| 1. |
- Galvosas, P., et al.
(författare)
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Rheo-NMR in food science - Recent opportunities
- 2019
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 57:9, s. 757-765
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Tidskriftsartikel (refereegranskat)abstract
- For over 25years, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques have been used to study materials under mechanical deformation. Collectively, these methods are referred to as Rheo-NMR. In many cases, it provides spatially and temporally resolved maps of NMR spectra, intrinsic NMR parameters (such as relaxation times), or motion (such as diffusion or flow). Therefore, Rheo-NMR is complementary to conventional rheological measurements. This review will briefly summarize current capabilities and limitations of Rheo-NMR in the context of material science and food science in particular. It will report on recent advances such as the incorporation of torque sensors or the implementation of large amplitude oscillatory shear and point out future opportunities for Rheo-NMR in food science. © 2019 John Wiley & Sons, Ltd.
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| 2. |
- Gubitosi, Marta, et al.
(författare)
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Stable, metastable and unstable cellulose solutions
- 2017
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Ingår i: Royal Society Open Science. - : The Royal Society. - 2054-5703. ; 4:8
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Tidskriftsartikel (refereegranskat)abstract
- We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous tetrabutylammonium hydroxide, TBAH(aq), at different concentrations of TBAH, by means of turbidity and small-angle X-ray scattering. The solubility of cellulose increases with increasing TBAH concentration, which is consistent with solubilization driven by neutralization. When comparing the two polymorphs, the solubility of cellulose I is higher than that of cellulose II. This has the consequence that the dissolution of MCC (cellulose I) may create a supersaturated solution with respect to cellulose II. As for the dissolution state of cellulose, we identify three different regimes. (i) In the stable regime, corresponding to concentrations below the solubility of cellulose II, cellulose is molecularly dissolved and the solutions are thermodynamically stable. (ii) In the metastable regime, corresponding to lower supersaturations with respect to cellulose II, a minor aggregation of cellulose occurs and the solutions are kinetically stable. (iii) In the unstable regime, corresponding to larger supersaturations, there is macroscopic precipitation of cellulose II from solution. Finally, we also discuss strong alkali solvents in general and compare TBAH(aq) with the classical NaOH(aq) solvent.
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| 3. |
- Koder Hamid, Mona, et al.
(författare)
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Slow dissolution kinetics of model peptide fibrils
- 2020
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 21:20
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the kinetics of peptide self-assembly is important because of the involvement of peptide amyloid fibrils in several neurodegenerative diseases. In this paper, we have studied the dissolution kinetics of self-assembled model peptide fibrils after a dilution quench. Due to the low concentrations involved, the experimental method of choice was isothermal titration calorimetry (ITC). We show that the dissolution is a strikingly slow and reaction-limited process, that can be timescale separated from other rapid processes associated with dilution in the ITC experiment. We argue that the rate-limiting step of dissolution involves the breaking up of inter-peptide β–sheet hydrogen bonds, replacing them with peptide–water hydrogen bonds. Complementary pH experiments revealed that the self-assembly involves partial deprotonation of the peptide molecules.
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| 4. |
- Kuczera, Stefan, et al.
(författare)
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Multilamellar Vesicle Formation Probed by Rheo-NMR and Rheo-SALS under Large Amplitude Oscillatory Shear
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:28, s. 8314-8325
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Tidskriftsartikel (refereegranskat)abstract
- The formation of multilamellar vesicles (MLVs) in the lyotropic lamellar phase of the system triethylene glycol mono n-decyl ether (C10E3)/water is investigated under large amplitude oscillatory shear (LAOS) using spatially resolved rheo-NMR spectroscopy and a combination of rheo-small angle light scattering (rheo-SALS) and conventional rheology. Recent advances in rheo-NMR hardware development facilitated the application of LAOS deformations in high-field NMR magnets. For the range of investigated strain amplitudes (10-50) and frequencies (1 and 2 rad s-1), MLV formation is observed in all NMR and most SALS experiments. It is found that the MLV size depends on the applied frequency in contrast to previous steady shear experiments where the shear rate is the controlling parameter. The onset of MLV formation, however, is found to vary with the shear amplitude. The LAOS measurements bear no indication of the intermediate structures resembling aligned multilamellar cylinders observed in steady shear experiments. Lissajous curves of stress vs strain reveal a transition from a viscoelastic solid material to a pseudoplastic material.
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| 5. |
- Kuczera, Stefan, et al.
(författare)
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Optimized bias and signal inference in diffusion-weighted image analysis (OBSIDIAN)
- 2021
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 86:5, s. 2716-2732
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Tidskriftsartikel (refereegranskat)abstract
- Purpose Correction of Rician signal bias in magnitude MR images. Methods A model-based, iterative fitting procedure is used to simultaneously estimate true signal and underlying Gaussian noise with standard deviation sigma g on a pixel-by-pixel basis in magnitude MR images. A precomputed function that relates absolute residuals between measured signals and model fit to sigma g is used to iteratively estimate sigma g. The feasibility of the method is evaluated and compared to maximum likelihood estimation (MLE) for diffusion signal decay simulations and diffusion-weighted images of the prostate considering 21 linearly spaced b-values from 0 to 3000 s/mm(2). A multidirectional analysis was performed with publically available brain data. Results Model simulations show that the Rician bias correction algorithm is fast, with an accuracy and precision that is on par to model-based MLE and direct fitting in the case of pure Gaussian noise. Increased accuracy in parameter prediction in a low signal-to-noise ratio (SNR) scenario is ideally achieved by using a composite of multiple signal decays from neighboring voxels as input for the algorithm. For patient data, good agreement with high SNR reference data of diffusion in prostate is achieved. Conclusions OBSIDIAN is a novel, alternative, simple to implement approach for rapid Rician bias correction applicable in any case where differences between true signal decay and underlying model function can be considered negligible in comparison to noise. The proposed composite fitting approach permits accurate parameter estimation even in typical clinical scenarios with low SNR, which significantly simplifies comparison of complex diffusion parameters among studies.
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| 6. |
- Kuczera, Stefan, et al.
(författare)
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Truly reproducible uniform estimation of the ADC with multi-b diffusion data- Application in prostate diffusion imaging
- 2023
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 89:4, s. 1586-1600
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The ADC is a well-established parameter for clinical diagnostic applications, but lacks reproducibility because it is also influenced by the choice diffusion weighting level. A framework is evaluated that is based on multi-b measurement over a wider range of diffusion-weighting levels and higher order tissue diffusion modeling with retrospective, fully reproducible ADC calculation. Methods: Averaging effect from curve fitting for various model functions at 20 linearly spaced b-values was determined by means of simulations and theoretical calculations. Simulation and patient multi-b image data were used to compare the new approach for diffusion-weighted image and ADC map reconstruction with and without Rician bias correction to an active clinical trial protocol probing three non-zero b-values. Results: Averaging effect at a certain b-value varies for model function and maximum b-value used. Images and ADC maps from the novel procedure are on-par with the clinical protocol. Higher order modeling and Rician bias correction is feasible, but comes at the cost of longer computation times. Conclusions: Application of the new framework makes higher order modeling more feasible in a clinical setting while still providing patient images and reproducible ADC maps of adequate quality.
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| 7. |
- Kuczera, Stefan, et al.
(författare)
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Two dimensional oblique molecular packing within a model peptide ribbon aggregate
- 2020
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Ingår i: Chemphyschem. - : Wiley. - 1439-4235 .- 1439-7641. ; 21:14, s. 1519-1523
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Tidskriftsartikel (refereegranskat)abstract
- A(10)K (A=alanine, K=lysine) model peptides self-assemble into ribbon-like beta-sheet aggregates. Here, we report an X-ray diffraction investigation on a flow-aligned dispersion of these self-assembly structures. The two-dimensional wide-angle X-ray scattering pattern suggests that peptide pack in a two-dimensional oblique lattice, essentially identical to the crystalline packing of polyalanine, A(n)(forn>4). One side of the oblique unit cell, corresponding to the anti-parallel beta-sheet, is oriented along the ribbon's axis. Together with recently published small angle X-ray scattering data of the same system, this work thus yields a detailed description of the self-assembled ribbon aggregates, down to the molecular length scale. Notably, our results highlight the importance of the crystalline peptide packing within its self-assembly aggregates, which is often neglected.
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| 8. |
- Maier, Stephan E, 1959, et al.
(författare)
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Prostate Cancer Diffusion-Weighted Magnetic Resonance Imaging: Does the Choice of Diffusion-Weighting Level Matter?
- 2022
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 55:3, s. 842-853
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Tidskriftsartikel (refereegranskat)abstract
- Background Diffusion-weighted magnetic resonance imaging plays an important role in multiparametric assessment of prostate lesions. The derived apparent diffusion coefficient (ADC) could be a useful quantitative biomarker for malignant growth, but lacks acceptance because of low reproducibility. Purpose To investigate the impact of the choice of diffusion-weighting levels (b-values) on contrast-to-noise ratio and quantitative measures in prostate diffusion-weighted MRI. Study Type Retrospective and simulation based on published data. Subjects Patient cohort (21 men with Prostate Imaging-Reporting and Data System (PI-RADS) version 2 score >= 3) from a single-center study. Field Strength/Sequence 3 T/diffusion-weighted imaging with single-shot echo-planar imaging. Assessment Both clinical data and simulations based on previously acquired data were used to quantify the influence of b-value choice in normal peripheral zone (PZ) and PZ tumor lesions. For clinical data, ADC was determined for different combinations of b-values. Contrast-to-noise ratio and quantitative diffusion measures were simulated for a wide range of b-values. Statistical Tests Tissue ADC and the lesion-to-normal tissue ADC ratios of different b-value combinations were compared with paired two-tailed Student's t-tests. A P-value Findings about b-value dependence derived from clinical data and from simulations agreed with each other. Provided measurement was limited to two b-values, simulation-derived optimal b-value choices coincided with PI-RADSv2 recommendations. For two-point measurements, ADC decreased by 15% when the maximum b-value increased from 1000 to 1500 seconds/mm(2), but corresponding lesion-to-normal tissue ADC ratio showed no significant change (P = 0.86 for acquired data). Simulations with three or more measurement points produced ADCs that declined by only 8% over this range of maximum b-value. Corresponding ADC ratios declined between 2.6% (three points) and 3.8% (21 points). Simulations also revealed an ADC reduction of about 19% with the shorter echo and diffusion time evaluated. Data Conclusion The comprehensive assessment of b-value dependence permits better formulation of protocol and analysis recommendations for obtaining reproducible results in prostate cancer diffusion-weighted MRI. Level of Evidence 4 Technical Efficacy Stage 2
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| 9. |
- Rüter, Axel, et al.
(författare)
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Arrested dynamics in a model peptide hydrogel system
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:11, s. 2642-2651
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Forskningsöversikt (refereegranskat)abstract
- We report here on a peptide hydrogel system, which in contrast to most other such systems, is made up of relatively short fibrillar aggregates, discussing resemblance with colloidal rods. The synthetic model peptides A8K and A10K, where A denotes alanine and K lysine, self-assemble in aqueous solutions into ribbon-like aggregates having an average length 〈L〉 on the order of 100 nm and with a diameter d ≈ 6 nm. The aggregates can be seen as weakly charged rigid rods and they undergo an isotropic to nematic phase transition at higher concentrations. Translational motion perpendicular to the rod axis gets strongly hindered when the concentration is increased above the overlap concentration. Similarly, the rotational motion is hindered, leading to very long stress relaxation times. The peptide self-assembly is driven by hydrophobic interactions and due to a net peptide charge the system is colloidally stable. However, at the same time short range, presumably hydrophobic, attractive interactions appear to affect the rheology of the system. Upon screening the long range electrostatic repulsion, with the addition of salt, the hydrophobic attraction becomes more dominant and we observe a transition from a repulsive glassy state to an attractive gel-state of the rod-like peptide aggregates.
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| 10. |
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