| 1. |
- Mohlin, Kristina, 1970, et al.
(author)
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Water pores in alkyl ketene dimer (AKD) dispersions studied by NMR diffusometry and optical microscopy
- 2007
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In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 297:1-3, s. 114-121
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Journal article (peer-reviewed)abstract
- Water borne alkyl ketene dimer (AKD) dispersions have been investigated by means of optical microscopy and NMR diffusometry (NMR-D). In two different formulations, different amounts of entrapped water in pores with different sizes are obtained, which can be compared to a waterin-oil-in-water (w/o/w) dispersion. It is shown that the amount of entrapped water inside the AKD particles can conveniently be measured with the NMR-D technique. The pore size is however not obtained correctly from the NMR-D experiment. Due to the small size of the water pores, the pore size is underestimated when measured with NMR-D. This effect is investigated in more detail by Brownian dynamic simulations from which a correction factor is obtained that allows a more correct value of the pore size from NMR-D measurements. When the pore size is too small to be observed by optical microscopy, typically below 0.5 mu m, NMR diffusometry combined with Brownian dynamic simulations are shown to be a rapid and reliable tool for quantifying the porosity in these types of systems.
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| 4. |
- Jonasson, Jenny, 1976, et al.
(author)
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A pixel-based likelihood framework for analysis of fluorescence recovery after photobleaching data
- 2008
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In: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 232:2, s. 260-269
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Journal article (peer-reviewed)abstract
- A new framework for the estimation of diffusion coefficients from data on fluorescence recovery after photobleaching (FRAP) with confocal laser scanning microscopy (CLSM) is presented. It is a pixel-based statistical methodology that efficiently utilizes all information about the diffusion process in the available set of images. The likelihood function for a series of images is maximized which gives both an estimate of the diffusion coefficient and a corresponding error. This framework opens up possibilities (1) to obtain localized diffusion coefficient estimates in both homogeneous and heterogeneous materials, (2) to account for time differences between the registrations at the pixels within each image, and (3) to plan experiments optimized with respect to the number of replications, the number of bleached regions for each replicate, pixel size, the number of pixels, the number of images in each series etc. To demonstrate the use of the new framework, we have applied it to a simple system with polyethylene glycol (PEG) and water where we find good agreement with diffusion coefficient estimates from NMR diffusometry. In this experiment, it is also shown that the effect of the point spread function is negligible, and we find fluorochrome-concentration levels that give a linear response function for the fluorescence intensity. © 2008 The Authors.
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| 5. |
- Kvarnström, Mats, 1974, et al.
(author)
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Brownian dynamics simulations in hydrogels using an adaptive time-stepping algorithm
- 2009
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In: Physical Review E. - 2470-0045 .- 2470-0053. ; 79:1, s. 16102-
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Journal article (peer-reviewed)abstract
- The adaptive time-stepping algorithm for Brownian simulation of solute diffusion in three-dimensional complex geometries previously developed by the authors of this paper was applied to heterogeneous three-dimensional polymer hydrogel structures. The simulations were performed on reconstructed three-dimensional hydrogels. The obstruction effect from the gel strands on water and diffusion of dendrimers with different sizes were determined by simulations and compared with experimental nuclear magnetic resonance diffusometry data obtained from the same material. It was concluded that obstruction alone cannot explain the observed diffusion rates, but an interaction between the dendrimers and the gel strands should be included in the simulations. The effect of a sticky-wall interaction potential with geometrically distributed residence times on the diffusion rate has been studied. It was found that sticky-wall interaction is a possible explanation for the discrepancy between simulated and experimental diffusion data for dendrimers of different sizes diffusing in hydrogels.
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| 6. |
- Loren, Niklas, et al.
(author)
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Dendrimer diffusion in ?-carrageenan gel structures
- 2009
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:2, s. 275-284
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Journal article (peer-reviewed)abstract
- The effect of the ?-carrageenan concentration on gel microstructure and self-diffusion of polyamideamine dendrimers has been determined by transmission electron microscopy (TEM), image analysis, and nuclear magnetic resonance (NMR) diffusometry. Different salt conditions of KCl, NaCl, and mixtures thereof allowed for formation of significantly different microstructures. The ?-carrageenan concentrations were varied between 0.25 and 3.0 w/w% for a salt mixture containing 20 mM KCl and 200 mM NaCl gels and between 0.5 and 4.0 w/w% for 250 mM NaCl gels. Furthermore, the effect of potassium ion concentration on the gel structure and the dendrimer diffusion rate was determined. The potassium ion concentration was varied between 20 mM KCl and 200 mM KCl. Two different dendrimer generations with significant difference in size were used: G2 and G6. Dendrimers were found to be sensitive probes for determination of the effect of the gel microstructure on molecular diffusion rate. A qualitative comparison between TEM micrographs, NMR diffusometry data and image analysis showed that the gel structure has a large impact on the dendrimers diffusion in ?-carrageenan gels. It was found that diffusion was strongly influenced by the ?-carrageenan concentration and the dendrimer generation. Small voids in the gel network gave strongly reduced diffusion. Image analysis revealed that the interfacial area between the gel network and the surrounding water phase correlated well with the dendrimer diffusion. © 2009 American Chemical Society.
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| 7. |
- Loren, Niklas, et al.
(author)
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Determination of local diffusion properties in heterogeneous biomaterials
- 2009
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In: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 150:1, s. 42139-
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Journal article (peer-reviewed)abstract
- The coupling between structure and diffusion properties is essential for the functionality of heterogeneous biomaterials. Structural heterogeneity is defined and its implications for time-dependent diffusion are discussed in detail. The effect of structural heterogeneity in biomaterials on diffusion and the relevance of length scales are exemplified with regard to different biomaterials such as gels, emulsions, phase separated biopolymer mixtures and chocolate. Different diffusion measurement techniques for determination of diffusion properties at different length and time scales are presented. The interplay between local and global diffusion is discussed. New measurement techniques have emerged that enable simultaneous determination of both structure and local diffusion properties. Special emphasis is given to fluorescence recovery after photobleaching (FRAP). The possibilities of FRAP at a conceptual level is presented. The method of FRAP is briefly reviewed and its use in heterogeneous biomaterials, at barriers and during dynamic changes of the structure is discussed. © 2009 Elsevier B.V. All rights reserved.
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| 8. |
- Walther, Bernhard, et al.
(author)
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Influence of ?-carrageenan gel structures on the diffusion of probe molecules determined by transmission electron microscopy and NMR diffusometry
- 2006
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22:19, s. 8221-8228
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Journal article (peer-reviewed)abstract
- The influence of the microstructures of different ?-carrageenan gels on the self-diffusion behavior of poly(ethylene glycol) (PEG) has been determined by nuclear magnetic resonance (NMR) diffusometry and transmission electron microscopy (TEM). It was found that the diffusion behavior was determined mainly by the void size, which in turn was defined by the state of aggregation of the ?-carrageenan. The ?-carrageenan concentration was held constant at 1 w/w%, and the aggregation was controlled by the amount of potassium and/or sodium chloride and, for samples containing potassium, also by the cooling rate. Gels containing potassium formed microstructures where ?-carrageenan strands are rather evenly distributed over the image size, while sodium gels formed dense biopolymer clusters interspersed with large openings. In a gel with small void sizes, relatively slow diffusion was found for all PEG sizes investigated. Extended studies of the self-diffusion behavior of the 634 g mol-1 PEG showed that there is a strong time dependence in the measured PEG diffusion. An asymptotic lower time limit of the diffusion coefficient was found in all gels when the diffusion observation time was increased. According to the ratio, D/D0, where D0 is the diffusion coefficient in D2O and D is the diffusion coefficient in the gels, the gels could be divided into three classes: small, medium, and large voids. For quenched ?-carrageenan solutions with salt concentrations of 20 mM K+, 100 mM K+, or 20 mM K+/200 mM Na + as well as slowly cooled solutions with only 20 mM K+, D/D0 ratios between 0.18 and 0.29 were obtained. By quenching a ?-carrageenan solution with 100 mM K+, the D/D0 was 0.5, while D/D0 ratios between 0.9 and 1 were obtained in a quenched solution with 250 mM Na+ and slowly cooled samples with 20 mM K +/200 mM Na+ or 250 mM Na+. © 2006 American Chemical Society.
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