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Publications (10 of 57) Show all publications
Röding, M., Lacroix, L., Krona, A., Gebäck, T. & Loren, N. (2019). A Highly Accurate Pixel-Based FRAP Model Based on Spectral-Domain Numerical Methods. Biophysical Journal, 116(7), 1348-1361
Open this publication in new window or tab >>A Highly Accurate Pixel-Based FRAP Model Based on Spectral-Domain Numerical Methods
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2019 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 116, no 7, p. 1348-1361Article in journal (Refereed) Published
Abstract [en]

We introduce a new, to our knowledge, numerical model based on spectral methods for analysis of fluorescence recovery after photobleaching data. The model covers pure diffusion and diffusion and binding (reaction-diffusion) with immobile binding sites, as well as arbitrary bleach region shapes. Fitting of the model is supported using both conventional recovery-curve-based estimation and pixel-based estimation, in which all individual pixels in the data are utilized. The model explicitly accounts for multiple bleach frames, diffusion (and binding) during bleaching, and bleaching during imaging. To our knowledge, no other fluorescence recovery after photobleaching framework incorporates all these model features and estimation methods. We thoroughly validate the model by comparison to stochastic simulations of particle dynamics and find it to be highly accurate. We perform simulation studies to compare recovery-curve-based estimation and pixel-based estimation in realistic settings and show that pixel-based estimation is the better method for parameter estimation as well as for distinguishing pure diffusion from diffusion and binding. We show that accounting for multiple bleach frames is important and that the effect of neglecting this is qualitatively different for the two estimation methods. We perform a simple experimental validation showing that pixel-based estimation provides better agreement with literature values than recovery-curve-based estimation and that accounting for multiple bleach frames improves the result. Further, the software developed in this work is freely available online.

National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-38231 (URN)10.1016/j.bpj.2019.02.023 (DOI)2-s2.0-85062705820 (Scopus ID)
Note

 Funding details: Vetenskapsrådet, 2016-03809; Funding details: Stiftelsen för Strategisk Forskning; Funding text 1: The financial support of the VINN Excellence Centre SuMo Biomaterials , the Swedish Foundation for Strategic Research project “Material structures seen through microscopes and statistics,” and the Swedish Research Council (grant number 2016-03809 ) is acknowledged. The computations were in part performed on resources at Chalmers Centre for Computational Science and Engineering provided by the Swedish National Infrastructure for Computing.

Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2019-06-28Bibliographically approved
Karlsson, K., Larsson, E., Loren, N., Stading, M. & Rigdahl, M. (2019). Extrusion Parameters for Foaming of a β-Glucan Concentrate. Journal of polymers and the environment, 27(6), 1167-1177
Open this publication in new window or tab >>Extrusion Parameters for Foaming of a β-Glucan Concentrate
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2019 (English)In: Journal of polymers and the environment, ISSN 1566-2543, E-ISSN 1572-8919, Vol. 27, no 6, p. 1167-1177Article in journal (Refereed) Published
Abstract [en]

Plastics is a group of materials commonly encountered on a daily basis by many people. They have enabled rapid, low-cost manufacturing of products with complicated geometries and have contributed to the weight reduction of heavy components, especially when produced into a foamed structure. Despite the many advantages of plastics, some drawbacks such as the often fossil-based raw-material and the extensive littering of the material in nature, where it is not degraded for a very long time, needs to be dealt with. One way to address at least one of the issues could be to use polymers from nature instead of fossil-based ones. Here, a β-glucan concentrate originating from barley was investigated. The concentrate was processed into a foam by hot-melt extrusion, and the processing window was established. The effect of different blowing agents was also investigated. Water or a combination of water and sodium bicarbonate were used as blowing agents, the latter apparently giving a more uniform pore structure. The porous structure of the foamed materials was characterized mainly by using a combination of confocal laser scanning microscope and image analysis. The density of the samples was estimated and found to be in a similar range as some polyurethane foams. A set of 3D parameters were also quantified on two selected samples using X-ray microtomography in combination with image analysis, where it was indicated that the porous structure had a pre-determined direction, which followed the direction of the extrusion process. © 2019, The Author(s).

Keywords
Extrusion, Hemicellulose, Image analysis, Starch, X-ray microtomography, Elastomers, Foamed products, Melt spinning, Pore structure, Porosity, Sodium bicarbonate, Tomography, X rays, Complicated geometry, Confocal laser scanning microscope, Extrusion parameter, Hot melt extrusion, Low cost manufacturing, Uniform pore structures, X ray microtomography, Blowing agents
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-38229 (URN)10.1007/s10924-019-01412-3 (DOI)2-s2.0-85062840732 (Scopus ID)
Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2019-06-28Bibliographically approved
Pihl, M., Kolman, K., Lotsari, A., Ivarsson, M., Schüster, E., Loren, N. & Bordes, R. (2019). Silica-based diffusion probes for use in FRAP and NMR-diffusometry. Journal of Dispersion Science and Technology, 40(4), 555-562
Open this publication in new window or tab >>Silica-based diffusion probes for use in FRAP and NMR-diffusometry
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2019 (English)In: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 40, no 4, p. 555-562Article in journal (Refereed) Published
Abstract [en]

Development of multi-purpose probes for mass transport measurements is of importance to gain knowledge in diffusional behaviour in heterogeneous structures such as food, hygiene or pharamceuticals. By combining different techniques, such as Fluorescence Recovery After Photobleaching (FRAP) and Nuclear Magnetic Resonance Diffusometry (NMR-d), information of both local and global diffusion can be collected and used to gain insights on for example material heterogeneities and probe-material interactions. To obtain a FRAP-responsive probe, fluorescent silica particles were produced using fluorescent preconjugates added in a modified Stöber process. A NMR-d responsive moiety was introduced by derivatizing the fluorescent silica particles with polyethylene glycol. The particle size distributions were determined by dynamic light scattering and transmission electron microscopy and these measurements were compared to value extrapolated from diffusion measurements using FRAP and NMR-d. The good agreement between the FRAP and NMR-d measurements demonstrates the potential of multi-purpose probes for future applications concerning mass transport at local and global scale simultaneously. © 2018, © 2018 The Author(s).

Keywords
Diffusion probes, fluorescent silica nanoparticles, FRAP, NMR-diffusometry, pegylated silica nanoparticles, Diffusion, Fluorescence, High resolution transmission electron microscopy, Light scattering, Light transmission, Particle size, Photobleaching, Probes, Silica nanoparticles, Transmission electron microscopy, Diffusion measurements, Fluorescence recovery after photobleaching, Heterogeneous structures, NMR diffusometry, Pegylated, Transport measurements, Nuclear magnetic resonance
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-35935 (URN)10.1080/01932691.2018.1472015 (DOI)2-s2.0-85054577994 (Scopus ID)
Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2019-07-01Bibliographically approved
Hagsten, C., Altskär, A., Gustafsson, S., Loren, N., Trägårdh, C., Innings, F., . . . Nylander, T. (2019). Structural and compositional changes during UHT fouling removal—Possible mechanisms of the cleaning process. Food Structure, 21, Article ID 100118.
Open this publication in new window or tab >>Structural and compositional changes during UHT fouling removal—Possible mechanisms of the cleaning process
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2019 (English)In: Food Structure, ISSN 2213-3291, Vol. 21, article id 100118Article in journal (Refereed) Published
Abstract [en]

Ultra-high temperature (UHT) treatment of milk forms a deposit or fouling in the processing equipment that is mineral-based with an enclosed protein network. This study addresses the fundamental mechanisms that control the removal of this deposit. For this purpose, the structural and compositional changes during the cleaning process have been studied. The structure analysis was performed with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) on samples that were quenched at different stages of the cleaning process. It was found for acid cleaning that the mineral content is rapidly decreasing in the fouling layer as the cleaning continues, but there is still an intact protein structure with the similar thickness as the original fouling. For alkali cleaning, part of the protein structure was subsequently removed from the outside towards the stain-less steel as a function of time, while the mineral structure was mostly remaining. The break-up of the organic network structure, which likely involves depolymerization of protein aggregates, were found to control the cleaning efficiency. The weakening of the protein network facilitates the removal of the UHT fouling layer during the acid cleaning step and allow for an efficient cleaning cycle. The chemical reactions that occur within the fouling layer between the hydroxyl ions and the protein network was modeled according to a depolymerization reaction and a mechanistic model of the cleaning process is presented. © 2019

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Cleaning, Fouling structure, Mechanistic model, Milk fouling, Mineral deposit, Protein depolymerization, Protein net-work
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39449 (URN)10.1016/j.foostr.2019.100118 (DOI)2-s2.0-85067823105 (Scopus ID)
Note

Funding details: Svenska Forskningsrådet Formas; Funding text 1: We acknowledge the financial support of TvärLivs , which is a cooperative venture between The Swedish Research Council Formas, The Swedish Farmers Foundation for Agricultural Research (SLF), the Swedish Governmental Agency for Innovation Systems Vinnova, Livsmedelsföretagen, and Svensk Dagligvaruhandel, as well as Tetra Pak Processing Systems and Arla Foods. Appendix A

Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2019-07-08Bibliographically approved
de Kort, D. W., Schuster, E., Hoeben, F. J., Barnes, R., Emondts, M., Janssen, H. M., . . . van Duynhoven, J. P. (2018). Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry.. Langmuir, 34(37)
Open this publication in new window or tab >>Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry.
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2018 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 37Article in journal (Refereed) Published
Abstract [en]

A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8-11 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H pulsed-field gradient NMR, fluorescence recovery after photobleaching, and raster image correlation spectroscopy revealed a fast and a slow component, pointing toward microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modeled with obstruction by a coarse network (average mesh size <100 nm), while the slower-diffusing nanoparticles are trapped in a dense network (lower mesh size limit of 4.6 nm). Overhauser dynamic nuclear polarization-enhanced NMR relaxometry revealed a reduced local solvent water diffusivity near 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-labeled nanoparticles trapped in the dense network, showing that heterogeneity in the physical network is also reflected in heterogeneous self-diffusivity of water. The observed heterogeneity in mesh sizes and in water self-diffusivity is of interest for understanding and modeling of transport through and release of solutes from heterogeneous biopolymer gels.

National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-35143 (URN)10.1021/acs.langmuir.8b01052 (DOI)30132676 (PubMedID)2-s2.0-85053514539 (Scopus ID)
Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2019-06-25Bibliographically approved
Longfils, M., Röding, M., Altskar, A., Schuster, E., Loren, N., Sarkka, A. & Rudemo, M. (2018). Single particle raster image analysis of diffusion for particle mixtures. Journal of Microscopy, 269(3), 269-281
Open this publication in new window or tab >>Single particle raster image analysis of diffusion for particle mixtures
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2018 (English)In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 269, no 3, p. 269-281Article in journal (Refereed) Published
Abstract [en]

Recently we complemented the raster image correlation spectroscopy (RICS) method of analysing raster images via estimation of the image correlation function with the method single particle raster image analysis (SPRIA). In SPRIA, individual particles are identified and the diffusion coefficient of each particle is estimated by a maximum likelihood method. In this paper, we extend the SPRIA method to analyse mixtures of particles with a finite set of diffusion coefficients in a homogeneous medium. In examples with simulated and experimental data with two and three different diffusion coefficients, we show that SPRIA gives accurate estimates of the diffusion coefficients and their proportions. A simple technique for finding the number of different diffusion coefficients is also suggested. Further, we study the use of RICS for mixtures with two different diffusion coefficents and investigate, by plotting level curves of the correlation function, how large the quotient between diffusion coefficients needs to be in order to allow discrimination between models with one and two diffusion coefficients. We also describe a minor correction (compared to published papers) of the RICS autocorrelation function. Lay description Diffusion is a key mass transport mechanism for small particles. Efficient methods for estimating diffusion coefficients are crucial for analysis of microstructures, for example in soft biomaterials. The sample of interest may consist of a mixture of particles with different diffusion coefficients. Here, we extend a method called Single Particle Raster Image Analysis (SPRIA) to account for particle mixtures and estimation of the diffusion coefficients of the mixture components. SPRIA combines elements of classical single particle tracking methods with utilizing the raster scan with which images obtained by using a confocal laser scanning microscope. In particular, single particles are identified and their motion estimated by following their center of mass. Thus, an estimate of the diffusion coefficient will be obtained for each particle. Then, we analyse the distribution of the estimated diffusion coefficients of the population of particles, which allows us to extract information about the diffusion coefficients of the underlying components in the mixture. On both simulated and experimental data with mixtures consisting of two and three components with different diffusion coefficients, SPRIA provides accurate estimates and, with a simple criterion, the correct number of mixture components is selected in most cases.

Keywords
Bootstrap; Confocal laser scanning microscopy; Diffusion; Fluorescent beads; Maximum likelihood; Particle mixtures; Single particle tracking
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-33367 (URN)10.1111/jmi.12625 (DOI)2-s2.0-85041951653 (Scopus ID)
Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2019-01-10Bibliographically approved
Kvist, P., Schuster, E., Loren, N. & Rasmuson, A. (2018). Using fluorescent probes and FRAP to investigate macromolecule diffusion in steam-exploded wood. Wood Science and Technology, 52(5), 1395-1410
Open this publication in new window or tab >>Using fluorescent probes and FRAP to investigate macromolecule diffusion in steam-exploded wood
2018 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 5, p. 1395-1410Article in journal (Refereed) Published
Abstract [en]

Diffusion of fluorescently labeled dextran of varying molecular weight in wood pretreated by steam explosion was studied with a confocal microscope. The steam explosion experiments were conducted at relatively mild conditions relevant for materials biorefinery at a pressure of 14 bars for 10 min. The method of fluorescence recovery after photobleaching (FRAP) was used to perform diffusion measurements locally in the wood microstructure. It was found that the FRAP methodology can be used to observe differences in the diffusion coefficient based on localization in the microstructure, i.e., earlywood, latewood, and cell wall. Microscopic changes due to steam explosion were seen to increase diffusion of the smaller 3-kDa dextran diffusion probe in the earlywood, while the latewood structure was not affected in any significant way. Macroscopic changes to the structure in the form of ruptures due to the steam explosion pretreatment were observed to increase the rate of diffusion for the larger 40-kDa dextran probe.

Keywords
Dextran, Explosions, Fluorescence, Microstructure, Photobleaching, Probes, Steam, Steam engineering, Biorefineries, Cell walls, Diffusion measurements, Earlywood, Fluorescence recovery after photobleaching, Fluorescent probes, Pre-Treatment, Steam explosion, Diffusion
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34478 (URN)10.1007/s00226-018-1039-5 (DOI)2-s2.0-85050675818 (Scopus ID)
Available from: 2018-08-08 Created: 2018-08-08 Last updated: 2018-12-20Bibliographically approved
Röding, M., Gaska, K., Kádár, R. & Loren, N. (2017). Computational Screening of Diffusive Transport in Nanoplatelet-Filled Composites: Use of Graphene To Enhance Polymer Barrier Properties. ACS Applied Nano Materials
Open this publication in new window or tab >>Computational Screening of Diffusive Transport in Nanoplatelet-Filled Composites: Use of Graphene To Enhance Polymer Barrier Properties
2017 (English)In: ACS Applied Nano Materials, ISSN 2574-0970Article in journal (Refereed) In press
Abstract [en]

Motivated by the substantial interest in various fillers to enhance the barrier properties of polymeric films, especially graphene derivatives, we perform a computational screening of obstructed diffusion to explore the design parameter space of nanoplatelet-filled composites synthesized in silico. As a model for the nanoplatelets, we use circular and elliptical nonoverlapping and impermeable flat disks, and diffusion is stochastically simulated using a random-walk model, from which the effective diffusivity is calculated. On the basis of ∼1000 generated structures and diffusion simulations, we systematically investigate the impact of different nanoplatelet characteristics such as orientation, layering, size, polydispersity, shape, and amount. We conclude that the orientation, size, and amount of nanoplatelets are the most important parameters and show that using nanoplatelets oriented perpendicular to the diffusion direction, under reasonable assumptions, with approximately 0.2% (w/w) graphene, we can reach 90% reduction and, with approximately 1% (w/w) graphene, we can reach 99% reduction in diffusivity, purely because of geometrical effects, in a defect-free matrix with perfect compatibility. Additionally, our results suggest that the existing analytical models have some difficulty with extremely large aspect ratio (extremely flat) nanoplatelets, which calls for further development.

Keywords
composites; computational screening; diffusivity; graphene; nanoplatelets
National Category
Polymer Chemistry Nano Technology Computational Mathematics Probability Theory and Statistics
Identifiers
urn:nbn:se:ri:diva-32845 (URN)10.1021/acsanm.7b00067 (DOI)
Funder
Swedish Research Council, 2016-03809
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-08-17Bibliographically approved
Gmoser, R., Bordes, R., Nilsson, G., Altskär, A., Stading, M., Loren, N. & Berta, M. (2017). Effect of dispersed particles on instant coffee foam stability and rheological properties. European Food Research and Technology, 243(1), 115-121
Open this publication in new window or tab >>Effect of dispersed particles on instant coffee foam stability and rheological properties
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2017 (English)In: European Food Research and Technology, ISSN 1438-2377, E-ISSN 1438-2385, Vol. 243, no 1, p. 115-121Article in journal (Refereed) Published
Abstract [en]

Properties of instant coffee foam constitute the focus of this study. The coffee, obtained from commercial sources, was dispersed in water at a concentration in the range of standard use. The resulting solution contained a substantial amount of micron and submicron size particles that were filtered with membranes having difference size cut-offs in order to investigate the relationship foam properties—particles size. The foams produced from these solutions have been imaged by confocal laser scanning microscopy, and their moduli and stability have been measured by oscillatory rheology, using an in-house developed rheometric set-up. The results show that particles larger than 0.8 µm have little effect on the reduction of drainage while a clear strengthening effect on the foam was evident. This was a result of their diffusion to the lamellae borders, which increases the viscosity of the liquid–air interface. Particles smaller than 0.2 µm affect bubble coarsening and likely hinder the migration of soluble surface active species to the bubble surface. Particles also participate in the stabilization of the air–water interface, and this affects both the foam stability and mechanical properties. Established models developed for ideal foam systems containing particles are difficult to apply due to the complexity of the system studied. Despite this limitation, these results provide increased understanding of the effect of particles on instant coffee foams.

Keywords
Foam microscopy, Foamability, Instant coffee, Particles, Rheology, Surface tension, Elasticity, Elementary particles, Stabilization, Confocal laser scanning microscopy, Dispersed particle, Oscillatory rheologies, Rheological property, Strengthening effect, Sub-micron size particles, Surface active species, Phase interfaces
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-27645 (URN)10.1007/s00217-016-2728-7 (DOI)2-s2.0-84975221929 (Scopus ID)
Available from: 2016-12-22 Created: 2016-12-21 Last updated: 2018-08-20Bibliographically approved
Röding, M., Svensson, P. & Loren, N. (2017). Functional regression-based fluid permeability prediction in monodisperse sphere packings from isotropic two-point correlation functions. Computational materials science, 134, 126-131
Open this publication in new window or tab >>Functional regression-based fluid permeability prediction in monodisperse sphere packings from isotropic two-point correlation functions
2017 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 134, p. 126-131Article in journal (Refereed) Published
Abstract [en]

We study fluid permeability in random sphere packings consisting of impermeable monodisperse hard spheres. Several different pseudo-potential models are used to obtain varying degrees of microstructural heterogeneity. Systematically varying solid volume fraction and degree of heterogeneity, virtual screening of more than 10,000 material structures is performed, simulating fluid flow using a lattice Boltzmann framework and computing the permeability. We develop a well-performing functional regression model for permeability prediction based on using isotropic two-point correlation functions as microstructural descriptors. The performance is good over a large range of solid volume fractions and degrees of heterogeneity, and to our knowledge this is the first attempt at using two-point correlation functions as functional predictors in a nonparametric statistics/machine learning context for permeability prediction.

Keywords
Correlation functions, Functional regression, Granular materials, Permeability, Sphere packings, Flow of fluids, Forecasting, Packing, Regression analysis, Spheres, Volume fraction, Correlation function, Microstructural descriptors, Microstructural heterogeneity, Non-parametric statistics, Permeability prediction, Two point correlation functions, Mechanical permeability
National Category
Condensed Matter Physics Materials Chemistry
Identifiers
urn:nbn:se:ri:diva-30877 (URN)10.1016/j.commatsci.2017.03.042 (DOI)2-s2.0-85017093852 (Scopus ID)
Available from: 2017-09-06 Created: 2017-09-06 Last updated: 2018-08-17Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9979-5488

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