| 1. |
- Borde, Annika, 1979, et al.
(författare)
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Increased water transport in PDMS silicone films by addition of excipients
- 2012
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 8:2, s. 579-588
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Tidskriftsartikel (refereegranskat)abstract
- The development of new adhesive wound care products intended for an application over a prolonged time requires good water transporting properties of the adhesive for the maintenance of a suitable environment around the wound. The ability of polydimethylsiloxane (PDMS)-based silicone films to transport water has led to its use in skin pressure-sensitive adhesives and it would be advantageous to find ways for controlling or increasing water transport across PDMS films in order to be able to develop improved skin adhesives. In this study we present a way to increase water transport in such films by the addition of hydrophilic excipients. Three hydrophilic additives, highly water-soluble sucrose and the two superabsorbent polymers (SAP) Carbopol® and Pemulen™, were investigated. The effect of the excipients was characterized by water transport studies, swelling tests, scanning electron microscopy imaging and confocal microscopy. The cross-linked polymers, primarily Pemulen™, were efficient water transport enhancers, whereas sucrose did not show any effect. The effect of the additives seemed to correlate with their water binding capacity. For SAPs the formation of a percolating structure by swollen polymer was also suggested, which enhances water penetration by the higher volume fraction of areas with a higher diffusion constant (swollen SAP), leading to a faster transport through the entire film. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 2. |
- Deschout, Hendrik, et al.
(författare)
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Straightforward FRAP for quantitative diffusion measurements with a laser scanning microscope
- 2010
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Ingår i: Optics Express. - 1094-4087. ; 18:22, s. 22886-22905
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Tidskriftsartikel (refereegranskat)abstract
- Confocal or multi-photon laser scanning microscopes are convenient tools to perform FRAP diffusion measurements. Despite its popularity, accurate FRAP remains often challenging since current methods are either limited to relatively large bleach regions or can be complicated for non-specialists. In order to bring reliable quantitative FRAP measurements to the broad community of laser scanning microscopy users, here we have revised FRAP theory and present a new pixel based FRAP method relying on the photo bleaching of rectangular regions of any size and aspect ratio. The method allows for fast and straightforward quantitative diffusion measurements due to a closed–form expression for the recovery process utilizing all available spatial and temporal data. After a detailed validation, its versatility is demonstrated by diffusion studies in heterogeneous biopolymer mixtures.
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| 3. |
- Hagman, Joel H, 1983, et al.
(författare)
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Effect of Gelatin Gelation Kinetics on Probe Diffusion Determined by FRAP and Rheology
- 2010
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:12, s. 3359-3366
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependent diffusion and mechanical properties of gelatin in solution, in the gel state, and during the sol/gel transition were determined using fluorescence recovery after photobleaching (FRAP) and rheology. The parameters in the experimental design were 2% w/w and 5% w/w gelatin concentration; 15, 20, and 25 degrees C end quench temperatures; and Na-2-fluorescein, 10 kDa FITC-dextran, and 500 kDa FITC-dextran as diffusion probes. The samples were monitored in solution at 60 degrees C, during quenching, for 75 min at end quench temperatures and after 1, 7, and 14 days of storage at the end quench temperature. The effect of temperature on the probe diffusion was normalized by determining the free diffusion of the probes in pure water for the different temperatures. The results gained by comparing FRAP and rheology showed that FRAP is able to capture structural changes in the gelatin before gelation occurs, which was interpreted as a formation of transient networks. This was clearly seen for 2% w/w gelatin and 20 and 25 degrees C end quench temperatures. The structural changes during sol/gel transition are detected only by the larger probes, giving information about the typical length scales in the gelatin structure. The normalized diffusion rate increased after 7 and 14 days of storage. This increase was most pronounced for fluorescein but was also seen for the larger probes.
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| 4. |
- Hagman, Joel H, 1983, et al.
(författare)
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Probe diffusion in κ-carrageenan gels determined by fluorescence recovery after photobleaching
- 2012
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 29:1, s. 106-115
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Tidskriftsartikel (refereegranskat)abstract
- The effects of free volume and heterogeneity on probe diffusion in κ-carrageenan gels were determined by fluorescence recovery after photobleaching (FRAP) and rheology. By changing the ionic conditions, biopolymer concentration and end temperature, different microstructures and aggregation kinetics in the κ-carrageenan gels were evaluated. The results of the FRAP measurements were compared to transmission electron microscopy (TEM) and nuclear magnetic resonance diffusometry (NMRd) data from previous studies. The results showed that the free diffusion rates of the probe (FITC dextran) in water were influenced by both temperature and ionic conditions. The free diffusion values were used for normalization of the diffusion rates in the κ-carrageenan gel measurements. The compatibility between FITC dextran with different molecular weights (10 and 500 kDa) and κ-carrageenan was evaluated. The results showed that the larger FITC dextran probe phase separates; therefore only the 10 kDa FITC dextran probe was used in the FRAP experiments. FRAP measurements and NMRd probe diffusion in combination with TEM in κ-carrageenan revealed that the void space, degree of aggregation and heterogeneity influence the probe diffusion rate. The κ-carrageenan gelation was analyzed at different end temperatures using rheology and FRAP. The FITC dextran probe diffusion was not influenced by κ-carrageenan aggregation, regardless of rheological gelation kinetics and storage modulus near the gel point. This indicates that the average void space between the gel strands is larger than the size of the probe. Good correlation between the microstructure and the probe diffusion rate in κ-carrageenan gel with different ionic conditions and constant biopolymer concentration were obtained with TEM and FRAP.
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| 5. |
- Hagman, Joel H, 1983
(författare)
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Structure Dynamics and Heterogeneity in Soft Materials Determined by FRAP
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A common interest in industry today is to be able to control the mass transport inside soft (bio) materials in order to tailor both release and uptake of substances. Most of the materials used are heterogeneous, quite often multiphase or compound materials and often undergo dynamic changes; it is therefore important to have control over the local microstructure in order to tailor the macroscale properties. The work in this thesis expands the toolbox of available techniques for studying diffusion in such materials. This has been achieved by enhancing the usability of a technique called fluorescence recovery after photobleaching (FRAP) as well as by performing FRAP measurements in dynamic and heterogeneous materials. FRAP is an optical technique capable of measuring locally at a micrometer scale in a material sample. The results obtained have given an increased understanding of the structure–mass transport relationship. The technique has been improved by improving the accuracy of the mass transport determination, by reducing the required measurement area, by increasing the range of available materials in which FRAP can be used as well as by analysing the impact of probe selection. The materials used in this thesis work have been used as model materials for FRAP development and at the same time been investigated using FRAP. The materials, along with the key interest, can be summarized to the following choises: κ-carrageenan for the structural heterogeneity, gelatin for the dynamic changes during gelation, gelatin/maltodextrin multiphase samples for the posibillty to tailor the domain sizes, super absorbing polymers (SAP) for the posibillity to alter the mass transport properties depending on the swelling and both β-lactoglobulin and pasta was used as model material for spatial correlation measurements of FRAP data. These results may be used for improved understanding of other materials as well and the FRAP technique is shown to be one promising tool when tailoring new structures.
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| 6. |
- Hagman, Joel, et al.
(författare)
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On the dissolution state of cellulose in cold alkali solutions
- 2017
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; , s. 2003-2015
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Tidskriftsartikel (refereegranskat)abstract
- We have characterized the dissolved state of microcrystalline cellulose (MCC) in cold alkali [2.0 M NaOH(aq)] solutions using a combination of small angle X-ray (SAXS) and static light scattering (SLS), (Formula presented.)H NMR, NMR self-diffusion, and rheology experiments. NMR and SAXS data demonstrate that the cellulose is fully molecularly dissolved. SLS, however, shows the presence of large concentration fluctuations in the solution, consistent with significant attractive cellulose-cellulose interactions. The scattering data are consistent with fractal cellulose aggregates of micrometre size having a mass fractal dimension (Formula presented.). At 25(Formula presented.) the solution structure remains unchanged on the time scale of weeks. However, upon heating the solutions above 35(Formula presented.) additional aggregation occurs on the time scale of minutes. Decreasing or increasing the NaOH concentration away from the “optimum” 2 M also leads to additional aggregation. This is seen as an increase of the SAXS intensity at lower q values. Addition of urea (1.8 and 3.6 M, respectively) does not significantly influence the solution structure. With these examples, we will discuss how scattering methods can be used to assess the quality of solvents for cellulose.
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| 7. |
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| 8. |
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| 9. |
- Hedlund, Artur, et al.
(författare)
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Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate : contrasting coagulation mechanisms
- 2019
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:3, s. 1545-1563
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].
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| 10. |
- Jonasson, Jenny, 1976, et al.
(författare)
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Pixel-based analysis of FRAP data with a general initial bleaching profile
- 2010
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 239:2, s. 142-153
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Tidskriftsartikel (refereegranskat)abstract
- Jonasson et al. (2008), we presented a new pixel-based maximum likelihood framework for the estimation of diffusion coefficients from data on fluorescence recovery after photobleaching (FRAP) with confocal laser scanning microscopy (CLSM). The main method there, called the Gaussian profile method below, is based on the assumption that the initial intensity profile after photobleaching is approximately Gaussian. In the present paper, we introduce a method, called the Monotone profile method, where the maximum likelihood framework is extended to a general initial bleaching profile only assuming that the profile is a non-decreasing function of the distance to the bleaching centre. The statistical distribution of the image noise is further assumed to be Poisson instead of normal, which should be a more realistic description of the noise in the detector. The new Monotone profile method and the Gaussian profile method are applied to FRAP data on swelling of super absorbent polymers (SAP) in water with a Fluorescein probe. The initial bleaching profile is close to a step function at low degrees of swelling and close to a Gaussian profile at high degrees of swelling. The results obtained from the analysis of the FRAP data are corroborated with NMR diffusometry analysis of SAP with a polyethylene glycol probe having size similar to the Fluorescein. The comparison of the Gaussian and Monotone profile methods is also performed by use of simulated data. It is found that the new Monotone profile method is accurate for all types of initial profiles studied, but it suffers from being computationally slow. The fast Gaussian profile method is sufficiently accurate for most of the profiles studied, but underestimates the diffusion coefficient for profiles close to a step function. We also provide a diagnostic plot, which indicates whether the Gaussian profile method is acceptable or not.
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