| 1. |
- Chen, Chao, 1986-
(författare)
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Development of Non-leaching Antibacterial Approaches on Cellulose-based Substrates and Their Mechanisms
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The layer-by-layer (LbL) technique is becoming a powerful tool that has been applied in many surface coatings and functionalizations in recent years. It has many advantages including a fast and mild process, the flexibility of choice of substrate, and the easiness to scale-up. Novel antibacterial materials can be achieved using this technique, by immobilizing selected antibacterial agents on surfaces of desired substrates. An ideal antibacterial agent, a cationic polyelectrolyte, can be LbL-deposited onto the surfaces in mono or multi layers, make the surfaces lethal to the bacteria due to their positive charge. This approach is able not only to effectively control the spreading of bacteria but also to minimize bacterial resistance as well as the environmental impact.Cellulose fibres modified by different cationic polyelectrolytes including PDADMAC, PAH, PVAm as either monolayer or multilayer assembled with PAA using LbL deposition have shown more than 99.99 % bacterial removal as well as the inhibition of bacterial growth. Among these modifications, two layers of PVAm assembled with one layer of PAA have shown the highest antibacterial efficiency due to the highest adsorbed amount and charge density. Secondly, PAA was replaced by a bio-based cellulose nano-fibril (CNF), as a middle layer between two layers of PVAm, which decreases the carbon-footprint and expands the possibility of using LbL technique in antibacterial applications, since the LbL technique can be used long as the alternate layers are oppositely charged. The fibres modified with this approach have shown similar and even better antibacterial properties than those of PAA.To develop the antibacterial approach using LbL on cellulose fibres, it is also essential to understand the antibacterial mechanism. It was found that the charge density and surface structures are two important factors affecting bacterial adhesion and the bactericidal effect. To study this, different charged cellulose model surfaces were made by coating oxidized, regenerated cellulose followed by PVAm/CNF/PVAm LbL deposition, and a better antibacterial effect was observed on the higher charged surface. By calculating the force between the bacteria and charged surface, it was suggested that a higher interaction due to the higher surface charge causes a large stress on the bacterial cell wall which leads to the disruption of the bacteria. To further improve the bactericidal effect, the flat surfaces were patterned with micro and nano structures using a femtosecond laser technique. The weakening of the bacterial cell wall caused by the charged surface makes the bacteria more vulnerable and easier to disrupt. This approach has been shown to be valid on both Gram-positive S. aureus, and Gram-negative E. coli. The effect was greater on E. coli with a weaker membrane structure and higher surface potential, which shows that the antibacterial mechanism is a physical disrupt of the bacterial cell.
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| 2. |
- Czibula, Caterina, et al.
(författare)
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Design of Friction, Morphology, Wetting, and Protein Affinity by Cellulose Blend Thin Film Composition
- 2019
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Ingår i: Frontiers in Chemistry. - : Frontiers Media SA. - 2296-2646. ; 7:MAY
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (FIPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption.
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| 3. |
- Gabriel, Martin, et al.
(författare)
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Influence of steam jet-cooking on the rheological properties of dry and wet cationized starch solutions
- 2022
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 285
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Tidskriftsartikel (refereegranskat)abstract
- Steam jet-cooking allows for efficient dissolution of cationic starch in paper production as it operates above the boiling point of water at elevated pressures. However, the processes involved during jet-cooking and its con- sequences on dissolution and finally paper properties have not been fully resolved so far. As cationic starch is the most important paper additive in the wet end, any energy or material savings during dissolution will enhance the ecologic and economic performance of a paper mill. Here, we address the topic of solubilization of four different industrially relevant cationic starches processed via steam jet-cooking. We showcase that rheology is a useful tool to assess the solubility state of starches. Some starches featured liquid-like rheological behavior (loss moduli, G", greater than storage moduli, G') in linear viscoelastic tests and anti-thixotropic behavior in hysteresis loop tests. In contrast, cationic corn starches exhibited gel-like behavior (G' > G′′) and negligible hysteresis directly after cooking.
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| 4. |
- Gösweiner, Christian, et al.
(författare)
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Tuning Nuclear Quadrupole Resonance : A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents
- 2018
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Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 8:2
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin transitions is fulfilled. This effect could be utilized as a frequency selective mechanism in novel, responsive T-1 shortening contrast agents (CAs) for magnetic resonance imaging (MRI). In particular, the proposed contrast mechanism depends on the applied external flux density-a property that can be exploited by special field-cycling MRI scanners. For the design of efficient CA molecules, exhibiting narrow and pronounced peaks in the proton T-1 relaxation dispersion, the nuclear quadrupole resonance (NQR) properties, as well as the spin dynamics of the system QN-H-1, have to be well understood and characterized for the compounds in question. In particular, the energy-level structure of the QN is a central determinant for the static flux densities at which the contrast enhancement appears. The energy levels depend both on the QN and the electronic environment, i.e., the chemical bonding structure in the CA molecule. In this work, the NQR properties of a family of promising organometallic compounds containing Bi-209 as QN have been characterized. Important factors like temperature, chemical structure, and chemical environment have been considered by NQR spectroscopy and ab initio quantum chemistry calculations. The investigated Bi-aryl compounds turned out to fulfill several crucial requirements: NQR transition frequency range applicable to clinical 1.5- and 3 T MRI systems, low temperature dependency, low toxicity, and tunability in frequency by chemical modification.
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| 5. |
- Hobisch, Mathias, et al.
(författare)
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How cellulose nanofibrils and cellulose microparticles impact paper strength - A visualization approach
- 2021
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Cellulosic nanomaterials are in the focus of academia and industry to realize light-weight biobased materials with remarkable strength. While the effect is well known, the distribution of these nanomaterials are less explored, particularly for paper sheets. Here, we explore the 3D distribution of micro and nanosized cellulosic particles in paper sheets and correlate their extent of fibrillation to the distribution inside the sheets and subsequently to paper properties. To overcome challenges with contrast between the particles and the matrix, we attached probes on the cellulose nano/microparticles, either by covalent attachment of fluorescent dyes or by physical deposition of cobalt ferrite nanoparticles. The increased contrast enabled visualization of the micro and nanosized particles inside the paper matrix using multiphoton microscopy, X-ray microtomography and SEM-EDX. The results indicate that fibrillary fines enrich at pores and fiber-fiber junctions, thereby increasing the relative bonded area between fibers to enhance paper strength while CNF seems to additionally form an inner 3D network.
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| 6. |
- Kádár, Roland, 1982, et al.
(författare)
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Cellulose Nanocrystal Liquid Crystal Phases: Progress and Challenges in Characterization Using Rheology Coupled to Optics, Scattering, and Spectroscopy
- 2021
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 15:5, s. 7931-7945
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Forskningsöversikt (refereegranskat)abstract
- Cellulose nanocrystals (CNCs) self-assemble and can be flow-assembled to liquid crystalline orders in a water suspension. The orders range from nano- to macroscale with the contributions of individual crystals, their micron clusters, and macroscopic assemblies. The resulting hierarchies are optically active materials that exhibit iridescence, reflectance, and light transmission. Although these assemblies have the potential for future renewable materials, details about structures on different hierarchical levels that span from the nano- to the macroscale are still not unraveled. Rheological characterization is essential for investigating flow properties; however, bulk material properties make it difficult to capture the various length-scales during assembly of the suspensions, for example, in simple shear flow. Rheometry is combined with other characterization methods to allow direct analysis of the structure development in the individual hierarchical levels. While optical techniques, scattering, and spectroscopy are often used to complement rheological observations, coupling them in situ to allow simultaneous observation is paramount to fully understand the details of CNC assembly from liquid to solid. This Review provides an overview of achievements in the coupled analytics, as well as our current opinion about opportunities to unravel the structural distinctiveness of cellulose nanomaterials.
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| 7. |
- Laukkonen Ravn, Jonas, 1987, et al.
(författare)
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Engineering Saccharomyces cerevisiae for targeted hydrolysis and fermentation of glucuronoxylan through CRISPR/Cas9 genome editing
- 2024
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Ingår i: Microbial Cell Factories. - 1475-2859. ; 23:85
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Tidskriftsartikel (refereegranskat)abstract
- Background The abundance of glucuronoxylan (GX) in agricultural and forestry residual side streams positions it as a promising feedstock for microbial conversion into valuable compounds. By engineering strains of the widely employed cell factory Saccharomyces cerevisiae with the ability to directly hydrolyze and ferment GX polymers, we can avoid the need for harsh chemical pretreatments and costly enzymatic hydrolysis steps prior to fermentation. However, for an economically viable bioproduction process, the engineered strains must efficiently express and secrete enzymes that act in synergy to hydrolyze the targeted polymers. Results The aim of this study was to equip the xylose-fermenting S. cerevisiae strain CEN.PK XXX with xylanolytic enzymes targeting beechwood GX. Using a targeted enzyme approach, we matched hydrolytic enzyme activities to the chemical features of the GX substrate and determined that besides endo-1,4-β-xylanase and β-xylosidase activities, α-methyl-glucuronidase activity was of great importance for GX hydrolysis and yeast growth. We also created a library of strains expressing different combinations of enzymes, and screened for yeast strains that could express and secrete the enzymes and metabolize the GX hydrolysis products efficiently. While strains engineered with BmXyn11A xylanase and XylA β-xylosidase could grow relatively well in beechwood GX, strains further engineered with Agu115 α-methyl-glucuronidase did not display an additional growth benefit, likely due to inefficient expression and secretion of this enzyme. Co-cultures of strains expressing complementary enzymes as well as external enzyme supplementation boosted yeast growth and ethanol fermentation of GX, and ethanol titers reached a maximum of 1.33 g L− 1 after 48 h under oxygen limited condition in bioreactor fermentations. Conclusion This work underscored the importance of identifying an optimal enzyme combination for successful engineering of S. cerevisiae strains that can hydrolyze and assimilate GX. The enzymes must exhibit high and balanced activities, be compatible with the yeast’s expression and secretion system, and the nature of the hydrolysis products must be such that they can be taken up and metabolized by the yeast. The engineered strains, particularly when co-cultivated, display robust growth and fermentation of GX, and represent a significant step forward towards a sustainable and cost-effective bioprocessing of GX-rich biomass. They also provide valuable insights for future strain and process development targets.
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| 8. |
- Nypelö, Tiina, 1982, et al.
(författare)
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Review: Periodate oxidation of wood polysaccharides—Modulation of hierarchies
- 2021
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 252
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Forskningsöversikt (refereegranskat)abstract
- Periodate oxidation of polysaccharides has transitioned from structural analysis into a modification method for engineered materials. This review summarizes the research on this topic. Fibers, fibrils, crystals, and molecules originating from forests that have been subjected to periodate oxidation can be crosslinked with other entities via the generated aldehyde functionality, that can also be oxidized or reduced to carboxyl or alcohol functionality or used as a starting point for further modification. Periodate-oxidized materials can be subjected to thermal transitions that differ from the native cellulose. Oxidation of polysaccharides originating from forests often features oxidation of structures rather than liberated molecules. This leads to changes in macro, micro, and supramolecular assemblies and consequently to alterations in physical properties. This review focuses on these aspects of the modulation of structural hierarchies due to periodate oxidation.
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| 9. |
- Orzan, Eliott, 1995, et al.
(författare)
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Elucidation of cellulose phosphorylation with phytic acid
- 2024
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Ingår i: Industrial Crops and Products. - 0926-6690. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- The worldwide ban on the use of halogenated flame retardants has accelerated the development of non-toxic alternatives from natural feedstock, such as phytic acid. The fire suppressing mechanisms which acidic phosphates impart on cellulosic materials rivals most solutions yet promotes cellulose hydrolysis and degradation. Current attempts to prevent degradation that results from the acid hydrolysis and to improve flame retardancy rely on the use of catalysts without evaluating the effect of curing temperature on cellulose phosphorylation. In this study, the fundamental condensation reaction between cellulose and phytic acid reveals how varying curing temperature affects the phosphorylation and degradation of cellulosic structures. Curing a low concentration of phytic acid on cellulose at 160 °C was shown to promote the phosphorylation of cellulose over the formation of oligo-phosphates. The addition of phytic acid and rise in curing temperature degraded non-crystalline moieties and improved thermo-oxidative stability credit to the char layer formation of the phosphorylated cellulose structure. Increased phosphorus content expectedly led to improved thermal stability, yet cross-linking of phytic acid to cellulose overcame the need for increased phytic acid concentrations. This work thus provides the basis for the application of heat-curing phytic acid at low concentrations to target cellulose fire-retardancy using a chemical catalyst-free and solvent-free approach.
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| 10. |
- Palasingh, Chonnipa, 1992, et al.
(författare)
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Morphology and swelling of thin films of dialcohol xylan
- 2023
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 313
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Tidskriftsartikel (refereegranskat)abstract
- Polysaccharides are excellent network formers and are often processed into films from water solutions. Despite being hydrophilic polysaccharides, the typical xylans liberated from wood are sparsely soluble in water. We have previously suggested that an additional piece to the solubilization puzzle is modification of the xylan backbone via oxidative cleavage of the saccharide ring. Here, we demonstrate the influence of the degree of modification, i.e., degree of oxidation (DO) on xylan solubilization and consequent film formation and stability. Oxidized and reduced wood xylans (i.e., dialcohol xylans) with the highest DO (77 %) within the series exhibited the smallest hydrodynamic diameter (dh) of 60 nm in dimethylsulfoxide (DMSO). We transferred the modified xylans into films credit to their established solubility and then quantified the film water interactions. Dialcohol xylans with intermediate DOs (42 and 63 %) did not form continuous films. The films swelled slightly when subjected to humidity. However, the film with the highest DO demonstrated a significant moisture uptake that depended on the film mass and was not observed with the other modified grades or with unmodified xylan.
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