CBE Centennial Seminar Series: Kenny Mineart (Bucknell University)

Abstract

Solute Diffusion in Block Copolymer Organogels Through the Lens of Transdermal Drug Delivery

Effective transdermal drug delivery patches must exhibit multiple characteristics including the ability to store and release desired pharmaceutical compounds, enhance permeation of those compounds through skin, and moderately adhere to skin while avoiding irritation. Gels composed of styrenic block copolymers and various aliphatic hydrocarbon ‘solvents’ (e.g., white mineral oil and tackifying resin) inherently exhibit the latter pair of these properties. Furthermore, recent in-vitro and in-vivo experiments have shown that these gels can be empirically formulation-matched to the performance of existing transdermal delivery products. In hopes of empowering bottom-up design, my research group has spent the past several years developing formulation-property relationships for solute diffusion through styrenic block copolymer organogels. This work is built upon our measurement of solute diffusion in gels varying in block copolymer concentration, block copolymer molecular weight, solvent viscosity, penetrant (i.e., solute) identity, and temperature using Fourier-transform infrared spectroscopy (FTIR). As anticipated, gels with low copolymer concentration, low solvent viscosity, and small penetrants exhibit the fastest diffusion (D ≈ 5x10-8 cm2/s at 21 °C) whereas materials composed at the opposite end of these ranges translates to the slowest diffusion (D ≈ 3x10-9 cm2/s at 21 °C). Diffusivity is also noted to exhibit an Arrhenius dependence (with temperature). Beyond these observations, we are able to draw generalizable meaning from our measured diffusivity values by fitting them with a model that considers gels as a heterogenous polymer network. This particular model’s strengths come from its physically-relevant basis and its ability to describe our data across all of the system parameters considered. Ultimately, this fitting allows us to approximate several fundamental and molecular-scale gel transport properties – such as, the solute hopping rate and diffusion activation energy – for these materials.