On the thickness uniformity of micropatterns of hyaluronic acid in a soft lithographic molding method

Abstract

A soft lithographic molding is a simple and yet robust method for fabricating well-defined microstructures of a hydrophilic biopolymer such as polyethylene glycol and polysaccharide over a large area. The method consists of three steps: placing a polydimethylsiloxane mold with a bas-relief pattern onto a drop-dispensed polymer solution typically dissolved in water, letting the mold and the solution undisturbed in contact until solvent evaporates completely, and leaving behind a polymer replica after mold removal. In such a molding process, water can only evaporate from the edges of the mold due to impermeable nature of polydimethylsiloxane to water, resulting in a nonuniform distribution of film thickness or pattern height. Here we examine systematically how the evaporation rate affects the thickness distribution of the resulting microstructures by evaporating the solution of hyaluronic acid in various conditions. To compare with a theory, we also present a simple theoretical model based on one-dimensional conservation equation for a liquid film, which is in good agreement with the experimental data.