Grayscale and Halftone Gel Lithography as Promising Techniques for Swelling-Induced Deformation of Smart Polymer Hydrogel Films

摘要

Differential swelling of spatially patterned gel sheets offers an indirect avenue to rational understanding how things in nature grows as time elapses. In the present study, we demonstrate swelling-driven deformation of spatially designed gel sheets sensitively relying on film thickness and pattern dimension. Through chemical copolymerization of poly (N-isopropyl acrylamide) (PNIPAm) with pendent benzophenone UV-crosslinkers, photo-crosslinkable hydrogels were prepared. Various kinds of spatially designed features with different equilibrium degrees of swelling are created by grayscale and halftone gel lithography techniques, wherein time-sequential UV exposures with a number of photomasks, thus selectively embedding densely-crosslinked features into a lightly-crosslinked area. Deformation of the photo-patterned gel sheets by energy competition between the regions strongly depends on a characteristic dimension and sheet thickness, providing fruitful information on the contrast in modulus between the regions.