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| 7. |
- Blom, Tobias, et al.
(författare)
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Fabrication and characterization of highly reproducible, high resistance nanogaps made by focused ion beam milling
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:28, s. 285301-
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Tidskriftsartikel (refereegranskat)abstract
- Nanoelectrodes were fabricated combining photolithography, electron beam lithography and focused ion beam milling allowing for large scale integration and nanoengineering of the electrode properties. The structure determination by transmission and scanning electron microscopy showed a highly reproducible gap width. The atomic scale electrode structure was characterized using scanning and transmission electron microscopy. The nanogap resistances were found to be the highest hitherto reported for nanogaps, namely in the 300–1300 TΩ range. Gold nanoparticles were trapped by ac dielectrophoresis, and the electrodes were shown to be stable enough to endure empty gap voltages as high as 5 V as well as currents high enough to induce fusing of trapped nanoparticles.
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| 8. |
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| 9. |
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| 10. |
- Brohede, Ulrika, et al.
(författare)
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A novel graded bioactive high adhesion implant coating
- 2009
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 255:17, s. 7723-7728
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Tidskriftsartikel (refereegranskat)abstract
- One method to increase the clinical success rate of metal implants is to increase their bone bonding properties, i.e. to develop a bone bioactive surface leading to reduced risks of interfacial problems. Much research has been devoted to modifying the surface of metals to make them become bioactive. Many of the proposed methods include depositing a coating on the implant. However, there is a risk of coating failure due to low substrate adhesion. This paper describes a method to obtain bioactivity combined with a high coating adhesion via a gradient structure of the coating. Gradient coatings were deposited on Ti (grade 5) using reactive magnetron sputtering with increasing oxygen content. To increase the grain size in the coating, all coatings were post annealed at 385 degrees C. The obtained coating exhibited a gradual transition over 70 nm from crystalline titanium oxide (anatase) at the surface to metallic Ti in the substrate, as shown using cross-section transmission electron microscopy and X-ray photoelectron spectroscopy depth pro. ling. Using scratch testing, it could be shown that the adhesion to the substrate was well above 1 GPa. The bioactivity of the coating was verified in vitro by the spontaneous formation of hydroxylapatite upon storage in phosphate buffer solution at 37 degrees C for one week. The described process can be applied to implants irrespective of bulk metal in the base and should introduce the possibility to create safer permanent implants like reconstructive devices, dental, or spinal implants.
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| 11. |
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| 12. |
- Brohede, Ulrika, 1969-
(författare)
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Drug Diffusion and Nano Excipient Formation Studied by Electrodynamic Methods
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New smart drugs demand new smart drug delivery systems and also new smart analysis methods for the drug delivery process and material characterization. This thesis contributes to the field by introducing a new electrodynamic approach for studying the drug diffusion proc-esses as well as the formation of a new type of drug delivery systems, the so called mesoporous nano excipients.Drug diffusion processes from different pharmaceutical materials were examined. The transport of charged drug substances was investigated by electrodynamic methods; either as a release process governed by diffusion using the alternating ionic current method or by applying a voltage, sinusoidal or dc, to force the drug ions to move in an electric field.Temperature-dependent drug release from microcrystalline cellulose tablets was examined in order to extract information about the diffu-sion process. Percolation theory was also employed to binary mixtures of an insoluble and electrically insulating matrix material together with a soluble and ionic conducting drug. Further, dielectric spectros-copy was proven to be a powerful method for examining the state of vesicle formation of drug and surfactant molecules in a carbopol gel. Finally, a new potential class of pharmaceutical materials were exam-ined, namely the AMS-n mesoporous materials, showing that the al-ternating ionic current method is powerful both in the study of the synthesis of and in the release process from these.
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| 13. |
- Brohede, Ulrika, et al.
(författare)
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Electrodynamic Investigations of Ion Transport and Structural Properties in Drug-Containing Gels : Dielectric Spectroscopy and Transient Current Measurements on Catanionic Carbopol Systems
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:32, s. 15250-15255
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to show the potential of using electrodynamic methods as characterization tools in the controlled drug release process, on complex drug release systems. The two formulations under study were a Carbopol gel containing diphenhydramine and an identical gel also containing the surfactant sodium dodecyl sulfate which forms catanionic vesicles with the diphenhydramine. The average diffusion coefficients were calculated from both the dielectric spectroscopy and the transient current measurements. Comparing the herein-obtained diffusion coefficients with those obtained in another study using a traditional USP technique for the same system, the values are virtually the same. The two electrodynamic methods proved to be potentially valuable tools for obtaining information about the concentration and the motion of the drug molecules inside the gel. The transient current measurements are particularly interesting in this case, as the method gives information not only on an average level, but also of the different charged moieties separately. Interestingly, it seems that the methods also are applicable for obtaining information about the mesh size in the gel.
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| 14. |
- Brohede, Ulrika, et al.
(författare)
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Multifunctional implant coatings providing possibilities for fast antibiotics loading with subsequent slow release
- 2009
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Ingår i: Journal of materials science. Materials in medicine. - : Springer Science and Business Media LLC. - 0957-4530 .- 1573-4838. ; 20:9, s. 1859-1867
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to fast-load biomimetic hydroxyapatite coatings on surgical implant with the antibiotics Amoxicillin, Gentamicin sulfate, Tobramycin and Cephalothin has been investigated in order to develop a multifunctional implant device offering sustained local anti-bacterial treatment and giving the surgeon the possibility to choose which antibiotics to incorporate in the implant at the site of surgery. Physical vapor deposition was used to coat titanium surfaces with an adhesion enhancing gradient layer of titanium oxide having an amorphous oxygen poor composition at the interface and a crystalline bioactive anatase TiO2 composition at the surface. Hydroxyapatite (HA) was biomimetically grown on the bioactive TiO2 to serve as a combined bone in-growth promoter and drug delivery vehicle. The coating was characterized using scanning and transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The antibiotics were loaded into the HA coatings via soaking and the subsequent release and antibacterial effect were analyzed using UV spectroscopy and examination of inhibition zones in a Staphylococcus aureus containing agar. It was found that a short drug loading time of 15 min ensured antibacterial effects after 24 h for all antibiotics under study. It was further found that the release processes of Cephalothin and Amoxicillin consisted of an initial rapid drug release that varied unpredictably in amount followed by a reproducible and sustained release process with a release rate independent of the drug loading times under study. Thus, implants that have been fast-loaded with drugs could be stored for ~10 min in a simulated body fluid after loading to ensure reproducibility in the subsequent release process. Calculated release rates and measurements of drug amounts remaining in the samples after 22 h of release indicated that a therapeutically relevant dose could be achieved close to the implant surface for about 2 days. Concluding, the present study provides an outline for the development of a fast-loading slow-release surgical implant kit where the implant and the drug are separated when delivered to the surgeon, thus constituting a flexible solution for the surgeon by offering the choice of quick addition of antibiotics to the implant coating based on the patient need.
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| 15. |
- Brohede, Ulrika, et al.
(författare)
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Percolating ion transport in binary mixtures with high dielectric loss
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ion transportpercolationproperties of a binary system of an ion conductor (NaCl) and an insulator (ethyl cellulose) for which the ac component of the conductivity is non-negligible over the entire measured frequency range. We find that the dc conductivity, extracted from a well-defined range of frequencies, can be described by a low percolation threshold, ϕc=0.06 three-dimensional conducting network. The low ϕc was explained by the water-layer-assisted ion conduction in micrometer-sized ethyl cellulose channels between NaCl grains. The present findings provide valuable knowledge for the analysis and design of a broad class of ion conducting functional materials.
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| 16. |
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| 17. |
- Brohede, Ulrika, et al.
(författare)
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Percolation phenomena in controlled drug release matrices studied by dielectric spectroscopy and the alternating ionic current method
- 2007
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 353:47-51, s. 4506-4514
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Tidskriftsartikel (refereegranskat)abstract
- The combined radial and axial ionic drug release from – as well as the percolating ionic conductivity in – cylindrical tablets was investigated by the alternating ionic current (AIC) method and dielectric spectroscopy (DS), respectively. The binary tablets consisted of mixtures of insulating ethyl cellulose and the poor ionic conductor model drug NaCl at nine different concentrations. We found that the dc conductivity, extracted from DS in a well-defined range of frequencies by a power-law method, could be described by a NaCl volume fraction percolation threshold of 0.06 in a 3D conducting network. The low threshold was explained by water-layer-assisted ion conduction in μm-sized ethyl cellulose channels between NaCl grains as probed by Hg porosimetry and SEM. The drug release process, as probed by AIC, could be described by a matrix porosity percolation threshold of 0.22, equivalent to a NaCl volume fraction of 0.13. The higher percolation threshold found in the drug release experiments as compared to the DS recordings could be explained by the different probing mechanisms of the analysis methods. The present study should provide valuable knowledge for the analysis of a broad class of ion conducting systems for which the frequency response of the dc ion conductivity is superimposed on other dielectric processes in the dielectric spectrum. It also brings forward knowledge important for the development of controlled drug-delivery vehicles as the presented findings show that the drug release from matrix tablets with unsealed tablet walls substantially differs from earlier investigated release processes for which the drug has only been allowed to escape through one of the flat tablet surfaces.
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| 18. |
- Brohede, Ulrika, et al.
(författare)
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Percolative drug diffusion from cylindrical matrix systems with unsealed boundaries
- 2007
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 96:11, s. 3087-3099
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Tidskriftsartikel (refereegranskat)abstract
- Release of NaCl in both the axial and radial directions from cylindrical ethyl cellulose tablets were investigated by the alternating ionic current method. The pore structure of the investigated binary mixtures was examined by mercury porosimetry and scanning electron microscopy, and the nm range fractal surface dimension of tablet pore walls was extracted from krypton gas adsorption isotherms. The drug release was shown to consist of two overlapping processes of which the first was ascribed to dissolution of NaCl close to the tablet boundary followed by subsequent diffusion through a thin ethyl cellulose layer and a second from which a porosity percolation threshold of 0.22 could be extracted. As well, a cross-over to effective-medium behaviour at a porosity of 0.44 was observed. The presented findings showed that drug release from matrix tablets with unsealed tablet walls substantially differs from earlier investigated release processes for which the drug has only been allowed to escape through one of the flat tablet surfaces. Thus, the present study brings forward knowledge important for the tailoring of controlled drug delivery vehicles with optimum release patterns.
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| 19. |
- Brohede, Ulrika, et al.
(författare)
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Sustained Release from Mesosporous Nanoparticles : evaluation of structural properties associated with controlled release rate
- 2008
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Ingår i: Current Drug Delivery. - : Bentham Science Publishers Ltd.. - 1567-2018 .- 1875-5704. ; 5:3, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- We present here a detailed study of the controlled release of amino acid derived amphiphilic molecules from the internal pore structure of mesoporous nanoparticle drug delivery systems with different structural properties; namely cubic and hexagonal structures of various degrees of complexity. The internal pore surface of the nanomaterials presented has been functionalised with amine moieties through a one pot method. Release profiles obtained by Alternating Ionic Current measurements are interpreted in terms of specific structural and textural parameters of the porous nanoparticles such as pore geometry and connectivity. Results indicate that diffusion coefficients are lower by as much as four orders of magnitude in 2-dimensional structures in comparison to 3-dimensional mesoporous solids. A fast release in turn is observed from mesocaged materials AMS-9 and AMS-8 where the presence of structural defects is thought to lead to a slightly lower diffusion coefficient in the latter. Amount of pore wall functionalisation and number of binding sites on the model drug are found to have little effect on the drug release rate.
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| 22. |
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| 23. |
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| 24. |
- Frenning, Göran, et al.
(författare)
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Finite element analysis of the release of slowly dissolving drugs from cylindrical matrix systems
- 2005
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 107:2, s. 320-329
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Tidskriftsartikel (refereegranskat)abstract
- Drug release from matrix systems of cylindrical shape is analyzed in detail by using the finite element method. The model used combines the Noyes-Whitney and diffusion equations, and thus takes the effects of a finite dissolution rate into account. The model is valid for all drug solubilities and dissolution rates, and allows accurate predictions of the drug release to be made. Anisotropic drug transport that may result from the manufacturing process is properly accounted for. Model calculations show that a finite dissolution rate may affect the release profile significantly, producing an initial delay. The equivalence between anisotropic release and isotropic release from a matrix with different dimensions is demonstrated. Comparisons are made with the predictions of a recently proposed pseudo-steady state (PSS) analysis of drug release from cylindrical matrices [Y. Zhou, J. S. Chu, T. Zhou, X. Y. Wu, Modeling of dispersed-drug release from two-dimensional matrix tablets, Biomaterials 26 (2005) 945-952]. This comparison reveals that important discrepancies exist between the numerical and analytical results, which are attributed to the simplifying assumption made in the PSS analysis that the region containing solid drug remains cylindrical in shape throughout the release process. The proposed model is shown to describe experimental release data well.
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| 25. |
- Garcia-Bennett, Alfonso E., et al.
(författare)
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A mechanistic study of the formation of mesoporous structures from in situ AC conductivity measurements
- 2007
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 23:19, s. 9875-9881
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work is to study the kinetics of self-assembly in the formation mechanism of anionic templated mesoporous solids (AMS-n) during die first few seconds of the synthesis as well as to demonstrate the use of alternating ion current (AIC) conductivity measurements to follow the self-assembly in complex hybrid systems. The formation of different AMS-n caged-type mesostructures through the delayed addition of the silica source is demonstrated and explained in terms of the interaction between the co-structure-directing agent (CSDA) and the oppositely charged surfactant headgroup regions. Our findings, supported by transmission electron microscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dynamic light scattering (DLS) measurements, and powder X-ray diffraction suggest that the interaction of the CSDA with the surfactant headgroup occurs within seconds after its addition to the synthesis gel leading to interaction between the polymerizing CSDAs and the oppositely charged micelle and to an increase in the micelle-CSDA aggregate size. Both DLS and AIC measurements agree that this process occurs within the first 1000 s after addition of the CSDA to the synthesis gel at room temperature. In addition to the mechanistic study it was found that the intermediate materials are comprised of a three-layer entity. Time-dependent 29Si MAS NMR studies reveal that an organo-silica layer forms around the micelles prior to a condensed outer inorganic shell of silica.
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| 26. |
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| 27. |
- Gelin, Kristina, et al.
(författare)
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Characterization of water in bacterial cellulose using dielectric spectroscopy and electron microscopy
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:26, s. 7623-7631
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that only 10% of the 99 wt% water present in bacterial cellulose (BC) gels, produced by Acetobacter xylinum, behave like free bulk water; the majority of the water molecules in the gels is more or less tightly bound to the cellulose. The magnitude of the diffusion coefficients of ions transported in the water phase of the BC gels as well as the information contained in freeze fracture transmission electron microscopic images of the gel structures indicates that the bulk-like water is confined in “lakes” rather than forming a continuous phase throughout the gel. Water desorption isotherms suggest that these “lakes” decrease in size with increasing oxygen concentration used during the biosynthesis process of the gels.
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| 28. |
- Gelin, Kristina, et al.
(författare)
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Potential controlled anion absorption in a novel high surface area composite of Cladophora cellulose and polypyrrole
- 2009
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Ingår i: Electrochimica Acta. - : Elsevier Ltd. - 0013-4686 .- 1873-3859. ; 54:12, s. 3394-3401
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical properties of a novel composite paper material of high surface area consisting of polypyrrole (PPy) deposited on cellulose derived from Cladophora sp. algae have been investigated in electrolytes containing different concentrations of nitrate, chloride and p-toluene sulfonate, as well as in solutions containing both p-toluene sulfonate and chloride. The oxidation mechanism and the dependence of the oxidation behavior of the polypyrrole, which was obtained by oxidation of pyrrole with iron(III) chloride, on the anion type and concentration have been studied. Current nucleation maxima, appearing at different times depending on the anion concentration, were obtained during the oxidation of the reduced polymers as a result of the combined action of the formation and growth of conducting polymer strands and anion diffusion. No loss of capacity was seen during repeated oxidation and reduction of the polymer indicating that trapping of anions in the reduced polymer did not limit the electroactivity of the present material. The latter can be explained by the thin polymer layer present on the cellulose substrate. During the oxidation of the polymer, the anions most likely first cover most of the surface of the composite before diffusing into the bulk of the polymer. The estimated distance between these surface sites was also found to match the size of the anions. For electrolytes containing a mixture of anions, the oxidation charge depends on the concentration and size of the different anions.The combination of the thin polymer coating and the large specific surface area of the composite give rise to a high ion absorption capacity even for large anions. Hence, the investigated material should be well-suited for use in biotechnological applications involving, e.g., desalting and extraction of proteins and DNA from biological samples.
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| 29. |
- Gråsjö, Johan, et al.
(författare)
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Determining the static dielectric permittivity of ion conducting materials
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:9, s. 092901-1
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Tidskriftsartikel (refereegranskat)abstract
- A method is derived for the determination of the static dielectric permittivity of ion conducting materials when this parameter is obscured by electrode polarization in as-recorded low frequency dielectric spectra. The method requires permittivity measurements at two different electrode separations, and is applicable when the electric fields created by charge separation near the electrode surfaces do not induce nonlinear effects in the frequency region where electrode polarization begins to affect the dielectric response. The performance of the method is illustrated by the analysis of an ion conducting cellulose gel biosynthesized by the Acetobacter. xylinum bacterium. The method opens up possibilities to obtain more detailed information about dynamic processes in ion conducting materials from dielectric spectroscopy.
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| 30. |
- Heidarian, Mina, et al.
(författare)
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Influence of water-cellulose binding energy on stability of acetylsalicylic acid
- 2006
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 323:1-2, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to investigate how the energies of water binding in cellulose tabletting excipients influence the availability of moisture to induce hydrolysis of acetylsalisylic acid (ASA). Cellulose powders of varying degree of order, denoted as low-crystallinity cellulose (LCC) and high-crystallinity cellulose (HCC), were produced by treating ordinary microcrystalline cellulose (MCC) in ZnCl2 solutions of varying concentrations. Microcrystalline cellulose (MCC) and lactose monohydrate were used as reference excipients. The samples were then studied by X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry (DSC). Different ratios of each excipient mixed with ASA were stored at 40% RH and 50 degrees C for 35 days to investigate the hydrolytic stability of the mixtures. Stability studies indicated that as concentration of HCC and MCC in binary mixtures with ASA was raised from 1 to 50% (w/w), ASA became increasingly unstable with respect to hydrolysis. Although LCC contained more moisture than the other celluloses, no such trend was observed in the LCC and lactose samples. DSC analysis revealed that each water molecule on the average was bound by more than three hydrogen bonds in the LCC and lactose structures and therefore remained predominantly unavailable to induce hydrolysis. The current study elucidates the necessity of evaluating the energy of water bindings in a pharmaceutical excipient when predicting the excipient's performance in mixtures comprising moisture-sensitive drugs.
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| 33. |
- Jönsson, M., et al.
(författare)
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Bacteria counting with impedance spectroscopy in a micro probe station
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:20, s. 10165-10169
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Tidskriftsartikel (refereegranskat)abstract
- A method to quantify the density of viable biological cells in suspensions is presented. The method is implemented by low-frequency impedance spectroscopy and based on the finding that immobilized ions are released to move freely in the surrounding suspension when viable Escherichia coli cells are killed by a heat shock. The presented results show that an amount of ions corresponding to ∼2 × 108 unit charges are released per viable bacterium killed. A micro probe station with coplanar Ti electrodes was electrically characterized and used as a measuring unit for the impedance spectroscopy recordings. This unit is compatible with common microfabrication techniques and should enable the presented method to be employed using a flow-cell device for viable bacteria counting in miniaturized on-line monitoring systems.
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| 34. |
- Mihranyan, Albert, et al.
(författare)
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A Novel High Specific Surface Area Conducting Paper Material Composed of Polypyrrole and Cladophora Cellulose
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:39, s. 12249-12255
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel conducting polypyrrole-based composite material, obtained by polymerization of pyrrole in the presence of iron(III) chloride on a cellulose substrate derived from the environmentally polluting Cladophora sp. algae. The material, which was doped with chloride ions, was molded into paper sheets and characterized using scanning and transmission electron microscopy, N2 gas adsorption analysis, cyclic voltammetry, chronoamperometry and conductivity measurements at varying relative humidities. The specific surface area of the composite was found to be 57 m2/g and the fibrous structure of the Cladophora cellulose remained intact even after a 50 nm thick layer of polypyrrole had been coated on the cellulose fibers. The composite could be repeatedly used for electrochemically controlled extraction and desorption of chloride and an ion exchanging capacity of 370 C per g of composite was obtained as a result of the high surface area of the cellulose substrate. The influence of the oxidation and reduction potentials on the chloride ion exchange capacity and the nucleation of delocalized positive charges, forming conductive paths in the polypyrrole film, was also investigated. The creation of conductive paths during oxidation followed an effective medium rather than a percolative behavior, indicating that some conduction paths survive the polymer reduction steps. The present high surface area material should be well-suited for use in, e.g., electrochemically controlled ion exchange or separation devices, as well as sensors based on the fact that the material is compact, light, mechanically stable, and moldable into paper sheets.
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| 35. |
- Mihranyan, Albert, et al.
(författare)
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Assessing Surface Area Evolution during Biomimetic Growth of Hydroxyapatite Coatings
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:3, s. 1292-1295
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Tidskriftsartikel (refereegranskat)abstract
- The surface area of biomimetically deposited hydroxyapatite (HA) coatings on metallic implants is important for the biological performance of the implant. Thus, a nondestructive method of assessing this quantity directly on the solid substrate would be highly valuable. The objective of this study was to develop such a method and for the first time assess the evolution of surface area of HA during biomimetic growth. The surface area of a TiO2-covered titanium substrate was measured prior to and following the biomimetic coating deposition using Ar gas adsorption at 77 K. The presence of HA on the surface was verified with scanning electron microscopy and X-ray diffraction. The specific surface area of the coating was found to increase linearly during 1 week of deposition at a rate of ∼100 cm2 day−1 (g substrate)−1. The presented method may be used as a tool for studying the evolution in surface area of coatings on solid substrates during biomimetic deposition or other growth processes.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
- Mihranyan, Albert, 1978-
(författare)
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Engineering of Native Cellulose Structure for Pharmaceutical Applications : Influence of Cellulose Crystallinity Index, Surface Area and Pore Volume on Sorption Phenomena
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose powders from various sources were manufactured and characterized to investigate the influence of their crystallinity index, surface area, and pore volume on sorption phenomena and the relevant pharmaceutical functionality. The influence of the cellulose crystallinity index on moisture sorption was important at low and intermediate relative humidities. At high relative humidities, properties such as surface area and pore volume took precedence in governing the moisture sorption process.The theory of physical adsorption of gases onto fractal surfaces was useful for understanding the distribution of water in cellulose and the inner nanoscale structure of cellulose particles. It was found that, as a consequence of swelling, moisture induces a fractal nanopore network in cellulose powders that have a low or intermediate degree of crystallinity. On the other hand, no swelling occurs in highly crystalline cellulose powders and moisture sorption is restricted to the walls of the open pores.No correlation was found between the cellulose crystallinity index and the incorporation and release of nicotine in cellulose mixtures. By loading nicotine in highly porous matrices of the Cladophora sp. algae cellulose, higher stability against oxidative degradation, higher loading capacity, and more steady release into an air-stream was achieved than when commercially available microcrystalline cellulose was loaded.It was also shown that, by manipulating the structure of cellulose, the undesired hydrolysis of acetylsalicylic acid in mixtures with cellulose can be avoided. It was suggested that a broad hysteresis loop between the moisture adsorption and desorption curves of isotherms at low relative humidities could be indicative of an improved compatibility between acetylsalicylic acid and cellulose.In all, this thesis demonstrates how the pharmaceutical functionality of microcrystalline cellulose can be improved via engineering of the structure of native cellulose powders.
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| 42. |
- Mihranyan, Albert, et al.
(författare)
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Fractal aspects of powder flow and densification
- 2007
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Ingår i: Particle & particle systems characterization. - : Wiley. - 0934-0866 .- 1521-4117. ; 24:3, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- Powder flowability is affected by a number of particulate properties including particle size, surface area, and surface roughness. Surface irregularities play an important role in controlling powder flow properties. In the present work, a relationship was derived between the reactive fractal dimension - representing the fractallity of the part of the surface participating in particle-particle interactions during powder flow - and the initial increase in density of a powder bed during densification. The reactive and true textural fractal dimensions for a model system comprised of silicified microcrystalline cellulose particles were also experimentally obtained. The concept of the reactive fractal dimension was shown to be helpful for a comprehensive description of the powder densification process. It indicates how rapidly the active interparticulate area involved in particle-particle interactions grows with powder size reduction. It is suggested that the reactive fractal dimension can be used for describing powder flow behavior and to elucidate the sensitivity of powder flowability to particle size changes.
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| 43. |
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| 44. |
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| 45. |
- Mihranyan, Albert, 1978-, et al.
(författare)
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Influence of fractal surface dimension on the dissolution process of sparingly soluble CaCO3 microparticles
- 2009
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 94:2, s. 299-305
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution process of sparingly soluble CaCO3 microparticles and how the fractal surface dimension of the particles changes during dissolution is analyzed. The particles and the dissolution process are studied using scanning electron microscopy, X-ray diffraction, nitrogen adsorption, laser diffraction and conductance measurements. Ball milling of the particles is shown to maintain the particle crystallinity, and to introduce an increased fractal surface dimension in the 1–10 μm size range. Dissolution is found to increase the surface dimension of initially smooth particles and to maintain the fractal surface roughness of milled particles. The dissolution process increases the relative number of small particles (50 nm–1 μm) whereas the larger ones decrease in size. The solubility of the milled fractal particles was ∼1.8 times higher than that for the initially smooth ones. The presented findings show that developing methods for increasing the fractal surface roughness of particles should be of interest for improving the solubility of poorly soluble drug candidates.
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| 46. |
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| 47. |
- Mihranyan, Albert, et al.
(författare)
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Order and disorder in powder mixtures : Spatial distribution functions as tools to assess powder homogeneity
- 2009
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Ingår i: Particle & particle systems characterization. - : Wiley. - 0934-0866 .- 1521-4117. ; 25:5-6, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- In interactive mixtures with small carrier particles, the content variability is often higher than predicted by available models despite the significant degree of interaction visualized with Scanning Electron Microscopy (SEM). The present work details how pair-correlation functions can be used to reveal information about the spatial distribution of mixture constituents and their interactions. SEM pictures of a 2 % w/w oxazepam/sodium starch glycolate (SSG) mixture were recorded (n = 14). The constituent coordinates were extracted and pair-correlation functions as well as the cross-correlation function were calculated. A significant degree of interaction was observed between the constituents in the experimental mixture, compared to a randomized control system. In particular, the probability of finding an oxazepam particle was especially high inside the perimeter of the carrier particle and along its edges. The observed cross-correlation between oxazepam and SSG particles was periodic and repeated at distances corresponding to 1-1.5 carrier diameters. It was concluded that interactive mixtures of powders can be compared to disordered/amorphous solids since both exhibit short-range order, whilst lacking long-range translational periodicity.
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| 48. |
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| 49. |
- Mihranyan, Albert, et al.
(författare)
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Rheological properties of cellulose hydrogels prepared from Cladophora cellulose powder
- 2007
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 21:2, s. 267-272
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Tidskriftsartikel (refereegranskat)abstract
- The rheological properties of cellulose hydrogels prepared from cellulose powder of algal origin (Cladophora sp. green algae) were investigated and compared to a commercially available dispersive cellulose grade (Avicel RC-591). The rheological properties of cellulose hydrogels were investigated using a controlled rate instrument of couette type in the dynamic oscillation mode. Cladophora cellulose powder was dispersed in carboxymethylcellulose solutions of different concentrations. It was found that Cladophora cellulose forms gel structures at cellulose concentrations as low as 0.2% (w/v), whereas the lower threshold for the commercially available analog is around 1.5% (w/v) solids contents. Carboxymethylcellulose, even though useful in aiding the dispersion, has a negative effect on the viscoelastic properties of Cladophora cellulose when used in high concentrations. Cladophora cellulose powder could be a useful alternative to commercially available dispersible cellulose grades when very low quantities of stabilizing agents are required.
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| 50. |
- Mihranyan, Albert, et al.
(författare)
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Solubility of Fractal Nanoparticles
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:2, s. 315-319
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Tidskriftsartikel (refereegranskat)abstract
- A relationship between the fractal surface dimension of dissolving nanoparticles and their solubility has been derived showing that fractally rough nanoparticles are expected to exhibit significantly higher solubility than predicted from the classical Ostwald–Freundlich equation. The derived relationship estimates the latent solubility increase for a given material by manipulating the surface of the particles to be dissolved, and can thus be used for developing new strategies for improving the solubility of poorly soluble drug candidates.
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