Freeform Nanopatterning of Hydrogel Surfaces

Hydrogels are a promising material for biomedical applications due to their tunable properties and biocompatibility. The ability to structure hydrogel surfaces with high precision leads to greater control over interactions at the hydrogel interface, which in turn impacts many applications, such as implant integration, drug delivery, and cancer modeling. However, freeform patterning of hydrogel surfaces at the nanometer scale and the characterization of their topography with atomic force microscopy have not yet been achieved. Here, we demonstrate a reliable process for nanopatterning hydrogel surfaces by combining thermal scanning-probe lithography and replica molding to create grayscale surface topographies with features as small as 138 nm on the hydrogel interface. During our fabrication process, the hydrogels are dehydrated, introducing shrinkage of the original patterns. We explore hydrogel shrinkage as a route for pattern miniaturization and investigate the shrinkage behavior. We determine a lateral shrinkage factor between 1.4 and 2.2, and a vertical shrinkage factor between 2.5 and 37.0, and demonstrate that the shrinkage can be varied by changing the water-to-monomer ratio in the hydrogel precursor. Furthermore, we show that the shrunken, dehydrated hydrogel patterns can be exploited as templates for metal deposition.