reduced mechanical performance. Keratin accumulation on the surface of the prepared filaments was observed. In addition, based on FTIR spectroscopy, it is likely that the morphology of cellulose changed from cellulose I to II and the β-sheets in feather keratin unfolded to unordered keratin upon dissolution and regeneration. The cellulose–protein filaments may find applications from areas where good biocompatibility and easy modifiability are required characteristics.

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.