| 1. |
- Bannow, J., et al.
(författare)
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Solid nanofoams based on cellulose nanofibers and indomethacin—the effect of processing parameters and drug content on material structure
- 2017
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Ingår i: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 526:1-2, s. 291-299
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Tidskriftsartikel (refereegranskat)abstract
- The unique colloidal properties of cellulose nanofibers (CNF), makes CNF a very interesting new excipient in pharmaceutical formulations, as CNF in combination with some poorly-soluble drugs can create nanofoams with closed cells. Previous nanofoams, created with the model drug indomethacin, demonstrated a prolonged release compared to films, owing to the tortuous diffusion path that the drug needs to take around the intact air-bubbles. However, the nanofoam was only obtained at a relatively low drug content of 21 wt% using fixed processing parameters. Herein, the effect of indomethacin content and processing parameters on the foaming properties was analysed. Results demonstrate that a certain amount of dissolved drug is needed to stabilize air-bubbles. At the same time, larger fractions of dissolved drug promote coarsening/collapse of the wet foam. The pendant drop/bubble profile tensiometry was used to verify the wet-foam stability at different pHs. The pH influenced the amount of solubilized drug and the processing-window was very narrow at high drug loadings. The results were compared to real foaming-experiments and solid state analysis of the final cellular solids. The parameters were assembled into a processing chart, highlighting the importance of the right combination of processing parameters (pH and time-point of pH adjustment) in order to successfully prepare cellular solid materials with up to 46 wt% drug loading.
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| 2. |
- Benjamins, Jan-Willem
(författare)
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Ellipsometry studies of liquid interfaces: New methodology and applications
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Adsorption of several surface active agents, such as nonionics, diblock copolymers, triblock copolymers, proteins and phospholipids at the oil/water and air/water has been studied. In order to be able to do this, a new ellipsometry setup, which utilizes light guides, was developed and tested. A new evaluation methodology was developed and tested as well. This methodology is based on performing each experiment twice, with two different substrates. The small difference in the refractive indices of these substrates will allow for resolving both the adsorbed amount and the layer thickness from deltaDelta alone, using the thin film approximation. It was also demonstrated in which way simulated ellipsometry experiments and Brewster angle microscopy (BAM) could be utilized in interpreting ellipsometry results. The influence of the viscosity of the oil phase on the adsorption kinetics of block coploymers at the oil/water interface has been investigated. Measurements suggest the formation of diffuse layers at the decane/water interface during the adsorption of nonionics such as C12E5 and C18E50. Further results show the formation of lamellar liquid crystalline phases at the oil/water interface when Phospholipids are added to the oil. These layers have been characterized using Small Angle X-ray diffraction (SAXD), ellipsometry, and BAM.
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| 3. |
- Benjamins, Jan-Willem, et al.
(författare)
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Ellipsometry studies of nonionic surfactant adsorption at the oil-water interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:1, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- In the presented study we have developed and implemented a methodology for ellipsometry measurements at liquid interfaces that makes it possible to determine the amount adsorbed without assumptions of refractive index or thickness of the adsorbed layer. It was demonstrated that this is possible by combined measurements from different aqueous phases, H2O and D2O, which were shown to have sufficiently different refractive indices. The methodology was tested by studying adsorption of two types of nonionic poly(ethylene glycol) alkyl ether surfactants, CnH2n+1(OC2H4)(m)OH or CnEm at the decane-aqueous interface, where C12E5 was adsorbed from the oil phase and C18E50 from the aqueous phase. The observed plateau values of the adsorbed amounts were 1.38 and 0.93 Mg/M-2 for C12E5 and C18E50, respectively, which is in agreement with the corresponding values of 1.49 and 1.15 Mg/M-2 obtained from applying the Gibbs equation to interfacial tension data for the same systems. We will briefly discuss the adsorption behavior in relation to the molecular structure of the surfactant and the phase behavior of the oil - surfactant- aqueous systems in relation to our experimental results.
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| 4. |
- Benjamins, Jan-Willem, et al.
(författare)
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Formation of a liquid crystalline phase from phosphatidylcholine at the oil-aqueous interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:7, s. 2804-2810
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of phospholipid (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) and formation of a surface phase at the oil-water interface has been followed by using ellipsometry. The properties of the interfacial phase were found to depend strongly on whether phospholipid was added to the oil phase or to the aqueous phase as liposomal structures. In the latter case a monolayer formed, while if the phospholipid was supplied from the oil phase a lamellar phase appeared at the interface. The effect on the stabilizing surface phase of a surface-active protein (P-lactoglobulin) was also investigated. The observations are important for understanding stabilizing properties of surface-active compounds commonly used to stabilize emulsions. In addition it has been demonstrated that ellipsometry can be used to study the initial process when a two-phase system consisting of a water and an oil phase is transformed into a three phase system or eventually to a one-phase system.
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| 5. |
- Benjamins, Jan-Willem, et al.
(författare)
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New experimental setup to use ellipsometry to study liquid-liquid and liquid-solid interfaces
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:16, s. 6437-6444
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Tidskriftsartikel (refereegranskat)abstract
- Different types of optical light guides were constructed and tested to enable convenient multiple angle of incidence ellipsometry, on solid and liquid interfaces in liquid solutions. Two light guides are needed on an ellipsometer, one to guide the incoming light and one to guide the light that is reflected at the test surface, and therefore one light guide was mounted on the laser arm and one on the detector arm of the ellipsometer. With this arrangement the optical windows automatically adjust to always be perpendicular to the direction of the light independent of the angle of incidence. The purpose with these light guides is to facilitate the passage of light through the air/solution interface. A thorough theoretical and experimental analysis of optical errors introduced by such light guides is presented. This discussion includes the effect of multiple reflections between and within the windows of the light guides' On the basis of this analysis a new ellipsometry setup with light guides, consisting of glass tube's with glued end windows, was developed. This setup makes it possible to perform accurate measurements in almost any type of measuring cell at any angle of incidence.
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| 6. |
- Cervin, Nicholas Tchang, et al.
(författare)
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Mechanisms behind the Stabilizing Action of Cellulose Nanofibrils in Wet-Stable Cellulose Foams
- 2015
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 16:3, s. 822-831
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Tidskriftsartikel (refereegranskat)abstract
- The principal purpose of the investigation was to clarify the mechanisms behind the stabilizing action of cellulose nanofibrils (CNFs) in wet-stable cellulose foams. Following the basic theories for particle-stabilized foams, the investigation was focused on how the surface energy of the stabilizing CNF particles, their aspect ratio and charge density, and the concentration of CNF particles at the air-water interface affect the foam stability and the mechanical properties of a particle-stabilized air-liquid interface. The foam stability was evaluated from how the foam height changed over time, and the mechanical properties of the interface were evaluated as the complex viscoelastic modulus of the interface using the pendant drop method. The most important results and conclusions are that CNFs can be used as stabilizing particles for aqueous foams already at a concentration as low as 5 g/L. The major reasons for this were the small dimensions of the CNF and their high aspect ratio, which is important for gel-formation and the complex viscoelastic modulus of the particle-filled air-water interface. The influence of the aspect ratio was also demonstrated by a much higher foam stability of foams stabilized with CNFs than of foams stabilized by cellulose nanocrystals (CNC) with the same chemical composition. The charge density of the CNFs affects the level of liberation within larger aggregates and hence also the number of contact points at the interface and the gel formation and complex viscoelastic modulus of the air-water interface. The charges also result in a disjoining pressure related to the long-range repulsive electrostatic pressure between particle-stabilized bubbles and hence contribute to foam stability. (Figure Presented).
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| 7. |
- Costa, Carolina, et al.
(författare)
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Interfacial activity and emulsion stabilization of dissolved cellulose
- 2019
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Ingår i: Journal of Molecular Liquids. - : Elsevier B.V.. - 0167-7322 .- 1873-3166. ; 292
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Tidskriftsartikel (refereegranskat)abstract
- Some aspects of the interfacial behavior of cellulose dissolved in an aqueous solvent were investigated. Cellulose was found to significantly decrease the interfacial tension (IFT) between paraffin oil and 85 wt% phosphoric acid aqueous solutions. This decrease was similar in magnitude to that displayed by non-ionic cellulose derivatives. Cellulose's interfacial activity indicated a significant amphiphilic character and that the interfacial activity of cellulose derivatives is not only related to the derivatization but inherent in the cellulose backbone. This finding suggests that cellulose would have the ability of stabilizing dispersions, like oil-in-water emulsions in a similar way as a large number of cellulose derivatives. In its molecularly dissolved state, cellulose proved to be able to stabilize emulsions of paraffin in the polar solvent on a short-term. However, long-term stability against drop-coalescence was possible to achieve by a slight change in the amphiphilicity of cellulose, effected by a slight increase in pH. These emulsions exhibited excellent stability against coalescence/oiling-off over a period of one year. Ageing of the cellulose solution before emulsification (resulting in molecular weight reduction) was found to favour the creation of smaller droplets.
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| 8. |
- Ghorbani, Morteza, et al.
(författare)
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Unravelling the Acoustic and Thermal Responses of Perfluorocarbon Liquid Droplets Stabilized with Cellulose Nanofibers
- 2019
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Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 35:40, s. 13090-13099
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Tidskriftsartikel (refereegranskat)abstract
- The attractive colloidal and physicochemical properties of cellulose nanofibers (CNFs) at interfaces have recently been exploited in the facile production of a number of environmentally benign materials, e.g. foams, emulsions, and capsules. Herein, these unique properties are exploited in a new type of CNF-stabilized perfluoropentane droplets produced via a straightforward and simple mixing protocol. Droplets with a comparatively narrow size distribution (ca. 1-5 μm in diameter) were fabricated, and their potential in the acoustic droplet vaporization process was evaluated. For this, the particle-stabilized droplets were assessed in three independent experimental examinations, namely temperature, acoustic, and ultrasonic standing wave tests. During the acoustic droplet vaporization (ADV) process, droplets were converted to gas-filled microbubbles, offering enhanced visualization by ultrasound. The acoustic pressure threshold of about 0.62 MPa was identified for the cellulose-stabilized droplets. A phase transition temperature of about 22 °C was observed, at which a significant fraction of larger droplets (above ca. 3 μm in diameter) were converted into bubbles, whereas a large part of the population of smaller droplets were stable up to higher temperatures (temperatures up to 45 °C tested). Moreover, under ultrasound standing wave conditions, droplets were relocated to antinodes demonstrating the behavior associated with the negative contrast particles. The combined results make the CNF-stabilized droplets interesting in cell-droplet interaction experiments and ultrasound imaging.
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| 9. |
- Kapilashrami, A, et al.
(författare)
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Ellipsometric studies of nonionic block copolymers adsorbed at the solid/water and oil/water interfaces
- 2003
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Ingår i: Colloids ad Surfaces a-Physicochemical and Engineering Aspects. ; 225:1-3, s. 181-192
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Tidskriftsartikel (refereegranskat)abstract
- We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C-18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological proper ies of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12 800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers. (C) 2003 Elsevier B.V. All rights reserved.
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| 10. |
- Kapilashrami, A., et al.
(författare)
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Ellipsometric studies of nonionic copolymers adsorbed at the solid/water and oil/water interfaces
- 2003
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 225, s. 181-192
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Tidskriftsartikel (refereegranskat)abstract
- We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological properties of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers
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| 11. |
- Nyström, Lina, et al.
(författare)
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In Vitro and In Vivo Performance of Pickering Emulsion-Based Powders of Omega-3 Polyunsaturated Fatty Acids
- 2024
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Ingår i: Molecular Pharmaceutics. - : American Chemical Society. - 1543-8384 .- 1543-8392. ; 21:2, s. 677-
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Tidskriftsartikel (refereegranskat)abstract
- Omega-3 polyunsaturated fatty acids (n-3 PUFA) are essential nutrients for human health and have been linked to a variety of health benefits, including reducing the risk of cardiovascular diseases. In this paper, a spray-dried powder formulation based on Pickering emulsions stabilized with cellulose nanocrystals (CNC) and hydroxypropyl methylcellulose (HPMC) has been developed. The formulation was compared in vitro and in vivo to reference emulsions (conventional Self-Emulsifying Drug Delivery System, SEDDS) to formulate n-3 PUFA pharmaceutical products, specifically in free fatty acid form. The results of in vivo studies performed in fasted dogs showed that Pickering emulsions reconstituted from powders are freely available (fast absorption) with a similar level of bioavailability as reference emulsions. In the studies performed with dogs in the fed state, the higher bioavailability combined with slower absorption observed for the Pickering emulsion, compared to the reference, was proposed to be the result of the protection of the n-3 PUFAs (in free fatty acid form) against oxidation in the stomach by the solid particles stabilizing the emulsion. This observation was supported by promising results from short-term studies of chemical stability of powders with n-3 PUFA loads as high as 0.8 g oil/g powder that easily regain the original emulsion drop sizes upon reconstitution. The present work has shown that Pickering emulsions may offer a promising strategy for improving the bioavailability and stability as well as providing an opportunity to produce environmentally friendly (surfactant free) and patient-acceptable solid oral dosage forms of n-3 PUFA in the free fatty acid form.
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| 12. |
- Rippner Blomqvist, Brita, et al.
(författare)
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Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:11, s. 5061-5068
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, Gamma) of a nonionic diblock copolymer, E106B16, of poly(ethylene oxide) (E) and poly(butylene oxide) (13) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles, T and A and (ii) by using the change of A only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m(2) (400 A(2)/molecule). Furthermore, the amount of E106B16 adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H2O or D2O as substrates to calculate values of d and F was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers.
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| 13. |
- Rippner Blomqvist, B., et al.
(författare)
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Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface
- 2005
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 21, s. 5061-5068
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, ¡) of a nonionic diblock copolymer, E106B16, of poly(ethylene oxide) (E) and poly(butylene oxide) (B) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles and ¢ and (ii) by using the change of ¢ only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m2 (400 Å2/molecule). Furthermore, the amount of E106B16 adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H2O or D2O as substrates to calculate values of d and ¡ was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers
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| 14. |
- Svagan, Anna J., et al.
(författare)
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Solid cellulose nanofiber based foams – Towards facile design of sustained drug delivery systems
- 2016
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 244, s. 74-82
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Tidskriftsartikel (refereegranskat)abstract
- Control of drug action through formulation is a vital and very challenging topic within pharmaceutical sciences. Cellulose nanofibers (CNF) are an excipient candidate in pharmaceutical formulations that could be used to easily optimize drug delivery rates. CNF has interesting physico-chemical properties that, when combined with surfactants, can be used to create very stable air bubbles and dry foams. Utilizing this inherent property, it is possible to modify the release kinetics of the model drug riboflavin in a facile way. Wet foams were prepared using cationic CNF and a pharmaceutically acceptable surfactant (lauric acid sodium salt). The drug was suspended in the wet-stable foams followed by a drying step to obtain dry foams. Flexible cellular solid materials of different thicknesses, shapes and drug loadings (up to 50 wt%) could successfully be prepared. The drug was released from the solid foams in a diffusion-controlled, sustained manner due to the presence of intact air bubbles which imparted a tortuous diffusion path. The diffusion coefficient was assessed using Franz cells and shown to be more than one order of magnitude smaller for the cellular solids compared to the bubble-free films in the wet state. By changing the dimensions of dry foams while keeping drug load and total weight constant, the drug release kinetics could be modified, e.g. a rectangular box-shaped foam of 8 mm thickness released only 59% of the drug after 24 h whereas a thinner foam sample (0.6 mm) released 78% of its drug content within 8 h. In comparison, the drug release from films (0.009 mm, with the same total mass and an outer surface area comparable to the thinner foam) was much faster, amounting to 72% of the drug within 1 h. The entrapped air bubbles in the foam also induced positive buoyancy, which is interesting from the perspective of gastroretentive drug-delivery.
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