Effects of shear and electrical properties on flow characteristics of pharmaceutical blends

This article examines the effects and interactions of shear rate, shear strain on electrical and flow properties of pharmaceutical blends. An unexpectedly strong relation between the flow and passive electrical properties of powders is observed to depend on the shear history of the powder bed. Charge density, impedance, dielectrophoresis, flow index, and dilation were measured for several pharmaceutical blends after they were subjected to a controlled shear environment. It was found that the increase in the shear strain intensified the electrical properties for blends that did not contain MgSt. The opposite effect was found in blends lubricated with MgSt. Different shear conditions resulted in different correlations between flow index and dilation. Flow properties of powders were found to improve with continuous exposure to shear strain. It was also found that flow properties correlated to charge acquisition and impedance for different shear treatments. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Role of technetium-99m sestamibi in localisation of thyroid cancer metastases

Technetium-99m sestamibi (MIBI) is a routinely used myocardial perfusion imaging agent. We have studied groups of patients with differentiated thyroid carcinoma, in order to evaluate the usefulness of this agent in localising regional neck and nodal disease and metastases. There are three groups of patients. Group 1 consisted of patients with known nodal disease or metastases (22 patients) and with raised serum thyroglobulin levels (Tg). Group 2 comprised patients with normal I-131 scans and normal Tg levels (nine patients). Non-thyroid malignancies (six patients) comprised an additional group 3. In group 1, the MIBI scan showed 47 sites of metastases, while the I-131 scan revealed 49 sites. The MIBI scan was positive in two patients where the I-131 scan was negative, while in two other patients, the MIBI study was negative whereas the I-131 scan was positive. In group 2, 6/9 patients had no disease, 2/9 had thyroid remnants, and 1/9 had a fresh primary lung tumour, unrelated to the earlier thyroid cancer. All of them had normal MIBI scans. In group 3, two patients with lung cancer and two with breast cancer and metastases had normal MIBI scans. A further two patients with nasopharyngeal cancer (NPC) had mildly increased MIBI localisation in neck nodes and bone metastases. In summary, Tc-99m sestamibi appears to be as good as I-131 in search for thyroid carcinoma metastatic spread, especially nodal disease and this tracer does not localise well in the primary or metastases of other cancers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Highly selective custom-made chitosan based membranes with reduced fuel permeability for direct methanol fuel cells

Custom-made nanocomposite proton exchange membranes (PEMs) are fabricated using the blends of sulfonated chitosan (S-Chitosan) and sulfonated graphene oxide (SGO) nanosheets for direct methanol fuel cells (DMFCs). Sulfonation of chitosan and GO are carried out by 1,3-propane sultone and sulfanilic acid, respectively. Scanning electron microscope (SEM) with energy dispersive X-ray investigation revealed that the thick, folded and wrinkled sheet-like morphology of SGO and the existence of elemental sulfur. SEM and atomic force microscopy images showed the uniform dispersion of hydrophilic SGO nanosheets. Besides the S-Chitosan/SGO membranes showed higher water uptake, swelling ratio and ion exchange capacity due to the enhancement in hydrophilicity. The modified PEMs displayed improvement in proton conductivity since the ion-exchangeable sulfonic acid groups facilitate the proton conduction and effectively resist the methanol permeability by forming a strong hydrogen bond network with chitosan and thus diminish the void volume. Particularly, S-Chiotsan-1 membrane showed superior proton conductivity of 4.86 × 10⁻³ Scm⁻¹ at (25°C), selectivity of 1.89 × 10⁵ Scm⁻³ s and lesser methanol permeability of 2.57 × 10⁻⁸ cm²s⁻¹. Overall results suggest that the S-Chitosan/SGO membranes found to be a suitable alternate for Nafion® in DMFCs.     

An observed correlation between flow and electrical properties of pharmaceutical blends

We study the relation between flow and electrical conductivity of multiple formulations of pharmaceutical powder blends. Ten formulations were tested, consisting of two excipient sets, two active preparations, and a variety of food-grade additives including magnesium stearate (MgSt), and ionic and conductive materials such as ascorbic acid, talc, sodium carbonate, colloidal silica and TiO₂. Electrical impedance, flow index and dilation were independently measured for all of the blends, and a strong correlation was found between every pair of these three properties. The relation between flow and dilation has been observed before; we find for the first time that there is an exponential relationship between flow index or dilation and impedance. This indicates that cohesive powder behavior depends on powder electrical properties, raising the questions of whether additives such as MgSt affect friction and conductivity per se and what mechanism and phenomenon links cohesion and conductivity.     

Radionuclide imaging in primary hyperparathyroidism using 99mTc sestamibi--four case reports

Radionuclide imaging using the 99mTc sestamibi either singly or as a subtraction technique with pertechnetate is a recent and reliable method in localising parathyroid adenomas prior to surgery. This is of use in pre-operative planning, as well as in failed first neck exploration. Four local patients with primary hyperparathyroidism whose parathyroid adenomas were localised by this scintigraphy are presented. The value and limitations of this imaging modality are discussed.     

Influence of sintering temperature and oxygen stoichiometry on electrical transport properties of La0.67Na0.33MnO3 manganite

With a view to investigate the influence of sintering temperature and oxygen stoichiometry on electrical and magnetic properties of sodium-doped lanthanum manganite sintered at different temperatures, a series of samples were prepared by the sol–gel route. The samples were characterized by the XRD studies and the data were analyzed using the Rietveld refinement technique and it has been observed that the materials are having rhombohedral structure with space group. The electrical resistivity and thermoelectric power studies were investigated both as a function of crystallite size and oxygen content. To understand the conduction mechanism, the electrical resistivity data have been analyzed and it has been concluded that the variation of electrical resistivity in the ferromagnetic region can be explained by electron–electron scattering process (T²) and two magnon scattering processes, while that in the paramagnetic region is explained by the small polaron hopping mechanism. Similarly, the variation of thermopower in the ferromagnetic region is explained on the basis of electron–magnon scattering.     

Method to study the effect of blend flowability on the homogeneity of acetaminophen

The aim of this study was to develop an enteric-coated multiunit dosage form containing aceclofenac, a nonsteroidal anti-inflammatory drug. The pellets were prepared by using extrusion/spheronization method, and the core pellets were coated with a pH-sensitive poly(meth) acrylate copolymer (Eudragit L100-55) to achieve site-specific drug release. The formulated pellets were characterized for percentage yield, size distribution, surface morphology studies, drug content, and flow properties. In vitro dissolution test was used for comparison of drug release profiles of various coated pellets. The practical yield was found to be 90–95%. The particle size of enteric-coated pellets was found to be in the range of 0.59–0.71 mm. The pellets were spherical in shape and surfaces of pellets were found to be rough and showing micropores. Enteric-coated pellets showed good flow properties and in vitro dissolution profile. Dissolution tests were carried out in a USP type II dissolution apparatus in media-simulating pH conditions of the gastrointestinal tract. The release of the aceclofenac from formulated pellets was established to be minimum in the pH 1.2 (<5%) for a period of 2 h, and at pH 6.8, it shows the maximum release (85 ± 5% release within 1 h) which indicates gastric resistance of the formulated pellets. The 20% wt/wt enteric-coated pellets were compared to that of marketed product (tablets), it was observed that pellets showed better release profile. The study concluded that the formulated multiparticulate dosage forms can be used as an ideal drug delivery system for the aceclofenac.