| 1. |
- Brohede, Ulrika, et al.
(författare)
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Characterization of the drug release process by investigation of its temperature dependence
- 2004
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 93:7, s. 1796-1803
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent drug release from disintegrating tablets made of NaCl-containing agglomerated micronized cellulose (AMC) granules has been studied to characterize the release process. Release measurements on tablets compacted at three different compaction pressures; 50, 100, and 200 MPa, were performed at seven different temperatures; 6, 23, 33, 43, 50, 55, and 63°C using the recently developed alternating ionic current method. Tablets compacted at different compaction pressures showed similar release rates. The release process was found to be diffusion-controlled, and the activation energy of the diffusion coefficient was comparable to that obtained for diffusion in pure water. The results show that the AMC granules in contact with water swell to a size and shape that is only slightly affected by their compaction history and the ion diffusion operates mainly within liquid-filled pores within the AMC granules. By using the temperature dependence of the release process, it was possible to reach this conclusion without any assumptions concerning the number and radii of the granules into which the tablets disintegrated. Further, the magnitude of the effective diffusion coefficient was found to be ∼7.5 · 10−10 cm2/s, which is ∼four orders of magnitude lower than for unhindered diffusion of Na+ and Cl− in water but similar to the diffusion coefficient for protons and OH− ions in microcrystalline cellulose.
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| 2. |
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| 3. |
- Frenning, Göran, et al.
(författare)
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A new method for characterizing the release of drugs from tablets in low liquid surroundings
- 2002
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 91:3, s. 776-784
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this article is to introduce a method capable of determining early drug dissolution in small amounts of liquid. The method is based on the measurement of the alternating ionic current through a cell containing the dissolution medium and the substance to be dissolved. Both the initial and more prolonged absorption of liquid into tablets can also be determined by using the same technique. The method has been tested on two tablet formulations containing agglomerated micronized cellulose and NaCl as a model drug. Release of NaCl was delayed from both formulations; the extent of the delay was strongly formulation-dependent only when the surrounding liquid was in short supply. This finding shows that new drug dissolution phenomena may be encountered in small liquid volumes; these phenomena would not have been seen with the large volume methods normally used in in vitro dissolution tests. Hence, for formulations intended for sublingual, buccal, or rectal administration, i.e., in areas where liquid is scarce, in vitro dissolution tests should be performed in small volumes of dissolution medium.
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| 4. |
- Frenning, Göran, et al.
(författare)
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Dielectric and Li transport properties of electron conducting and non-conducting sputtered amorphous Ta2O5 films
- 2001
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Ingår i: Electrochimica Acta. - 0013-4686 .- 1873-3859. ; 46:13-14, s. 2041-2046
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Tidskriftsartikel (refereegranskat)abstract
- Two types of sputtered thin film amorphous tantalum oxide (Ta2O5) were studied: one electron conducting Ta2O5 (ec-Ta2O5) and the other non-conducting Ta2O5 (nc-Ta2O5). The as-deposited films were characterized by impedance spectroscopy (IS) and isothermal transient ionic current (ITIC) measurements. From IS, the dc conductivity 2×10−14 S/cm was obtained for the ec-Ta2O5 film at an applied ac potential of 50 mV whereas a value ≤1×10−17 S/cm was obtained for the nc-Ta2O5 film. Li conducting properties were studied using the galvanostatic intermittent titration technique and ITIC measurements on the intercalated samples. Despite the very dissimilar dc conductivities of the as-deposited films, the two Ta2O5 samples showed surprisingly similar Li ion conducting properties for small Li/Ta2O5 ratios. The Li ion mobility was in the range 1.1×10−9–3.0×10−9 cm2/V s for both films. However, the Li storage behaviour as well as the chemical diffusion coefficient differed. For the nc-Ta2O5 film a plateau was observed in the equilibrium potential vs. composition curve for Li/Ta2O5 ratios between 7×10−5 and 2×10−3. This plateau was likely to have been caused by attractive interactions between the intercalated ions, possibly large enough to cause phase separation. The attractive interactions were shown to suppress the chemical diffusion coefficient in this composition range.
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| 5. |
- Frenning, Göran, et al.
(författare)
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Drug release modeled by dissolution, diffusion, and immobilization
- 2003
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Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 250:1, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a novel drug release model that combines drug dissolution, diffusion, and immobilization caused by adsorption of the drug to the tablet constituents. Drug dissolution is described by the well-known Noyes–Whitney equation and drug adsorption by a Langmuir–Freundlich adsorption isotherm, and these two processes are included as source and sink terms in the diffusion equation. The model is applicable to tablets that disintegrate into a number of approximately spherical fragments. In order to simplify the analysis it is assumed that liquid absorption, matrix swelling, and tablet disintegration are much faster than drug dissolution and subsequent drug release. The resulting model is shown to yield release characteristics in good agreement with those observed experimentally.
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| 6. |
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| 7. |
- Frenning, Göran, et al.
(författare)
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Li conduction in sputtered amorphous Ta2O5
- 2001
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 148:5, s. A418-A421
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Tidskriftsartikel (refereegranskat)abstract
- Electron and Li ion conducting properties of room temperature sputtered amorphous tantalum oxide (a-Ta2O5) films were studied in order to evaluate the feasibility of using a-Ta2O5 in electrochromic device applications. The films were investigated using the galvanostatic intermittent titration technique, impedance spectroscopy, and isothermal transient ionic current measurements. It was found that the a-Ta2O5 met two out of three requirements posed on a Li ion conductor in a WO3 based electrochromic device. There was a negligible intercalation in the potential window used in WO3-based electrochromic devices (above 2.4-2.5 V vs. Li/Li+). Furthermore, in this potential region, the chemical diffusion coefficient for Li was larger than the corresponding quantity in WO3. However, there was a nonzero electron conductivity in the a-Ta2O5 films, not observed in the chemical vapor deposition-made β-Ta2O5 investigated earlier. Still, the ionic conductivity was approximately one order of magnitude larger than the electronic one.
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| 8. |
- Frenning, Göran, et al.
(författare)
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Theoretical derivation of the isothermal transient ionic current in an ion conductor : Migration, diffusion, and space-charge effects
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:11, s. 5570-5575
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Tidskriftsartikel (refereegranskat)abstract
- The Green’s function technique was used to determine the isothermal transient ionic current (ITIC) caused by the application of a constant potential across an ion conductor which initially contained the ions under consideration. The analysis included migration, diffusion, and space-charge effects as contributions to the ionic motion. Furthermore, the relative importance of diffusion and space-charge effects as currentlimiters was investigated. It was found that ion concentrations as low as ∼1016–1017 cm−3 are sufficient to make space-charge effects the dominant contribution to the decay of the ITIC at low applied electric fields(∼104 V/cm). Hence such effects should be taken into consideration when the ITIC method is used to determine conduction parameters.
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| 9. |
- Frenning, Göran, et al.
(författare)
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Theoretical investigation of ion conduction in three-layered ion-conductor systems : Derivation of the isothermal transient ionic current and frequency-dependent impedance
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94, s. 1629-
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Tidskriftsartikel (refereegranskat)abstract
- Ion conduction in three-layered ion-conductor systems is considered. Explicit analytic expressions for the isothermal transient ionic current and frequency-dependent impedance are derived. The analysis includes migration, diffusion and space-charge effects as contributors to the ionic motion. The resulting model allows conduction parameters such as diffusion coefficients and ion concentrations in three different layers to be obtained from one single measurement, either in the time or in the frequency domain. The implications of one or more of the layers being mixed ionic/electronic conductors are discussed, and it is argued that the proposed model provides a useful description of the coupled ionic/electronic motion occurring in such a mixed-conductor system.
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| 10. |
- Hedenus, P, et al.
(författare)
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Characterisation of instantaneous water absorption properties of pharmaceutical excipients.
- 2000
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Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 202:1-2, s. 141-9
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Tidskriftsartikel (refereegranskat)abstract
- Powders absorb water by both capillary imbibition and swelling. The capillary process is almost instantaneous but swelling occurs over a period of time. An isothermal transient ionic current technique was used in this study to characterise the instantaneous absorption properties (rate and capacity) of a few selected pharmaceutical excipients. The results indicate that the instantaneous and long term water absorption properties of pharmaceutical powders can differ considerably. The rate of instantaneous water absorption appears to correlate with the total surface area while the absorption capacity correlates more with the porosity of the powder.
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| 11. |
- Hägerström, Helene, et al.
(författare)
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Low-frequency dielectric spectroscopy as a tool for studying the compatibility between pharmaceutical gels and mucous tissue
- 2003
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 92:9, s. 1869-1881
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Tidskriftsartikel (refereegranskat)abstract
- This interdisciplinary work demonstrates how low-frequency dielectric spectroscopy, a technique that is frequently used within physics, can be used to assess the possibilities of intimate surface contact between a polymer gel and mucous tissue, which is generally considered to be the first step in the mucoadhesion process. The dielectric responses of five different gels, of freshly excised porcine nasal mucosa and of systems made by combining the two were measured. All spectra were modeled by a Randles electric circuit containing a diffusion element, a barrier resistance in parallel with a capacitance, and a high-frequency resistance. The results were used to create a measure of the compatibility between the gel and the mucus, which we have named the compatibility factor. Thus, the compatibility factor provides us with a measure of the ease with which a charged species passes the interface between a gel and the mucus layer. The compatibility factor is calculated from the high frequency (kHz region) response of the gel, of the mucosa, and of the combined system. The two highest compatibility factors in this study were obtained for gels based on crosslinked poly(acrylic acid) and chitosan, which was in agreement with the results from mucoadhesion measurements that were performed using a tensile strength method.
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| 12. |
- Jonsson, AnnaKarin, et al.
(författare)
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Dielectric study of thin films of Ta2O5 and ZrO2
- 2001
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Ingår i: IEEE transactions on dielectrics and electrical insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1070-9878 .- 1558-4135. ; 8:4, s. 648-651
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Tidskriftsartikel (refereegranskat)abstract
- Electronic conduction in sputtered Ta2O5 and ZrO2 thin films have been studied using impedance spectroscopy, isothermal transient ionic current, and current-voltage measurements. The dielectric properties of Ta2O5 were shown to be sensitively dependent on deposition parameters with two different frequency responses: a flat loss behavior with very low DC conductivity, or a relaxation peak together with a somewhat higher DC conductivity. ZrO2 has different dielectric properties when fresh, i.e. newly deposited, or aged. A fresh sample arbitrarily can show two different behaviors, consisting of a DC conductivity with a relaxation peak superimposed on it. The DC conductivity shows either of two different values. The aged sample has a lower permittivity and DC conductivity, and the relaxation peak is found at much lower frequencies. Fresh samples of ZrO2 also show switching behavior
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| 13. |
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| 14. |
- Mihranyan, Albert, et al.
(författare)
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Capillary condensation of moisture in fractal pores of native cellulose powders
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 393:4-6, s. 389-392
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Tidskriftsartikel (refereegranskat)abstract
- This study was performed to investigate the applicability of the theory of capillary condensation of moisture in fractal nanopores of native cellulose powders of various origins. The characteristic fractal dimensions D were calculated and their physical meaning discussed. The method proved useful for obtaining versatile information about the water–cellulose interactions as well as the bulk structure of cellulose particles.
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| 15. |
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| 16. |
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| 17. |
- Niklasson, Gunnar A., et al.
(författare)
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Surface roughness of pyrolytic tin dioxide films evaluated by different methods
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 359:2, s. 203-209
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Tidskriftsartikel (refereegranskat)abstract
- The scaling of surface roughness in thin spray pyrolyzed fluorinated tin dioxide films of different thicknesses was obtained from atomic force microscopy. The data show that, within experimental uncertainties, the effective dimensionality of the surface is 2; hence no evidence of fractal surface roughness was found. Other methods – based upon light scattering and cyclic voltammetry – gave additional information on the surface topography. Cyclic voltammetry measurements show that the reaction sites on the surface are distributed in a fractal structure and may be identified with hillocks seen in surface reliefs.
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| 18. |
- Nilsson, Martin, et al.
(författare)
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Water-induced charge transport in tablets of microcrystalline cellulose of varying density : Dielectric spectroscopy and transient current measurements
- 2003
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 295:2, s. 159-165
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature dielectric frequency response data taken over 13 decades in frequency on microcrystalline cellulose (MCC) tablets of varying density are presented. The frequency response shows on three different processes: the first one is a high-frequency relaxation process whose magnitude increases and reaches a plateau as the tablet density increases. This process is associated with orientational motions of local chain segments via glycosidic bonds. The second relaxation process, related to the presence of water in the MCC matrix, is insensitive to changes in tablet density. At lower frequencies, dc-like imperfect charge transport dominates the dielectric spectrum. The dc conductivity was found to decrease with increasing tablet density and increase exponentially with increasing humidity.Transient current measurements indicated that two different ionic species, protons and OH− ions, lied behind the observed conductivity. At ambient humidity of 22%, only one in a billion of the water molecules present in the tablet matrix participated in long range dc conduction. The diffusion coefficient of the protons and OH− ions were found to be of the order of 10−9 cm2/s, which is the same as for small salt building ions in MCC. This shows that ionic drugs leaving a tablet matrix may diffuse in the same manner as the constituent ions of water and, thus, elucidates the necessity to understand the water transport properties of excipient materials to be able to tailor the drug release process from pharmaceutical tablets.
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| 19. |
- Strömme, Maria, 1970-, et al.
(författare)
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A new method of characterising liquid uptake within particles over short time periods.
- 2000
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Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 199:2, s. 179-85
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Tidskriftsartikel (refereegranskat)abstract
- A method of measuring both the capacity and rate of absorption of liquid by powders of small particles over short time periods (of the order of a few seconds or less) is presented. The method is based on the measurement of the isothermal transient ionic current in a sample cell containing the absorbant material and the liquid. The method has been tested on solid glass beads, porous glass beads and cellulose agglomerates. Properties such as the instantaneous absorption capacity and rate can be characterised within a few seconds. No other technique is currently able to measure these fast outcomes.
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| 20. |
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| 21. |
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| 22. |
- Strömme, Maria, et al.
(författare)
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Densification-induced conductivity percolation in high-porosity pharmaceutical microcrystalline cellulose compacts
- 2003
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 82:4, s. 648-650
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Tidskriftsartikel (refereegranskat)abstract
- The percolation theory is established as a useful tool in the field of pharmaceutical materials science.It is shown that percolation theory, developed for analyzing insulator–conductor transitions, can beapplied to describe imperfect dc conduction in pharmaceutical microcrystalline cellulose duringdensification. The system, in fact, exactly reproduces the values of the percolation threshold andexponent estimated for a three-dimensional random continuum. Our data clearly show a crossoverfrom a power-law percolation theory region to a linear effective medium theory region at a celluloseporosity of ;0.7.
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| 23. |
- Strömme, Maria, et al.
(författare)
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Fractal dimension of cellulose powders analyzed by multilayer BET adsorption of water and nitrogen
- 2003
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 107:51, s. 14378-14382
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to show that multilayer fractal Brunauer-Emmett-Teller (mfBET) theory can be used as a tool to obtain information about the distribution of water in cellulose powder particles of varying crystallinity. Microcrystalline cellulose, agglomerated micronized cellulose, low-crystallinity cellulose, and cellulose powders from green and brown algae were characterized by scanning electron microscopy and mfBET analysis on water and nitrogen adsorption isotherms. The distribution of water in the cellulose materials was found to be characterized by a fractal dimension smaller than 1.5 for all powders. The results showed that for highly crystalline cellulose materials, such as Cladophora cellulose, the cellulose-water interactions take place mainly on cellulose fibril surfaces adjacent to open pores without causing any significant swelling of the material. For less ordered celluloses the water interaction was found to take place inside the bulk material and the water uptake process caused the pore volume to swell between 1 and 2 orders in magnitude. For the Cladophora cellulose, the thickness of the adsorbed water layer at the outer cut off of the fractal region was found to coincide very well with the average pore size obtained from nitrogen adsorption measurements. The multilayer fractal BET analysis on nitrogen adsorption isotherms showed that the particles could be characterized by fractal dimensions between 2.13 and 2.50. We conclude that water adsorption has the ability to alter the structure of the studied material and reveal a sorption-induced, "apparent" fractal structure over a relatively narrow length scale interval, while nitrogen adsorption probes the substrate morphology over a wide range of length scales and reveals the "true" fractal structure.
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| 24. |
- Strömme, Maria
(författare)
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How can a physicist create better drugs?
- 2004
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Ingår i: The Swedish Academy of Pharmaceutical Sciences conference “Styrning av läkemedelstillförsel aktuell svensk forskning”, 2-3 june, Göteborg, contribution S1 (2004).
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Konferensbidrag (refereegranskat)
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| 25. |
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| 26. |
- Strömme, Maria, 1970-
(författare)
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Physics of drug delivery : dielectric spectroscopy to probe mucoadhesion
- 2003
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Ingår i: Proc. SPIE. - : SPIE. ; 5118, s. 310-322
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Tidskriftsartikel (refereegranskat)abstract
- This work presents how dielectric spectroscopy can be used as a tool to obtain insight about properties on the nano-scale of interfaces of pharmaceutical interest. An outline for studying the adhesion in terms of a compatibility factor between pharmaceutical gels and biological tissue is put forward. The proposed compatibility factor is calculated from the high frequency response (kHz region) of the gel and porcine nasal mucosa separately, and from that of the combined system. It gives an assessment of the possibilities of intimate surface contact, which is generally considered to be the first step in the mucoadhesion process. The results from dielectric spectroscopy were compared to measurements using a tensile strength method and it was found that the gels with the highest compatibility factors were the same as those pointed out as having the highest mucoadhesion using the tensile strength method.
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| 27. |
- Strömme, Maria, et al.
(författare)
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(Ta1-xNbx)(2)O-5 films produced by atomic layer deposition : Temperature dependent dielectric spectroscopy and room-temperature I-V characteristics
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:9, s. 4532-4542
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Tidskriftsartikel (refereegranskat)abstract
- Temperature dependent ac dielectric spectroscopy and room-temperature I–V characterization were performed on atomic layer deposited(Ta1−xNbx)2O5films. The high frequency permittivity, as well as the dc conductivity of the films, were found to increase with increasing Nb content. The conduction mechanism in the mixed Ta–Nb oxide films was of the Poole–Frenkel type, while the high field conduction in pure Ta2O5 was space-charge limited. The activation energy for dc conduction was higher in mixed Ta–Nb oxides compared to pure Ta2O5 and Nb2O5films. Irreversible changes in the conduction mechanism took place upon heat treatment above a certain irreversibility temperature. This temperature was higher for the mixed oxides than for the binary ones.
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| 28. |
- Strömme, Maria, et al.
(författare)
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What do we do with all these algae?
- 2002
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Ingår i: Materials letters (General ed.). - 0167-577X .- 1873-4979. ; 57:3, s. 569-572
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Tidskriftsartikel (refereegranskat)abstract
- The severe eutrophication of coastal areas is considered to be one of the most serious environmental threats of our time S. Nixon, Ambio 19 (1990) 101. Even if the nutrient outlet is curtailed, carpets of green algae filaments will remain for a long time as the algae life cycle feeds itself S. Naeem, D.R. Hahn, G. Schuurman, Nature 403 (2002) 762. One way to master this ecological problem is to remove algae from the cycle O. Jousson, J. Pawlowski, L. Zaninetti, F.W. Zechman, F. Dini, G. Di Guiseppe, R. Woodfield, A. Millar, A. Meinensz, Nature 408 (2000) 157. Hence, the necessity of finding some relevant use for green algae is obvious. It has been shown that cellulose powder from green algae sources has a higher level of crystallinity and a relatively larger surface area than higher plant cellulose R. Ek, C. Gustafsson, A. Nutt, T. Iversen, C, Nyström, J. Mol. Recognit. 11 (1998) 263. Could these properties possibly be advantageous in pharmaceutical tablet manufacturing? Here, we show that green algae filaments provide an alternative raw material source for the production of microcrystalline cellulose with a hitherto unobserved combination of properties desirable for a tableting excipient.
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| 29. |
- Welch, Ken, et al.
(författare)
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Simultaneous Measurement of Drug Release and Liquid Uptake in Pharmaceutical Tablets
- 2003
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 92:6, s. 1242-1249
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Tidskriftsartikel (refereegranskat)abstract
- A new method is introduced that allows drug release and liquid absorption to be studied simultaneously. The drug release is measured by the alternating ionic current (AIC) method, and the study of liquid uptake is accomplished with a sensitive microbalance from a processor tensiometer. We show that the method can be employed to study anomalous diffusion in the initial phase of the drug release process of disintegrating systems. We also demonstrate that the diffusion layer thickness and the diffusion coefficient in a dissolving system can be obtained with the new measurement technique.
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