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Publications (10 of 17) Show all publications
Larsson, P. A., Riazanova, A., Ciftci, G. C., Rojas, R., Ovrebo, H. H., Wågberg, L. & Berglund, L. (2019). Towards optimised size distribution in commercial microfibrillated cellulose: a fractionation approach. Cellulose (London), 26(3), 1565-1575
Open this publication in new window or tab >>Towards optimised size distribution in commercial microfibrillated cellulose: a fractionation approach
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2019 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, no 3, p. 1565-1575Article in journal (Refereed) Published
Abstract [en]

For the successful commercialisation of microfibrillated cellulose (MFC) it is of utmost importance to carefully characterise the constituent cellulose particles. This could for instance lead to the development of MFC grades with size distributions tailored for specific applications. Characterization of MFC is challenging due to the heterogeneous chemical and structural nature of MFC. This study describes a fractionation approach that combines two steps of physical sieving of larger particles and a final centrifugation step to separate out the smallest, colloidally stable particles, resulting in four distinctly different size fractions. The properties, such as size and charge, of each fraction were studied, as well as MFC filtration time, film formation, and film properties (mechanical and optical). It was found that virtually all surface charges, determined by polyelectrolyte adsorption, are located in the colloidally stable fraction of the MFC. In addition, the amount of available surface charges can be used as an estimate of the degree of fibrillation of the MFC. The partly fibrillated particles frequently displayed a branching, fringed morphology. Mechanical testing of films from the different fractions revealed that the removal of large particles may be more important for strength than achieving full fibrillation. Overall, this study demonstrates that by controlling the size distribution in MFC grades, property profiles including dewatering time to make films by filtration, rheology, film strength and optical transmittance could be optimised. [GRAPHICS] .

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Cellulose nanofibrils, Cellulose films, Fractionation, Microfibrillated cellulose, Nanocellulose, Nanopaper
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-247842 (URN)10.1007/s10570-018-2214-4 (DOI)000460617900011 ()2-s2.0-85059322104 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-21Bibliographically approved
Ohm, W., Rothkirch, A., Pandit, P., Koerstgens, V., Mueller-Buschbaum, P., Rojas, R., . . . Roth, S. V. (2018). Morphological properties of airbrush spray-deposited enzymatic cellulose thin films. Paper presented at 13th Coatings Science International Conference (COSI), JUN 26-30, 2017, Noordwijk, NETHERLANDS. JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, 15(4), 759-769
Open this publication in new window or tab >>Morphological properties of airbrush spray-deposited enzymatic cellulose thin films
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2018 (English)In: JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, ISSN 1945-9645, Vol. 15, no 4, p. 759-769Article in journal (Refereed) Published
Abstract [en]

We investigate the layer formation of enzymatic cellulose by airbrush spray coating on silicon oxide surfaces. The layer structure and morphology of enzymatic cellulose films in the thickness range between 86 nm and 2.1 A mu m is determined as a function of the spray coating procedures. For each spray coating step, layer buildup, surface topography, crystallinity as well as the nanoscale structure are probed with atomic force microscopy and surface-sensitive X-ray scattering methods. Without intermittent drying, the film thickness saturates; with intermittent drying, a linear increase in layer thickness with the number of spray pulses is observed. A closed cellulose layer was always observed. The crystallinity remains unchanged; the nanoscale structures show three distinct sizes. Our results indicate that the smallest building blocks increasingly contribute to the morphology inside the cellulose network for thicker films, showing the importance of tailoring the cellulose nanofibrils. For a layer-by-layer coating, intermittent drying is mandatory.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-232911 (URN)10.1007/s11998-018-0089-9 (DOI)000439757000011 ()2-s2.0-85046905803 (Scopus ID)
Conference
13th Coatings Science International Conference (COSI), JUN 26-30, 2017, Noordwijk, NETHERLANDS
Note

QC 20180808

Available from: 2018-08-08 Created: 2018-08-08 Last updated: 2018-08-08Bibliographically approved
Herrera, M., Thitiwutthisakul, K., Yang, X., Rujitanaroj, P.-o., Rojas, R. & Berglund, L. (2018). Preparation and evaluation of high-lignin content cellulose nanofibrils from eucalyptus pulp. Cellulose (London), 25(5), 3121-3133
Open this publication in new window or tab >>Preparation and evaluation of high-lignin content cellulose nanofibrils from eucalyptus pulp
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2018 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, no 5, p. 3121-3133Article in journal (Refereed) Published
Abstract [en]

High Klason lignin content (23 wt%) cellulose nanofibrils (LCNF) were successfully isolated from eucalyptus pulp through catalyzed chemical oxidation, followed by high-pressure homogenization. LCNFs had a diameter of ca. 13 nm according to AFM evaluation. Dense films were obtained through vacuum filtration (nanopaper) and subjected to different drying methods. When drying under heat and mild vacuum (93 degrees C, 95 kPa) a higher water contact angle, lower roughness and oxygen transmission rate were observed, compared to those drying at room temperature under compression conditions. DSC experiments showed difference in signals associated to T-g of LCNF compared to CNF produced from spruce bleached pulp through enzymatic pre-treatment. The LCNF-based nanopaper showed mechanical properties slightly lower than for those made from cellulose nanofibrils, yet with increased hydrophobicity. In summary, the high-lignin content cellulose nanofibrils proved to be a suitable material for the production of low oxygen permeability nanopaper, with chemical composition close to native wood.

Place, publisher, year, edition, pages
SPRINGER, 2018
Keywords
Lignocellulose nanofibrils, Oxygen barrier, Eucalyptus
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-228268 (URN)10.1007/s10570-018-1764-9 (DOI)000431788000028 ()2-s2.0-85045090612 (Scopus ID)
Note

QC 20180522

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2019-08-20Bibliographically approved
Li, Y., Fu, Q., Rojas, R., Yan, M., Lawoko, M. & Berglund, L. (2017). Lignin-Retaining Transparent Wood. ChemSusChem, 10(17), 3445-3451
Open this publication in new window or tab >>Lignin-Retaining Transparent Wood
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2017 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 17, p. 3445-3451Article in journal (Refereed) Published
Abstract [en]

Optically transparent wood, combining optical and mechanical performance, is an emerging new material for light-transmitting structures in buildings with the aim of reducing energy consumption. One of the main obstacles for transparent wood fabrication is delignification, where around 30wt% of wood tissue is removed to reduce light absorption and refractive index mismatch. This step is time consuming and not environmentally benign. Moreover, lignin removal weakens the wood structure, limiting the fabrication of large structures. A green and industrially feasible method has now been developed to prepare transparent wood. Up to 80wt% of lignin is preserved, leading to a stronger wood template compared to the delignified alternative. After polymer infiltration, a high-lignin-content transparent wood with transmittance of 83%, haze of 75%, thermal conductivity of 0.23WmK(-1), and work-tofracture of 1.2MJm(-3) (a magnitude higher than glass) was obtained. This transparent wood preparation method is efficient and applicable to various wood species. The transparent wood obtained shows potential for application in energy-saving buildings.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2017
Keywords
building materials, delignification, energy saving, lignin, wood
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-214873 (URN)10.1002/cssc.201701089 (DOI)000410136800018 ()2-s2.0-85029175474 (Scopus ID)
Note

QC 20171024

Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2018-02-26Bibliographically approved
Tummala, G. K., Joffre, T., Rojas, R., Persson, C. & Mihranyan, A. (2017). Strain-induced stiffening of nanocellulose-reinforced poly(vinyl alcohol) hydrogels mimicking collagenous soft tissues. Soft Matter, 13(21), 3936-3945
Open this publication in new window or tab >>Strain-induced stiffening of nanocellulose-reinforced poly(vinyl alcohol) hydrogels mimicking collagenous soft tissues
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2017 (English)In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 13, no 21, p. 3936-3945Article in journal (Refereed) Published
Abstract [en]

Soft tissues possess remarkable mechanical strength for their high water content, which is hard to mimic in synthetic materials. Here, we demonstrate how strain-induced stiffening in hydrogels plays a major role in mimicking the mechanical properties of collagenous soft tissues. In particular, nanocellulose reinforced polyvinyl alcohol (PVA) hydrogels of exceptionally high water content (90-93 wt%) are shown to exhibit collagen-like mechanical behavior typical for soft tissues. High water content and co-existence of both soft and rigid domains in the gel network are the main factors responsible for strain-induced stiffening. This observed effect due to the alignment of rigid components of the hydrogel is simulated through modeling and visualized through strain-induced birefringence experiments. Design parameters such as nanocellulose aspect ratio and solvent composition are also shown to be important to control the mechanical properties. In addition, owing to their transparency (90-95% at 550 nm) and hyperelastic properties (250-350% strain), the described hydrogels are promising materials for biomedical applications, especially in ophthalmology.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-210473 (URN)10.1039/c7sm00677b (DOI)000402744100012 ()28504291 (PubMedID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council Formas, 232-2014-202
Note

QC 20170705

Available from: 2017-07-05 Created: 2017-07-05 Last updated: 2017-07-05Bibliographically approved
Ingverud, T., Larsson, E., Hemmer, G., Rojas, R., Malkoch, M. & Carlmark, A. (2016). High water-content thermoresponsive hydrogels via electrostatic macrocrosslinking of cellulose nanofibrils. Journal of Polymer Science Part A: Polymer Chemistry, 54(21), 3415-3424
Open this publication in new window or tab >>High water-content thermoresponsive hydrogels via electrostatic macrocrosslinking of cellulose nanofibrils
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2016 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 54, no 21, p. 3415-3424Article in journal (Refereed) Published
Abstract [en]

Atom transfer radical polymerization (ATRP) has been utilized to synthesize tri- and star-block copolymers of poly(di(ethylene glycol)methyl ether methacrylate) (PDEGMA) and quaternized poly(2-(dimethylamino)ethyl methacrylate) (qPDMAEMA). The block copolymers, all with a minimum of two cationically charged blocks, were sequentially used for electrostatic macrocrosslinking of a dilute dispersion of anionic TEMPO-oxidized cellulose nanofibrils (CNF, 0.3 wt%), forming free-standing hydrogels. The cationic block copolymers adsorbed irreversibly to the CNF, enabling the formation of ionically crosslinked hydrogels, with a storage modulus of up to 2.9 kPa. The ability of the block copolymers to adsorb to CNF was confirmed by quartz crystal microbalance with dissipation monitoring (QCM-D) and infrared spectroscopy (FT-IR), and the thermoresponsive properties of the hydrogels were investigated by rheological stress and frequency sweep, and gravimetric measurements. This method was shown to be promising for the facile production of thermoresponsive hydrogels based on CNF.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
ATRP, cationic block copolymer, cellulose nanofibrils, hydrogels, thermoresponsive, Atom transfer radical polymerization, Block copolymers, Cellulose, Electrostatics, Ethylene, Ethylene glycol, Free radical reactions, Infrared spectroscopy, Nanofibers, Quartz crystal microbalances, 2-(dimethylamino)ethyl methacrylate, Cross-linked hydrogels, Gravimetric measurements, Quartz crystal microbalance with dissipation monitoring, Star block copolymer, Thermo-responsive, Thermo-responsive hydrogels
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-195220 (URN)10.1002/pola.28225 (DOI)000386657600003 ()2-s2.0-84988040360 (Scopus ID)
Note

QC 20161117

Available from: 2016-11-17 Created: 2016-11-02 Last updated: 2019-04-11Bibliographically approved
Huo, J., Rojas, R., Bohlin, J., Hilborn, J. & Gamstedt, E. K. (2014). Parametric elastic analysis of coupled helical coils for tubular implant applications: experimental characterization and numerical analysis.. Journal of The Mechanical Behavior of Biomedical Materials, 29(SI), 462-469
Open this publication in new window or tab >>Parametric elastic analysis of coupled helical coils for tubular implant applications: experimental characterization and numerical analysis.
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2014 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 29, no SI, p. 462-469Article in journal (Refereed) Published
Abstract [en]

Coupled helical coils show promising mechanical behavior to be used as tubular organ constructs, e.g., in trachea or urethra. They are potentially easy to manufacture by filament winding of biocompatible and resorbable polymers, and could be tailored for suitable mechanical properties. In this study, coupled helical coils were manufactured by filament winding of melt-extruded polycaprolactone, which was reported to demonstrate desired in vivo degradation speed matching tissue regeneration rate. The tensile and bending stiffness was characterized for a set of couple helical coils with different geometric designs, with right-handed and left-handed polymer helices fused together in joints where the filaments cross. The Young's modulus of unidirectional polycaprolactone filaments was characterized, and used as input together with the structural parameters of the coupled coils in finite element simulations of tensile loading and three-point bending of the coils. A favorable comparison of the numerical and experimental results was found, which paves way for use of the proposed numerical approach in stiffness design under reversible elastic conditions of filament wound tubular constructs.

Keywords
Coupled helical coils, Finite element simulation, Structural stiffness, Tubular implants
National Category
Mechanical Engineering Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-140873 (URN)10.1016/j.jmbbm.2013.09.026 (DOI)000330085700042 ()24211355 (PubMedID)2-s2.0-84887235432 (Scopus ID)
Note

QC 20140210

Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-12-06Bibliographically approved
López, A., Persson, C., Hilborn, J. & Rojas, R. (2013). Comparative characterization of oligomeric precursors intended for injectable implants. Polymers for Advanced Technologies, 24(1), 15-21
Open this publication in new window or tab >>Comparative characterization of oligomeric precursors intended for injectable implants
2013 (English)In: Polymers for Advanced Technologies, ISSN 1042-7147, E-ISSN 1099-1581, Vol. 24, no 1, p. 15-21Article in journal (Refereed) Published
Abstract [en]

The use of injectable materials is a simple approach for drug delivery and tissue repair, in, e. g. minimally invasive surgery applications. If these materials are used past their glass transition temperature and have a low viscosity, they will be able to flow while delivered in situ. Whether these materials are to be used as low viscosity drug carriers or further crosslinked for tissue repair, there is a need for a better understanding of their handling properties. In this study, oligo(trimethylene carbonate) (oTMC) and oligo[D, L-lactide-co-(epsilon-caprolactone)] (oDLLA-co-CL) of various molecular weights within a relevant injectability range were synthesized via ring-opening polymerization. The materials were comparatively characterized by H-1 NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and rheological measurements. After comparing the viscosities and molecular weights of the materials, it was concluded that oDLLA-co-CLs were, generally, better suited as an injectable in situ crosslinking network, whereas oTMCs were found to be better candidates as injectable drug carriers. This study provides useful data and guidelines on the use of these and other similar oligomers intended for injectable implants.

Keywords
oligomer(s), polyester(s), polycarbonate(s), rheology, injectable implant(s)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-124758 (URN)10.1002/pat.3042 (DOI)000312887500005 ()
Note

QC 20130813

Available from: 2013-07-30 Created: 2013-07-30 Last updated: 2017-12-06Bibliographically approved
Schizas, N., Rojas, R., Kootala, S., Andersson, B., Pettersson, J., Hilborn, J. & Hailer, N. P. (2013). Hyaluronic acid-based hydrogel enhances neuronal survival in spinal cord slice cultures from postnatal mice. Journal of biomaterials applications, 28(6), 825-836
Open this publication in new window or tab >>Hyaluronic acid-based hydrogel enhances neuronal survival in spinal cord slice cultures from postnatal mice
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2013 (English)In: Journal of biomaterials applications, ISSN 0885-3282, E-ISSN 1530-8022, Vol. 28, no 6, p. 825-836Article in journal (Refereed) Published
Abstract [en]

Numerous biomaterials based on extracellular matrix-components have been developed. It was our aim to investigate whether a hyaluronic acid-based hydrogel improves neuronal survival and tissue preservation in organotypic spinal cord slice cultures. Organotypic spinal cord slice cultures were cultured for 4 days in vitro (div), either on hyaluronic acid-based hydrogel (hyaluronic acid-gel group), collagen gel (collagen group), directly on polyethylene terephthalate membrane inserts (control group), or in the presence of soluble hyaluronic acid (soluble hyaluronic acid group). Cultures were immunohistochemically stained against neuronal antigen NeuN and analyzed by confocal laser scanning microscopy. Histochemistry for choline acetyltransferance, glial fibrillary acidic protein, and Griffonia simplicifolia isolectin B4 followed by quantitative analysis was performed to assess motorneurons and different glial populations. Confocal microscopic analysis showed a 4-fold increase in the number of NeuN-positive neurons in the hyaluronic acid-gel group compared to both collagen (p < 0.001) and control groups (p < 0.001). Compared to controls, organotypic spinal cord slice cultures maintained on hyaluronic acid-based hydrogel showed 5.9-fold increased survival of choline acetyltransferance-positive motorneurons (p = 0.008), 2-fold more numerous resting microglial cells in the white matter (p = 0.031), and a 61.4% reduction in the number of activated microglial cells within the grey matter (p = 0.05). Hyaluronic acid-based hydrogel had a shear modulus (G′) of ≈1200 Pascals (Pa), which was considerably higher than the ≈25 Pa measured for collagen gel. Soluble hyaluronic acid failed to improve tissue preservation. In conclusion, hyaluronic acid-based hydrogel improves neuronal and - most notably - motorneuron survival in organotypic spinal cord slice cultures and microglial activation is limited. The positive effects of hyaluronic acid-based hydrogel may at least in part be due to its mechanical properties.

Keywords
apoptosis, extracellular matrix-based biomaterials, hyaluronic acid-based hydrogel, microglial cells, motorneurons, Neuroprotection
National Category
Biomaterials Science
Identifiers
urn:nbn:se:kth:diva-124760 (URN)10.1177/0885328213483636 (DOI)000329317100003 ()2-s2.0-84891606942 (Scopus ID)
Note

QC 20140320

Available from: 2013-07-30 Created: 2013-07-30 Last updated: 2017-12-06Bibliographically approved
Lewitus, D. Y., Rios, F., Rojas, R. & Kohn, J. (2013). Molecular design and evaluation of biodegradable polymers using a statistical approach. Journal of materials science. Materials in medicine, 24(11), 2529-2535
Open this publication in new window or tab >>Molecular design and evaluation of biodegradable polymers using a statistical approach
2013 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 24, no 11, p. 2529-2535Article in journal (Refereed) Published
Abstract [en]

The challenging paradigm of bioresorbable polymers, whether in drug delivery or tissue engineering, states that a fine-tuning of the interplay between polymer properties (e.g., thermal, degradation), and the degree of cell/tissue replacement and remodeling is required. In this paper we describe how changes in the molecular architecture of a series of terpolymers allow for the design of polymers with varying glass transition temperatures and degradation rates. The effect of each component in the terpolymers is quantified via design of experiment (DoE) analysis. A linear relationship between terpolymer components and resulting T-g (ranging from 34 to 86 A degrees C) was demonstrated. These findings were further supported with mass-per-flexible-bond analysis. The effect of terpolymer composition on the in vitro degradation of these polymers revealed molecular weight loss ranging from 20 to 60 % within the first 24 h. DoE modeling further illustrated the linear (but reciprocal) relationship between structure elements and degradation for these polymers. Thus, we describe a simple technique to provide insight into the structure property relationship of degradable polymers, specifically applied using a new family of tyrosine-derived polycarbonates, allowing for optimal design of materials for specific applications.

Keywords
Tyrosine-Derived Polycarbonates, Poly(Ethylene Glycol), In-Vitro, Hydrolytic Degradation, High-Throughput, Biomaterials, Combinatorial, Bone, Technologies, Copolymers
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-124761 (URN)10.1007/s10856-013-5008-0 (DOI)000326049900005 ()2-s2.0-84887198898 (Scopus ID)
Note

QC 20150629

Available from: 2013-07-30 Created: 2013-07-30 Last updated: 2017-12-06Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1161-9311

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