1,720,960 research outputs found
Preparation of glibenclamide nanocrystals by a simple laboratory scale ultra cryo-milling
No full textThe objective of this study is to evaluate the ability to reduce the particle size of glibenclamide to the nanometric scale through a very simple and well-known laboratory scale method, the laboratory scale ultra cryo-milling. The effect of milling on glibenclamide crystalline properties and dissolution behavior was deliberately evaluated in the absence of any surfactants as stabilizers.
The milling procedure consisted in adding particles to liquid nitrogen and milling them in a mortar with a pestle for different time intervals (15, 30, 40 minutes). For comparison, the same milling procedure was also applied without liquid nitrogen. The particle size reduction was evaluated for the coarsest samples (> 3 m) by measuring the particle Ferret’s diameter through scanning electron microscopy, while for the smallest one (< 3 m) by dynamic light scattering. A time grinding of 40 minutes in presence of liquid nitrogen was revealed highly efficacious to obtain particles of nanodimensions, with a geometric mean particle size of 0.55 ± 0.23 m and more than the 80% of particles lower than 1000 nm. Interestingly, non-agglomerated particles were obtained. Differential Scanning Calorimetry and X-Ray Powder Diffractometry allowed to assess that under mechanical treatment no polymorphic transitions were observed, while a decrease in crystallinity degree occurred depending on the milling procedure (presence or absence of liquid nitrogen) and the milling time (crystallinity decreases at increasing milling time from 15 to 40 minutes). A comparison of the Intrinsic Dissolution Rate and the dissolution from particles revealed an interesting improvement of particle dissolution for nanoparticles due to an increase in particle surface area and concentration gradient, according to the Noyes-Whitney equation
Indomethacin nanocrystals prepared by different laboratory scale methods: effect on crystalline form and dissolution behavior
No full textThe objective of this study is to select very simple and well-known laboratory scale methods able to reduce particle size of indomethacin until the nanometric scale. The effect on the crystalline form and the dissolution behavior of the different samples was deliberately evaluated in absence of any surfactants as stabilizers. Nanocrystals of indomethacin (native crystals are in the c form) (IDM) were obtained by three laboratory scale methods: A (Batch A: crystallization by solvent evaporation in a nano-spray dryer), B (Batch B-15 and B-30: wet milling and lyophilization), and C (Batch C-20-N and C-40-N: Cryo-milling in the presence of liquid nitrogen). Nanocrystals obtained by the method A (Batch A) crystallized into a mixture of a and c polymorphic forms. IDM obtained by the two other methods remained in the c form and a different attitude to the crystallinity decrease were observed, with a more considerable decrease in crystalline degree for IDM milled for 40 min in the presence of liquid nitrogen. The intrinsic dissolution rate (IDR) revealed a higher dissolution rate for Batches A and C-40-N, due to the higher IDR of a form than c form for the Batch A, and the lower crystallinity degree for both the Batches A and C-40-N. These factors, as well as the decrease in particle size, influenced the IDM dissolution rate from the particle samples. Modifications in the solid physical state that may occur using different particle size reduction treatments have to be taken into consideration during the scale up and industrial development of new solid dosage forms
Preformulation study of nicergoline solid dispersions
No full textNicergoline, a semisynthetic ergot derivative, which, in its crystalline state, is insoluble in water, was dispersed in polyvinylpyrrolidone K30 (PVP K30) to improve drug particle dissolution. Preformulation studies were carried out initially by Differential Scanning Calorimetry (DSC) and X-ray Powder Diffraction (XRPD) in order to predict the conditions and the possibility to actually obtain solid dispersions by mixing the two components at different proportions.
Solid dispersions were finally prepared by dissolving nicergoline and PVP K30 in chloroform that was next evaporated under reduced pressure. Under these conditions, an amorphous powder was recovered in every proportion of the two components. Nicergoline demonstrated to be physically and chemically stable for one year. The dissolution studies revealed a very high dissolution rate of nicergoline from solid dispersions only lower than the pure amorphous form.
This is the consequence of the molecular dispersion of nicergoline in the polymer that enhances the rate of drug release from the polymer
A new nanospray drying method for the preparation of nicergoline pure nanoparticles
No full textThree different batches of pure nanoparticles
(NPs) of nicergoline (NIC) were prepared by
spray drying a water:ethanol solution by a new Nano
Spray Dryer Bu ̈chi B-90. Spherical pure NPs were
obtained, and several analytical techniques such as
differential scanning calorimetry and X-ray powder
diffractometry permitted to assess their amorphous
character. A comparison of the solubility, intrinsic
dissolution, and drug release of original particles and
pure amorphous NPs were determined, revealing an
interesting improvement of biopharmaceutical properties
of amorphous NPs, due to both amorphous
properties and nanosize dimensions. Since in a
previous work, the high-thermodynamic stability of
amorphous NIC was demonstrated, this study is
addressed toward the formulation of NIC as pure
amorphous NPs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
