Sequentially Controlled Deformations of Patterned Hydrogels into 3D Configurations with Multilevel Structures

Abstract

Sequential deformations of patterned hydrogels into 3D configurations with multilevel structures are reported, which are realized for the first time in self‐shaping materials. The periodically patterned single‐layer hydrogels with different polymers are fabricated by multi‐step photolithography. After swelling in water, the expansion of compartmentalized high‐swelling gels is constrained by the dispersed non‐swelling gels, resulting in out‐of‐plane buckling with high cooperativity and thus forming alternating concave–convex configuration. When the dispersed non‐swelling gels are partly replaced by thermoresponsive ones, the preformed overall flat, yet locally undulant, hydrogel deforms further into dome‐, saddle‐, or sandglass‐like configurations at elevated temperature. As such, multilevel 3D structures can be achieved via prebuilt mechanical/geometric cues in a sequentially controlled manner. This conceptual design and sequential deformation of patterned hydrogels to form 3D configurations with multilevel structures should enrich the deformation/functioning modes of morphing materials and broaden their applications in diverse areas.

Transformer Hydrogels: A Review

“…Eventually, the internal stresses generated within the materials lead to an out‐of‐plane buckling deformation which is energetically more favorable. Patterning of stimuli‐responsive hydrogels can strategically place these internal stresses to program complex shape transformations …”

“…f) Shape‐transformations of patterned dual responsive hydrogels. Adapted with permission . Copyright 2018, Wiley‐VCH.…”

“…Besides the patterned hydrogel strips, design architectures involving distributed disks can transform flat hydrogels to more complex 3D shapes . Kim et al employed halftone gel lithography where they used pNIPAM copolymers with tunable cross‐linking .…”

“…They were able to demonstrate that by changing the dot patterns and their geometric arrangements, laterally patterned hydrogels can transform their shapes into saddle surfaces, cones, spherical caps, and Enneper's surfaces as the temperature changes (Figure e). Ma et al adopted a similar approach where they patterned pAAm, pNIPAM, and p(AAm‐ co ‐AMPS) gels into periodic architectures . Their specifically patterned hydrogels changed into complex programmable shapes including dome/saddle and concave‐convex surfaces.…”

Programmable Multistable Hydrogel Morphs

“…Among the synthetic materials undergoing preprogrammed deformations, hydrogels are particularly interesting because of their open network structures and the drastic volume changes under the actions of external stimuli . Heterogeneous expansion or contraction of a responsive gel generates localized internal stresses that govern the transformation of the originally planar gel sheet into a 3D configuration . A seminal strategy pioneered by Hu et al relies on the variation in gel composition across the bilayer film .…”