Membrane permeation of testosterone from either solutions, particle dispersions, or particle-stabilized emulsions

Regular Solution Theory for Polymer Permeation Transients: A Toolkit for Understanding Experimental Waveshapes

The accurate measurement of permeation is important at the product design stage for a variety of industries as diverse as conveyance methods for oil and gas produced fluids, such as mixtures of carbon dioxide, methane, hydrogen sulfide, water, and hydrocarbons, and in polymer-lined, unbonded flexible risers and flow lines through connectors and valves, hydrogen and methane gas carrying domestic lines, hydrogen storage tanks, sulfur hexafluoride circuit breakers for high power-carrying lines, oxygen through display technology, and drug delivery. It would also be appropriate to monitor the permeation rate through the polymer, composite, and elastomeric layers during the in-service times where applications allow. In the future, any alteration in the short term and long-term transport rates could be analyzed in terms of an initial alteration or degradation of the polymeric materials and, in some cases, metallic components. Crucially, such measurements would serve as an early warning system of any change in a polymeric material that could result in the loss of function of the fluid of a gas containing barrier material. Most experimental determinations are made through recording flux transients (varying flux) through permeation cells in which a polymer membrane or film separates a donor compartment (usually an infinite supply) and an acceptor compartment and in which membrane transport is considered to be slow. Treatment of the resulting experimental data is usually, but not always, undertaken through comparison with a steady-state model based on Fickian diffusion through the membrane, so as to extract the membrane permeability, the diffusion coefficient of the permeant, and the solubility of the permeant in the membrane phase. However, in spite of these measurements being undertaken routinely using closed cell manometric or continuous flow methods, there is a lack of literature in which experimental flux transients are provided, and in several cases, it is clear that the experimental data do not conform to the expected model of slow, Fickian diffusion through the membrane, even though experiments are performed at temperatures much higher than the glass transition temperature of the polymer membrane. In this paper, we first re-examine the classical model for an infinite source and extend it to account for (1) molecular interactions between membrane and permeant, using regular solution theory, (2) slow transport in the acceptor phase, and (3) slow kinetics across the membrane|acceptor interface. We demonstrate that all three aspects can cause permeation flux transients to exhibit unusual, nonclassical waveshapes, which have nevertheless been experimentally realized without rationalization. This enables the development of an algorithmic toolkit for the interpretation of permeation flux transients, so as to provide reliable and accurate data analysis for experimentalists.

Giant Pickering Droplets: Effect of Nanoparticle Size and Morphology on Stability

The interaction between a pair of millimeter-sized nanoparticle-stabilized n-dodecane droplets was analyzed using a high-speed video camera. The droplets were grown in the presence of either poly(glycerol monomethacrylate)-poly(benzyl methacrylate) (PGMA-PBzMA) diblock copolymer spheres or poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate)-poly(benzyl methacrylate) (PGMA-PHPMA-PBzMA) triblock copolymer worms prepared by polymerization-induced self-assembly. The effect of nanoparticle morphology on droplet coalescence was analyzed by comparing 22 nm spheres to highly anisotropic worms with a mean worm width of 26 nm and comparable particle contact angle. Both morphologies lowered the interfacial tension, providing direct evidence for nanoparticle adsorption at the oil-water interface. At 0.03 w/v % copolymer, an aging time of at least 90 s was required to stabilize the n-dodecane droplets in the presence of the worms, whereas no aging was required to produce stable droplets when using the spheres, suggesting faster diffusion of the latter to the surface of the oil droplets. The enhanced stability of the sphere-coated droplets is consistent with the higher capillary pressure in this system as the planar interfaces approach. However, the more strongly adsorbing worms ultimately also confer stability. At lower copolymer concentrations (≤0.01 w/v %), worm adsorption promoted droplet stability, whereas the spheres were unable to stabilize droplets even after longer aging times. The effect of mean sphere diameter on droplet stability was also assessed while maintaining an approximately constant particle contact angle. Small spheres of either 22 or 41 nm stabilized n-dodecane droplets, whereas larger spheres of either 60 or 91 nm were unable to prevent coalescence when the two droplets were brought into contact. These observations are consistent with the greater capillary pressure stabilizing the oil-water interfaces coated with the smaller spheres. Addition of an oil-soluble polymeric diisocyanate cross-linker to either the 60 or the 91 nm spheres produced highly stable colloidosomes, thus confirming adsorption of these nanoparticles.

Sustained Administration of Hormones Exploiting Nanoconfined Diffusion through Nanochannel Membranes

Implantable devices may provide a superior means for hormone delivery through maintaining serum levels within target therapeutic windows. Zero-order administration has been shown to reach an equilibrium with metabolic clearance, resulting in a constant serum concentration and bioavailability of released hormones. By exploiting surface-to-molecule interaction within nanochannel membranes, it is possible to achieve a long-term, constant diffusive release of agents from implantable reservoirs. In this study, we sought to demonstrate the controlled release of model hormones from a novel nanochannel system. We investigated the delivery of hormones through our nanochannel membrane over a period of 40 days. Levothyroxine, osteocalcin and testosterone were selected as representative hormones based on their different molecular properties and structures. The release mechanisms and transport behaviors of these hormones within 3, 5 and 40 nm channels were characterized. Results further supported the suitability of the nanochannels for sustained administration from implantable platforms.

How membrane permeation is affected by donor delivery solvent

We investigate theoretically and experimentally how the rate and extent of membrane permeation is affected by switching the donor delivery solvent from water to squalane for different permeants and membranes. In a model based on rate-limiting membrane diffusion, we derive explicit equations showing how the permeation extent and rate depend mainly on the membrane-donor and membrane-receiver partition coefficients of the permeant. Permeation results for systems containing all combinations of hydrophilic or hydrophobic donor solvents (aqueous solution or squalane), permeants (caffeine or testosterone) and polymer membranes (cellulose or polydimethylsiloxane) have been measured using a cell with stirred donor and re-circulating receiver compartments and continuous monitoring of the permeant concentration in the receiver phase. Relevant partition coefficients are also determined. Quantitative comparison of model and experimental results for the widely-differing permeation systems successfully enables the systematic elucidation of all possible donor solvent effects in membrane permeation. For the experimental conditions used here, most of the permeation systems are in agreement with the model, demonstrating that the model assumptions are valid. In these cases, the dominant donor solvent effects arise from changes in the relative affinities of the permeant for the donor and receiver solvents and the membrane and are quantitatively predicted using the separately measured partition coefficients. We also show how additional donor solvent effects can arise when switching the donor solvent causes one or more of the model assumptions to be invalid. These effects include a change in rate-limiting step, permeant solution non-ideality and others.