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  • 1.
    Al-Soubaihi, Rola
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Furesi, G.
    Saoud, K. M.
    Al-Muhtaseb, S. A.
    Khatat, A. E.
    Delogu, L. G.
    Dutta, Joydeep
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Silica and carbon decorated silica nanosheet impact on primary human immune cells2018In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 172, p. 779-789Article in journal (Refereed)
    Abstract [en]

    Silica nanosheets (SiO 2 NS) are considered to be a promising material in clinical practice for diagnosis and therapy applications. However, an appropriate surface functionalization is essential to guarantee high biocompatibility and molecule loading ability. Although SiO 2 NS are chemically stable, its effects on immune systems are still being explored. In this work, we successfully synthesized a novel 2D multilayer SiO 2 NS and SiO 2 NS coated with carbon (C/SiO 2 NS), and evaluated their impact on human Peripheral Blood Mononuclear Cells (PBMCs) and some immune cell subpopulations. We demonstrated that the immune response is strongly dependent on the surface functionalities of the SiO 2 NS. Ex vivo experiments showed an increase in biocompatibility of C/SiO 2 NS compared to SiO 2 NS, resulting in a lowering of hemoglobin release together with a reduction in cellular toxicity and cellular activation. However, none of them are directly involved in the activation of the acute inflammation process with a consequent release of pro-inflammatory cytokines. The obtained results provide an important direction towards the biomedical applications of silica nanosheets, rendering them an attractive material for the development of future immunological therapies.

  • 2. Bogdanovic, G.
    et al.
    Meurk, A.
    Rutland, Mark W
    KTH, Superseded Departments, Chemistry.
    Tip friction - torsional spring constant determination2000In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 19, no 4, p. 397-405Article in journal (Refereed)
    Abstract [en]

    A non-destructive technique is presented for verifying torsional spring constants used in lateral force microscopy. Various calibrations of the microscope are required and these are detailed. The technique produces reasonable values which tend to be larger than those predicted from considerations of the cantilever dimensions. The differences are discussed in terms of length corrections and particularly the uncertainty in the thickness of the cantilevers, which has an enormous effect on the values obtained through a priori calculations. Methods for inferring the thickness are discussed. Further, artefacts in conventional force measurements related to the experiments performed here are discussed.

  • 3. Cozzolino, C. A.
    et al.
    Nilsson, Fritjof
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Iotti, M.
    Sacchi, B.
    Piga, A.
    Farris, S.
    Exploiting the nano-sized features of microfibrillated cellulose (MFC) for the development of controlled-release packaging2013In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 110, p. 208-216Article in journal (Refereed)
    Abstract [en]

    Microfibrillated cellulose (MFC) was used in this study to prepare films containing an active molecule, lysozyme, which is a natural antimicrobial agent. The main goal of this research was to assess the potential for exploiting the nano-sized dimension of cellulose fibrils to slow the release of the antimicrobial molecule, thus avoiding a too-quick release into the surrounding medium, which is a major disadvantage of most release systems. For this purpose, the release kinetics of lysozyme over a 10-day period in two different media (pure water and water/ethanol 10. wt.%) were obtained, and the experimental data was fitted with a solution of Fick's second law to quantify the apparent diffusion coefficient (D). The results indicate that the MFC retained lysozyme, presumably due to electrostatic, hydrogen, and ion-dipole interactions, with the largest release of lysozyme-approximately 14%-occurring from the initial amount loaded on the films. As expected, ethanol as a co-solvent slightly decreased the diffusion of lysozyme from the MFC polymer network. The addition of two potential modulating release agents-glycerol and sodium chloride-was also evaluated. Findings from this work suggest that MFC-based films can be considered a suitable candidate for use in controlled-release packaging systems.

  • 4. Evertsson, H.
    et al.
    Stilbs, Peter
    KTH, Superseded Departments, Chemistry.
    Lindblom, G.
    Engstrom, S.
    NMR self diffusion measurements of the monooleoylglycerol/poly ethylene glycol/water L-3 phase2002In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 26, no 02-jan, p. 21-29Article in journal (Refereed)
    Abstract [en]

    The monooleoylglycerol (GMO)/poly ethylene oxide (PEG)/water sponge (L-3) phase has been investigated by pulsed-gradient spin-echo NMR self-diffusion. The data allow the L-3 phase to be modeled as a bicontinuous system with respect to the lipid and water domains. It is proposed by using the interconnected rod model that the solvent PEG mainly distributes to the water domain, but has a higher weight fraction partition to the lipid head groups of the local GMO bilayer than water. The data is put in relation to earlier self-diffusion measurements on the binary GMO/water cubic phase, as well as earlier conductivity and X-ray diffraction measurements on the very same L-3 phase.

  • 5. Fang, Wenwen
    et al.
    Nonappa, Nonappa
    Vitikainen, Marika
    Pezhman, Mohammadi
    Koskela, Salla
    Soikkeli, Miika
    Westerholm-Parvinen, Ann
    Christopher, Landowski
    Penttilä, Merja
    Linder, Markus
    Laaksonen, Päivi
    Coacervation of resilin fusion proteins containing terminal functionalities2018In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 171, p. 590-596Article in journal (Refereed)
    Abstract [en]

    Liquid-liquid phase transition known as coacervation of resilin-like-peptide fusion proteins containing different terminal domains were investigated. Two different modular proteins were designed and produced and their behavior were compared to a resilin-like-peptide without terminal domains. The size of the particle-like coacervates was modulated by the protein concentration, pH and temperature. The morphology and three-dimensional (3D) structural details of the coacervate particles were investigated by cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET) reconstruction. Selective adhesion of the coacervates on cellulose and graphene surfaces was demonstrated.

  • 6.
    Hedberg, Jonas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Karlsson, Hanna L.
    Hedberg, Yolanda
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
    Wallinder, Inger Odnevall
    The importance of extracellular speciation and corrosion of copper nanoparticles on lung cell membrane integrity2016In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 141, p. 291-300Article in journal (Refereed)
    Abstract [en]

    Copper nanoparticles (Cu NPs) are increasingly used in various biologically relevant applications and products, e.g., due to their antimicrobial and catalytic properties. This inevitably demands for an improved understanding on their interactions and potential toxic effects on humans. The aim of this study was to investigate the corrosion of copper nanoparticles in various biological media and to elucidate the speciation of released copper in solution. Furthermore, reactive oxygen species (ROS) generation and lung cell (A549 type II) membrane damage induced by Cu NPs in the various media were studied. The used biological media of different complexity are of relevance for nanotoxicological studies: Dulbecco's modified eagle medium (DMEM), DMEM+ (includes fetal bovine serum), phosphate buffered saline (PBS), and PBS + histidine. The results show that both copper release and corrosion are enhanced in DMEM+, DMEM, and PBS + histidine compared with PBS alone. Speciation results show that essentially no free copper ions are present in the released fraction of Cu NPs in neither DMEM+, DMEM nor histidine, while labile Cu complexes form in PBS. The Cu NPs were substantially more membrane reactive in PBS compared to the other media and the NPs caused larger effects compared to the same mass of Cu ions. Similarly, the Cu NPs caused much more ROS generation compared to the released fraction only. Taken together, the results suggest that membrane damage and ROS formation are stronger induced by Cu NPs and by free or labile Cu ions/complexes compared with Cu bound to biomolecules.

  • 7.
    Hedberg, Yolanda
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Dobryden, Illia
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Chaudhary, Himanshu
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Wei, Zheng
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Claesson, Per M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Lendel, Christofer
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Synergistic effects of metal-induced aggregation of human serum albumin2019In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 173, p. 751-758Article in journal (Refereed)
    Abstract [en]

    Exposure to cobalt (Co), chromium (Cr), and nickel (Ni) occurs often via skin contact and from different dental and orthopedic implants. The metal ions bind to proteins, which may induce structural changes and aggregation, with different medical consequences. We investigated human serum albumin (HSA) aggregation in the presence of Co-II, Cr-III, and/or Ni-II ions and/or their nanoparticle precipitates by using scattering, spectroscopic, and imaging techniques, at simulated physiological conditions (phosphate buffered saline - PBS, pH 7.3) using metal salts that did not affect the pH, and at HSA:metal molar ratios of up to 1:8. Co ions formed some solid nano particles in PBS at the investigated conditions, as determined by nanoparticle tracking analysis, but the Cr-III anions and Ni-II ions remained fully soluble. It was found that all metal ions induced HSA aggregation, and this effect was significantly enhanced when a mixture of all three metal ions was present instead of any single type of ion. Thus, the metal ions induce aggregation synergistically. HSA aggregates formed linear structures on a mica surface in the presence of Cr-III ions. A clear tendency of aggregation and linearly aligned aggregates was seen in the presence of all three metal ions. Spectroscopic investigations indicated that the majority of the HSA molecules maintained their alpha helical secondary structure and conformation. This study highlights the importance of synergistic effects of metal ions and/or their precipitates on protein aggregation, which are highly relevant for implant materials and common exposures to metals.

  • 8.
    Hedberg, Yolanda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Karlsson, Maria-Elisa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
    Odnevall Wallinder, Inger
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Hedberg, Jonas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Correlation between surface physicochemical properties and the release of iron from stainless steel AISI 304 in biological media2014In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 122, p. 216-222Article in journal (Refereed)
    Abstract [en]

    Stainless steel is widely used in biological environments, for example as implant material or in food applications, where adsorption-controlled ligand-induced metal release is of importance from a corrosion, health, and food safety perspective. The objective of this study was to elucidate potential correlations between surface energy and wettability of stainless steel surfaces and the release of iron in complexing biological media. This was accomplished by studying changes in surface energies calculated from contact angle measurements, surface oxide composition (X-ray photoelectron spectroscopy), and released iron (graphite furnace atomic absorption spectroscopy) for stainless steel grade AISI 304 immersed in fluids containing bovine serum albumin or citric acid, and non-complexing fluids such as NaCl, NaOH, and HNO3. It was shown that the surface wettability and polar surface energy components were all influenced by adventitious atmospheric carbon (surface contamination of low molecular weight), rather than differences in surface oxide composition in non-complexing solutions. Adsorption of both BSA and citrate, which resulted in ligand-induced metal release, strongly influenced the wettability and the surface energy, and correlated well with the measured released amount of iron.

  • 9.
    Henschen, Jonatan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Illergård, Josefin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Larsson, Per A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Contact-active antibacterial aerogels from cellulose nanofibrils2016In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 146, p. 415-422Article in journal (Refereed)
    Abstract [en]

    The use of cellulose aerogels as antibacterial materials has been investigated by applying a contact-active layer-by-layer modification to the aerogel surface. Studying the adsorption of multilayers of polyvinylamine (PVAm) and polyacrylic acid to aerogels comprising crosslinked cellulose nanofibrils and monitoring the subsequent bacterial adhesion revealed that up to 26 mg PVAm g aerogel−1 was adsorbed without noticeably affecting the aerogel structure. The antibacterial effect was tested by measuring the reduction of viable bacteria in solution when the aerogels were present. The results show that >99.9% of the bacteria adhered to the surface of the aerogels. Microscopy further showed adherence of bacteria to the surfaces of the modified aerogels. These results indicate that it is possible to create materials with three-dimensional cellulose structures that adsorb bacteria with very high efficiency utilizing the high specific surface area of the aerogels in combination with their open structure.

  • 10.
    Henschen, Jonatan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Larsson, Per A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Illergård, Josefin
    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.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bacterial adhesion to polyvinylamine-modified nanocellulose films2017In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 151, p. 224-231Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibril (CNF) materials have been widely studied in recent years and are suggested for a wide range of applications, e.g., medical and hygiene products. One property not very well studied is the interaction between bacteria and these materials and how this can be controlled. The current work studies how bacteria adhere to different CNF materials modified with polyelectrolyte multilayers. The tested materials were TEMPO-oxidized to have different surface charges, periodate-oxidized to vary the water interaction and hot-pressed to alter the surface structure. Then, multilayers were constructed using polyvinylamine (PVAm) and polyacrylic acid. Both the material surface charge and water interaction affect the amount of polymer adsorbed to the surfaces. Increasing the surface charge decreases the adsorption after the first PVAm layer, possibly due to conformational changes. Periodate-oxidized and crosslinked films have low initial polymer adsorptions; the decreased swelling prevents polymer diffusion into the CNF micropore structure. Microscopic analysis after incubating the samples with bacterial suspensions show that only the materials with the lowest surface charge enable bacteria to adhere to the surface because, when adsorbing up to 5 layers PVAm/PAA, the increased anionic surface charge appears to decrease the net surface charge. Both the amounts of PVAm and PAA influence the net surface charge and thus the bacterial adhesion. The structure generated by the hot-pressing of the films also strongly increases the number of bacteria adhering to the surfaces. These results indicate that the bacterial adhesion to CNF materials can be tailored using polyelectrolyte multilayers on different CNF substrates.

  • 11.
    Illergård, Josefin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Bacterial-growth inhibiting properties of multilayers formed with modified polyvinylamine2011In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 88, no 1, p. 115-120Article in journal (Refereed)
    Abstract [en]

    New methods are needed to fight antibiotic-resistant bacteria. One alternative that has been proposed is non-leaching, permanently antibacterial surfaces. In this study, we test multilayers formed with antibacterial cationic polyvinylamine (PVAm) and polyacrylic acid (PAA) in a growth-inhibition assay. Both hydrophobically modified and native PVAm were investigated. Multilayers did reduce the bacterial growth, as compared to single layers. However, the sampling time in the assay was critical, as the treated surface area is a capacity-limiting factor. After 2 h incubation, a maximal growth inhibition of more than 99% was achieved with multilayers. In contrast, after 8 h we observed a maximal growth-inhibition of 40%. At longer incubation times, the surface becomes saturated, which explains the observed time-dependent effectiveness. The polymers giving multilayers with the strongest growth-inhibiting properties were native PVAm and PVAm modified with C(8), which also were the polymers with highest charge density. We therefore conclude that this effect is mainly an electrostatically driven process. Viability staining using a fluorescent stain showed a high viability rate of the adhered bacteria. The multilayers are therefore more bacteriostatic than antibacterial.

  • 12. Loureiro, A.
    et al.
    Nogueira, E.
    Azoia, N.G.
    Sárria, M.P.
    Abreu, A.S.
    Shimanovich, U.
    Rollett, A.
    Härmark, Johan
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Hebert, Hans
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Guebitz, G.
    Bernardes, G.J.L.
    Preto, A.
    Gomes, A.C.
    Cavaco-Paulo, A.
    Size controlled protein nanoemulsions for active targeting of folate receptor positive cells2015In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 135, p. 90-98Article in journal (Refereed)
    Abstract [en]

    Bovine serum albumin (BSA) nanoemulsions were produced by high pressure homogenization with a tri-block copolymer (Poloxamer 407), which presents a central hydrophobic chain of polyoxypropylene (PPO) and two identical lateral hydrophilic chains of polyethylene glycol (PEG). We observed a linear correlation between tri-block copolymer concentration and size - the use of 5. mg/mL of Poloxamer 407 yields nanoemulsions smaller than 100. nm. Molecular dynamics and fluorescent tagging of the tri-block copolymer highlight their mechanistic role on the size of emulsions. This novel method enables the fabrication of highly stable albumin emulsions in the nano-size range, highly desirable for controlled drug delivery. Folic Acid (FA)-tagged protein nanoemulsions were shown to promote specific folate receptor (FR)-mediated targeting in FR positive cells. The novel strategy presented here enables the construction of size controlled, functionalized protein-based nanoemulsions with excellent characteristics for active targeting in cancer therapy.

  • 13.
    Lundin, Maria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Elofsson, Ulla
    YKI, Institute for Surface Chemistry, Stockholm.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Adsorption of lysozyme, beta-casein and their layer-by-layer formation on hydrophilic surfaces: Effect of ionic strength2010In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 77, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The adsorbed amount and layer structure of lysozyme, beta-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and beta-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though beta-casein and silica are negatively charged at the pH used. No beta-casein remained adsorbed after rinsing with a 150 mM buffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. beta-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and beta-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/beta-casein layers contain higher amounts of protein compared to those of pure lysozyme or beta-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and beta-casein. The protein layers are probably highly interpenetrated with no clear separation between them.

  • 14.
    Sonesson, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Callisen, Thomas H.
    Novozymes A/S, Bagsvaerd.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Elofsson, Ulla
    YKI, Institute for Surface Chemistry, Stockholm.
    A comparison between Dual Polarization Interferometry (DPI) and Surface Plasmon Resonance (SPR) for protein adsorption studies2007In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 54, no 2, p. 236-240Article in journal (Refereed)
    Abstract [en]

    This work was performed with the aim of comparing protein adsorption results obtained from the recently developed dual polarization interferometry (DPI) with the well-established surface plasmon resonance (SPR) technique. Both techniques use an evanescent field as the sensing element but completely different methods to calculate the adsorbed mass. As a test system we used adsorption of the lipase from Thermomyces lanuginosus (TLL) on C18 surfaces. The adsorbed amount calculated with both techniques is in good agreement, with both adsorption isotherms saturating at 1.30-1.35 mg/m(2) at TLL concentrations of 1000 nM and above. Therefore, this supports the use of both SPR and DPI as tools for studying protein adsorption, which is very important when comparing adsorption data obtained from the use different techniques. Due to the spot sensing in SPR, this technique is recommended for initial kinetic studies, whereas DPI is more accurate when the refractive index and thickness of the adsorbed layer is of more interest.

  • 15.
    Sonesson, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Callisen, Thomas H,
    Novozymes A/S, Bagsvaerd.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Elofsson, Ulla
    YKI, Institute for Surface Chemistry, Stockholm.
    Adsorption and activity of Thermomyces lanuginosus lipase on hydrophobic and hydrophilic surfaces measured with dual polarization interferometry (DPI) and confocal microscopy2008In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 61, no 2, p. 208-215Article in journal (Refereed)
    Abstract [en]

    The adsorption and activity of Thermomyces lanuginosus lipase (TLL) was measured with dual polarization interferometry (DPI) and confocal microscopy at a hydrophilic and hydrophobic surface. In the adsorption isotherms, it was evident that TLL both had higher affinity for the hydrophobic surface and adsorbed to a higher adsorbed amount (1.90 mg/m(2)) compared to the hydrophilic surface (1.40-1.50 mg/m(2)). The thickness of the adsorbed layer was constant (similar to 3.5 nm) on both surfaces at an adsorbed amount > 1.0 mg/m(2), but decreased on the hydrophilic surface at lower surface coverage, which might be explained by partially unfolding of the TLL structure. However, a linear dependence of the refractive index of the adsorbed layer on adsorbed amount of TLL on C18 surfaces indicated that the structure of TLL was similar at low and high surface coverage. The activity of adsorbed TLL was measured towards carboxyfluorescein diacetate (CFDA) in solution, which upon lipase activity formed a fluorescent product. The surface fluorescence intensity increase was measured in a confocal microscope as a function of time after lipase adsorption. It was evident that TLL was more active on the hydrophilic surface, which suggested that a larger fraction of adsorbed TLL molecules were oriented with the active site facing the solution compared to the hydrophobic surface. Moreover, most of the activity remained when the TLL surface coverage decreased. Earlier reports on TLL surface mobility on the same surfaces have found that the lateral diffusion was highest on hydrophilic surfaces and at low surface coverage of TLL. Hence, a high lateral mobility might lead to a longer exposure time of the active site towards solution, thereby increasing the activity against a water-soluble substrate.

  • 16.
    Thormann, Esben
    et al.
    MEMPHYS, Physics Department, University of Southern Denmark.
    Hansen, Per Lyngs
    Simonsen, Adam Cohen
    Mouritsen, Ole G.
    Dynamic force spectroscopy on soft molecular systems: Improved analysis of unbinding spectra with varying linker compliance2006In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 53, no 2, p. 149-156Article in journal (Refereed)
    Abstract [en]

    Dynamic force spectroscopy makes it possible to measure the breaking of single molecular bonds or the unfolding of single proteins subjected to a time-dependent pulling force. The force needed to break a single bond or to unfold a domain in a protein depends critically on the time dependence of the applied force. In this way the elastic response couples to the unbinding force. We have performed an experimental and theoretical examination of this coupling by studying the well-known biotin-streptavidin bond in systems incorporating two common types of linkers. In the first case biotin is linked by bovine serum albumin (BSA) and it is observed that this linker has a linear elastic response. More surprisingly we find that its force constant varies significantly between repeated force curves. It is demonstrated that by sorting the force curves according to the force constant of the linker we can improve the data analysis and obtain a better agreement between experimental data and theory. In the second case biotin is linked by poly(ethylene glycol) (PEG), which has a soft nonlinear elastic response. A numerical calculation of the unbinding statistics for the polymer system agrees quantitatively with experiments. It demonstrates a clear decrease in unbinding forces resulting from the polymer linker.

  • 17. Zander, Thomas
    et al.
    Wieland, D. C. Florian
    Raj, Akanksha
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Wang, Min
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Nowak, Benedikt
    Krywka, Christina
    Dédinaité, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. SP Tech Res Inst Sweden.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Tech Res Inst Sweden.
    Garamus, Vasil M.
    Schreyer, Andreas
    Willumeit-Romer, Regine
    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.

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