The partitioning model of retention for reversed-phase liquid chromatography, described by mean-field statistical thermodynamic theory, asserts that one principal driving force for solute retention is the creation of a solute-sized cavity in the stationary phase. Beyond a critical stationary phase bonding density, increased grafted chain density should result in enhanced chain ordering, which will increase the energy necessary for solute cavity formation and result in decreased chromatographic partition coefficients. We have evaluated chromatographic partition coefficients over an octadecyl bonding density range of 1.6-4.1 mumol/m2 and have found a maximum in partition coefficient at approximately 3.1 mumol/m2. Retention, however, approximately plateaus due to compensating changes in the partition coefficient and stationary phase volume. This provides unequivocal evidence that partitioning is the dominant form of retention for small nonpolar solutes.

In vitro lipid adsorption varied greatly depending on the lens material for both polar and nonpolar lipids. Overall, there was less in vitro adsorption of lipid to the lotrafilcon A and B polymers than for any of the other silicone hydrogel polymers tested. The quantity of lipid adsorption by lotrafilcon polymers was similar to "conventional" hydrogel lenses.

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The use of a contact lens as a polymeric delivery vehicle is presented. Specifically, the elution of nonfunctionalized poly (vinyl alcohol) (PVA) from nelfilcon A hydrogel lenses is presented as a model of delivering polymeric active agents to the eye. High molecular weight nonfunctionalized PVA is added to the lens matrix for later release into the tears. This is made possible by photo crosslinking a macromer species in lieu of monomeric polymerization. Consistent near zero order release of 0.062% (wt/wt) was demonstrated in vitro over a 20-h period. The result is a new contact lens device based on the slow release of PVA. In vivo results demonstrate that this product improves the wearing comfort of this type of contact lens and acts as a model basis for drug delivery.

Using the inversion/recovery method, deuterium (2H) longitudinal relaxation times, (TO, of deuterium oxide were measured for binary solutions of methanol and D20 and acetonitrile and D20 and for these mixtures in contact with two different reversed-phase liquid chromatographic stationary phases. Changes in the D20 Ti for the solutions in contact with the stationary phase compared to those observed for the solutions alone give a qualitative understanding of the degree of association of water with the stationary phase. The results for two stationary phases with greatly different Ci8-bonding densities are reported and discussed. The results are also compared and contrasted to our previous work, which examined changes in 2H T\ for deuterated methanol and acetonitrile in the same binary hydroorganic solutions as well as for these mixtures in contact with the same two stationary phases.