Avalanching flow of cohesive powders

The flow dynamics of cohesive powders is investigated in rotating cylinders with an L : R ratio of 3 : 1 using experiments and DEM simulations. Flow onset and steady-state behavior are compared for free-flowing (cohesionless) dry glass beads, wet glass beads, and “dry” cohesive powders (lactose, microcrystalline cellulose). The avalanching dynamics of powders is substantially different from those observed for free-flowing or wet-cohesive glass beads. Dry cohesive powders exhibit history-dependent flow dynamics, significant dilation, aperiodic avalanche frequencies, and variable avalanche size. These behaviors also provide a route for effective characterization of cohesive forces under dilated conditions characteristic of unconfined flows.     

A method for predicting hopper flow characteristics of pharmaceutical powders

This communication correlates two empirical methods; flow in a rotating drum with flow in bench scale hoppers. The flow characteristics of 13 cohesive granular materials were studied in the gravitational displacement Rheometer (GDR) and compared to flow in hoppers of varying angle and discharge diameter at fixed temperature and moisture conditions. The GDR proved to be an effective and convenient tool for examining flow properties of pharmaceutical materials, both pure and mixtures. A flow Index obtained from GDR measurements is directly correlated to the flow through hoppers, providing a predictive method for hopper design and a convenient experimental test for screening materials and determining their suitability for specific hopper systems. Analysis of industrial scale hoppers will be addressed in future communication.     

A modeling approach for understanding effects of powder flow properties on tablet weight variability

In this paper we focus on the effect of cohesion and compression speed on the outcome of the compression process for both monodisperse and polydisperse granular systems. A three dimensional discrete element model (DEM) which incorporates static and dynamic friction is used in this study to simulate die filling, and the compaction and decompaction of cohesive granular system in a confined cylindrical die similar to those used in a commercial tablet press driving the pre-compressive stage. The magnitude of the cohesive force is represented in terms of a parameter K = F_cohes/mg, where K is called the bond number and is the measure of cohesiveness. Force displacement curves are used to characterize the compression and deformation properties of the materials and are obtained by measuring the force on the upper punch and the corresponding displacements in the die. Results show that a considerable more energy is needed to compress the cohesive material as compared to free flowing materials. It is found that the time required to fill the die strongly depends on the cohesion of the material. The energy for the tableting process is directly proportional to the upper punch speed.     

Constitutive model to predict flow of cohesive powders in bench scale hoppers

This communication empirically correlates flow in two systems; an instrumented rotating drum (GDR) and a set of bench scale hoppers. A flow index obtained from measurements in the GDR is directly correlated to the flow through hoppers, providing a predictive method for hopper design and a convenient experimental test for screening materials and determining their suitability for specific hopper systems. Simulations were performed to understand the dynamics of flow in hoppers by using the same flow parameters in hoppers and rotating cylinders. Simulations showed that as cohesion increased it becomes harder for the particles to flow through the hoppers, in good agreement with the experiments. The effect of hopper angle also yields similar findings to experiments for Avicel, K=60, where the powder does not flow through the 45° hopper but flows well in a 75° hopper. Simulations were also used to calculate the normal forces on the walls of the hopper and the wall pressure distributions in both hoppers. As depth increases, the wall pressure increases for all cases. Finally, the simulations also helped understand the different flow behaviors (funnel and mass flow) that take place in a hopper. The simulated dynamics of flow in the rotating drum and in the hopper correlate very closely to experiments, indicating that the model cohesion parameters are, as desirable, material-specific but independent of geometry.     

Extracorporeal shock wave lithotripsy for lower pole nephrolithiasis: efficacy and variables that influence treatment outcome

OBJECTIVES: To clarify the role of the membranous glycoprotein gp-170 in renal cell carcinoma (RCC) cell lines and their multidrug resistant (MDR) sublines. and to correlate gp-170 with the natural and acquired drug resistance of these cell lines to anthracyclines. MATERIALS AND METHODS: The expression of gp-170 in five cultured RCC cell lines and serial RCC8701 MDR sublines was analysed by immunofluorescent flow cytometry. The chemosensitivity of these tumour cells to the anthracycline anticancer drugs adriamycin and epirubicin was measured using the microplate tetrazolium (MTT) cytotoxicity assay, and the results correlated with gp-170 expression. RESULTS: All six natural RCC cell lines showed a variably increased expression of gp-170, with the A704 and Caki-1 cell lines the highest. In contrast, gp-170 expression increased and then was suppressed in acquired MDR sublines of RCC8701 cultured in increasing concentrations of adriamycin. The A704 and Caki-1 cells were much more resistant to adriamycin and epirubicin than the A498, ACHN and RCC8701 cell lines, in parallel with the expression of gp-170. The resistant cell line cultured long-term in 800 ng/mL adriamycin, RCC8701/ADR800, was 122 times more resistant to adriamycin and 238 times more resistant to epirubicin than the parent cell line: the pattern differed from that in native RCC cell lines and was unrelated to the expression of gp-170. CONCLUSION: Membranous gp-170 plays an important role in MDR of native RCC cell lines, while acquired MDR cells have different mechanisms of obtaining drug resistance in addition to gp-170. This phenomenon may be applicable to the clinical treatment of patients newly diagnosed with RCC or those with disease refractory to chemotherapy.     

Effectiveness of intermittent iron treatment of two- to six-year-old Jordanian children with iron-deficiency anemia

BACKGROUND: Iron deficiency is a common nutritional problem in young children among vulnerable populations in Jordan. Several studies have shown the effectiveness of intermittent iron supplementation in improving iron status. Such a study has not been carried out in 2- to-6-year-old Jordanian children diagnosed with iron deficiency anemia in a clinical setting. OBJECTIVE: To study the effectiveness of intermittent versus daily iron treatment in a clinical setting in 2- to 6-year-old Jordanian children with iron-deficiency anemia. METHODS: About 4400 children aged 2 to 6 years who visited Prince Hashim Military Hospital in Zarqa, Jordan, from August 2000 to June 2001 were screened for age, general health, and birthweight. About 10% of these children were screened for anemia, using complete blood count (defined as a hemoglobin level < or = 10.5 g/dL, and a mean corpuscular volume < or =75 ft). Anemic children underwent further screening for iron deficiency, defined as serum ferritin level < or =12 microg/L. Children with iron-deficiency anemia, as indicated by hemoglobin < or = 10.5 g/dL, mean corpuscular volume < or =75 fL, and serum ferritin < or =12 microg/L, or as indicated by mean corpuscular volume < or =75 fL and hemoglobin < or = 10.5 g/dL, were enrolled in the study after informed oral consent by their parents. Study children (n=134) were assigned randomly to one of three groups. Subjects in group 1 (n=45), group 2 (n=45), and group 3 (n=44) received iron treatment daily, weekly, and twice weekly, respectively. Out of 134 children recruited for the study, only 63 (39 boys and 24 girls) completed the 3-month treatment period. All of the children received medicinal iron drops at a dosage of 5 mg elemental iron as ferrous sulfate per kilogram of body weight. The parents also received nutritional counseling. RESULTS: At the end of treatment, hemoglobin, serum ferritin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration increased significantly in all groups with no significant differences between groups. The increases in hemoglobin in groups 1, 2, and 3 were 2.47 +/- 0.17, 2.12 +/- 0.18, and 2.18 +/- 0.18 g/dL, respectively. Measurements of final serum ferritin concentration were available for only 12, 12, and 10 children in groups 1, 2, and 3, respectively. In all children who completed the study, except for one in group 1, hemoglobin, mean corpuscular volume, and serum ferritin reached normal values in response to iron treatment. CONCLUSIONS: Weekly and twice-weekly iron therapy with 5 mg elemental iron as ferrous sulfate per kilogram of body weight accompanied by nutritional counseling was as effective as daily iron therapy in correcting iron-deficiency anemia in 2- to 6-year-old children under the clinical conditions of this study.