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  • 151.
    Porsch, Christian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Zhang, Yuning
    Montanez, Maria I.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Malho, Jani-Markus
    Kostiainen, Mauri A.
    Nyström, Andreas M.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Disulfide-Functionalized Unimolecular Micelles as Selective Redox-Responsive Nanocarriers2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602Article in journal (Refereed)
    Abstract [en]

    Redox-sensitive hyperbranched dendritic-linear polymers (HBDLPs) were prepared and stabilized individually as unimolecular micelles with diameters in the range 25–40 nm. The high molecular weight (500–950 kDa), core–shell amphiphilic structures were synthesized through a combination of self-condensing vinyl copolymerization (SCVCP) and atom transfer radical polymerization (ATRP). Cleavable disulfide bonds were introduced, either in the backbone, or in pendant groups, of the hyperbranched core of the HBDLPs. By triggered reductive degradation, the HBDLPs showed up to a 7-fold decrease in molecular weight, and the extent of degradation was tuned by the amount of incorporated disulfides. The HBDLP with pendant disulfide-linked functionalities in the hyperbranched core was readily postfunctionalized with a hydrophobic dye, as a mimic for a drug. An instant release of the dye was observed as a response to a reductive environment similar to the one present intracellularly. The proposed strategy shows a facile route to highly stable unimolecular micelles, which attractively exhibit redox-responsive degradation and cargo release properties.

  • 152.
    Prakobna, Kasinee
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Galland, Sylvain
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    High-Performance and Moisture-Stable Cellulose-Starch Nanocomposites Based on Bioinspired Core-Shell Nanofibers2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 3, p. 904-912Article in journal (Refereed)
    Abstract [en]

    Moisture stability and brittleness are challenges for plant fiber biocomposites intended for load-bearing applications, for instance those based on an amylopectin-rich (AP) starch matrix. Core-shell amylopectin-coated cellulose nanofibers and nanocomposites are prepared to investigate effects from the distribution of AP matrix. The core-shell nanocomposites are compared with nanocomposites with more irregular amylopectin (AP) distribution. Colloidal properties (DLS), AP adsorption, nanofiber dimensions (atomic force microscopy), and nanocomposite structure (transmission electron microscopy) are analyzed. Tensile tests are performed at different moisture contents. The core-shell nanofibers result in exceptionally moisture stable, ductile, and strong nanocomposites, much superior to reference CNF/AP nanocomposites with more irregular AP distribution. The reduction in AP properties is less pronounced as the AP forms a favorable interphase around individual CNF nanofibers.

  • 153. Pääkkö, M.
    et al.
    Ankerfors, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kosonen, H.
    Nykänen, A.
    Ahola, S.
    Österberg, M.
    Ruokolainen, J.
    Laine, J.
    Larsson, Per Tomas
    Ikkala, O.
    Lindström, Tom
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Enzymatic hydrolysis combined with mechanical shearing and high-pressure homogenization for nanoscale cellulose fibrils and strong gels2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 6, p. 1934-1941Article in journal (Refereed)
    Abstract [en]

    Toward exploiting the attractive mechanical properties of cellulose I nanoelements, a novel route is demonstrated, which combines enzymatic hydrolysis and mechanical shearing. Previously, an aggressive acid hydrolysis and sonication of cellulose I containing fibers was shown to lead to a network of weakly hydrogen-bonded rodlike cellulose elements typically with a low aspect ratio. On the other hand, high mechanical shearing resulted in longer and entangled nanoscale cellulose elements leading to stronger networks and gels. Nevertheless, a widespread use of the latter concept has been hindered because of lack of feasible methods of preparation, suggesting a combination of mild hydrolysis and shearing to disintegrate cellulose I containing fibers into high aspect ratio cellulose I nanoscale elements. In this work, mild enzymatic hydrolysis has been introduced and combined with mechanical shearing and a high-pressure homogenization, leading to a controlled fibrillation down to nanoscale and a network of long and highly entangled cellulose I elements. The resulting strong aqueous gels exhibit more than 5 orders of magnitude tunable storage modulus G' upon changing the concentration. Cryotransmission electron microscopy, atomic force microscopy, and cross-polarization/magic-angle spinning (CP/MAS) C-13 NMR suggest that the cellulose I structural elements obtained are dominated by two fractions, one with lateral dimension of 5-6 nm and one with lateral dimensions of about 10-20 nm. The thicker diameter regions may act as the junction zones for the networks. The resulting material will herein be referred to as MFC (microfibrillated cellulose). Dynamical rheology showed that the aqueous suspensions behaved as gels in the whole investigated concentration range 0.125-5.9% w/w, G' ranging from 1.5 Pa to 10(5) Pa. The maximum G' was high, about 2 orders of magnitude larger than typically observed for the corresponding nonentangled low aspect ratio cellulose I gels, and G' scales with concentration with the power of approximately three. The described preparation method of MFC allows control over the final properties that opens novel applications in materials science, for example, as reinforcement in composites and as templates for surface modification.

  • 154.
    Quero, Franck
    et al.
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Ingn Quim Biotecnol & Mat, Lab Nanocelulosa & Biomat, Beauchef 851, Santiago, Chile..
    Opazo, Genesis
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Ingn Quim Biotecnol & Mat, Lab Nanocelulosa & Biomat, Beauchef 851, Santiago, Chile..
    Zhao, Yadong
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Feschotte-Parazon, Aymeric
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Ingn Quim Biotecnol & Mat, Lab Nanocelulosa & Biomat, Beauchef 851, Santiago, Chile..
    Fernandez, Jeimy
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Ingn Quim Biotecnol & Mat, Lab Nanocelulosa & Biomat, Beauchef 851, Santiago, Chile..
    Quintro, Abraham
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Ingn Quim Biotecnol & Mat, Lab Nanocelulosa & Biomat, Beauchef 851, Santiago, Chile..
    Flores, Marcos
    Univ Chile, Fac Ciencias Fis & Matemat, Dept Fis, Lab Superficies & Nanomat, Beauchef 850, Santiago, Chile..
    Top-down Approach to Produce Protein Functionalized and Highly Thermally Stable Cellulose Fibrils2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 8, p. 3549-3559Article in journal (Refereed)
    Abstract [en]

    Protein-functionalized cellulose fibrils, having various amounts of covalently bonded proteins at their surface, were successfully extracted from the tunic of Pyura chilensis tunicates using successive alkaline extractions. Pure cellulose fibrils were also obtained by further bleaching and were used as reference material. Extraction yields of protein-functionalized cellulose fibrils were within the range of 62-76% by weight based on the dry initial tunic powder. Fourier-transform infrared and Raman spectroscopy confirmed the preservation of residual protein at the surface of cellulose fibrils, which was then quantified by X-ray photoelectron spectroscopy. The protein-functionalized cellulose fibrils were found to have relatively high crystallinity and their cellulose I crystalline structure was preserved upon applying alkaline treatments. The extracted cellulosic materials were found to be constituted of fibrils having a ribbon-like morphology with widths ranging from 30 nm up to similar to 400 nm. These protein-functionalized cellulose fibrils were found to have outstanding thermal stability with one of them having onset and peak degradation temperatures of similar to 350 and 374 degrees C, respectively. These values were found to be 24 and 41 degrees C higher than for bleached cellulose.

  • 155.
    Ragnarsson, Lina
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Total Luminescence Intensity as a Tool to Classify Degradable Polyethylene Films by Early Degradation Detection and Changes in Activation Energy2003In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 4, no 4, p. 900-907Article in journal (Refereed)
    Abstract [en]

    Total luminescence intensity (TLI) was shown to be a valuable tool to monitor early degradation and thereby classify degradable polyethylene. The photo oxidation and thermal oxidation of polyethylene films containing different prooxidant systems were monitored. The chemiluminescence results were compared with results from FTIR, DSC, and SEC measurements. TLI gave an earlier detection of degradation and offered complementary information regarding changes in activation energies during the course of the degradation. TLI measurements were more sensitive to relative differences in degradation between the materials than the carbonyl index and crystallinity measurements, especially in the case of the UV-aged samples.

  • 156.
    Rashad, Ahmad
    et al.
    Univ Bergen, Dept Clin Dent, Bergen, Norway..
    Mohamed-Ahmed, Samih
    Univ Bergen, Dept Clin Dent, Bergen, Norway..
    Ojansivu, Miina
    Univ Bergen, Dept Clin Dent, Bergen, Norway.;Univ Tampere, Fac Med & Life Sci, Adult Stem Cell Res Grp, Tampere, Finland.;Univ Tampere, BioMediTech Inst, Tampere, Finland..
    Berstad, Kaia
    Univ Bergen, Dept Clin Dent, Bergen, Norway..
    Yassin, Mohammed A.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. Univ Bergen, Dept Clin Dent, Bergen, Norway..
    Kivijärvi, Tove
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Heggset, Ellinor Baevre
    RISE PFI, Trondheim, Norway..
    Syverud, Kristin
    RISE PFI, Trondheim, Norway.;Norwegian Univ Sci & Technol NTNU, Dept Chem Engn, Trondheim, Norway..
    Mustafa, Kamal
    Univ Bergen, Dept Clin Dent, Bergen, Norway..
    Coating 3D Printed Polycaprolactone Scaffolds with Nanocellulose Promotes Growth and Differentiation of Mesenchymal Stem Cells2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 11, p. 4307-4319Article in journal (Refereed)
    Abstract [en]

    3D printed polycaprolactone (PCL) has potential as a scaffold for bone tissue engineering, but the hydrophobic surface may hinder optimal cell responses. The surface properties can be improved by coating the scaffold with cellulose nanofibrils material (CNF), a multiscale hydrophilic biocompatible biomaterial derived from wood. In this study, human bone marrow-derived mesenchymal stem cells were cultured on tissue culture plates (TCP) and 3D printed PCL scaffolds coated with CNF. Cellular responses to the surfaces (viability, attachment, proliferation, and osteogenic differentiation) were documented. CNF significantly enhanced the hydrophilic properties of PCL scaffolds and promoted protein adsorption. Live/dead staining and lactate dehydrogenase release assays confirmed that CNF did not inhibit cellular viability. The CNF between the 3D printed PCL strands and pores acted as a hydrophilic barrier, enhancing cell seeding efficiency, and proliferation. CNF supported the formation of a well-organized actin cytoskeleton and cellular production of vinculin protein on the surfaces of TCP and PCL scaffolds. Moreover, CNF-coated surfaces enhanced not only alkaline phosphatase activity, but also collagen Type-I and mineral formation. It is concluded that CNF coating enhances cell attachment, proliferation, and osteogenic differentiation and has the potential to improve the performance of 3D printed PCL scaffolds for bone tissue engineering.

  • 157.
    Regnell Andersson, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Tuning the Polylactide Hydrolysis Rate by Plasticizer Architecture and Hydrophilicity without Introducing New Migrants2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 12, p. 3617-3623Article in journal (Refereed)
    Abstract [en]

    The possibility to tune the hydrolytic degradation rate of polylactide by plasticizer architecture and hydrophilicity without introduction of new degradation products was investigated by subjecting polylactide with cyclic oligolactide and linear oligolactic acid additives to hydrolytic degradation at 37 and 60 degrees C for up to 39 weeks. The more hydrophilic oligolactic acid plasticizer led to larger water uptake and rapid migration of plasticizer from the films into the aging water. This resulted in a porous material more susceptible to further hydrolysis. During hydrolysis at 37 degrees C the mass loss was generally 10-20% higher for the material containing linear oligolactic acid plasticizers. The hydrolysis accelerating effect of the linear oligolactic acid is probably counteracted by the higher degree of crystallinity in the films containing oligolactic acid additives. The degradation process was monitored by measurements of mass loss, water uptake, molar mass changes, material composition changes, surface changes, and thermal properties. The water-soluble degradation products were analyzed by following pH changes and identified by electrospray ionization-mass spectrometry (ESI-MS). The time frame for formation of water-soluble products was influenced by the architecture and hydrophilicity of the plasticizer. Furthermore, the advantage with oligolactide and oligolactic acid plasticizers was clearly demonstrated as they do not introduce any new migrants into the degradation product patterns.

  • 158.
    Regnell Andersson, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Inkinen, Saara
    Tate & Lyle Finland Oy, Turku, Finland.
    Södergård, Anders
    Tate & Lyle Finland Oy, Turku, Finland.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Polylactide Stereocomplexation Leads to Higher Hydrolytic Stability but More Acidic Hydrolysis Product Pattern2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 4, p. 1067-1073Article in journal (Refereed)
    Abstract [en]

    Poly-L-lactide/poly-D-lactide (PLLA/PDLA) stereocomplex had much higher hydrolytic stability compared to plain PLLA, but at the same time shorter and more acidic degradation products were formed. Both materials were subjected to hydrolytic degradation in water and in phosphate buffer at 37 and 60 C, and the degradation processes were monitored by following mass loss, water uptake, thermal properties, surface changes, and pH of the aging medium. The degradation product patterns were determined by electrospray ionization-mass spectrometry (ESI-MS). The high crystallinity and strong secondary interactions in the stereocomplex prevented water uptake and resulted in lower mass loss and degradation rate. However, somewhat surprisingly, the pH of the aging medium decreased much faster in the case of PLLA/PDLA stereocomplex. In accordance, the ESI-MS results showed that hydrolysis of PLLA/PDLA resulted in shorter and more acidic degradation products. This could be explained by the increased intermolecular crystallization clue to stereocomplexation, which results in an increased number of tie chains. Because mainly these short tie chains are susceptible to hydrolysis this leads to formation of shorter oligomers compared to hydrolysis of regular PLLA.

  • 159.
    Regnell Andersson, Sofia Regnell
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Inkinen, Saara
    Södergård, Anders
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Customizing the Hydrolytic Degradation Rate of Stereocomplex PLA through Different PDLA Architectures2012In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 13, no 4, p. 1212-1222Article in journal (Refereed)
    Abstract [en]

    Stereocomplexation of poly(L-lactide) (PLLA) with star shaped D-lactic acid (D-LA) oligomers with different, architectures and end-groups clearly altered the degradation rate and affected the degradation product patterns. Altogether, nine materials were studied: standard PLLA and eight blends of PLLA with either 30 or 50 wt % of four different D-LA. oligomers. The influence of several factors, including temperature, degradation time, and amount and type of D-LA oligomer, on the hydrolytic degradation process was investigated using a fractional factorial experimental design. Stereocomplexes containing star shaped D-LA oligomers with four alcoholic end-groups underwent a rather slow hydrolytic degradation with low release of degradation products. Materials with linear D-LA oligomers exhibited similar mass loss but released higher concentrations of shorter acidic degradation products. Increasing the fraction of D-LA oligomers with a linear structure or with four alcoholic end-groups resulted in slower mass loss due to higher degree of stereocomplexation. The opposite results were obtained after addition of D-LA oligomers with carboxylic chain-ends. These materials demonstrated lower degree of stereocomplexation and larger mass and molar mass loss, and also the release of degradation products increased. Increasing the number of alcoholic chain-ends from four to six decreased the degree of stereocomplexation, leading to faster mass loss. The degree of stereocomplexation and degradation rate were customized by changing the architecture and end-groups of the D-LA oligomers.

  • 160. Roos, Alexandra Andersson
    et al.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Sjoberg, John
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Stalbrand, Henrik
    Protein release from galactoglucomannan hydrogels: Influence of substitutions and enzymatic hydrolysis by beta-mannanase2008In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 9, no 8, p. 2104-2110Article in journal (Refereed)
    Abstract [en]

    O-Acetyl-galactoglucomannan (AcGGM) is the major soft-wood hemicellulose. Structurally modified AcGGM and hydrogels of AcGGM were prepared. The degree of substitution (DS) of AcGGM was modified enzymatically with beta-galactosidase, and chemically with an acrylate derivative, 2-hydroxyethylmethacrylate (HEMA). The hydrolysis of AcGGM with beta-mannanase was shown to increase with decreasing DS. AcGGM hydrogels were prepared from chemically modified AcGGM with varying DS of HEMA. Bovine serum albumin (BSA) was encapsulated in hydrogels. A spontaneous burst release of BSA was decreased with increased DS of HEMA. The addition of beta-mannanase significantly enhanced the BSA release from hydrogels with a DS of 0.36, reaching a maximum of 95% released BSA after eight hours compared to 60% without enzyme. Thus, both the pendant group composition and the enzyme action are valuable tools in the tailoring of hydrogel release profiles of potential interest for intestine drug delivery.

  • 161. Ryner, M.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity2002In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 3, no 3, p. 601-608Article in journal (Refereed)
    Abstract [en]

    New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different Poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new Poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content, The receding contact angle varied from 27 to 44degrees. The tensile proper-ties of the copolymers were controlled by altering the PDXO block length. The tensile, testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximate to 600-800% and sigma(b) approximate to 8-20 MPa) throughout the in vitro degradation study (59 days).

  • 162.
    Saadatmand, Soheil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Danielsson, Sverker
    Dahlman, Olof
    Karlström, Katarina
    Turning Hardwood Dissolving Pulp Polysaccharide Residual Material into Barrier Packaging2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 8, p. 2929-2936Article in journal (Refereed)
    Abstract [en]

    Birch chips were subjected to pilot-scale pre-hydrolysis under various sets of conditions to mimic a pre-hydrolysis step in a dissolving pulp process. The process generates residual process liquor, a wood hydrolysate, and the treated chips may be directly utilized in a dissolving process. The wood hydrolysates were rich in xylan and utilized in the production of fully renewable films that provide very good oxygen barrier function and mechanical integrity also at high relative humidity. Membrane filtration had an effect in enriching higher molecular weight fractions from the hydrolysates, but noteworthy, a hydrolysate used in the crude state without any membrane filtration performed just as well as upgraded fractions in forming films providing acceptable tensile properties and a good barrier against oxygen permeation.

  • 163.
    Saito, Tsuguyuki
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Kuramae, R.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Isogai, A.
    An ultrastrong nanofibrillar biomaterial: The strength of single cellulose nanofibrils revealed via sonication-induced fragmentation2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 1, p. 248-253Article in journal (Refereed)
    Abstract [en]

    We report the mechanical strength of native cellulose nanofibrils. Native cellulose nanofibrils, purified from wood and sea tunicate, were fully dispersed in water via a topochemical modification of cellulose nanofibrils using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) as a catalyst. The strength of individual nanofibrils was estimated based on a model for the sonication-induced fragmentation of filamentous nanostructures. The resulting strength parameters were then analyzed based on fracture statistics. The mean strength of the wood cellulose nanofibrils ranged from 1.6 to 3 GPa, depending on the method used to measure the nanofibril width. The highly crystalline, thick tunicate cellulose nanofibrils exhibited higher mean strength of 3-6 GPa. The strength values estimated for the cellulose nanofibrils in the present study are comparable with those of commercially available multiwalled carbon nanotubes.

  • 164. Schagerlof, H.
    et al.
    Richardson, S.
    Momcilovic, Dane
    Brinkmalm, G.
    Wittgren, B.
    Tjerneld, F.
    Characterization of chemical substitution of hydroxypropyl cellulose using enzymatic degradation2006In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 1, p. 80-85Article in journal (Refereed)
    Abstract [en]

    The distribution of substituents along the polymer backbone will have a strong influence on the properties of modified cellulose. Endoglucanases were used to degrade a series of hydroxypropyl cellulose (HPC) derivatives with a high degree of substitution. The HPCs were characterized with cloud-point analysis prior to degradation. The extent of enzymatic degradation was determined with size-exclusion chromatography with online multi-angle light scattering and refractive index detection and also with high-pH anion exchange chromatography with pulsed amperometric detection. To further characterize the formed products, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was employed for analysis of short-chained oligosaccharides. The different endoglucanases showed varying degradation capability depending on structure of the active site. The highly substituted HPCs had different susceptibility to degradation by the endoglucanases. The results show a difference in substituent distribution between HPCs, which would explain the differing cloud-point behaviors. Increased number of regions with low substitution could be, correlated with lower polymer cloud point. The study shows the usefulness of enzymatic degradation to study the distribution of substituents in soluble biopolymer derivates.

  • 165. Schagerlof, U.
    et al.
    Schagerlof, H.
    Momcilovic, Dane
    Brinkmalm, G.
    Tjerneld, F.
    Endoglucanase sensitivity for substituents in methyl cellulose hydrolysis studied using MALDI-TOFMS for oligosaccharide analysis and structural analysis of enzyme active sites2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 8, p. 2358-2365Article in journal (Refereed)
    Abstract [en]

    The properties of modified cellulose polymers, such as methylcellulose, are significantly influenced by the distribution of substituents along the polymer backbone. This distribution is difficult to determine due to the lack of suitable analytical methods. One approach is to use cellulose-degrading enzymes to gain information from the capability of the enzymes to cleave the bonds between glucose units. Endoglucanases are cellulase enzymes that can break internal glycosidic linkages and degrade low substituted regions of modified cellulose where the substituents do not interfere with the enzyme active site. In this work methyl cellulose was degraded using five endoglucanases from glycosyl hydrolase families 5 and 7 from three different species. The products were analyzed with reducing end analysis, chromatography (SEC-MALS-RI), and MALDI-TOFMS. The results were correlated with available determined enzyme structures and using structural alignment for unknown enzyme structures. This was performed in order to elucidate the relationship between active site structures and sensitivity for substituents on derivatized cellulose. The evaluation of endoglucanase hydrolysis of methyl cellulose showed that differences in sensitivity could be related to differences in steric hindrance of substituents in the active site, which could explain differences within family 5 and 7 enzymes, as well as the generally higher substituent tolerance for family 5 enzymes. This information is important for use of endoglucanases as tools for characterization of substituent distribution. The results are also valuable since soluble cellulose derivatives are generally used as substrates during enzyme characterization and in endoglucanase activity assays.

  • 166.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Liu, Andong
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Biotechnology (BIO), Glycoscience.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Fast Preparation Procedure for Large, Flat Cellulose and Cellulose/Inorganic Nanopaper Structures2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 9, p. 2195-2198Article in journal (Refereed)
    Abstract [en]

    Nanostructured materials are difficult to prepare rapidly and as large structures. The present study is thus significant because a rapid preparation procedure for large, flat, smooth, and optically transparent cellulose nanopaper structures is developed using a semiautomatic sheet former. Cellulose/inorganic hybrid nanopaper is also produced. The preparation procedure is compared with other approaches, and the nanopaper structures are tested in uniaxial tensile tests. Optical transparency and high tensile strength are demonstrated in 200 mm diameter nanopaper sheets, indicating well-dispersed nanofibrils. The preparation time is 1 h for a typical nanopaper thickness of 60 pm. In addition, the application of the nanopaper-making strategy to cellulose/inorganic hybrids demonstrates the potential for "green" processing of new types of nanostructured functional materials.

  • 167.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Morimune, Seira
    Nishino, Takashi
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Stretchable and Strong Cellulose Nanopaper Structures Based on Polymer-Coated Nanofiber Networks: An Alternative to Nonwoven Porous Membranes from Electrospinning2012In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 13, no 11, p. 3661-3667Article in journal (Refereed)
    Abstract [en]

    Nonwoven membranes based on electrospun, fibers are of great interest in applications such as biomedical, filtering, and protective clothing.. The poor, mechanical performance is a limitation, as is some of the electrospinning Solvents. To address these problems, porous nonwoven membranes based on nanofibrillated cellulose (NFC) modified by a hydroxyethyl cellulose (HEC) polymer coating. are prepared. NFC/HEC aqueous suspensions are subjected to simple vacuum filtration: in a Paper-making fashion,, followed by supercritical CO2. drying., These nonwoven nanocomposite membranes are truly nanostructured and exhibit a nanoporous, network structure with high specific surface area, as analyzed by nitrogen adsorption and FE-SEM. Mechanical properties by tensile tests show high strength combined with remarkable high strain to failure up to 55%. XRD analysis revealed significant fibril realignment during tensile stretching. After postdrawing of the random mats, the modulus and strength are strongly increased. The present preparation route uses components from renewable resources, is environmentally friendly, and results in permeable membranes of exceptional imechanical performance.

  • 168.
    Sehaqui, Houssine
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Zhou, Qi
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Biotechnology (BIO), Glycoscience.
    Ikkala, Olli
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Strong and Tough Cellulose Nanopaper with High Specific Surface Area and Porosity2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 10, p. 3638-3644Article in journal (Refereed)
    Abstract [en]

    In order to better understand nanostructured fiber networks, effects from high specific surface area of nanofibers are important to explore. For cellulose networks, this has so far only been achieved in nonfibrous regenerated cellulose aerogels. Here, nanofibrillated cellulose (NFC) is used to prepare high surface area nanopaper structures, and the mechanical properties are measured in tensile tests. The water in NFC hydrogels is exchanged to liquid CO(2), supercritical CO(2), and tert-butanol, followed by evaporation, supercritical drying, and sublimation, respectively. The porosity range is 40-86%. The nanofiber network structure in nanopaper is characterized by FE-SEM and nitrogen adsorption, and specific surface area is determined. High-porosity TEMPO-oxidized NFC nanopaper (56% porosity) prepared by critical point drying has a specific surface area as high as 48(2) m(2) g(-1). The mechanical properties of this nanopaper structure are better than for many thermoplastics, but at a significantly lower density of only 640 kg m(-3). The modulus is 1.4 GPa, tensile strength 84 MPa, and strain-to-failure 17%. Compared with water-dried nanopaper, the material is softer with substantially different deformation behavior.

  • 169.
    Sjöberg, John
    et al.
    University of Natural Resources and Applied Life Sciences, Austria .
    Potthast, A.
    Rosenau, T.
    Kosma, P.
    Sixta, H.
    Cross-sectional analysis of the polysaccharide composition in cellulosic fiber materials by enzymatic peeling/high-performance capillary zone electrophoresis2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 6, p. 3146-3151Article in journal (Refereed)
    Abstract [en]

    A combined enzymatic, chemical, and analytical approach was used to determine the cross-sectional carbohydrate composition in cellulosic fibers. The outer surface of cellulosic fibers was enzymatically removed layer-by-layer with precise quantitative control, and the monosaccharides in the peelings were subsequently analyzed by high-performance capillary electrophoresis (HPCE) after precolumn derivatization with a UV label. This method was applied to dissolving pulps and regenerated cellulose fibers, with special emphasis on the cross-sectional distribution of hemicelluloses. Commercially available enzyme solutions were used, resulting in a reproducible peeling. Significant differences were found in the hemicellulose distribution across the fiber of different dissolving pulps, dependent on both natural source (beech or spruce) and preparation process (acidic sulfite cook or prehydrolysis kraft cook). Among the dissolving pulps, beech prehydrolysis kraft pulp showed the highest enrichment of surface xylan. Similar, albeit smaller, differences were noticed between various regenerated fibers (viscose, viscose Modal, and Lyocell): a thin hemicellulose-rich outermost layer was found in all the regenerated fibers studied.

  • 170.
    Srivastava, Rajiv
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Porous scaffolds from high molecular weight polyesters synthesized via enzyme-catalyzed ring-opening polymerization2006In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 9, p. 2531-2538Article in journal (Refereed)
    Abstract [en]

    Several aliphatic polyesters have been synthesized until now using enzyme-catalyzed ring-opening polymerization (ROP) of different lactones, although their molecular weight, hence mechanical strength, was not sufficient enough to fabricate porous scaffolds from them. To achieve this target, 1,5-dioxepan-2-one (DXO) and epsilon-caprolactone (CL) were polymerized in bulk with Lipase CA as catalyst at 60 degrees C, and porous scaffolds were prepared from the polymers obtained thereof using a salt leaching technique. The CL/DXO molar feed ratio was varied from 1.5 to 10, and the reactivity ratios of CL and DXO were determined using the Kelen-Tudos method under such conditions of polymerization. NMR results showed a slightly lower CL/DXO molar ratio in the copolymers than in the feed due to high reactivity of DXO toward Lipase CA catalysis. The crystallinity of the PCL segment of the copolymers was affected by the presence of soft and amorphous DXO domains. The copolymers having high CL content were thermally more stable. The porosity of the scaffolds was in the range 82-88%, and the SEM analysis showed interconnected pores in the scaffolds. Of the two parameters which could affect the mechanical properties, viz., the copolymer composition and the scaffold pore size, the pore size showed a significant effect on the mechanical properties of the scaffolds. The porous scaffolds developed in this way for tissue engineering are free from toxic organometallic catalyst residues, and they are highly suitable for biomedical applications.

  • 171. Stark, M.
    et al.
    Grip, S.
    Rising, A.
    Hedhammar, My
    Department of Anatomy, Physiology, and Biochemistry, The Biomedical Centre, Swedish University of Agricultural Sciences, SE-751 23 Uppsala, Sweden.
    Engstrom, W.
    Hjalm, G.
    Johansson, J.
    Macroscopic fibers self-assembled from recombinant miniature spider silk proteins2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 5, p. 1695-1701Article in journal (Refereed)
    Abstract [en]

    Strength, elasticity, and biocompatibility make spider silk an attractive resource for the production of artificial biomaterials. Spider silk proteins, spidroins, contain hundreds of repeated poly alanine/glycine-rich blocks and are difficult to produce recombinantly in soluble form. Most previous attempts to produce artificial spider silk fibers have included solubilization steps in nonphysiological solvents. It is here demonstrated that a miniature spidroin from a protein in dragline silk of Euprosthenops australis can be produced in a soluble form in Escherichia coli when fused to a highly soluble protein partner. Although this miniature spidroin contains only four poly alanine/glycine-rich blocks followed by a C-terminal non-repetitive domain, meter-long fibers are spontaneously formed after proteolytic release of the fusion partner. The structure of the fibers is similar to that of dragline silks, and although self-assembled from recombinant proteins they are as strong as fibers spun from redissolved silk. Moreover, the fibers appear to be biocompatible because human tissue culture cells can grow on and attach to the fibers. These findings enable controlled production of high-performance biofibers at large scale under physiological conditions.

  • 172.
    Stenström, Patrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hjorth, Erik
    Zhang, Yuning
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Andrén, Oliver C. J.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Guette-Marquet, Simon
    Schultzberg, Marianne
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Synthesis and in Vitro Evaluation of Monodisperse Amino-Functional Polyester Dendrimers with Rapid Degradability and Antibacterial Properties2017In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 18, no 12, p. 4323-4330Article in journal (Refereed)
    Abstract [en]

    Amine functional polymers, especially cationically charged, are interesting biomacromolecules for several reasons, including easy cell membrane entrance, their ability to escape endosomes through the proton sponge effect, spontaneous complexation and delivery of drugs and siRNA, and simple functionalization in aqueous solutions. Dendrimers, a subclass of precision polymers, are monodisperse and exhibit a large and exact number of peripheral end groups in relation to their size and have shown promise in drug delivery, biomedical imaging and as antiviral agents. In this work, hydroxyl functional dendrimers of generation 1 to 5 based on 2,2-bis(methylol)propionic acid (bis-MPA) were modified to bear 6 to 96 peripheral amino groups through esterification reactions with beta-alanine. All dendrimers were isolated in high yields and with remarkable monodispersity. This was successfully accomplished utilizing the present advantages of fluoride-promoted esterification (FPE) with imidazole-activated monomers. Straightforward postfunctionalization was conducted on a second generation amino functional dendrimer with tetraethylene glycol through NHS-amidation and carbonyl diimidazole (CDI) activation to full conversion with short reaction times. Fast biodegradation of the dendrimers through loss of peripheral beta-alanine groups was observed and generational- and dose-dependent cytotoxicity was evaluated with a set of cell lines. An increase. in neurotoxicity compared to hydroxyl-functional dendrimers was shown in neuronal cells, however, the dendrimers were slightly less neurotoxic than commercially available poly(amidoamine) dendrimers (PAMAMs). Additionally, their effect on bacteria was evaluated and the second generation dendrimer was found unique inhibiting the growth of Escherichia coli at physiological conditions while being nontoxic toward human cells. Finally, these results cement a robust and sustainable synthetic route to amino-functional polyester dendrimers with interesting chemical and biological properties.

  • 173.
    Sterner, Martin
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Edlund, Ulrica
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    High-Performance Filaments from Fractionated Alginate by Polyvalent Cross-Linking: A Theoretical and Practical Approach2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 8, p. 3311-3330Article in journal (Refereed)
    Abstract [en]

    A series of alginate fractions with significant differences in molecular weight and uronic acid compositions were produced by consecutive fractionation and converted to thin and strong cross-linked polymer filaments via extrusion into calcium, aluminum, or polyaluminum (PolyAl) polyvalent solutions followed by drawing and drying. Models were elaborated to relate the alginate uronic acid composition to the tensile performance in both the wet gel filament and the dry filament states. The wet gel model was compared to the theory of the unidirectional elongation of charged polyelectrolyte gels based on the classical rubber elasticity of dilated polymer networks, extended to include the contributions of non-Gaussian chain extensions and the effect of electrostatic interactions. The theory of equilibrium swelling pressure was applied to describe the observed shrinkage of the alginate gels following immersion in a polyvalent solution. Congruent with the theoretical model of charged gels, the tensile performance of the gel filaments prepared from CaCl2 depended on the compositional ratio of guluronic acid dyads in the alginate fraction multiplied by the alginate concentration, while the tensile behavior of wet gel filaments prepared by AlCl3 instead resembled that of elastic solid materials and depended only on the alginate concentration. The dry filament tensile properties were greatly dependent on the preparation conditions, particularly the ratio of stress to alginate concentration and the nature of the ions present during filament drawing. The PolyAl solution effectively caused shrinkage of alginate to a strong extent, and the resulting filaments behaved as highly stiff materials able to withstand stresses of approximately 500 MPa and having elastic moduli as high as 28 GPa.

  • 174.
    Stiernstedt, Johanna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Brumer III, Harry
    KTH, School of Biotechnology (BIO).
    Zhou, Qi
    KTH, School of Biotechnology (BIO).
    Teeri, Tuula
    KTH, School of Biotechnology (BIO).
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Friction between cellulose surfaces and the effect of and xyloglucan adsorption2006In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 7, p. 2147-2153Article in journal (Refereed)
    Abstract [en]

    The forces and friction between cellulose spheres have been measured in the absence and presence of xyloglucan using an atomic force microscope. The forces between cellulose are monotonically repulsive with negligible adhesion after contact is achieved. The friction coefficient is observed to be unusually high in comparison with other nanotribological systems. We have confirmed that xyloglucan adsorbs strongly to cellulose, which results in a much stronger adhesion, which is dependent on the time the surfaces are in contact. Xyloglucan also increases the repulsion on approach of the cellulose surfaces, and the friction is markedly reduced. The apparently incompatible observations of decreased friction in combination with increased adhesion fulfills many of the necessary criteria for a papermaking additive.

  • 175.
    Stjerndahl, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wistrand, Anna Finne
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Industrial utilization of tin-initiated resorbable polymers: synthesis on a large scale with a low amount of initiator residue2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 3, p. 937-940Article in journal (Refereed)
    Abstract [en]

    This article presents the successful large-batch synthesis of a resorbable polymer with a minimal amount of residual tin. Ring-opening polymerization of ε-caprolactone was performed in toluene, with a tin (IV) alkoxide as the initiator. A number of parameters were varied in order to study the polymerization with respect to the purity of solvent, batch size, and the residual amount of tin in the polymers. The synthesis of ε-caprolactone in undistilled toluene with 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane as the initiator was successfully performed in batches of 5, 20, and 50 g with no differences in the final conversion, molecular weight, or molecular-weight distribution. The residual amount of tin was significantly reduced from over 1000 to 23 ppm. This study examines the industrial utility of the materials regarding the size and purity of the synthesis.

  • 176.
    Sullivan, Mitchell A.
    et al.
    The University of Queensland.
    Li, Jiong
    Wuhan University.
    Li, Chuanzhou
    Wuhan University.
    Vilaplana, Francisco
    The University of Queensland.
    Stapleton, David
    University of Melbourne.
    Gray-Weale, Angus A.
    Monash University.
    Bowen, Stirling
    Southern Cross University.
    Zheng, Ling
    Wuhan University.
    Gilbert, Robert G.
    The University of Queensland.
    Molecular Structural Differences between Type-2-Diabetic and Healthy Glycogen2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 6, p. 1983-1986Article in journal (Refereed)
    Abstract [en]

    Glycogen is a highly branched glucose polymer functioning as a glucose buffer in animals. Multiple-detector size exclusion chromatography and fluorophore-assisted carbohydrate electrophoresis were used to examine the structure of undegraded native liver glycogen (both whole and enzymatically del;ranched) as a function of molecular size, isolated from the liver; of healthy and db/db mice (the latter a type 2 diabetic model). Both the fully branched and debranched levels of glycogen structure showed fundamental differences between glycogen from healthy and db/db mice. Healthy glycogen had a greater population of large particles, with more a particles (tightly linked assemblages of smaller,8 particles) than glycogen from db/db mice. These structural differences suggest a new understanding of type 2 diabetes.

  • 177.
    Sullivan, Mitchell A.
    et al.
    The University of Queensland.
    Vilaplana, Francisco
    The University of Queensland.
    Cave, Richard A.
    The University of Queensland.
    Stapleton, David
    University of Melbourne.
    Gray-Weale, Angus A.
    Monash University.
    Gilbert, Robert G.
    The University of Queensland.
    Nature of alpha and beta Particles in Glycogen Using Molecular Size Distributions2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 4, p. 1094-1100Article in journal (Refereed)
    Abstract [en]

    Glycogen is a randomly hyperbranched glucose polymer. Complex branched polymers have two structural levels: individual branches and the way these branches are linked. Liver glycogen has a third level: supramolecular clusters of beta particles which form larger clusters of alpha particles. Size distributions of native glycogen were characterized using size exclusion chromatography (SEC) to find the number and weight distributions and the size dependences of the number- and weight-average masses. These were fitted to two distinct randomly joined reference structures, constructed by random attachment of individual branches and as random aggregates of beta particles. The z-average size of the alpha particles in dimethylsulfoxide does not change significantly with high concentrations of LiBr, a solvent system that would disrupt hydrogen bonding. These data reveal that the beta particles are covalently bonded to form alpha particles through a hitherto unsuspected enzyme process, operative in the liver on particles above a certain size range.

  • 178.
    Sun, Yang
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Xing, Zhe
    Xue, Ying
    Mustafa, Kamal
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Surfactant as a Critical Factor When Tuning the Hydrophilicity in Three-Dimensional Polyester-Based Scaffolds: Impact of Hydrophilicity on Their Mechanical Properties and the Cellular Response of Human Osteoblast-Like Cells2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 4, p. 1259-1268Article in journal (Refereed)
    Abstract [en]

    In tissue engineering, the hydrophilicity of porous scaffolds is essential and influences protein and cell adhesion as well as nutrient diffusion into the scaffold. The relative low hydrophilicity of degradable polyesters, which limits diffusion of nutrients, is a major drawback in large porous scaffolds of these materials when used for bone tissue engineering and repair of critical size defects. Designing porous biodegradable polymer scaffolds with improved hydrophilicity, while maintaining their mechanical, thermal, and degradation properties is therefore of clinical interest. Here, surfactants were used to tune the hydrophilicity and material properties. A total of 3-20% (w/w) of surfactant, polysorbate 80 (Tween 80), was used as an additive in poly(L-lactide-co-1,5-diozepan-2-one) [poly(LLA-co-DXO)] and poly(L-lactide)-co-(epsilon-caprolactone) [poly(LLA-co-CL)] scaffolds. A significantly decreased water contact angle was recorded for all the blends and the crystallinity, glass transition temperature and crystallization temperature were reduced with increased amounts of surfactant. Copolymers with the addition of 3% Tween 80 had comparable mechanical properties as the pristine copolymers. However, the E-modulus and tensile stress of copolymers decreased significantly with the addition of 10 and 20% Tween 80. Initial cell response of the material was evaluated by seeding human osteoblast-like cells (HOB) on the scaffolds. The addition of 3% Tween 80 did not significantly influence cell attachment or proliferation, while 20% Tween 80 significantly inhibited osteoblast proliferation. RT-PCR results showed that 3% Tween 80 stimulated mRNA expression of alkaline phosphatase (ALP), osteoprotegerin (OPG), and bone morphogenetic protein-2 (BMP-2).

  • 179.
    Svagan, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Azizi Samir, My Ahmed Said
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 8, p. 2556-2563Article in journal (Refereed)
    Abstract [en]

    Plant cell walls combine mechanical stiffness, strength and toughness despite a highly hydrated state. Inspired by this, a nanostructured cellulose network is combined with an almost viscous polysaccharide matrix in the form of a 50/50 amylopectin-glycerol blend. Homogeneous films with a microfibrillated cellulose (MFC) nanofiber content in the range of 10-70 wt % are successfully cast. Characterization is carried out by dynamic mechanical analysis, field-emission scanning electron microscopy, X-ray diffraction, and mercury density measurements. The MFC is well dispersed and predominantly oriented random-in-the-plane. High tensile strength is combined with high modulus and very high work of fracture in the nanocomposite with 70 wt % WC. The reasons for this interesting combination of properties include nanofiber and matrix properties, favorable nanofiber-matrix interaction, good dispersion, and the ability of the MFC network to maintain its integrity to a strain of at least 8%.

  • 180. Svagan, Anna J.
    et al.
    Musyanovych, Anna
    Kappl, Michael
    Bernhardt, Max
    Glasser, Gunnar
    Wohnhaas, Christian
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Risbo, Jens
    Landfester, Katharina
    Cellulose Nanofiber/Nanocrystal Reinforced Capsules: A Fast and Facile Approach Toward Assembly of Liquid-Core Capsules with High Mechanical Stability2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 5, p. 1852-1859Article in journal (Refereed)
    Abstract [en]

    Liquid-core capsules of high mechanical stability open up for many solid state-like applications where functionality depending on liquid mobility is vital. Herein, a novel concept for fast and facile improvement of the mechanical properties of walls of liquid-core capsules is reported. By imitating nature's own way of enhancing the mechanical properties in liquid-core capsules, the parenchyma plant cells found in fruits and vegetables, a blend of short cellulose nanofibers (<1 mu m, NFC) and nanocrystals (CNC) was exploited in the creation of the capsule walls. The NFC/CNC blend was prepared from a new version of the classical wood pulp hydrolysis. The capsule shell consisted of a covalently (by aromatic diisocyanate) cross-linked NFC/CNC structure at the outer capsule wall and an inner layer dominated by aromatic polyurea. The mechanical properties revealed an effective capsule elastic modulus of 4.8 GPa at 17 wt % NFC/CNC loading, about six times higher compared to a neat aromatic polyurea capsule (0.79 GPa) and 3 orders of magnitude higher than previously reported capsules from regenerated cellulose (0.0074 GPa). The outstanding mechanical properties are ascribed to the dense nanofiber structure, present in the outer part of the capsule wall, that is formed by oriented NFC/CNC of high average aspect ratio (L/d similar to 70) and held together by both covalent (urethane bonds) and physical bonds (hydrogen bonds).

  • 181.
    Takwa, Mohamad
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Xiao, Yan
    Simpson, Neil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malmström, Eva M.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Koning, Cor.
    Heise, Andreas
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry.
    Lipase Catalyzed HEMA Initiated Ring-Opening Polymerization: In Situ Formation of Mixed Polyester Methacrylates by Transesterification2008In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 9, no 2, p. 704-710Article in journal (Refereed)
    Abstract [en]

    2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the enzymatic ring-opening polymerization (ROP) of ω-pentadecalactone (PDL) and ∈-caprolactone (CL). The lipase B from Candida antarctica was found to catalyze the cleavage of the ester bond in the HEMA end group of the formed polyesters, resulting in two major transesterification processes, methacrylate transfer and polyester transfer. This resulted in a number of different polyester methacrylate structures, such as polymers without, with one, and with two methacrylate end groups. Furthermore, the 1,2-ethanediol moiety (from HEMA) was found in the polyester products as an integral part of HEMA, as an end group (with one hydroxyl group) and incorporated within the polyester (polyester chains acylated on both hydroxyl groups). After 72 h, as a result of the methacrylate transfer, 79% (48%) of the initial amount of the methacrylate moiety (from HEMA) was situated (acylated) on the end hydroxyl group of the PPDL (PCL) polyester. In order to prepare materials for polymer networks, fully dimethacrylated polymers were synthesized in a one-pot procedure by combining HEMA-initiated ROP with end-capping using vinyl methacrylate. The novel PPDL dimethacrylate (>95% incorporated methacrylate end groups) is currently in use for polymer network formation. Our results show that initiators with cleavable ester groups are of limited use to obtain well-defined monomethacrylated macromonomers due to the enzyme-based transesterification processes. On the other hand, when combined with end-capping, well-defined dimethacrylated polymers (PPDL, PCL) were prepared.

  • 182.
    Tchang Cervin, Nicholas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Andersson, Linnéa
    Sing, Jovice
    Olin, Pontus
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bergström, Lennart
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lightweight and Strong Cellulose Materials Made from Aqueous Foams Stabilized by Nanofibrillated Cellulose2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 2, p. 503-511Article in journal (Refereed)
    Abstract [en]

    A lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified nanofibrillated cellulose (NFC). This material differs from other dry, particle stabilized foams in that renewable cellulose is used as stabilizing particles. Confocal microscopy and high speed video imaging show that the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface prevent the air bubbles from collapsing or coalescing. Stable wet foams can be achieved at solids content around 1% by weight. Careful removal of the water results in a cellulose-based material with a porosity of 98% and a density of 30 mg cm(-3). These porous cellulose materials have a higher Young's modulus than porous cellulose materials made from freeze-drying, at comparable densities, and have a compressive energy absorption of 56 kJ m(-3) at 80% strain. Measurement with the aid of an autoporosimeter revealed that most pores are in the range of 300 to 500 mu m.

  • 183.
    Terenzi, Camilla
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Prakobna, Kasinee
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Nanostructural Effects on Polymer and Water Dynamics in Cellulose Biocomposites: H-2 and C-13 NMR Relaxometry2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 5, p. 1506-1515Article in journal (Refereed)
    Abstract [en]

    Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characteriied separately. Nanocornposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolynier matrix are investigated at different hydration states Films of XG, CNF, and CNF/XG composites are subjected to detailed H-2 and C-13 NMR relaxation studies. Since the H-2 NMR. signal arises from heavy water and the C-13 signal from the polysaccharides, - molecular Water and polymer dynamics is for the first time investigated separately In the neat components, H-2 transverse relaxation (T-2), data are consistent. With water Clustering at the CNF fibril sulfaces, but bulk spread of moisture in XG. The-new method results in a description of water interaction with the nanoscale phases. At low hydration) water molecules at the CNF/XG interface exhibit higher water-mobility-than in neat CNF or XG, due to locally high Water concentration. At the same time, CNF-associated interphase segments of XG Slower NMR-dynamics that in teat XG.

  • 184.
    Torron, Susana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Semlitsch, Stefan
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Martinell, Mats
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Biocatalytic Synthesis of Epoxy Resins from Fatty Acids as a Versatile Route for the Formation of Polymer Thermosets with Tunable Properties2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 12, p. 4003-4010Article in journal (Refereed)
    Abstract [en]

    The work herein presented describes the synthesis and polymerization of series of bio-based epoxy resins prepared through lipase catalyzed transesterification. The epoxy-functional polyester resins with various architectures (linear, hi branched, and tetra-branched) were synthesized through condensation of fatty acids derived from epoxidized soybean oil and linseed oil with three different hydroxyl cores under bulk conditions. The selectivity of the lipases toward esterification/transesterification reactions allowed the formation of macromers with up to 12 epoxides in the backbone. The high degree of functionality of the resins resulted in polymer thermosets with T-g values ranging from 25 to over 100 degrees C prepared through cationic polymerization. The determining parameters of the synthesis and the mechanism for the formation of the species were determined through kinetic studies by H-1 NMR, SEC, and molecular modeling studies. The correlation between macromer structure and thermoset properties was studied through real-time FTIR measurements, DSC, and DMA.

  • 185.
    Tyson, Therese
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Degradable Porous Scaffolds from Various L-Lactide and Trimethylene Carbonate Copolymers Obtained by a Simple and Effective Method2009In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 1, p. 149-154Article in journal (Refereed)
    Abstract [en]

    A simple and effective method of fabricating scaffolds with open pore structures was successfully used on several copolymers. The method, which is straightforward and fast, was developed to overcome problems such as low pore interconnectivity and to achieve thick three-dimensional scaffolds. Copolymers are of particular interest because it is possible to tune their mechanical and degradable properties, and in this work, copolymers of L-lactide (LLA) and trimethylene carbonate (TMC) were synthesized through ring-opening polymerization. The copolymers formed had molecular weights ranging from close to 60000 g/mol to over 300000 g/mol and they were composed of 12-55 molar percentages of TMC and 88-45 molar percentages of LLA. The synthesized copolymers were evaluated as scaffold materials using a combined phase separation and particulate leaching technique, in which sugar templates were used as the leachable porosifiers. Differences in molecular weights, molar compositions, and degrees of crystallinity were all factors that influenced the properties of the prepared scaffolds. The copolymers with high LLA contents and high degrees of crystallinity were best suited for the scaffold fabrication technique used and gave degradable scaffolds with interconnected pores.

  • 186.
    Ullsten, Henrik
    et al.
    STFI-Packforsk.
    Cho, Sung-Woo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Spencer, Gwen
    SLU, Alnarp.
    Gällstedt, Mikael
    STFI-Packforsk.
    Johansson, Eva
    SLU, Alnarp.
    Hedenqvist, Mikael S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Properties of Extruded Vital Wheat Gluten Sheets with Sodium Hydroxide and Salicylic Acid2009In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 3, p. 479-488Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel approach to improve the barrier and mechanical properties of extruded glycerol-plasticized vital wheat gluten sheets. The sheets were extruded with a single screw extruder at alkaline conditions using 3-5 wt % NaOH. Salicylic acid (SA), known to improve the extrudability of wheat gluten, was also added alone or in combination with NaOH. Oxygen transmission rate and volatile mass measurements, tensile tests, protein solubility, glycerol migration, infrared spectroscopy, and electrophoresis were used to assess the properties of the extrudate. Electrophoresis showed that the gluten/glycerol sheet and the sheet with 3 wt % NaOH and I wt % SA contained the same building blocks in terms of proteins and protein subunits, although the protein solubility in these samples was different. The oxygen barrier, at dry conditions, was improved significantly with the addition of NaOH, On the other hand, the addition of salicylic acid yielded poorer barrier properties. The extrudate was placed on a blotting paper and its aging properties were investigated during the first 120 days. It was observed that the extrudate with 3 wt % NaOH had the most suitable combination of properties (low oxygen permeability, large strain at break, and relatively small aging-induced changes in mechanical properties); the reason is probably due to low plasticizer migration and an optimal protein aggregation/polymerization.

  • 187. Ullsten, Henrik
    et al.
    Gällstedt, Mikael
    Johansson, Eva Lena
    Gräslund, Astrid
    Hedenqvist, Mikael S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Enlarged processing window of plasticized wheat gluten using salicylic acid2006In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 3, p. 771-776Article in journal (Refereed)
    Abstract [en]

    The temperature window for the extrusion of glycerol-plasticized wheat gluten was increased by the use of salicylic acid, a known scorch retarder and radical scavenger. It was possible to extrude 30 wt % glycerol-wheat gluten films with a die-head temperature as high as 135 °C, rather than 95 °C, by incorporating only 1 wt % salicylic acid. Small effects of shear-induced heating during extrusion at the higher temperatures suggested that the acid acted as a lubricant and viscosity reducer. The latter was suggested to originate primarily from the salicylic-acid-induced reduction in the degree of protein aggregation/cross-linking, as indicated by size-exclusion high-performance liquid chromatography and chemiluminescence. Electron paramagnetic resonance spectroscopy on extruded films indicated that the beneficial effect of salicylic acid was due to its radical scavenging effect. Tensile tests on extrudates revealed that the materials produced at the substantially higher processing temperature were still ductile. The complex shear modulus increased more slowly with increasing salicylic acid content above 110-120 °C, indicating that the aggregation/cross-linking rate was slower with salicylic acid, th t is, that it did have a scorch-retarding effect, besides yielding a lower final degree/complexity of aggregation.

  • 188.
    Undin, Jenny
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Adjustable Degradation Properties and Biocompatibility of Amorphous and Functional Poly(ester-acrylate)-Based Materials2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 7, p. 2800-2807Article in journal (Refereed)
    Abstract [en]

    Tuning the properties of materials toward a special application is crucial in the area of tissue engineering. The design of materials with predetermined degradation rates and controlled release of degradation products is therefore vital. Providing a material with various functional groups is one of the best ways to address this issue because alterations and modifications of the polymer backbone can be performed easily. Two different 2-methylene-1,3-dioxepane/glycidyl methacrylate-based (MDO/GMA) copolymers were synthesized with different feed ratios and immersed into a phosphate buffer solution at pH 7.4 and in deionized water at 37 degrees C for up to 133 days. After different time intervals, the molecular weight changes, mass loss, pH, and degradation products were determined. By increasing the amount of GMA functional groups in the material, the degradation rate and the amount of acidic degradation products released from the material were decreased. As a result, the composition of the copolymers greatly affected the degradation rate. A rapid release of acidic degradation products during the degradation process could be an important issue for biomedical applications because it might affect the biocompatibility of the material. The cytotoxicity of the materials was evaluated using a MTT assay. These tests indicated that none of the materials demonstrated any obvious cytotoxicity, and the materials could therefore be considered biocompatible.

  • 189.
    Undin, Jenny
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Copolymerization of 2-methylene-1,3-dioxepane and glycidyl methacrylate, a well-defined and efficient process for achieving functionalized polyesters for covalent binding of bioactive molecules2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 6, p. 2095-2102Article in journal (Refereed)
    Abstract [en]

    The understanding of cell-material interactions is important for creating personalized implants for tissue engineering. This has resulted in an interest in developing polymers with functional groups with the possibility of controlling the macromolecular surface. We have in a one-pot reaction synthesized a series of amorphous and degradable polyester-based copolymers with active functional groups by copolymerization of 2-methylene-1,3-dioxepane and glycidyl methacrylate. The properties of the final polymers were varied by varying the feed ratios of the monomers, and it was seen that it was possible to control the amount of active functional groups. The resulting epoxy-functionalized polyester was further modified by covalent immobilization of heparin. The heparinization was done in order, in a future aspect, to enhance the osteogenic differentiation of mesenchymal stem cells. Heparin binds directly with the growth factor bone morphogenetic protein-2 and helps to retain its activity. The molecular structure of the copolymers was characterized by nuclear magnetic resonance, size exclusion chromatography, and Fourier transform infrared spectroscopy. Differential scanning calorimetry and tensile testing showed that the monomer feed ratio had a great influence on the properties of the final polymer and that it thus was possible to control the mechanical properties to suit an intended application. The presence of heparin was verified by toluidine blue staining, and all of the films tested showed positive signals for heparin.

  • 190.
    Voepel, Jens
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Percec, Virgil
    Hemicellulose-Based Multifunctional Macroinitiator for Single-Electron-Transfer Mediated Living Radical Polymerization2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 1, p. 253-259Article in journal (Refereed)
    Abstract [en]

    A multifunctional macroinitiator for single-electron-transfer mediated living radical polymerization (SET-LRP) was designed from acetylated galactoglucomannan (AcGGM) by alpha-bromoisobutyric acid functionalization of the anomeric hydroxyl groups on the heteropolysaccharide backbone. This macroinitiator, with a degree of substitution of 0.15, was used in the SET-LRP of methyl acrylate, catalyzed by Cu-0/Me-6-TREN in DMSO, DMF, or DMSO/H2O in various, concentrations. Kinetic analyses confirm high conversions of up to 99.98% and a living behavior of the SET-LRP process providing high molecular weight hemicelluloses/methyl acrylate hybrid copolymers with a brush-like architecture.

  • 191. Wang, Miao
    et al.
    Olszewska, Anna
    Walther, Andreas
    Malho, Jani-Markus
    Schacher, Felix H.
    Ruokolainen, Janne
    Ankerfors, Mikael
    Laine, Janne
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Österberg, Monika
    Ikkala, Olli
    Colloidal Ionic Assembly between Anionic Native Cellulose Nanofibrils and Cationic Block Copolymer Micelles into Biomimetic Nanocomposites2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 6, p. 2074-2081Article in journal (Refereed)
    Abstract [en]

    We present a facile ionic assembly between fibrillar and spherical colloidal objects toward biomimetic nanocomposites with majority hard and minority soft domains based on anionic reinforcing native cellulose nanofibrils and cationic amphiphilic block copolymer micelles with rubbery core. The concept is based on ionic complexation of carboxymethylated nanofibrillated cellulose (NFC, or also denoted as microfibrillated cellulose, MFC) and micelles formed by aqueous self-assembly of quaternized poly(1,2-butadiene)-block-poly(dimethylaminoethyl methacrylate) with high fraction of the NFC reinforcement. The adsorption of block copolymer micelles onto nanocellulose is shown by quartz crystal microbalance measurements, atomic force microscopy imaging, and fluorescent optical microscopy. The physical properties are elucidated using electron microscopy, thermal analysis, and mechanical testing. The cationic part of the block copolymer serves as a binder to NFC, Whereas the hydrophobic rubbery micellar cores are designed to facilitate energy dissipation and nanoscale lubrication between the NFC domains under deformation. We show that the mechanical properties do not follow the rule of mixtures, and synergistic effects are observed with promoted work of fracture in one composition. As the concept allows wide possibilities for tuning, the work suggests pathways for nanocellulose-based biomimetic nanocomposites combining high toughness with stiffness and strength.

  • 192.
    Wang, Min
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Liu, Chao
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dédinaité, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Hyaluronan and Phospholipid Association in Biolubrication2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 12, p. 4198-4206Article in journal (Refereed)
    Abstract [en]

    It is becoming increasingly clear that the outstanding lubrication of synovial joints is achieved by a sophisticated hierarchical structure of cartilage combined with synergistic actions of surface-active components present in the synovial fluid. In this work we focus on the association of two components of the synovial fluid, hyaluronan and dipalmitoyl phosphatidyl choline (DPPC), in bulk solution and at interfaces. We demonstrate that hyaluronan associates with DPPC vesicles and adsorbs to supported DPPC bilayers. The association structures formed at the interface are sufficiently stable to allow sequential adsorption of DPPC and hyaluronan, whereby promoting the formation of thick composite layers of these two components. The lubricating ability of such composite layers was probed by the AFM colloidal probe technique and found to be very favorable with low friction coefficients and high load bearing capacity. With DPPC as the last adsorbed component, a friction coefficient of 0.01 was found up to pressures significantly above what is encountered in healthy synovial joints. Hyaluronan as the last added component increases the friction coefficient to 0.03 and decreases the load bearing capacity somewhat (but still above what is needed in the synovial joint). Our data demonstrate that self-assembly structures formed by hyaluronan and phospholipids at interfaces are efficient aqueous lubricants, and it seems plausible that such self-assembly structures contribute to the exceptional lubrication of synovial joints.

  • 193.
    Wang, Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Kochumalayil, Joby J.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Molecular Adhesion at Clay Nanocomposite Interfaces Depends on Counterion Hydration-Molecular Dynamics Simulation of Montmorillonite/Xyloglucan2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 1, p. 257-265Article in journal (Refereed)
    Abstract [en]

    Nacre-mimetic clay/polymer nanocomposites with clay platelet orientation parallel to the film surface show interesting gas barrier and mechanical properties. In moist conditions, interfacial adhesion is lowered and mechanical properties are reduced. Molecular dynamic simulations (MD) have been performed to investigate the effects of counterions on molecular adhesion at montmorillonite clay (Mnt)-xyloglucan (XG) interfaces. We focus on the role of monovalent cations K+, Na+, and Li+ and the divalent cation Ca2+ for mediating and stabilizing the Mnt/XG complex formation. The conformation of adsorbed XG is strongly influenced by the choice of counterion and so is the simulated work of adhesion. Free energy profiles that are used to estimate molecular adhesion show stronger interaction between XG and clay in the monovalent cation system than in divalent cation system, following a decreasing order of K-Mnt, Na-Mnt, Li-Mnt, and Ca-Mnt. The Mnt clay hydrates differently in the presence of different counterions, leading to a chemical potential of water that is highest in the case of K-Mnt, followed by Na-Mnt and Li-Mnt, and lowest in the case of Ca-Mnt. This means that water is most easily displaced from the interface in the case of K-Mnt, which contributes to the relatively high work of adhesion. In all systems, the penalty of replacing polymer with water at the interface gives a positive contribution to the work of adhesion of between 19 and 35%. Our work confirms the important role of counterions in mediating the adsorption of biopolymer XG to Mnt clays and predicts potassium or sodium as the best choice of counterions for a Mnt-based biocomposite design.

  • 194.
    Westman, Eva-Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Enarsson, Lars-Erik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Assessment of Antibacterial Properties of Polyvinylamine (PVAm) with Different Charge Densities and Hydrophobic Modifications2009In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 6, p. 1478-1483Article in journal (Refereed)
    Abstract [en]

    Hydrophobically modified and unmodified polyvinylamines (PVAm), including a total of five polymers, were tested against both gram-negative (Escherichia coli) and gram-positive (Bacillus subtilis) bacteria for antimicrobial activity. The assessment of PVAm in solution against bacteria is described, and the influence of the charge density and of the hydrophobic modification of the polyelectrolyte is discussed. The antimicrobial activity was found to depend upon the concentration of PVAm and also on the type of bacteria used. The results also indicated that no direct relationship exists between antimicrobial activity and charge density of the different PVAms. It was, however, observed that an alkyl chain length of six or eight alkane units had a substantial effect on the bacteria investigated. The best combined antibacterial activity for the two bacteria tested was achieved for PVAm with a C-6 alkane substituent (PVAm C-6). To evaluate the antimicrobial activity on a solid substrate, PVAm C-6 was further studied after being deposited onto a glass slide and the results show a large reduction in bacterial infection.

  • 195. Wirsen, A.
    et al.
    Sun, H.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Solvent-free vapor-phase photografting of acrylamide onto poly(ethylene terephthalate)2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 5, p. 2697-2702Article in journal (Refereed)
    Abstract [en]

    Poly(ethylene terphthalate) (PET) films were photografted under reduced pressure in a solvent-free vapor of acrylamide and a co-initiator, benzophenone. Characterization of grafted samples by ESCA and contact angles showed that the grafting increased with grafting time and temperature. The amide groups obtained by the acrylamide grafting were converted into amine groups by the Hofmann rearrangement to be used in coupling reactions. The amine groups were confirmed by reaction with pentafluorobenzoyl chloride, which provides a fluorine label for ESCA. Surface grafting of polymeric substrates in the vapor phase induced by plasma or high energy and UV irradiation is reviewed.

  • 196. Wirsen, A.
    et al.
    Sun, H.
    Emilsson, L.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Solvent free vapor phase photografting of maleic anhydride onto poly(ethylene terephthalate) and surface coupling of fluorinated probes, PEG, and an RGD-peptide2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 4, p. 2281-2289Article in journal (Refereed)
    Abstract [en]

    Poly(ethylene terephthalate) (PET) was photografted in a solvent free vapor of maleic anhydride and benzophenone. After hydrolysis of the initially grafted succinic anhydride groups, the carboxylic PET surfaces were modified by coupling reactions in organic and aqueous solutions. 2,2,2-Trifluoroethylan-fine and diamino PEGs of molecular weight 3400 and 2000 were reacted with acid chloride groups obtained by treating the PET-COOH surface with PCl5. Furthermore, fluoro substituted thiols and a cystein terminated RGD containing peptide were bound to PET-COOH surfaces via a disulfide link by a three step coupling sequence. Coupling yields and surface concentrations of the fluoro substituted ligands were calculated from ESCA data. The RGD-peptide surfaces were evaluated by cultivation with rat smooth muscle cells.

  • 197.
    Wu, Duo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Samanta, Archana
    Srivastava, Rajiv K.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Starch-Derived Nanographene Oxide Paves the Way for Electrospinnable and Bioactive Starch Scaffolds for Bone Tissue Engineering2017In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 18, no 5, p. 1582-1591Article in journal (Refereed)
    Abstract [en]

    A straightforward process that enabled electrospinning of bioactive starch-based nanofiber scaffolds was developed by utilizing starch derived nano graphene oxide (nGO) as a property enhancer and formic acid as a solvent and esterification reagent. The reaction mechanism and process were followed by detailed spectroscopic investigation. Furthermore, the incorporation of nGO as a “green bioactive additive” endorsed starch nanofibrous scaffolds several advantageous functionalities including improved electrospinnability and thermal stability, good cytocompatibility, osteo-bioactivity, and retained biodegradability. The biodegradable starch/nGO nanofibers underwent simultaneous degradation and mineralization process during 1 week of cell culture and mineralization test, thus, mimicking the structure and function of extracellular matrices (ECMs) and indicating promise for bone tissue engineering applications.

  • 198.
    Wu, Qiuju
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Henriksson, Marielle
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Liu, Xiaohui
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A High Strength Nanocomposite Based on Microcrystalline Cellulose and Polyurethane2007In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 12, p. 3687-3692Article in journal (Refereed)
    Abstract [en]

    A high-strength elastomeric nanocomposite has successfully been prepared by dispersing microcrystalline cellulose in a polyurethane matrix. The resulting nanocomposites show increased strain-to-failure in addition to increased stiffness and strength compared to the unfilled polyurethane. The optimal composite contained 5 wt % cellulose. The average true strength for this composition was 257 MPa, compared with 39 MPa for the neat polyurethane, and showed the highest strain-to-failure. The improvements of stiffness, strength, as well as strain-to-failure are believed to be due to good interaction, by both covalent and hydrogen bonds, between the polyurethane and the cellulose nanofibrils.

  • 199. Xu, Huan
    et al.
    Xie, Lan
    Jiang, Xin
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Chen, Jing-Bin
    Zhong, Gan-Ji
    Li, Zhong-Ming
    Structural Basis for Unique Hierarchical Cylindrites Induced by Ultrahigh Shear Gradient in Single Natural Fiber Reinforced Poly(lactic acid) Green Composites2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 5, p. 1676-1686Article in journal (Refereed)
    Abstract [en]

    A local shear flow field was feasibly generated by pulling the ramie fiber in single fiber reinforced poly(lactic acid) (PLA) composites. This was featured by an ultrahigh shear gradient with a maximum shear rate up to 1500 s(-1), a level comparable to that frequently occurring during the practical polymer processing. To distinguish shear-induced self-nucleation and ramie fiber-induced heterogeneous nucleation, the shear history was classified by pulling the fiber for 5 s (pulled sample) and pulling out the fiber during 10 s (pulled-out sample), while the static fiber-induced crystallization was carried out as the counterpart. As a result of the ultrahigh shear gradient, the combination of primary shear-induced nucleation in the central region and secondary nucleation in the outer layer assembled the unique hierarchical superstructures. By comparing the architectural configurations of interphases formed in the static, pulled, and pulled-out samples, it was shown that the hierarchical cylindrites underwent the process of self-nucleation driven by the applied shear flow, very different from the formation of fiber-induced transcrystallinity (TC) triggered by the heterogeneous nucleating sites at the static fiber surface. The twisting of transcrystallized lamellae may take place due to the spatial hindrance induced by the incredibly dense nuclei under the intense shearing flow, as observed in the synchrotron X-ray diffraction patterns. The influence of chain characteristics on the crystalline morphology was further explored by adding a small amount of poly(ethylene glycol) (PEG) to enhance the molecular mobility of PLA. It was of interest to find that the existence of PEG not only facilitated the growth rates of TC and cylindrites but also improved the preferential orientation of PLA chains and thus expanded the ordered regions. We unearthed lamellar units that were composed of rich fibrillar extended chain crystals (diameter of 50-80 nm). These results are of importance to shed light on tailoring crystalline morphology for natural fibers reinforced green composite materials. Of immense practical significance, too, is the crystalline evolution that has been tracked in the simple model penetrated with an ultrahigh shear gradient, which researchers have so far been unable to replicate during the practical melt processing, such as extrusion and injection molding.

  • 200.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Sichuan University, Chengdu, China.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Conformational Footprint in Hydrolysis-Induced Nanofibrillation and Crystallization of Poly(lactic acid)2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 3, p. 985-995Article in journal (Refereed)
    Abstract [en]

    The origin of hydrolysis-induced nanofibrillation and crystallization, at the molecular level, was revealed by mapping the conformational ordering during long-term hydrolytic degradation of initially amorphous poly(lactic acid) (PLA), a representative model for degradable aliphatic polyesters generally displaying strong interplay between crystallization and hydrolytic erosion. The conformational regularization of chain segments was essentially the main driving force for the morphological evolution of PLA during hydrolytic degradation. For hydrolysis at 37 degrees C, no significant structural variations were observed due to the immobilization of frozen PLA chains. In contrast, conformational ordering in PLA was immediately triggered during hydrolysis at 60 degrees C and was responsible for the transition from random coils to disordered trans and, further, to quasi-crystalline nanospheres. On the surfaces, the head-by-head absorption and joining of neighboring nanospheres led to nanofibrillar assemblies following a gluttonous snake-like manner. The length and density of nanofibers formed were in close relation to the hydrolytic evolution, both of which showed a direct rise in the initial 60 days and then a gradual decline. In the interior, presumably the high surface energy of the nanospheres allowed for the preferential anchoring and packing of conformationally ordered chains into lamellae. In accordance with the well-established hypothesis, the amorphous regions were attacked prior to the erosion of crystalline entities, causing a rapid increase of crystallinity during the initial 30 days, followed by a gradual fall until 90 days. In addition to adequate illustration of hydrolysis-induced variations of crystallinity, our proposed model elucidates the formation of spherulitic nuclei featuring an extremely wide distribution of diameters ranging from several nanometers to over 5 mu m, as well as the inferior resistance to hydrolysis observed for the primary nuclei. Our work fuels the interest in controlling nanofibrillation mechanism during hydrolysis of PLA, opening up possibilities for straightforward nanofiber formation.

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