Preparation of La2NiO4+δ powders as a cathode material for SOFC via a PVP-assisted hydrothermal route

Uniform submicron La₂NiO_4+δ (sm-LNO) powders have been synthesized by a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal route. In the presence of PVP, sm-LNO of pure phase has been obtained by calcination at the relatively low temperature of 900 °C for 8 h. Compared micron-sized LNO (m-LNO) particles obtained at 1,000 °C by hydrothermal synthesis route without PVP assisted, the sm-LNO-PVP displays regularly shaped and well-distributed particles in the range of 0.3–0.5 μm. The scanning electron microscopy (SEM) results showed that the sm-LNO sample is submicronic and that the m-LNO sample shows agglomerates with a broad size distribution. The electrochemical performance of m-LNO and sm-LNO-PVP has been investigated by electrochemical impedance spectroscopy. The polarization resistance of the sm-LNO-PVP cathode reaches a value of 0.40 Ω cm² at 750 °C, which is lower than that of m-LNO (0.62 Ω cm²). This result indicates that a fine electrode microstructure with submicron particles can help to increase the active sites, accelerate oxygen diffusion, and reduce polarization resistance. An anode-supported single cell with sm-LNO cathode has been fabricated and tested over a temperature range from 650 to 800 °C. The maximum power density of the cell has achieved 834 mW cm⁻² at 750 °C. These results therefore show that this PVP-assisted hydrothermal method is an effective approach to construct submicron-structured cathode and enhance the performance of intermediate temperature solid oxide fuel cell.

Examination of the flow rheological and textural properties of polymer gels composed of poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone): rheological and mathematical interpretation of textural parameters.

The purpose of this study was to mathematically characterize the effects of defined experimental parameters (probe speed and the ratio of the probe diameter to the diameter of sample container) on the textural/mechanical properties of model gel systems. In addition, this study examined the applicability of dimensional analysis for the rheological interpretation of textural data in terms of shear stress and rate of shear. Aqueous gels (pH 7) were prepared containing 15% w/w poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone) (PVP) (0, 3, 6, or 9% w/w). Texture profile analysis (TPA) was performed using a Stable Micro Systems texture analyzer (model TA-XT 2; Surrey, UK) in which an analytical probe was twice compressed into each formulation to a defined depth (15 mm) and at defined rates (1, 3, 5, 8, and 10 mm s-1), allowing a delay period (15 s) between the end of the first and beginning of the second compressions. Flow rheograms were performed using a Carri-Med CSL2-100 rheometer (TA Instruments, Surrey, UK) with parallel plate geometry under controlled shearing stresses at 20.0°?±?0.1°C. All formulations exhibited pseudoplastic flow with no thixotropy. Increasing concentrations of PVP significantly increased formulation hardness, compressibility, adhesiveness, and consistency. Increased hardness, compressibility, and consistency were ascribed to enhanced polymeric entanglements, thereby increasing the resistance to deformation. Increasing probe speed increased formulation hardness in a linear manner, because of the effects of probe speed on probe displacement and surface area. The relationship between formulation hardness and probe displacement was linear and was dependent on probe speed. Furthermore, the proportionality constant (gel strength) increased as a function of PVP concentration. The relationship between formulation hardness and diameter ratio was biphasic and was statistically defined by two linear relationships relating to diameter ratios from 0 to 0.4 and from 0.4 to 0.563. The dramatically increased hardness, associated with diameter ratios in excess of 0.4, was accredited to boundary effects, that is, the effect of the container wall on product flow. Using dimensional analysis, the hardness and probe displacement in TPA were mathematically transformed into corresponding rheological parameters, namely shearing stress and rate of shear, thereby allowing the application of the power law (??=?k?n) to textural data. Importantly, the consistencies (k) of the formulations, calculated using transformed textural data, were statistically similar to those obtained using flow rheometry. In conclusion, this study has, firstly, characterized the relationships between textural data and two key instrumental parameters in TPA and, secondly, described a method by which rheological information may be derived using this technique. This will enable a greater application of TPA for the rheological characterization of pharmaceutical gels and, in addition, will enable efficient interpretation of textural data under different experimental parameters.

Formulation and characterisation of tetracycline-containing bioadhesive polymer networks designed for the treatment of periodontal disease.

This study described the drug release, rheological (dynamic and flow) and textural/mechanical properties of a series of formulations composed of 15% w/w polymethylvinylether-co-maleic anhydride (PMVE-MA), 0-9% w/w polyvinylpyrrolidone (PVP) and containing 1-5% w/w tetracycline hydrochloride, designed for the treatment of periodontal disease. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing the concentration of PVP sequentially increased the zero-rate viscosity (derived from the Cross model) and the hardness and compressibility of the formulations (derived from texture profile analysis). These affects may be accredited to increased polymer entanglement and, in light of the observed synergy between the two polymers with respect to their textural and rheological properties, interaction between PVP and PMVE-MA. Increasing the concentration of PVP increased the storage and loss moduli yet decreased the loss tangent of all formulations, indicative of increased elastic behaviour. Synergy between the two polymers with respect to their viscoelastic properties was observed. Increased adhesiveness, associated with increased concentrations of PVP was ascribed to the increasing bioadhesion and tack of the formulations. The effect of increasing drug concentration on the rheological and textural properties was dependent on PVP concentration. At lower concentrations (0, 3% w/w) no effect was observed whereas, in the presence of 9% w/w PVP, increasing drug concentration increased formulation elasticity, zero rate viscosity, hardness and compressibility. These observations were ascribed to the greater mass of suspended drug in formulations containing the highest concentration of PVP. Drug release from formulations containing 6 and 9% PVP (and 5% w/w drug) was prolonged and swelling/diffusion controlled. Based on the drug release, rheological and textural properties, it is suggested that the formulation containing 15% w/w PMVE-MA, 6% w/w PVP and tetracycline hydrochloride (5% w/w) may be useful for the treatment of periodontal disease.

The resistance of polyvinylpyrrolidone–Iodine–poly(e-caprolactone) blends to adherence of Escherichia coli

In this study, the resistance of biodegradable biomaterials, composed of blends of poly(e-caprolactone) (PCL) and the polymeric antimicrobial complex, polyvinylpyrrolidone–iodine (PVP-I) to the adherence of a clinical isolate of Escherichia coli is described. Blends of PCL composed of a range of high (50,000 g mol1) to low (5000 g mol1) molecular weight ratios of polymer and either
devoid of or containing PVP-I (1% w/w) were prepared by solvent evaporation. Following incubation (4 h), there was no relationship between m. wt. ratio of PCL in ?lms devoid of PVP-I and adherence ofE. coli. Conversely, microbial adherence to PCL containing PVP-I decreased as the ratio of high:low m. wt. polymer was decreased and was approximately 1000 fold lower than that to comparator ?lms devoid of PVP-I. Following periods of immersion of PVP-I containing PCL ?lms under sink conditions in phosphate buffered saline, subsequent adherence of E. coli was substantially reduced for 2 days (40:60 m. wt. ratio) and 6 days (100:0 m. wt. ratio). Concurrent exposure of PCL and E. coli to sub-minimum inhibitory concentrations (sub-MIC) of PVP-I signi?cantly reduced microbial adherence to the biomaterial; however, the molecular weight ratio of PCL did not affect this outcome. Pretreatment of PCL with similar sub-MIC of PVP-I prior to inclusion within the microbial adherence assay signi?cantly decreased the subsequent adherence of E. coli. Greatest reduction in adherence was observed following treatment of PCL (40:60 m. wt. ratio) with 0.0156% w/w PVP-I. In conclusion, this study has illustrated the utility of PVP-I as a suitable therapeutic agent for incorporation within PCL as a novel biomaterial. Due to the combined antimicrobial and biodegradable properties, these biomaterials offer a promising strategy for the reduction in medical device related infection. © 2004 Elsevier Ltd. All rights reserved.

Evaluation of a poly(vinyl pyrollidone)-coated biomaterial for urological use

The associated problems of bacterial biofilm formation and encrustation that may cause obstruction or blockage of urethral catheters and ureteral stents often hinders the effective use of biomaterials within the urinary tract. In this in vitro study, we have investigated the surface properties of a hydrophilic polyvinyl pyrollidone) (PVP)-coating applied to polyurethane and determined its suitability for use as a urinary tract biomaterial by comparing its lubricity and ability to resist bacterial adherence and encrustation with that of uncoated polyurethane and silicone. The PVP-coated polyurethane was significantly more hydrophilic and more lubricious than either uncoated polyurethane or silicone. Adherence of a hydrophilic Escherichia coli isolate to PVP-coated polyurethane and uncoated polyurethane was similar but significantly less than adherence to silicone. Adherence of a hydrophobic Enterococcus faecalis isolate to PVP-coated polyurethane and silicone was similar but was significantly less than adherence to uncoated polyurethane. Struvite encrustation was similar on the PVP-coated polyurethane and silicone but significantly less than on uncoated polyurethane. Furthermore, hydroxyapatite encrustation was significantly less on the PVP-coated polyurethane than on either uncoated polyurethane or silicone. The results suggest that the PVP-coating could be useful in preventing complications caused by bacterial biofilm formation and the deposition of encrustation on biomaterials implanted in the urinary tract and, therefore, warrants further evaluation. (C) 2002 Elsevier Science Ltd. All rights reserved.

Poly(epsilon-caprolactone) and poly(epsilon-caprolactone)-polyvinylpyrrolidone-iodine blends as ureteral biomaterials: characterisation of mechanical and surface properties, degradation and resistance to encrustation in vitro.

This study describes the physicochemical properties and in vitro resistance to encrustation of solvent cast films composed of either poly(epsilon-caprolactone) (PCL), prepared using different ratios of high (50,000) to low (4000) (molecular weight) m.wt., or blends of PCL and the polymeric antimicrobial complex, poly(vinylpyrrolidone)-iodine (PVP-I). The incorporation of PVP-I offered antimicrobial activity to the biomaterials. Films were characterised in terms of mechanical (tensile analysis, dynamic mechanical thermal analysis) and surface properties (dynamic contact angle analysis, scanning electron microscopy), whereas degradation (at 37degreesC in PBS at pH 7.4) was determined gravimetrically. The resistance of the films to encrustation was evaluated using an in vitro encrustation model. Reductions in the ratio of high:low-m.wt. PCL significantly reduced the ultimate tensile strength, % elongation at break and the advancing contact angle of the films. These effects were attributed to alterations in the amorphous content and the more hydrophilic nature of the films. Conversely, there were no alterations in Young's modulus, the viscoelastic properties and glass-transition temperature. Incorporation of PVP-I did not affect the mechanical or rheological properties of the films, indicative of a limited interaction between the two polymers in the solid state. Manipulation of the high:low m.wt. ratio of PCL significantly altered the degradation of the films, most notably following longer immersion periods, and resistance to encrustation. Accordingly, maximum degradation and resistance to encrustation was observed with the biomaterial composed of 40:60 high:low m.wt. ratios of PCL; however, the mechanical properties of this system were considered inappropriate for clinical application. Films composed of either 50:50 or 60:40 ratio of high:low m.wt. PCL offered an appropriate compromise between physicochemical properties and resistance to encrustation. This study has highlighted the important usefulness of degradable polymer systems as ureteral biomaterials

Co-melt fluidised bed granulation of pharmaceutical powders: Improvements in drug bioavailability

This study investigates the use of co-melt fluidised bed granulation for the agglomeration of model pharmaceutical powders, namely, lactose mono-hydrate, PEG 10000, poly-vinyl pyrolidone and ibuprofen as a model drug. Granulation within the co-melt system was found to follow a nucleationâ??steady growthâ??coating regime profile. Using high molecular weight PEG binder, the granulation mechanism and thus the extent of granulation was found to be significantly influenced by binder viscosity. The compression properties of the granulate within the hot fluidised bed were correlated using a novel high temperature experimental procedure. It was found that the fracture stress and fractural modulus of the materials under hot processing conditions were orders of magnitude lower than those measured under ambient conditions. A range of particle velocities within the granulator were considered based on theoretical models. After an initial period of nucleation, the Stokes deformation number analysis indicated that only velocities within the high shear region of the fluidised bed were sufficient to promote significant granule deformation and therefore, coalescence. The data also indicated that larger granules de-fluidised preventing agglomeration by coalescence. Furthermore, experimental data indicated that dissipation of the viscous molten binder to the surface was the most important factor in the latter stages of the granulation process. From a pharmaceutical perspective the inclusion of the model drug, ibuprofen, combined with PVP in the co-melt process proved to be highly significant. It was found that using DSC analysis on the formulations that the decrease in the heat of fusion associated with the melting of ibuprofen within the FHMG systems may be attributed to interaction between PVP and ibuprofen through inter-molecular hydrogen bonding. This interaction decreases the crystallinity of ibuprofen and facilitates solubilisation and bioavailability within the solid matrix.

Design, characterisation and preliminary clinical evaluation of a novel mucoadhesive topical formulation containing tetracycline for the treatment of periodontal disease

This study describes the formulation, characterisation and preliminary clinical evaluation of mucoadhesive, semi-solid formulations containing hydroxyethylcellulose (HEC, 1-5%, w/w), polyvinylpyrrolidine (PVP, 2 or 3%, w/w), poly carbophil (PC, 1 or 3%, w/w) and tetracycline (5%, w/w, as the hydrochloride). Each formulation was characterised in terms of drug release, hardness, compressibility, adhesiveness (using a texture analyser in texture profile analysis mode), syringeability (using a texture analyser in compression mode) and adhesion to a mucin disc (measured as a detachment force using the texture analyser in tensile mode). The release exponent for the formulations ranged from 0.78+/-0.02 to 1.27+/-0.07, indicating that drug release was non-diffusion controlled. Increasing the concentrations of each polymeric component significantly increased the time required for 10 and 30% release of the original mass of tetracycline, due to both increased viscosity and, additionally, the unique swelling properties of the formulations. Increasing concentrations of each polymeric component also increased the hardness, compressibility, adhesiveness, syringeability and mucoadhesion of the formulations. The effects on product hardness, compressibility and syringeability may be due to increased product viscosity and, hence, increased resistance to compression. Similarly, the effects of these polymers on adhesiveness/mucoadhesion highlight their mucoadhesive nature and, importantly, the effects of polymer state (particularly PC) on these properties. Thus, in formulations where the neutralisation of PC was maximally suppressed, adhesiveness and mucoadhesion were also maximal. Interestingly, statistical interactions were primarily observed between the effects of HEC and PC on drug release, mechanical and mucoadhesive properties. These were explained by the effects of HEC on the physical state of PC, namely swollen or unswollen. In the preliminary clinical evaluation, a formulation was selected that offered an appropriate balance of the above physical properties and contained 3% HEC, 3% PVP and 1% PC, in addition to tetracycline 5% (as the hydrochloride). The clinical efficacy of this (test) formulation was compared to an identical tetracycline-devoid (control) formulation in nine periodontal pockets (greater than or equal to 5 mm depth). One week following administration of the test formulation, there was a significant improvement in periodontal health as identified by reduced numbers of sub-gingival microbial pathogens. Therefore, it can be concluded that, when used in combination with mechanical plaque removal, the tetracycline-containing semi-solid systems described in this study would augment such therapy by enhancing the removal of pathogens, thus improving periodontal health. (C) 2000 Elsevier Science B.V. All rights reserved.

The manufacture and characterisation of hot-melt extruded enteric tablets

The aim of this highly novel study was to use hot-melt extrusion technology as an alternative process to enteric coating. In so doing, oral dosage forms displaying enteric properties may be produced in a continuous, rapid process, providing significant advantages over traditional pharmaceutical coating technology. Eudragit (R) L100-55, an enteric polymer, was pre-plasticized with triethyl citrate (TEC) and citric acid and subsequently dry-mixed with 5-aminosalicylic acid, a model active pharmaceutical ingredient (API), and an optional gelling agent (PVP (R) K30 or Carbopol (R) 971P). Powder blends were hot-melt extruded as cylinders, cut into tablets and characterised using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and dissolution testing conducted in both pH 1.2 and pH 6.8 buffers. Increasing the concentration of TEC significantly lowered the glass transition temperature (T,) of Eudragit (R) L100-55 and reduced temperatures necessary for extrusion as well as the die pressure. Moreover, citric acid (17% w/w) was shown to act as a solid-state plasticizer. HME tablets showed excellent gastro-resistance, whereas milled extrudates compressed into tablets released more than 10% w/w of the API in acidic media. Drug release from HME tablets was dependent upon the concentration of TEC, the presence of citric acid, PVP K30, and Carbopol (R) 971P in the matrix, and pH of the dissolution media. The inclusion of an optional gelling agent significantly reduced the erosion of the matrix and drug release rate at pH 6.8; however, the enteric properties of the matrix were lost due to the formation of channels within the tablet. Consequently this work is both timely and highly innovative and identifies for the first time a method of producing an enteric matrix tablet using a continuous hot-melt extrusion process.

Characterization of the Rheological, Mucoadhesive, and Drug Release Properties of Highly Structured Gel Platforms for Intravaginal Drug Delivery

This investigation describes the formulation and characterization of theologically structured vehicles (RSVs) designed for improved drug delivery to the vagina. Interactive, multicomponent, polymeric platforms were manufactured containing hydroxyethylcellulose (HEC, 5% w/w) polyvinylpyrrolidone (PVP, 4% w/w), Pluronic (PL, 0 or 10% w/w), and either polycarbophil (PC, 3% w/w) or poly(methylvinylether-co-maleic anhydride) (Gantrez S97, 3% w/w) as a mucoadhesive agent. The rheological (torsional and dynamic), mechanical (compressional), and mucoadhesive properties were characterized and shown to be dependent upon the mucoadhesive agent used and the inclusion/exclusion of PL. The dynamic theological properties of the gel platforms were also assessed following dilution with simulated vaginal fluid (to mimic in vivo dilution). RSVs containing PC were more rheologically structured than comparator formulations containing GAN. This trend was also reflected in formulation hardness, compressibility, consistency, and syringeability. Moreover, formulations containing PL (10% w/w) were more theologically structured than formulations devoid of PL. Dilution with simulated vaginal fluids significantly decreased rheological structure, although RSVs still retained a highly elastic stnicture (G' > G '' and tan delta <1). Furthermore, RSVs exhibited sustained drug release properties that were shown to be dependent upon their rheological structure. It is considered that these semisolid drug delivery systems may be useful as site-retentive platforms for the sustained delivery of therapeutic agents to the vagina.

Freeze-dried, mucoadhesive system for vaginal delivery of the HIV microbicide, dapivirine: Optimisation by an artificial neural network

Dapivirine mucoadhesive gels and freeze-dried tablets were prepared using a 3 x 3 x 2 factorial design. An artificial neural network (ANN) with multi-layer perception was used to investigate the effect of hydroxypropyl-methylcellulose (HPMC): polyvinylpyrrolidone (PVP) ratio (XI), mucoadhesive concentration (X2) and delivery system (gel or freeze-dried mucoadhesive tablet, X3) on response variables; cumulative release of dapivirine at 24 h (Q(24)), mucoadhesive force (F-max) and zero-rate viscosity. Optimisation was performed by minimising the error between the experimental and predicted values of responses by ANN. The method was validated using check point analysis by preparing six formulations of gels and their corresponding freeze-dried tablets randomly selected from within the design space of contour plots. Experimental and predicted values of response variables were not significantly different (p > 0.05, two-sided paired t-test). For gels, Q(24) values were higher than their corresponding freeze-dried tablets. F-max values for freeze-dried tablets were significantly different (2-4 times greater, p > 0.05, two-sided paired t-test) compared to equivalent gets. Freeze-dried tablets having lower values for X1 and higher values for X2 components offered the best compromise between effective dapivirine release, mucoadhesion and viscosity such that increased vaginal residence time was likely to be achieved. (C) 2009 Elsevier B.V. All rights reserved.

Physicochemical Characterization of Hot Melt Extruded Bicalutamide–Polyvinylpyrrolidone Solid Dispersions

Solid molecular dispersions of bicalutamide (BL) and polyvinylpyrrolidone (PVP) were prepared by hot melt extrusion technology at drug-to-polymer ratios of 1:10, 2:10, and 3:10 (w/w). The solid-state properties of BL, physical mixtures of BL/PVP, and hot melt extrudates were characterized using differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD), Raman, and Fourier transform infrared (FTIR) spectroscopy. Drug dissolution studies were subsequently conducted on hot melt extruded solid dispersions and physical mixtures. All hot melt extrudates had a single Tg between theTg of amorphous BL and PVP indicating miscibility of BL with PVP and the formation of solid molecular dispersions. PXRD con?rmed the presence of the amorphous form of BL within the extrudates. Conversely, PXRD patterns recorded for physical mixtures showed sharp bands characteristic of crystalline BL, whereas DSC traces had a distinct endotherm at 1968C corresponding to melting of crystalline BL. Further investigations using DSC con?rmed solid-state plasticization of PVP by amorphous BL and hence antiplasticization of amorphous BL by PVP. Experimentally observed Tg values of physical mixtures were shown to be signi?cantly higher than those calculated using the Gordon–Taylor equation suggesting the formation of strong intermolecular interactions between BL and PVP. FTIR and Raman spectroscopy were used to investigate these interactions and strongly suggested the presence of secondary interaction between PVP and BL within the hot melt extrudates. The drug dissolution properties of hot melt extrudates were enhanced signi?cantly in comparison to crystalline BL and physical mixtures. Moreover, the rate and extent of BL release were highly dependent on the amount of PVP present within the extrudate. Storage of the extrudates con?rmed the stability of amorphous BL for up to 12 months at 208C, 40% RH whereas stability was reduced under highly humid conditions (208C, 65% RH). Interestingly, BL recrystallization after storage under these conditions had no effect on the dissolution properties of the extrudates.