| 1. |
- Abrahmsén-Alami, Susanna, et al.
(författare)
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New release cell for NMR microimaging of tablets Swelling and erosion of poly(ethylene oxide)
- 2007
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 342:1-2, s. 105-114
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Tidskriftsartikel (refereegranskat)abstract
- A small release cell, in the form of a rotating disc, has been constructed to fit into the MRI equipment. The present work show that both qualitative and quantitative information of the swelling and erosion behavior of hydrophilic extended release (ER) matrix tablets may be obtained using this release cell and non-invasive magnetic resonance imaging (MRI) studies at different time-points during matrix dissolution. The tablet size, core size and the gel layer thickness of ER matrix formulations based on poly(ethylene oxide) have been determined. The dimensional changes as a function of time were found to correspond well to observations made with texture analysis (TA) methodology. Most importantly, the results of the present study show that both the erosion (displacement of the gel-dissolution media interface) and the swelling (decrease of dry tablet core size) proceed with a faster rate in radial than in axial direction using the rotating disk set-up. This behavior was attributed to the higher shear forces experienced in the radial direction. The results also indicate that front synchronization (constant gel layer thickness) is associated with the formation of an almost constant polymer concentration profile through the gel layer at different time-points.
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| 2. |
- Arumughan, Vishnu, 1994, et al.
(författare)
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Anion-Specific Adsorption of Carboxymethyl Cellulose on Cellulose
- 2023
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 39:42, s. 15014-15021
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Tidskriftsartikel (refereegranskat)abstract
- Integration of fiber modification step with a modern pulp mill is a resource efficient way to produce functional fibers. Motivated by the need to integrate polymer adsorption with the current pulping system, anion-specific effects in carboxymethylcellulose (CMC) adsorption have been studied. The QCM-D adsorption experiments revealed that CMC adsorption to the cellulose model surface is prone to anion-specific effects. A correlation was observed between the adsorbed CMC and the degree of hydration of the co-ions present in the magnesium salts. The presence of a chaotropic co-ion such as nitrate increased the adsorption of CMC on cellulose compared to the presence of the kosmotropic sulfate co-ion. However, anion-specificity was not significant in the case of salts containing zinc cations. The hydration of anions determines the distribution of the ions at the interface. Chaotropic ions, such as nitrates, are likely to be distributed near the chaotropic cellulose surface, causing changes in the ordering of water molecules and resulting in greater entropy gain once released from the surface, thus increasing CMC adsorption.
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| 3. |
- Borgquist, Per, et al.
(författare)
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A model for the drug release from a polymer matrix tablet - effects of swelling and dissolution
- 2006
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 1873-4995 .- 0168-3659. ; 113:3, s. 216-225
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Tidskriftsartikel (refereegranskat)abstract
- A model for simulating the drug release from a swelling and dissolving polymer tablet is presented and verified to data. The model is based on a mechanistic approach, and it can therefore be employed to study the sensitivity of true physical constants, for instance the drug diffusion coefficient or the drug solubility. The model generates the drug and polymer release profiles and the front positions of the total tablet, the solid core, and of the solid-drug-solubilized-drug interface. The convective contribution to mass transfer is shown to be of great importance. This is most markedly noticed for slowly diffusing drugs. In a simulation with a low value of the drug diffusion coefficient, it is shown that the initial drug release rate is faster than the polymer dissolution rate, followed by a second stage with a slower drug release rate. Furthermore, it is shown that polymer dissolution influences the drug release profile significantly, but not the front position of saturated drug in the gel layer. The model is verified against drug release and polymer dissolution data for the slightly soluble drug Methyl paraben and the soluble drug Saligenin in a poly (ethylene oxide) tablet, resulting in good agreement between model and experiments. (c) 2006 Elsevier B.V. All rights reserved.
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| 4. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Effect of alkalinity on the diffusion of solvent-fractionated lignin through cellulose membranes
- 2023
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 30:6, s. 3685-3698
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Tidskriftsartikel (refereegranskat)abstract
- Mass transport of liberated lignin fragments from pits and fiber walls into black liquor is considered a determining step in the delignification process. However, our current understanding of the diffusion of lignin through cellulose and the influential parameter on this process is very limited. A comprehensive and detailed study of lignin mass transport through cellulosic materials is, therefore, of great importance. In this study, diffusion cell methodology is implemented to systematically investigate the transport of fractionated kraft lignin molecules through model cellulose membranes. Pulping is a complex process and lignin is very heterogenous material therefore to perform a more detailed study on lignin diffusion, we included an additional solvent fractionation step. One of the benefits of this method is that the setup can be adjusted to various experimental conditions allowing the complex chemical reactions occurring during pulping, which would affect the mass transfer of lignin, to be avoided. Here, the effects of the alkalinity of the aqueous solution and molecular weight of the kraft lignin molecules on their diffusion were investigated. Additionally, NMR spectroscopy, size exclusion chromatography, and UV/Vis spectroscopy were used to characterize the starting material and the molecules that passed through the membrane. Lignin molecules detected in the acceptor chamber of the diffusion cells had lower molecular weights, indicating a size fractionation between the donor and acceptor chamber. UV/Vis showed higher concentrations of ionized conjugated kraft lignin molecules in the acceptor chamber, which is a sign of chemical fractionation. This study suggests that the diffusion of lignin through small cellulose pores can be enhanced by decreasing the average molecular weight of the diffusing kraft lignin molecules and increasing alkalinity.
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| 5. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Mass Transport of Lignin in Confined Pores
- 2022
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- A crucial step in the chemical delignification of wood is the transport of lignin fragments into free liquor; this step is believed to be the rate-limiting step. This study has investigated the diffusion of kraft lignin molecules through model cellulose membranes of various pore sizes (1-200 nm) by diffusion cells, where the lignin molecules diffuse from donor to acceptor cells through a membrane, where diffusion rate increases by pore size. UV-vis spectra of the donor solutions showed greater absorbance at higher wavelengths (similar to 450 nm), which was probably induced by scattering due to presence of large molecules/clusters, while acceptor samples passed through small pore membranes did not. The UV-vis spectra of acceptor solutions show a characteristic peak at around 350 nm, which corresponds to ionized conjugated molecules: indicating that a chemical fractionation has occurred. Size exclusion chromatography (SEC) showed a difference in the molecular weight (M-w) distribution between lignin from the donor and acceptor chambers. The results show that small pore sizes enable the diffusion of small individual molecules and hinder the transport of large lignin molecules or possible lignin clusters. This study provides more detail in understanding the mass transfer events of pulping processes.
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| 6. |
- Gårdebjer, Sofie, 1985, et al.
(författare)
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An overview of the transport of liquid molecules through structured polymer films, barriers and composites - Experiments correlated to structure-based simulations
- 2018
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686. ; 256, s. 48-64
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Tidskriftsartikel (refereegranskat)abstract
- Films engineered to control the transport of liquids are widely used through society. Examples include barriers in packaging, wound care products, and controlled release coatings in pharmaceutics. When observed at the macroscopic scale such films commonly appear homogeneous, however, a closer look reveals a complex nano and microstructure that together with the chemical properties of the different domains control the transport properties. In this review we compare and discuss macroscopic transport properties, measured using the straightforward, yet highly powerful technique "modified Ussing chambers", also denoted side-by-side diffusion cells, for a wide range of structured polymer films and composites. We also discuss and compare the macroscopic observations and conclusions on materials properties with that of lattice Boltzmann simulations of transport properties based on underlying material structure and chemistry. The survey of the field: (i) highlights the use and power of modified Ussing Chambers for determining liquid transport properties of polymer films, (ii) demonstrates the predictability in both directions between macroscopic observations of transport using modified Ussing chambers and structure-based simulations, and (iii) provides experimental and theoretical insights regarding the transport-determining properties of structured polymer films and composites. (C) 2018 Elsevier B.V. All rights reserved.
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| 7. |
- Kaunisto, Erik, et al.
(författare)
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A mechanistic modelling approach to polymer dissolution using magnetic resonance microimaging
- 2010
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 147:2, s. 232-241
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a computationally efficient mathematical model describing the swelling and dissolution of a polyethylene oxide tablet is presented. The model was calibrated against polymer release, front position and water concentration profile data inside the gel layer, using two different diffusion models. The water concentration profiles were obtained from magnetic resonance microimaging data which, in addition to the previously used texture analysis method, can help to validate and discriminate between the mechanisms of swelling, diffusion and erosion in relation to the dissolution process. Critical parameters were identified through a comprehensive sensitivity analysis, and the effect of hydrodynamic shearing was investigated by using two different stirring rates. Good agreement was obtained between the experimental results and the model. (C) 2010 Elsevier B.V. All rights reserved.
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| 8. |
- Kaunisto, Erik, et al.
(författare)
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Mechanistic modelling of drug release from a polymer matrix using magnetic resonance microimaging.
- 2013
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Ingår i: European Journal of Pharmaceutical Sciences. - : Elsevier BV. - 1879-0720 .- 0928-0987. ; 48:4-5, s. 698-708
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a new model describing drug release from a polymer matrix tablet is presented. The utilization of the model is described as a two step process where, initially, polymer parameters are obtained from a previously published pure polymer dissolution model. The results are then combined with drug parameters obtained from literature data in the new model to predict solvent and drug concentration profiles and polymer and drug release profiles. The modelling approach was applied to the case of a HPMC matrix highly loaded with mannitol (model drug). The results showed that the drug release rate can be successfully predicted, using the suggested modelling approach. However, the model was not able to accurately predict the polymer release profile, possibly due to the sparse amount of usable pure polymer dissolution data. In addition to the case study, a sensitivity analysis of model parameters relevant to drug release was performed. The analysis revealed important information that can be useful in the drug formulation process.
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| 9. |
- Kazlauske, Jurgita, 1981, et al.
(författare)
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The importance of the molecular weight of ethyl cellulose on the properties of aqueous-based controlled release coatings
- 2017
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 519:1-2, s. 157-164
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Tidskriftsartikel (refereegranskat)abstract
- Previous investigations of aqueous based ethyl cellulose (EC) latex dispersions have mainly focused on the commercially available viscosity grade 20 cps. In this study, dispersions of EC with varying viscosity grades (which correspond to molecular weights), ranging from 4 to 100 cps, were produced and characterised. The dispersions showed particle sizes around 200 nm and highly negative ζ-potentials (approx. −100 mV), which indicated stable dispersions as confirmed by sedimentation studies. The different latexes were used to produce free-standing film coatings. We hypothesised that the different viscosity grades of EC would result in different properties of the films. We found that an increase in viscosity grade (and higher molecular weight) resulted in lower coalescence between the particles during film formation and thus to higher water permeability than in film coatings of lower molecular weight. After exposure to water the EC 4 cps and 20 cps film coatings had a more porous structure in the side facing the air during production and drying after immersion in water. Molecular weight is therefore a factor that should be considered when producing pharmaceutical coatings for controlled release.
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| 10. |
- Korner, Anna, et al.
(författare)
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Influence of Different Polymer Types on the Overall Release Mechanism in Hydrophilic Matrix Tablets
- 2009
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Ingår i: Molecules. - : MDPI AG. - 1420-3049. ; 14:8, s. 2699-2716
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Tidskriftsartikel (refereegranskat)abstract
- The effect of three different types of polymer chain structures on the polymer release from hydrophilic matrix tablets was investigated by comparing a synthetic semi-crystalline linear polymer (PEO), a branched amorphous polysaccharide (dextran) and an amorphous substituted cellulose derivative (HPMC). The polymer release rates for tablets containing mixtures of high and low molecular weight grades in different ratios were determined by using a modified USP II method and a SEC-RI chromatography system. The results showed that independent of polymer type: (i) plots of the release versus time had similar shapes, (ii) the release of long and short polymer chains was equal and no fractionation occurred during the release and (iii) the release rate could be related to the average intrinsic viscosity of the polymer mixtures. This confirms the hypothesis that the release rate can be related to a constant viscosity on the surface of the hydrophilic matrix tablet and that it is valid for all the investigated polymers.
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