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At least 775 records · Page 43Linked to original sources
PubMed2006

Statistical optimisation of the mucoadhesivity and characterisation of multipolymeric propranolol matrices for buccal therapy.

A Box-Behnken experimental design was employed to optimise a polymeric blend for the preparation of propranolol HCl matrices with maximum mucoadhesivity and was thereafter modified for achieving controlled drug release. The quantitative effects of the polymers used i.e. poly(acrylic acid) (PAA) and poly(vinyl pyrrolidone) (PVP) on mucoadhesion could be predicted using polynomial equations. A formulation of 20% PAA, 20% CMC and 20% PVP was identified for maximising mucoadhesivity and obtaining a controlled drug release profile. Reproducibility of the optimal formulation in terms of mucoadhesivity and controlled drug release was confirmed. The optimal formulation was characterised in terms of mucoadhesivity, release kinetics, swelling/erosion, hydration dynamics and surface pH. From the model fitting analyses, drug release was found to be diffusion, polymeric relaxation and erosion based with the former two being more dominant over erosion. This was in agreement with the erosion and swelling studies which showed swelling and erosion occurring in the tablet matrix. Textural profiling showed initial rapid hydration, which could be beneficial for enhanced mucoadhesivity. Surface pH of the multipolymeric matrices was similar to salivary pH and did not show extremes in changes over the test period. The optimal preparation of multipolymeric propranolol matrices identified in this study shows potential for buccal administration.

Acrylic Resins↗
PubMed2006

Freeze-drying of nanocapsules: impact of annealing on the drying process.

Freeze-drying process was recently applied to improve the long-term storage stability of nanocapsules. Thermal treatment by annealing is an interesting process to optimize a freeze-drying cycle of these colloidal vectors. The objective of this paper is to investigate the impact of annealing on primary and secondary drying characteristics and on nanocapsules (NC) properties. Nanocapsules were prepared from poly-epsilon-caprolactone (PCL) biodegradable polymer and stabilized by polyvinyl alcohol (PVA), and then freeze-dried with two cryoprotectants: sucrose and poly vinyl pyrrolidone (PVP). Freeze-dried nanocapsules were characterized by size measurement and transmission electron microscopy after reconstitution. The effect of annealing on the kinetics of sublimation, on the mass transfer resistance and on the porosity of the freeze-dried product has been studied in the case of PVP. Finally, the effect of annealing on the kinetic of secondary drying was studied and the results were coupled with the isotherm of sorption. Results showed that PCL nanocapsules could be freeze-dried without any modification of their properties in presence of the two cryoprotectants used. Annealing of nanocapsules suspensions could accelerate the sublimation rate without any modification of nanocapsules size in the case of the two studied cryoprotectants. Such improvement could be explained by the increase of ice crystals size after annealing and by the diminution of mass transfer resistance by the dried layer. The acceleration of sublimation rate seems to depend on the temperature of annealing. The annealing of sucrose solution slows down the secondary drying kinetic whereas no effect is observed in the case of PVP.

Capsules↗
PubMed2006

Preparation of hydrogels of griseofulvin for dermal application.

In an attempt to prepare topical formulations of griseofulvin that can deliver the drug locally in effective concentration, various hydrogel formulations were prepared using carbomer (940 NF) as base; essential oils, propylene glycol (PG), N-methyl-2-pyrrolidone (NMP) as penetration enhancers. The in vitro skin permeation studies through Laca mouse skin were performed using vertical type cells. PG in the hydrogel formulation was found to influence drug release rate by increasing its solubility and partitioning. Further combinations of PG with varying amounts of NMP in the hydrogel formulations exhibited a significantly greater increase in the flux on comparison with the control and formulation containing PG alone. The diffusion samples obtained by in vitro permeation studies through mouse skin when subjected to microbioassay using Microsporum gypseum as tester microorganism exhibited antifungal activity. This indicates that the drug permeated through the mouse skin possess sufficient antifungal activity in vitro against the tested microorganism. The prepared hydrogels did not show any skin sensitization and histological studies were carried out to check the safety of permeation enhancers used. Further these formulations were found to be stable at three different temperatures 4, 25 and 40 degrees C with respect to percent drug content, release characteristics, pH, transparency, feel and viscosity.

Acrylic Resins↗
PubMed2006

A novel in situ forming drug delivery system for controlled parenteral drug delivery.

The objective of this study was to investigate the in vitro drug (diltiazem hydrochloride and buserelin acetate) release from different in situ forming biodegradable drug delivery systems, namely polymer solutions (in situ implants) and in situ microparticle (ISM) systems. The drug release from ISM systems [poly(d,l-lactide) (PLA) or poly(d,l-lactide-co-glycolide) (PLGA)-solution dispersed into an external oil phase] was investigated as a function of the type of solvent and polymer, polymer concentration and internal polymer phase:external oil phase ratio and was compared to the drug release from in situ implant systems and microparticles prepared by conventional methods (solvent evaporation or film grinding). Upon contact with the release medium, the internal polymer phase of the ISM system solidified and formed microparticles. The initial drug release from ISM systems decreased with increasing polymer concentration and decreasing polymer phase:external oil phase ratio. The type of biocompatible solvent also affected the drug release. It decreased in the rank order DMSO>NMP>2-pyrrolidone. In contrast to the release of the low molecular weight diltiazem hydrochloride, the peptide release (buserelin acetate) was strongly dependent on the polymer degradation/erosion. One advantage of the ISM system when compared to in situ implant systems was the significantly reduced burst effect because of the presence of an external oil phase. ISM systems resulted in drug release profiles comparable to the drug release of microparticles prepared by the solvent evaporation method. Therefore, the ISM systems are an attractive alternative to existing complicated microencapsulation methods.

Buserelin↗
PubMed2006

Comparative effects of some hydrophilic excipients on the rate of gabapentin and baclofen lactamization in lyophilized formulations.

The aim of this study was to gain insights into the role played by some excipients on the stability of gabapentin 1 and baclofen 2 which can undergo degradation giving rise to the corresponding lactams 2-azaspiro[4.5]decan-3-one 3 and 4-(4-chlorophenyl)-2-pyrrolidone 4, respectively. A screening study was carried out on drug and drug-excipient freeze-dried mixtures at 50 degrees C and under three different humidity values by using a number of commonly available excipients. These include hydroxypropyl-beta-(HP-beta-CD), sulfobutyl-beta-cyclodextrin (SBE-beta-CD), lactose, raffinose, trehalose, PVP-K30 and mannitol. For most cases, it was found that the lactam formation can be satisfactory described by an apparent zero-order equation. Excipients shown to negatively impact gabapentin stability are HP-beta-CD, SBE-beta-CD, lactose and PVP K30 while only this last excipient had a significant effect on the degradation of baclofen. The results can be rationalized in terms of conformational factors favouring the intramolecular dehydration reaction. A positive effect of moisture on the lactamization process was observed under some circumstances. Water may provide a favourable environment for degradation. These findings, taken together, should be considered during the selection of excipients for a possible formulation of gabapentin and baclofen.

Amines↗
PubMed2005

Aggregated structure analysis of polymer-protected platinum/ruthenium colloidal dispersions using EXAFS, HRTEM, and electron diffraction measurements.

Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed.

Journal Article↗
PubMed2005

Synthesis of silver nanoprisms in formamide.

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.

Journal Article↗
PubMed2005

Controlling the agglomeration of anisotropic Ru nanoparticles by the microwave-polyol process.

A rapid polyol process for the synthesis of ruthenium nanoparticles was developed using microwave irradiation. A colloidal solution of monodispersed anisotropic Ru metal nanoparticles (mean particle size 2-6 nm) with different aspect ratios was obtained first. Particles with different degrees of agglomeration have also been synthesized using monodisperse particles as seeds and PVP (poly-N-vinyl-2-pyrrolidone) as the stabilization reagent. The stabilization mechanisms of different protective reagents were studied by UV-vis spectra. The HRTEM images indicated that dendritic particles formed by controlling agglomeration consisted of single-crystal domains with a random crystalline orientation.

Journal Article↗
PubMed2005

Synthesis of fluorescent silica-coated gibbsite platelets.

We describe the fluorescent labeling of gibbsite particles. Gibbsite particles are first stabilized with polyvinyl pyrrolidone. Subsequently the particles are covered with a silica layer in which a fluorescent dye is incorporated. Both fluorescein and rhodamine dyes have been used. The fluorescent labeling is applicable to gibbsite particles of various sizes. Particles are transferred to dimethyl formamide by vacuum distillation after dialysis. These particles are used for confocal scanning laser microscopy and confocal fluorescence-recovery after photobleaching.

Journal Article↗
PubMed2005

Solvent-induced shape evolution of PVP protected spherical silver nanoparticles into triangular nanoplates and nanorods.

The reaction between silver nitrate and poly(N-vinyl-2-pyrrolidone) (PVP) in pyridine at ambient conditions could lead to the formation of spherical nanoparticles or quadrilateral and triangular silver nanoplates, depending on the silver-to-PVP ratio used. It is proposed that the spherical Ag nanoparticles, which were formed early in the reaction, were transformed into nanoplates through an Ostwald ripening process driven by the bridging flocculation of small spherical Ag nanoparticles. This unique and hitherto unreported shape evolution process was carefully followed by a combination of techniques, viz., UV-visible spectroscopy, TEM, and powder X-ray diffraction.

Journal Article↗
PubMed2005

Rapid preparation and characterization of uniform, large, spherical Ag particles through a simple wet-chemical route.

In this article we report the rapid preparation of uniform, large, spherical Ag particles through a simple wet-chemical route. The formation of Ag particles with about 750 nm in diameter occurs in a single process, carried out by direct mix of AgNO3 aqueous solution and ortho-phenylenediamine N-methyl-2-pyrrolidone solution at room temperature, producing a relatively low-polydispersity product. It is also found that raising the temperature results in larger particles. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra have been used to characterize the resulting product.

Particle Size↗
PubMed2005

Synthesis of colloidal dispersions of rhodium nanoparticles under high temperatures and high pressures.

Colloidal dispersions of rhodium (Rh) nanoparticles have been synthesized by the reduction of Rh ions (III) in high-temperature and high-pressure water, ethanol, or water-ethanol mixture under the existence of the protective polymer of poly(N-vinyl-2-pyrrolidone). The possibility of the regulation of the particle size and size distribution has been tested under several solvents at various temperatures and pressures. At 473 K and 25 MPa, particularly, concentrated colloidal dispersions of Rh particles of 2.5+/-0.5 nm were synthesized from the ionic solution of ethanol ([Rh]=15 mM) within a few seconds. Dilute colloidal dispersions of Rh particles were also synthesized from the dilute ionic solution ([Rh]=1.5 mM) with a diameter of 2.0+/-0.4 nm. From the water solution, Rh particles tended to form aggregates, especially for the lower concentration solution. In the case of solutions in water and ethanol mixture, the average diameter of Rh particles tended to be larger than in ethanol solution, and their distribution became broad.

Colloids↗
PubMed2005

Aerosol size standards in the nanometer size range II. Narrow size distributions of polystyrene 3-11 nm in diameter.

A technique for generating charged aerosols of polystyrene (pSty) with narrow size distributions has been developed. It is based on electrospraying commercial narrow mass standards of pSty dissolved in l-methyl-2-pyrrolidone (NMP) seeded with the newly synthesized salt dimethyl ammonium formate. This salt imparts a much larger electrical conductivity than previously known NMP electrolytes, leading to higher quality sprays with greatly reduced attachment of impurities. Controlling the solute concentration enables forming polystyrene particles containing from one up to more than ten single polystyrene molecules, whereby 4 mass standards with molecular weights from 9200 up to 96,000 g/mol yield particles covering densely the diameter range from 3 to 11 nm. Combined mobility and mass measurement with a differential mobility analyzer and a mass spectrometer in tandem are carried out with a pSty sample 9200 amu in molecular weight. They fix directly the mass versus mobility relation near 9200 amu, and indirectly for the other standards and their clusters. The apparent particle density resulting from mobility versus mass data agrees with the bulk density of the polymer, indicating that the particles are dense and spherical. Although these standards have been studied only in gaseous suspension, their injection in liquids such as water where pSty is insoluble should keep them spherical.

Journal Article↗
PubMed2006

Organic dye molecules as reducing agent for the synthesis of electroactive gold nanoplates.

Highly crystalline, hexagonal and triangular nanoplates of gold are synthesized in high yield by a new wet chemical method using multifunctional molecules, Bismarck brown R (BBR) and Bismarck brown Y (BBY). This method involves a simple approach by keeping a mixture of aqueous HAuCl4 solution and BBR/BBY solution in presence of poly(vinyl pyrrolidone) for 24 h. These nanostructures show unprecedented electrochemical properties exhibiting surface confinement effect. The UV-visible (UV-vis) spectrum shows certain distinct features with absorptions at 300, 400, and 650 nm extending up to the near infrared region. Selected area electron diffraction patterns of these nanoparticles show highly oriented (111) crystal facets. X-ray diffraction analysis also confirms the predominant orientation in the (111) crystal planes with lattice constant approximately 4.07 angstroms of face-centered-cubic (fcc) gold. X-ray photoelectron (XP) and Fourier transform infrared (FTIR) spectroscopic analysis shows the presence of a fraction of reducing molecules as surface passivating agent either in the unreacted molecular state or as a mixture of reacted and unreacted product, which probably undergoes charge transfer with gold nanocrystals giving absorption at approximately 300 nm.

Journal Article↗
PubMed2006

Synthesis of highly monodisperse polystyrene microspheres via dispersion polymerization using an amphoteric initiator.

The highly monodisperse polystyrene (PS) microspheres were produced by dispersion polymerization using an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057). The polymerization characteristics were investigated and compared with conventional initiators, 2,2-azobis(isobutyronitrile) (AIBN) and benzoyl peroxide (BPO). The monodisperse PS microspheres having the coefficient of variation (C(v)) of diameter all less than 4% are obtained at very low stabilizer, poly(vinyl pyrrolidone) (PVP) concentrations of 1 and 2 wt%. It is found that the size dependence of the VA-057 system, D(n) proportional, variant [VA-057](0.267), is less sensitive than a conventional initiator system. When the same amount, 2 wt%, of AIBN, BPO, and VA-057 is used under the identical PVP concentration of 2 wt%, the D(n)/C(v)'s are 1.95/11.57, 1.47/22.44, and 2.08 microm/2.50%, respectively. The uniformity of particles was characterized employing an optical analyzer, Turbiscan. For the VA-057 system, the back scattering intensity is linearly reduced with time having a constant sedimentation rate of 48.98 microm/min throughout the settling process. The uniformity of PS particles in the VA-057 system stems from (1) the higher rate of polymerization in early stage of polymerization, followed by significantly faster reduction of the rate, and (2) good dispersion stability of primary particles. Therefore, it is found that the use of an amphoteric initiator, VA-057, is promising for producing monodisperse particles in dispersion polymerization.

Journal Article↗
PubMed2006

Successive interaction of pairs of soluble organics with nanosilica in aqueous media.

Successive interaction of different pairs of water-soluble polymers (poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA)), proteins (bovine serum albumin (BSA), ovalbumin, gelatin, and ossein), and smaller organics such as lecithin (1-stearoyl-2-oleoyl phosphatidylcholine, SOPC) and Aethonium (1,2-ethylene-bis(N-dimethyl carbodecyl oxymethyl) ammonium dichloride) with nanosilicas A-300 (S(BET)=232 and 297 m(2) g(-1)) and A-50 (S(BET)=52 m(2)g(-1)) was studied using dynamic light scattering, adsorption, and infrared (FTIR) spectroscopy methods. Time-dependent rearrangement of particle size distributions (PSDs) depicts appearance of both smaller and larger aggregates for silica/PEG(I-first adsorbate)/BSA(II-second adsorbate) and silica/PVP(I)/BSA(II) (i.e., BSA adsorbs onto PEG/silica or PVP/silica) than that for silica/organic compound I. However, in the cases of PVA(I)-BSA(II) and PVA(I)-SOPC(II) a similar effect is not observed because only increased aggregation occurs. The successive equilibrium adsorption of similar pairs shows a diminution of the adsorption of the second compound (gelatin, ovalbumin) with increasing amount of the first adsorbed polymer (PEG or PVP).

Journal Article↗
PubMed2006

Integral equation for calculation of distribution function of activation energy of shear viscosity.

A new technique of calculation of a distribution function of activation energy (f(E)) of shear viscosity based on a regularization procedure applied to the Fredholm integral equation of the first kind has been developed using the Baxter-Drayton and Brady model for concentrated and flocculated suspensions. This technique has been applied to the rheological data obtained at different shear rates for aqueous suspensions with fumed silica A-300 and low-molecular (3,4,5-trihydroxybenzoic acid and 1,5-dioxynaphthalene) or high-molecular (poly(vinyl pyrrolidone) of 12.7 kDa and ossein of 20-29 kDa) compounds over a wide concentration range (up to 25 wt% of both components) and at different temperatures. Monomodal f(E) distributions are observed for the suspensions with individual A-300 or A-300 with a low amount of adsorbed organics. In the case of larger amounts of nanosilica and organics the f(E) distributions are multimodal because of stronger structurization and coagulation of the systems that require a high energy to break the coagulation structures resisting to the shear flow.

Journal Article↗
PubMed2006

Controlled synthesis and association behavior of graft Pluronic in aqueous solutions.

Poly(vinyl pyrrolidone) (PVP) was grafted onto Pluronic F127 (PEO-PPO-PEO) to produce novel amphiphilic PVP-g-F127 graft copolymers. A controlled synthesis method was used to graft PVP onto different parts of F127. Two types of graft polymers were obtained: one has PVP grafted onto the PEO part of F127 and the other has PVP grafted onto the PPO part of F127. The association behavior of the two modified polymers was examined using differential scanning calorimetry, surface tension measurements, and dynamic light scattering.

Journal Article↗