Biomedical subjects

James L Wright

Publications and source records attributed to James L Wright.

3 recordsLinked to original sources

PubMed2006

Percolative transport and cluster diffusion near and below the percolation threshold of a porous polymeric matrix.

PURPOSE: The purpose of this research was to develop a quantitative mass transport model to describe the release of a drug from a porous inert matrix dosage form near and below the percolation threshold for the system. METHODS: Cumulative release profiles were generated for a series of tablets composed of a binary mixture of varying amounts of non-conducting (poly(vinyl stearate)) and conducting (benzoic acid) components. The porous microstructure was analyzed using re-constructed three-dimensional images of leached microtomed tablet sections. Poly(vinyl stearate) was characterized for transport properties, molecular weight and thermal properties. RESULTS: Based on percolation theory, the binary matrix was determined to have a percolation threshold of 0.09 +/- 0.02. Transport, which could not be explained by "classical" percolation theory or surface diffusion alone, was observed below the percolation threshold for the system. CONCLUSIONS: A model describing transport near and below the percolation threshold in matrices composed of two phases, polymer and drug, was developed. The percolation model developed accounts for diffusion within the porous structure and through the inert, insoluble polymeric amorphous regions of the matrix. The low percolation threshold and subsequently high coordination was concluded to be due to the biphasic classical porous and nonclassical polymeric diffusional transport mechanisms associated with the system studied.

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PubMed2006

Modeling of aqueous transport in rigid porous matrices near the percolation threshold.

PURPOSE: To demonstrate control of passive diffusion of small molecules through rigid ceramic matrices via manipulation of matrix porosity near the percolation threshold, and to model such control using percolation scaling relationships on both infinite and finite lattices. MATERIALS AND METHODS: Rigid alumina disks of controlled porosity were prepared using standard ceramic casting and sintering techniques. Structural void space distributions in sintered disks were measured by dimensional and volume displacement (pycnometry) methods. The impact of void space on transport was determined by tracking the diffusion of ionized benzoic acid across sintered disks mounted in Stokes diffusion cells. Critical percolation thresholds were estimated by fitting structural and transport-dependent results to percolation scaling relationships. Finite-size scaling studies were performed by adding polymer microspheres of known diameter to the disks to generate artificially large pores. RESULTS: Nonlinear least squares techniques were used to fit both structural and transport-dependent properties of rigid alumina disks to total disk porosity using percolation scaling relationships. The critical percolation threshold determined from structural properties (0.129) was lower than that determined from benzoic acid transport (0.169). The transport-derived percolation threshold exactly matched that expected for a tetrakaidecahedral (14 sided) lattice. Finite-size scaling was demonstrated through a nonzero effective volume fraction for transport at the percolation threshold. CONCLUSIONS: Manipulation of total disk porosity near the percolation threshold was shown to be a suitable means of controlling the transport rate of a model small molecule, while deliberate enlargement of individual pores was demonstrated to decrease this threshold without increasing total porosity. The lower-than-expected percolation threshold obtained from the structural model was ascribed to limitations of the measurement technique. The threshold determined from the aqueous transport model was concluded to represent the true threshold for this system.

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PubMed2002

A kidney epithelial cell line from a Bolivian squirrel monkey.

Squirrel monkeys are the most commonly used New World primates in biomedical research, but in vitro studies are restricted by the limited number of cell lines available from this species. We report here the development and characterization of a continuous, kidney epithelial cell line (SQMK-FP cells) derived from a newborn squirrel monkey. Karyotype was consistent with Bolivian squirrel monkey (submetacentric chromosome pair 15 and acrocentric chromosome pair 16). All cells examined were hyperdiploid with chromosome numbers ranging from 52 to 57. Ultrastructural analysis of SQMK-FP cells revealed the presence of cell junctions with radiating filaments, indicating desmosomes and numerous surface projections containing longitudinally oriented filaments typical of tubular epithelium. Biochemically, SQMK-FP cells exhibit glucocorticoid resistance typical of the squirrel monkey. Glucocorticoid receptor (GR) binding is low in SQMK-FP cells because of high expression of the FK506-binding immunophilin FKBP51 that inhibits GR binding. SQMK-FP cells constitute a tubular epithelial cell line that has biochemical properties characteristic of squirrel monkeys and represents an alternate cell model to B-lymphoblast SML cells to study the biology of the squirrel monkey in vitro.

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