Victor F. Smolen

Oxygen permeability coefficients of polymers for hard and soft contact lens applications

Abstract The oxygen permeability of several polymeric materials used for hard and soft contact lens applications was determined using a gas-to-water oxygen permeation technique. The technique measures oxygen permeation through polymeric films kept between a gaseous and an aqueous phase at 34°C, where the oxygen is dissolved and measured with an oxygen analyzer. Oxygen permeabilities were measured for poly(methyl methacrylate), cellulose acetate butyrate, a blend of PMMA and CAB with silicone networks, poly (hydroxyethyl methacrylate) hydrogels, and a series of amorphous and semicrystalline poly (vinyl alcohol) hydrogels. Dissolved oxygen permeabilities ranging from 0.155 x 10 −10 cm 3 (STP)·cm/sec·cm 2 ·cmHg for PMMA to 78.95 x 10 −10 cm 3 (STP)·cm/sec·cm 2 ·cmHg for an amorphous PVA membrane with degree of hydration of H = 0.866 were observed. For amorphous hydrogels, the oxygen permeability is a function of thickness and degree of hydration. Boundary layer effects and the effect of structural characteristics of the polymer on the permeability coefficients are discussed.

Theoretical and computational basis for drug bioavailability determinations using pharmacological data. I. General considerations and procedures

The use of data deriving from monitoring the time variation of the intensity of pharmacological effect(s) following dosing can often present an advantageous alternative to the more conventional approach of using chemical or radiological assay of blood and/or urine level data for bioavailability evaluations of drug products: bioavailability studies can be performed with drugs where no assay exists. A relatively simplified discussion of the general theoretical principles on which the use of pharmacological data is based and a stepwise description of the approach for its routine application in bioavailability studies are presented. Approaches for computing rates and extents of drug bioavailability vs. time profiles on analog and digital computers are qualitatively described and quantitatively presented in a subsequent report. The concept of preabsorption (gastrointestinal bioavailability) is introduced and biophasic availability of drugs to local sites of action is discussed.

Theoretical and computational basis for drug bioavailability determinations using pharmacological data. II. Drug input ⇄ response relationships

Mathematical expressions and approaches to the computation of rates and extents of drug bioavailability for implementation on analog and digital computers are derived. The equivalency of expressions derived on the basis of assuming compartment models to an approach based on using experimentally determined weighting functions is demonstrated. The relative merits of the two techniques are discussed: their application for use with temporal pharmacological data is emphasized. The applicability of the computational techniques to determining the availability of drugs at local sites of action (biophasic availability) and to computing preabsorptive drug release into the gastrointestinal contents (gastrointestinal bioavailability) is pointed out. An approach to computationally predicting in vivo blood level or pharmacological response vs. time profiles from in vitro dissolution testing results is presented and its limitations are discussed.

A water membrane hypothesis: Behavior of hydrated polycation-polyanion salt complexed membranes as apparent lipoidal barriers to solute transport☆

Abstract Polyanion-polycation salt complex membranes were prepared by casting from a ternary solvent mixture. The permeability coefficients of the membranes were determined for several solutes whose diffusive permeability of biological barriers had previously been reported to correlate with their lipid/aqueous phase distribution coefficients. The observed permeabilities of the polysalt membranes were found to correlate well with the biological permeabilities and the distribution coefficients of the solutes. The observed permeability behavior of the membranes is attributed to the properties of the water structured within their polymeric matrix. The lipoid barrier properties of biomembranes is similarly postulated as attributable to their content of structured water. An alternative to the classical lipid-membrane theory is presented.

An in vivo study of the interaction of ionic surfactants with human epidermis

Abstract A bioelectrometric technique was implemented to the study of the interaction of a cationic, cetylpyridinium chloride (CPC), and an anionic, sodium lauryl sulfate (SLS), surfactant with human epidermis. The method permitted the study to be performed in vivo without causing any injury to the subjects. Electrometric determinations of the influence of pH on the extent of CPC interaction with epidermis were corroborated by similar results obtained from the spectrophotometric determination of the quantities of CPC elutriatively recovered following the sorption of CPC from solutions of varying pH. The fixed charge density of the epidermal surface was calculated from measured potentials. Plots of these results as a function of pH resemble hydrogen ion titration curves of amphoteric molecules. Above pH 1.14, CPC consistently increased the net fixed positive charge on the epidermal surface as compared to an untreated control. Above pH 4.6 SLS induced an effect similar to that of CPC, whereas below pH 4.6 a reduction in the net positive surface charge was observed. The operation of inductive and electrostatic field effects emanating from surfactantinteracted surface sites are suggested as operative in the submolecular mechanisms of the observed phenomena.