Micro-wrinkled hydrogel patterned surfaces using pH-sensitive monomers

Abstract

Herein, we report the fabrication of wrinkled hydrogel films with tunable pH sensitivity by using tertiary amine methacrylate-based monomers. On the one hand, hydrogels composed of 2-hydroxyethyl methacrylate (HEMA), N,N-diethylaminoethyl methacrylate (DEAEMA), and poly(ethylene glycol) diacrylate (PEGDA) were synthesized using different monomer feed. Their pH responsiveness was tested via contact angle measurements using different buffers (pH 5.4, 7.4 and 8.3) as aqueous media. On the other hand, the same buffers were used as solvent during synthesis instead of water. Later, hydrogel films were deposited by spin coating onto methacryloyl-functionalized substrates, in order to form a covalent anchoring to the surface. The monomer conversion ratio was inspected by H NMR analysis, demonstrating a partial conversion in the first thermo-polymerization step and a complete reaction upon at the end. AFM and FE-SEM micrographs provide topographical information about the surfaces, like wrinkled pattern width, height, and wrinkles preferential direction. Force spectroscopy measurements depict some clues about the local micromechanical properties of the films, evidencing a clear influence of the monomer feed composition on the final characteristics of the hydrogel patterns. Contact angle measurements evidence an important pH responsiveness which is increased by adding a larger amount of DEAEMA to the feed.