Solute Diffusion in Aliphatic Oil-Based Block Copolymer Gels

Solute diffusion within gels has been studied almost exclusively in hydrogels due to their wide applicability including in drug delivery and tissue engineering. Recently, several studies have considered aliphatic oil-based gels for transdermal drug delivery specifically. Oil-based gels, referred to here as organogels, offer several benefits over hydrogels including a wider thermal processing window and elimination of ‘drying out’ effects due to several oils’ considerably lower volatility relative to water. Additionally, a variety of aliphatic oils that range in molecular weight and/or degree of branching theoretically allow gel transport properties to be tailored even at a fixed temperature and polymer concentration. In this work, solute diffusivity within styrenic block copolymer organogels was characterized using FTIR-based, release experiments in which passive diffusion of the solute occurs from gels into supernatant oil. Organogels for this analysis were formulated to vary in solute size, oil viscosity, and copolymer molecular weight and gel fraction so that each parameter’s effect on solute transport could be scrutinized. Furthermore, resultant diffusivity values, which range from 1x10^-9 – 1x10^-7 cm²/s, will be modeled using several gel transport models including hydrodynamic, free volume, and obstruction theory to gain a better understanding of the diffusion process. These findings will be subsequently compared to preexisting hydrogel studies and ultimately will inform the future design of organogels for transdermal drug delivery devices.