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  • 1.
    An, Junxue
    et al.
    KTH Royal Institute of Technology, Sweden.
    Liu, Xiaoyan
    KTH Royal Institute of Technology, Sweden.
    Dedinaite, Andra
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Korchagina, Evgeniya
    University of Montreal, Canada.
    Winnik, Francoise M.
    University of Montreal, Canada; National Institute for Materials Science, Japan; University of Helsinki, Finland.
    Claesson, Per M.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Dedinaite, Andra
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers2017In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 487, p. 88-96Article in journal (Refereed)
    Abstract [en]

    Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40 °C. A local force minimum at short separation develops at 40 °C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25 °C are significantly lower after exposure to a temperature of 40 °C than prior to heating, which is due to higher polymer chain density on the surface after heating.

  • 2.
    Besharat, Zahra
    et al.
    KTH Royal Institute of Technology, Sweden.
    Wakeham, Deborah
    KTH Royal Institute of Technology, Sweden.
    Johnson, C. Magnus
    KTH Royal Institute of Technology, Sweden.
    Luengo, Gustavo S.
    L’Oréal Research and Innovation, France.
    Greaves, Andrew
    L’Oréal Research and Innovation, France.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Göthelid, Mats
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Mixed monolayers of alkane thiols with polar terminal group on gold: Investigation of structure dependent surface properties2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 484, p. 279-290Article in journal (Refereed)
    Abstract [en]

    Adsorption of thiols with cationic or anionic terminal group on gold has been studied from mixed solutions of 11-Amino-1-undecanethiol (AUT) and 3-Mercaptopropionic acid (MPA) using Quartz Crystal Microbalance with Dissipation (QCM-D), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and contact angles. The goal is to probe the nature of such layers, and the additivity or otherwise of the pH responsiveness, with a view to evaluate their suitability as smart materials. For each of the two pure (unmixed) cases, ordered molecular monolayers are formed with sulfur binding to gold and the alkane chain pointing out from the surface as expected. Adsorption from the thiol mixtures, however, leads to a more complex behaviour. The surface concentration of thiols from the mixtures, as determined by QCM-D, is considerably lower than for the pure cases and it reaches a minimum at a 3:1 MPA/AUT relative concentration in the solution. The XPS results confirm a reduction in adsorbed amount in mixtures with the lowest overall intensity for the 3:1 ratio. Monolayers formed from mixtures display a wettability which is much lower and less pH sensitive. Collectively these results confirm that for adsorption from mixed systems, the configuration is completely different. Complex formation in the mixed solutions leads to the adsorption of molecules parallel to the surface in an axially in-plane configuration. This parallel layer of thiols is mechanically relatively robust to nano-shaving based on AFM measurements. These results will have a significant impact on the design of biomimetic surface coatings particularly when mixtures of oppositely charged molecules are present on the surface, as is commonly the case in biological, proteinaceous surfaces (e.g. hair and skin).

  • 3.
    Boge, Lukas
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. Chalmers University of Technology, Sweden.
    Bysell, Helena
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Ringstad, Lovisa
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Wennman, David
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Process Development, Analys och fastfas.
    Umerska, Anita
    University of Angers, France.
    Cassisa, Viviane
    CHU Angers, France.
    Eriksson, Jonny
    Uppsala University, Sweden.
    Joly-Guillou, Marie-Laure
    CHU Angers, France.
    Edwards, Katarina
    Uppsala University, Sweden.
    Andersson, Martin
    Chalmers University of Technology, Sweden.
    Lipid-based liquid crystals as carriers for antimicrobial peptides: Phase behavior and antimicrobial effect2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 17, p. 4217-4228Article in journal (Refereed)
    Abstract [en]

    The number of antibiotic-resistant bacteria is increasing worldwide, and the demand for novel antimicrobials is constantly growing. Antimicrobial peptides (AMPs) could be an important part of future treatment strategies of various bacterial infection diseases. However, AMPs have relatively low stability, because of proteolytic and chemical degradation. As a consequence, carrier systems protecting the AMPs are greatly needed, to achieve efficient treatments. In addition, the carrier system also must administrate the peptide in a controlled manner to match the therapeutic dose window. In this work, lyotropic liquid crystalline (LC) structures consisting of cubic glycerol monooleate/water and hexagonal glycerol monooleate/oleic acid/water have been examined as carriers for AMPs. These LC structures have the capability of solubilizing both hydrophilic and hydrophobic substances, as well as being biocompatible and biodegradable. Both bulk gels and discrete dispersed structures (i.e., cubosomes and hexosomes) have been studied. Three AMPs have been investigated with respect to phase stability of the LC structures and antimicrobial effect: AP114, DPK-060, and LL-37. Characterization of the LC structures was performed using small-angle X-ray scattering (SAXS), dynamic light scattering, ζ-potential, and cryogenic transmission electron microscopy (Cryo-TEM) and peptide loading efficacy by ultra performance liquid chromatography. The antimicrobial effect of the LCNPs was investigated in vitro using minimum inhibitory concentration (MIC) and time-kill assay. The most hydrophobic peptide (AP114) was shown to induce an increase in negative curvature of the cubic LC system. The most polar peptide (DPK-060) induced a decrease in negative curvature while LL-37 did not change the LC phase at all. The hexagonal LC phase was not affected by any of the AMPs. Moreover, cubosomes loaded with peptides AP114 and DPK-060 showed preserved antimicrobial activity, whereas particles loaded with peptide LL-37 displayed a loss in its broad-spectrum bactericidal properties. AMP-loaded hexosomes showed a reduction in antimicrobial activity.

  • 4.
    Colombo, Stefan
    et al.
    Uppsala University, Sweden.
    Brisander, Magnus
    XSpray Microparticles AB, Sweden.
    Haglöf, Jakob
    Uppsala University, Sweden.
    Sjövall, Peter
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Medicinteknik.
    Andersson, Per
    XSpray Microparticles AB, Sweden.
    Østergaard, Jesper
    University of Copenhagen, Denmark.
    Malmsten, Martin
    Uppsala University, Sweden.
    Matrix effects in nilotinib formulations with pH-responsive polymer produced by carbon dioxide-mediated precipitation2015In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 494, no 1, p. 205-217, article id 15114Article in journal (Refereed)
    Abstract [en]

    Factors determining the pH-controlled dissolution kinetics of nilotinib formulations with the pH-titrable polymer hydroxypropyl methylcellulose phthalate, obtained by carbon dioxide-mediated precipitation, were mechanistically examined in acid and neutral environment. The matrix effect, modulating the drug dissolution, was characterized with a battery of physicochemical methodologies, including ToF-SIMS for surface composition, SAXS/WAXS and modulated DSC for crystallization characterization, and simultaneous UV-imaging and Raman spectroscopy for monitoring the dissolution process in detail. The hybrid particle formulations investigated consisted of amorphous nilotinib embedded in a polymer matrix in single continuous phase, displaying extended retained amorphicity also under wet conditions. It was demonstrated by Raman and FTIR spectroscopy that the efficient drug dispersion and amorphization in the polymer matrix were mediated by hydrogen bonding between the drug and the phthalate groups on the polymer. Simultaneous Raman and UV-imaging studies of the effect of drug load on the swelling and dissolution of the polymer matrix revealed that high nilotinib load prevented matrix swelling on passage from acid to neutral pH, thereby preventing re-precipitation and re-crystallization of incorporated nilotinib. These findings provide a mechanistic foundation of formulation development of nilotinib and other protein kinase inhibitors, which are now witnessing an intense therapeutic and industrial attention due to the difficulty in formulating these compounds so that efficient oral bioavailability is reached.

  • 5.
    Cooper, Peter K.
    et al.
    University of Newcastle, Australia.
    Li, Hua
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Webber, Grant B.
    University of Newcastle, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Tribotronic control of friction in oil-based lubricants with ionic liquid additives2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 34, p. 23657-23662Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy (AFM) reveals that tribotronic control of friction using an external potential applied to a gold surface is possible for ionic liquid (IL) concentrations as low as 5 mol% in hexadecane. The IL used is trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, in which both the cation and anion have surfactant-like structures, and is miscible with hexadecane in all proportions. For IL concentrations less than 5 mol% friction does not vary with applied potential, but for 5 mol% and above changing the potential changes the composition of the IL boundary layer from cation-enriched (negative potentials) to anion-enriched (positive potentials). As the lubricities of the cation-rich and anion-rich boundary layers differ, this enables active control of friction in oil-based lubricants.

  • 6.
    Eneborg, Alexander
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Improvement and Characterization of Aqueous Graphene Dispersions2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Graphene has many outstanding properties which make it a prime candidate for new technology. At the current time it is very difficult and expensive to produce large sheets of graphene, but there are many applications where that is not necessary and smaller flakes of graphene can be used instead. A practical way of handling these graphene flakes is in a dispersion, especially a water-based dispersion have many benefits. Such a stable dispersion of functionalized graphene is produced, improved, and characterized in this project. An aqueous system that was developed in two previous M.Sc. theses, each determining a suitable graphene powder and stabilizer, was used as a starting point with the main purpose being to improve the yield. The method used to produce these dispersions can be described as sonicating graphene powder in a solution of water and stabilizer followed by centrifuging to remove un-dispersed graphene particles. Experiments were carried out examining the possibility of dispersing those previously undispersed graphene flakes, combining the stabilizer with several surfactants, optimizing the centrifuge speed and time, refining the sonication procedure with longer exposure time and cooling, narrowing the size-distribution of the original stabilizer through ultrafiltration, and removing excessive unbound stabilizer through ultrafiltration. Samples were characterized with UV-vis, SEM, TGA, Electrophoretic light scattering, and Laser diffraction spectroscopy. It was discovered that the yield from the graphene powder was heavily dependent on sonication time and centrifugation conditions. The gain from increasing sonication time showed that most, if not all, of the un-dispersed graphene flakes previously considered lost could in fact be dispersed. In an industrial setting any un-dispersed flakes could simply be added to the next batch. Reducing the centrifugation speed as well as time increased the concentration of graphene to more than twice as high, and that gain comes solely from the larger graphene flakes. Thusly the previous problem with a low yield was shown to have been caused by too little sonication and too much centrifugation. The particle size analysis did show a small reduction in flake size as the sonication time was increased, but when those dispersions were characterized in SEM they all formed even films with no discernable difference between them. Purifying the scaled up dispersions by removing excess stabilizer through ultrafiltration was performed to three different degrees, 0 %, 50 % and 95 %, for a total of three dispersions of 100ml. All three dispersions were shown to be highly stable, with no apparent reduction in graphene concentration over 5 weeks and a zeta potential averaging below -50mV. The TGA results reinforce the UV-vis results, proving that the purification worked as intended.

  • 7.
    Falk, Julia
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. Uppsala University, Sweden.
    Freeze-drying of protein pharmaceutical in vials with different character2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Freeze-drying of protein pharmaceuticals is a procedure frequently used to obtain stability of the active pharmaceutical ingredientduring distribution and storage. It can be performed in pre-filled syringes, with a lubricous coating of silicone on the inside, to enable the piston moving. The coating changes the environment potentially affecting the features of the freeze-dried cake since the wetting behavior and adhesion to the inner wall is affected.This project aimed to investigate the effect of the siliconization of the cakes. Three different formulations were freeze-dried in nonsiliconized (NS) and siliconized vials using different siliconization protocols. Analysis was done using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA),scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and an embedding method, intended to give information about the cake’s shrinkage, cracking and pore-structure. The water content in the bottom of the cakes was consistently higher than in the top, a difference decreasing over time. Increased surface hydrophobicity lead to increased shrinkage of the cake’s volume and a decrease in fogging. The bottom of the protein cake in the vial siliconized with a commercial silicone emulsion consisted of pores with regularly equal pore size and thick pore walls, a structure not seen in any other cake. All cakes in the silicone emulsion siliconized vials had lower water content than the cakes in the vials using the other siliconization method. The XPS-analysis showed that the cakes in the emulsion siliconized vials contained silicon, indicating an excess of silicone when siliconizing and/or an unstable coating.

  • 8.
    Gårdebjer, Sofie
    et al.
    Chalmers University of Technology, Sweden.
    Andersson, M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Engström, J.
    AkzoNobel, Sweden.
    Restorp, P.
    AkzoNobel, Sweden.
    Persson, Michael
    Chalmers University of Technology, Sweden; AkzoNobel, Sweden.
    Larsson, Anette
    Chalmers University of Technology, Sweden.
    Using Hansen solubility parameters to predict the dispersion of nano-particles in polymeric films2016In: Polymer Chemistry, ISSN 1759-9954, E-ISSN 1759-9962, Vol. 7, no 9, p. 1756-1764Article in journal (Refereed)
    Abstract [en]

    We suggest a rough and straightforward method to predict the dispersibility of modified cellulose nanocrystals (CNC) in nanocomposites using Hansen solubility parameters (HSP). The surface of CNC was modified using a novel approach where Y-shaped substituents with two different carbon chain lengths were attached to the surface. Approximate HSP values were calculated for the modified CNC, and dispersions of unmodified and modified CNC in solvents with varying HSPs were studied. The best dispersibility was observed in dichloromethane, when the CNC surface was modified with longer carbon chains. Dichloromethane has HSP similar to low-density polyethylene (LDPE). Nanocomposites with both unmodified and modified CNC were produced. The materials with modified CNC showed increased adhesion between the filler and the matrix, followed by a decreased water permeability compared to unmodified CNC, suggesting a better dispersibility of modified CNC in LDPE and confirming the usefulness of this approach.

  • 9.
    Hedberg, Yolanda S.
    et al.
    KTH Royal Institute of Technology, Sweden; Karolinska Institute, Sweden.
    Pettersson, Maria
    Uppsala University, Sweden.
    Pradhan, Sulena
    KTH Royal Institute of Technology, Sweden.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Persson, Cecilia
    Uppsala University, Sweden.
    Can Cobalt(II) and Chromium(III) ions released from joint prostheses influence the friction coefficient?2015In: ACS Biomaterial Science and Engineering, E-ISSN 2373-9878, Vol. 1, no 8, p. 617-620Article in journal (Refereed)
    Abstract [en]

    Cobalt chromium molybdenum alloys (CoCrMo) are commonly used as articulating components in joint prostheses. In this tribocorrosive environment, wear debris and metal ionic species are released and interact with proteins, possibly resulting in protein aggregation. This study aimed to investigate whether this could have an effect on the friction coefficient in a typical material couple, namely CoCrMo-on-polyethylene. It was confirmed that both Co(II) and Cr(III) ions, and their combination, at concentrations relevant for the metal release situation, resulted in protein aggregation and its concomitant precipitation, which increased the friction coefficient. Future studies should identify the clinical importance of these findings.

  • 10.
    Hellsing, Maja
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Rennie, Adrian
    Uppsala University, Sweden.
    Rodal, Michael
    Biolin Scientific AB, Sweden.
    Höök, Fredrik
    Chalmers University of Technology, Sweden.
    Charged polystyrene nanoparticles near a SiO2/water interface2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 1, p. 222-228Article in journal (Refereed)
    Abstract [en]

    Quartz crystal microbalance with dissipation (QCM-D) monitoring is traditionally used to investigate adsorption processes at liquid-solid interfaces but has also been applied increasingly to characterize the viscoelastic properties of complex liquids. Here, we contribute new insights to the latter field by using QCM-D to investigate the structure near an interface and high-frequency viscoelastic properties of charge stabilized polystyrene particles (radius 37 nm) dispersed in pure water. The study reveals changes with increasing ionic-strength from the crystalline order at low salt concentration to that with a less-structured particle distribution at high ionic strength. Replacing pure water with an aqueous particle dispersion is due to an increased mass load expected to give rise to a decrease in frequency, f. In the present work increases in both f and dissipation, D, were observed on exchanging pure water for the particle dispersion at low ionic strength. However, the QCM-D data are still well-represented by a viscoelastic Voigt model, with the viscosity increasing from 1.0 to 1.3 mPa s as the particle volume fraction changed from 0.005 to 0.07. This increase is higher than predicted for dilute dispersions according to Einstein’s equation for the viscosity of non-interacting hard spheres particles in liquids but can be explained by the charge repulsion between the particles giving rise to a higher effective volume fraction. It is also concluded that the polystyrene particles did not adhere to the solid surface but rather were separated by a layer of pure dispersion medium. The QCM-D response was successfully represented using a viscoelastic Kelvin-Voigt model, from which it was concluded that the thickness of the Newtonian dispersion medium layer was of the order of the particle-particle bulk separation, in the range 50 to 250 nm and was observed to decrease with both particle concentration and with addition of salt. Similar anomalous frequency and dissipation responses have been seen previously for colloidal systems containing weakly adherent colloidal particles and bacteria and in these cases interpreted in terms of coupled resonators. We here demonstrate that surface attachment is not required for such phenomena to occur, but that a viscoelastic liquid separated from the oscillating surface by a thin Newtonian layer can give rise to very similar responses.

  • 11.
    Heydari, Golrokh
    et al.
    KTH Royal Institute of Technology, Sweden.
    Sedighi Moghaddam, Maziar
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Tuominen, Mikko
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Fielden, Matthew
    KTH Royal Institute of Technology, Sweden.
    Haapanen, Janne
    TUT Tampere University of Technology, Finland.
    Mäkelä, Jyrki M.
    TUT Tampere University of Technology, Finland.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Wetting hysteresis induced by temperature changes: Supercooled water on hydrophobic surfaces2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 468, p. 21-33Article in journal (Refereed)
    Abstract [en]

    The state and stability of supercooled water on (super)hydrophobic surfaces is crucial for low temperature applications and it will affect anti-icing and de-icing properties. Surface characteristics such as topography and chemistry are expected to affect wetting hysteresis during temperature cycling experiments, and also the freezing delay of supercooled water. We utilized stochastically rough wood surfaces that were further modified to render them hydrophobic or superhydrophobic. Liquid flame spraying (LFS) was utilized to create a multi-scale roughness by depositing titanium dioxide nanoparticles. The coating was subsequently made non-polar by applying a thin plasma polymer layer. As flat reference samples modified silica surfaces with similar chemistries were utilized. With these substrates we test the hypothesis that superhydrophobic surfaces also should retard ice formation. Wetting hysteresis was evaluated using contact angle measurements during a freeze-thaw cycle from room temperature to freezing occurrence at -7 °C, and then back to room temperature. Further, the delay in freezing of supercooled water droplets was studied at temperatures of -4 °C and -7 °C. The hysteresis in contact angle observed during a cooling-heating cycle is found to be small on flat hydrophobic surfaces. However, significant changes in contact angles during a cooling-heating cycle are observed on the rough surfaces, with a higher contact angle observed on cooling compared to during the subsequent heating. Condensation and subsequent frost formation at sub-zero temperatures induce the hysteresis. The freezing delay data show that the flat surface is more efficient in enhancing the freezing delay than the rougher surfaces, which can be rationalized considering heterogeneous nucleation theory. Thus, our data suggests that molecular flat surfaces, rather than rough superhydrophobic surfaces, are beneficial for retarding ice formation under conditions that allow condensation and frost formation to occur.

  • 12.
    Heydari, Golrokh
    et al.
    KTH Royal Institute of Technology, Sweden.
    Tyrode, Erik
    KTH Royal Institute of Technology, Sweden.
    Visnevskij, Ceslav
    Vilnius University, Lithuania.
    Makuska, Ricardas
    Vilnius University, Lithuania.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Temperature-dependent deicing properties of electrostatically anchored branched brush layers of poly(ethylene oxide)2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 17, p. 4194-4202Article in journal (Refereed)
    Abstract [en]

    The hydration water of hydrophilic polymers freezes at subzero temperatures. The adsorption of such polymers will result in a hydrophilic surface layer that strongly binds water. Provided this interfacial hydration water remains liquidlike at subzero temperatures, its presence could possibly reduce ice adhesion, in particular, if the liquidlike layer is thicker than or comparable to the surface roughness. To explore this idea, a diblock copolymer, having one branched bottle-brush block of poly(ethylene oxide) and one linear cationic block, was electrostatically anchored on flat silica surfaces. The shear ice adhesion strength on such polymer-coated surfaces was investigated down to -25 °C using a homebuilt device. In addition, the temperature dependence of the ice adhesion on surfaces coated with only the cationic block, only the branched bottle-brush block, and with linear poly(ethylene oxide) was investigated. Significant ice adhesion reduction, in particular, at temperatures above -15 °C, was observed on silica surfaces coated with the electrostatically anchored diblock copolymer. Differential scanning calorimetry measurements on bulk polymer solutions demonstrate different thermal transitions of water interacting with branched and linear poly(ethylene oxide) (with hydration water melting points of about -18 and -10 °C, respectively). This difference is consistent with the low shear ice adhesion strength measured on surfaces carrying branched bottle-brush structured poly(ethylene oxide) at -10 °C, whereas no significant adhesion reduction was obtained with linear poly(ethylene oxide) at this temperature. We propose a lubrication effect of the hydration water bound to the branched bottle-brush structured poly(ethylene oxide), which, in the bulk, does not freeze until -18 °C.

  • 13.
    Hjalmarsson, Nicklas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Atkin, Rob
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Effect of Lithium ions on rheology and interfacial forces in Ethylammonium Nitrate and Ethanolammonium Nitrate2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 47, p. 26960-26967Article in journal (Refereed)
    Abstract [en]

    The effect of added Li+ to two ionic liquids (ILs), ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), has been investigated using rheology and colloidal probe atomic force microscopy (AFM). Rheology data revealed a complex viscosity dependence that can be ascribed to the different bulk nanostructures. AFM force curves revealed steps for the neat ILs, analogous to those in previous studies. The addition of Li+ broadened the steps, which is likely an effect of ion clusters formed. Friction measurements corroborate this data and also showed that the structure of EtAN is much more prone to change as Li+ is added. These results demonstrate the complex behavior of ILs on interfaces and the effect of perturbing such interactions. (Graph Presented).

  • 14.
    Hjalmarsson, Nicklas
    et al.
    KTH The Royal Institute of Technology, Sweden.
    Atkin, Rob
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Is the boundary layer of an ionic liquid equally lubricating at higher temperature?2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 13, p. 9232-9239Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C. Force curves revealed a strong fluid dynamic influence at room temperature, which was greatly reduced at elevated temperatures due to the reduced liquid viscosity. A fluid dynamic analysis reveals that bulk viscosity is manifested at large separation but that EAN displays a nonzero slip, indicating a region of different viscosity near the surface. At high temperatures, the reduction in fluid dynamic force reveals step-like force curves, similar to those found at room temperature using much lower scan rates. The ionic liquid boundary layer remains adsorbed to the solid surface even at high temperature, which provides a mechanism for lubrication when fluid dynamic lubrication is strongly reduced. The friction data reveals a decrease in absolute friction force with increasing temperature, which is associated with increased thermal motion and reduced viscosity of the near surface layers but, consistent with the normal force data, boundary layer lubrication was unaffected. The implications for ILs as lubricants are discussed in terms of the behaviour of this well characterised system.

  • 15.
    Hjalmarsson, Nicklas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Wallinder, Daniel
    Attana AB, Sweden.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium.
    Atkin, Rob
    University of Newcastle, Australia.
    Aastrup, Teodor
    Attana AB, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Weighing the surface charge of an ionic liquid2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 38, p. 16039-16045Article in journal (Refereed)
    Abstract [en]

    Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively "weigh" the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.

  • 16.
    Kronberg, Bengt
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    The hydrophobic effect2016In: Current Opinion in Colloid & Interface Science, ISSN 1359-0294, E-ISSN 1879-0399, Vol. 22, p. 14-22Article, review/survey (Refereed)
    Abstract [en]

    Abstract This review is a brief discussion on the development of the understanding of hydrophobicity, or the hydrophobic effect. The hydrophobic effect is primarily discussed in terms of partitioning of hydrocarbons between a hydrophobic environment and water as well as solubility of hydrocarbons in water. Micellization of surfactants is only briefly reviewed. It is emphasized that (i) the cause of the hydrophobic effect, e.g. the low solubility of a hydrocarbon in water, is to be found in the high internal energy of water resulting in a high energy to create a cavity in order to accommodate the hydrophobe, (ii) the “structuring” of water molecules around a hydrophobic compound increases the solubility of the hydrophobe. The “structuring” of water molecules around hydrophobic compounds is discussed in terms of recent spectroscopic findings. It is also emphasized that (iii) the lowering of entropy due to a structuring process must be accompanied by an enthalpy that is of the same order of magnitude as the TΔS for the process. Hence, there is an entropy–enthalpy compensation leading to a low free energy change for the structuring process. The assumption of a rapid decay of the entropy with temperature provides an explanation of the enthalpy–entropy compensation so often found in aqueous systems. It is also emphasized (iv) that the free energy obtained from partitioning, or solubility limits, needs to be corrected for molecular size differences between the solute and the solvent. The Flory–Huggins expression is a good first approximation for obtaining this correction. If the effect of different molecular sizes is not corrected for, this leads to erroneous conclusions regarding the thermodynamics of the hydrophobic effect. Finally, (v) micellization and adsorption of surfactants, as well as protein unfolding, are briefly discussed in terms of the hydrophobic effect.

  • 17.
    Li, Hua
    et al.
    University of Newcastle, Australia.
    Somers, Anthony E.
    Deakin University, Australia.
    Howlett, Patrick C.
    Deakin University, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Forsyth, Maria
    Deakin University, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Addition of low concentrations of an ionic liquid to a base oil reduces friction over multiple length scales: A combined nano- and macrotribology investigation2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6541-6547Article in journal (Refereed)
    Abstract [en]

    The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials. Silica surfaces lubricated with mixtures of the IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate and hexadecane are probed using atomic force microscopy (AFM) (nanoscale) and ball-on-disc tribometer (macroscale). At both length scales the pure IL is a much more effective lubricant than hexadecane. At the nanoscale, 2.0 mol% IL (and above) in hexadecane lubricates the silica as well as the pure IL due to the formation of a robust IL boundary layer that separates the sliding surfaces. At the macroscale the lubrication is highly load dependent; at low loads all the mixtures lubricate as effectively as the pure IL, whereas at higher loads rather high concentrations are required to provide IL like lubrication. Wear is also pronounced at high loads, for all cases except the pure IL, and a tribofilm is formed. Together, the nano- and macroscales results reveal that the IL is an effective lubricant additive - it reduces friction - in both the boundary regime at the nanoscale and mixed regime at the macroscale.

  • 18.
    Li, Hua
    et al.
    University of Newcastle, Australia.
    Somers, Anthony E.
    Deakin University, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Howlett, Patrick C.
    Deakin University, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Combined nano- and macrotribology studies of titania lubrication using the oil-ionic liquid mixtures2016In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 4, no 9, p. 5005-5012Article in journal (Refereed)
    Abstract [en]

    The lubrication of titania surfaces using a series of ionic liquid (IL)-hexadecane mixtures has been probed using nanoscale atomic force microscopy (AFM) and macroscale ball-on-disk tribometer measurements. The IL investigated is trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, which is miscible with hexadecane in all proportions. At both length scales, the pure IL is a much more effective lubricant than pure hexadecane. At low loads, which are comparable to common industrial applications, the pure IL reduces the friction by 80% compared to pure hexadecane; while the IL-hexadecane mixtures lubricate the titania surface as effectively as the pure IL and wear decreases with increasing IL concentration. At high test loads the adsorbed ion boundary layer is displaced leading to surface contact and high friction, and wear is pronounced for all IL concentrations. Nonetheless, the IL performs better than a traditional zinc-dialkyl-dithophosphate (ZDDP) antiwear additive at the same concentration.

  • 19.
    Li, Jing
    et al.
    KTH Royal Institute of Technology, Sweden.
    Huang, Hui
    KTH Royal Institute of Technology, Sweden.
    Fielden, Matthew
    KTH Royal Institute of Technology, Sweden.
    Pan, Jinshan
    KTH Royal Institute of Technology, Sweden.
    Ecco, Luiz
    University of Trento, Italy.
    Schellbach, Carsten
    Enthone GmbH, Germany.
    Delmas, Grégory
    Arkema Coating Resins, France.
    Claesson, Per Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Towards the mechanism of electrochemical activity and self-healing of 1 wt% PTSA doped polyaniline in alkyd composite polymer coating: Combined AFM-based studies2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 23, p. 19111-19127Article in journal (Refereed)
    Abstract [en]

    A composite solvent-borne alkyd coating with 1 wt% p-toluene sulfonic acid (PTSA) doped polyaniline (PANI) was prepared. The mechanisms of electrochemical activity and self-healing properties of the composite coating were investigated by in situ atomic force microscopy (AFM), intermodulation AFM (ImAFM), electrochemical controlled (EC)-AFM combined with cyclic voltammetry (CV), Kelvin force microscopy (KFM), and Fourier transform infrared spectroscopy (FTIR), as well as open-circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) methods. The ImAFM demonstrates the multiphase structure of the composite coating and a high compatibility between the doped PANI and alkyd matrix. The CV and EC-AFM results reveal a high electrochemical activity of the doped PANI in the composite coating as well as reversible redox reactions between the emeraldine salt (ES) and leuco emeraldine base (LB) forms. The Volta potential mapping of KFM demonstrates a strong self-healing ability of the doped PANI in air conditions. The good electrochemical connection between the fine network of PANI in the composite coating and metal surface underneath enable the occurrence of reversible redox reaction between the ES/LB forms of doped PANI and a concomitant release of dopant anions both in air and in 3 wt% NaCl solution as demonstrated by OCP and EIS results. These therefore lead to the strong passivation and self-healing effect of the composite coated on the carbon steel surface.

  • 20.
    Limbach, René
    et al.
    Friedrich Schiller University of Jena, Germany.
    Karlsson, Stefan
    RISE - Research Institutes of Sweden, Built Environment, Building Technology.
    Scannell, Garth
    Friedrich Schiller University of Jena, Germany.
    Mathew, Renny
    Stockholm University, Sweden.
    Edén, Mattias
    Stockholm University, Sweden.
    Wondraczek, Lothar
    Friedrich Schiller University of Jena, Germany.
    The effect of TiO2 on the structure of Na2O-CaO-SiO2 glasses and its implications for thermal and mechanical properties2017In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 471, no C, p. 6-18Article in journal (Refereed)
    Abstract [en]

    Titania represents an important compound for property modifications in the widespread family of soda lime silicate glasses. In particular, such titania-containing glasses offer interesting optical and mechanical properties, for example, for substituting lead-bearing consumer glasses. Here, we provide a systematic study of the effect of TiO2 on the structural, thermal, and mechanical properties for three series of quaternary Na2O–CaO–TiO2–SiO2 glasses with TiO2 concentrations up to 12 mol% and variable Na2O, CaO, and SiO2 contents. Structural analyses by Raman and magic-angle spinning 29Si NMR spectroscopy reveal the presence of predominantly four-fold coordinated Ti[4] atoms in glasses of low and moderate TiO2 concentrations, where Si–O–Si bonds are replaced by Si–O–Ti[4] bonds that form a network of interconnected TiO4 and SiO4 tetrahedra, with a majority of the non-bridging oxygen ions likely being located at the SiO4 tetrahedra. At higher TiO2 contents, TiO5 polyhedra are also formed. Incorporation of TiO2 strongly affects the titanosilicate network connectivity, especially when its addition is accompanied by a decrease of the CaO content. However, except for the thermal expansion coefficient, these silicate-network modifications seem to have no impact on the thermal and mechanical stability. Instead, the compositional dependence of the thermal and mechanical properties on the TiO2 content stems from its effect on the network energy and packing efficiency.

  • 21.
    Lobov, Gleb S.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Zhao, Yichen
    KTH Royal Institute of Technology, Sweden.
    Marinins, Aleksandrs
    KTH Royal Institute of Technology, Sweden.
    Yan, Min
    KTH Royal Institute of Technology, Sweden.
    Li, Jiantong
    KTH Royal Institute of Technology, Sweden.
    Sugunan, Abhilash
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Thylén, Lars
    Hewlett-Packard Laboratories, US; KTH Royal Institute of Technology, Sweden.
    Wosinski, Lech
    KTH Royal Institute of Technology, Sweden.
    Östling, Mikael
    KTH Royal Institute of Technology, Sweden.
    Toprak, Muhammet S.
    KTH Royal Institute of Technology, Sweden.
    Popov, Sergei
    KTH Royal Institute of Technology, Sweden.
    Size impact of ordered P3HT nanofibers on optical anisotropy2016In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935, Vol. 217, no 9, p. 1089-1095Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline structures with semiconductor properties. When P3HT nanofibers are dispersed in nonconducting solvent, they react to external alternate electric field by aligning along the field lines. This can be used to create layers of ordered nanofibers and is referred to as alternating current poling method. P3HT nanofibers with three different size distributions are fabricated, using self-assembly mechanism in marginal solvents, and used for the alignment studies. Anisotropic absorption of oriented 2 μm long nanofibers exponentially increases with the magnitude of applied field to a certain asymptotic limit at 0.8 V μm-1, while 100-500 nm long nanofibers respond to electric field negligibly. Effective optical birefringence of oriented 2 μm long nanofibers is calculated, based on the phase shift at 633 nm and the average layer thickness, to be 0.41. These results combined with further studies on real-time control over orientation of P3HT nanofibers in liquid solution or host system are promising in terms of exploiting them in electroabsorptive and electrorefractive applications.

  • 22.
    Lundgren, Anders
    et al.
    Chalmers University of Technology, Sweden.
    Munktell, Sara
    Uppsala University, Sweden.
    Lacey, Matthew
    Chalmers University of Technology, Sweden.
    Berglin, Mattias
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. University of Gothenburg, Sweden.
    Björefors, Fredrik
    Chalmers University of Technology, Sweden.
    Formation of gold nanoparticle size and density gradients via bipolar electrochemistry2016In: ChemElectroChem, ISSN 2196-0216, Vol. 3, no 3, p. 378-382Article in journal (Refereed)
    Abstract [en]

    Bipolar electrochemistry is employed to demonstrate the formation of gold nanoparticle size gradients on planar surfaces. By controlling the electric field in a HAuCl4-containing electrolyte, gold was reduced onto 10nm diameter particles immobilized on pre-modified thiolated bipolar electrode (BPE) templates, resulting in larger particles towards the more cathodic direction. As the gold deposition was the dominating cathodic reaction, the increased size of the nanoparticles also reflected the current distribution on the bipolar electrode. The size gradients were also combined with a second gradient-forming technique to establish nanoparticle surfaces with orthogonal size and density gradients, resulting in a wide range of combinations of small/large and few/many particles on a single bipolar electrode. Such surfaces are valuable in, for example, cell-material interaction and combinatorial studies, where a large number of conditions are probed simultaneously.

  • 23.
    Matougui, Nada
    et al.
    Inserm, France.
    Boge, Lukas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Groo, Anne-Claire
    Inserm, France.
    Umerska, Anita
    Inserm, France.
    Ringstad, Lovisa
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Bysell, Helena
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Saulnier, Patrick
    Inserm, France; CHU Angers, France.
    Lipid-based nanoformulations for peptide delivery2016In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 502, no 1-2, p. 80-97Article, review/survey (Refereed)
    Abstract [en]

    Nanoformulations have attracted a lot of attention because of their size-dependent properties. Among the array of nanoformulations, lipid nanoformulations (LNFs) have evoked increasing interest because of the advantages of their high degree of biocompatibility and versatility. The performance of lipid nanoformulations is greatly influenced by their composition and structure. Therapeutic peptides represent a growing share of the pharmaceutical market. However, the main challenge for their development into commercial products is their inherent physicochemical and biological instability. Important peptides such as insulin, calcitonin and cyclosporin A have been incorporated into LNFs. The association or encapsulation of peptides within lipid-based carriers has shown to protect the labile molecules against enzymatic degradation. This review describes strategies used for the formulation of peptides and some methods used for the assessment of association efficiency. The advantages and drawbacks of such carriers are also described.

  • 24.
    Moghaddam, Maziar Sedighi
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Van den Bulcke, J.
    Ghent University, Belgium.
    Wålinder, M. E. P.
    KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    KTH Royal Institute of Technology, Sweden.
    J., Van Acker
    Ghent University, Belgium.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    X-ray computed tomography on chemically modified wood2016In: Proceedings of the 12th meeting of the Northern European Network for Wood Science and Engineering (WSE): Wood science and engineering - a key factor on the transition to Bioeconomy / [ed] Bruno Andersons and Arnis Kokorevics, Riga: Latvian State Institute of Wood Chemistry , 2016, p. 184-190Conference paper (Refereed)
    Abstract [en]

    Mapping and visualization of structural changes due to the modification of wood would increase the understanding of chemical modification processes and facilitate optimization of the process parameters. The 2D and 3D microstructure of acetylated and furfurylated softwood and hardwood were visualized using X-ray computed tomography and some anatomical features were investigated such as total porosity, cell wall thickness and maximum opening of tracheid lumens. The wetting properties of chemically modified samples were related to the microstructural properties. Significant changes in the wood structure were observed for furfurylated sapwood samples mainly indicated by a change in tracheid shape and filling of tracheids by furan polymer, whereas no microstructural changes were noted for acetylated samples. Furfurylation significantly decreased the porosity of the sample in both earlywood and latewood regions; whereas for acetylated samples the total porosity of modified and unmodified samples was rather similar. This is in line with results of wetting showing that furfurylation reduced both swelling and capillary uptake in contrast to acetylation which reduced mostly swelling.

  • 25.
    Moghaddam, Maziar Sedighi
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Van den Bulcke, J.
    Ghent University, Belgium.
    Wålinder, M. E. P.
    KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    KTH Royal Institute of Technology, Sweden.
    Van Acker, J.
    Ghent University, Belgium.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    X-ray computed tomography on chemically modified wood2016Conference paper (Refereed)
    Abstract [en]

    Mapping and visualization of structural changes due to the modification of wood would increase the understanding of chemical modification processes and facilitate optimization of the process parameters. The 2D and 3D microstructure of acetylated and furfurylated softwood and hardwood were visualized using X-ray computed tomography and some anatomical features were investigated such as total porosity, cell wall thickness and maximum opening of tracheid lumens. The wetting properties of chemically modified samples were related to the microstructural properties. Significant changes in the wood structure were observed for furfurylated sapwood samples mainly indicated by a change in tracheid shape and filling of tracheids by furan polymer, whereas no microstructural changes were noted for acetylated samples. Furfurylation significantly decreased the porosity of the sample in both earlywood and latewood regions; whereas for acetylated samples the total porosity of modified and unmodified samples was rather similar. This is in line with results of wetting showing that furfurylation reduced both swelling and capillary uptake in contrast to acetylation which reduced mostly swelling.

  • 26.
    Moghaddam, Maziar Sedighi
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Van den Bulcke, Jan
    Ghent University, Belgium.
    Wålinder, Magnus E. P.
    KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Van Acker, Joris
    Ghent University, Belgium.
    Swerin, Agne
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Microstructure of chemically modified wood using X-ray computed tomography in relation to wetting properties2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 2, p. 119-128Article in journal (Refereed)
    Abstract [en]

    X-ray computed tomography (XCT) was utilized to visualize and quantify the 2D and 3D microstructure of acetylated southern yellow pine (pine) and maple, as well as furfurylated pine samples. The total porosity and the porosity of different cell types, as well as cell wall thickness and maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. The data show significant changes in the wood structure for furfurylated pine sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for the acetylated pine samples at the high resolution of 0.8

  • 27.
    Nuzzo, Marine
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. Lund University, Sweden.
    Sloth, Jakob
    GEA Process Engineering A/S, Denmark.
    Bergenstahl, Björn
    Lund University, Sweden.
    Millqvist-Fureby, Anna
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Phase segregation in individually dried particles composed of biopolymers2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 40, p. 10946-10954Article in journal (Refereed)
    Abstract [en]

    Mixing of two biopolymers can results in phase separation due to their thermodynamically incompatibility under certain conditions. This phenomenon was first reported when the solution was allowed to equilibrate, but it has later been observed also as a consequence of drying. The challenges of this study were to observe phase segregation by confocal Raman microscopy and LV-SEM on dried film, individually dried particles, and spray dried particles. The influence of the solid content and the phase ratio (composition) of a HPMC/maltodextrin mixture on the localization of the ingredients in the individually dried particles was investigated. We observed that phase segregation of HPMC and maltodextrin is induced by solvent evaporation in film drying, single particle drying, as well as spray drying. The phase ratio is an important parameter that influences the localization of the HPMC-enriched phase and maltodextrin-enriched phase, i.e., to the particle surface, to the core, or in a more or less bicontinuous pattern. The drying time, affected by the solids content, was found to control the level of advancement of the phase segregation.

  • 28.
    Nyström, Lina
    et al.
    Uppsala University, Sweden.
    Nordström, Randi
    Uppsala University, Sweden.
    Bramhill, Jane
    University of Manchester, UK.
    Saunders, Brian R.
    University of Manchester, UK.
    Álvarez-Asencio, Rubén
    KTH Royal Institute of Technology, Sweden; IMDEA Nanoscience, Spain.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Malmsten, Martin
    Uppsala University, Sweden.
    Factors affecting peptide interactions with surface-bound microgels2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 2, p. 669-678Article in journal (Refereed)
    Abstract [en]

    Effects of electrostatics and peptide size on peptide interactions with surface-bound microgels were investigated with ellipsometry, confocal microscopy, and atomic force microscopy (AFM). Results show that binding of cationic poly-l-lysine (pLys) to anionic, covalently immobilized, poly(ethyl acrylate-co-methacrylic acid) microgels increased with increasing peptide net charge and microgel charge density. Furthermore, peptide release was facilitated by decreasing either microgel or peptide charge density. Analogously, increasing ionic strength facilitated peptide release for short peptides. As a result of peptide binding, the surface-bound microgels displayed pronounced deswelling and increased mechanical rigidity, the latter quantified by quantitative nanomechanical mapping. While short pLys was found to penetrate the entire microgel network and to result in almost complete charge neutralization, larger peptides were partially excluded from the microgel network, forming an outer peptide layer on the microgels. As a result of this difference, microgel flattening was more influenced by the lower Mw peptide than the higher. Peptide-induced deswelling was found to be lower for higher Mw pLys, the latter effect not observed for the corresponding microgels in the dispersed state. While the effects of electrostatics on peptide loading and release were similar to those observed for dispersed microgels, there were thus considerable effects of the underlying surface on peptide-induced microgel deswelling, which need to be considered in the design of surface-bound microgels as carriers of peptide loads, for example, in drug delivery or in functionalized biomaterials.

  • 29.
    Nyström, Lina
    et al.
    Uppsala University, Sweden.
    Álvarez-Asencio, Rubén
    KTH Royal Institute of Technology, Sweden; IMDEA Nanoscience, Spain.
    Frenning, Göran
    Uppsala University, Sweden.
    Saunders, Brian R.
    University of Manchester, UK.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Malmsten, Martin
    Uppsala University, Sweden.
    Electrostatic swelling transitions in surface-bound microgels2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 40, p. 27129-27139Article in journal (Refereed)
    Abstract [en]

    Herein, electrostatic swelling transitions of poly(ethyl acrylate-co-methacrylic acid) microgels covalently bound to silica surfaces are investigated. Confined at a solid surface, microgel swelling is anisotropically hindered and the structure is flattened to an extent dictated by pH and microgel composition. Microgel deformation under applied load is also shown to depend on microgel charge density, with the highest deformation observed at intermediate charge densities. Two modes of microgel deformation under load were observed, one elastic and one viscoelastic, related to polymer strand deformation and displacement of trapped water, respectively. Results on polymer strand dynamics reveal that the microgels are highly dynamic, as the number of strand-tip interaction points increases 4-fold during a 10 s contact time. Furthermore, finite element modeling captures these effects qualitatively and shows that stress propagation in the microgel network decays locally at the rim of contact with a solid interface or close to the tip probe. Taken together, the results demonstrate a delicate interplay between the surface and microgel which determines the structure and nanomechanical properties of the latter and needs to be controlled in applications of systems such as pH-responsive surface coatings in biomaterials.

  • 30.
    Oko, Asaf
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Polymer och fiber.
    Brandner, Birgit
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 456, no 1, p. 92-99Article in journal (Refereed)
    Abstract [en]

    Papers coated with salts containing divalent cations exhibit superior inkjet print quality, which has been suggested to be due to fast aggregation of the colorant pigments close to, or even on, the surface of the paper. In this work we show the pivotal role of the carboxylic acid containing dispersing polymer. We report a series of aggregation and sedimentation experiments with commercial inks, generic ink formulations and specific ingredients comprising these formulations, and find differences in their response to the presence of MgCl2 or CaCl2. In particular, flocs and sediments formed in the presence of MgCl2 are denser than those formed in the presence of CaCl2. These differences are not predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We suggest that ion specific interactions occurring between Mg2+ or Ca2+, and charged carboxylate groups residing on the dispersing polymers, provoke the observed behavior.

  • 31.
    Oko, Asaf
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Medicinteknik.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Infiltration and dimensional scaling of picoliter inkjet drops on nano- and microporous materials – isotropic porous glass and anisotropic paper2016In: Annual Surface and Materials Chemistry Symposium and Materials for tomorrow (ASMCS 2016), 2016Conference paper (Refereed)
  • 32.
    Ovaska, Sami-Seppo
    et al.
    Lappeenranta University of Technology, Finland.
    Hiltunen, Salla
    Lappeenranta University of Technology, Finland.
    Ernstsson, Marie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Schuster, Erich
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Food and Bioscience, Structure Design.
    Altskär, Annika
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Food and Bioscience, Structure Design.
    Backfolk, Kaj
    Lappeenranta University of Technology, Finland.
    Characterization of rapeseed oil/coconut oil mixtures and their penetration into hydroxypropylated-starch-based barrier coatings containing an oleophilic mineral2016In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 101, p. 569-576Article in journal (Refereed)
    Abstract [en]

    A study was conducted that demonstrated that the blending of edible oils leads to changes in surface tension, thermal properties, viscosity, and oil penetration times through a barrier-coated paperboard. The results emphasize the significance of testing the oil and grease resistance (OGR) oil blends in order-to verify the suitability of the packaging material for real-life end-use applications. The results of the OGR determinations suggest that hydroxypropylated-starch-based composite coatings containing an oleophilic high aspect ratio mineral can be tailored for food shaving different fatty acid compositions by varying the pigmentation level. Compared to standard OGR tests, confocal laser scanning microscopy (CLSM)-based techniques make it possible to evaluate the oil penetration time and its diffusion behavior very accurately, both inside the coating layer and in the bulk matrix. It was found that, at room temperature, coconut oil tends to crystallize inside the substrate, inducing swelling of the coating layer, which probably has an influence on the physicomechanical properties of the packaging material.

  • 33.
    Pradhan, Sulena
    et al.
    KTH Royal Institute of Technology, Sweden.
    Hedberg, Jonas
    KTH Royal Institute of Technology, Sweden.
    Blomberg, Eva
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Wold, Susanna
    KTH Royal Institute of Technology, Sweden.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Effect of sonication on particle dispersion, administered dose and metal release of non-functionalized, non-inert metal nanoparticles2016In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 18, no 9, article id 285Article in journal (Refereed)
    Abstract [en]

    In this study, we elucidate the effect of different sonication techniques to efficiently prepare particle dispersions from selected non-functionalized NPs (Cu, Al, Mn, ZnO), and corresponding consequences on the particle dose, surface charge and release of metals. Probe sonication was shown to be the preferred method for dispersing non-inert, non-functionalized metal NPs (Cu, Mn, Al). However, rapid sedimentation during sonication resulted in differences between the real and the administered doses in the order of 30–80 % when sonicating in 1 and 2.56 g/L NP stock solutions. After sonication, extensive agglomeration of the metal NPs resulted in rapid sedimentation of all particles. DLVO calculations supported these findings, showing the strong van der Waals forces of the metal NPs to result in significant NP agglomeration. Metal release from the metal NPs was slightly increased by increased sonication. The addition of a stabilizing agent (bovine serum albumin) had an accelerating effect on the release of metals in sonicated solutions. For Cu and Mn NPs, the extent of particle dissolution increased from <1.6 to ~5 % after sonication for 15 min. A prolonged sonication time (3–15 min) had negligible effects on the zeta potential of the studied NPs. In all, it is shown that it is of utmost importance to carefully investigate how sonication influences the physico-chemical properties of dispersed metal NPs. This should be considered in nanotoxicology investigations of metal NPs. Graphical Abstract: [Figure not available: see fulltext.]

  • 34.
    Röding, Magnus
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Effective diffusivity in lattices of impermeable superballs2018In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 98, no 5, article id 052908Article in journal (Refereed)
    Abstract [en]

    Granular materials constitute a broad class of two-phase media with discrete, solid par-ticles i.e. granules surrounded by a continuous void phase. They have properties that arekey for e.g. separation and chromatography columns, cathode materials for batteries, andpharmaceutical coatings for controlled release. Controlling mass transport properties suchas effective diffusivity is crucial for these applications and the subject of targeted designand optimization. The prototypical granule is a sphere, but current manufacturingtechniques allow for more complicated shapes to be produced in a highly controlled manner,including ellipsoids, cubes, and cubes with rounded edges and corners. The impactof shape for self-assembly, phase transitions, crystallization, and random close packing hasalso been studied for these shapes

  • 35.
    Tuominen, Mikko
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Teisala, Hannu
    Tampere University of Technology, Finland.
    Haapanen, Janne
    Tampere University of Technology, Finland.
    Mäkelä, Jyrki M.
    Tampere University of Technology, Finland.
    Honkanen, Mari
    Tampere University of Technology, Finland.
    Vippola, Minnamari
    Tampere University of Technology, Finland.
    Bardage, Stig
    Wålinder, Magnus E. P.
    KTH Royal Institute of Technology, Sweden.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Superamphiphobic overhang coating on a biobased material2016In: Annual Surface and Materials Chemistry Symposium and Materials for tomorrow (ASMCS 2016), 2016Conference paper (Refereed)
  • 36.
    Wakeham, Deborah
    et al.
    KTH Royal Institute of Technology, Sweden.
    Crivoi, Dana G.
    Rovira i Virgili University, Spain.
    Medina, Francesc
    Rovira i Virgili University, Spain.
    Segarra, Anna M.
    Rovira i Virgili University, Spain.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    In-situ study of substrate - catalyst interactions in a Juliá-Colonna epoxidation using quartz crystal microbalance with dissipation2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 469, p. 263-268Article in journal (Refereed)
    Abstract [en]

    Quartz crystal microbalance with dissipation (QCM-D) analysis of the hexa-l-Leucine (PLL)-catalyzed epoxidation of chalcone gives in-situ experimental evidences which demonstrate that the reaction proceeds mainly via the formation of a PLL-bound hydroperoxide complex followed by the reversible addition of chalcone. The observations offer an alternative rationalization for the viability of the preferred catalytic pathway.

  • 37.
    Wang, Xuying
    et al.
    KTH Royal Institute of Technology, Sweden.
    Herting, Gunilla
    KTH Royal Institute of Technology, Sweden.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Blomberg, Eva
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Adsorption of bovine serum albumin on silver surfaces enhances the release of silver at pH neutral conditions2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 28, p. 18524-18534Article in journal (Refereed)
    Abstract [en]

    Metallic biomaterials are widely used to replace and/or restore the function of damaged bodily parts. The use of silver as antibacterial coatings onto implants has recently gained large interest in medical applications. The extent of silver that can be released into different biological fluids from such coatings is, except for the surface characteristics of the coating, governed by parameters such as protein characteristics, adsorbed layer properties, formation of silver-protein complexes as well as concentrations of proteins in the solution. This study aims to relate the structure of adsorbed net negatively charged bovine serum albumin (BSA), which is the most abundant protein in serum, to the release of silver from metallic silver surfaces in order to elucidate if the net charge of the protein has any effect of the silver release. Simultaneous adsorption measurements were performed in real time on the very same surface using combined ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements to provide a more comprehensive understanding on adsorption kinetics and layer structures. The amount of released silver into solution was measured by means of graphite furnace atomic absorption spectroscopy (GF-AAS). The structure of the adsorbed BSA layer largely influenced the amount of released silver, an enhancement that increased with BSA concentration. These observations are in complete contrast to the effect of net positively charged lysozyme (LSZ) adsorbed on silver, previously studied by the authors, for which a complete surface coverage suppressed the possibility for silver release. The underlying mechanisms behind the enhanced release of silver in the presence of BSA were mainly attributed to surface complexation between BSA and silver followed by an enhanced exchange rate of these surface complexes with BSA molecules in the solution, which in turn increase the amount of released silver in solution.

  • 38.
    Wieland, D. C. Florian
    et al.
    Helmholtz-Zentrum Geesthacht, Germany.
    Degen, Patrick
    Technical University of Dortmund, Germany.
    Zander, Thomas
    Helmholtz-Zentrum Geesthacht, Germany.
    Gayer, Sören
    Helmholtz-Zentrum Geesthacht, Germany.
    Raj, Akanksha
    KTH Royal Institute of Technology, Sweden.
    An, Junxue
    RISE, SP – Sveriges Tekniska Forskningsinstitut. KTH Royal Institute of Technology, Sweden.
    Dédinaité, Andra A.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Willumeit-Römer, Regine
    Helmholtz-Zentrum Geesthacht, Germany.
    Structure of DPPC-hyaluronan interfacial layers-effects of molecular weight and ion composition2016In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 12, no 3, p. 729-740Article in journal (Refereed)
    Abstract [en]

    Hyaluronan and phospholipids play an important role in lubrication in articular joints and provide in combination with glycoproteins exceptionally low friction coefficients. We have investigated the structural organization of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Langmuir layers at the solution-air interface at different length scales with respect to the adsorption of hyaluronan (HA). This allows us to assemble a comprehensive picture of the adsorption and the resulting structures, and how they are affected by the molecular weight of HA and the presence of calcium ions. Brewster angle microscopy and grazing incident diffraction were used to determine the lateral structure at the micro- and macro scale. The data reveals an influence of HA on both the macro and micro structure of the DPPC Langmuir layer, and that the strength of this effect increases with decreasing molecular weight of HA and in presence of calcium ions. Furthermore, from X-ray reflectivity measurements we conclude that HA adsorbs to the hydrophilic part of DPPC, but data also suggest that two types of interfacial structures are formed at the interface. We argue that hydrophobic forces and electrostatic interactions play important rules for the association between DPPC and HA. Surface pressure area isotherms were used to determine the influence of HA on the phase behavior of DPPC while electrophoretic mobility measurements were used to gain insight into the binding of calcium ions to DPPC vesicles and hyaluronan.

  • 39.
    Wieland, D. C. Florian
    et al.
    Helmholtz-Zentrum Geestacht, Germany.
    Garamus, Vasil M.
    Helmholtz-Zentrum Geestacht, Germany.
    Zander, Thomas
    Helmholtz-Zentrum Geestacht, Germany.
    Krywka, C.
    Helmholtz-Zentrum Geestacht, Germany.
    Wang, M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Dédinaité, Andra A.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Willumeit-Römera, Regine
    Helmholtz-Zentrum Geestacht, Germany.
    Studying solutions at high shear rates: A dedicated microfluidics setup2016In: Journal of Synchrotron Radiation, ISSN 0909-0495, E-ISSN 1600-5775, Vol. 23, no 2, p. 480-486Article in journal (Refereed)
    Abstract [en]

    The development of a dedicated small-angle X-ray scattering setup for the investigation of complex fluids at different controlled shear conditions is reported. The setup utilizes a microfluidics chip with a narrowing channel. As a consequence, a shear gradient is generated within the channel and the effect of shear rate on structure and interactions is mapped spatially. In a first experiment small-angle X-ray scattering is utilized to investigate highly concentrated protein solutions up to a shear rate of 300000 s-1. These data demonstrate that equilibrium clusters of lysozyme are destabilized at high shear rates.

  • 40.
    Zander, Thomas
    et al.
    Helmholtz-Zentrum Geesthacht, Germany.
    Wieland, D. C. Florian
    Helmholtz-Zentrum Geesthacht, Germany.
    Raj, Akanksha
    KTH Royal Institute of Technology, Sweden.
    Wang, Min
    KTH Royal Institute of Technology, Sweden.
    Nowak, Benedikt
    Technical University of Dortmund, Germany.
    Krywka, Christina
    Helmholtz-Zentrum Geesthacht, Germany.
    Dédinaité, Andra A.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Garamus, Vasil M.
    Helmholtz-Zentrum Geesthacht, Germany.
    Schreyer, Andreas
    Helmholtz-Zentrum Geesthacht, Germany.
    Willumeit-Römer, Regine
    Helmholtz-Zentrum Geesthacht, Germany.
    The influence of hyaluronan on the structure of a DPPC-bilayer under high pressures2016In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 142, p. 230-238Article in journal (Refereed)
    Abstract [en]

    The superior lubrication properties of synovial joints have inspired many studies aiming at uncovering the molecular mechanisms which give rise to low friction and wear. However, the mechanisms are not fully understood yet, and, in particular, it has not been elucidated how the biolubricants present at the interface of cartilage respond to high pressures, which arise during high loads of joints. In this study we utilize a simple model system composed of two biomolecules that have been implied as being important for joint lubrication. It consists of a solid supported dipalmitoylphosphatidylcholin (DPPC) bilayer, which was formed via vesicles fusion on a flat Si wafer, and the anionic polysaccharide hyaluronan (HA). We first characterized the structure of the HA layer that adsorbed to the DPPC bilayers at ambient pressure and different temperatures using X-ray reflectivity (XRR) measurements. Next, XRR was utilized to evaluate the response of the system to high hydrostatic pressures, up to 2 kbar (200 MPa), at three different temperatures. By means of fluorescence microscopy images the distribution of DPPC and HA on the surface was visualized. Our data suggest that HA adsorbs to the headgroup region that is oriented towards the water side of the supported bilayer. Phase transitions of the bilayer in response to temperature and pressure changes were also observed in presence and absence of HA. Our results reveal a higher stability against high hydrostatic pressures for DPPC/HA composite layers compared to that of the DPPC bilayer in absence of HA.

1 - 40 of 40
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