Biomedical subjects

A K Stubos

Publications and source records attributed to A K Stubos.

5 recordsLinked to original sources

PubMed2003

Effect of liquid films on the isothermal drying of porous media.

We study the effects of liquid films on the isothermal drying of porous media. They are important for the transport of liquid to an evaporation interface, far from the receding liquid clusters. Through a transformation, the drying problem is mapped to the Laplace equation around the percolation liquid clusters. From its solution, the properties of drying are obtained in terms of the capillary number. Consistent with experimental evidence, film flow is shown to accelerate drying significantly.

Journal Article↗

PubMed2003

Low Peclet mass transport in assemblages of spherical particles for two different adsorption mechanisms.

The problem of flow and mass transport within an assemblage of spherical solid absorbers is investigated. We present and compare results from the numerical solution of the convection-diffusion equation in the sphere-in-cell geometry and in stochastically constructed 3-D spherical particle assemblages. In the first case, we make use of an analytical solution of the creeping flow field in the sphere-in-cell model while in the second we employ a full numerical solution of the flow field in the realistic geometry of sphere assemblages. Low to moderate Peclet numbers (Pe<10(2)) are considered where the validity of the sphere-in-cell model is uncertain. On the other hand, the selected porosities range from values close to unity, where the sphere-in-cell approximation is expected to hold, to intermediate values, where its applicability becomes again uncertain. In all cases, instantaneous and Langmuir adsorption is studied. It is found that the simplified sphere-in-cell approach performs adequately provided that proper account of the actual porous media properties (porosity and internal surface area) is taken. A simple match of porosity is not sufficient for a reliable estimation of adsorption efficiencies.

Journal Article↗

PubMed2001

Numerical and experimental investigation of the diffusional release of a dispersed solute from polymeric multilaminate matrices.

In the present work the release behavior of special, multilaminate matrix-type polymer systems, is studied both theoretically and experimentally. Two different mathematical models have been employed to describe the release of a dispersed solute from both single- and multilayer matrices. A parameter sensitivity study shows that the incorporation of supersaturated matrices in the formation of multilaminate devices, with a nonuniform initial solute loading, can provide a delivery system with optimized performance compared to monolithic ones. Finally, the findings of this theoretical analysis show good agreement with measurements of the release rates of a model disperse dye from both single- and multilayer matrices.

Diffusion↗

PubMed2000

A study on structural and diffusion properties of porcine stratum corneum based on very small angle neutron scattering data.

PURPOSE: Generation of valuable information about the biphasic geometrical configuration of porcine stratum corneum from Very Small Angle Neutron Scattering (VSANS) data and investigation of its effect on the corresponding effective diffusivity. METHODS: Spectra of porcine stratum corneum are mathematically transformed in order to obtain the corresponding auto-correlation function (ACF). Model stratum corneum structures, matching this experimentally determined ACF, are then produced based on the "brick-and-mortar" configuration. The effective diffusivity through these model domains is calculated using an appropriate numerical method. RESULTS: The most appropriate geometry of porcine stratum corneum's lipid and protein phases in a "brick-and-mortar" configuration is quantitatively determined and correlated with the barrier properties (diffusivity) of the stratum corneum model structures. CONCLUSIONS: The ACF analysis indicates the most appropriate values for the dimensions of the corneocyte thickness and the surrounding lipid gap, while the corneocyte length is estimated from the diffusion study.

Animals↗

PubMed1998

A two-phase model for controlled drug release from biphasic polymer hydrogels.

A comprehensive two phase model is developed to describe the sustained release of a solute or drug from a biphasic hydrogel substrate. Such a material consists of a continuous hydrophilic phase (polymer backbone in water) and a dispersion of spherical microdomains made of the hydrophobic side chains of the polymer organised in a micelle like fashion. The solute or drug is assumed to be encapsulated within the dispersed microdomains, and to diffuse from the interior to the surface of the microdomain where it exchanges following a Langmuir isotherm. Mass transfer to the bulk phase occurs by desorption of the drug from the surface through a driving force that is proportional to the difference of surface and bulk concentration. Accordingly the drug is released to the surroundings by diffusion through the bulk. Depending on the values of the Langmuir constant and assuming well stirred behaviour in the interior of the microdomain, the present model results in either of the two asymptotic models developed in previous studies. The results of a parametric study show that the desired steady state flux of a specific drug to the surroundings may be obtained given appropriate values of structural properties of the material. This conclusion is further supported when using this model to simulate earlier experimental results. The polymer structural properties can be manipulated easily during the fabrication of dispersed-phase networks, as indicated by preliminary experiments.

Delayed-Action Preparations↗