(62aa) The Use of Variable Depth Hydrogel Stamps as An Efficient Means for Providing Biocompatible Gradients

The controlled application of proteins and other biomolecules to generate patterned surfaces is a crucial part of many processes, for example creating biosensors and directing cell growth for tissue engineering. Traditionally, poly-dimethylsiloxane (PDMS) elastomeric stamps have successfully been used to transfer proteins with sub-micron resolution. However, the resulting patterns are limited to a single, uniform protein concentration. The technique presented here utilizes variable depth hydrophilic stamps as a diffusion medium, allowing protein gradients to be easily applied and accurately reproduced. Specifically, stamps of a 2-hydroxyethyl acrylate (HEA) hydrogel made with poly(ethylene glycol) diacrylate (PEG 400 DA) as a crosslinker and 2% agarose hydrogel are used to demonstrate variable-concentration pattering of a fluorescently-labeled protein. Both hydrogels were able to provide a wide range of diffusion for varying depths. The HEA had the widest range, about 2.5 times larger than agarose when compared at equal depths. From these results, it can be concluded that it is possible to create protein gradients via variable stamp depth. Ultimately, optimization studies can be undertaken to find the best suited hydrogel for varying proteins.