Biomedical subjects

E S Kikkinides

Publications and source records attributed to E S Kikkinides.

5 recordsLinked to original sources

PubMed2003

Correlation of structural and permeation properties in sol-gel-made nanoporous membranes.

The aim of the present work was to establish a fundamental link between the basic structural properties of ceramic nanoporous membranes made by the sol-gel process and their respective transport properties, for a systematic evaluation of their performance in gas and liquid applications. For this purpose, supported and unsupported gamma-Al2O3 and TiO2 membranes were prepared from different colloidal dispersions (sols) by a sol-gel dipping process followed by drying and calcination, resulting in structures of crystallites of different shape and stacking arrangement. Accordingly, the pore structure of each membrane was simulated employing process-based reconstruction techniques and the permeation properties were predicted by solving the appropriate transport equations in the generated structures. Excellent agreement was achieved between the computed and experimental permeability values in the Knudsen and viscous flow regimes, validating the considerations made regarding the basic structural characteristics and the procedure for generation of the membrane structures. Moreover, it was shown that the shape and stacking arrangement of the primary particles (crystallites) of the sol have a major impact on the formation of pathways in the membrane pore structures and control the transport and therefore also the separation properties of these materials.

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↗

PubMed1999

Structural and flow properties of binary media generated by fractional Brownian motion models.

In the present paper, the structural and flow properties of binary media generated by two-dimensional lattices that follow fractional Brownian motion statistics are studied. A modification of the midpoint displacement and random addition method is employed in order to generate multicell binary media with sizes that are considerably larger than the correlation length of the medium. Several structural properties, such as the autocorrelation function, the surface area, and the percolation threshold, are studied for different values of porosity and degree of correlation. In addition, transport properties are investigated in the above media, by solving numerically the momentum and continuity equations, to determine the absolute permeability of the medium in directions parallel and normal to the fractional Brownian motion (fBm) plane. It is found that multicell fBm porous media possess very interesting structural properties that are functions of the Hurst exponent and porosity, and are independent of the lattice size, in contrast to the traditional single-cell fBm media. In addition, they exhibit stronger structural correlation, lower specific surface area, higher percolation threshold, and lower permeabilities than those of the corresponding single-cell porous media.

Journal Article↗

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↗