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A simple correlation method has been developed to predict effective diffusivities of small molecules in heterogeneous materials such as immobilized cell systems. This correlation uses a single diffusivity measurement at one cell volume fraction to predict diffusivities for any other volume fraction of cell. The method has been applied to 20 sets of(More)
We investigate mixing in a viscoelastic and shear-thinning fluid-a very common combination in polymers and suspensions. We find that competition between elastic and viscous forces generates self-similar mixing, lobe transport, and other characteristics of chaos. The mechanism by which chaos is produced is evaluated both in experiments and in a simple model.(More)
We report that the formation of much reported axial segregation bands in rotating cylinders loaded with different sized particles depends critically on scale and inertia. Specifically, when the ratio, δ, of the diameter of the cylinder to the average diameter of the particles is large, axial bands invariably appear, when δ is small, bands never appear, and(More)
a r t i c l e i n f o Continuous powder mixing has attracted a lot of interest within the pharmaceutical industry. Much work has been done recently that targets the characterization of continuous powder mixing. In this paper, a quantitative scaling up strategy is introduced that allows the transition from lab to industrial scale. The proposed methodology is(More)
A combination of analytical and statistical methods is used to improve a tablet coating process guided by quality by design (QbD) principles. A solid dosage form product was found to intermittently exhibit bad taste. A suspected cause was the variability in coating thickness which could lead to the subject tasting the active ingredient in some tablets. A(More)
The hydrodynamics within the United States Pharmacopeia Apparatus 2 have been shown to be highly non-uniform with a potential to yield substantial variability in dissolution rate measurements. Through the use of readily available engineering tools, several geometric modifications to the device were evaluated in this study. Specifically, we examined the(More)
In this article, three well-established engineering tools are used to examine hydrodynamics in dissolution testing apparatuses. The application of these tools would provide detailed information about the flow, shear, and homogeneity in dissolution tests. Particle image velocimetry successfully measures two-dimensional cross-sections of the velocity field in(More)
Computational analysis is used to examine the hydrodynamic environment within the USP Apparatus II at common operating conditions. Experimental validation of the computational model shows that the simulations of fluid motion match the dispersion of dye observed in experiments. The computations are then used to obtain data that cannot be easily measured with(More)
In this article the gravitational displacement rheometer (GDR) is used to characterize the effects of formulation composition and environmental conditions (moisture) on flow properties of cohesive pharmaceutical powders under unconfined conditions. The amount of moisture in the sample often has important effects on the physical and chemical properties of(More)
It is desirable for a pharmaceutical final dosage form to be manufactured through a quality by design (QbD)-based approach rather than a quality by testing (QbT) approach. An automatic feedback control system coupled with PAT tools that is part of the QbD paradigm shift, has the potential to ensure that the pre-defined end product quality attributes are met(More)